advisable to exceed router bit's maximum rpm?

[rlim]

Hello,
I bought the Hitachi KM12SC a while back when it was on sale at Amazon, and now am in the process of buying a 3/4" round over bit from Holbren. Upon checking that bit on their website, I found out that the maximum rpm is 18000. The KM12SC, being a fixed-speed router at 24000rpm with soft-start and electronic control, I am wondering if it's advisable to still try it out. My thought is if I mount the router on my table and feed the workpiece several passes, taking off only minimally every time, I should be okay. No? The easy route, of course is to get another router with variable speed, but I already have a variable speed with a 1/4" collet. The other option is to try and get the electronic control module for the KM12VC (variable) and try and retrofit it into the SC housing. The 3rd option is to remove the control module and see if I can slow down the speed manually by hacking the module (I'm an EE by trade). Of course not knowing the inner workings of the module would make me a dangerous EE.

Any suggestions?

Richard

[vanguard]

I think I'd find another router bit. Exceeding the maximum speed specified doesn't sound like a good idea, nor does modifying an expensive router motor. The soft start means you can't add an external speed control, so the cheapest method might be to find another bit.

[LarryG]

My thought is if I mount the router on my table and feed the workpiece several passes, taking off only minimally every time, I should be okay. No?

No. Table-mounting the router and making multiple passes (which ought to be done anyway, when making all but the smallest of cuts) doesn't address the root problem. The larger the bit diameter, the greater the mass and the faster the tip speeds. A teensy-tiny amount of imbalance that wouldn't even cause the slightest vibration in a smaller bit could well cause a larger bit to shake itself, or the router's bearings, apart. Deciding what speed at which to run a bit is usually somewhat of a guessing game, but as a starting point one should never exceed the maximum stated by the bit manufacturer/vendor. In this case, that's 18,000 RPM.

Vanguard is right, you can't use an external speed controller with a soft-start router. Hard to know what to suggest, other than to consider getting another router, with VS, for table use. The Hitachi would make a nice handheld router. VS is often useful for handheld routing but you can get by without it, since bits large enough to require a slower speed may be a little dicey to use handheld anyway.

[Tom Miller]

My thought is if I mount the router on my table and feed the workpiece several passes, taking off only minimally every time, I should be okay. No?

That assumes you know the failure mode of the bit....

If I were you, I'd send an e-mail to Brian Holbren, and ask him if he could verify maximum bit speed for this bit. There's a possibility that this is a misquoted max, for any of a number of reasons. Also, perhaps he could recommend another bit.

And, rather than gambling on hacking the speed module of the router, I'd look into getting a speed controller. It'll be useful for other bits, too, and could help keep you out of trouble.

[oops -- missed the part about the soft-start -- Larry and Vanguard have got you covered, though.]

Regards,
Tom

[LCHIEN]

3/4" roundover is a fairly large bit. I'm guessing its about 1.75"-2.0" in diameter. I'd believe the rating for that large a bit would be around 18K RPM or less. I think MLCS's 3/4 roundover is 2" dia.
I would not exceed it (the rating).

Though you might get away with it the risk of something bad happening goes up very fast when you exceed the ratings. Just not worth the chance. Don't want to end up in the darwin awards, eh? "Man knowingly exceeds router bit ratings"

Here's a chart I swiped off the Rockler Blog pages:

Manufacturers don't always agree on top speeds for router bits of a given diameter, and as mentioned above, there are other factors to consider. For a rough guide, here's a typical maximum router bit speed chart:
Router Bit Diameter Maximum Speed
Up to 1" 22,000 - 24,000 rpm
1" to 2" 18,000 - 22,000 rpm
2" to 2-1/2" 12,000 - 16,000 rpm
2-1/2" to 3-1/2" 8,000 - 12,000 rpm
Remember, that's just a reference; Always follow manufacturers recommendations and the sage advice that if something doesn't feel like it's working right, there's a good chance that it isn't. Better yet, pick up a Router Book and get to know your router inside and out. Or, for a beginning-level overview of router bits, read Rockler's article "Router Bit Basics".

Somewhere around 18,000 RPM MAXIMUM for that bit is about right.
I don't think you'll find another maker's bit with the same profile that will have a much higher rating.

[newood2]

About 5 years ago I used a MLCS 1-7/8" dia. cove bit in the PC 690 router (27500 rpm) on some maple. It worked out quite well.
I didn't know at the time that I was messing with danger until I started reading everything about using every tool I owned. I promised I'll never again disobey the rules of the craft.
Back in 1991, out of ignorance I broke the rule by using a dull blade on a home-made tablesaw(circular saw fitted under a plywood table) to cut thin strips of oak for picture frames and cut off my pinky. The good doctors of Kings County did re-attach it.
So thank guys for these reminders.

Howie

[rlim]

Thanks!

Thanks guys. Sounds like getting another router with VS is the way to go. Interestingly, I was comparing the 3/4" roundover and the 1" roundover from Holbren, and the 1" roundover's maximum rpm is actually higher than the 3/4" - 24000 versus 18000. Go figure. I'll take the advise and send Holbren and email.

Richard

[steve-norrell]

Here's a chart I swiped off the Rockler Blog pages:
Manufacturers don't always agree on top speeds for router bits of a given diameter, and as mentioned above, there are other factors to consider. For a rough guide, here's a typical maximum router bit speed chart:
Router Bit Diameter Maximum Speed
Up to 1" 22,000 - 24,000 rpm
1" to 2" 18,000 - 22,000 rpm
2" to 2-1/2" 12,000 - 16,000 rpm
2-1/2" to 3-1/2" 8,000 - 12,000 rpm

A timely and important thread . . .

But, how does one really calibrate router speed? How reliable is the manufacturer's data? This is from the Bosch webpage and applies to their electron speed control router (Setting;speed):

#1=8,000 RPM, #2=13,500 RPM, #3=16,500 RPM,
#4=20,000 RPM, #5=21,500 RPM, and, #6=25,000 RPM

How reliable are these numbers? Any advice or comments?

Regards, SN

[jackellis]

Thanks for raising this point. I just received a set of new bits that includes some large roundovers and I need to remember to slow my M12V down.

FYI, a 2 inch diameter bit at 1800 RPM has a tip speed of around 100 MPH (18,000 RPM = 300 RPS, 2 inch diameter ~ 6 inch circumfrence, 1800 inches per second is 150 fps which equates to a little over 100 MPH). If a piece of sparpened carbide comes off and hits you, it's going to penetrate something.

[LCHIEN]

A timely and important thread . . .

But, how does one really calibrate router speed? How reliable is the manufacturer's data? This is from the Bosch webpage and applies to their electron speed control router (Setting;speed):

#1=8,000 RPM, #2=13,500 RPM, #3=16,500 RPM,
#4=20,000 RPM, #5=21,500 RPM, and, #6=25,000 RPM

How reliable are these numbers? Any advice or comments?

Regards, SN

Funny you should ask, I got a laser-RPM tachometer a couple of weeks ago and was wanting to calibrate my VS Bosch router. Watch for the post here.

[cgallery]

Funny you should ask, I got a laser-RPM tachometer a couple of weeks ago and was wanting to calibrate my VS Bosch router. Watch for the post here.

What a kewl geek toy. I can't wait to read more on this.

[ragswl4]

Hitachi Router and Speed

I have the variable speed version of that router and it works great in my router table. I have been cutting raised panels in hardrock maple using a vertical raising bit from whiteside. Whiteside advised me that max speed for that bit was 18,000 rpm. I have been running it on position 3 (16,500) and I take 6 cuts to raise the panel. Works great. The bit is 1" in diameter but has more mass than a normal 1" bit due to its height. I think you are miles ahead if you replace your router with a variable speed model of some type. Gonna need that function someday anyway.

[LCHIEN]

Funny you should ask, I got a laser-RPM tachometer a couple of weeks ago and was wanting to calibrate my VS Bosch router. Watch for the post here.

http://www.bt3central.com/showthread...575#post261575

[LCHIEN]

What a kewl geek toy. I can't wait to read more on this.

Done.

http://www.bt3central.com/showthread...575#post261575