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Author Topic: Making your own concave cutter mandrels  (Read 1414 times)

Faceting Frank

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Re: Making your own concave cutter mandrels
« Reply #15 on: November 18, 2021, 11:35:55 AM »
Just a tip on tin-alloy mandrels. I sanded the surfaces with 400 grit sandpaper before using to give the diamond something to grip on. That worked great,
perfect final polish on every facet. But found if you let the mandrel smooth out it will start scratching. So the mandrels need re-sanded on every stone.

FlashGP

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Re: Making your own concave cutter mandrels
« Reply #16 on: November 20, 2021, 08:23:58 AM »
Hi Frank,


it's been a while since I was on the forum, work has kept me busy.  Great to read about your mandrel making.  Also interesting to read about the need to sand your mandrels.


I overcame the scratching issue by pressing the diamond into my mandrel with a bearing and then constantly cleaning the mandrel with a face wipe with a few drops of cutting fluid and a spray of diamond on it as I cut.  I just need to be careful about the facewipe wrapping around the mandrel. 


My sequence is 3k, 8k and polish.  It takes a while to cut the concave with the 3k, but at that grit size it is less than the runout on my cutters so all my mandrels can be the same size.


By the way, congratulations on your AFG comp entry.[size=78%]  [/size]
[/size]

Yours Sincerely
Flash (Gordon)

Faceting Frank

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Re: Making your own concave cutter mandrels
« Reply #17 on: November 20, 2021, 08:29:13 PM »
Hi Gordon, noticed you had not been on the forum for a while and thanks for the compliment.

Haven’t tried to roll the diamond into the mandrel.

I just sand the mandrels to roughen the surface, put the diamond on the same way as my BATT laps. Mixing diamond powder with baby oil and wiping it on, though in this case with a cotton bud. Also adding more diamond oil mix to the mandrel from time to time to keep the cutting speed consistent.
The issue I had with scratching was while cutting “Autumn blaze concave variant” which is one of the stones I’m cutting for the I.F.C. The pavilion is simple with 16 concaves going to a point and I had no problem cutting it. Going from a flat 1200, to concave copper 1200, BATT 3k and BATT 60k.
Had a problem with the 3k stage on the crown concaves, not so much scratching, but tearing up the remnants of the 1200 grit pits into ruts. Found re-sanding the mandrel fixed this problem.
So, the only thing I can think of is letting the mandrel smooth out causes the problem.
I used 240 grit sandpaper this time on both the 3k and 60k with no issues.

FlashGP

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Re: Making your own concave cutter mandrels
« Reply #18 on: November 20, 2021, 09:45:03 PM »
Hi Frank,


I found that scratching occurs when swarf builds up on the cutting mandrel or lap.  The swarf buildup also slows the cutting speed.


You can test if your mandrel has taken a charge by just using a little baby oil on the mandrel and seeing if it will cut.  If it does, the furrows could be swarf/excess diamond buildup.


regards Gordon
Yours Sincerely
Flash (Gordon)

Faceting Frank

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Re: Making your own concave cutter mandrels
« Reply #19 on: November 21, 2021, 03:38:30 PM »
Yes, I agree that swarf will no doubt be the problem.
 I found washing the mandrels in hot soapy water and sanding them left to right fixed it.

 

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