#62
|
|||
|
|||
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 ) |
#63
|
|||
|
|||
Double drat!!
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. |
#64
|
|||
|
|||
This will make it curve the other way:
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. |
#65
|
|||
|
|||
Bow
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 |
#66
|
|||
|
|||
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.
|
#67
|
|||
|
|||
Double drat!!!
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 |
#68
|
|||
|
|||
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#?
|
#69
|
|||
|
|||
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...
|
#70
|
|||
|
|||
@ 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? |
#71
|
|||
|
|||
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.
|
#72
|
|||
|
|||
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. |
#73
|
|||
|
|||
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 |
#74
|
|||
|
|||
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) |
#75
|
|||
|
|||
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/showt...4&postcount=22 |
#76
|
|||
|
|||
Quote:
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. |
#77
|
|||
|
|||
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 section_beam.JPG Last edited by smreish; Thu 16 July 2009 at 10:07.. |
#78
|
|||
|
|||
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. |
#79
|
|||
|
|||
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? |
#80
|
|||
|
|||
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. |
#81
|
|||
|
|||
Quote:
Of course, I realize this doesn't solve Heath's problem, as weight adds up with i-beams as well. 006.JPG |
#82
|
|||
|
|||
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.
|
#83
|
|||
|
|||
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. |
#84
|
|||
|
|||
That's some beautiful work John. Really clean and professional.
|
#85
|
|||
|
|||
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 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. Last edited by KenC; Sat 18 July 2009 at 09:58.. |
#86
|
|||
|
|||
and your motors won't drop down far enough.
|
#87
|
|||
|
|||
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. |
#88
|
|||
|
|||
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? Last edited by KenC; Mon 20 July 2009 at 06:39.. |
#89
|
|||
|
|||
My mistake, 18.5ib/ft=27.27kg/m.
Shouldn't have huge cost different. |
#90
|
|||
|
|||
Quote:
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? |
|
|