Frankenbot CNC Router

[dpgoldberg]

If the rails are parallel, you could have just let the machine flatten it.

Nice work so far. I've got a bag of dowel nuts I'll be using on my next build. Do you think you'll need to use Locktite on them? My concern is that they may get loose over time?

The Y Axis wasn't long enough to span the table with the rails mounted on the outside of the base. So this temporary gantry sled proved to be the easiest and fastest way to flatten to top. And it only took about half a day to build the sled and router the top flat.

I'm becoming a big fan of dowel nuts! You'll notice I used them to hold together the temporary gantry as well. I doubt they'll loosen over time but a drop of locktite during final assembly couldn't hurt.

[dpgoldberg]

Now that the table is flat, the X Axis rails have been attached and the Y axis gantry assembled. The bearing blocks for the X and Y axises have been machined. I choose to use 1/2"-8 4-start (.500" lead) lead screws from Roton with anit-backlash nuts from DumpsterCNC. I turned the ends of the lead screws down to 3/8". The bearing blocks hold 3/8" bore ball bearings for the rotational movement, needle thrust bearings and shaft collars transfer longitudinal force to the blocks, which are anchored securely to the ends of the linear rails. The turned ends of the lead screw project about 3/4" out of the backside of the bearing blocks for attachment to the couplers.

[dpgoldberg]

Well, the X and Y Axises are at least. It's pretty exciting to see it moving back and forth under power. The 387 oz. steppers are hooked up with helical couplers. I've wired up limit switches at both ends of each axis. Even though I'm using Soft Limits, it's nice to have the back up should I do something stupid like turn the Soft Limits off in Mach 3. The limit switch at the drive end also doubles as a Home switch. Pretty clever of Mach 3 to know how to read the signal depending on what it's doing.

[dpgoldberg]

Well, all the mechanical fabrication is done and all three axises are moving as they should. The limit and home switches all seem to function correctly. I've got the Porter Cable 892 Router mounted using a bracket from K2. At this point all that's left is to rangle the cables so they don't get fouled. Then I can start cutting!

[dpgoldberg]

Installed T-slot tracks and hold downs from Rockler and ordered a set of Ultra-Precision collets from Think & Tinker. Once I get all the cables and wires worked out I'll make a cover for the exposed terminal strip on the end of the table.

[CarveOne]

Installed T-slot tracks and hold downs from Rockler and ordered a set of Ultra-Precision collets from Think & Tinker. Once I get all the cables and wires worked out I'll make a cover for the exposed terminal strip on the end of the table.

Looks like you are ready to do some serious cutting. It would be a shame to mess up that nice tabletop by cutting through the project material. If you keep some low cost luan door skin sheets around you can cut it to size and put it under the material that you are cutting. Then you can cut slightly through into something other than your table and T-slots.

CarveOne

[dpgoldberg]

Looks like you are ready to do some serious cutting. It would be a shame to mess up that nice tabletop by cutting through the project material. If you keep some low cost luan door skin sheets around you can cut it to size and put it under the material that you are cutting. Then you can cut slightly through into something other than your table and T-slots.

CarveOne

Already doin' it! That previous picture was just to show the clamps in action. Here are some pictures of some of the first parts I've cut out, with a disposable layer on MDF underneath. There's also a photo of the vacuum hose attachment, which was in fact the first thing I cut with the machine. Once I get some brush material I'll make a full on Dust Shoe.

[CarveOne]

Already doin' it! That previous picture was just to show the clamps in action. Here are some pictures of some of the first parts I've cut out, with a disposable layer on MDF underneath. There's also a photo of the vacuum hose attachment, which was in fact the first thing I cut with the machine. Once I get some brush material I'll make a full on Dust Shoe.

I've been thinking of doing that on a 48" section of my table the first time I surface plane the top or replace the spoil board layer. There are shallow cut marks in the top now. The T-track comes in 48" sections, and it would be too expensive to do it over the full 134" cutting length. The simplest method I have been using for MDF and wood is to drill 1/16" holes at the corners of the material and use 1-1/4" brad nails to hold the material down. I trim the ends a little to get rid of the holes. Brad nails put little holes in the table top, but there is no real harm to the MDF table top, and they hold really well. A carpenter's chisel will pry the material up easily.

CarveOne

[dpgoldberg]

I've been thinking of doing that on a 48" section of my table the first time I surface plane the top or replace the spoil board layer. There are shallow cut marks in the top now. The T-track comes in 48" sections, and it would be too expensive to do it over the full 134" cutting length.

Another option would be to lay down a full sheet of 3/4" of 1" thick MDF and cut you own T-slots using a bit like this one from Rockler.

Hanging Slot Router Bits - Rockler Woodworking Tools

It takes very little clamping pressure to hold down a workpiece and the MDF slots are likely to hold up just fine.

Another, in between option would be to buy some lengths of 1/2" x 3/4" rectangular aluminum tubing and use the machine to mill a 5/16 slot along the entire length. Then use the machine to drill and countersink mounting holes every 4 inches.

[CarveOne]

Another option would be to lay down a full sheet of 3/4" of 1" thick MDF and cut you own T-slots using a bit like this one from Rockler.

Hanging Slot Router Bits - Rockler Woodworking Tools

It takes very little clamping pressure to hold down a workpiece and the MDF slots are likely to hold up just fine.

Another, in between option would be to buy some lengths of 1/2" x 3/4" rectangular aluminum tubing and use the machine to mill a 5/16 slot along the entire length. Then use the machine to drill and countersink mounting holes every 4 inches.

Your second idea with the rectangle tubing sounds pretty reasonable for a long table like mine. I'll keep that on my back burner for a later upgrade. When I don't use a bit that lifts the material I just box it in with wood strips using the brad nails and it works well enough. Sometimes the wood strips have a little ledge on them to help hold material down. I'll do that when I cut the aluminum router mounts for my new PC7518 router. That will be a good project for a video.

CarveOne

[dpgoldberg]

So I dug around in my box of router bits and it turns out I had one of those T-Slot cutting bits. So I cut a little test piece. First a 3/8" wide by 3/8" deep slot was cut with a regular straight bit, then the slot cut with the slotting bit. The resulting slots are amazingly strong, certainly strong enough for this application. I wish I'd thought of this before spending $125 on aluminum T-Slot extrusions. (Well, not really, the anodized blue looks really sharp!)

I think I linked to the wrong bit before, the correct one is:

Rockler T-Slot Cutter Router Bit - Rockler Woodworking Tools

[dpgoldberg]

I guess one of the great things about this hobby is learning what works and what doesn't and improving our machines. After only a week of cutting with my newly finished CNC, it was obvious that the salvaged linear mover I was using for the Z axis just wasn't up to the task. Too much lateral slop.

So I tore it apart and rebuilt the moving carriage. I used bushings instead of bearings and mounted them based on idea perfected by John (Microcarve) on his brilliant little desktop machines.

For each rail, a pair of bearings was press fit into the ends of an aluminum tube. The tube was 1.25" OD x .75" ID. The ID was about .010" undersize so I bored out each end of the tube on the lathe to just .001" under the OD of the bushings (.75"). Each tube was milled flat and drilled and tapped for mounting to the carriage plate.

A new carriage plate was made from .375" aluminum plate. Holes were drilled and tapped for mounting the bracket for the anti-backlash nut and the K2 router mount. Holes for the mounting screws were drilled and counter sunk. The holes on for the bushing tube on the left were drilled just to fit the #10 cap screws so the plate would stay square to the rails. The holes for the tube on the right were drilled and countersunk oversize so the tube could be locked down once the rails were assembled, to avoid binding.

I was able to reuse all of the rail and lead screw assembly with no modification. The end result is simple, solid and works like a charm! It took only a couple of hours to make the new parts, far less time than I've spent monkeying around with the old bearing slide trying to get it to work.