Thread: Router Speed vs Bit Size

I found the following advice when I researched it. I'm only learning myself so others may have better advice to give.

Bob

"The speed chart below is presented as a general MAXIMUM SPEED guide for setting router speed according to bit diameter. The best operating speed may be slower than listed here.
Always follow the bit manufacturers speed recommendations as some bit designs require specific speeds for safety or performance.
If you are unsure of the proper speed or are experiencing any type of problem, contact the bit manufacturer for a specific recommendation or other solution to the problem!"

Up to 1" - 24000
11/4" to 2" - 18,000
21/4 to 21/2" - 16,000
3" to 31/2" -12,000

The issue is the tip speed of the cutting edge. Obviously as the bit gets larger in diameter, the cutting edge travels further with each revolution, and at some point in increasing bit diameter, it becomes practical to operate the bit at a slower speed to limit the tip speed.

Mass itself is not really an issue for a given overall diameter. Therefore is is practical to run a tall crown moulding bit at the same speed as a say a 45 deg mitre bit or draw lock bit of the same diameter, despite the probable significant difference in mass between the bits.

Similarly, a slot cutter and arbour set is generally fairly low in mass but of large diameter, and needs to run at the slower end of the scale and at a similar speed to a very heavy raised panel bit of similar diameter.

As suggested, bit manufacturers will generally recomend a speed range for larger bits, or use the info in the previous post as a guide.

Hope this helps

This may help also:



Ray

This Bit Speed chart courtesy of Infinity Cutting Tools might help
<TABLE border=1 cellSpacing=0 cellPadding=0 width=387><TBODY><TR align=middle><TD>Bit Diameter</TD><TD>Maximum Speed (RPM)</TD></TR><TR align=middle><TD>Up to 1"</TD><TD>24,000</TD></TR><TR align=middle><TD>1 1/4" to 2"</TD><TD>18,000</TD></TR><TR align=middle><TD>2 1/4" to 2 1/2"</TD><TD>16,000</TD></TR><TR align=middle><TD>3" to 3 1/2"</TD><TD>12,000</TD></TR></TBODY></TABLE>

Hi All,

Great information, thank you. I note there is a significant difference in the charts with Ray's being quite a bit more conservative than Bob and Ian who have quoted the same numbers.

Just for interest though, not one of my router bits has a recommended rotation speed listed.

Thank you
Brian

Originally Posted by Dovetail

I note there is a significant difference in the charts with Ray's being quite a bit more conservative ... Just for interest though, not one of my router bits has a recommended rotation speed listed.

The "significant difference" is also that my example is from the router manufacturer and includes variance for various materials, not from a bit manufacturer - I know which one I'd trust.

Bit speed recommendations will always be for maximum speeds. Unfortunately, many people see these as target speeds, so bit makers tend to be a little shy of publishing stuff that may later form the basis of a claim against them - this is particularly true at the budget end of the market.

Ray

Originally Posted by Dovetail

Hi All,

Great information, thank you. I note there is a significant difference in the charts with Ray's being quite a bit more conservative than Bob and Ian who have quoted the same numbers.

Just for interest though, not one of my router bits has a recommended rotation speed listed.

Thank you
Brian

Rays is more comprehensive then what I had found (material listed) so I've saved his too.

Bob

Ray
also, the bit manufacturer must assume that the router spinning the bit has almost unlimited torque, whereas the router manufacturer knows the torque available and can adjust the recommended cutting speeds accordingly.

in Australia, I know one manufacturer sells two 1/2" collet routers, one rated at 1400W, the other rated at 2200W. Personally I follow the guideance provided by the router manufacturer

G'day Dovetail,

Here is a little jig to ensure you never overspeed a bit in your router again.

First check on the router how many speed steps there are on the speed control; ie 1 to 6 or A to F. Check via the manual what these steps actually relate to in RPM (or use a tacho if you just happen to have one lying around).

Then drill a series of holes in an offcut. The number of holes needs to be the same number of speed steps on the router, the sizes to be determined by whatever speed vs diameter chart you choose to follow. Clearly mark each hole with the relevant router speed step.

When you pick up a router bit to use, the appropriate MAXIMUM speed will be indicated by whichever hole the bit will pass through. Very quick and easy

A variation on this theme would be two angled strips of wood with the speed steps marked along one of them.

Hey Chief,

Great tip! Thanks.
I'll just have to figure out how best to incorporate the variances depending on the material to be routed. Essentially, it seems to me (according to Ray's chart) that one click back on the speed controller should suffice for recommendations relating to soft vs hard wood and roughly another for plastic. At least the jig offers a rapid, graphic idea of what maximum speed one should be using. Good one.

Cheers
Brian

Thanks so much for all the handy info guys. I particularly like your jig idea Tiff.
Being new to routers adjusting the router speed has been by guess all the way, good to have some more reliable figures.
What i'd like to know is just what are the risks to using a bit at too high a speed? I understand that the wider the bit tip diameter the faster it travels per revolution. Do you run the risk of the bit self-destructing or does it burn the wood?

Mainly it burns the wood as the peripheral speed is too high, but also it can burn out your router motor due to the extra torque required. If you're going to run big raised panel bits you really need to dial the speed down if your only running a low-wattage 1/2" router.

I wouldn't worry too much about bits self destructing, even really cheap bits are manufactured pretty well these days. I'd draw the line however at buying no-name second hand bits from E-Bay!

Originally Posted by Rattrap

What i'd like to know is just what are the risks to using a bit at too high a speed? I understand that the wider the bit tip diameter the faster it travels per revolution. Do you run the risk of the bit self-destructing or does it burn the wood?

Well everyone has been sort of skirting around the issue but not actually spelling it out so, as eloquently as i can after a beer or 10 at nearly midnight on a saturday, heres my 2c worth:

- the maximum speed quoted by manufacturers of bits and routers as well as authors of woodworking books is a very arbitary figure for the blind obedience of fools and as a guide for the wise.

- In real life in the workshop the actual (as opposed to theoretical) maximum speed of the router for a particular bit is determined by a complex relationship between:
- density of the timber
- depth of cut (which determines how much of the surface of the bit is in contact with the timber and the friction thereby produced)
- sideways, and in some cases downwards pressure applied to the router, which determines the speed at which the body of the router moves in relation to the workpiece (very different from and unrelated to the speed of rotation of the router bit)
- the actual speed of the fastest moving part of the router bit, which is of course the extreme tip of the blade, hence the generally accepted adage that the bigger the diameter the slower the speed.
- the age/sharpness of the bit (obviously new and sharp bits create less friction and therefore less heat, not to mention a cleaner cut, less tearout and less friction through the cut.

Now, what does all this mean? good question!

well if the timber isn't burning when you cut it you probably aren't cutting at too fast a setting on your router

if the cut is clean and smooth you are definitely not going too fast

if you are cutting down in steps with the router there can be a lot to be gained in finish and accuracy by switching to a new or sharper bit for the final cut of the last 1 to 2 mm after doing the roughing out with an older, blunter bit. most router jobs need to be taken down in steps anyway so use the older blunter bits to remove most of the waste before using the new bits do do the final touches. the new bits hold their edge longer that way then eventually become the roughing out bits.

the general hint is to not to try to take too much off anyway, if you smell smoke you are taking off too much, going too fast or using a bit that is not sharp enough or not up to the job for whatever reason and you are ruining the workpiece as well as the cutting bit.

i hope this helps


dg

Thanks for that info guys, its cleared it well for me. Pretty much what i have been doing instinctively.