Three Jaw or Four Jaw for Barrel Crowning

I have a Pratt Burnerd 3 jaw adjust true chuck that has 4 adjusting screws at 90 degrees to each other. A Bison 6 jaw set true chuck is the same way. The Pratt is a far better chuck than the Bison. Both chucks are 6" chucks and use a 3/16" hex key to adjust the chucks to center.
 
Mike Bryant said:
I have a Pratt Burnerd 3 jaw adjust true chuck that has 4 adjusting screws at 90 degrees to each other. A Bison 6 jaw set true chuck is the same way. The Pratt is a far better chuck than the Bison. Both chucks are 6" chucks and use a 3/16" hex key to adjust the chucks to center.
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Maybe there alot more 90 degrees out there than I have seen.

If so, I wonder why some mfg. have used the 60/120 degree design which I feel is inferior, unless I am missing something.......................Don
 
You guys are blowing my mind!! Could someone show some pictures.

I've never seen universal-scroll chucks with centering adjustment screws on 60-degree spacing on the OD. You are talking about the OD aren't you, not the chuck face?

Face retainer screws screws on a 3-jaw or a 6-jaw would be on 60 degree increments or multiples of 60 degrees because the jaw spacing on them is 60 or 120 depending on if they are 3-jaw or 6-jaw.

Is this bailout crap getting to my mind??? It's certainly getting on my nerves. We are being systematically being stolen from and no body seems to give a damn.
 
Which do you guys prefer for barrel crowning three jaw and steady rest or four jaw from the Head Stock? What is the best setup for a 11 degree crown?
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I like a three jaw scroll chuck that is indexable like a four jaw. Buck makes a nice one.

Now the real question. Who's done the testing to see if .005" runout even matters? I haven't and I couldn't bring myself to ship a customer gun this way but it'd still be interesting to see if we are all wasting our time.
 
JerrySharrett said:
You guys are blowing my mind!! Could someone show some pictures.

I've never seen universal-scroll chucks with centering adjustment screws on 60-degree spacing on the OD. You are talking about the OD aren't you, not the chuck face?

Face retainer screws screws on a 3-jaw or a 6-jaw would be on 60 degree increments or multiples of 60 degrees because the jaw spacing on them is 60 or 120 depending on if they are 3-jaw or 6-jaw.

Is this bailout crap getting to my mind??? It's certainly getting on my nerves. We are being systematically being stolen from and no body seems to give a damn.
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Oh, I do mister! I write to my rep almost daily. I'll probably be served with a restraining order when I get home next week.
 
NesikaChad said:
Oh, I do mister! I write to my rep almost daily. I'll probably be served with a restraining order when I get home next week.
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You coming home next week?

Great!!!!!

As to trueness of barrel bore for crowning, it has to do with the crowns final shape. If the crown has a sharp bore/face intersection I'd bet that even as rough as 0.020" or even more would not make a measurable difference.

If, like I do, make a sharp crown then put a 0.005" x 45 bevel, then I feel the bore must be aligned really true. Matter of fact for that type crown that indicating the grooves as opposed to the lands is significant.

For the 11-degree target crown, close alignment, again, is important but not as important as a 45-degree bevel.

Then then there was an article in PS mag a few years ago where the barrel was sawed off at a slight angle then shot like that...no difference.
 
Extra Yuasa adjustable available

I have been using the adjustable "set tru" style lathe chucks on prototype projects for a long time. They make it easy to repeat setups and I have even used it to make small offsets for cam action screws. I have a 3 jaw and 6 jaw Burnerds for my Colchester and a 3 jaw Buck for the Monarch. As I am already covered for size range, I don't need a the nearly new 8.25" 3 jaw Yuasa Accu-chuck ... "Yuasa's name" ... that was originally for the Monarch. It has the 2 piece reverable jaws and chuck key. It does not come with backing plate .... available from MSC catalog (p 1526) to adapt to your spindle. $375 shipped lower 48. PM me if interested.
 

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jackie schmidt said:
You sure that isn't a 3/8 hex????...........jackie
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I just checked it and it is a 3/16" hex key. The adjusting screw appear to be 3/8" diameter screws. I've had to replace the adjusting screws in the Bison once because of the inside hex rounding off. A 3/8" key would have been better. I haven't had any trouble with the Pratt yet, but it's only 3 or 4 years old.
 
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Butch Lambert said:
Jerry,
Look at RoyB's photo. 2 on one side are 60 deg apart and 120 deg apart are the other 2 adjusters.
Butch
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Butch, I saw that. The lighting on that photo makes it hard for me to interpret. One of them optical collisions!!

Maybe that chuck needs a bailout ARGGGG!!
 
Mike

Both of mine use a 1/2 hex, I really do not know what the bolt sizes are, probably 5/8.

I like them, you can really 'honk down' to get that final "tenth'........jackie
 
jackie schmidt said:
Both of mine use a 1/2 hex, I really do not know what the bolt sizes are, probably 5/8.

I like them, you can really 'honk down' to get that final "tenth'........jackie
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Jackie/Mike or Butch,

Do you torque the face bolts after adjustment?

Or just leave it loaded on the jacking screws opposed, with face bolts lighly torqued?

Ben
 
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