# why such high rpms

the routers get occasional use but lately i discovered i avoid them just because they are so noisy
i never thought about it until now and i cannot understand why they have to spin so fast
5000 rpm should be plenty
what am i missing
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On 1/18/2017 3:49 PM, Electric Comet wrote:

um, aside from a brain?
5000 is not enough. It all depends on the size of the bit, a 1/8 bit needs to spin at a high speed to cut since it is moving so slowly.
--
Jeff

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On 1/18/2017 2:53 PM, woodchucker wrote:

Cutting tip speed. The smaller the diameter the faster the cutter has to spin.
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On Wednesday, January 18, 2017 at 2:49:41 PM UTC-6, Electric Comet wrote:

Its really about the strength of the bit while cutting. Bits are commonly 1/4", 1/2", 3/4", 1" diameter and bigger. Smaller is weaker of course. Ev eryone moves the router bit through the wood at roughly the same pace. Mor e or less. The smaller bit, because it is weaker, has to take a smaller bi te. Lets pretend this bite is one third as large as the big bit. (Pi at 3 .14 comes in here to get the bite of one third.) So it has to spin faster than a large bit so when you push it through the wood at the predetermined speed everyone uses, the wood all gets cut. If the small bit spun at the s low speed of the big bit, then you the operator would have to push the rout er through the wood at one third the pace. Doubt people are going to do th is, so you solve it by speeding up the router speed.
Lets use your example of slow speed, or fixed speed, from the table saw. T able saws all spin the same speed no matter how thick wood is you are cutti ng. Cut 1/2" wood or 3" wood. Blade spins the same speed. I'll bet you p ush the 1/2" wood through the blade much faster than you push the 3" wood t hrough the blade. You manually vary the feed rate of the wood through the fixed speed blade. You could do the same with routers by being 1/3 as fast with the small bit compared to the large bit. With table saws you vary th e feed speed so the amount of wood, thickness of wood divided by amount of teeth, is the same over a given time period. You cut the 1/2" thick wood 6 times faster than you cut the 3" wood.
I'm guessing some engineer, scientist figured out the optimal cut speed, fe ed rate, bit size, teeth number, etc. some time ago for router bits, saw bl ades, etc.
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On Wed, 18 Jan 2017 16:54:14 -0800 (PST)

am still not convinced so i guess i need to do more research
also using a router table changes things a bit there is a pun
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Electric Comet wrote:

You'll only achieve the exact results you desire with moulding planes.

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I do know this: I had a variable speed Ridgid router, and experiemented with the speed. Once I hit 16,000 RPM, the cuts were happening very nicely so I just left it there.
Is it the optimal for every material? Probably not. Is it more than good enough for wood? Yep!
Puckdropper
--
http://www.puckdroppersplace.us/rec.woodworking
A mini archive of some of rec.woodworking's best and worst!
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On 1/18/2017 8:57 PM, Electric Comet wrote:

Put a router bit in the drill press and see how well it works at lower rpm. Try it in a hand drill too. The bits are designed to perform at high rpm and there is a lot of thought and design experience that determine the cutting edge for best finish and chip removal.
I rarely use a hand held router as I have a table and lift that works very well.
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On Wed, 18 Jan 2017 22:06:55 -0500

5000 rpm whould be enough but no way to test that since the drill press does not do that
i think 20000 plus is higher than needed
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On 1/21/17 12:02 PM, Electric Comet wrote:

Please stop, it's embarrassing. Do you even have a router and do you use it. I can assure you that not only would 5000rpm be way to slow for the typical router bit, but it would be more dangerous as well. You're much more likely to get kick-back and jumpy action at slower speeds. That slow of a speed is also going to give you a really crappy cut.

You think? Maybe get a variable speed router and do some test cutting before you throw around completely unwarranted and uninformed opinions about it.
I'm sure all the mechanical and electrical engineers who have been designing and manufacturing routers and router bits for the past century have no idea what they've been doing.
--

-MIKE-

"Playing is not something I do at night, it's my function in life"
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On 1/21/2017 12:24 PM, -MIKE- wrote:

No.
I can assure you that not

He does not understand tip speed. Small bits demand higher RPM's to have the proper tip speed. 10" saw blades turn under 5K because the tip is 10" from the center of rotation, so the tip is moving very fast.
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Leon wrote:

C = 2 *Pi * d, where d is the diameter. Or, replacing d by 2r, C=4*Pi*r~~ 12.52*r. In particular, C is a linear function of r. As an example, if r=1/4" then 5000RPM corresponds to 3.14*5000000 inches per minute, or 15000/60 %0 inches per second. I s'pose whether that is fast, is relative. The length of the edge of the cutting bit, as well is its shape, would seem to be important too. Intuitively, I would want to cut a complex shape slower, but I suspect that is backwards thinking--surely better to cut a complex shape by taking shallower cuts. If all that the reader remembers is the previous sentence, they may be well-served by this post.
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Bill wrote:

Oops, C = Pi*d. Divide by 2 accordingly. Sorry 'bout that.
Bill

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On 1/21/2017 5:50 PM, Bill wrote:

I think you may have missed something in your calculations...
If your bit diameter is 1/2" the circumference would be 1.57 inches, not 3.14.
1.57" *5000 = 7850 inches per minute, and that = 130 inches per second or about 7.4 MPH, way too slow to make a smooth cut.
Ideally and if a 1/2" diameter router bit could withstand being spun this fast, 50,000 would be the idea cutting speed. The tip speed at 50K would be 74 MPH and or about the same speed as a 1" diameter bit spinning at 25K.
I am not sure what you are trying to say here and understand that you have corrected part of you equation in another post. I appreciate the effort.....
The speed at which the tip of a cutter strikes wood is important within a specific range. Too slow and the cut ends up rough, maybe splintery, and maybe stall the motor.
Feed rate has little to no effect on the optimum cutting speed other than taking small bites typically yields a flatter result with a router bit. Feed too fast and you get bigger bites out of the wood and smooth scallops, too slow and you get flatter results and maybe burn marks. The proper feed rate for any given tool is something a woodworker has to learn by practicing to get the best result.
Anyway the typical 10" saw blade has a tooth tip speed of approximately 104 MPH, assuming 3500 RPM
A 1" diameter router bit has a tip speed of approximately 74 MPH, assuming it is spinning at 25000.
I think ideally router bits in this size range and smaller should spin faster but this becomes dangerous. Typically 2 or 3 cutting tips are removing all of the wood, compared to a 10 saw blade with a tooth doing 1/10 of the amount of wood as the router bit.
Go up to a 1.5" diameter router bit and slowing the speed down to 18000 RPM and you get a speed of 80 MPH.
Go up to something like a panel raising bit that is 3" in diameter and the speed should be reduced to about 12,000 for a tip speed of 107 MPH
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Leon wrote:

Yes, I was able to confirm this (it took me a few tries without a pencil to get the units right!) 130 inches per second sounds faster than 7.4 mph (think of "how fast" we push a chisel by hand).

Thanks, I was mostly just doing my own "investigation", for the sake of my own learning/curiosity, and that of anyone else concerned.
Thanks for the tips below!
Bill

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You are very welcome, Bill! ;~)
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On 1/21/2017 1:02 PM, Electric Comet wrote:

If 5,000 is enough, 500 should work too. if 20000 is too high, maybe 2000 is too. You are contending that decades of experience of router and bit makers are wrong so why not give it a try?
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On Sat, 21 Jan 2017 13:38:12 -0500

nothing i have does 5000
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On Sat, 21 Jan 2017 10:59:08 -0800, Electric Comet

Then why are you wasting everyone time with your bullshit?
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On 1/18/2017 6:54 PM, snipped-for-privacy@yahoo.com wrote:

Actually, smoothness of cut is what it is about. The faster the speed the more cuts with a given speed.
Bits are

Many routers have fixes single speeds.

Actually many TS do not run at the same speed. The larger the blade the slower they typically run. Again, tip speed. A number of miter saws spin their blades even faster that a TS and typically have more teeth than you commonly see on a TS. If you are saying the TS's are not variable speed, that is close to true, Shopsmith's have variable speed, but should be run at a suggested speed.
Cut 1/2" wood or 3" wood. Blade spins the same

Except when it does not. Under ideal conditions the blade maintains its speed but time and again under powered saws spin slower when cutting thicker material. Hence think kerf blades.
I'll bet you push the 1/2" wood through the blade much faster

You learn to not do that to get smoother cuts.. Smaller bites normally mean smoother cuts.
You manually vary the

Really? 6 times faster? I go the same speed regardless, I strive for smooth cuts. Fast feed rates result in a cut that is less smooth than slower feed rates.

Yes and I doubt any would agree with your thoughts. While your comments make sense to some degree. The results yield less than the best outcome.
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