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Slowing down my bench grinder

DonMitchell's picture

I have a delta 6" bench grinder that spins at ~3500, I need a slower speed grinder that spins at ~ 1700. I want to use it to grind bevels on chisels, plane irons etc without blueing the steel.  I would rather not spend the cash on another bench tool (lack of space is a bigger issue than the cash) so, give me your thoughts on the the speed controls that are available for router motors.  Will they work on a bench grinder?  What kind of damage will it do if I do use it.  Any other ideas? Appreciate the help in advance.


Don   

Don

Measure, cut, cuss

 

JimV's picture

(post #99675, reply #1 of 25)

Router speed controls only work with universal motors. Your grinder is almost certainly powered by a impulsion motor. Attempting to use a router control on this will destroy your motor.

"There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery, and the other is that heat comes from the furnace." - Aldo Leopold
USANigel's picture

(post #99675, reply #2 of 25)

I can understand you noy wishing to buy another tool but 1700 rpm is still a little fast and still very easy to "burn" tool steel. For the price of a dpeed control go to sears and get one of their slow speed with water bath grinders. Works great!!


 


http://www.sears.com/sr/javasr/product.do?cat=Bench+Power+Tools&pid=00921174000&vertical=TOOL&subcat=Bench+Grinders&BV_UseBVCookie=Yes

highfigh's picture

(post #99675, reply #3 of 25)

Harbor Freight has a low-speed grinder with a water bath for about $59. A speed controller would probably cost more than that.

"I cut this piece four times and it's still too short."

"I cut this piece four times and it's still too short."
BruceS's picture

(post #99675, reply #4 of 25)

I'am not one to pass up power tools, But.  Here I would.  I'de look into Scary Sharp.  Go for a Veritas sharpening guide and silicon carbide paper on a chunk of plate glass.   Once sharp! Keeping them sharp with a little honing now and then is easy.

Work Safe,  Count to 10 when your done for the day !!


Bruce S. 


 

Work Safe,  Count to 10 when your done for the day !!

Bruce S. 

 

lwilliams's picture

(post #99675, reply #5 of 25)

Don,

Tell us what grinding wheel you're using. Grit and type. How do you dress it? What are your tool rests like?

I think you'd be better served to improve your grinding technique using the grinder you have rather than buy one that is difficult to properly dress because it turns so slow. I'm also guessing you won't find much difference in heat build-up between a 3400 rpm and an 1800 rpm grinder, especially if you put too fine a wheel on the slower one.

I do a lot of grinding and wouldn't want a low speed bench grinder.

USANigel's picture

(post #99675, reply #8 of 25)

I would agree you still need the high speed grinder. But the slow speed with water cooling makes the first step in sharping easy without fear of over heating the soon to be cutting edge.

Oldtool's picture

(post #99675, reply #6 of 25)

I recommend keeping your grinder as is. Go to a antique place and get a sharping stone for $2 and learn how to sharpen your irons. You might change your mind on the grinder speeds and control. Perhaps later, you can rethink the whole process of sharping irons and what you need. I see so many people with several methods of sharpening, tools, stones, and various machines, while the process is so simple.....and they still have dull irons!

citrouille's picture

(post #99675, reply #7 of 25)

There is a difference between sharpening and honing.
One uses a grinder when using a stone would take for ever.
A can of water handy will solve the heating problems.

C.

AdamCherubini's picture

(post #99675, reply #9 of 25)

Its my understanding that heating and quenching repeatedly is not good.  While I agree its good to have water close at hand, I don't think its a good idea to get that steel too hot to touch.  At least, don't be convinced that it does nothing harmful to the steel.


The temper temperatures for really hard high carbon steel are pretty low (sub 500F)- easily achievable on a grinder.  Also, the HAF (heat affected zone) (shouldn't that be effected?) is larger than any bluing that can be seen. 


So not so much a disagreement as a note of caution about water quenching when grinding.  Its probably safer not to count on it as a soultion to overheating.


Adam


Edited 7/26/2006 12:34 pm ET by AdamCherubini

AdamCherubini's picture

(post #99675, reply #10 of 25)

In one of his plane videos, Rob Cosman demonstrates grinding technique with a "nothing special" grinder. He uses a very light touch.  I think that's the key.  Saw Ian Kirby do the same at a woodworking show once and never forgot it. I work with antique high carbon steels and am very careful grinding.  That said, I don't think there's any panacea.  Every stone will work quickly if you are patient enough.  Its important to get out of the habit of trying to "do it quickly so it won't get hot".  This doesn't work in my experience.


Just for kicks I thought I'd include a photo of my slow speed grinder.  (Its from an article I just finished on sharpening that won't help you.)


Adam 


 

DonMitchell's picture

(post #99675, reply #11 of 25)

First off, I'm not wanting to sharpen with the grinder, only interested in maintaining a hollow ground bevel on chisels and plane irons.  I'm very happy with the sharpening process I already use  (Japanese waterstones).  But thanks for the suggestions on sharpening just the same. 


Further research (googling) confirms that a speed control is not the ticket!  But thanks to those of you that confirmed that here as well.


For those of you that ask, currently I'm using a very old hand crank bench grinder with a coarse wheel (no idea of the grit, just know its coarse with a 4 1/2 - 5 inch diameter).  The configuration of the grinder limits me in wheel size, 6 inch just won't fit and still turn freely.  The tool rest is patterned after the one Krenov describes in his books for use with his hand cranked grinder.  I like the results just fine, its just cumbersome, hard on my shoulder and tricky cranking the handle, holding the tool, applying even pressure all the while trying to maintaining the edge square to the wheel.  It's like patting your head and rubbing your stomach while eating a sandwich and landing a plane!! 


I think my plan of attack will be to buy a finer wheel for my current 3500 speed grinder, and use as AdamC suggest "a very light touch".  But first I'll try it on some junk before I commit to trying the high $$ chisels or plane irons!


Thanks again to everyone for your advice and information!


Don 

Don

Measure, cut, cuss

 

Napie's picture

(post #99675, reply #14 of 25)

All I use is a high speed grinder, just go with a pretty coarse wheel, (they grind cooler), I use a 60 grit white 6" and a light touch with a can of water to cool it if needed.  It makes for a great hollow grind very fast, then the oil stones take over.  Also, a diamond wheel dresser makes a world of difference.

GDH2's picture

(post #99675, reply #17 of 25)

Ain't no way I can fail to say a BIG THANKS for your photo - you brought a huge smile to my face. Thanks

Doug, The Wood Loon, Acton, MA
philip's picture

(post #99675, reply #12 of 25)

Don, there is absolutely no reason to overheat the steel , provided you have the correct wheel for the job and a good wheel dresser-preferably a diamond dresser. Neither of these are expensive.
The speed of 3500 is good-remember it is only a 6 inch wheel, so the periphery speed is not that high.
The correct wheel, such as a white Aluminium Oxide (white) wheel , of grit around 80 or so , frequently dressed , will enable you to grind chisels etc without even quenching-your fingers are the temperature sesnsor. Quenching in water of some steels is not a good practice anyway-can lead to "shock" which means hair line cracking..
It is my belief that dressing these wheels is as important as having the right wheel. When the wheel is loaded with grit, or glazed more pressure is required-resulting in overheating.Also, frequent dressing maintains trueness and balance-essential for good results and easy grinding.
Spend some money on the correct wheel(s) and a diamond dresser-you will be amazed at the difference.

Philip Marcou

Philip Marcou
DonStephan's picture

(post #99675, reply #13 of 25)

After using a similar bench grinder for many years, one day last winter I noticed the air current produced by the spinning wheel was making my fingers cold. Now I lightly grind for a couple passes, then back off the tool just enough to keep in the moving air for about 30 seconds. Another grinding and cooling, then I check the grinding process. Takes a bit longer than water quenching, but seems to moderate the temp and more convenient than the water dunking. May not be the solution for everyone, but okay for me.

Handrubbed's picture

(post #99675, reply #15 of 25)

One of the best/cheapest sorces for good 1750 rpm motors is your local heating contractor.  When furnaces are replaced, the old furnace with the motor attached is taken to the junk yard.  Usually those furnaces sit aroung the shop waiting for the junk man to come.  If you go and ask the contractor, he probably would let you cannabalize a motor for nothing.  I have built grinder/polishers and dust filtration systems using these scrap motors and blower wheels.  For grinding and polishing wheels, I buy a basic belt drive mandrel at the hardware store.  This allows you to have two wheels driven at the same time.  Mine is mounted on a formica sink cutout, which allows me to move the whole rig anywhere I want it.


Let me know if you want more details.

GDH2's picture

(post #99675, reply #16 of 25)

Mr. Rubbed -

You say "I buy a basic belt drive mandrel at the hardware store. This allows you to have two wheels driven at the same time."

I am curious exactly what you mean by "drive mandrel" so I will ask you for more details if you would be so kind.

And thanks, Hand.

Wood Loon

Doug, The Wood Loon, Acton, MA
Handrubbed's picture

(post #99675, reply #19 of 25)

Sorry I didn't give you enough detail.  A mandrel is a shaft mounted in two support bearings that fasten to the solid surface of your choice.  The shaft has threads on either end for two wheels and retaining nuts.  In the middle of this shaft is a pulley that allows you to use a short belt to your (furnace) motor.  These pulleys give you a chance to adjust your speed, by the way, by changing the pulley sizes.  Most of the belt drive furnace motors will have an adjustable pulley attached.  Here is the mandrel I used: http://www.acehardware.com/product/index.jsp?productId=1291895&cp=1254873.1254950.1304602&parentPage=family&searchId=1304602


One idea for mounting is to put the mandrel and wheels on the bench top and the motor down below.  You will need a slot in the bench top for the belt, of course.


Another great use for this setup is the use of the Beall wood buffing system.  Google that for a look at a great way to finish small wood items.  I use it on plane handles, pens, etc. 


Hope this helps.


 

mike4244's picture

(post #99675, reply #18 of 25)

I have a similar 6" grinder. Turn the grinder on until it comes to full speed, a couple of seconds or so.Turn the grinder off, grind the tool until the wheel stops.Repeat as many times as necessary.


For lathe chisels, usually only one or two times switching the machine on and off. Plane irons and chisels that need a complete new grind, as many as six times on and off. You will find that controlling the grind is easier this way, even if you had a 1725 rpm motor.Use a friable wheel. Water cooling is rarely necessary except on thin edge tools such as knives and 1/16" parting tools.


mike

Steinmetz's picture

(post #99675, reply #20 of 25)

Don, as I perused all twenty previous posts, I was surprised that no one suggested using a smaller diameter wheel...

The determing factor in material removal (and heat buildup)is the surface speed at the periphery of the wheel.(The circumference)

The larger the circumference- the larger the peripheral speed. I'm no 'whiz' aa mathematics, but,by knowing the speed of the motor and the diameter of the wheels, one might determine the correct sized wheel to choose

The correct wheel size should be 1/2 the circomference of the
larger wheel's circumference.

Wrap a strip of paper around the six inch diameter wheel and cut it to fit.
Measure the strip and slice it at half it's.length. When formed in a circle, the new loop's diameter can then be measured Steinmetz.


Edited 7/28/2006 11:13 pm ET by Steinmetz

dgreen's picture

(post #99675, reply #21 of 25)

Good luck finding a three inch wheel with the proper bore, grit and composition, let alone of any quality. Unless your time is'nt worth much that's probably a loser.

Since the house is on fire let us warm ourselves. ~Italian Proverb

 

 

................................................

Men will never be free until the last king is strangled with the entrails of the last priest.
~ Denis Diderot

Steinmetz's picture

(post #99675, reply #22 of 25)

dgreen
Probably four inch?? If you'll notice,I edited the post as I initially confused the terms circumference with diameter. In any event, a choice of a slightly larger stock sized wheel can be
'dressed down'to the exact size Steinmetz.

dgreen's picture

(post #99675, reply #23 of 25)

I must have been reading as you were editing. Nevertheless thats a lot of dressing.

Since the house is on fire let us warm ourselves. ~Italian Proverb

 

 

................................................

Men will never be free until the last king is strangled with the entrails of the last priest.
~ Denis Diderot

philip's picture

(post #99675, reply #24 of 25)

Stein,
That is not a practical idea. To reduce the peripheral speed to the equivalent from a 1700rpm the grindwheel would have to be 2.9" diameter.So he would be looking for a 3" wheel to dress down-not good because 1)the tool rests would probably be "out"
2) the curvature of such a small diameter wheel is too acute for hollow grinding as required by woodworking edges.
3)The rate of wear increases constantly against diameter reduction.
Apart from these considerations one should bear in mind that these grindwheels are designed to operate efficiently within a narrow range of peripheral speeds.
The answer is the right stone used with a dresser.

Philip Marcou

Philip Marcou
AdamCherubini's picture

(post #99675, reply #25 of 25)

While I agree a 3" wheel may not be practical, I'm glad Steinmetz raised this important point. I remember oogling an inexpensive 8" low speed grinder at woodcraft. But while it seems its 1700rpm motor would be half as fast as my current 6" 3400rpm grinder, the reality is the 8" grinder's surface speed is only about a third slower. Just for sake of reference, my 20" grinder is 10 times slower than the 8" 1720rpm. Tormek is probably in that ball park.

So let's thank Steinmetz for reminding us that the diameter is related to the surface speed of the grinder. Thanks.

Adam