Green wheels for Carbide tools: do they work? (1 Viewer)

[e9999]

I had always thought that one needs to grind carbide tools and inserts with diamond wheels but I was just told that it can also be done well with much less expensive green wheels (which I thought were (silicon?) carbide as well). I was surprised, so I thought I'd ask the experts here:
Have you had success with grinding carbide tools or inserts with non-diamond green (or similar) wheels? Worth trying? If so, can you do full sharpening with the green wheel or do you need to finish on diamonds anyway? TIA

 

[ntsqd]

I have a small green stone for final dressing of carbide lathe tools. Can sharpen them or put a small nose radius on them with it as well. Diamond might work faster, but all that I've ever used on cemented carbide has been green stones & wheels.

 

[aztoyman]

Yep, our field machinists that came out, welded up worn out bores and re-machined them always had a small grinder they broke out with green wheels to sharpen their tooling. That was 20 years ago since I've been there so I have no idea if that has changed.

 

[e9999]

dang, I bought a green wheel. Bestish review on Amazon but still an unknown undoubtedly chinese brand. It was rated (in small print) on the listing at just about the max speed of all my grinders - 3450rpm or so, so marginal, but when received it turns out it is actually stamped at 3300 something rpm, so even lower. So, not great. Not that I have much trust at what the no-name chinese companies rate their items at all but I doubt they are erring by underestimating the stated ratings... So do I keep this wheel that will run at 3400 rpm next to my face, considering all the others are also probably overestimating the limit rpm, and who knows, or do I try to get one that has a true higher rating if that can even be found? Or is this the sort of thing you can't find on Amazon and need to go to specialty houses and pay an exorbitant price for still unknown quality?

 

[aztoyman]

I wouldn't chance it. Can you return it?

 

[ntsqd]

Since heat is less than ideal for carbides, maybe find a slower spindle speed grinder to use that or any green wheel on?

Ideally a clone of one of these: BALDOR 6" CARBIDE TOOL GRINDER - #500 | eBay - https://www.ebay.com/itm/235605562206 Even used those aren't cheap, so maybe a clone can be found at a justifiable price?

 

[e9999]

Yes, I can probably return it.
Yes, I could buy another grinder but I'd rather not, as I already have too many. And I can buy a higher rpm rated wheel -if I am to believe those numbers- at much less than the cost of a good grinder. But I wonder if I could get an inexpensive variable speed controller to work on one of them. Unfortunately, they are all single phase 120V.

 

[ntsqd]

VariAC?

 

[e9999]

Good thought! I have a couple. Isn't there something about lack of torque at lower rpm with those, though? Forgot... But easy enough to check.
They only affect the voltage not the frequency , the latter being -with the number of poles- what is mostly determining the speed I imagine, I'm guessing that this not a very efficient way to go, if it works at all. Any reduction of speed is probably due to losses. Oddly, I do remember reading about people using dimmers on motors. Probably depends on the type of motor, induction vs universal or something like that?

 

[ntsqd]

Something like that, I'm no expert on that topic at all.

 

[e9999]

I should read up some more on motors again, I can't keep track of it all, it's a mess. I'm guessing that most bench grinders use induction motors so seeing some slip but that is generally small I think. I guess that at lower voltage the slip would increase somewhat but the motor would probably heat up. I might try just to see what happens.

I just looked up on Amazon to see if they have affordable VFDs that output 1 phase and they do have some 220V, not many, probably cuz it's not a great way to go.


added: well, I tried. Nope, no suitable control of speed with just a Variac. The one grinder I tried was likely an induction motor, it's rated at 3500 rpm. The speed stayed around 3,580 rpm with no load at 100% and close to that even down to 20% voltage, and would immediately bog down then if I put any load on it at low voltage. I have others, but it'll likely be the same. Unfortunately, that also means that I should stay away from wheels that are rated only to 3,500 or 3,600 rpm, I guess, too close for comfort.

 

[e9999]

well, the more I read about the silicon carbide wheels, the less impressed I am. I am seeing a lot of conflicting opinions and comments about just biting the bullet and going for diamond wheels instead because of poor life expectancy, ugly dust, rough edges etc with the green wheels. Not to mention that I could not find any good source so far with info on desirable surface speed for grinding of carbide tools, besides a couple of AI comments making analogies with diamond wheels at 3000 sfm. About half of what seems to be the recommendation for aluminum oxide wheels. Not sure about any of that.
I have found a 1750 rpm motor in my piles and a couple of shafts and pulleys so I'm set for lower speeds. I might try and see what happens.

 

[ntsqd]

My experience in grinding carbide has been that my little 6" bench grinder and my pedestal mount 10" grinder both go too fast.

Diamond is better, but is another step up in $$$. If you're going to go diamond I'd strongly suggest saving up your pennies until you can swing one of the specialized tool bit grinders discussed earlier.

 

[Malleus]

Have you tried calling Norton product support? I've always found their product engineers very helpful.

The dedicated tool grinders are designed for steel tools, not carbide, AFAIK, so there probably won't be any wheels for them that suit your needs. Building a Quorn is on my list to do before I die.

 

[e9999]

I contacted Norton with a question about an unlabelled wheel of theirs I have but had to do it by online message, did not see a phone number. Should look again.

I did see some inexpensive 3" diamond wheels on amazon but of course generic chinese stuff. Less worried about those exploding than a grinding wheel though. Wondering if this may not be a good way to go on a 3600 rpm bench grinder since the sfm will be half of usual 6" wheel. Plus the smaller radius may help with clearance angles.

Am I correct in thinking that diamond will handle steel where silicon carbide won't? My carbide tools are all brazed so that may help.

 

[e9999]

I think I will get a higher speed-rated silicon carbide wheel to play with a bit while I research diamond wheels more seriously, and end up with both. I have now seen mentions of desirable higher surface speeds with the silicon carbide wheels so it should be OK on my 3,500 rpm grinders, I think. I should of course really dig into the Machinery's Handbook but as usual that is a daunting task, and a cursory glance did not show much on silicon carbide wheels.

 

[e9999]

Well, I got another green wheel. Oddly enough, at McMaster it did list it as for Brass, Alum and other soft metals but not specifically for carbide. But I hope it should work at least OK for the latter. Interestingly, they do claim the silicon carbide does not get clogged up with the soft metals. That would be a pleasure, cuz I've had to redress a number of AO wheels that folks used with aluminum, with dire results.