[KT88saturate]

I want to bolt my 30mm spacing linear rails to the inside of an square(ish) frame constructed of 3060 extruded aluminum from 80/20. The linear rails are 1300mm sbr16 and it appears their bolt holes line up with the 3060 drawings.

For background, I've fabbed up the whole cnc using mild steel 1"x2" tubing and the pillow bearings are binding in the Y axis. The base frame is as square as my square can indicate, and all sides are as completely parallel that I can measure.

The only problem I can see is that I had to weld the frame together on my garage floor (not the flattest surface), and perhaps there is an issue I don't know to look for.

If linear rails + extruded aluminum will work, then I don't mind starting with factory cut parts as I don't have a solid surface to work from yet.

[vger]

That is what I will be doing with some sbr20 rails on some 50x100mm extrusions. I have done a large machine with much larger rails on some 6 inch square aluminum tubing. The tubing was 1/4” wall and I just tapped into the aluminum to mount the rails. I think those rails were 30mm, been to long ago to remember for sure.

[peteeng]

Hi KT88 - You need to back the bolts off until it works then figure out what needs straightening or shimming then slowly pull the tracks down or move the bearings until they work. Peter

[machinedude]

the t slots of extrusion have draft angles that act like a built in lock washer. i bolted aluminum flat bar to two of the t slots then machined two bosses in the flat bar to keep them straight and parallel to each other and finished both those at the same time so they were both on the same plane. then i drilled and tapped all mounting holes for the rails in the flat bar. i worked of the center to center between the two rails and it worked out good for mounting the bearing blocks because i knew the location already.

[adam_m]

Yes you can, it's how my machine is built and plenty of pthers on the forum...

https://www.cnczone.com/forums/diy-c...64803-cnc.html

Adam,

[Sterob]

the t slots of extrusion have draft angles that act like a built in lock washer. i bolted aluminum flat bar to two of the t slots then machined two bosses in the flat bar to keep them straight and parallel to each other and finished both those at the same time so they were both on the same plane. then i drilled and tapped all mounting holes for the rails in the flat bar. i worked of the center to center between the two rails and it worked out good for mounting the bearing blocks because i knew the location already.

Got any pics handy?
I was thinking along these lines as well, if I understand correctly.

[machinedude]

nothing that shows under the rails but you need material thick enough to be able to sink the rails around .1 into the flats and counter bore for a 5/16-18 cap screw so that sits under the surface so the rails can sit flat on the slots you machine in. just stagger the the 5/16-18 holes between the mounting holes of the rails. mine i think were 60 mm center to center on the rail mounting holes. just use some common sense for the spacing on the 5/16-18 holes to attach the flats and you should be fine. it's a pretty simple straight forward concept. 5/8 thick flat bar would probably be a pretty good starting point to work from. i think i ended up at 5/8 x 1.5 wide. hopefully this description helps you out. the 5/16-18 holes i think might have been 120 mm on center on my build. just make sure to catch one on the ends as far out as you can get and you should be fine.

[KT88saturate]

Hi KT88 - You need to back the bolts off until it works then figure out what needs straightening or shimming then slowly pull the tracks down or move the bearings until they work. Peter

I did that and noticed it's probably an issue with the Y-axis legs. I suspect one of the legs is slightly warped from welding, so it's exerting a pulling force on the bearings with all bolts in because when the bolts are loose there one leg pulls from the bearings in the front. I removed the assembly from the cnc and sure enough the leg is not straight. I've already rebuilt this tray, so I am not confident I can keep it from warping under weld temps again. Also, I am not sure how an 11" piece of 1"x2" mild steel warps with Tig at 110amps. Maybe I need to weld hotter and move faster?

Yes you can, it's how my machine is built and plenty of pthers on the forum...

https://www.cnczone.com/forums/diy-c...64803-cnc.html

Adam,

Fantastic. I am not sure of my workmanship at the moment hahaha. If I can get accurate cuts from 80/20, then I'd much rather have a control variable assuming it doesn't add another 1k$ in cost.

[KT88saturate]

Hi KT88 - You need to back the bolts off until it works then figure out what needs straightening or shimming then slowly pull the tracks down or move the bearings until they work. Peter

You can see the gap I was talking about between the leg of the tray and the pillow bearing. Disconnecting this takes care of the issue entirely. I shimmed it with a washer between the bearing and the leg and it works well.

[peteeng]

Hi KY88 - Its impossible to weld anything without distortion. That's because steel shrinks more then 2% by volume when it solidifies, then there is the thermal expansion shrinkage due to the temp delta on top of that. So the weld puddle expands when molten then shrinks pulling metal together at a huge strain, then as it cools it shrinks further. So at best you can compensate the shrinkage if you think through the weld sequence and have very good fits. 100% welds are not required for machine frames so you can strategically stitch them satisfactorily and save some distortion. The connection will still be stiff enough for its application...

So as a TIG welder you are trained to weld close to 100% penetration for structural soundness. (I'm an ex TIG welder and trainer) In this application try for a 40 or 50% penetration so the back unmelted material supports the area when the puddle solidifies. This is predicated on a tight fit, if you have a gap then the weld pulls it together no matter what.... Plus do lots of tacks and small runs and move around alot. Long runs will get you into trouble...cheers Peter