MichaelHenry -
Thanks. I'm slow when it comes to spending money, but I'll start checking these out.
Randy -
OK, I've done the test. I faced a piece of brass rod with the shell mill, then switched to the Proxxon. I used an old broken #80 carbide drill and stepped Z down until the bit just left a mark. I drew a few lines with it, did a rapid to Z4 and back, and then a few more lines. I did that a few times. The Tormach was repeatable to the 0.0005" that I was stepping.
Next, I removed and replaced the bit and tried again several times. The Z placement was off every time, sometimes as much as 0.012". I faced the collet nut so that I could let the ring touch the collet face, and the numbers came down to under 0.005" or so. I could see that I was getting the ring flush to the collet every time (using a strong backlight), so I went looking for the problem. Yup, the ring on that bit was cracked, and I was apparently moving it slightly every time.
I found another broken drill (with a good ring) and tried again. The result is the top row of circles. The left one is where I zeroed Z, and the next one I came up 0.0005 to check the pattern. For the rest, I did a rapid to Z4, replaced the bit, rapid to 0.1, G1Z0.0005, and stepped over and did it again.
As long as I could not see light between the collet and ring, it repeated just fine. So now we know (but check the rings before you start).
Regards,
- Just Gary |