Electric die grinder speed control

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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.



Re: Electric die grinder speed control

Tom Gardner wrote:
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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.

Re: Electric die grinder speed control
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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

Re: Electric die grinder speed control
On Mon, 27 Feb 2012 14:40:17 -0800 (PST), Stanley Schaefer

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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

Re: Electric die grinder speed control
An auto transformer works well with those tools.

Hul

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Re: Electric die grinder speed control
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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.

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    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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Re: Electric die grinder speed control


"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


Re: Electric die grinder speed control
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    [ ... ]

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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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Re: Electric die grinder speed control
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.

 --
WB
.........


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Re: Electric die grinder speed control
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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Re: Electric die grinder speed control
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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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