Calibrating a speed controller for your router

[KLF]

Been meaning to post this for awhile.

I am building a set of raised panel closet doors using a set of bits that I bought from Holbren, and I was warned not to run the large panel pit about about 10,000-11,000 rpm. My old Makita 3612BR router is single-speed, 23,000 rpm, too fast, but still a very nice router that I wanted to use. So I went to the local Rocker store and bought a speed controller. However, I figured the dial was not a linear scale, in other words setting it at 1/2 way would not necessarily mean the router was running at half-speed. Not wanting to trust my ear to find the speed I needed, I tried to find a way to calibrate the speed controller. Hmmm...

My dad passed away last Spring, and he was an avid airplane modeller. One of the many tools I found in his arsenal was an electronic RPM gauge for prop engines. It was pretty basic, you set a switch on the front for either a 2 or 3 blade prop, run the engine, then hold the thing so the sensor was in front of the spinning prop. Amazingly, it says on the box that it will read up to 35,000 rpm! Hmmm...

Finally getting started on this project, one of the next things I did was to go down to the Rockler store and snap up that nifty router table kit for $99. Heck of a deal, nice setup, huge upgrade on my router table. Then I started thinking about the speed controller issue again. Hmmm.... fished an old 1/4" arbor out of my stash of Craftsman router bits, then started hunting thru my tray of nylon bushings. But, what to use for a "prop"? I was afraid that even the hardest wood would fly apart if spin at these speeds, kinda dangerous. Wait... why not just use a plastic model airplane prop? Found a nice 4" prop at the local hobby shop for $2, and it looked like it would work:



Set it all up, and darned if it doesn't work like a champ:



What you see above is the business end of the router, mounted in the Rocker deck plate. The meter is now reading 11,500 rpm, with the speed controller all the way down at the "0" setting. Initially the rpm meter couldn't "find" the prop, and the fluorescent lights in the shop were messing it up. The index card and the super-bright Surefire flashlight washed out the background lighting, and it could see the prop. Sure enough, it reads all the way up to 22,400 rpm when I hit the "Full" toggle on the switch.

I made up an index card for the rpm at each index setting, will keep it in the speed controller box.

[Tom Slick]

Interesting solution!

[LCHIEN]

See this post for my tachometer measurements on a Bosch 1617EVS compared to the factory charts... big surprise!

http://www.bt3central.com/showthread...eed+tachometer

[just started]

KLF, be ready for the router to slow down when you start cutting, maybe even stall with the control knob in 0-2 range.

[LCHIEN]

I did not have enough hands to try putting the router under load while measuring speed. However, my sense of pitch and the fact that it has constant speed control electronics tells me it doesn't slow appreciably under load when I'm using it.

[KLF]

KLF, be ready for the router to slow down when you start cutting, maybe even stall with the control knob in 0-2 range.

Ya, I was wondering about that.

[os1kne]

Interesting solution, nice use of what you had available. And, nice flashlight!

[jonmulzer]

I did not have enough hands to try putting the router under load while measuring speed. However, my sense of pitch and the fact that it has constant speed control electronics tells me it doesn't slow appreciably under load when I'm using it.

You tested the internal speed controller while he is testing an external box. Do the external speed control boxes compensate for load and maintain RPMs like the internal controls do? If not, then it really is possible that you could stall one.

[crokett]

I'd just run it at the slow speed and see if it does stall. Easy enough to test it and find out. If it does, hog most of the waste off with straight bits or a table saw before putting the larger panel raising bits on.

[LCHIEN]

You tested the internal speed controller while he is testing an external box. Do the external speed control boxes compensate for load and maintain RPMs like the internal controls do? If not, then it really is possible that you could stall one.

external boxes can only compensate for loading if they have a speed feedback signal. Most general purpose speed contollers don't; there's no such thing as a standard speed sensor for routers and a connector for such... don't know anything about the one shown.

[vaking]

One pro woodworker once explained to me that best way to set router speed and feed is to simply look at the wood that router cuts off. "You are supposed to get saw dust from table saw, router should produce shavings, not dust". Accurate enough?