Linear rails bolted to steel members with hard epoxy surface in between.

[hoggie]

Hi all
Can you bolt linear rails to steel members with a gravity cast thin epoxy on top of the steel?
Questions are
Will the bolt tightness crush the epoxy and therefore bend the rails?
Can you tighten the rails down to the required spec?
What is the best epoxy to use?

Im planing to build a frame with heavy steel hollow sections(200 x 200 x 10) welded and then back fill with EG to get a little vibration dampening.
Thoughts?

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[handlewanker]

Hi.....200 X 200 X10.....wow, that is going to be a very big biggie.

The problem is, with tubing that size, and I assume the overall frame size/length will be out of this World....you won't be able to successfully align the two rails for the Y axis with any degree of accuracy, and straight edges that span that distance would cost more than the machine itself, so to answer your question, I think self leveling epoxy with a retaining wall around the edges of the rail mount to contain the epoxy could do the trick.

You don't want to make it too thick as this will make it compressible and unstable.......how thick?......God knows.

There's no other real way to get a long structure truly flat and level, and we're talking about tenths of a mil over 10 metres or so.....the moment you move it, it will bend and/or twist to some degree, so the build would work best if it was assembled in the position it is going to work on.

Initial leveling with a good bubble level will help, and spot checking along the length with a straight edge too.
Ian.

[ger21]

Questions are
Will the bolt tightness crush the epoxy and therefore bend the rails?
Can you tighten the rails down to the required spec?
What is the best epoxy to use?

Yes, as long as the epoxy is fully cured. There's a UK CNC forum where most member's have built machines this way.

[hoggie]

Thanks for the replies guys.
The 200 x 200 might turn out to be 180 x 75 PFC stich welded front to front to make 180 x 150 box, i have some of this left over (24m) from a construction project.
The machine im planing to build is not going to be too big, I,m aiming for 1220 x 1200 x 400 XYZ travels.
The style of the machine will be fixed table with fixed uprights on the sides with a moving gantry on top of that.So two x drives with ball screws then gantry on top of that.with the usual Y and z axis.
I already have a Bridgeport mill with r8 spindle so might go with another r8 or maybe bt30 for a little more rigidity.
Im hoping to be able to make small cuts in steel. with not to much vibration.
The gantry will weigh approx 500 kg
This is going to be a long term project...
Cheers
Steve

[charlieslasher]

Standard epoxy self leveled is good to about 0.2mm /600mm. Better than the steel but can be scaped to be better if you have a strait edge or steel wire setup. Its a good start to getting close to an accurate machine.

[InMesh]

Just a thought I had my rails wash ground and they are 2 meters long done as a pair .

[hoggie]

Just a thought I had my rails wash ground and they are 2 meters long done as a pair .

What do you mean "wash ground"?
some sort of surface grinding process?