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Best way to balance this?

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:

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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

Reply to
etpm
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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.

Reply to
Tim Wescott

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
Reply to
etpm

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

Reply to
Tim Wescott

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)

Reply to
Larry Jaques

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