# Router Bit Sizes And Variable Speed Settings



## mack. (Jan 31, 2010)

Hi,
I just brought a Skil 1825 combo kit, and despite all the plastic that It's has, it seems to have a lot of power. I'm a little uncertain about using the variable speed setting's. 

It's my understanding that the bigger the bit, the lower the speed setting, and the smaller the bit the higher the speed setting. 

I would like to know what size bits are considered big, and what size bit's are considered small? 

For example, I have a pattern following bit that is: 
1/2" shank
3/4" diameter
2" cut length
3-1/4" overall length

I think that this would be considered a large bit.

The variable speed setting on the router is from 1-6. What number should I set the router speed at to cut 1-3/4" poplar with the bit mentioned above?

Thanks for all your help.

Mack.


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## cgreene (Nov 7, 2009)

Go to Woodline’s site and look at the Speed chart. Woodline.com. Look in their insturction section and you will find the speed chart.

The speed has more to do with the diameter of the bit. The farther you get away from the center the faster the tip spins. If you are turning a bit at 20,000 rpm at the shaft, the tip of a bit 3" in diameter will be maybe 3 to 4 times that speed. This starts to put too much stress on the carbide tips and bit itself. 

If you have 6 speed settings, look at the specs and see what the speed range is. Divide the speed range by 6 and you will have a rough estimate of the various speeds each number gives. If you know anyone that in into radio controlled modeling, specifically R/C airplanes, see if they have an optical RPM meter. You can use that with a bit to find the exact speeds you are getting at each setting. 

For the bit you are using, you can use the router at full speed. What to be careful of is how much you cut in one pass. Usually try and cut


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## cgreene (Nov 7, 2009)

Sorry, the end of my post got cut off. Anyway, try and make cuts in several passes. This will make for a better cut and help prevent wood and bit burning. Flush trimming you should be good to go.


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## BigJimAK (Mar 13, 2009)

mack. said:


> Hi,
> I just brought a Skil 1825 combo kit, and despite all the plastic that It's has, it seems to have a lot of power. I'm a little uncertain about using the variable speed setting's.
> 
> It's my understanding that the bigger the bit, the lower the speed setting, and the smaller the bit the higher the speed setting.
> ...


Mack,

This is a good question, and "big" is certainly in the eye of the beholder. The upper end for router bits are generally cabinet door panel bits (often with back-cutters that cut both sides of the wood at once. These can range up to 3-1/2" in diameter. The large bits are generally used with large (~15 Amp) routers and should only be used with the router well-mounted in a router table for safety purposes.

What is the maximum diameter bit you should use hand-held? That is a topic where opinions vary between individuals and things (such as bearings and skiis) that limit the maximum depth of cut. My personal rule-on-thumb is around 1" although a good case can be made for going larger in certain controlled setups. As for myself, even with a 1" bit I'd look carefully at cut depth, but that's another topic. <g>

The guideline for router bit maximum speed is given below (pasted from Tom Hintz's www.newwoodworker.com web site. Tom is also a member here. 

As Tom and others say, this is the *maximum* when manufacturers data is not available for the specific bit. The manufacturer's recommendation may be higher or lower.

When you first start out, this is a good guideline. As use your various bits you will tune in to the sound the bit makes as it is cutting and the level of resistance it makes to being pressed through the wood. Every bit has its own "sweet spot" where you get your best cut, minimum burning and lowest vibration for a certain hardness of wood. You'll get the feel for this over time. 

I've pasted the maximum post from Tom's web site (originally credited to Infinity Tools) below.


Suggested Maximum Router Bit Speeds
Bit Diameter
Maximum Speed
1" 24,000 RPM
1.25 to 2" 18,000 RPM
2.25 to 2.5" 16,000 RPM
3 to 3.5" 12,000 RPM
Suggested Speed Chart courtesy Infinity Cutting Tools.
Remember that these are SUGGESTED maximum speeds! Your equipment and/or situation could require much lower speeds for performance and safety!


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## mack. (Jan 31, 2010)

Sorry I couldn't respond sooner, I had a class.
Thanks cgreene & Bigjim for the information, and for telling me about the Woodline Speed Chart, (nice). I doubt If i will ever use a bit larger than 3/4" but It's possible. Those cabinet door panel bits scare me. I know I won't be using anything that big. I had no idea that the bit tip (3" diameter) can spin at 3-4 times faster than the shaft, yikies!!! Thats really scary, but good to know. 

Bigjim, good point you made about tuning in on the sound and feel of the router bit and finding the "sweet spot" the router seems to be a tool that requires your full attention. I will check out Tom Hintz's website after posting my reply.

Thanks a bunch to you both for taking the time to provide me with all the useful information, It's appreciated.

Mack.


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