The CNC Project Mark III

I got the Auto z-zero adjustment working tonight. Here is the set up without the router installed.

Here it is in action

Just before baby arrived several weeks ago, I successfully cut my first real project. And it only took 2 tries!

This is a trivet, in other words a thing to put a hot pot on. The design is a hilbert curve, actually 4 hilbert curves connected to make the one continuous line. The wood is cherry. I really like cherry because of how well it sands to a glossy finish.

A couple things I learned. If you cut cherry too slowly, it burns your bit. I think I can still smell the smoke in the basement. Also if you have 2 programs, one to cut the curve and one to cut the outside perimeter, and in between you change the bit and accidentally move the alignment, it, looks like this:

This is also how it looks before you give it a quick sanding.

Here is the vac shoe with the broom bristles glued in. Later I trimmed the bristles to length and didn’t bother with the outside row of bristles.

Here is how it is mounted

While new baby was settled today, I cut out the new version of the vac shoe with the new router installed.

Here is a short video to give you an idea of the cutting speed:

After drilling the holes for the brush bristles, the piece looks like this:

Once the holes are done, the perimeter is cut, then the piece is flipped over to cut the centre hole.

Here is the finished piece with vac attachment installed. It fits like a glove!

Here is the bottom side. The bristles get glued in as shown.

Compare the new piece (left) to first try (right). Notice the old piece has the groove for the vac attachment cut on the wrong side (whoops).

Spent part of yesterday making prototype mounts for the new router. This is why they are made of particle board.

Here is the drawing:

Setting up to cut the parts. The backstop is trimmed with the CNC to make sure it is square to the CNC. It also cuts the notch. The wood to be cut has a pin in the end to locate it against the backstop. This makes sure the two mounts are cut the same. Later, the pin is used to accurately align the mount to the plate it bolts to.

Here is a cut-out part (several prototypes later). The 2 round marks near the base are there to line up my doweling jig to drill the bolts holes through the edge.

Here is the router in the mounts.

As a follow up to my last post, I did a bunch of measuring to compare the hole drilling to the original drawing I did. This tests not only the CNC, but my drawing to code conversion.

My goal for this project was fairly ambitious, I wanted an accuracy of less than plus/minus 0.01 “. This is what I was shooting for, but I was realistic enough to be happy with less than that. So my measurements show that compared to my original drawing, I am out by 0.0014″ (1.4 thousandths on an inch), so naturally I am ecstatic! I then measured the repeatability, in other words, the holes are out 0.0014″, but are they consistently that much out. After measuring about twelve different ways, I found the variation between similar holes to be less than 0.001 (less than one thousandth of an inch). I am frankly in shock. Now here come the disclaimers.

1. I could be dreaming
2. I could be inept at measuring, though I have repeated the measuring many times in different ways and I though I was out more until I realized I wasn’t calculating for the right hole size.
3. Hole drilling puts little or no side pressure on the machine. When cutting, there will be much greater loads. This could greatly decrease the accuracy. This, though, can be somewhat controlled by how fast you cut and such and the machine is built fairly heavily with the weak link being any stretch in the drive belts.
4. I believe the smallest step the CNC can take is 0.0025″, so you are dependent of your dimensions being in multiples of a step.
5. I could be dreaming

The thing is that, even if the loading decreases my accuracy, I can still make deer shaped silhouettes like nobody’s business!

Anyhow, wish me luck, I really hope I am not dreaming.

I am designing my new vac shoe. It is going to involve drilling a lot of holes and inserting brush bristles from a dollar store broom. It will make more sense when you see it. Today I drew up the design and wrote the software to write the Gcode. Writing code to write code again…

Here is the drawing, minus all the guide lines, I drew it in Google Sketchup.

And here is a pic of the Gcode simulater (which I wrote too) to show it should work.