Plunge router speed?

[MrMayor]

I was trying to cut a 3/4 inch T-channel into my work bench starting with a 1/2 inch straight bit. The bench has a 1/4 inch layer of the same material as pegboards are made of with 3/4 ply underneath as the bench top.

I'm going to buy a good 3/4 inch bit but don't know what speed to use on my plunge router (Dewalt) so as not to cause it to smoke while cutting it. I think I should make several passes at various depths until I get to the 3/8 ths depth. Thoughts?

Thanks

[Coop]

I think the depth would be more important than the speed. Just go with the preset increments on your plunge router. Especially if you are going to use a quality bit. 

[Chet]

A 3/4 inch bit can probably run at what ever you max speed is on the router.  The bigger the diameter of the cutter the slower speed you should set you router at. It never hurts to make multiple passes going deeper as you go.  For something 3/8 deep doing it in two passes should be enough.  Smoking can sometimes be caused by moving too slow of a pass.  The bit sits there and turns against a surface that has already been cut.  Also ply can smoke easier then some hardwoods because of the gain of the laminates running 90° of each other and the glue.

I would suggest an up spiral bit from a good company like Whiteside or Amana.

[MrMayor]

I used the router going from front to back which is left to right. Is that correct?

[Coop]

Clockwise is correct. 

[MrMayor]

Thanks!

[gee-dub]

I would probably run a 3/4" bit about 1/8" deep per pass unless the material was particularly nasty.  Full speed should be fine and the sound, smell or visual effect will help you adjust.  I will add that I make liberal use of variable speed on my routers to match the operation with the material.  A simple method on an "unknown" operation is to start small (1/16") and work up.  Feed rate, material, profile, etc. all contribute to the "right" thing to do.

My rule of thumb that runs in my mind when I am setting up a cut is to remove no more than a square 3/8" of material.  Just picture the area in your head regardless of shape.  I am regularly conservative and do things like 1/4" x 1/4", 1/8" x 3/8", 3/8" radius roundover in 1 pass, 3/4" radius roundover in 2 (or 3 if you use a shallow clean-up pass) passes, and similar.

[Mick S]

I'm going to go against the grain here. Not trying to step on anyone's toes, but this "full speed ahead" idea is a very common misconception.

Anytime you see smoke from a router bit (or any chip cutting tool) you need to do one of two things, or both. Slow down the rotation speed or increase your forward feed rate. The burning is caused by the chip load being too small. The chip load is the actual thickness of each chip as it's cut and is a function of the rotation speed, feed rate and the numbers of flutes or cutting edges. The formula is Chip Load = Feed Rate (inches per minute) / (RPM x number of flutes). 

Spinning too fast for the feedrate results in a thinner chip, as do more flutes on the cutter. The chips carry heat away from the cut. Thinner chips don't carry as much heat as thicker chips so the heat builds up in the cut and burning happens.

Slow down your rotation speed or increase your feed rate.

10 hours ago, MrMayor said:

I used the router going from front to back which is left to right. Is that correct?

This depends on where or how you're guiding it from. If the guide is a straightedge clamped to the bench on the opposite or far side of the router, then yes, left to right. If the guide is between you and the router, then right to left. 

[BillyJack]

Manufactures like Amanda usually will tell the recommended speed of the bit being used. I look before you run on odd sized bits.. Most  of the time you don’t need to do anything.,

[gee-dub]

We were all taught something by someone along the way.  I was taught that you should remove no more than a 1/4" square of material per pass.  Some folks say a square 3/8" but I find that a bit aggressive and it yields rough results.  Obviously not all router profiles are square so just guesstimate the surface area of the profile to be removed.

Material type factors in of course.  Plywood is full of all sorts of nasty stuff so your feed speed and bit speed should be adjusted.  the glue between layers can be prone to burning so here's the balancing act.  Too deep or large a cut and you get poor results.  Too slow a feed speed and you get poor results.  Too high a bit speed and you get poor results.  Wow, that sounds like all is lost .

Certainly plowing the bulk of the spoil out with a straight bit will get you a better result.  When running the final profile you want a good speed for the bit diameter.  BillyJack is on the money in that manufacturers will tell you the optimal speed for a given product.  There are generic speed charts as well . . .

. . . this is just the first one I found, not a recommendation.

Combined with bit speed is your feed speed.  If you take some scraps of your material and run a cut through them you will get a "feel" for the right speed.  Listen to your router.  The sound will tell you how your doing.