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How do I reduce tool marks on CNC routed PVC?

mjkjr

mjkjr

New Member
Hi Everyone,

I've got a small DIY CNC router that I am fairly new to using. So far I've been cutting Pine boards on it with great results. For what its worth, I'm using Cam-Bam software to create my G-code, and my machine runs with Mach3. I'm getting comfortable with the software and I like it so far.

Now, I have a client project that I am working on that is routed out of PVC (King ColorCore), and the issue that I am having is with burrs on the edges and tool-marks on the inside (flat) of the routed letters. I used a 1/8th bit to rout the letters, but there are very visible tool marks and little lines of stringy "burrs" where the paths overlapped.

What I've done for now is knock off the burrs from the edges with an x-acto blade, and smoothed the flats of the letters out manually with a cylindrical dremel bit. But, the time it took would easily triple the cost of these signs.

Do any of you have any tips or advice on what I should do to reduce these tool marks? I'm thinking for the edge burrs that I can do a "round-over" profile pass (not sure if that's the right term) on the CNC to knock the burrs of the edges at the end, but I'm not really sure how to approach smoothing out the inside flats of the letters.

Thanks in advance!

The photos I've attached show the burrs, then the tool marks before, and then finally the result after I've manually cleaned this up (still not totally happy):

20181025_192532.jpg
20181026_111145.jpg
20181026_115642.jpg
 
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GB2

Old Member
King Color Core is a great material but can be challenging to rout. You obviously do not have the correct bits and furthermore it looks like there is some play in your router or it is underpowered for this job as those cleanout marks are very irregular. You need a bottom surfacing bit like an Onsrud 66-314 for the clean out cuts and probably need a different bit to resolve the burr issue.
 
mjkjr

mjkjr

New Member
Hi GB2,

Thanks for the info on the bits, I was just using a straight bit, I didn't realize there was a whole other bit for bottom surfacing, though that makes sense now.

If you are referring to the last photo there, as I mentioned in my post, I did that manually with a drill and a cylindrical dremel tool in an effort to smooth out the bottom, so that's why it's so irregular.

For clarification: First photo is before any cleanup, second is after I used an xacto on the edge burrs, and third is after I dremeled out the flats.

I'll get one of those bits and try it out for the next one.
 
tbullo

tbullo

Superunknown
I have the best luck routing color core with straight flute bits. And I always use the largest bit as well. Then if any little edge is left after routing, I hit it with a flame real fast.
 
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Eric H

New Member
Make sure it's a good sharp bit. Single O flute bits work well you could also try down cut bits also they will leave a clean edge. No bit will give you a perfect mark free bottom some will be better than others and your machine makes a difference also. Colorcore is HDPE not PVC.
 
mjkjr

mjkjr

New Member
Thanks for the info guys!

tbullo: the bit I was using was a carbide 2 flute straight bit, 1/8th". Thanks for the flame idea, I will try that on the next one. I was thinking I could do a rough pass with a 1/4" bit and then a second pass with the 1/8" bit to get into the tighter corners. Do you think this would make much of a difference on the overall tool mark appearance? I don't have a tool changer so it would be slower for me to switch between bits rather than run one bit through the whole job.

Eric H: I'll get one of those O flute bits to try as well. I'm OK with some tool marks, but I do want reduce it as much as possible so they aren't so drastic. Thanks for the clarification on the material, I guess I didn't realize that it wasn't PVC. It is very heavy too, I suppose that explains why.

My machine has an old router in it for now, but I just ordered a proper spindle on ebay, it should arrive end of next week, though then I need to find time to wire it and the inverter all up :)
 
Jester1167

Jester1167

Premium Subscriber
I haven't read all the replies, but put a layer of mask over the top before you route
the PVC.
 
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Sandman

New Member
I'm thinking your bit was very dull to produce rough top edges and machine problems for the bottom finish. I usually cut this stuff with a single O Flute and don't end up with bottoms looking that bad and my top edges never need anything done to them, sharp and clean. Even a sharp spiral up cut won't leave that bad of a top edge.
 
mjkjr

mjkjr

New Member
So, I ended up ordering a couple of bits from Onsrud based on GB2 's recommendation, and I finally got a proper spindle wired into my machine, so I'm about to do some test cuts and see what results I get. Before I do, I was wondering if anyone here might have any good idea about what a sane speed & feed would be for this material?
 
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Sandman

New Member
When I cut King Color Core I had a plunge rate of 30 ipm, 150 ipm feed rate, and 18,000 rpm. It cut extremely clean.
 
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Andy D

Active Member
My workaround to avoid trash on the edge is to do the main route and then a second route file that's a hair larger or smaller.
 
P

player

New Member
Your DIY machine most likely doesn't have the resolution in steps or the rigidity needed to produce a chatter free route.
 
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