first cuts, Z height issues, tiling and profiling

After owning a handibot for almost a year and a half I finally got a chance to make some cuts today. Since my Y limit switch is out of commission, I hand zeroed x, y, and z.

I cut a piece that was 4 tiles wide using the large materials jig, and they came out mostly as expected, but I had 2 issues with z settings:

1) At the beginning of tiles 2, 3, and 4, I had to manually re-zero the z axis. Tiles 2, 3, and 4 started out "cutting" several mm above the surface of the material. At the end of each tile, the router would return to 0x, 0y, 20z. It seemed like the z zero was being reset at the end of one tile, or at the beginning of the next while the bit was still in the air, but I don't see any zz commands in any of the files, and in the demos I don't see people re-zeroing in between tiles, so I'm guessing the user did something consistently wrong. Any ideas what that might have been?

2) I did a series of pockets and one profile that was supposed to cut through the material and leave tabs. The material was 15mm thick, the pockets were at 4mm, 5,5mm and 7mm, and all came out correct. The profile was supposed to be 15mm deep, but was only cut to 12mm deep in all 4 tiles, with no apparent tabs. The previews in VCarve Pro and in the Shopbot control software looked correct: cut through the material with only tabs remaining.

Again, this was consistent across all 4 tiles, so again, something I'm consistently doing wrong. I thought I said "Yes, I meant to do that" to the "cutting deeper than your material" warning. Is there some kind of software limit/stop I might have missed somewhere?

Shoptime is a really rare and precious thing for me, so any help in getting this figured out before my window closes again would be greatly appreciated.


Thanks,
-Dave

VCarve Pro v7.514
Shopbot Control Software v3.8.10

Just spitballing here but what are your feed rates? Z especially, you could be dropping feed pulses from trying to feed too fast.

Sadly, most problems like this require time in the shop to get to know your machine.

It looks like I had 1 inch per second instead of the suggested .75 inch per second for the 1/8" bit. Skipping a couple of steps during the profile plunge would definitely explain what I was seeing. Hopefully I will get a chance to try again tomorrow.

Thanks!!!

Well, steps were skipped, but not due to plunge rate. It turns out that a 61-040 bit chucked so that the end of the flute is just outside the collet will hit the bottom of the z axis travel approx 12mm below the surface of what the handibot is sitting on.

It also turns out that even if I weren't hitting the end of my travel, there is only about 13.5mm of straight 1/8" diameter cutting surface on a 61-040 before it starts to shoulder out to the 1/4" shaft, so I would have been cutting a bit of a chamfer into the top couple of mm of my material if I could have made it that full15mm down from zero.

When a new handibot is getting being assembled, (or an older one is getting a replacement router) what is the procedure for determining how far down it should sit in the collar that attaches it to the z axis? It seems like mine might be sitting a little bit high.

Hey Dave,

Here's how I set the router height on my Handibot:

*) Remove the bit and loosely hand-thread the collet nut back onto the router.

*) Move the Z-axis down until it hits the hard stop at the bottom and can't go down any farther.

*) Loosen the bracket bolts that clamp the router in place and slide the router down until the collet touches the table surface so is flush with the bottom of the baseplate.

*) Tighten the bolts to lock the router into place.

That's worked well for me and gives me working room when cutting with most bits. If you end up needing to use a very long bit at some point you may need to move the router back up to be able to completely retract from the material, but it's a quick process.

Also if you need 1/8" bits with a little longer cutting length, Centurion Tools in Virginia makes them with 5/8" and 3/4" cut length. When they get long like that they get pretty delicate, but if you need the length it's an option.

[www.centuriontools.com]

Bill