Speed Control for Bench Grinder
ThreePuttJoe
| Posted in Power Tools and Machinery on
I don’t know if this is a dumb question or not…but does anyone know if one of those router speed control switches would work for a bench grinder? I realize the rpms are much different, but I would think that it is relative to the tool it is controlling. I recently inherited a forty year old Craftsman Industrial Bench Grinder. Amazingly, it was made in the USA, and it hums like it was brand new. I could get a lot more use out of it if I could slow it down, but I don’t know if a speed control switch would work. Any of you “motorheads” know the answer?
Another cool feature is that he little spark windows are actually steel framed 1/4″ glass.
Replies
If the grinder has an induction motor rather than a universal motor (with brushes and a communtator) the speed is fixed by the stator configuration and can't be changed. Those old grinders are real work horses in removing iron but too fast for sharpening tool steel.
A number of years ago I saw bench grinder with an 8 inch wheel on one end and an 8 inch pulley on the other. A salvaged motor with a 2 inch or so pulley drove it. Clutzy and ugly but it worked. The owner said that the motor burned out.
Harry
I've the same grinder (or darned near it), and am going in the same direction for tool sharpening. Harry D is right on the mark with remarks about motors.
I was planning to simply reduce speed with pulleys. Even a 1750rpm induction motor will be a tad fast, as the grinder head won't tolerate too large a pulley - I figure I can get it to something near 1175 wheel rpm with a 3" on the grinder and a 2" on the motor (with a Power Twist segmented belt.)
However, conversation with Norton got me some words about running their wheels below spec range. The new friable white wheels are made for 3400 rpm operation, and I've a sneaking hunch that even a "high" 1175 will perform well in manual application.
Which carries us to the last and worst problem. It's darned hard to manually control passes uniformly at .001" depth. I'm blue-skying about fabbing an attachment that will let me manually pass across wheel, but will clamp the blade and slide on height-adjustable rails for depth management. Just the ticket for dressing, too (Norton recommends no more than .001" per pass for diamond dressing.) Will post when I get there.
Note that Norton is custom-making 8x1x80grit friable wheels for Lee Valley, and at a reasonable price. (3/4" is the widest I've found elsewhere.)
Good hunting...
---John
Edited 6/2/2005 3:03 am ET by John
Which carries us to the last and worst problem. It's darned hard to manually control passes uniformly at .001" depth. I'm blue-skying about fabbing an attachment that will let me manually pass across wheel, but will clamp the blade and slide on height-adjustable rails for depth management.
I use a high speed grinder to shape all my metal working tools..
The key is good quality wheels AND TAKE YOUR TIME!
Making a jig that will hold your steel firm and has a fine adjustment screw so you can adjust in/out from the wheel in fine increments is the key...
Nothing wrong with a slow speed wheel.. Far from it. But it is really not needed.
Even hand holding your tool (if your good at it works)..
TAKE YOUR TIME and just 'kiss' the stone and you can grind ALL DAY and never over heat your steel...
EDIT::: Long ago.. My first job was sharpening tools for brown and sharps.. Did it all day long ...LOL... Good pay (for the time) and just a high speed grinder and a water bucket.. My Super.. He said on the first day.. If I see ya 'dunkin' a steel in that bucket... YOUR FIRED!
Edited 6/2/2005 11:40 am ET by Will George
Hi, Will...Great post!I've hand-sharpened my blades on a high-speed wheel for the last 40 years, and get along pretty well with it, though I sometimes have a little difficulty in getting the exact angle I want what with big 'ol fingers in the way on a fixed toolrest. I'm pretty fussy, and don't consider it a "good grind" unless it's dead square and shows only one pass. Go through a lot of steel that way ...A good traversing jig would just enable better first-time accuracy and save some time, especially on wide blades.You're dead-on about light touch. I used to dunk 'em, but finally concluded that it takes the time it takes, and slowing down was a better approach. Seems ya always need a sharpening when it's inconvenient and time is at a premium....Norton's comment got me thinking pretty hard about wheel speed. Though I'm prepared to slow it down (easy enough to change pulleys), I'm going to try a friable wheel at 3400 before I get too gay with modifications.Funny how the old timers (your super) have a way of passing on expertise in their rumbledy comments....Best to ya...---John
Try this instead of buying a 1725 rpm grinder ot trying to reduce the speed on yours.
Turn grinder on and let it come up to full speed. Turn grinder off, make your passes until wheel stops. Repeat as needed. I sharpen all turning tools this way. When grinding a plane iron or chisel, if only a touchup is needed, do the same thing. If the chisel needs a lot of work, grind at 3450 rpm until you get close, then use the previous method.
mike
I haven't posted in a while. Don't mess around slowing your grinder down, it's counter productive. Buy some decent coarse wheels and a good dresser. It's difficult to dress and true wheels at slower speeds and properly trued and dressed wheels are critical. A properly maintained coarse wheel (36/46 grit) turning at normal speed (3400 rpm) will generate considerably less heat than a finer wheel at slower speeds.
Shaping chisels and plane irons is just coarse grinding and it only takes a couple passes on a sharpening stone to remove the signatures of a coarse wheel. Maybe one or two more passes than removing finer signatures. If you're not a turner looking to go directly from the grinder to the lathe, skip all the hype about friable wheels and slow speeds.
I've got more information on our web site at:
http://www.planemaker.com/articles/grinding2.html
Larry,
.......and a good dresser"- I was wandering if or when someone was going to mention this essential tool. For the benefit of 3putt and some others:-
Loss of both types of temper when grinding steel -the main culprit for this is (assuming the correctgrade and type of wheel is in use) glazing of the wheel which causes rapid heat build up.The wheel should be run at the makers specified speed,or reasonably near to work well.
Nowadays the best wheel dresser is one with a diamond face- throw away anything else - it is obsolete.
I am retiring to my air raid shelter now .
Edited 6/4/2005 5:33 am ET by mookaroid
Hey, Mook ...You and Larry are both spot-on - I've a couple of diamond dressers and use them to make dust whenever it's needed ... I'm sure you're gonna catch flak from the "I don't need no stinking dresser" bunch, but you're right, and I encourage you to emerge from the bunker soon.---John
Nowadays the best wheel dresser is one with a diamond face- throw away anything else - it is obsolete.
I am retiring to my air raid shelter now .
******************Want a beer? Looks like we'll be down here for a while ...Leon Jester
Cheers!
So far no reaction so either they are faint of heart or they have been given the wrong GPS raeding!
Edited 6/4/2005 11:15 pm ET by mookaroid
3Putt, Why not use a smaller diameter wheel?
It's the surface speed that's the culprit.
A 2 in wheel has a lot less diameter than a 6 in wheel even at the same rpms.
If you dress your wheel occasionally, it exposes fresh sharp granules to the tool and creates a perfectly round wheel.
A light right to left/left to right traverse across the moving wheel
and 'over reaching' the edge of the wheel before reversing the direction and continuing beyond the wheel will give you an even 'footprint' as well as even wheel wear. Stein.
Thanks...good advice all. I didn't have a bench grinder before I got this one, and since it is such a great old tool, I wanted to get as much use from it as possible. I love all that old stuff. I had always assumed from what I had read that a high speed (3400) grinder was good for lawnmower blades and not much else. And those (baldor?) ones are exxxpensive. I've got some ideas to work with now.Joe
Old thread, but since it's one of the first results when searching google for "bench grinder speed control", I will post anyway.
These days, there are (relatively) affordable single phase input, single phase output variable frequency drives (VFDs). No-name Chinese units are available on eBay for 60-70 USD including shipping.
Whether or not it's worth it, is up to you.
I was taught to keep my fingers as close to the tip as possible and when it got warm give it a spritz .You can make a great gig by asking the Philadelphia woodworking school for a copy of their plans
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