Grinding tool steel & carbide

What do you do when you need to grind something with a carbide insert brazed into a hardened tool steel?

I just started at a cold heading facility and needed to sharpen a knife and since I'm new to the shop their 20 year veteran tool and die maker went over grinding with me and he pulled out a diamond wheel. Now I was always told never to grind hardened steel or any tool steel on a diamond wheel because it kills the diamond and loads the wheel, but there's the carbide and the generic aluminum oxide wheels won't cut it.. but as we're grinding it's like 10% carbide.

I'm not sure how to properly dress a diamond wheel and he said "you don't really" and it skipped along until it settled itself out and he didn't use coolant either.

My experience with diamond wheels is on baldor grinders grinding micro100 boring bars and then hand dressing radii and honing by hand, and I always soaked the wheel with a mix of varsol and machine oil soaked into a rag pressed up against the opposite side of the wheel, as I was taught because it cleans the wheel really nicely and keeps things cool. they've got diamond cup wheels and they're so loaded from dry cutting and cutting tool steels, I haven't tried them yet but I can't imagine they cut very much in their state.. but I mean, I'm the new guy right so it's really freaking hard to bite my tongue because who am I to tell some dude who's been at this for 20 years that he's doing it wrong? Or maybe I'm wrong? I mean, I use diamond plates to take edges off hardened steel, but thats by hand, and not at the speeds of a grinding wheel, which as I understand causes enough heat to chemically destroy the diamond bonded into the wheel, rendering it useless.

Anyway, since there's an unavoidable mix of carbide and hardened steel, what is the best wheel for this, even if the carbide is only 10% of the surface needing to be ground? The wheel looked rough as heck and the surface finish was absolutely trash (though I suppose not critcal in this case).

I just want to do things right.

Appreciate any insight.

Generally you should remove the steel with an aluminum oxide wheel first with a regular bench grinder. Then grind the carbide with the diamond wheel.

I spent some time working in a cutter grinding operation and we had dovetail form tools for screw machines that had carbide silver soldered to steel. We always used a surface grinder to gang grind the steel away before hitting the carbide. Always wet too on both.

I use diamond wheels unless there is a lot of steel to be removed.
It costs some in diamond but cheaper than two operations.
Tool steel loads diamond wheels so stick often to free it up.
Bob

QT: [ their 20 year veteran tool and die maker went over grinding with me and he pulled out a diamond wheel.]

likely not good to argue with the shop 20 yr pro. Grinding steel and carbide with a diamond wheel dry will heat and stress the steel and so be more likely to stress and bend the carbide..carbide does not bend much with not break.

To snag off much/some of the steel on a bench grinder might be my choice. Agree to change the wheel can soak up time so having a diamond wheel on its own mount is a good idea.

But bide your time and when you are the 20 yr pro try to avoid diamond wheel steel grinding when you can.

As Bob said: Tool steel loads diamond wheels so stick often to free it up.

interestingly the guy who came in recently to check out a spindle taper to be reground on the mill said he would use a diamond wheel.

dian said:

interestingly the guy who came in recently to check out a spindle taper to be reground on the mill said he would use a diamond wheel.

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It would be logical for an experienced guy to use a CBN or diamond wheel for such work. The CBN or diamond wheel would hold its size/height much longer than an aluminum oxide wheel. With frequent stoning and light feeds it would not be highly likely to cause a burn.

Also, a small diameter AO wheel as needed to regrind a spindle taper ID would break down even faster but it is also common to see spindle grinder hands using white, pink, and black AO wheels.

Grinding a spindle ID would be best done by an experienced person. Some/many spindle hands have a special grinding fixture because the machine travel can not always be true enough for that job.

Stone cleaning of a CBN or diamond wheel is done with a stone made specifically for those wheels, and /or a broken green wheel can be used (best wet),.so not just any stone.

*Do let us know what grit size wheel he uses.

It used to be common to get a free dressing stick with a new wheel.
https://www.mscdirect.com/industrialtools/cleaning-stick-diamond-cbn-grinding-wheel-accessories.html

dian said:

interestingly the guy who came in recently to check out a spindle taper to be reground on the mill said he would use a diamond wheel.

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Are you sure he didn't mean CBN? I have had *many* conversations with people who mistakenly say diamond when they really mean CBN.

just to clarify, usually on a carbide inserted knife the carbide is ground on a different angle then the tool steel. Giving you a primary and secondary angle when cutting. When using a diamond wheel to grind the carbide angle, its natural that you'll dip into the tool steel a bit. After your carbide angle is ground you can rotate your bed to grind the tool steel with CBN wheel back towards the insert, stopping just short of the carbide.

In short dipping into steel surface with a diamond wheel wont harm anything. Provided you are using sufficient coolant

dian said:

interestingly the guy who came in recently to check out a spindle taper to be reground on the mill said he would use a diamond wheel.

Click to expand...

OT dian, I think it good to keep your life jacket handy it seems the dam is under a lot of stress.

dian said:

interestingly the guy who came in recently to check out a spindle taper to be reground on the mill said he would use a diamond wheel.

Click to expand...

In which case I would not hire this person.
A very, very bad idea for ID grinding a machine tool taper but as above perhaps meant CBN.
This is small wheel world.
I grind steel soft and hard with diamond to clear it a lot on brazed tip in many diamond types, grits and bonds. This I would not try.
A few thou off of a few steel blocks on the Blanchard and for sure I'll use the 120 grit diamond wheel mounted rather than do a wheel change.
Nice finish and one can count on parallel so a touch up off the mill better than hand stoning.

Danger, danger Will Robinson for this use inside a spindle taper. I see no way it comes out correct without huge amount of time, dresses and passes used.
Bob

the guy specifically said he would rough with cbn and finish with diamond. (are there pcd stones?)

there are endless dicussions about grinding steel with diamond. imo it depends on how you do it. there is a temperature where the diamond beginns to diffuse into iron but i have no idea what the relationship looks like and what other factors might be (pressure?).

anyway, this is a kaindl diamond wheel that i have been using to sharpen tools, axes, chisels, blades, whatever for probably 30 years now. its perforated, which probably provides just enough cooling so it does a good job (3000 rpm).

A picture is worth a thousand words.

That wheel looks to be electroplated. And are you sure that drill turns 3000 RPM? Sure doesn't look like it would. It is generally the resin bond wheels that are the biggest problem in my experience. The diamond grit gets dulled and ripped right out of the binder. In short order the wheel is used up/wasted. Electroplated wheels the grit gets dulled but much of it stays in place, still cutting even though it's considerably dulled. Even dull diamond is harder than most anything you're going to rub against it.

My first shop job was in a header die shop running grinders. We ground assembled steel and carbide dies as well as carbide inserts with diamond and flood coolant, minimize steel as possible.
On another job, offhand tool sharpening of cemented carbide was roughed with a green wheel and finished with diamond cooled with some kind of detergent mix.