Anorak Bob 17th April 2012, 11:10 AM A few photos of the aluminium face plated motor for diamond paste lapping and the ball bearing burnishing tool. Might be useful for those that didn't run around with a camera.
BT
Steamwhisperer 17th April 2012, 06:55 PM some more
Anorak Bob 18th April 2012, 11:32 AM I removed these photos yesterday. They are back with Phil's approval.
Michael G 18th April 2012, 10:28 PM I lashed out and bought a small bench grinder for lap conversion today.
Oh dear. The disease is spreading...
Michael
Anorak Bob 18th April 2012, 11:47 PM I can't read the motor speed in Phil with the moustache's photo of the motor with the lapping wheel. Most bench grinder motors are two pole. Is 2850rpm too fast for lapping?
BT
jhovel 19th April 2012, 12:48 AM Michael,
please let us know how it woeks for you. I am under the impression that 2800 rpm (grinder speed) is too fast for a lap and I used a very cheap 4 pole 1450rpm single phase 1/3HP motor for mine and it works well.
Cheers,
Joe
Bryan 19th April 2012, 09:06 AM My lap is on a little 2 pole grinder but the wheel is only 100mm dia, and that seems fine. For a bigger wheel slower might be better.
Michael G 19th April 2012, 03:53 PM Recently there was an article in Home Shop Machinist where a 6" grinder was converted to a rotary lap. This one is a 5" job, so surface speed on the edge will be slightly less. I would like to convert one end to a diamond lap and the other take a CBN wheel so I can sharpen lathe & shaper tools up properly.
Michael
Bryan 19th April 2012, 04:22 PM I have read that grinding grit is not desirable to have near a lap.
Michael G 19th April 2012, 09:49 PM You're right - it's not. I was thinking of a very fine wheel that would effectively be the same as a lap for using on ferrous materials. I guess the other option is to use something like carborundum as a lapping compound on the ferrous side. A CBN wheel just means not having to charge a lap every so often.
The plan would be that the diamond side would only be used for carbide while the 'other side' would be for ferrous. I could take a chance on diamond for ferrous but heat+diamond+Fe is not good. I suspect that running some form of coolant would just spray the stuff around at the speeds being talked about.
I think too in a mixed workshop a cover for the lap would be essential to prevent airborne particles settling and disturbing the charged lap.
Michael
Machtool 19th April 2012, 10:13 PM I could take a chance on diamond for ferrous but heat+diamond+Fe is not good. Is that something that you have yourself & found to be true? Or is that something you have read in theory / read on the internet.
Phil
Michael G 19th April 2012, 10:43 PM That's something that has been said to me by numerous people both personally and via the internet. I've now personally checked two references that I have.
Michael
On edit - Machinery's Handbook (2008, 28E) p770 "Polycrystaline diamond has one big limitation: it can not be used to machine steel or any other ferrous material without rapid chemical break down"
Tool and Manufacturing Engineers Handbook (1983, 4E) p3-42 "One limitation to the use of polycrystalline diamond tools which also applies to single crystal diamond tools is that they care not generally suited for machining ferrous metals such as steel and cast iron. Diamonds - both natural and synthetic - are carbon , which reacts chemically with ferrous materials at high temperatures"
Another piece suggests that using a hand diamond lap is fine but a powered lap may get hot enough to degrade the diamonds. Based on that I'd suggest that steel with light pressure and diamonds on a rotary lap may work, but the question would be for how long.
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