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JoeLee
09-06-2011, 10:04 AM
I have an old diamond nib off of a radial dressing fixture that I'm restoring. Some one at one time had run it into the wheel, more than once it looks like. My queastion here is if I zap it real quick with my MIG to fill in the ground out area with out generating a lot of heat will it have any effect on the diamond or the set of it??? This nib is special made as it has a long threaded stem and a knurled knob, not easiy replaced.
Also........ would there be any adverse effects of putting this in a hot blue tank??

JL..................






http://i911.photobucket.com/albums/ac317/JoeLee09/Grinder%20Base%20Sketch/Image003.jpg
http://i911.photobucket.com/albums/ac317/JoeLee09/Grinder%20Base%20Sketch/Image002.jpg

MichaelP
09-06-2011, 12:01 PM
I'd be afraid to weld that close to the diamond. Not only may it disturb its bonding, but it may also damage the diamond itself.

Gentle brazing could be an option if you don't care about the color and absolutely need to fill the area. However, making a whole new part will be much easier and better, IMO.

JoeLee
09-06-2011, 12:44 PM
Gentle brazing wold put more heat to it than a quick zap with the mig would.

JL.......................

Black_Moons
09-06-2011, 03:03 PM
Why not just leave it as is? it seems fine functionality, just a little ulgy.

Evan
09-06-2011, 03:22 PM
It would almost certainly destroy the diamond. Hot blue shouldn't hurt it.

tdmidget
09-06-2011, 03:57 PM
Hot blue might attack the brazing alloy that the diamond is mounted in. Test first.

JoeLee
09-06-2011, 04:26 PM
A close look reveals that the diamond is brazed in place. Makes me wonder how brass might stick to diamond...... I doubt it does, I think it's like potted in the brass. So much for the hot blue. I don't know what hot blue will do to brass but I do know what it'll do to aluminum.
Best not chance it.

JL..............................

Evan
09-06-2011, 05:35 PM
There are very low temperature brazing alloys which is probably what was used. Regular bronze brazing alloy will definitely toast the diamond.

For everything you ever wanted to know about brazing and a lot more you didn't know existed have a look at the Handy Harman Brazing Book.

http://www.fpga-faq.org/sb-metal_hold/CD_08/TheBrazingBook.pdf

JoeLee
09-06-2011, 05:53 PM
Thanks Evan.

JL...................

JCHannum
09-06-2011, 06:11 PM
They are set in spelter, which is another name for zinc and/or low melting point alloys of zinc.

The diamond nibs are considered consumeables, and replacements are available.

Black_Moons
09-06-2011, 06:29 PM
They are set in spelter, which is another name for zinc and/or low melting point alloys of zinc.

The diamond nibs are considered consumeables, and replacements are available.

Hmm, If the mount is so important, He could weld/grind it up, then get a new diamond mounted?

JoeLee
09-06-2011, 08:19 PM
They are set in spelter, which is another name for zinc and/or low melting point alloys of zinc.

The diamond nibs are considered consumeables, and replacements are available.

What color is spelter????

JL.....................

JCHannum
09-06-2011, 08:31 PM
The color would depend on the alloy. On a couple of diamonds I have here it appears to have a black oxide which reveals a pale yellow when hit with a file.

On some diamonds, the diamond is simply set in a hole and the parent steel of the nib is peened or spun to retain it.

JoeLee
09-06-2011, 08:50 PM
OK, the material on this one "looks" like brass and doesn't look to be peened which is what I originally thought was the way of securing the diamond.

JL..........................

Jpfalt
09-07-2011, 12:01 AM
The diamond is set in wurtzmetal, which is a combination of bronze, zinc and traces of iron powder. The set was done by making the threaded shank with a hole about 3/16 dimeter and about 3/8 inch deep. The hole was filled with the metal powder and the diamond was placed on top of the powder oriented with a point up. A short graphite rod with a conical hole in one end was placed over the diamond and the holder and graphite rod were placed in a small hand press. With pressure applied, the holder and graphite rod were heated to orange heat and the powdered metal melts and flows around the diamond to hold it in place. Once cooled, the holder and rod were cut back on the lathe to put a chamfer around the diamond point.

I wouldn't fiddle with that holder.

I used diamond setting powder from Wall-Colmonoy company for regular sets or tungsten carbide powder from Macro Kennametal along with nickel brazing compound for dianond dressers used in more abrasive environments and for cluster diamind dressers.

A method for setting diamonds for dressers before commercial setting metal powders were commonly available was to take a silver quarter, mount it on a shaft and spin it in a drill press while filing the quarter and collecting the filings in a pan. The coin silver works interchangeably with the Wall-Colmonoy product, but is not as abrasive resistant as the tungsten carbide powder and nicobraze.

When setting in threaded shanks, I made a shouldered dresser and then drilled and reamed the threaded shank to press in the replacement nib.

tdmidget
09-07-2011, 12:39 AM
I think jpfalt has it. All I have ever examined were set in a light yellow metal about like 70/30 brass. Spelter is white and a diamond in use would get hot enough to melt it.

jp, does the metal adhere to the diamond or does it depend on lapping over to hold it?

JoeLee
09-07-2011, 09:48 AM
I think that answers it too.

TNX...

JL......................

Jpfalt
09-13-2011, 10:55 PM
The diamond setting alloy generally retains by mechanically surrounding the diamond. The iron powder actually etches the surface of the diamond like sanding to put some "bite" into the diamond surface. If the setting metal gets ground back too far in use, it is very common for the diamond to turn in the set and fall out.