Slow Speed Grinder?

I asked someone what the point was and he said “it just takes twice as long to grind anything”. I should add that he kept a straight face! I understand these may be aimed at wood turners. I’m not sure why as the majority of wood turning tools are HSS. I’m happy using a standard grinder and a belt grinder, I just wondered. Any opinion?

The angles on a wood chisel or gouge may be 25degrees where as a lathe tool could be 80-85 degrees and are therefore not overheated so easily. Plus if my Tormek ran that fast it would through all the water over the workshop.

The one I have like the Tormek you can dress the stone to have two different grits as well as being water cooled which is ideal for the chisels as Jason said to aid keeping them cool on the opposite end there is a leather coated wheel to strop the chisels to a very fine cutting edge. Not just chisels but planer irons. With the various attachments axes scissors and other tools can also be sharpened.

I use this along side my normal bench grinder which is ideal for fast metal removal when reshaping tools. I also use this one to sharpen my wood turning tools but they are sharpened little and often as some woods take the edge off very fast and the finer sharpening of the slow grinder is not suitable for those tools except possibly the skew chisel

A wet stone grinder such as the Tormek is another beast entirely. I was asking about a slow speed grinder.

An example:

I have a Tormek water cooled slow speed grinder and I use it mostly for my wood working tools. It does run slowly and is water cooled so the tools do not over heat. The slow speed also makes it very safe to use, much less hazardous than the usual high speed bench grinder used for metal working tools.

I am not sure if the majority of wood turning tools are made of HSS nowadays, traditionally they were carbon steel. Most woodworking tools for hand woodworking; chisels, plane blades, carving tools, knives, and axes etc are still made with carbon steel blades and they are difficult to sharpen on a high speed grinder without the risk of drawing the temper.. Some woodworking chisels are made with HSS blades but they are not very popular as far as I can see, perhaps because they are hard to hone on the usual woodworkers' bench stones.

The 2 types of grinder, high and slow speed, are used for different purposes and both are very good at what they do.

Add, I was typing my post before Vic put up his second post.

Edited By Rod Renshaw on 04/12/2022 21:10:50

Edited By Rod Renshaw on 04/12/2022 21:28:45

Not impossible but you’ll be hard pressed to find wood turning tools that aren’t HSS or with Carbide inserts.

The last woodturning chisel I bought was made of HSS and cryogenically hardened. That's a long way away from carbon steel. The sharpening instructions specify slow grinding using lots of coolant. As I understand it, the slow speed is to ensure less aggressive removal of metal. However, I'm not convinced that achieves anything like an optimum cutting speed (wheel-to-work). I use a 'normal speed' grinder when I need to sharpen woodworking tools, but I can see the advantages of using a slow speed when trying to grind something like a fingernail gouge (the Drozda finial gouge being a great test of skill on a 'standard speed' grinder). You probably get more thinking time, which seems like a good thing.

Marcus

So-called low speed grinders seem to be rated at 1400rpm which is not all that slow. But they tout it as creating less heat build up when sharpening tools, which as Jason said would be more critical on fine woodworking edges than 85 degree lathe tools etc. I will have to check my ancient bench grinder next time in the shed to see what speed they used to run at before the marketing department got involved. I would have thought 1400 pretty standard for a single phase motor but maybe not in the case of the type used on grinders with no start windings etc.

The Axi one shown is really a half way house between a standard grinder and the very slow* watercooled ones. Fast enough for initial shaping on the grey wheel but slow enough not to remove too much metal when using the white wheel to just touch up a tool that has simply lost it's edge

Motor speed is a bit irrelevant as the diameter of the cutting stone will play a part in the cutting speed. This is another reason for the Tormek having a slow rotational speed as at 10" dia the surface is moving faster than say a 6" grinder with the same spindle speed. The woodworking tools like a flatter grind hence the larger dia wheels or flat belts like the Sorbey.

The Axi description says almost the same as my reply yesterday- 

• Especially suited to the edge tool grinding needs of the woodworker or turner
• Slow running speed of 1,425rpm, less chance of overheating the tool

Edited By JasonB on 05/12/2022 07:28:06

Guessing also quieter and less vibration. I regret not buying an industrial bench grinder that I was offered once, I declined because it was large and 3 phase but since then I have thought that it plus a VFD inverter would have been a much nicer thing to use than my current DIY store one, and would have allowed slow speed use as well. I suppose brushless DC would do similar now without taking up so much space.

We all sharpened wood chisels and plane blades on a standard 6" bench grinder in high school woodwork class and it seemed to work ok. Not sure if a slow speed grinder is all that necessary really.

I mean even a grinder is unnecessary, I know at least two skilled joiners who just use a fine garnet belt on a standard belt sander, held upturned in a workmate with a zip tie round the trigger...

"I need to do it about once a month for some minor damage or when the abuse chisel gets too worn, so why waste van or shed space on a grinder"

I have to agree, whilst you might sharpen woodworking tools every day or few days whilst using them frequently, if you're keeping on top of it, only a minute with a fine oilstone is required.

Wood turning tools and wood carving tools are different, and there's benefit to having a grinder to hand there (with a leather stropping/polishing wheel for carving tools), but they're also static workshop based activities which blunt their respective tools far faster than normal woodworking.

Standard grinder at Skool woodwork section was a water blathered 6" wide by about 2 1/2 foot diameter slow running sandstone. Secondary op was on well oil soaked oilstones followed by a liberal stropping on leather pads.. Never managed to detemper the cutting tools and yes, some can manage to kill the hardness of HSS using a standard bench grinder due to over heating.

Regards Ian.

In my woodwork class, boys were forbidden to wheel-grind the tools. That privilege was reserved for the elite doing A-Level woodwork. I used to lurk in the storeroom with the other layabouts. There was a big box full of ruined chisels where cack-handed schoolboys had ground inches off the blade.

Though not allowed to wheel-grind, we were taught 'little and often', and encouraged to frequently touch edges up on an oil-stone. I think a wet slow grinder would be essential for Carbon Steel blades because the edge overheats so easily, and pretty good for restoring slightly nicked HSS. My speedy grinder is pretty aggressive, and in my wobbly hands often removes too much metal from the wrong places.

By the by, chaps with a natural talent for grinding go round telling everyone it's easy. I hate to disabuse them, but there are plenty of unfortunates like myself who find grinding difficult and only get half decent results after lots of practice. For people like me I propose founding the "Society of Clumsy, Unskilled Machinists", SCUM for short. We need all the help we can get...

Dave

That might be me... Sharpening woodwork tools, then grinding my own carving gouges, and then later shaping lathe/boring/slotter tools all felt entirely natural and easy.

That said, I suspect that I benefited from no-one telling me that as a mere mortal I wouldn't be able to do X, Y, or Z, and having examples of tools from my grandfather and great grandfather to show what good should look like, without really giving too much thought to how good they were themselves at the peak of their respective talents.

Ignorance can sometimes be a great gift, unfortunately it is very hard to apply wisely, judiciously, or even consciously.

I've had the Axminster 8-inch slow speed grinder for a week. I bought it to accommodate the CBN wheel I bought from them only a few days prior to that. My reasons for buying a CBN wheel are set out here.

I can't presently recommend either this Axminster slow-speed grinder or their CBN wheel. I'm awaiting some replacement parts before I decide whether I'll keep either.

Problems are as follows: whilst I can get the supplied white stone wheel [the one out of the two stone wheels supplied that I want to use] to run so true that no lateral wobble is detectable by eye, the CBN wheel with its special CNC-made bushes has at least 0.5mm of lateral wobble that can't be rectified no matter how the bushes or the wheel are rotated before tightening the lock nut.

The shaft of the grinder is acceptably straight, with only 0.02mm of runout, so the problem is probably either the bushes or the wheel or the lock nut, or a combination of all three. Axminster are sending out replacement bushes to see if it cures the problem, but it's turning into a rather long wait for these to turn up.

I've tried placing cardboard washers between the small shoulder on the shaft and the inner bushing, as well as underneath the locknut, and this reduces runout by about two fifths, but it's still unacceptable runout in my view for a wheel that I bought specifically to be able to use the side for grinding drills on.

You would think it would be the other way round with the wheels - that the stone wheel with its crudely cast bushings/washers would be the one that was difficult to cure of wobble, and the precision turned CBN wheel with its CNC-made bushings would be dead straight, but sadly that's not the way things presently are.

ETA: I forgot to say that with both wheels installed the grinder vibrates horribly when powered up. If only one wheel is installed [doesn't make any difference whether this is the stone wheel or the CBN wheel] the vibration reduces considerably.

Edited By Bill Phinn on 05/12/2022 14:30:54

If you do a lot of woodwork then I expect a Tormek or other wet stone grinder is a good choice. For woodturning tools though they are rather tiresome and completely useless for reprofiling turning tools due to the time it takes. I know because I’ve tried. Most folks at my wood turning club seem to use a standard speed grinder without any issues. Some use Cubic Boron Nitride wheels. I use a variable speed belt grinder myself.

Bill Phinn

Sorry to hear about your problems with CBN on the slow speed grinder. I am using one of these on a standard (2850 rpm) machine with reasonable satisfaction but, as you will know, CBN wheels are typically heavier than their conventional equivalent and any vibration is going to be worse when using them.

I've had a couple of these wheels from different sellers and have been surprised by the variable standard of machining and balance found. Of course, you need a good grinder to start with, the more powerful the better as standard machines seem to struggle on start up.

Thanks, Ega.

We'll see how it goes with the replacement bushes. Axminster are being quite proactive in trying to resolve things.

I think a slow speed grinder might give you a fighting chance of not drawing the temper of carbon steel wood chisels and plane irons. As a casual woodworker I have never mastered putting the keenest edge on a blade of any sort. A chance stroll through a Claas Ohlsen shop made me buy a baby T3 Tormek at a very keen price as the T4 was just coming in. If you follow the instructions you will have very sharp tools, for the first time my tools were as sharp as I could wish for and my plane blade was sharp as it was after I asked the workshop technician at school to sharpen it when I was a schoolboy. He used a water cooled sandstone wheel to tidy up the mess I brought him and a few strokes on the oil stones made a super sharp blade, his test was to shave the back of his wrist. My Tormek efforts produced an edge sharp enough to shave my wrist and pare crap softwood without crushed fibres.

Mike