Polycarbonate engraving

[twelchPTM]

Hey so I am engraving polycarbonate using a 30 degree tipped engraving bit from harvey tool. I am cutting a depth of .009 at .7 IPS and 21000 RPM. I am engraving a reversed image into what becomes the back of the piece. When the piece is finished it all looks good but I am getting a slight ridge on the back of the piece where the lines are. This is not critical in this case but I have some up coming projects where it will be. I am pretty sure this can be resolved my adjusting my speeds and feeds but am having no luck. Any info anyone could share would be great

[mcmark]

My trick is to run the piece, then re-run it at .001 or .002" deeper. I just move the tool off the part, move Z to -.001 or -.002 and re-zero Z. This gets rid of that ridge you are talking about. Make sure to jog your tool up above your part after the re-zero. Also, I zero on the top of the part, not the table. I don't know if 21K RPM is burning the polycarbonate or not, but it may be to your advantage to slow the spindle some (just something to try).

[twelchPTM]

Thanks for the tip, When using this particular bit in the past the manufacturer told me to run at my max rpm, however that was aluminum so you may be right. As far as going back over the cut it... I ran several samples at the same depth with 1,2,3,and 4 passes to see if the multiple passes would clean it up but the single pass had far less of a ridge then the multi pass but even as I type this I realize that could also be because of the rpms being so high. I even tried running a clean up pass, same depth opposite direction and that actually had ugly results. I will try some samples at lower rpms and post my findings....

[twelchPTM]

So I ran my test and here what happened... The PC router has 6 settings 21, 19, 16, 13, and 10 (thousand RPMs), I engraved those numbers into the polycarbonate and at 21,000 it had a slight ridge but I could see fuzzies in the lines, at 19,000 it looked good and had almost no ridge at 16,000 it looked just as good as 19,000 but under close inspection i could see some fuzzies at 13 the ridge came back as well as the fuzzies and at 10,000 the ridge and the fuzzies were no were near acceptable. I think the RPM I really need is somewhere around 17,500 or 18,000 (suppose this is where a spindle would come in handy over the PC router. I am thinking I can tweak the IPMs to get even better results but this leads back to something I was trying to figure out before-actual IPM. I know when working with very small detailed cuts I can set the IPM as high as I want but that doesn't mean the bot is actually going that fast due to ramping, so just because I set the machine to .7 IPS doesn't mean I actually get there considering my lettering is 3/16". I there a way to know the actual max IPS the machine reaches or am I just being anal at this point (the piece looks flawless to the naked eye and feels flat to the untrained finger)

[mcmark]

Hi Thomas,

I actually run at 6000 rpm. One thing that polycarbonate doesn't like is being heated by the cut. I don't know if this is an option, but a moat made out of something like Mortite and a little water/Dawn mixture does wonders as well, but you'll have to evaluate if that will work for you or not. Just enough water/Dawn to cover the engraving area by about .030. Not so much that you are slinging the mixture everywhere, just cooling the tip.

[twelchPTM]

I found that when I run my engraving bit under 16000 the cut quality worsens. I imagine this could be due to the type of bit as well as the specific formulation of the PC i am using. I found a configuration that provides the quality I am looking for, 30 degree tipped engraver , 19000 RPM, .07 IPS, .009 depth and as I am not one to mix water and power tools I rigged up an air cooling set on my bot. The end result is a very smooth finished project although I feel my efforts may have been a little over the top. When I showed my boss the first run and what I have as a final product and explained how I got there, he laughed and told me I was picking fly $**t from pepper.

[gene]

I aint never heard that one . its a good explanation