Hdpe colorcore material issues

Hi I’m doing 24 signs for an rv park. the signs are 7x12x.5" thick colorcore hdpe. I used the recommended speeds and feeds from amana tools to cut with the spektra o flute bits but I continually get swirl marks on the surface. Does anybody know how to get this to stop. I have a 1/4" 0 flute that is suppose to run at 18,000 rpm at 150 IPM with plunge at 50 IPM. I have also added ramping and lead ins to help prevent these issues as King Plastics recommends for there Colorcore but I still get them. the profile cuts are beautiful but the surface has swirls all over it. I’m also using double sided tape and I do not see any deflections. Is there a different bit like a ball end mill not a ball nose that will cut hdpe and keeps a smooth surface

. Thanks for any help.

I’ve done a few projects with colorcore, and have not run into this issue, but I’m carving inverted to what you’re doing here. Your machine tram looks good based on the cutter marks. Are you using a downcut bit? I didn’t have good luck using one on my projects. I also hold mine down with carpet tape. A ball nose will not do you any good, you’d have much too small of a step-over. For bottom finish, I think you should try a standard upcut bit (unless that’s what you’re already using).

Before fighting 24 of these, can you sell the customer on an inverted carve, or are they stuck on this design?


I am not a pro sign cutter. I do have a fair understanding of polymers. Polyethylene is a thermoplastic and very susceptible to temp above 250 f and deflection above 150. When machining temp at the end of the cutting bit can gum up and heat up. This will cause all kinds of havoc, color, tecture,detail etc. Because you are following manufacture specifications for this material and bit.I have to wonder if you have a dull tool. I know Bill spoke to tram and said it’s not an issue but it would not hurt to check .

Jason - I’ve cut dual color HDPE at 60ipm without a problem - I have not pushed beyond that, but I was cutting with a 0.03125 cutter. Recommend slowing down a little and see if heating is the culprit.


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Thank you for the suggestions. I will talk with my client and see if he wants GWG colorcore which is a 2 week wait due to shipping or go WGW but inverted as stated. Thank you very much for the info. I was pulling my hair out trying to get a smooth background. This all makes more sense. Thank you Onefinity Forum Peeps.

So glad we could help! I think inverted would make the project much more successful for both you and the customer.


I worked with color core for about 5 years making signs with a shopbot for a friend to sell. I always had the marks you are showing in your picture no matter what I tried when clearing out a large area. The attached shamrock picture was cut using an onsrud 66-315. It’s an end mill with radius corners. It helps a lot but not perfectly smooth. I tried glass beading and it made it look like a perfect prefect matt finish until I ran my finger nail over it. It made a mark that there is no way to get rid of. I know you can’t reverse the colors at this point but I included a version where the center was white just to show that you can make it hard to see but it’s still there. Good luck. P.S. I like my OF much better than the shopbot.

What about doing a texture pass to give it intentional looks instead of tooling marks

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That is a great suggestion.