rough edge from router bit

[Ben Grunow]

I am running some simple MDF casings and having problems with rough corners. I have an older Delta router table (aluminum grooved top, crappy fence and jerky adjustments, model unknown) that I have fitted with a 3/8" diameter beading bit. I am running 3 1/2" strips of 3/4" MDF (standing up, nice and slow, with a brand new quality bit, with feather boards to hold down and against fence and full support for the piece front and rear) to create a bead along 1 edge of the piece. THe shoulder where the flat face of the MDF stops and the recess before the bead begins is very rough. I can sand this out but I have MANY pieces to make and I would rather not.

Anyone ever have this problem and solve it? Might be time for a new RT.

Do I need to make 2 passes?

[Bruce Wrenn]

Get a maginifing glass and take a look at the bit. Is this area sharp and crisp? Could be a defective bit. Worth a look.

[Jim Becker]

MDF will rapidly take the edge off your cutters...very abrasive stuff. As the edge deteriorates, your surface will suffer more and more. Nature of the beast. That said, you might try running one pass at "almost" where it needs to be with a final, finishing pass at the full profile. Even in hardwood, that can help keep things clean as the bit doesn't work so hard on the final cut.

[Jim Chilenski]

I have an older Delta router table (aluminum grooved top, crappy fence and jerky adjustments, model unknown) that I have fitted with a 3/8" diameter beading bit.

Ben,

It sounds like you are using a Delta Router / Shaper. I'm betting that this is the case and that you don't have a router in a Delta router table. If this is the case then the problem IS your Router / Shaper. I have the same unit and use it all the time. It is a great machine with a couple of exceptions. The biggest one, and the one that is probably your problem, is that the rpm of this machine is too low to spin a beading bit fast enough for a clean cut. Its perfectly fine for large bits, panel raising, etc. But way too slow for small diameter bits even with a slower feed rate.

I would try using the same bit in a hand held router mounted to a piece of plywood as a table with a make shift fence just to see if it's performance improves. If it does then your idea of a new router and router table is on target.

Jim

[glenn bradley]

What Jim Becker said.

Also, this might be a job for a couple-three bits; if you're doing a lot of MDF you will dull a bit before you're done. One bit can go out for sharpening (or just be replaced depending on cost) while you use the next. The third bit is for when the second dulls before the first one is back from the sharpening service or you've had a chance to replace it. :D

[Ben Grunow]

Great ideas. THink I'll try 2 passes first and if that doesn't solve it, try another router. Pretty sure the bit is good. Seems like the MDF wouldn't be a challenge for the bit to cut in 1 pass but it's worth a try. I wonder what RPM that thing is turning anyway. Tomorrow is the day-200 pcs to run. Thanks guys. Ben

[Norman Hitt]

Ben, without changing the setting, try running a piece that's been milled back through the opposite direction, (climb cut). I had some rough edges on some red oak I was beading similar to what you are doing, and the climb cut as a second pass did the trick.

[Ben Grunow]

Well, I think Jim hit the nail on the head. The hand held router made the cuts nice and clean with only minimal tear out. The RPM of the hand held is clearly WAY higher than my POS router table and the cuts were great and what a relief to not have to sand about 1300' of casings!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Thanks Jim and I owe you one.

THe MDf does have some tear out but I think that is unavoidable because the bit is coming out of the material on a square corner and MDF is soft. THe corners will be knocked off by the painters so the paint will stick anyway and the tear out is small enough that it will be gone when they sand (not me).

Is there a set of guidelines for router speeds for various bits or materials or a simple rule of thumb for gauging speeds? Anyone?

What a great place and great people. Made my weekend.

[Mark Rios]

Is there a set of guidelines for router speeds for various bits or materials or a simple rule of thumb for gauging speeds? Anyone?


Here's one from Tom:

http://www.newwoodworker.com/ref/rtrbtspds.html

And one from Porter Cable:

http://www.portercable.com/index.asp?e=5836

I'm sure there are others out there but I think these are pretty close to the others if not the same.

[Ben Grunow]

Thanks Mark. Ben