Attaching Rails to Welded X-Gantry

[kenz]

I've decided to join the welded gantry club and wanted to get some opinions on how I should attach the rails.

I've decided to do something like Steve_M's welded gantry. I will be using 1.5"x3"x.125" rectangular tubing. On his he used plug welding, and I would like to try to avoid doing it that way if I can help it. Also, the bolts will be spaced 7.188" apart.

I thought of two different ways the first way is with a large hole (1.1" diameter) in the bottom of the tubing that allow a socket wrench to tighten the nut inside the tubing. But this is a pretty big hole going almost all the way to the walls of the tubing, and I wonder if compromises too much lateral strength.

The other way is with putting a hole in the bottom of the tubing the same size as the top and having the bolt go all the way through the tubing with the nut on the outside on the bottom of the tubing. This way seems easier to do, but I'm not sure if it will hold the rail good enough.

I'm completely open to other suggestions as well.

117

[mikejohn]

Ken,
If you look here (http://www.talkshopbot.com/forum/show.cgi?tpc=7&post=19477#POST19477) you will find some alternative methods of doing what you are looking to do.
This thread is part of a series of three threads, (split because of their size) that covers almost everything about making your own steel table.

.........Mike

[Brady Watson]

Ken,
I welded mine up too and just tapped the 1/8" steel walled tubing to accept the original bolts. I ran it like that for about 2yrs with NO loostening of the bolts on the Y rails. I also tack-welded the rails where they met the 3X3 bulkheads on the gantry.

I doubt that you are going to compromise any strength or have deflection issues if you thru-bolt them as you have illustrated above.

You can see how I did mine www.bradywatson.com (edited by request) (http://www.bradywatson.com)

-B

[gerald_d]

Re-post of most of what was here before:

Ken, if you are placing bolts/screws at 7" centers, then a 5/16" (8mm) diameter, high-tensile bolt/screw is more than adequate. Going to a 1/2" gives no advantage, because the surrounding plate is the weaker part.

Bolting all the way through the tube is "spongy" and reduces the working height under the gantry.

The rail you drew does not show the v-tip for the "hold-down" rollers. Do you use rollers on that edge, or can you get small welds in there? (We put some tiny welds there, and also behind the rack, but that was with the original unistrut)If the welds (or bolting) gives a small distortion, you put dummy welds on the other side to pull it back.

I can suggest the following way to attach 8mm screws in 0.125" wall...
- drill 6.0mm pilot holes
- drive a hard, sharpened spike of 6.7mm diameter through the hole. This "flows" metal down the hole.
- Tap a M8x1.25 thread into the stretched hole.
Test this on some scrap first - you should see that you can tighten that screw to its limits without stripping the hole. For 2mm wall, I pilot 5.5mm.

You can also get "RivNuts" but they tend to stand a little proud.

Then you can make your own square nuts (so that they don't turn inside the tube. Lay the square nuts into notches on top of a plank and slide them into the tube..... (use 2 planks, one on top of the other, to remove, slide bottom one out first).

You can put allen-key headed cap screws up from the bottom of the tube with nuts on top - that reduces the size of the wrench hole.

Enough food for thought?


You can get more ideas here: http://www.mechmate.com/Forum/messages/9/9.html

[kenz]

Thanks guys for all the excellent ideas!
I'm not sure which method I'm going to use yet, but it's sure nice to have many good options.