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Union 3 jaw chuck disassembly

jabberwoki

Cast Iron
Joined
May 15, 2009
Location
TACOMA
I`ve got all the bolts and the jaws out but I cannot get any further.
Looks like the plate in the back is a separate piece.
The turning screws won`t budge out either?
 

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Expect an interference fit and there may be locating pins to align the two sections.
First...match mark the two sections at the split line.
Set on edge and smack with a big dead blow soft face hammer against the back is sometimes enough to start separation.
Think of billiards/pool.
Use a bit of cardboard or carpet to set the chuck on, minimize scratches.
One can also insert the chuck key into the pinion and tap towards the back of the chuck so the pinion is not driven into the gear side of the scroll.
If an opening is started banding or shim stock will hold the split open. Do not use a screwdriver or such to pry the finished surfaces apart.
John
 
I used to stand the chuck on it's outside diameter then just give the scroll a sharp tap in all three places with an aluminium drift or an hard piece of wooden dowel. That'll normally separate the two halves. Mark them up first though if the two halves haven't already been marked. The " turning screws " are normally held in place by a fluted dowel. You need to split the chuck to access these dowels. They are drilled and tapped on the end to aid removal. You can remove the dowels by putting a small screw into the dowel and pulling on the screw. Failing that it's slide hammer time.

As for four jaw chucks - remove the jaws first. When you've removed all four jaws if you look at the back you'll normally see the rear face of the 4 retaining forks. On a good chuck they'll be held in place with small screws. Remove the screws. Again on a good chuck the retaining forks will be drilled and tapped for removal. If you have a slide hammer you can remove them easily. Failing that make a small bridge and a strong back and wind the forks out with a screw. Failing all that and if the fork isn't drilled and tapped you may tap the fork out with a small drift from the front. Sometimes it's possible to drill and tap the fork but normally they are hardened so then it's almost impossible.
The jaw adjusting scroll screws should slide out easily after that.

You can get other issues IE the jaws won't slide all the way out because the outside of the chuck has been damaged. Ditto the jaw adjusting scroll screws won't come all the way out either. There are techniques to overcome these problems but we'll cross that bridge if we come to it.

Regards Tyrone.
 
That helps a lot . I got the 4 jaw apart so that's getting cleaned.
I`ll prolly just soak the 3 jaw in gas and clean it up that way.
Don`t plan on using it as I intend to start off using the 4 jaw and learn that way.
I`ll see how brave I feel once it`s clean.
 
Well I grew a set and got it apart , not to bad in there should clean up nice.
The question is to grease of not to grease? It does have an oil port so im thinking oil better than grease?
 
Good you hot it open.

We usually back out the screws that hold it together a few turns then smack them with mallet or handy 2x4 and it drives the Chuck parts apart and retains them by the screws still being in place.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
Thanks for that guys. I've never seen a three jaw chuck that splits more or less in half like that one. I've got to say that you don't come across 6" chucks in heavy engineering very often. Usually chucks have the main body and what is more or less a backing plate. Having said that it's great that here's always something new to learn on this site.

Regards Tyrone.
 
That helps a lot . I got the 4 jaw apart so that's getting cleaned.
I`ll prolly just soak the 3 jaw in gas and clean it up that way.a
Don`t plan on using it as I intend to start off using the 4 jaw and learn that way.
I`ll see how brave I feel once it`s clean.

Mastering four jaw work isn't easy at first but it's worth the effort.

Regards Tyrone.
 
There are 3 jaws split differently - on those the pinions have to come out first

Here is the Union No. 81 chuck that is just the opposite of what Johnoder mentioned. The pinions are loaded before the back plate is set in place. Pinions are 'loose' as there are no half-washers to hold them in place.
This 6 inch chuck has taller jaws with a double slot and it uses the identical scroll of the #123 - K.
The #81 chuck is likely older as the face of the chuck is marked CLASS S a turn of the century ordering code.
This is a one piece body and the back plate drops into a counterbore in the back of the chuck.
Union 6 inch No 81 extended depth chuck.jpgUnion No 81 Chuck.jpg
John
 
All done with the 3 jaw.
Thanks for all the help.
 

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I am having the same problem with a 3 jaw Pratt chuck. I have tried mallet blows on holding bolts. no luck. I pressed it in a press and moved the backing plates approx 1/16inch then it does not move. I am wondering about the pinions- they are still in. I removed the set screws but the pinions do not come out. It looks like there is a small pin in the hole that the set screw pushed on. Not sure how i would get those out. Anyone have experience with taking apart a pratt 3 jaw chucks (from a DSG. thanks Mumf
 
I am having the same problem with a 3 jaw Pratt chuck. I have tried mallet blows on holding bolts. no luck. I pressed it in a press and moved the backing plates approx 1/16inch then it does not move. I am wondering about the pinions- they are still in. I removed the set screws but the pinions do not come out. It looks like there is a small pin in the hole that the set screw pushed on. Not sure how i would get those out. Anyone have experience with taking apart a pratt 3 jaw chucks (from a DSG. thanks Mumf

If the pins you are referring to are the small dowels they are usually threaded so you can withdraw them with a slide hammer.

Regards Tyrone.
 
thanks Tyrone. I just spent 4 hours getting one out. It was a small cap- disk 1/4 diam and about 1/8 long. The set screw set on this. There are 3 of them on the back side just besides the pinions. The only thing i can think of is that they retain the pinions, stop them coming out. Not sure, since i still cannot get the pinion out. As John O said, i think the 3 pinions have to come out before it can be split. My wife is away-with cell phone (camera) i will get soe pictures during the week.

thanks Mumf
 
thanks Tyrone. I just spent 4 hours getting one out. It was a small cap- disk 1/4 diam and about 1/8 long. The set screw set on this. There are 3 of them on the back side just besides the pinions. The only thing i can think of is that they retain the pinions, stop them coming out. Not sure, since i still cannot get the pinion out. As John O said, i think the 3 pinions have to come out before it can be split. My wife is away-with cell phone (camera) i will get soe pictures during the week.

thanks Mumf

Yes a few photos would help.

Regards Tyrone.
 
Here are a couple of photos. The firsy shows the small hole close to being in line with the pinion. The secone show the set screww and small cap. Th pinion would still not come out. Not how they are removed, any help appreciated.
tks Mumfchuck 3 jaw 2.jpgchuck 3 jaw 1.jpg
 
Here are a couple of photos. The firsy shows the small hole close to being in line with the pinion. The secone show the set screww and small cap. Th pinion would still not come out. Not how they are removed, any help appreciated.
tks MumfView attachment 297880View attachment 297881

If you look down the hole the grub screw and little pad came out of you should be able to see the top of a dowel that holds the pinion in place. On every chuck I've worked on those dowels are drilled and tapped so they can be withdrawn with a slide hammer. If you haven't got a slide hammer a length of threaded rod or a long bolt, a nut and some big washers will also do the job. The dowels retain the pinions.

Regards Tyrone.
 








 
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