I’m wondering what the minimum RPM is at which a router bit can be used with good results. The reason that I ask is that I have a shaper that runs at up to 10,000 RPM, but most routers run at 22,000+ RPM. I can install a router collett in the shaper, but will 10,000 RPM be sufficient compared to the higher (presumably optimum) speed of a router? I don’t have a router table to use instead, although this is on my short list of tools to buy. I know that the answer to this question will somewhat depend on the diameter of the bit that is being used, so to give you an idea of what I’m likely to be doing: Most of my use for this set-up will be in running dadoes, making mortises, rounding over small pieces, etc.
Thank, Bob
Replies
Bob,
I have never liked the slower speed shaper for router bits. It is true a larger bit would yield somewhat better results, but IMHO it's not worth the trouble. A dedicated router table for router bits and a shaper for the larger stuff has always worked well for me.
Charles
Bob,
Your router bits will work just fine in your shaper. The only ones that may give you a slightly rough finish are the very smallest, like a 1/8" roundover bit.
Router bits don't need to spin at 20,000 rpm, but people think that they do because that's how fast routers spin. Router manufacturers are even making new routers that spin even faster, but that's not for the benefit of the routerbit. It's so the manufacturer can make ridiculouly high claims about the motor horsepower.
A lot of woodworkers run their router bits too fast because they think they have to. Then they usually wonder why the bit is burning the wood. Go ahead and use your router bits in the shaper. There is not a single router bit that I own that hasn't been in the shaper.
I agree than router bits can be used in a shaper without any problem. The truth is that a router bit when cutting well at optimum feed rate of the stock is well below the "high speed" rating of the machine. A 20,000 rpm router slows down to 15,000, maybe 12,00 rpm when cutting efficiently.
The horespower rating of a router (small "universal" motor) is inflated and is genrally a number derived with no load. A shaper motor (induction) is far more robust and a shaper spinning at 10,000 rpm will slow much less under load.
All that said, however, I have found that running a router bit on a shaper works somewaht better if the shaper is running a little higher than 10,000 rpm. 12,000 to 15,000 rpm is better.
Rich
Routing cutting efficiency is speed dependent. The material, cutter design, sharpness etc. also play a part. See the FAQ link no.5 for more.
See for your self, make the same cut in the same material at 5 different speeds.
I never know what the correct speed is, charts help me not. A 2 minute preview on a same spieces sample helps me set the speed & feed rate.
To be sure, big cutters, cutters out of balance (more common than you make think), cutters just re-ground, and cutters you've never used before should start at medium speed and minimal depths of cut. Way too many surprises in Routerdom.
Surface feet per minute is the unit of measure to consider. I won't try to explain it as my brain seems at a loss for words at the moment. The upshot is that a small diameter bit must rotate faster than a large diameter bit to move the cutting edge the same number of surface feet per minute. My router has a speed control so that I can lower the speed of rotation which is important if my bit has a large diameter. I use a lower speed for dovetailing. It lowers the noise level also. Personally, I worry more about using a speed that is too high rather than too low. I had a bit come apart -- dramatically -- probably because I was spinning it too fast.
I read the previous posts with which I agree mostly.
Cadiddlehopper
Be prepared for a poor finished cut at slow speeds with many woods.
Jeff
When I first started working with a router, I thought faster was better. I suffered terribly from tearout and burning. The speed of cut (how fast you push the board) was so critical. and then I slowed down to 10,000-12,000 rpm, and everything changed.So now I never run faster than 14,000 rpm, and almost all my problems went away.If you run at slower speeds, it is a slower feed rate, but a much more trouble free cut.Buy the biggest router, and run it at the slowest speed.
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