Troubleshooting Fuzzy Edges on CNC-Made Moldings

Advice on reducing surface roughness and fuzz when machining complicated molding details in Poplar. July 15, 2014

Question
We have a CNC supplier cutting the moulding below for us. We have found that we must do a great deal of hand sanding to remove the fuzzy around the bottom edge of the ball surface. Is this a problem caused by the CNC program? Is it cutting speed, tooling or etc.? Maybe it is because we are using yellow poplar and should have used soft maple or beech? I would appreciate some help from people that are experienced in this area. I am not sure how much I can trust the CNC supplier to solve this.


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Forum Responses
(CNC Forum)
From contributor N:
The fuzz is likely one of three things. The material does make a difference. Poplar does fuzz up, especially with cuts against the grain as your photo indicates. You will get less with a tighter grain material, but will not eliminate it. The CNC people could go with a smaller diameter cutter, but that would increase the run time significantly. Beaded molding of this type is really tough. The best cut strategy to reduce fuzz is to cut perpendicular to the grain, but on a bead this will leave tool marks. So to reduce tool marks you switch the cutting strategy to a sprial cut path. This eliminates the tool marks, but leaves fuzz. I don't hand sand my work, I use star wheel sanders on a drill.180 grit followed by 220. The photo below is cut in cherry. On a personal note, I would not ship a product with fuzz, but one gets what he/she is willing to pay for. Ask your supplier what it would cost per foot to have them sand if capacity on your end is an issue.


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From contributor N:
Another option if this is a painted product could be to switch to super refined MDF. I will do carvings for paint, as well as casting models and this is the material to use. The regular MDF won't work, but I have had success with the double (super) refined product.

From Contributor D:
Another method would be to use a round-over bit. It’s more than likely have to be custom made, however you made with this method loose a few dots if the grain is the least bit flaky.

From contributor N:
I agree with Contributor D here. On further thought, a plunge round over run with the grain first, followed by the program to run the beads would probably eliminate the majority of the fuzz. This would increase run time but not significantly. Your CNC supplier should address these issues though. You are the customer and not happy, you need to work together to arrive at a product that you are happy with and at a price point that is good for all.

From Contributor E:
Poplar is just about the fuzziest wood you can use. Maple would be a better choice for paint grade. Maybe even birch or alder? You're still probably going to have some chatter unless they do a roughing and a finish pass.

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