Setting the gantry straight with epoxy

In trying to mill some bearings I found that the gantry wasn't plumb. It was tilted a couple of degrees backwards.

Since I do not have access to a big mill to flatten the contact points of the carriages, casting some kind of epoxy filler was the most common solution for me to try.

Day 1

The set-up
I have some plates of granite that could serve as a base plate and after buying a measuring clock I cleared my schedule for a weekend and got started.

After removing the gantry I added some adjustable feet made of m6 bolts. These can be adjusted with the gantry in its normal position.

Adjusting
Then after over an hour of adjusting the feet I could get started on preparing for casting. The pictures tell most of the story. I did not use the machine clamp to hold the square as shown in te picture, it made the set-up less precise. Also, be sure to check if the square is actually square!

Casting
I had some fine silica-carbide left over from an old project and that seemed a good filler.

After making some dams to enclose the cast epoxy from foam-tape and tilting one side of the gantry slightly up I poured epoxy with the filler. After lowering it I did the same on the other side.

Oh, I almost forgot to mention this as it is so natural to me as I have done castings for such a long time:
Use a release agent to prevent the epoxy from sticking to the table!
I used release wax for poly urethane casting.
If you are unsure if your release agent will work, test it! You will not be able to take off the table if it does not work!

I placed dowels in the holes just after casting. Drilling out these holes after setting would probably be nearly impossible with this stuff... Epoxy is hard, silica-carbide is hard...

After letting it set for about two hours I scraped the sides so there would be no need to remove it after setting.

Day 2

Day two started with trying to release the granite from the gantry. Some serious banging with a plastic hammer was required but there was no residue of granite on the epoxy.

Removing the dowels from the holes was a bit harder. Some of them were well bonded to the frame. Banging with the hammer helped. After this it turned out that the filler could still be drilled. But I do think it caused some serious wear on the cutting edges though, if my chisel was any kind of reference.

I flattened some dents that had turned in to bumps on the cast bottom with a chisel. This went well but this compound is clearly abrasive, the cutting edge of the chisel had changed.

After this I encountered an unexpected job. Because the gantry was now a bit higher, the ball screws were too low. It took me over an hour to file out the holes to the new positions. After that setting up to working order seemed to go well but proof will be in using the mill next week.

Conclusion

This was the first time for me to use a measuring clock. This is a very useful piece of kit. Without it this job would have been much more difficult.

It turned out that my 18 mm mdf bed flexes so much that it is difficult to check the actual result. But it means that you really have to have a very flat and stiff base to do the measuring and casting on, my granite was for surfacing buildings but for this purpose could have been a lot flatter.