Cutting PVC Edge Finish Help

[Ken Sully]

I have been cutting PVC and am not happy with the edge finish. I know I could do an offset and then a final full depth final pass. Wondering if there is away around that.
Thickness 1" and.75
Using a single edge O flue .25 Vortec Tool
17,000 2.3 in/sec chip .0081
.1587 cut depth
I get a pattern on the edge that looks like a cross cut metal file.Should I use a different cutter or different feed/speed? Picture attached

[coryatjohn]

What do your chips look like?

[srwtlc]

Hey Ken,

I still think that bit is screamin' for more food. Try pushing it up to 3.2 - 3.5. Need to get the chip load up to around 0.012 at least . Also try increasing the depth per pass to at least 0.25, but maybe 0.375. If you can, jump up to a 0.375 diameter O-flute. With that, you'll need very good hold down. Time for a vac table....:)

https://www.google.com/url?sa=t&source=web&rct=j&url=https://versatex.com/PDF/C-4_Moulding_n_Millwork.pdf&ved=2ahUKEwiGu9bGsLDvAhWKKs0KHXZhCj0QFjALegQIHRAC&usg=AOvVaw2fTwh6hJTvjNlL_hM7bKuq

[Ken Sully]

No sure this is the best way to describe the chips....mouse turds. I will push it harder. Larger bit is a problem thing to squeeze as much out of a 4x8 as we can

[steve_g]

You’re not going to like what I have to say…

I’ve cut TRUCKLOADS of HDPE and UHMW this last year… I tried everything I know to improve my cut quality including resetting up my machine. (PRT Alpha). The best I can get is when cutting with a 3/8” 2 flute up cut spiral “O” flute bit and a .010” chip load. When I run the same material with the exact same bits and speeds on my customers ShopSabre, the parts are glass smooth.
Machine mass does enter the equation!

SG

http://www.talkshopbot.com/forum/attachment.php?attachmentid=34451&stc=1
The best my PRT Alpha can do...

http://www.talkshopbot.com/forum/attachment.php?attachmentid=34452&stc=1
What my customers machine does at the same settings

PS:
I've fiddled with these images to show the cuts better.

[Ken Sully]

Dang! Steve did you try a .020 off set and then doing the final cut at the exact size? Doing full depth pass

[steve_g]

Yes… a .010” onion skin. It looked the same as my other cuts but without the stepdown watermarks…

After posting the above photos, I got to wondering how much difference a spindle vs: my PC 7518 would make.

SG

[Ken Sully]

I am running Spindle my marks appear to be some what less than what you have. BUT not smooth

[EricSchimel]

Ken, I'll add to what the others have said as well, for plastics like this there's only so much smoothness you can get out of V rollers, I've tried dialing it out as much as I can and while I can get close, I don't think I could ever get to the cut quality that we see from the ShopSabre in the pictures above. Whether that's because of mass, or that those machines have beefy linear rails (or both) I'm not sure.

What I would recommend specifically for PVC is see if there are some bits that are meant just for it. Contact/look at Onsrud or Amana Tools.

A few years ago I had to cut some very dense model foam. I tried it with some plastics bits and I ended up finding out that there are bits specific to that material. Once I got those things were a lot better looking.

[srwtlc]

Eric, just for fun and somewhat unrelated, but do you think you get better edge quality out of your Centroid/Acorn conversion? I know I do on mine, although the backlash on my 5:1 planetaries is considerably less (resolution is higher as well). Just curious.

[EricSchimel]

The Centroid upgrade I did resulted in better quality cuts on my HDPE. It's likely because that controller is much smoother. However it's not magic.. It's not going to help account for a sloppy worn out machine, or hardware that's just not as tight/has as much mass as a beefier machine.

[srwtlc]

Yep, agreed!