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View Full Version : Forrest 4 jaw ... ping ... balancing act ??



nheng
12-09-2005, 12:46 PM
Forrest and other 4 jaw lovers http://bbs.homeshopmachinist.net//smile.gif, what do you usually reach for to safely balance odd sized and odd shaped parts in the 4 jaw?

After balancing, do you generally spin it as fast as you feel comfortable with or what?

Den

Alistair Hosie
12-09-2005, 02:25 PM
I wonder if you mean 4 jaw independent.I have two four jaws of the same size for my lathe.One is independent and the other is scroll were the jaws all move with one twist of the key.Mostly this is seen on 3 jaw chucks but there are 4 jaw models out there too.so it is not just the number of jaws which are important it is the design of the chuck.Mostly for round/roundish stock scroll chucks are used but I think were Forest is referring to independent jaws were the key has an individual hole over each jaw and moves them seperately from one another this is very handy for setting or holding more awkward, non round stock which has to be offset.Setting this up is more difficult and newcomers are slightly wary of this, as it is more awkward to cenralize. However if you think of it as two, two jaw set up (instead of one four jaw) and set up two of the jaws more or less correctly then it should be just a case (as I understand it,as I am a not an expert myself)of bringing the last two jaws in to add further gripping power hope this helps Alistair

mochinist
12-09-2005, 02:34 PM
I think alistair missed what you are talking about. Generally when I have had heay odd sized stuff in the four jaw I have found there is not a whole lot you can do, I mean you dont want to just attach something half ass on the chuck to balance it, so I just usually turn those parts a little slower. Honestly though I have only had to deal with this a couple of times, so it will be interesting to see what others have done.

nheng
12-09-2005, 03:09 PM
Yes, I was thinking about the independent 4 jaw and odd shaped work. I was facing part of a small aluminum die casting the other night and it was off center by about 2" on a 5" part.

I ran it slowly but got to wondering how others deal with it on a more regular basis.

Forrest Addy
12-09-2005, 03:10 PM
That's one of the reasons for the T slots you see on 8" and larger 4 jaws: so you can bolt scrap iron on them to balance odd shaped parts. You spin the work as fast as it needs to go. Obviously you're limited by FPM and raw fear but generally so long as the counter balance is well secured and you don't have to get into the upper RPM's there's no special precautions.

Remember that long irregular pieces and the chuck counter balance can be in static balance but in substantial dynamic unbalance.

I recall some candy cane shaped pipe boat davits whose bend end had nearly a 3 ft sweep. There was a welded on collar and pin on the length of this thing that went into a deck socket about 3 ft. It had to be machined. Being 6" pipe ir was perfect for an oil country lathe that would swallow 11" and has chucks on both ends of the spindle. The bend end barely cleared the floor.

An older hand, Bob Choinard got the job and he balanced the swung portion with a long cast iron parallel that was close to the right weight and length. He was running this at 100 RPM or so and at that speed it seemed like an airplane propellor spinning past the change gear door. No barracade of oil drums and 2 x 4's could make it seem safe. So for the duration of the job those old Bob worked on the far side of the flailing pipe unsupervised. He sat on a stool, munched on a sandwich during working hours, and played his radio - all proscribed sins in the shop - but no boss came to chastise him while the spindle was revolving death and destruction.

[This message has been edited by Forrest Addy (edited 12-09-2005).]

nheng
12-09-2005, 03:19 PM
Forrest, My ancient 8" import ("Sole" chuck) has no T slots but now I recall seeing them elsewhere (and on faceplates, of course).

Lacking the T slots, and on a somewhat sacrificial chuck, I suppose I could distribute some tapped holes to hold stacks of washers or something ... keeping safe speed in mind of course.

[This message has been edited by nheng (edited 12-09-2005).]