1020440S Cross Member Tubes

[Gerald_D]

In this thread we can talk about:
- what if 100x50 box section is not available?
- can the wall thickness be thicker or thinner?
- how long must the tubes be to replace a SB gantry?
- what if they are not cut square?
- etc. Anything to do with the selection of material, size, shape of cutting the cross tubes/members.

[Kim Mortensen]

I'm about to get these cut for my Y Gantry. Is my reading the plans correct, that the beems should be 500mm longer than the max size of the workpiece I'm going to use in the machine..???

I mean, if the max board size is 1220*2440 mm the I need to make the Y-size 500 mm longer, ia. 1720mm and the X lenght is going to be 3040mm long right..??????

[Gerald_D]

Yes, the drawing 102044S is correct. This how the 500mm is used:..............

1. the center of the cutter must be able to move further than the edge of the board because you often use the side of a cutter to cut the edge. Allowing the center of the cutter to move 50mm past on all sides adds 100mm to the beams.

2. The wheels of the car riding on the gantry must not fall off the ends of the rails. The distance between the Y-car wheels is 381mm and so we need to add that to the 100mm above.

Total 481mm. Using 500mm then leaves less than 10mm tolerance on each end.

(for the x-rails the distance between the gantry's wheels is 475mm leaving 12.5mm tolerance each end)

[Doug_Ford]

Gerald,

I got a great deal on 2"x4"X1/4" tube at the local scrap yard. Do you think this will be too heavy for the cross member tubes in the gantry or will it be okay? I priced new 1/8" stock at a local supplier and he wants $120. Yeow!

Doug

[Gerald D]

A heavy gantry means that the machine must slow down a lot before it can take a sharp corner. I think that the 1/4" will be too heavy.

[ldorta]

Hi friends.. the cut of mine 100x50 pipes are not realy square... on the afternoon I can post some pics. My doubt is:
What`s the square tolerance to this cuts?

Leandro

[Gerald D]

Look at Note 2 on the drawing for cutting the tubes

[dragonfinder1]

Gerald

I want to cut 1525mm ( 60 in ). So my tubes should be 1525 + 500 = 2025 mm long, is this correct? Sorry for the dumb question. I'm getting the metal as soon as the roads clear up enough to pull a trailer on safely. It only takes a few inches of snow and the Pacific North West Coast shuts down.

Dave

[Gerald D]

That's what the drawing says.

[Jeffn11]

Hey Guys - Local steel supplier doesn't have 14 gauge for the gantry tube - can I move to 11 gauge and still be okay? - Not much weight difference.

[Gerald D]

Sounds okay, but I am not familiar with gauge sizes. The tube can be 2-3mm wall thickness. You might have to drop your acceleration setting for heavier metal.

[smreish]

Gerald and Jeff.
I used 2 different wall sizes mentioned in both machines. 11 gauge on mine and 3/16" wall on Nils machines. The added weight & mass, using the geared motors, has not been noticed. The 11 gauge, which is 1/8" thickness, is a little easier to weld to. The 3/16 wall on Nils machine was really nice because I was able to tap his Tube members and not use the clamping strip internally. Lot's of choices, all worked on our builds.

If your using direct drive motors, I would highly recommend using the specified tube. The extra mass on the thicker cross tube members is noticeable.

Sean

[Gerald D]

Also, for a 1220mm [4 ft] Y-dimension, the bit of extra mass is less significant than on a 1830 [6ft] Y-dimension.

[MAC2009]

I don't want to be the dope here(to late) but where is the thickness of the gantry spec in the plans.


MAC

[MAC2009]

10 20 440 !!!!!

[Gerald D]

The wall thickness is hidden away in these two places:

5981

[bolingerbe]

I have become stuck on the cross member tube. Instead of using the normal steel I have used square tubing for the main beams and most of the formulas will not work. My overall outside main beam outside to outside length is 1952.625. I have looked throw the plans using the formula 1010300 to make sure of Y figure. The Y length is 1522.625mm using this formula. Now using the formula from 1020440S I have added 500mm to my Y length and have came up with 2022.625mm. When I cut the tube to length I have 25.4mm over hang on the outside of the x-rails. Is overhang length correct? I would like some input before welding the Gantry Frame.

Thanks, Bryan

[Gerald D]

. . . When I cut the tube to length I have 25.4mm over hang on the outside of the x-rails. . . .

Are you sure you mean x-rails? (Not the beams?)
Is that overhang equal each side?
Is that overhang to the tip of the beam? (Inside the gantry it will be less)

[Gerald D]

Have gotten to my drawings now . . .

Your rail should overhang the beam by about 21mm

The tube should overhang the beam by about 34mm and overhang the rail by 13mm

[bolingerbe]

Gerald thank you for your assistance.

Bryan:)

[oddname]

Im a bit confused on these tubes, why are tubes needed for this?

I was thinking about getting precisionwelded profiles that are 100x50x2-3mm

[Gerald D]

What does a "precisionwelded profile" look like?

[oddname]

like a regular profile I'd say, just the non-rounded corners, and they are like super-awesome in precision :)

Is radius of the cornerns needed somehow? Since not many other parts have them

[Alan_c]

I think Frallen is refering to cold rolled steel tubing, greater precision and greater cost but no better strength wise than normal hot rolled steel and for this application the super awesome precision is overkill, but it will work.

[oddname]

So the "tubes" can be perfectly rectangular? or they need to be rounded?
Thats my main issue atm :)

[Gerald D]

They do not need to be rounded. But you will then need to file out the inside corners of 1020451 and 1020452 where the tube corners will touch.

[oddname]

Ahh great, i can get rounded ones, but I thought it was more to it that what you just wrote. So its all clear now.

[Besser]

100x50 twist. Just got my steel and one tube is twisted slightly. Anyone experienced this before?

[aniljangra]

My tubes were twisted but as the assembly is done upside down, either the center or two edges of tube were parallel providing reference surface for rails when turned around, other small gap is filled up with shims. I think it wont matter but I had no option anyway. I'll post closeup pictures when I am home.

[Besser]

Any luck with those Pics? I'm thinking a sharp twist back may help my cause.

[aniljangra]

Sorry Besser, I nearly forgot about the pics as I was struggling with aligning rails on those tubes. Here are the pics showing twist, the fist one shows one edge parallel to stiffner and no gap between rail and tube
7719

Next one is the other edge of same side, showing the gap between rail and tube, also notice that tube edge is not parallel to stiffner.
7720

Better pic below (with flash off on camera) showing the amount of twist :eek:
7721

I am thinking of laying some welds where the temporary washers are, on the tubes and grinding off.

[tufanca]

The application was made friends mechmate miles? You can mail me at if? Thanks
talbistan@hotmail.com

[swatkins]

Today I was at the steel suppliers and they were out of the 4" x 2" x .125 wall thickness... So.... I thought that more weight would make a better machine and splurged on the 4 x 2 x .25 tubing... :D

Then tonight I read where it might be too heavy :(

I plan on using a belt drive for the motors and a 50" Y width... Has anyone had good results or should I just go ahead and find the light weight tubing?

Steve

[smreish]

Steve,
I used 2 x 3 .25 wall on my second machine and have not noticed a bit of trouble with the added mass of the gantry. 7.2 geared motors, 30T pinions, 56vdc G203 drives.

Plus, the wall thickness allowed for me to tap the rail holes instead of using a clamp strip.

[Gerald D]

When I started this CNC lark, it had been totally drummed into me that lighter is better. Fortunately, I had a background in metalworking machines and my experience there was the heavier the better. So I loaded some ballast on the Shopbot to see what went wrong when it got heavier, suspecting that the motors would loose steps or something like that. Well, basically nothing went wrong and from then on the MM went in the opposite direction to all other DIY machine plans . . . . .

[swatkins]

I had to pick up some metal for another project today and the metal yard had the correct tubing in stock... I decided to go ahead and stick to the plans, why mess with a known winner! :)

[Robert M]

Gerald,
Unfortunately for me, like some, the metal suppliers I contacted then, all had NO stock on that gauge, std around here is 0.120” !
If I remember correctly, and please correct me if I have either Alzheimer’s or delusional thoughts, haven’t I read heavier tubing in our case, for gantry or I believe even other moving parts my motors, is not really desirable !
Doesn’t it put more unnecessary strain & “moving time” on the motion to either start or stop this motion !?
Robert ;)

[Gerald D]

The distance required before you reach full speed is increased if you want to keep the same torque on the motor and not overload it. Therefore, if the mass is increased, the motor's acceleration and deceleration values (times/distances) must be increased. In reality we saw very little change to the motor tuning for quite big mass. With the Shopbot, we had high flexibility and had to have low acceleration for that - with the greater mass came greater stiffness and nothing really changed in the motor tuning.

[KenC]

All tube available here bulge, will it be a problem?
8352

[Gerald D]

No, that is not a problem. Just be careful to keep the rail surface flat (relative to opposite rail)

[KenC]

Thanks.

[AuS MaDDoG]

Hi All,

My Gantry beams are 100 x 50 x 3mm thick, would I still be better to add the metal backing strip drilled and tapped or would I get away with drilling and tapping the 3mm thick RHS ??

Thanks
Tony.

[Gerald D]

Do a test hole and see if you can really tighten a screw in there before it strips.

[zumergido]

hi .. iam collecting parts but i found beams of 5mm thick almost free. they are heavy 10kilograms per meter while 3mm thick is 6.60 kilograms per meter.
what do you think? the inertia will be more but the resistense will increase. UNBENDABLE
http://mimg.ugo.com/201108/8/4/9/206948/cuts/2-unbendable_528_poster.jpg

[Gerald D]

If you accept that the inertia is higher (less acceleration) then it should be good. If you have geared/belt reduction motors, you might not notice any drop in acceleration. With direct-drive motors I will be slightly nervous, but my stomach says it is still going to be good. Nobody has yet complained that their MM gantries are too heavy - it is not a point of discussion yet.

[Besser]

Mechmates are to heavy (just wanted to be the first)

[Gerald D]

Maybe your floor is too weak?

[smreish]

...Funny, I found myself astounded at the simplicity and lightweight nature of the MM. I have owned many CNC machine's in my lifetime, and they usually require an entire team, forklift, heavy lifting equipment to move or even assemble.

My particular 5x10 MM, was built, moved and moved again by myself and a mate with no special needs or additional cost. A Bakkie and a trailer was all that was needed both times.

Not sure I agree with your statement "MM are to heavy"

[Alan_c]

Hey Sean, you have Bakkies in the States, thought you only had trucks there? :D

Oh, and I think Besser was just trying to get a rise out of somebody...

[KenC]

Lets be specific.
MM is too heavy for 2 fingers to lift. :D
Too heavy to float on water.
Too heavy to for transporting with bicycle without a bakkie.
Too heavy to balance on my head...

[KenC]

Definitely too heavy for this mode of transport
Transportation (http://www.loupiote.com/photos/3711220786.shtml)

[Gerald D]

You remind me of this one http://www.youtube.com/watch?v=_8HyTyTbS5A

[sailfl]

That is amazing. It is amazing that he could get them stacked that high and then to be able to walk away with out dropping them.

[revved_up]

When I was stationed in Korea in the 80's the craziest thing I saw was 5-6 people on a bicycle or cages of live chickens stacked 8-9 high on the back of a bicycle and best yet a washing machine on the back of a bicycle. And that was in downtown Seoul.

[Tom Ayres]

I guess my question whether .188 thick tube would be too heavy has been answered. Thanks to all who have gone before me, may the force be with you.