Best way to balance this?

et...@whidbey.com

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Apr 12, 2017, 12:26:18 PM4/12/17

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I will be mounting a dead length air collet closer to a lathe spindle
for an upcoming job. The closer is meant to be fastened to a
stationary object. See the link:
http://yabe.chudov.com/Eagle-Rock-Tech-5C-Air-Pneumatic-Collet-Closer-Fixture-A1-21200-8223/ebayhist.html
It links to one being sold by Iggy.
Anyway, the one in the link is identical to the one I have and as the
link shows there is a big boss on the side that is tapped for air
fittings. I adapted mine for rotary table use by drilling holes in the
base for the air. The closer bolts to a base that bolts to the 4th
(rotary) axis in the mill. I made a two passage rotary union to pass
air through the 4th axis and into the closer. It all works very well
but the 4th axis spins slow. Now the closer is going to be in a lathe
spinning at 4000 rpm. I'm thinking that at that speed it should be
balanced. Would placing two weights, each at 120 degrees from the
boss, be better than one weight placed 180 degrees from the boss?
Anyone know?
Thanks,
Eric

Gunner Asch

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Apr 12, 2017, 1:05:13 PM4/12/17

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Not..not a good choice for a lathe. Need a standard rotary collet
closer? I have a number of them kicking around. Some are air operated,
others are manually operated. The Air units are Dunhams.

http://www.dunhamtool.com/air_collet_closer.html

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Tim Wescott

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Apr 12, 2017, 1:34:46 PM4/12/17

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One weight opposite the boss should be fine, and the assembly would be
lighter. But two weights would give you flexibility in getting the
balance just right.

At that speed you might need to worry about dynamic balance as well as
static. I'm not sure how to achieve that in a machine shop, but starting
by eyeballing the thing and trying to get the weight at the same height
as the boss should be a start. If you disassemble the thing to install
the weight inspect the inside for irregularities that might affect
balance.

I'd also eyeball the assembly to make sure that the centripetal
acceleration doesn't mess up any seals.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!

et...@whidbey.com

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Apr 12, 2017, 2:24:29 PM4/12/17

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Greetings Tim,
Thanks for your reply. I was thinking of screwing weights of the same
size and shape to the closer. The existing boss will have two steel
1/8 pipe plugs in it because the air will be supplied through the
bottom of the closer. So screwing the weights on should pretty well
match the existing boss. I'll check balance the way I check surface
grinding wheel balance. The added bosses will start off a little
heavier because there will be no air passages in them. Drilling some
dimples in the bosses is how I plan to lighten them. The inside of the
closer is all cylindrical and the seals are O-rings so they will be
OK. The way the closer works, by pushing up a sleeve that surrounds
the collet, should not be a problem. Since the air pressure remains
constant if the housing and sleeve expand from spinning the sleeve
will just rise a little higher, thereby maintaining clamping pressure.
Eric

Tim Wescott

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Apr 12, 2017, 2:44:14 PM4/12/17

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Sounds good to me. Aluminum plugs would save weight, but it's probably
not worth it.

Larry Jaques

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Apr 13, 2017, 2:36:58 PM4/13/17

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Are you sure, Tim? If you're counterbalancing 20 grams, 20g of
aluminum and 20g of cast iron weigh the same, don't they?
(2x 10g in this case)

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It is useless to put on your brakes when you're upside down.
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