Using metal mills in a router?

[Jim R.]

I have a ball-end mill that would normally be used in a milling machine and I wonder if it is safe to use something like this in a wood router? This is a decent mill high quality steel and triple flute.

I ask this because a typical wood router works at a much higher RPM than a typical milling machine and I really don't want chunks of sharp metal flying off and putting holes in me.

Thanks,

Jim

[Paul Birkeland]

Generally, a tool manufacturer will specify the rated RPM for each bit that they make.

There are some woodworking bits that look an awful lot like milling bits:
http://www.woodcraft.com/Product/2084902/38526/Whiteside-Model-UDP9112-Pattern-Trim-Bit-12-SH-X-78-D-X-1-18CL.aspx

What leaves me kinda uneasy is that when you're milling steel, there is some expectation that you will be using cutting fluid and milling into a material that is a decent conductor of heat.  The steel will also be relatively thin, which exposes most of the tool to air to help it cool down.

When you mill into wood, the thermal conditions will be very different.  Even a 1/2" thick piece of wood will drastically reduce how much of the tool can be cooled at a given time, the wood itself will conduct heat poorly, and using cutting fluids is relatively out of the question.  Then you need to understand how much cut depth your end mill will allow.  1/4" of cutting depth wouldn't be surprising, so if you plunge 3/8" into your material and try to move your router, you'll probably burn the wood.

Still, there are references online to folks using end mills for mortising.  These are the same people who also say they are routing into aluminum with their hand held plunge router, which seems incredibly risky. 

[Jim R.]

Paul,

Great info -- yes, I'll check out that link and also look up the max RPM for the bit I have.

I should point out that this is really for a very superficial detail and no more than 1/8" deep and 1" wide. That would mean that roughly 10% of the bit would be in contact with the bit, which also means that 2 of the flutes will be mostly exposed to air during each turn of the bit. And this would be birch, not 304 stainless or lignum vitae :-).

Of course I can do this other ways in two passes with a dado blade and radius router bit or a straight router bit in place of the dado, but that opens possibilities for gouges and tear-outs and more sanding.

Well, one way or another this is great information and I'll just have to do some more investigating, but my gut tells me that if the RPM is ok, then for what I want to do, this will work fine.

Thanks,

Jim