Best carbide lapping method?

I'm no expert at it and you've probably got more experience, but the old tool-making books I've got all seem to indicate that a steel lapping surface with the diamond grit rolled into it under significant pressure is the way to go and that some kind of added oil for swarf removal is needed. They specifically warn against having loose grit because it rolls and will mark up the work surface. One book mentioned using olive oil(old book), another said gasoline(inside, don't think so!) for keeping the lap's surface cleaned off. One picture showed a hydraulic press with a roller for pressing the grit into the lapping plate. If you're using the commonly available diamond lapping pastes, this might be your finishing problem. One book also had a "listening stick" for determining the optimum pressure to put on the workpiece, apparently there's a particular sound when it's cutting correctly. The idea being that you'd put one end on the workpiece and the other next to your ear. Said that crowding the workpiece wouldn't make it cut any faster and it messed up the surface finish because the diamond grit came loose and rolled.

Stan

Greetings Stan, Thanks for the reply, though I'm not sure if I have a problem or not. I am charging the laps properly. But even a properly charged lap will lose some abrasive over time. I use lamp oil, which is basically deodorized kerosene, as a cutting fluid. It works very well but I know that some grit may be carried around the wheel and may be affecting the cutting edge. I am trying for the utmost in sharpness on carbide. Eric

I'm no expert at it and you've probably got more experience, but the old tool-making books I've got all seem to indicate that a steel lapping surface with the diamond grit rolled into it under significant pressure is the way to go and that some kind of added oil for swarf removal is needed. They specifically warn against having loose grit because it rolls and will mark up the work surface. One book mentioned using olive oil(old book), another said gasoline(inside, don't think so!) for keeping the lap's surface cleaned off. One picture showed a hydraulic press with a roller for pressing the grit into the lapping plate. If you're using the commonly available diamond lapping pastes, this might be your finishing problem. One book also had a "listening stick" for determining the optimum pressure to put on the workpiece, apparently there's a particular sound when it's cutting correctly. The idea being that you'd put one end on the workpiece and the other next to your ear. Said that crowding the workpiece wouldn't make it cut any faster and it messed up the surface finish because the diamond grit came loose and rolled.

Stan

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This is a really tough one. I've studied diamond lapping for steel and carbide, but it was for making gage blocks and other flat gage faces (snap gages; micrometer faces; etc.) in the 1920s through the early '50s. The method you're describing, Stan, originated when gagemakers crushed their own boort (dirty natural diamonds, called "industrial" diamonds) and suspended the crushed diamond in olive oil, drawing off some at a certain depth after a certain time to get a fairly uniform grit. Then the oil and diamond was washed in gasoline or alcohol and the diamond was dried.

It was then spread out on a mild steel plate and rolled, as you say, or driven into the steel with a special toolmaker's hammer. It was like a small bumping hammer with the face highly polished and fully hardened -- often case-hardened, with no tempering or drawing. The primary use of these hammers was charging tiny diamond laps for internal lapping of small holes in master gage plates for clockmaking drill jigs and such.

This is how Dick Moore did it, whose account I relied on. I still have about

6 carats of boort and I tried the whole routine around 30 years ago. Believe me, those gagemakers and master toolmakers earned their pay.

Regarding the question of whether to lap into or away from the edge of a micrograin carbide tool, I haven't a clue. And I have no one I could call for an answer. For one thing, the service companies that prepare special edges in tools are very secretive. For another, I don't know of anyone who is doing this work. There are some who specialize in radiusing PCBN tools, but I don't know of any doing carbide.

My feeling is that one would lap into the edge, unless that damaged the lap's surface. But I'm only guessing here.

Damn, Ed, it's good to hear your voice. I was just getting ready to start checking obituaries.

Paul K. Dickman

Damn, Ed, it's good to hear your voice. I was just getting ready to start checking obituaries.

Paul K. Dickman

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Well, thanks, Paul. But I'm not really here. I'm killing time, waiting on the arrival of a metrology book I have to edit. I put a couple of days aside to do a quick estimate on the job but the book is a little late coming. Once I get started, it's balls-to-the-wall for me for a couple of months.

Please excuse the messy formatting. I'm using Windows (Dead) Mail, and I'm not digging out Agent again for just a few days worth of posting.

If you do find my name in the obits, I can only say they're exaggerating the situation. d8-)

Greetings Ed, Good to hear from you. There must be old farts like me still active who used to grind and lap their own tools and still do. I hope one of them reads my post. Eric

Let us know when the book comes out (if it's any good). Metrology is one thing I am interested in professionally.

Greetings Ed, Good to hear from you. There must be old farts like me still active who used to grind and lap their own tools and still do. I hope one of them reads my post. Eric

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Hello, Eric. And greetings to you, too.

I'm sorry I don't have any helpful info for you. I covered cutting tools for several metalworking magazines, as a reporter and editor, but lapping carbide cutters is something I haven't learned about.

I hope someone pops up who knows something about it.

Let us know when the book comes out (if it's any good). Metrology is one thing I am interested in professionally.

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Ok. It will be interesting, but it's not a deep technical book. It's being written by the guy who wrote this:

I was supposed to write that one but I got sick and couldn't do it. Suga is a font of knowledge about the subject.

I had not seen that book before. Looking at some of the previews it looks like it could be a very useful practical manual.

However, I see a CMM probe on the cover. I hope the author makes the point somewhere that a CMM is not always to best way to measure something. Too many machine shops seem to be relying only on their CMM these days. It is much too easy to miss high spots or things like burrs or dings on the lip of a precision bore. I design optics that have to fit in precision bores where this problem comes up too often. Another thing the CMM is not so good at is measuring precise angles of small surfaces (again, like you might find in optics). An autocollimator along with other tooling often does a better job at that.

I had not seen that book before. Looking at some of the previews it looks like it could be a very useful practical manual.

However, I see a CMM probe on the cover. I hope the author makes the point somewhere that a CMM is not always to best way to measure something. Too many machine shops seem to be relying only on their CMM these days. It is much too easy to miss high spots or things like burrs or dings on the lip of a precision bore. I design optics that have to fit in precision bores where this problem comes up too often. Another thing the CMM is not so good at is measuring precise angles of small surfaces (again, like you might find in optics). An autocollimator along with other tooling often does a better job at that.

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Ya know, I've only read bits and pieces of it, although I read about ten other books on the subject when I was expecting to write that one, and I think it covered the breadth of the field. Suga is a gage-block/micrometer/laser/CMM/optical guy. He covers the field himself. He's the head of Mitutoyo's education department, so he knows the stuff. I doubt if he encourages excessive or inappropriate use of CMMs. He knows their limitations.

I used to give talks at his metrology training classes, back in the early '90s. I don't think there's an aspect of dimensional measurement they haven't dealt with. Suga and I share an interest in self-correcting gages and the design philosophies of Richard Moore (Moore Jig Grinders and Jig Borers). We've known each other for close to 30 years.

I am sure Suga does understand CMM limitations. My beef is that most other people involved in making and procuring parts do not, and perhaps it is worth a bit of proselytizing to get that point across. The prevalent thinking is that a state-of-the-art CMM can do no wrong. We get very expensive parts with nice, printed CMM reports, but they do not work. I go to the project manager at my client who says, "But... It's been CMM'd! How could it be bad?" Then he goes to the guy in purchasing who says, "But... It's been CMM'd! How could it be bad?". Then he goes to the machine shop manager who says, "But... Its been CMM'd! How could it be bad?" Each time, I am called-in to explain what is wrong and why the CMM missed this issue.

I am sure Suga does understand CMM limitations. My beef is that most other people involved in making and procuring parts do not, and perhaps it is worth a bit of proselytizing to get that point across. The prevalent thinking is that a state-of-the-art CMM can do no wrong. We get very expensive parts with nice, printed CMM reports, but they do not work. I go to the project manager at my client who says, "But... It's been CMM'd! How could it be bad?" Then he goes to the guy in purchasing who says, "But... It's been CMM'd! How could it be bad?". Then he goes to the machine shop manager who says, "But... Its been CMM'd! How could it be bad?" Each time, I am called-in to explain what is wrong and why the CMM missed this issue.

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I think your point is a good one, and it's true that some people consider the CMM to be a panacea, which it definitely is not. And CMM manufacturers have oversold them more than a bit, IMO.

The probe is a key. Individual Individual CMM probes can't handle everything. And with non-contact CMMs, software can be a big culprit.

It's another case of using the right tool for the job. There is no universal gage, not even a top-end CMM.

Hey Stan,

Do you happen to know the names of those books off hand?