Setting Correct Router speed

You only need to slow down for larger bits. I don’t own any bits that require me to run anything slower than the fastest speed. I don’t know what the official rule is for when to slow the router down but I would guess it to be on bits that are more than 1.5” in diameter.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

up to 3/4 @22,000 – 1” @18,000 – 1 1/2 @16,000 – 2” @15,000 – 3” @12,000

-- -erik & christy-

Greetings Joe:.... If you have a variable speed router, one way you know is run some stock at different speeds. If the router starts burning the wood, your’re too slow on the speed, or the bit is getting dull. In which case you will (may) get tear-out. I have a Hitachi M12V with 5 speeds in my table, and also one for hand-held stock. For most operations I do, I usually run on about 2- 2 1/2 for roundovers, spiral bits, etc. It’s all gonna depend on what is comfortable for you… just play with it at different settings, untill you get the right “feel”... it’s all in the feel. But for big bits like door making and raised panels, run it pretty slooww. The stock you’re running, the type of router you use, all play a role in what you’re making or routing, I should say…

-- " At my age, happy hour is a crap and a nap".....

One of my Freud router bits came with this little chart:

Up To RPM
1” 24,000
1-1/4” 18,000
2-1/4” 16,000
3-1/2” 12,000

I added a column for the associated setting on my router and put it by my router table.

This is at least a guideline.

-- “Big man, pig man, ha ha, charade you are.” ― R. Waters

It’s interesting to analyze those recommended settings in terms of Surface Feet/Minute (SFM), since that is how lathe cutting rates are calculated. I calculated this out at (Maximum Diameter X pi /12) * Router Speed in RPM. In the interest of simplicity, I’m only considering the outer cut, since the inner portion will cut at a lower SFM rate.

Effective Cutting Rates in “Surface Feet Per Minute” (at the outer edge of a router bit)
Diameter…..............Webwood…...............ChuckV
...............................SFM/RPM…................SFM/RPM
3/4”......................................................4,320/22,000
1”.........................6,280/22,000…..........4,710/18,000
1.25”.....................5,890/18,000
1:5…......................6,280/16000
2”.........................................................7,850/15,000
2.25”......................9,424/16,000
3.5”......................10,990/12,000

Sorry about the dots, but when I first posted it, the web site put everything in a single column.

So the consensus seems to be that the wider the router bit, the faster in effective SFM you can go, but Freud is clearly choosing on the side of caution (or liability), whereas Webwood (Eric & Christie) got their data from a more daring, ambitious or experienced source.

But the resulting formula and chart should allow anyone to calculate a safe and effective speed for router bits of larger than 1” diameter. If there is any serious further interest, I’d be willing to produce a graph that shows these two sets of choices and post it on a photo site.

-- Bob www.singularengineering.com - A sideline, not how I earn a living

I also have a couple of LONG router bits for which I slow things down. The biggest offender is a dual bearing pattern bit (bearings on both ends) with 2” of cutting length in between. It’s a fantastic bit, but it has so much mass way out there that things start to wobble and jump at high speed. Play around and see if speed changes help.

-- -Michael

I think most people would be surprised to learn that you can actually cut at much lower speeds than are typically used. With the 7518 in my router table, I typically keep it at 16,000 rpm for work with 1/2” bits, and even slower with larger bits. With smaller bits, you may need to spin a bit faster.

I’ve been running big CNC routers for over 10 years, and rpm and feedrate are calculated using a recommended chipload, which is the amount of material (size of chip) each tooth or flute removes. Unfortunately, most carbide tipped bit manufacturers won’t give you a chipload, but instead a max rpm, which is more for safety than cut quality.

The biggest enemy with carbide router bits is heat. Heat is what causes carbide tools to dull. The cooler you keep them while cutting, the longer they will last. You keep tools cool by increasing the chip load; taking the biggest bite per tooth that you can. There are two ways to do this. Increase the rate the your feeding material into the bit (or pushing the router through material), or lowering the rpm.

There is a trade off, though. As chip load increases, cut quality can suffer. If that happens, then increase the rpm until you get an acceptable quality of cut. If you use any higher rpm’s than that, you’re just decreasing the tool life.

As for burn marks, that’s typically a sign of a dull bit, or to many rpm’s. When the bit is spinning too fast, it takes very small cuts, and does more “rubbing” the wood than cutting it. This creates tremendous friction, which quickly caused dulling. Which leads to a vicious cycle of more burning. If you’re getting burning, try lowering the rpm, or pushing the bit through faster. If it still burns, you may need a sharper bit. Some woods, like maple, and especially cherry, are very prone to burning. Be sure to use very sharp bits with these woods for best results.

Bottom line, if you have a variable speed router, try using lower rpm’s. You may be surprised that your cuts are the same quality, your bits may last longer, and you also get the added benefit of much less noise.

-- Gerry, http://www.thecncwoodworker.com/index.html http://www.jointcam.com