Linear bearing on 8020 mounting ????

[jzurek]

Hi all,

I am in the process of designing my machine. The basic dimensions will be 60" x 44".

While I am using THK rails and bearings for my Z-Axis I cannot afford them for my X and Y. So I am planning on using linear bearings (fully supported) from Glacern. My frame will be made out of 8020 1515 and 1530. My problem is that I cannot easily mount the linear rails to the fractional 8020. So I plan on putting a plate on top of the 8020 so I can bolt the plate using t-bolts to the 8020 and drill and tap the plate to mount my rails to it. The biggest issue I see is that the plate will overhang the 8020 on the inside of the machine and I am worried that it will deflect and bind. Would adding angle clips to the inside be enough to stiffen this up?

Has anyone used similar rails with 8020 fractional? Thoughts and comments about the design are welcome.

Thanks
Jeremy

[DonFrambach]

I did pretty much what you have planned when I built my small router. I bolted Glacern 20mm supported rails to 3/8" steel which was bolted to 8020 extrusions (1530).

[DonFrambach]

Originally Posted by jzurek The biggest issue I see is that the plate will overhang the 8020 on the inside of the machine and I am worried that it will deflect and bind.

You could use 3030 pieces instead of 1530. That would avoid the problem of the steel plate overhanging your aluminum extrusion.

You could also use one or two pieces of 1530 as cross braces thus limiting the length of unsupported steel plate.

Don

[jzurek]

Originally Posted by DonFrambach I did pretty much what you have planned when I built my small router. I bolted Glacern 20mm supported rails to 3/8" steel which was bolted to 8020 extrusions (1530).

Interesting pics and very helpful. I did not model this properly and did not realize there was a relief under the rail that I could put a bolt head into. This actually simplifies my plate design significantly. You don't by chance know how big the relief is so I can adjust my model accordingly do you? What size screw did you use to bolt the plate to the t-track?

Thanks for the help!

[DonFrambach]

I'm at work but will try to get the measurements from my machine tonight. Here's a drawing of the rail system:

[DonFrambach]

I measured my SB20 extrusions tonight.

I don't have complete access to the openings and they're not rectangular. That said, the openings are about 1/2" wide and 1/4" deep.

The opening is there to provide relief for the screw that holds the steel rail to it's base. You might notice that the screws I used to hold the steel to the 8020 extrusion were not exactly evenly spaced. That was to avoid the other screws.

It occured to me that you can cut a larger relief (in a small area of the SB20 aluminum extrusion) to accomodate any screw size you want.

I used 10/32 button head cap screws to secure the SB20 aluminum extrusion to the steel plate. A word of caution, the hole spacing of the SB20 extrusion shown in the Glacern drawing is an approximation. It's best to use the extrusion itself as a guide to where you make your tapped holes in the steel plate. (Two of the holes were a little out of place so I used round head 10/32 screws instead of the fancy button head cap screws in these two spots.)

I'm pretty sure that I used 1/4 20 socket head cap screws to secure the steel plate to the 8020 extrusion. They might have been 5/16 x 18 though. Sorry they're "buried" in my construction so I can't confirm.

Hope this is helpful.

Don

[DonFrambach]

Oops! I just remembered that I used "low head" socket head cap screws that I got from McMaster-Carr to secure the steel plate to the 8020 extrusion. Here's a link: McMaster-Carr

[jzurek]

Thanks Don! This is a huge help.