slow speed bench grinder

[rfurzer]

I have just read a book about sharpening planes and chisels that recommends a grinder wired to run at half speed. I note that Carbatec have them but they are fairly exxie compared with the standard.

Can a sparkie do something to make it run at the slow speed?

[Stustoys]

Just how slow do you want to go?
Have you seen these.
NEW WET & DRY COMBINATION BENCH GRINDER & SHARPENER (eBay item 120651482120 end time 04-Dec-10 14:36:44 AEDST) : Home (http://cgi.ebay.com.au/NEW-WET-DRY-COMBINATION-BENCH-GRINDER-SHARPENER-/120651482120?pt=AU_Power_Tools&hash=item1c17638408)

Stuart

[rsser]

You don't need a slow grinder. Std speed + care + the right wheel will get results.

With HSS you can go to dull red before damaging the steel.

HC plane blades and chisels are in trouble if you get to blue but you can avoid this as per the above.

[derekcohen]

Heat is the enemy. Too much of it burns blades.

Hard wheels glaze over quickly and increase heat. The average grey wheel is very hard and unsuited to woodworking (and are more appropriate for HSS). White or blue wheels are suited to woodworking blades.

Look for coarse wheels (36 - 46 grit) as they run coolest. Keep them clean.

Slower speeds run cooler: a full speed (2800 rpm) 6" grinder runs at about the same speed as a half-speed (1400 rpm) 8" grinder. A full speed 8" grinder can be Trouble, especially if you add a hard and high grit (100+) wheel into the mix.

And, no, there is no electrical step down to slow a grinder. You can, however, use pulleys to slow it mechanically.

Regards from Perth

Derek

[BobL]

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Slower speeds run cooler: a full speed (2800 rpm) 6" grinder runs at about the same speed as a half-speed (1400 rpm) 8" grinder.

I agree with Derek, but just a reminder that besides the rpm, it is the wheel size rather that the grinder size that matters so a small but useful grinding speed reduction can be made by running a smaller wheel on a bigger grinder.

Given that most of the grey hard wheels that come with grinders should be tossed, one can for example put a 6" wheel on an 8" grinder. This reduces the grind speed by 25% but leaves the option of running a bigger wheel for other grinding purposes.

Below a table of wheel size in inches / RPM / speed (fpm) that you might find useful:
Slower is better but as Derek says a coarser softer stone will also help.

[mic-d]

I have the C'tec slow speed grinder. It comes with a grey wheel and a 120 grit white wheel. As Bob says, the grey wheel is not much use, replace it with a 46 grit white wheel of j or k hardness. The annoying thing is that particular grinder has strange specs, the bore is 32mm, the standard is 31.75mm so you have to ream the wheel out with a bit of wet and dry (easy enough), AND the minimum width wheel it accepts is 30mm (comes with 32mm). Try finding a coarse wheel with those specs. It is impossible to buy them off the shelf (Carbatec stock the 120 grit and possibly an 80 grit to fit). You have to use a 25mm width wheel and a spacer. It's not a bad grinder otherwise. You need to watch the heat in most metals, as Ern says HSS is fine to dull red (if you can get it red on that grinder you're doing well). The thing that HSS does not like is rapid cooling by eg water dipping. Best to air cool it only.
Here's an interesting link to some vital stats about different metals. You can see that M2HSS hardness is really unaffected by heats up to 1150ºF and the annealing temperature is way up at 1600ºF. Link might give you some idea of how heat sensitive your metal is.
Heatreat (http://www.knives.com/heatreat.html)

Cheers
Michael

[rfurzer]

Thanks

[rsser]

Folk wisdom has grey wheels as bad news.

Hock says that with care they are not.

Some grinders these days come with white wheels; many come with grey.

Suggest you try the grey if that's what comes with your grinder, with a light touch, esp when you are close to grinding the full bevel, and dress the wheel often.

If you want to try this, I'd suggest you not grind right to the cutting edge but save that for a 2ndary bevel on a benchstone.

[Mr Brush]

mic-d....I just bought the same grinder, and found this out the hard way. I bought a pink 60 grit alox wheel with all the push-out plastic cores, thinking it would fit just about any shaft on a grinder.

Took the original wheel off, only to find a silly 32mm flange built-in to the inner washer. What a stupid idea....:((

I'll have to return the nice alox wheel I bought and find something else. Has anyone found a coarse wheel anywhere to fit this grinder?

Of course, I suppose one possibility would be to remove the flange from that inner washer, then the wheel would only have to fit over the actual shaft (which looks like a fairly sensible size).

[mic-d]

mic-d....I just bought the same grinder, and found this out the hard way. I bought a pink 60 grit alox wheel with all the push-out plastic cores, thinking it would fit just about any shaft on a grinder.

Took the original wheel off, only to find a silly 32mm flange built-in to the inner washer. What a stupid idea....:((

I'll have to return the nice alox wheel I bought and find something else. Has anyone found a coarse wheel anywhere to fit this grinder?

Of course, I suppose one possibility would be to remove the flange from that inner washer, then the wheel would only have to fit over the actual shaft (which looks like a fairly sensible size).

Mr Brush sorry to hear that you had the same experience. I did some extensive searches, including contacting Abrasiflex and Aidco and have found to the best of my knowledge and theirs that the only way is to have coarse wheels custom made. I have spoken to C'tec about it but I think more need to complain-maybe they will actually order some coarse wheels to spec. It's pretty easy to fit a 31.75mm bore/25mm wheel with a 5/8" washer behind (actually the shaft is marginally bigger than 5/8" too, I had to fine tune the washer with a dremel:doh::doh: ) but then you can buy pretty much any wheel you want.

Cheers
Michael

[Mr Brush]

Since the grinder is new, and for once I still have the receipt, I'm very inclined to return it.

The description on their webpage just says the arbor shafts are M16 x 2, it doesn't say anything about "but contain a hidden 32mm flange so that no standard grinding wheel will fit" :((

That's just plain stupid.

[mic-d]

Would be good if you do want to return it to speak to Tony at the Brissie warehouse about it. Myself and one other have raised the 'fault'/'feature' with him, however I did not specifically suggest they should stock say a 46 grit white wheel that fits, my bad.

Cheers
Michael

[Mr Brush]

Thanks Michael - I got mine from Sydney, so I'll give them a call tomorrow.

From their product description I was under the impression I was getting a grinder with standard 5/8" arbors (i.e. M16 threaded). If they are going to sell a product that only takes completely non-standard wheels they should at least mention it in passing.

I'll let you know how we get on.....

Cheers

[jatt]

We just run an elchapo Toolex slow speed grinder in the shop next to the old Crompton Parkinson unit. Runs in a water bath, bit wobbly in the wheel, but good enuf for us. Bit of a challenge hand sharpening endmills on it, but I get by. Also sharpen scissors on it Know it is heaps cheaper than the brand name stuff.

[Mr Brush]

Well, kudos to Carbatec Sydney, when I returned the grinder and explained the issue they were happy to take it back against a different model. They were unaware of the problem, and of course it isn't many customers who get the grinder home and immediately try to change a wheel on it. I suspect that a few people who have this grinder will be disappointed in 12-18 months when they need a need a new wheel and wonder why nothing seems to fit....

The large 32mm flange causing the problem is part of the casting that is the inner washer, so only wheels with a 32mm bore will fit. I've explained to Carbatec that they could fix this by getting more of the OUTER washers (which don't have the flange), and swapping out the inner washers for these. The grinder would then have a standard 5/8" arbor between two flat washers suitable for standard grinding wheels.

As luck would have it, the (normally more expensive) Taiwanese-made 8" slow speed grinder is on special at the moment, so I only had to pay an extra $50 to get this one instead-

Carba-Tec Slow Speed 8" Bench Grinder : CARBA-TEC (http://www.carbatec.com.au/carba-tec-slow-speed-8-bench-grinder_c20301)

Only problem was the weird downward pointing dust ports, which are metal and built-in to the guards, interfere with the Tru-Grind. I got around this by neatly sawing about 1/2" off each port. :D

This grinder has coarse and fine alox wheels as standard, and runs very smoothly and quietly. The Tru-Grind does a fantastic job on the turning tools - highly recommended !

Once again, thanks to Carbatec for the excellent service/support.:2tsup:

[rsser]

Good outcome Mr B.

[Mr Brush]

A quick happy snap of the finished setup......:rolleyes:

A piece of reclaimed kitchen benchtop from the local timber yard, a little spotted gum edging just for the hell of it, Tru-Grind mounted under the finer alox wheel and my Veritas grinder jig set up on the coarser wheel.

So far I've tried the Tru-Grind on a bowl gouge, spindle gouge, parting tool and roughing gouge with excellent results. The finer alox wheel on this slow speed grinder is plenty aggressive enough, but leaves a good surface finish.

Only tool I'm not convinced about on the Tru-Grind is my skew chisel - tricky getting the bevel angles the way I'd like them. Might have to try the Veritas instead I think.

[rsser]

AFAIK there is a Veritas add-on for skews. Click (http://www.leevalley.com/US/wood/page.aspx?p=32976&cat=1,43072)

But that's all over the top.

A cheap Chinese platform x 2 (for the mitre gauges) or a Sabre (http://www.cws.au.com/shop/item/sabre-grinding-jig) from Carrolls would do the job.