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Author Topic: Problem cutting very steep angles  (Read 317 times)

ianRobinson

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Problem cutting very steep angles
« on: February 26, 2020, 09:11:19 AM »
Hi Folks
Probably a dumb question but I wondered if anyone has any advice.

I have cut a few designs, such as Jeff Graham's Smithsonian bar that require very steep crown angles of less than 10 degrees. On my Polyhedron mast machine these are dammed tricky to hold and risk a nasty jamming incident with the stone being almost vertical.

I'm thinking of using a 45 or 90 degree adapter though this will introduce alignment problems and I suspect I will be cutting mostly by eye.

Is this the normal technique with a mast machine? - Any tips would be very gratefully received.

Thanks
Ian

Ghost

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Re: Problem cutting very steep angles
« Reply #1 on: February 26, 2020, 12:16:23 PM »
Cut 3 Smithsonian Bars on my Hall Xtra with no problems.
Position on lap may be causing judder and jamming.
If directly between mast and spindle is 12 o'clock, try coming around to 3 o'clock as a working area.
Lovely design so keep trying.
Regards,
Ghost


Lowjiber

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Re: Problem cutting very steep angles
« Reply #2 on: February 27, 2020, 12:00:32 AM »
@Ghost's suggestion above should work well. Just use very gentle pressure on the quill when bringing the stone to the lap.

I've also used a table adapter.  However, getting the gem properly realigned at the correct index(s) can be more trouble than it's worth.

FlashGP

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Re: Problem cutting very steep angles
« Reply #3 on: February 27, 2020, 07:06:30 PM »
Agree, I have an Apex adapter to use on the 45 degree dop on my facetron, but it is not very accurate and requires careful allignment of the facet.

Just make sure the lap is spinning towards you as you move the quill gently into the lap when cutting steep angles.  This way you are pushing on the lap and if the stone jams it is pushed back to you. 

When my machine was new, I cut a stone with the lap rotating away from me.  The stone jammed and pulled the stone and quill through under the mash head.  The head lifted up then dropped back on the mast.  Loud bang and head was rouating aroun md the mast.

I think it bent the mast a little.  Andrew realligned the madt to the mast to the platten when the machine was in for a motor bearing problem, but I think it is at the end of the allignment. I have to use -.7 cheeter adjustment to get the girdle meets in, and +.7 on crown girdle meets.  But allignment is degrees off if I rotate the mast base 180 degrees and lock for cutting.
Yours Sincerely
Flash (Gordon)

Faceting Frank

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Re: Problem cutting very steep angles
« Reply #4 on: February 28, 2020, 10:08:25 AM »
Bit confused as to where the clock position advice is on the lap with the above posts.
I always cut steep angles with the lap traveling in a line from the girdle to the facet being cut to the stone centre. So, if you’re sitting at the machine with the mast to your right, then the lap 12 o’clock position relative to you would be on the far side of the machine. 3 o’clock at the mast side, 6 o’clock nearest to you.
So, if the lap is traveling in a clockwise direction, to achieve what I described above you would be cutting in the 6 o’clock position.
Another thing I find helpful is to rest the quill on the hard stop and lower the stone onto the lap with the mast fine adjustment. Partly cutting all facets in that row and repeating the process till they are all cut. Resting the quill on the stop with the other laps as well.
Hope that helps.
Frank.

Faceting Frank

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Re: Problem cutting very steep angles
« Reply #5 on: February 28, 2020, 12:41:05 PM »
Got that after reading it again Ghost.

FlashGP

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Re: Problem cutting very steep angles
« Reply #6 on: March 02, 2020, 06:50:41 PM »
Good point Ghost.  But at high angles and with a 6 inch lap, i am pretty much restricted to cutting in the 3 o'clock quadrant.  So I jave to make sure the lap is turning clockwise.

Regards
Flash
Yours Sincerely
Flash (Gordon)

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