Electric die grinder speed control

What is the best/cheapest way to get the speed of this electric die grinder down to 10k rpm? http://www.harborfreight.com/electric-die-grinder-with-long-shaft-44141.html
BTW. these are on sale for $35, seems like a great deal. I bought one this morning and made a mount for it for a lathe and ground out a bore in a 3/4" die by 0.012" in a couple of minutes. Nice tool! If/when I can get it down to 10k rpm, I'll have other uses for them.


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Tom Gardner wrote:

Probably the $10 or so router speed control HF also sells. Oddly enough, I'm doing the same improvised toolpost grinder setup with one of those grinders.



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They do sell a speed control for universal motors, usually listed as a router speed control. You'll lose torque with it along with speed. I use several of the mini/micro pneumatic die grinders for most places that a Dremel or flex shaft would be used. They were cheaper and have a built-in throttle. I've got a Foredom flex shaft, it tends to run hot after extensive use and if you don't lube the core, it'll snap eventually. Hand grinders can make a fairly decent substitute for a tool post grinder as long as you don't try to do too big a job with one. Had a Dremel rigged up on a mount for years on the SB carriage.
Stan



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On Mon, 27 Feb 2012 14:40:17 -0800 (PST), Stanley Schaefer

My "big" toolpost grinder is a 50-year-old Black & Decker industrial die grinder (aluminum housing) with my big Variac controlling speed, mounted in my SB milling attachment. Very slick.
--
Ed Huntress




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An auto transformer works well with those tools.
Hul




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    Well ... since it is a universal motor, cheapest way (not the best) is to plug it into a Variac (if you have one) and turn the voltage down. You won't get really steady speed with anything, however, unless you get really fancy with a controller which produces PWM power and monitors the back EMF (to measure the speed) between pulses. That would probably require a replacement power cord to get the voltage sensing close to the motor and separate from the voltage drop in the power cord.

    Note that at the slower speed, you will need harder stones for a given workpiece material. Hardness is a function of speed at the grinding surface.
    Good Luck,         DoN.
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"DoN. Nichols" wrote in message
Note that at the slower speed, you will need harder stones for a given workpiece material. Hardness is a function of speed at the grinding surface.
Good Luck, DoN. __________________________________________________
I want to spin a 6" x 1/32" cut-off disk at 10k max to trim solid-fill end brushes. http://www.spiralbrushes.com/end.html




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    [ ... ]

    Hmm ... does it have enough torque -- especially at reduced voltage, to handle that large a diameter? You might wind up burning out the motor rather quickly.
    You might be better off gearing it down with pulleys to get the needed speed -- at an increase in torque. If you want to mount it as part of the machine, you should be able to find space for the belt and pulleys to allow the motor to run at its normal speed.
    Good Luck,         DoN.
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Both the variac/autotransformer and the HF triac-diac-Router Speed Control methods of variable speed will exhibit significant motor power loss at reduced speed settings.
FWIW vari-speed AC corded drills have used PWM circuits in the trigger-switch speed controls, and operate well with only 2-wire connections to the motor (no external feedback component required), when SCR speed control circuits contain a low value series "sense" resistor in their circuitry. Some DC motor vari-speed control modules from several manufacturers have selectable sense resistor recommendations for using a specific controller model number with different HP size motors.. the resistor value selected is different if using a 1/4 HP or a 1/2 HP motor when utilizing the same model of controller.
I haven't had any of the newer drill trigger/speed circuits apart recently to verify if PWM controller circuits are still being used, but they likely are, as a commonly used circuit design generally gets cheaper to produce as millions more are manufactured.
Without using PWM for speed control, most drills would be problematic/useless at reduced output torque when used at lower speeds.
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Hum - that is a 500W unit. How about a 500 to 750 watt Lamp dimmer You know those that fit in the wall as a ceiling lamp dimmer ?! - mount in a nice electrical box - cord and a socket. Maybe you can find a square rounded electrical box - for drop boxes - with a switch on one side and the other - standard wall plug - 3-way.
It has brushes which makes it a universal motor - AC/DC and controlled by a switch or electronic light / speed / motor controller.
Martin
On 2/27/2012 4:29 PM, Tom Gardner wrote:






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Looks like a universal brush motor so...
Simple set control, just get the router speed control from Harbor Freight too. http://www.harborfreight.com/router-speed-control-43060.html
However, if you want quick variable control, get this unit instead. The foot pedal works fine. I have two of them, and five different hand pieces. http://www.harborfreight.com/flexible-shaft-grinder-and-carver-40432.html
If you want programmable with power compensation to hold speed (manual or CNC control) get a SuperPid. http://www.vhipe.com/product-private/SuperPID.htm





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