Base for the ShapeOko

I built a new base for my ShapeOko mill. It’s not quite done, and I’m not quite happy with it, but I took some photos.

Here is what I did.

I started with a 2′ x 4′ sheet of 3/4″ MDF. This is a dense fiberboard that is pretty flat. I decided that I would bore and counterbore holes in it for 1/4-20 tee-nuts. Then I could thread bolts in from the top to hold down my work pieces and jigs and fixtures. I decided on a 3″ x 3″ hole pattern for the tee nuts, so I laid out the dimensions of the mill and centered a pattern inside it.

I had temporarily mounted my mill to another piece of 3/4″ MDF that I had around, but it was not the permanent base. When I mounted the mill to it, I knew I was going to want to be able to work on a large sheet of MDF, so I put some 3/4″ risers (strips of plywood) under the end plates. This made enough space to slide a 3/4″ sheet under the motor mount plates.

So that’s what I did.

It turns out that the frame of the mill is just wide enough to do three rows of holes. Each row had five holes in it for a total of 15 holes per setup. I laid out a 3″ x 3″ grid and just eyeballed the starting location for the endmill. I wrote a Perl script that generates G-Code for arrays of holes (with or without counterbores) and used that to make the program.

Unfortunately I seem to have entered an incorrect value for the first run and after the counterbore was done the endmill took a dive to the center of the earth! Sure wish I had the E-Stop button wired up. I managed to hit the reset button on the GRBL Shield before any real damage was done, but the first hole is pretty ugly. Oh well, you have to crash your mill at least once!

After that excitement I generated the program again, looked it over to make sure it was all good, and started it up one more time. This time it milled the holes without crashing and 15 holes were done in about 12 minutes. I probably could have sped up the feed rate and taken more material per pass, but I’m still learning what this mill is capable of.

I slid the sheet of MDF over, lined it up and ran the program again. And then again…

I turned the sheet around for the last few rows so it wasn’t hanging completely out in the air.

Finally I was done with all the holes.

Here is the first part I’m not happy about. The counterbores are not quite as deep as they should be, and the depths are not all quite uniform either. Unfortunately this means that when I drove in the tee-nuts they didn’t all seat flush. It’s my own fault, so I’m doubly annoyed. I’ll probably buy another sheet in the future and do it all again. In any case, I decided to forge ahead, and seated all the tee-nuts.

I spread some Tite-Bond III glue on the back and put a 1/4″ sheet of MDF over it. This is another area I’m not super happy about. I bought 1/4″ for the backing on the spur of the moment and now I think that I should have used another sheet of 3/4″ to make it more rigid. That’s what I’ll do when I do it over. And I’ll probably glue and screw them together.

Anyway, I glued it up, put some cinder blocks on it and went away.

I wanted even more height under the mill, since I plan on making some jigs and fixtures out of 3/4″ MDF, so I made 1-1/2″ risers by gluing and screwing two strips of MDF down where the end plates sit.

I also made some new angle brackets out of some 1/8″ x 1-1/2″ x 1-1/2″ aluminium and bolted the mill down with some 1/4″ lag bolts.

After that I grabbed my dial indicator and checked the height of the rail on both sides of each end. They were pretty close — .004″ – .008″ but the middles of the rails are way off. I don’t know if it’s sag, or if the MDF isn’t flat. I plan on milling some 2x4s and screwing them under the MDF as stiffeners, so maybe that will flatten it out a bit.