Avoiding Blowout Cutting Hardwood on CNC

      Multiple passes, with climb cutting, seems to do the trick. February 20, 2008

I cut a lot of hardwood maple for different companies in flutes, radius, design work. 1/2" to 1-1/2" thick. I get blow-out. I have tried different speeds, feeds, single flute, double flute, triple flute, up cut, down cut. Can anyone offer me ideas?

Forum Responses
(CNC Forum)
From contributor J:
A lot of guys will try the multiple pass routine to avoid blow-outs. I would say if you have the ability to change tools with your machine, then go to a left rotation cutter to relief the corners you have blow-out on, and then go back with your regular cutter and finish the part. If not, you can program a simple vertical route where the blow-out happens, feeding vertically around .5 meters per minute and then process the entire cut. This again will allow the cutter to work through the blow-out areas with minimum blow-out, if any. Give it a try.

From contributor G:
Contributor J did hit on the spot. I would suggest a slow helix tool with chip breakers. You may also try a left hand tool.

From the original questioner:
Thanks for the responses. I will try those. Most of the blow-out happens on a radius coming in and out of the wood. Let's say I have a 3" x 70" piece that I am cutting a 40" radius along the edge that comes in and then out - in the middle of the board - that is where I get a lot of blow-out and of course corners. A lot of the pieces are exact and I am just rounding the corners.

From contributor C:
Multiple passes is what we do. We have had a few cases with some chip/blow-out in various woods doing flutes. Started doing 2-3 passes instead and this eliminated that. Also I can do a final pass that only cuts .5-1mm off to clean things up a bit. Adds a little bit of time to my runs but time cutting is less than time redoing.

From contributor U:
If you have a drill bank, put a 10mm bit into a LH rotation spindle and drill a hole where the blow-out occurs first.

From contributor W:
Maple is just freakin' hard. I treat it as if I was running on an old two spindle shaper and climb feed both ways along the grain.

From contributor A:
I work with oak, maple, jatoba (Brazilian cherry). When I first started I had a lot of issues with blow-out. I try to stay away from multiple passes when it comes to blow-out issues, as it adds a lot of machining time. What I do is first make sure your programming in climb cut. This is the recommended method for routing solid wood. Secondly and most importantly on sharp corners I make a small radius .010"-.025". This technique has made a night and day difference in reducing blow-out.

Certainly drilling a hole with a drill bit will do the trick, but it is another tool change. Same goes for using a left hand bit; it will solve the problem, but with an extra operation. Chip breaker bits certainly will reduce blow-out, but unfortunately, if you use large profile tools as I do after routing, they are not made with serrations as the straight router bits.

From contributor B:
Multiple passes works for us. The first pass is a climb cut that is typically 1/32" off the final line. Next is a climb cut to the line, and then finally a conventional cut to the line to clean up any fuzz left by the second climb cut. These are all full depth passes up to 1 1/8" thick material, running at around 150 to 200 ipm depending upon the hardwood involved. It's all usually done with a 2 flute HSS downcut spiral bit. Doing this we rarely get chip-out at the corners.

From contributor M:
This takes just a little more time per piece, but it's faster than trying to repair every part after it is torn out. Cut the end grain first. Then cut with the grain.

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