[Bob La Londe]

I mostly work with aluminum, so please bear with me. I don't normally do much wood work. Just some quick and dirty awards plaques for my fishing club, but...

I told a friend (he has helped me out before) I would take a shot at cutting his company logo out of a piece of mohogany he is bringing over. Its big enough to do what he wants atleast three times and the scrap is mine, so I get a minimum of three tries to get it decent. Its an old piece of wood that has been thickness plained, so I don't know how dry it is going to be. The rough work and the cut out can be done with .250, but the main body of the logo needs to be cut out with a .1875, and there is a secondary background feature that will look better with the smallest cutter I can use. I can get it roughly close all over with the .1875, but I am thinking I am going to need to finish with .125 or smaller to cut one the profiles to "look" square on the inside corners. I know. I know. Finish it with a hammer and chisel, but then I'll have to make a chisel. I don't have one that small.

I figured I would just use the numbers from G-Wizard for speed and feed, but I am wondering which cutter is going to give me the best over all cut with the least amount of tearing.

My CNC router currently has a fixed speed head on it, but I do have a variable speed head I've been meaning to make a mount for on one of the mills if lower speeds are going to really make the difference on this cut. Currently its turning about 34000 RPM and I have it capped at 300IPM for rapids. I don't hesitate to cut MDF at feeds upto 225 IPM but it always needs some cleanup.

My main questions is what cutter geometry is going to give the best over all finish for this piece of mohogany?

[smdysmf]

I have used cutters from Stewart- MacDonald with good luck.
STEWMAC.COM : Carbide Downcut Inlay Router Bits
They are designed for cutting inlays in musical instruments, and go down to 1/32 diameter, but they have a short LOC.
I would suggest a down cut in whatever cutter you decide to go with they have less tear out in wood.
I would keep the RPM high on the small cutters and about .002 per flute chip load. That would be 34000RPM X .002chipload X 2flutes = 136 IMP feed
If you go down to a 1/16 or 1/32 cutter you might want to cut that in half, I don't know I haven't used them that small.

[Bob La Londe]

Thanks smdysmf. I appreciate the feedback.

I use cutters (ball end mills mostly) that small for aluminum, and your thoughts parallel my experience there. I'll look into picking up a few down cut router bits for my arsenal.

[ger21]

Downcuts will give the least amount of tearout. Whenever I cut mahogany with a 1/4" downcut, I usually stay between 250-300ipm @18,000 rpm.

Generally, the higher the chip loads, the longer the tool life. The lower the chip load, the better the finish. There's a very large middle ground that should work fine for you.

[Bob La Londe]

Thanks Ger. I seem to recall a lot of folks liking speeds around 18000 RPM for stuff like this. That's why I was considering tackling the spindle swap first.

[Bob La Londe]

Well, I just spent more money than I had on some of those downcuts from Stewmac. We shall see how they do.

[Bob La Londe]

The overall job was ok, but I had a few issues. Mostly its that wood is touchy stuff compared to metal. The incut letters were done with a standard upcut micro end mill. I didn't order any down cut router bits quite that small. Its going to need a little gentle work there with a needle file. Overall I am not unhappy with the down cut router bits. No finish work has been done on this piece yet. Not even rough block sanding.