Pattern Bits

[Mike OMelia]

I need to shape some 3/4 MDF for guitar molds. I have a router table, PC 7539 router. I am looking for advice on pattern bits (top or bottom bearings), bit diameter, etc. There will be a good amount of shaping, so longevity is a big factor. 1/2" shanks (but I do have reducers).

Honestly, I know very little about pattern cutting and pattern bits, so I am asking the pros. Assuming ignorance on my part is a very good assumption (not all things!! for now, just this issue) ;)

Mike

[Bill Huber]

I really like the Freud downshear bit, it cut very well and does not want to grab like some straight bits do. I have some spiral bits but I have found that I like the downshear better.

The Freud bits are very good and have lasted me very well, never broke one and they hole a good edge for a long time. With MDF that will be your biggest problem is the edge will dull faster then with just wood.

I can not really tell you why but I like the trim bits better then the pattern bits, just like to have the bearing on top.

http://www.freudtools.com/p-176-downshear-helix-flush-trim-bits.aspx

[pat warner]

You have a mess on your hands.
Moreover, you need power and a big bit to do this, and get some product.
I would pin-rout with a cutter ~1" x 1" x .5 shank.
A bearing guided tool, with this much dust/chip, will be bouncing and work hardening.
What??? The bearing guided cutter will chatter for the entire circumnavigation.
You have to have perfect chip/dust collection and pin routing affords that too.