1010322S Main Long. Beams - table edge carrying x-rails

[Gerald_D]

Drawing sheet number 1010322S refers:

The main beams, or girders, of the stationary table are made of channel iron, or C-section steel.

- Length of the channel is X plus 600mm

- Depth (height) of channel, in the range 150 to 200mm. This height affects the clearance under the gantry. The MechMate beam is 180mm high.

The most important criteria when selecting the beams at the steel supplier are not the dimensions, but the STRAIGHTNESS. Don't worry about twist, the beams are very flexible for twist and that will be corrected during the build.

- Width (breadth) of channel, in the range 50 to 100mm. Very little affect on overall dimensions. Mechmate beam is 70mm wide.

The 60 degree angles at the ends are purely for aesthetics.

[Evan Curtis]

Gerald,

On you original table for your SB you used square tubing, why did you go to the C-section steel for the MechMate?

[Mike John]

I don't know why he changed, but the instructions he gave me for making my table used C-section, and it is incredibly solid.
He says the 60º angles are for aesthetics, but you can get two side pieces from one 6m length if building a 10 foot table, which you can not with square cuts.
Gerald also told me this!

...............Mike

[Gerald_D]

C-channel is a "lazier" option for the DIY bloke http://www.mechmate.com/Forum/clipart/happy.gif

Seriously though, C-channel is more widely available around the world, and bolting through it is easier. Strength-wise, it doesn't make a huge difference.

C-channels are available with either tapered or parallel flanges. Chose parallel flange if you want to use bolts and nuts through the flanges - otherwise you'll need tapered washers. The MechMate plans are for welded joints - there are no nuts inside the beams - the threads for the rails are tapped into the beams.

If the standard beam length in your country is *just* too short, then Mike John will explain a trick to you. Also, the x-rails may hang over the main beams by up to 100mm on each end, but it won't look too pretty.

[Evan Curtis]

Thanks,
I like the parallel flanges. And aesthetics are important, and as you've pointed out it can prove economical as well.

[fabrica]

Gerald, I just purchased a C channel (74 x 150 mm). For Main longitudnal beams. If I use this will I be restricted to only 6" of Z axis travel. If I need to extend this further in the future(Maybe to 12").Could I just mount (Bolt) another C channel having same dimensions into the existing one.

[Gerald_D]

The z-travel depends on a lot of things, the beam size, the table top thickness, that 1" of rail height you are making, the diameter of the V-roller under the gantry, the length of the router's collet and cutter, etc. A 6" beam is fine for cutting thick boards - if you want to get into thick 3D stuff later, you can add a spacer beam as you suggest.

[Bill McGuire]

X and Y stop question:
How much extra length is given for the x and y distances over the size of the cutting material? For instance, will the router bit center hang 12, 25, or 50 mm past the edges of the material when at the end of the x and y rails?
Thanks much..

[Gerald_D]

Center of bit can go 50mm [2"] over on all 4 sides of the material. (100mm [4"] added in total per axis)

[Kim Mortensen]

I'm not planning on going into hard 3D with this machine, my plans is to build another machine later on with a cuttin are of 3*3 feet for typical 3D cuts.
But, will a 120mm c-beam be good enough for the main beams..??? Cause this I can get cheap from work... The other size 180mm is a little more expensive. Actually alot even...

[Gerald_D]

What is your total X dimension? What is the width of that 120mm C-section and how thick is it?

You realise the issue of the reduced z-height, but the beam must also still be strong enough to carry the mass of the machine.

[Kim Mortensen]

The Complete length of my machine will be 3100mm
The beam is. this one here...
Height=120mm
Width=55mm
thikness of wall=7mm
thickness of ends=9mm

[Gerald_D]

Those 9mm ends - are they tapered or parallel?

This beam doesn't sound too bad if you can get it cheap (free?). But, before I make a final answer, can you you get 4 lengths of this steel? (to make a "sandwich"). Can you get other slightly smaller sizes to make sandwiches?

[Kim Mortensen]

the 9mm is tapered....
What do you mean with sandwich..???

Do you mean stacking them on top of eachother, or..????

[Gerald_D]

Some guys do stack the beams on top of each other, but I was thinking something like this:

http://www.mechmate.com/Forum/messages/8/3346.gif

Left is the recommended channel, middle is your channel, right is a sandwich of your channels (20mm long welds, 300mm apart).

Single channels will be strong enough for light board cutting.

[Kim Mortensen]

So you mean that the channel won't be strong enough as a single channel.. you think it would be better to go with the 180mm channel instead..??? I can get a 6meter lengthe for around $200

[Kim Mortensen]

Or is it just to get the hight in order.???

[Gerald_D]

I repeat "Single channels will be strong enough for light board cutting." (as in the middle picture)

[Kim Mortensen]

Yes. but light cutting, I'm hoping to get it to do single pass when cutting, instead of doing multiple passes for each iten.

[Gerald_D]

If the table is too light it:
- vibrates (cut quality suffers)
- flexes with temperature and humidity changes because the wood surface then starts to bend the steel.

$200 for a pair of beams is a good price (you can cut 2x3.1m from 1x6m)

[Kim Mortensen]

I can't get 2*3.1meter from one beam. I can get 3.09 if I cut the ends in 45 degrees instead of 60...

[Gerald_D]

It is no problem if the x-rails are a little longer (say up to 100mm) than the beams.

[Kim Mortensen]

But offcourse if the tool is already going to go 50mm over the ends then maybe it kan be possible to make it long enough to reach from one end to the other... So maybe 6 meters cut in 60 degrees should be good enough I will stille have a few centimeters on each end of the X axis...

[Gerald_D]

Look at drawing 1010246D and realise the beam needs only to go to the last screw hole. (Also see that extra length shown on the points of the rails - I cut those points after everything is assembled and I have looked how far I need to run the gantry). The design of the MechMate is very "forgiving" http://www.mechmate.com/Forum/clipart/happy.gif

[Kim Mortensen]

I thiink I will be going for the 180mm beam... But with tapered ends instead of parralell.... this is what I have gotten a price for... But it should be ever as straight as the ones that arent tapered...

[chris saintdenis]

If have come across some used free C-channel for my main long beams, but the problem is the upper and lower surface are not running parallel to one and other. One side is about 1mm out of square with the outside long edge of the c section and the other side is 3.5mm out of square.

Looking at the construction of the Mechmate it seems critical that these surfaces run parallel. I include pictures because I am sure the above explanation is not all that helpful. Any thoughts?

Thanks for your time.

[Gerald D]

Good pictures! :) Bad problem :(

Channels seldom have perfectly square flanges, and the 1mm case looks typical. You should be able to use that without problems - the flatness is not super-critical for the MechMate. Bad spots can always be shimmed up. (Your rack & pinion will show uneven wear for a while, but the cutting quality and accuracy will not suffer)

But the 3.5mm situation looks rather bad. Avoid that channel. Unless you want to weld the whole channel at an angle so that the top face comes flat. Those 60 degree ends on the channel points will make it hard to see whether the channel has been welded at an angle :)

[chris saintdenis]

Thanks for info!! Great site.

[Greg J]

Gerald,

I'm using C7x14.75 channels for the main beams. At 10 foot in length, just one beam weighs 147.5 lbs. I would like to reduce the weight of the table by drilling 4 inch diameter holes along the beam. This will reduce the weight considerably.

The table legs support the beams, so I don't think bending (along the X axis)is a concern (correct me if I'm wrong). What are your thoughts/design for this beam. If I reduce the weight by 30%, am I sacrificing structural integerity.

I want to reduce weight, because I'm a one man show and fabricating this table is getting more than I can bear.

Greg

[Gerald D]

Each 4" hole will weigh about -1.5 lbs. About 1% of the total weight. To save 30% in weight you will have to drill about 30 holes. You can't put 30 holes of 4" diameter side-by-side along a 10 ft beam because then holes will have to touch each other.

Sorry Greg, it will severely mess up the structural integrity. All I can suggest is getting some lifting equipment or people. Realise also that a typical production board laid on the table for cutting will also be in this weight class - an investment in lifting equipment is probably going to be needed in any case.

[Greg J]

Thanks Gerald,

If I don't ask, then I can't learn.

I'll figure something out. Maybe if I tie a couple of mules to the .... :)

Greg

[gmessler]

Hello Gerald,
Regarding the c7 channel. I originally had C7x14.75 quoted but when I read JR's xl spreadsheet he had the C7x9.8 listed. Are there any problems with using the lighter (and thinner) channel?

[Greg J]

Don't forget that the flange width is 2.090 inches versus 2.299 inches on the two channels.

I don't think it's a big issue, just needs to be accounted for.

Greg

[Gerald D]

The lighter channel should work okay, but I have no experience of it - ours is 21 kg/m [14#/ft]

[cobra427mnsi]

Hi Gerald,

I know that the 60 degree angle on the ends of the main long beams is for looks. Has anyone used a 45 degree angle instead? The reason I'm asking is I would like to get 2 pieces 123.6" long (x=100"+23.6"=123.6"), for a 50"x100" table, out of a 20'-0" channel (the standard length). A 60 degree cut will not allow 2 pcs from the 20 footer where a 45 degree angle will allow 2 pieces. If a 45 degree angle is not acceptable, I could shorten the table size to 98.5 and be able to use the 60 degree angle. What is your opinion of a 45 degree angle?

Paul

[Gerald D]

45 degree is 100% okay. It is also okay to have the rails overhang the main beams a bit (maybe 50mm [2"]??) - just move the last screw hole closer to the tip of the beam.

[cobra427mnsi]

Thanks Gerald, for the info. You are a fantastic resource!

Paul

[Greg J]

Paul,

I think you will find that the 20 foot channel will actually be longer than 20 feet. I had enough to square the ends, for a 2 inch depth, and then 45 them.

Greg

[cobra427mnsi]

Thanks Gerald, that's a good idea. It will eliminate that sharp groin injuring point.

Paul

[Greg J]

I would enjoy being in Gerald league, but still learning in the minors. ;)

Greg J.

[Roadkill_321]

I had a question about the X rail placement. Is there an exact measurement for this distance or is it the same distance as the thickness of the rack? How much clearance should there be between the vertical section on the main X beam and the rack?

John829

[Gerald D]

There is clearance between the rack and the beam, about 5mm [3/16"] very roughly speaking. The metric rack is 15mm wide, while the inch rack is 1/2". The rack is flush with the outside of the rail.

The clearance is left there for the guys who don't have perfect beams after welding. Right now I can't remember the exact amount, but it can not be one specific number - depends on other tolerances and rack width.

[Roadkill_321]

Thanks Gerald.

[smreish]

My table measured out to plan. I have 23/32" space - evenly on both sides.

[domino11]

The main beams, or girders, of the stationary table are made of channel iron, or C-section steel.

The most important criteria when selecting the beams at the steel supplier are not the dimensions, but the STRAIGHTNESS. Don't worry about twist,


Gerald,
What is the best way to quickly and accurately check for straightness of your beams when you get them? :confused: And how much off of perfect is acceptable?

[Gerald D]

Sighting along them with the eye is good enough. Final straightness in the rails is by shims, you just want to keep shimming to a minimum.

[Marc Shlaes]

Gerald,

I have this question that I have kicked around with JR on multiple occasions.

Do you see any disadvantage to turning the main beams the other way? That way, sawdust falls right down and the hollow outside could store bits, clamps, shuttle pro and the like. Not that the storage is that important but it would me "nice".

I didn't want to do it when the time comes without asking you if it was stupid for some reason I didn't consider.

Thoughts?

[Gerald D]

Pointing the beam out, and used for storage, could become messy. It can't be considered as clean storage, because sawdust does collect there. Table vibration could cause the goods to move and foul a passing X-motor. The table will always look cleaner with the dust collecting ledge pointing inwards.

The only reason for which I would turn the beams out, would be to run the x-motors inside the beam, inboard of belt-drives, reducing the overall width of the machine. That's one for JR to think about :), but it won't work for the other axes :(

Other advantages of pointing the beams in:
- oversized/odd-sized boards/signs can protrude into that space.
- wide, hinging-open dust feet can protrude into that space
- clamping the rails with C/G-clamps during alignment is a lot easier

[bosox79]

Hello all,
First I would like to say that I am new to this forum and I am very excited about getting started. I have been reading and reading and reading ( and subsequently getting more excited). I talked with Joe from Alabama and will probably start by getting the laser cut parts from him. However after looking through the parts I started making a shopping list of the other parts that I would need for the frame. And so I called around to some steel mills to get quotes. The problem that I am having is with the x main beam. After converting from 21kg/m (plan 10 10 322) I came up with something roughly 31 lbs/ft, and the steel mills had nothing even close about 9-11 lbs/ft. Am I looking at this wrong? I am sorry if this is a real stupid question I am a complete amateur when it comes to steel, so this is going to be a real challenge but one I am excited to tackle.

[bosox79]

I want to clarify that I am NOT trying to go cheap, I want my build to be as close to Gerald's (structurally) as possible. I just want to make sure that my calculations are correct when going from kg/m to lbs/ft. I used and online calculator and that is where I got the roughly 31lbs/ft. I also noticed in another thread that someone mentioned that it was roughly 15lbs/ft (about half of what my calc) which is why I am confused. Also the steel the I was inquiring about was 7" x 2" which fell in the range listed in the drawings, I might have to go taller and wider to get the appropriate gauge which is fine.
Again thank you for looking.

[Gerald D]

1 kg = 2.2 lbs
1 meter = 3.208 ft
1 kg/m = 2.2/3.2808 = 0.670 lb/ft
21 kg/m = 21 x 0.67 = 14 lb/ft

A 7" x 2" beam at 11 lbs/ft will be fine.

[Gerald D]

And of course; Welcome Derek! :)

[bosox79]

I am sorry for repeating something that was already stated (and for posting it in the wrong section). The sad thing is I remember reading all this early on and must have forgotten it or had it pushed out with all the other reading. Hopefully I will not do it again. I will have many posts as I get closer to ordering my parts. :D And thank you very much Gerald for all the hard work that you have put into this.

[sailfl]

Derek,

I know I drove Sean crazy with all the questions I asked him. We want to be sure we get the right stuff because we want our MM to be the best we can build.

[SteveE]

Gerald, I've just about completed the table assembly and am getting ready to mount the X rails and rack. I'm going the optional route by using aluminum angle with purchased V track. My question is this: since my overall table size is 5x12, is there a possibility that the weight of the gantry will cause the aluminum angle to deform? My concern is that since the entire weight of the gantry rests on the 4 V rollers, and the V track( and associated vertical leg of the aluminum X rail) overhang the main beams with no support under the vertical leg of the aluminum angle, that it might deform.
I am not so worried about the Y rails, since the weight of the car isn't as much. Am I missing something in the drawings that provide support, or am I just worrying too much.....

Steve

[Gerald D]

The overhang is only about 5/8" to the center of the V and the alu is 1/4" thick. That is actually massively stiff (the ratio, length to thickness, is 2.5)

If you are loosing sleep over it, put the vertical screws (that hold the rail down on the beam) closer to each other, to prevent twisting between the screws.

For more peace of mind, space those screws so that both gantry wheels are not in the middle of "spaces" at the same time.

[SteveE]

Next problem to overcome. As I sight down the main X beams(14 feet) they are bowed outwards. haven't strung out a sight string yet, so I'm not sure exactly how much of a bow I've got, but by my seasoned eye, it looks like it's probably close to an inch of bow. I've read posts where welding was the preferred solution to pull the bow back in line. Can anyone elaborate more on this? I've never tried this technique. My welder is a Hobart handler 210, hopefully that will get hot enough to do this. Oh yea, I haven't welded on the legs or cross beams yet (actually I plan to bolt on the cross beams). Don't know if this will make a difference or not.

SteveE...

[Gerald D]

Steve, correcting 1" of bow is not going to be easy. Are you sure it is that much?

[SteveE]

I'll rig up a sight line and snap a picture of it later this afternoon. Let's hope my eyesight is bad....

[Gerald D]

If the beams are bowing out, that means you have to shrink (shorten) the flanges pointing to the right side of the sketches below:

4391

Welding causes shrinkage. Therefore apply welding to the parts that need to be shrunk. Suggest you start with some welds about 24" apart and then see the effect on the beam after it has cooled. You then play with the spacing and length of welds to get it into shape, but you must wait for the cooling. Welder current set to max.

[SteveE]

Here's a snapshot of the bow. Sorry that the focus isn't better

4392

I should mention that the string is on the opened side of the C channel.

The bow looks to be about 1/2 to 5/8 at the middle.


SteveE

[Gerald D]

Okay, that bow is opposite to what I first thought. 5/8" over 14ft sounds reasonable. Will make another sketch when I get home from the commute that is starting in 5 minutes.

(That beam is not supposed to be drilled & tapped yet - we can't promise to get all the holes in a straight line ;))

[SteveE]

I have a tendency to jump in before I check the water a lot of times!!!!

One of these days, I'm going to learn to write down all the steps needed in project in the order they need to be performed in, and then follow it!

SteveE.

[Gerald D]

This will make it curve the other way:

4393

Again I suggest you start at 24" intervals. To make a nice straight weld, run the gas nozzle against a bit of scrap used as a straight-edge.

Don't worry about the holes at this stage. You could enlarge them later and put washers & nuts below. (If the oversized holes in the rails don't give enough tolerance)

The bolted/welded cross-supports will also help tremendously to hold the beams straight.

[SteveE]

Gerald, last couple of questions before I fire up the welder.

1) Is it better to start in the middle of the beam and work my way out to the ends, or does it not make a difference?

2) After all is straight, true and cooled down, can I go back and grind the welds down smooth. Or will that just let the beam bow again?


Thanks for the input and help!!!

SteveE

[Gerald D]

It doesn't matter where you start, but you see results quicker if you start in the middle. Grinding the welds will relax them very slightly and re-introduce a little of the original bow.

[SteveE]

Just a note for those that are in the planning stages and have not yet purchased steel. When you find a supplier of the large C channel, be sure to check for the squareness of the channel before purchasing. I purchased 2 20' channels to get the 2 14' rails I needed. After all welding and drilling I discovered that one of the channels was not even close to square(flanges were not parallel to each other nor were the flanges perpendicular to the face of the channel), while the other was perfect. I contacted my supplier and found out that they normally purchase from American Steel, but just prior to my delivery they got in a shippment from an import supplier. So my order was mixed. So let my woe's be a word of warning........ By the way, it was the import steel that was way out of square...... On a good note though, my supplier is replacing the bad channel for free, just my time and effort lost....

SteveE

[cvriv.charles]

I was researching steel channel online. I ran across this one site that listed the channel size like this: (7" x 12.25#). I'm assuming that 7" is the height. What is the 12.25#?

[MattyZee]

it refers to the weight of the beams. 12.25lb (#=pound) per foot. I think the drawings state ~21kg/m which is ~ 14.1lb/ft. I don't think the couple of pound variation will make much difference...

[cvriv.charles]

@ Steve - Your problem totally answered my question about purchasing really long beams like this. I was assuming that the longer the beam the greater the chance it would be out of whack. How do you check out he material before buying?!?! I was going to purchase what I need online or maybe call them up over the phone and explain to them the importance of straightness with my order.

I found a place discountsteel.com where I will probably purchase my material. I can buy pretty much exactely what I need size wise. I can buy the main x beams in several sizes. In my situation, two 7" x 12.25# x 11' beams for 268 without shipping and tax.

I actually found out about the 12.25# thing. My cad software gave me the specs for it. I just dont know how all that was derived from 12.25#. About the x rails,... I was thinking about using .375" unequal angle for my rails. The v-groove bearings would have more of a surface to roll on maye lengthening the life of the rails?!?! What do you think?

[cvriv.charles]

Oh ok,... thats fine. I'll get the 14.74 if thats what the plans call for. I need this router to be rock solid.

[domino11]

Gerald,
I found one thread where someone used bent up c channel for the table cross bearers and main beam. You didnt seem to have any objections to that at the time. Do you see any downside to doing this? I am pricing some steel for my table and my supplier, who also does my bending for the laser cut parts, said he could bend me up any size I needed cheaper. They are a little slow in work right now so it would be cheap. :)

If the bent channel is ok do you have any recommendations for plate thickness etc?

The main reason I am entertaining this is I am thinking of having a larger height than stock for 3D work and the larger beams add up in weight rather quickly. :)

[smreish]

Heath,
Knowing what I know about cutting 3D stuff. I would recommend using the 8" channel and then building a spacer or step down frame for the extra depth. This would put your cross bearers lower in the z direction.
This has already been done on one MM recently.

For routine work, you can have a "boxed out wooden or mdf" riser in place that if done well, could double as a vacuum plenum.

Just my 2 cents.

Sean

[Gerald D]

Heath, are you thinking in terms of bending up one wide C-channel instead of bolting together two narrower ones? How tall do you want to go?

(PS. it would help if you could point me that other discussion to refresh my head)

[domino11]

Gerald,
I was thinking of going in the 10 to 12 inch range for the main beam. My bender, who is probably going to supply my steel as well, suggested he could bend me some beams more economically than buying the standard channel. Also I was looking in some tables and for the 12 inch beams they get pretty heavy real fast. The smallest lbs/ft was 20.5.

The thread was Ries in Equador.
http://www.mechmate.com/forums/showthread.php?p=22004&postcount=22

[Gerald D]

. . You didnt seem to have any objections to that at the time. . . .

. . . . his beams were a fait accompli, so I decided rather to just keep quiet.

As an absolute minimum, I would pick 6mm thick, but 5/16" or 3/8" would be better.

Few bending companies will bend that accurately over 3m. Their tools are typically worn in the middle and the frame of their bender will flex at the huge tonnage required. Typically, the ends of your channel will be bent 93 degrees while the center part is only bent 87 degrees.

And then you must realise that plate of that thickness will have an outer bend radius of more than 1/2". That means your angle rail will have at least 1/2" less support.

[smreish]

Gerald,
So, I will ask the question. Would it be more accurate in this situation to use a 5/16 or 3/8 HRS flat bar and control your stitch welding and setup?
It's a lot more work, but feasible if the Section modulus/centroid/bending numbers worked out for the new made up section.
You still have the issue of unsupported rail in my picture below, albeit only 3/8" The angle section could be moved inboard, but that brings up the challenge of structural members and angle of the flanges, etc.

Picture below show with 3x3x5/16 angle and 3/8 x 12" HRS flat bar. Overall height as shown is 12-3/4" face to face

5308

[Gerald D]

I would rather start investigating rectangular box tubing (maybe a stacked pair) before trying to weld an angle iron in a straight line.

(The flanges of a channel beam are always thicker than the web)

Also if one goes to a wide channel (tall) then it should start getting vertical ribs.

[KenC]

Welding on angle iron longitudinally is the best recipy to make it cure (violently) What about using I-Beam or H-section? They are nrmally heavier and more stable in shape.
Trim off excess pertrusion under the rail angle using the Skate. Do you think it will work?

[sailfl]

Gerald,

I like the idea of rectangular tubing. Since I have problems with my C Channel, I thought it would be another way to go.

[buibui]

What about using I-Beam or H-section? They are nrmally heavier and more stable in shape.
Trim off excess pertrusion under the rail angle using the Skate. Do you think it will work?

Ken, an i-beam will work and is what I used in my build. I notched the excess the way you describe, except with a jigsaw and metal cutting blade. This was really just for aesthetics though, and an overhang would work the same.

Of course, I realize this doesn't solve Heath's problem, as weight adds up with i-beams as well.

5309

[Gerald D]

We must understand clearly that the more weight we have in these beams, the better. When we engrave small signs at high speed, even the heaviest of our tables start to dance.

[domino11]

Thanks all for the input,

Gerald, yes I understand the benefits of added mass in the table structure, but was concerned on the handling of the parts. Maybe I just have to get more beer for the helpers I will need to erect the table. :)

My initial interest in some added Z clearance was for smallist 3D stuff and a small indexer. I think I will entertain a drop table arrangement as Sean suggested for anything larger later on. :)

[Doug_Ford]

That's some beautiful work John. Really clean and professional.

[KenC]

John, beautiful work there!

What size I beam did you used? If I can source suitable H-section, I will screw the angle flash to the beam edge and glue the ract direct on the beam. More Structural stability and less work:cool:

I won't worry about bulking and bowing in the case of the C-channel.

BTW, what did you coat the rail with? Looks professional! I like.

[Gerald D]

I will screw the angle flash to the beam edge and glue the ract direct on the beam. More Structural stability and less work:cool:


and your motors won't drop down far enough.

[buibui]

Doug and Ken, thank you. I hope to have more updates this weekend.

Ken, my beam is 8" x 4" and 18.5 pounds/foot. The finish on the rails is just black Rustoleum spray paint, and the blue is a polyurethane paint (imron).

As Gerald mentioned, the motor may not reach if the rack is mounted directly to the beam. But also keep in mind that the flange of the beam may be tapered (such as mine) and the rack would not sit flat and mesh with the pinion properly.

[KenC]

Gerald, John,
Thanks for the info and advise, will follow suit. I'll look out for the 4"x8" I-beam, 18.5 lb/ft=101.33kg/m? Very heavy! is that correct? I read from my table that there is a 178x102x21.54kg/m I beam should improve the rigidity significantly without the weight penalty..

I recon with the 4"x8" I beam will also increase the effective Z-travel by 1"? with minimum lost of Z-axis rigidity?

[KenC]

My mistake, 18.5ib/ft=27.27kg/m.

Shouldn't have huge cost different.

[swatkins]

If have come across some used free C-channel for my main long beams, but the problem is the upper and lower surface are not running parallel to one and other. One side is about 1mm out of square with the outside long edge of the c section and the other side is 3.5mm out of square.

Looking at the construction of the Mechmate it seems critical that these surfaces run parallel. I include pictures because I am sure the above explanation is not all that helpful. Any thoughts?

Thanks for your time. I have run into a similar problem.. My channel is made with a tapered flange. When I hold a square with one leg on the flange and the other on the side of the beam I see a void of about 1/8", the outside edge of the flange is lower than where the flange attaches to the beam.. The beam is in otherwise good shape and I am trying to keep costs low so I was thinking about shaping the profile of the flange by removing the High edge of the material...

Has anyone ever tried to modify the skate so that it could be used to grind the top edge of the Beam?

I have not cut my 20' long 8' wide channel into the two beams yet so this is the time to correct the problem..

I was thinking about placing the beam on saw horses with the flanges facing down. That would give me a wide flat surface for a modified skate to rest against. I need some way to keep the two flanges parallel and the grind depth equal so I was thinking of making a fixture that would allow the grinding plate to be held at a 90 degree angle to the flat portion on the beam and having a gauge roller ride along the opposite flange to control the depth of the grind..

To use this fixture I would place it on the beam's wide side, adjust the roller gauge so it would take a light grind, and push the grinder to the other end of the beam.. Then I would adjust the roller gauge so that the grinder would take another light grind and push the grinder along the opposite side thus flattening it also... By alternating the sides I should be able to square up the corners and grind the beams evenly...


Think this will work?

[Gerald D]

Forget about grinding the channels, because the volume of metal to be removed is far too much for our DIY methods.

1/8" off square can easily be fixed with long strip shims in the right places.

[cvriv.charles]

Is it a good idea to add an extra inch or two to the x and y dimension for clearance? Or does the x + 600mm[23.6"] allow for enough clearance? Im building a 3d model of what I want and it just doesnt look like it will clear. Maybe its just a problem with my model.

Does the spindle face the 0,0 corner or does it face away? im thinking about adding an inch to all sides just to be sure. I see guys with tables that are 50" x 100". Why? For the same reason? if I want to be able to cut up 48" x 96" sheets,... should my x = 96" and y = 48"?

What do you think?

[Gerald D]

The x + 600mm[23.6"] allows the center of the spindle to go 50mm[2"] clear of the table top. Spindle faces 0,0

Have a good read through the whole of The starting points for building your own MechMate - selecting table size, etc. (http://www.mechmate.com/forums/showthread.php?t=63)

[cvriv.charles]

Thank you sir. Another question,... Im not saying you should but it would be very cool if there was a gallery of nothing but pics of the machines. I am still a bit clueless as to a few things. But if there was a gallery of machine pics with short comments of what we are looking at,... it would be a great help. A pic is worth a 1000 words. I know there are pic all off this forum but having to scrolling through all the threads hoping to find what you are looking for is kind of time consuming. If there was one place to go that would be awesome. Multiple pics of every square inch of the machines. I bet it cut cut down on the number of questions asked. Thanks gerald. just a thought.

[KenC]

........ I know there are pic all off this forum but having to scrolling through all the threads hoping to find what you are looking for is kind of time consuming.........

Charles, That is the whole idea ;)

Having the Mechmate plan & build advise for free are already a gift handed to you on a diamond studded gold platter, what else do you want? Who said learning is easy??? :eek:

Read, read & read.... Then search, search, search, then read over again & again & again...

[cvriv.charles]

You are right.

[Temuba]

I have a question more about design strength and not looks or "making a better mouse trap". My question is to the X-rail. I am able to purchased TS5x2x.25 steel tube for $94/20 ft. length as apposed to a C6x13 C-Channel for $150/20 ft length. My desision to use the steel tube is purely based on money.

I know Gerald has mentioned before that there is no difference in using either other than availabilty and easier to bolt and work with the c-channel. I have two options below using the steel tube and would like the opinion of anyone who could help me decide which is the better design.

The steel tube will be tapped and both will bolt the v-rail to the steel tube using 1/4"x3/4" hex bolts with washers, unless someone thinks 5/16" bolt would be better. However I am concerned about the surface area between the tube and v-rail. Option A only has 1" of mating area. Option B, if I weld an 1/8" thick by 2" wide steel to the top of the tube would have 2" of mating surface. I would like to know, if considering the current weight of the Gantry, movement, deep 3D cutting and any possible additonal weight for upgrades (bells & whistles), would Option A cause too much stess on the v-rails and cause them to twist outward and bend? Or would welding an 1/8" (or 1/4") steel on top of the tube be a better to minimize or prevent any twist or bending of the v-rail.

Any opinions would greatly be appreciated. Thanks all.

http://i585.photobucket.com/albums/ss292/temuba/CNC/TABLEX-RAILOPTIONS.jpg

Sorry, some of the dim lines and 1/8" steel callout may not be visible in photo.

[Temuba]

One other factor I forgot to mention. Option B would have a minimum of 3/8" material for the tapped hex bolt, unlike Option A would only have the 1/4" thickness of the steel tube, thus more holding power for the threads. Thanks for any help.-David

[bradm]

Wouldn't option B have a very large risk of distortion from welding, potentially resulting in even less surface area (in spots)?

[Temuba]

Wouldn't option B have a very large risk of distortion from welding, potentially resulting in even less surface area (in spots)?

Brad-Thanks for the reply. I thought of that and was only thinking of stitch welding 1" long beads every 4-6" down the length of the v-rail on bothe sides. Or in addition to the stitch welding add plug welds through the top of the 1/8" or 1/4" steel plate to prevent any distortion of the plate.-David.

[Temuba]

Instead of stitch welding every 4-6" as stated before, I can place 1" beads at every bolt location every 6-8" down the length of the x-beam. Possibly setting up the components for welding in the manner below would keep the 1/8 or 1/4 inch plates true and flat, like using cauls to glue up long lenghts of wood when using multiple clamps.-David

http://i585.photobucket.com/albums/ss292/temuba/CNC/TABLEX-RAILOPTIONS02.jpg

[bradm]

Disclaimer: I should just shut up now, I'm NOT a metalworking pro, it's perhaps my weakest area. However:

What about an Option C: using a clamping strip inside the tube, similar to the gantry rail mounts?

I note that the gantry rail uses that strip because the specified tube is definitely too thin to rely on for threads, however the strip is only 1/4", and thus threading into just 1/4" is well proven for at least the weight of the Y-Car assembly.

So it seems to me that option A is sufficient, and has less manufacturing risk. If you want more insurance, than option C involves a well documented procedure.

Hopefully one of the real metal pros will decloak and set us both straight.

[Temuba]

Yes true, I'm familiar with that detail. However I wasn't too concern with the thickness of the tubing member for tapping. With what I can purchase the 1/4" think tubing will probably be sufficient for the hex bolts. My issue is with the 1" matting surface on the top of the tube to the v-rails. The tube is 2" wide but with the two 1/2" radius corners, it will only leave 1" of bearing for the v-rail.

If using c-channels with square corners currently leaves a rough 1/2"-3/4" over hang for the v-rail. With the steel tube you can easily add another 1/2" to the above overhang. This is where my concern is. I'm thinking by welding on an 1/8"-1/4" steel plate, I would be back to the original overhang of 1/2-3/4" for the v-rail. I feel that the larger overhang would be too much of a cantilever, thus possibly twisting or bending down the v-rails over time enough to cause problems. Thanks-David

[KenC]

Dave,
Your concern is irrelevant. The rails requires 0.25mm (0.01") tolerance. Without machining/surfacing/milling, steel fabrication achieving tolerance to 1mm is consider very good. So you must shim to get to the desired tolerances. When you shim your rail, the contact/mating area will be as big as the shim you put in. One thing about shimming, it will take forever to shim the whole mating surface.
I cut out shim washer & insert them in the bolt, max contact of my 25mm sq shim are about 25mm sq (1" sq) or less at each shim location.
I will stick to option A
About your concern over cantilever effect, will that little flat plate give meaningful improvement? IT would be more meaningful to scrutinize the height of the tube to increase torsional resistance. Also, will the load ever cause this cantiliver effect to give detectable/measuarable problem? Have a finite element analysis modal & see how much the improvement will be, then you decide.

[Gerald D]

The gantry tubes are thinner wall and the outer radius at the corners is much smaller, leaving a nice wide contact area.

[Temuba]

KenC- True, I did forget to consider any shims under the bolt contacts. The reason for my inquiry regarding the mating contact is because I read earlier in another thread someone mentioning the radius versus 90° corner in regards to contact area for the x-rail.

Gerald- I'm not sure if we're on the same page. I am familiar with the gantry tube assembly, but I'll be using tube for the x beam where the x v-rails and x-car will ride on. My current tubing will only leave 1" of contact and I'm worried if after shimming the x v-rail that the weight of the gantry will twist the v-rail downward and cancell any shimming done. However with the weight distributed over four v-wheels, will the small 1" contact matter anyway?

[Regnar]

Dave, For 56 dollars (less than a tank of gas for most) I know I wouldnt be the ginnea pig for this. Time is money as well. Tapping holes, welding on strips and worrying if the outcome will work...........doesnt seem cheap anymore.

[cvriv.charles]

Dave, For 56 dollars (less than a tank of gas for most) I know I wouldnt be the ginnea pig for this. Time is money as well. Tapping holes, welding on strips and worrying if the outcome will work...........doesnt seem cheap anymore.

True that. Even though the plans call for the machine to be welded together,... doesnt mean we can go nuts with it. The more you weld the more out of shape everything could possibly end up. Why do you think the Y Car is welded together with small welds all in strategic spots?

What you plan on doing will end up being very crooked and twisted and flat out messy. You need to try and figure out another way to do it if you cant go according to plan.

Or,... you can ignore us and learn it the hard way:) Up to you:) You life. Your money. Your time.

[Temuba]

KenC- True, I did forget to consider any shims under the bolt contacts. The reason for my inquiry regarding the mating contact is because I read earlier in another thread someone mentioning the radius versus 90° corner in regards to contact area for the x-rail.

This idea was abandon. I did not want to create more work for myself, I just wanted to see if it would be an issue later on, but after forgetting that shims are required, the addition of a plate cancels out the shimming. Between using 1" wide shims at the bolt locations and the large 1/4" thick cross-section of the L-steel v-rail, I believe any twisting due to the canteliver will be removed from the equation.

Also this part of the project is much larger and bulkier than the gantry, requiring longer, thicker and stronger cross-section steel members, which should have very little movement if welded together or other components added on. The gantry on the other hand are all large area steel plates (minus the 2 tubes in the Y diretion), which can be more prone to warping if too many welds are applied without the proper jigging. If proper precautions are taken for the table/base during the welding process such as squaring, jigs, clamps, etc., any distortion should be minimal. Whether there are any distortions or not, shims will always be required to fine tune the entire machine after the build.

Also the $54 savings is only "so far" on these two steel members. When you start to add additional savings throughout the entire project it may add to several hundred dollars if not more. For some it's a big factor, for many it's irrelevant. Also, the only additonal work required is tapping all the whole on the top of the beam. Holes would have still have to be drilled if using the additonal nuts underneath.

Thanks-David

[Kart]

We are just starting our build. We have left over material that we want to use as much as possible to save on cost. We have some 3" x 8" square tube that I want to use for the main beams. Anyone see a problem with that? They are pretty hefty with 1/4" wall.

[Gerald D]

Those would be great.

[smreish]

Sounds perfect size for the main beams. Make sure you put the mechanical seam on the bottom of the tube so you don't hit it with your drill and tap.

[Father-of-Ash]

Hello all,
I need help determining my X length. The Y will carry 2 cutters, cutting points are about 14" apart. Do I just add the 14" along with the 600mm to the X length or am I missing something?

Thanks,
Bilal

[darren salyer]

Are you widening the Y car and space between the gantry beams?

[Father-of-Ash]

No I am not, I might have to trim just a bit from the inside of Y car for clearance of drill.

[darren salyer]

How will you address dust collection?
It seems your logic of adding 14" to the length is sound. I can think of nothing off the top of my headthat you might be missing...

[Father-of-Ash]

I know it's a bit of a silly question, I just want to make sure I'm not missing anything.

I wasn't really worried about dust collection for the time being, 95% of what I plan to cut is acrylic and aluminum plate.eventually I'll bring it out along the corner of the Y car from the spindle side of the gantry.

Could you check out the last two comments herehttp://www.mechmate.com/forums/showthread.php?p=72116#post72116
and give me your recommendations?

Thanks,
Bilal

[darren salyer]

Should be rock solid...I think the x bracing is overkill , but I have no formal training in designing steel structures.

[Father-of-Ash]

ok Darren, thank you.