Grinder Wheel Sizing Questions

[BikerDad]

I'm looking at getting a slow speed grinder to use for sharpening lathe tools. I'll be using one, or perhaps 2 CBN wheels. Unfortunately, none of the preferred grinder size / speed options land in the sweet spot for SFPM as recommended by the CBN wheel makers. A 10" wheel at slow speed (1725-1800 rpm) DOES land right there in the sweet spot. So that's the setup I'd like to go with.

My question is, using a CBN wheel, is there anything problematic about putting a 10" wheel on an 8" grinder? The guard(s) will be removed anyway because the wheels are 1.5" wide.

Keep in mind that CBN wheels are solid metal, not prone to flying apart.

 

[2oolhound]

Man those things are pricey. I just use a 1/3 hp grinder with 6" wheels turning at 3600 rpms and it does the job. I like using the flatness on the side of the stone too which is something the CBN's don't have much of. Looks like a 5" at 3600 is close to a 10" at 1750 but the radius of the 5" wheel would be a little much to deal with alright.

 

[1982fxr]

how heavy are those wheels compared to 8" stones? what grinder?

 

[pepi]

This might be a suggestion, it is a HF chain saw blade sharpener. Has a diamond wheel, I use it to sharpen tungsten electrodes

 

[1982fxr]

This might be a suggestion, it is a HF chain saw blade sharpener. Has a diamond wheel, I use it to sharpen tungsten electrodes

i'm not a welder; you sharpen arc welding rods?

 

[turbowoodworker]

For the amount you'll spend on a low speed quality grinder that will be used for specialty sharpening, why not investigate a dedicated grinding system made for lathe tools and chisels?
Tormek is godawful expensive but Delta and others make machines made for your expressed purpose...slow speed, water bathed, softer stones.

 

[Buckgnarly]

i'm not a welder; you sharpen arc welding rods?

He's talking TIG

 

[woody 73]

I myself like to stick with the correct items like using an 8" wheel for the right size grinder and I sharpen wood lathe tools 24/7 using the following stones:

http://www.rockler.com/norton-white-aluminum-oxide-grinding-wheels-8-grinding-wheels

Now there are exceptions to the rule like using pvc for all your air needs, using chrome sockets on your air guns, using grinders without their guards, using the side of the grinding wheel, leaving a mushroom on your chisels, striking a builders hammer on a harder tool steel, etc. you get the point hey guys do it everyday more power to them.

Me I like safe and slow...

 

[tool_scrounge]

Just buy a cheap belt driven grinder and use whatever motor pulley gives you the desired speed. Or get variable speed using a DC motor or a 3 phase motor with a variable frequency drive (VFD).

Link to an example:
http://vintagemachinery.org/photoindex/detail.aspx?id=15301

 

[terryo1965]

Only electroplated wheels are solid steel. Resin, vitrified, and metal bond wheels all have CBN "segments" bonded to the OD of a solid steel hub and can break apart while in use. I would verify exactly what type of wheel you have before you remove the guard but personally I would never run a grinder without a guard.

If you are grinding without coolant I would run the wheel between 3,000 and 4,500 SFPM so your 8" wheel at 1800 rpm would be about 3700 SFPM. I would be concerned about burning the tools by going much faster. CBN cuts so much faster than conventional abrasives you really don't need to max out the SFPM, you will only risk overheating the part.

 

[BikerDad]

To respond to some of the questions:

These are the wheels in question. Electroplated solid steel, 9lbs for the 10", an 8" composite wheel is around 3.5lbs. The preferred grinder will be a Baldor 8100W, although it's likely that in interim I'll get a cheapie Chinese unit. As 2oolhound noted, the wheels are pricey. They are also, in a non-production environment, not a consumable, unlike regular wheels.

I've already ruled Tormek out, they are too slow and the stone demands too much babysitting. The CBN wheel on a slow speed grinder is a proven system. It is effectively a dedicated sharpening system. You never have to dress the wheel. Or change the water. Or dress the wheel. Nor is there any dicking around with balancing the wheel. While not as particulate free as a wet grinding/sharpening system, it is far less messy than a normal dry composite grinding wheel.

The HF chainsaw sharpener is interesting, may be quite handy for carbide router bits and such. However diamond wheels and steel tools don't mix well.

Tool-Scrounge, your suggestion sounds like it would suit you quite well, but I'm not really looking for a project, even one as modest as that would be. Plus, for whatever reason, I really don't like the separate belt driven motor setup. Call it an irrational prejudice if you will.

personally I would never run a grinder without a guard. - terryo1965

Do you run a buffer without a guard? A Baldor 8" 3/4hp buffer runs at 1800rpm, without a guard. If whatever is being spun can't come apart, I don't see what your concern would be. Note that I can't imagine a situation where I would run a composite/stone grinding wheel without a guard, but that's not what's in question here. To use guards with the 1.5" wide wheels, regardless of diameter, I'd have to fab up the guard myself, as all the guards on 8" grinders out there are sized for 1" (at most) wheels. I used a 1" wide wheel all last Friday, and while it does the trick, a wider wheel will reduce skating spindle and bowl gouges off the edge of the stone.

 

[2oolhound]

I thought you were talking about metal lathe tools but I suppose they get pretty big too. Mine are only 3/8" so it doesn't take much to sharpen them. I usually hand hold them and water dip them when they get too hot on the finger tips. Gently sharpening a lathe bit is a different thing from leaning into something and grinding it. I can understand the logic in CBN system specially the longevity end of it. They need to make some wheels with flat sides so you're not hollow grinding everything.

 

[BikerDad]

I thought you were talking about metal lathe tools but I suppose they get pretty big too.

My bad, I'm so used to asking questions like this on woodworking forums, so there's no need to specify "wood lathe tools" vs "metal lathe tools."

I can understand the logic in CBN system specially the longevity end of it. They need to make some wheels with flat sides so you're not hollow grinding everything.

They do make some with flat sides. The hollow grinding is another reason I'd like to go with a 10". It apparently doesn't present much of a problem with 8" wheels though, as the system is widely used by professional and elite turners, both wheels with flat sides and without.