Cutting MDF on a CNC

      MDF is rough on bits. Here's a discussion on bit choices and operating techniques. January 13, 2009

What are some of your cutting methods for MDF and/or flake? I'm using a 3/8" compression with a single pass at 165000 rpm and 850ipm. Large parts cut fine, but smaller parts I'm having trouble with. My bits are also heating up quite fast. I was thinking of changing to something like spacing parts out a half inch and using a 3/8 upcut to create an onionskin. Then using a 1/2 compression to finish the job. Let me know if anyone has had any success with this or can suggest something better.

Forum Responses
(Finishing Forum)
From contributor B:
MDF, I have found, will heat up your bit a lot because of its abrasiveness. You need a bit that will give you chips and not dust. The 3/8 compression bit I use is a 3 flute and there is not enough chip clearance to do a good job on MDF. Onsrud makes a good 1/2 compression bit for this. Its number is 60-163C. It is also a chipbreaker style and although it looks like it would give you a ratty finish, it does not. On your small parts I would leave about .030 (1/32 inch) onionskin and finish it with second pass. Your S/F is right on and about what I use on 1/2 in. plywood with the 3/8 compression bit. You will be able to cut 3/4 in. MDF at that S/F with the Onsrud bit I mentioned. Slightly faster on thinner material.

From contributor K:
I'm not sure what flake is, but I presume it is melamine faced chipboard. 99% of my sheet materials cut on the CNC are 18mm thickness MDF core melamine and MDF core veneer, and for these purposes I use an 18mm pcd up/down cut bit. It literally leaves a polished edge and both sides of the cut perfect and you can set the feed rate fairly high. I get over 500 sheets per new bit and half that on a resharpened one. If I cut melamine chip the cutter gets damaged and will leave lines on the MDF till it's resharpened.

From contributor B:
These PCD bits you are using, are they indeed Polycrystalline Diamond Bits? If so I just might give them a go. 500 sheets of material on one bit is very impressive.

From the original questioner:
So contributor B, you recommend using a 1/2 2 flute, rather than a 1/2 3 flute? I think I like the idea of using a chipbreaker compression. It might create less dust. But as for part hold down, you think a 1/2" 2 flute will be good?

From contributor B:
Yes, so long as you leave a thick onionskin like the .030 I recommended, it should work fine. You shouldn't get any tool side pressure, which is what moves the parts.

From the original questioner:
Okay, so I create the onion skin. What method would you suggest to clean the skin?

From contributor M:
If you are rough cutting 3/4 MDF or flake, I use a 1/2" Onsrud 60-053 at 14,500RPM and 1100 IPM. This is a slow helix hogging bit with a corrugated edge. Not so good for veneers or paint, but for templates, diewall ribs, general parts, etc. it works great. If you need a smoother edge, the bit contributor B uses is perfect. Leaves a nice finish and works with veneers pretty well or plastic faces.

Definitely onion skin at least the small parts. I like a dedicated cleaning bit, a full upcut turned down to a slightly smaller diameter from 1/4" on up, a 2 flute solid carbide works well for this, though you could just do the second pass with the same bit - it just leaves a little more dust in the grooves.

From contributor B:
I agree with contributor M. I also use the 60-153 but like he says, it does leave a rough edge. The thickness of onion skin depends on the size of the part. .030 works well on 3/4 MDF. I generally clean it with the same bit or a dedicated finisher because we have a 10 Station Tool Changer and can get the finish desired. It just depends so much on the finish required. We do cabinets also but they often get edge banded and that has to have a nice flat finish and at a perfect 90 degrees to the face of the material for the edge bander.

From contributor K:
Yeah, Polycristalline Diamond as you say. I have one in the same tool holder since January (6 months). They cost me 250 new but work out very cheap over the life of them especially if you cut MDF and stay away from melamine chip which seems to be full of sand. Another advantage is I can run the spindle at 120% and as long as I remember to give generous lead in and out ramps, I never need to use onion skinning or progressive cuts - just cut the pieces out in one go. This also ensures the bit is doing work along the length of the cutter and not just the half inch at the tip when onion skinning.

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