Cut MDF in One Pass, or Several?

A single pass is faster, but if you have time there might be reasons to make multiple passes. April 20, 2008

What is everybody’s preferred cutting method? Currently I am cutting with 3/4 material, usually mdf with a 3/8 compression bit in one pass.I have talked to people who cut in two or more depths for cutting this material. Does anyone have any input?

Forum Responses
(CNC Forum)
From contributor S:
There's nothing wrong with cutting in one pass, however you're cutting 3/4" mdf with a 3/8" bit. First of all mdf is killer for bits, specially 3/8". I would suggest cutting with 1/2" bits, you'll get more life out of it. The only time I cut pieces in 2 passes is when I’m using small pieces that could move on the table. I'm assuming you’re using a vacuum table to hold your pieces in place.

From contributor J:
If you can cut in one pass and get a clean cut and good speed - do it. This is the fastest way to go. If not, check your vacuum system (clean the filters, look for damaged hoses, proper spoilboard, etc). Also verify your feeds and speeds.

If you need to cut in two passes and are using a compression tool, make sure that the first cut is at least as deep as the height of the up-shear cutter on the tool (typically .4") so you don't chip or fuzz the top veneer surface of the material.

From contributor G:
I would suggest that you cut it in a single pass. Make sure your rpm's are correct based on your feed speeds.

From contributor M:
If you are looking for speed, that is if your router runs most of the time, cut in one pass if you can. Only onion skin small parts that need the extra holding power.

Take as much on the first pass as possible. It’s best to cut all the way through as the tip of a bit wears twice as fast taking two passes instead of one. The best bit life is had with top speed and most material removed per pass within the limit of cut quality. 1/2" bits do last a bit longer, but there is more kerf waste.

I get average sheet waste on the order of 10 to 12% on 4 by 8 material with 3/8 bits and large nests. Smaller nests equals more waste.

If you don't need the speed, there are some good reasons to onion skin all your parts. If you take the second pass with a full up-shear you will remove very near all dust from the sheet.

In reality it does not add too much cut time to a sheet, maybe 20 to 30 percent depending on what other ops you do. Have a full up-shear bit turned down for most of its length, except the bottom 1/8 to 1/4 inch by about 1/2mm to prevent any blowout. It's worth it to me if I am not under huge time pressure. Dust is the enemy for health too.