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Grinding the Jaws on 10" Pratt Burnerd 6-Jaw Chuck

dian

Titanium
Joined
Feb 22, 2010
Location
ch
i have not read the whole thread but dont gring the chuck, hard turn it. it so much easier, you dont have to disassemble it afterwards, cover stuff up and its even fun watching the sparks. go as fast as you can.

btw, dont assume a drill rod is straight without having checked it.
 

jbacc

Cast Iron
Joined
May 5, 2009
Location
New Jersey
i have not read the whole thread but dont gring the chuck, hard turn it. it so much easier, you dont have to disassemble it afterwards, cover stuff up and its even fun watching the sparks. go as fast as you can.

btw, dont assume a drill rod is straight without having checked it.

Thank you, what insert would you use to turn it? What size boring bar? Please forgive the simplistic questions but aside from trying to fix the problem, I am being educated as well.

Thanks again.

Joe
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
Thank you, what insert would you use to turn it? What size boring bar? Please forgive the simplistic questions but aside from trying to fix the problem, I am being educated as well.

Thanks again.

Joe

Joe, did you mention what you had pre-grind, and what after grind.

and if the chuck body seems to have a common wobble.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
I thought it was a good try and just your wheel arbor was too light.

An interesting experiment might be to put your chuck jaws collar back on, tighten about the same as you did, and then run your indicator to the jaws for an in-circle test, and the straightness of the jaws.
 

dian

Titanium
Joined
Feb 22, 2010
Location
ch
Thank you, what insert would you use to turn it? What size boring bar? Please forgive the simplistic questions but aside from trying to fix the problem, I am being educated as well.

Thanks again.

Joe

set the chuck to middle opening or where you thik you will be using it most. bar as big as will fit. cbn insert.
 

jbacc

Cast Iron
Joined
May 5, 2009
Location
New Jersey
Hi all,

Just a follow up to the saga of my chuck. I read and reread every comment, suggestion, words advice and searched the internet for manny hours in an effort to figure out how best to proceed. I must admit, I went the cheap route and purchased an extended length die grinder from none other than Harbor Freight.

I also used a harder grinding wheel and did as Ekretz suggested and thinned the disk I used for the jaws to clamp down on. I took light cuts and took my time and the final results were excellent. Ekretz and others were on point when they questioned my original set up which was a die grinder and a homemade 1/4" rod as an extension. I'm guessing it flexed far more I could have imagined (how stupid of me) and actually made things worse.

The only negative is due to all the grinding, the minimum diameter the chuck can clamp down on is about .640. I think originally the spec. is about 3/16" so I am a bit disappointed but considering I thought the chuck was toast, I should be happy.

I do have a 3-Jaw Toolmex Chuck (Chinese) that is pretty accurate but the 6-jaw chuck is a setrite/adjust-tru which is why I was so fixated on making it useable. Since the spindle is on my lathe is an A1-6, swapping chucks is a little less convenient than other style spindles so I am torn whether to keep the 6-jaw on or go back to the 3-jaw.

In any event, I again want to thank each of you who took the time to guide me and provide very helpful information, I truly appreciate it.

Joe

PB 6-jaw chuck.jpg
 
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jermfab

Cast Iron
Joined
Jul 25, 2013
Location
atlanta, ga
One good rule about general grinding on a lathe is that you have to use your wife's best pillowcases or favorite towels for the cover-up.

Doesn’t pertain to the question at hand, but I had a dear friend who SWORE that the absolute best media for cleaning up carborundum leavings was his wife’s cotton panties. Those panties had to be clean. He said that he would make a stop by her underwear drawer on his way to the shower on days when we had been doing lots of grinding.

I’m as certain now as I was then, that if the missus has enough cotton “granny” panties to get away with disappearing them… well you’re doing SOMETHING wrong.

Thankfully all the women I’ve been involved with have tended towards underwear lacking meaningful surface area for such endeavors.






Be safe




Jeremy
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
Congrats, and well done. You can get some of that lost small end back by grinding away some of the angled portion of the jaws if you have a surface grinder. You could also get some soft jaws and shape them appropriately then bore them in place. Then of course there's the possibility of procuring a collet chuck just for small stuff.
 

gbent

Diamond
Joined
Mar 14, 2005
Location
Kansas
If you ground out those jaws from 3/16 to .640 you very badly need to clean every thing around, including disassembling the chuck. You also deserve a big attaboy for your perseverance.
 

CalG

Diamond
Joined
Dec 30, 2008
Location
Vt USA
I'm puzzled about the non-repeatability issue being addressed by trimming the jaws..

It just seems like assigning fault to the part that is not guilty.

The comment that the original jaws were cracked or broken tells much.

Also, For small work, just pull every other jaw and use the device as a three jaw.

For myself, A 6 jaw is ONLY useful for holding thin pipe or tube , rings etc. And not nearly as good as machinable pie jaws. I had one once, Sold it, Never to be regretted.

I'm surprised that the technique of Lapping the jaw contact surfaces hasn't been mentioned.

A solid piece, turned to suit. A dead center in the spindle, and solid center in the. tailstock.

Charge the lap, and hold it by hand. Tighten the jaws down "just enough" to rub.
 

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
I'm puzzled about the non-repeatability issue being addressed by trimming the jaws..

It just seems like assigning fault to the part that is not guilty.

The comment that the original jaws were cracked or broken tells much.

Also, For small work, just pull every other jaw and use the device as a three jaw.

For myself, A 6 jaw is ONLY useful for holding thin pipe or tube , rings etc. And not nearly as good as machinable pie jaws. I had one once, Sold it, Never to be regretted.

I'm surprised that the technique of Lapping the jaw contact surfaces hasn't been mentioned.

A solid piece, turned to suit. A dead center in the spindle, and solid center in the. tailstock.

Charge the lap, and hold it by hand. Tighten the jaws down "just enough" to rub.

Probably addressed due to a combination of stiffer grinding setup and a better job of individual preload on all the jaws. No way to tell for sure without disassembling the chuck and measuring/checking everything. Cracked jaws does not sound good, but would depend on how they were cracked. It would be good to hear what the final results actually were, not just that they were excellent.

Removing 3 jaws will grip smaller. That can work too. I used to do that now and again on the ones at work. Just remember to swap between sets every other time to even out wear. I.E. 1-3-5 this time, 2-4-6 next time.
 

jbacc

Cast Iron
Joined
May 5, 2009
Location
New Jersey
Probably addressed due to a combination of stiffer grinding setup and a better job of individual preload on all the jaws. No way to tell for sure without disassembling the chuck and measuring/checking everything. Cracked jaws does not sound good, but would depend on how they were cracked. It would be good to hear what the final results actually were, not just that they were excellent.

Removing 3 jaws will grip smaller. That can work too. I used to do that now and again on the ones at work. Just remember to swap between sets every other time to even out wear. I.E. 1-3-5 this time, 2-4-6 next time.

After this round of grinding, I took a 3/4" piece of oil hardened drill rod and dialed it in. I then loosened the jaws and slid the drill rod out of the chuck further and tighetened the jaws again. It was still dead on as it was in the previous position. I repeated this seevral times with the same results. If you recall, this was not the case with my first ill attempt to grind the jaws.

I then had a few pieces of 4140 in various diamaeters, without doing anything other than placing them in the chuck and tightening the jaws, I was within 1 1/2 thousandths which i think is excellent for a self-centering chuck. And, since the chuck is a setrite/adjust tru, I could dial it in to almost zero if needed.

Hence my conclusion that this latest attempt at grinding was a success. I appreciate the idea of using only three jaws under normal circumstances, just curious if the setrite/adjust tru feature will work properly with only three jaws?

There is no doubt my first failed attempt was due to my flimsy 1/4" extension rod which made things worse than they were before.

As far as the carcks in the original jaws, based on the damage I see on the cross slide, it seems that careless operators ran the carriage into the chuck. The jaws are thinner at the tips on a 6-jaw chuck and they were cracked from carlessness of the operator. I do not believe it was a catostrophic accident but enough to scar the cross slide and crack some of the jaws.

Again, I thank you all for your input.

Joe
 
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jbacc

Cast Iron
Joined
May 5, 2009
Location
New Jersey
Congrats, and well done. You can get some of that lost small end back by grinding away some of the angled portion of the jaws if you have a surface grinder. You could also get some soft jaws and shape them appropriately then bore them in place. Then of course there's the possibility of procuring a collet chuck just for small stuff.

I do have a Harig surface grinder, would each jaw need to be ground individually? I am trying to picture the set up in my head.

Many thanks for your help.

Joe
 
Last edited:

eKretz

Diamond; Mod Squad
Joined
Mar 27, 2005
Location
Northwest Indiana, USA
I do have a Harig surface grinder, would each jaw need to be ground individually? I am trying to opicture the set uo in my head.

Many thanks for your help.

Joe

Yes. Ideally you'd set up a grinding vise or tilt table, something of that sort, with repeatable stops.
 

dian

Titanium
Joined
Feb 22, 2010
Location
ch
I'm puzzled about the non-repeatability issue being addressed by trimming the jaws..

It just seems like assigning fault to the part that is not guilty.

The comment that the original jaws were cracked or broken tells much.

Also, For small work, just pull every other jaw and use the device as a three jaw.

For myself, A 6 jaw is ONLY useful for holding thin pipe or tube , rings etc. And not nearly as good as machinable pie jaws. I had one once, Sold it, Never to be regretted.

I'm surprised that the technique of Lapping the jaw contact surfaces hasn't been mentioned.

A solid piece, turned to suit. A dead center in the spindle, and solid center in the. tailstock.

Charge the lap, and hold it by hand. Tighten the jaws down "just enough" to rub.

that works and is less of a mess, provided the spindle center has no runout.
 

jbacc

Cast Iron
Joined
May 5, 2009
Location
New Jersey
If you ground out those jaws from 3/16 to .640 you very badly need to clean every thing around, including disassembling the chuck. You also deserve a big attaboy for your perseverance.

Spent a couple of hours this morning meticulously disassembling and cleaning the chuck and the lathe. All good.

Thank you.

BTW, the bracket I made to hold the die grinder was bored using the Gamet boring head I purchased from you. Worked perfect.

Thanks again.

Joe
 

Turbowerks

Cast Iron
Joined
Nov 9, 2018
Location
Windom
For a small parts get yourself a 4 inch 3 jaw quality one, and chuck it in the chuck i have several small workholding devices that get chucked. Like this
cd25b29b740146ea08660b447efadffa.jpg



When I find it I don’t need it
When I need it I can’t find it!
 








 
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