View Full Version : PVC Help needed

04-20-2010, 02:37 PM
The other day, I purchased PVC and installed it on my system.

First off, I really like the ease of use with this software, but unfortunately have run into a snag already on my first attempt at it's use.

I took a photo of my '58 chevy and imported it into PVC. Ran thru each step and selected a 1/4" dia 60 deg v-carve bit. cut depth of .015 into a /75" piece of oak. Set in a 33 deg angle with 100% line spacing and the result after hitting Calculate looked suitable so I saved the gcode and then loaded it into Mach3.

At the CNC, I surfaced the piece of oak first to ensure that it was nice and flat. Inserted the vcarve bit (1/4" 60 deg) that I had in the program and then ran it. My resultant cut is horrendous and there is no image apparent anywhere in the wood. Even after applying a darker colored stain there is nothing and it only appears that a 3" W x 5" high profile cut of an interior rectangle had been cut.

Even though being new to the CNC world, it would seem as if the Z axis is not moving enough to bring out the photo. I can see the Z DRO changing in Mach3, but never see the actual system Z axis move and not sure that it will be noticible when changing from -0.01554 to -0.01532

I'm using a homebuild Blacktoe V2.2 system from Buildyourcnc.com. on the Z, it is using a 1/2-10 5 turn 2 start lead screw and I do have 8000 steps per set in mach3 motor tuning which is correct for 1/8 microstepping.

Am open for any ideas or suggestions on how to achieve success with this software.


Oh. including screen shot and results photo:

04-20-2010, 06:03 PM
Um, yeah, I don't think it's the software.

You have a few basic issues. 1. Your homemade wooden router will never be able to mill to a depth difference of .0001". Most pro machines that cost 50-100k can't do that. I would be surprised if you could see a difference of .01" in depth. 2. The material you are carving on is too porous to give you a photo carved relief. Something more homogeneous, such as plastic or maple, would yield better results.

Maybe try something more pronounced like a black and white pattern. Work from this to see what settings you need to change to get better results with a greyscale image.

04-20-2010, 08:21 PM
Cut your Z axis velocity and accel in half and see if it helps. If not, cut it in half again.

But he's right, 1 step on your machine is more than .0001. In my homebuilt machine, I can easily see .002 jogs in the Z axis. But even with a 2 start screw, the screw barely moves at all.

04-21-2010, 01:34 AM
Will start with cutting the vel and accel and go from there.
I fully agree that regardless of the system, you won't see the .0001 increments the program jogs in Z when cutting the image, but hate to think that I'd be limited to just plastic or maple only cuz then this was just an extreme waste of $$ for software that is unuseable.

I did have a 20" x 40" table before that I had some limited success with using the trial version of PVC, but with other system problems, that experiment didn't go far. I upped the build from that to a BlackToe v2.2 and my tolerances are much tighter than before, so if I had success with that previous system, this newer one should be just that much better.

I don't think I'll gain anything by trying to carve images at a deeper depth, and I think you guys are on the right track with my initial thought that it is the system. Definitely am really starting to lead toward that the Z Velocity and Accel, coupled with a high feed rate are way to quick for the machine to respond before the next depth increment is feed to it.

Thanks much for the assist thus far. Will make adjustments tomorrow morning and see how it goes.

04-21-2010, 03:04 PM
Found an old black and white photo of my wife from many many years ago and scanned it into PVC. Setup for using a .25 dia 60 deg v carve bit to cut into .75 mdf at a depth of 0.05.

Made some adjustments in Mach 3 to slow down the Z axis accel and velocity and set PVC to cut this at 50 ipm.

Here is a pic of my results.

She looks good enough to marry..oh wait..I did :D