I picked up a nice Jacobs chuck that seems to be wobbling about .100 out of true when run in both my drill press and lathe tail stock. Yes, I cleaned both the arbor and inside the spindle...

It's mounted on a #2 Morse taper arbor and I'm wondering if it was dropped or hit at some point in it's use. Perhaps the arbor was pressed in at a slight angle???

If any machinist types out there have any insight on how to fine tune a Jacobs chuck, I hope they will take a few minutes to share with the class...

See if it is dented on the face of the chuck near where the jaws protrude. If it is damaged that way the bit will sit in the jaws very cockeyed. I ruined on that way by wacking it with a hammer trying to make it stay on the drill press spindle.

You first have to determine if its the chuck, the arbor, or the bore on your machine.

My suggestion would be to first mount the arbor, sans chuck, and check it with a dial indicator to see if it is running true.

Get some chuck forks and take it apart...

try rick's suggestion...

then chuck the chuck in your lathe, and indicate the ID and OD (if possible for delta in run out...)


then, put the arbor in dry ice for 24 hours... and put the chuck in the stove (wraping in alum foil) for at least 2 hours at 400....

(make certain both are totally degreased prior to starting hot and cold...)


"drop" the chuck (it should be DANG hot) onto the arbor (which should be dang cold)...

Since I put dry ice into a cooler, I sugest you ahve the chuck ready (in an oven mit) then have someone open the cooler, unwrap the arbor(keeping it inside the cooler) and IMMEDIATELY dropping the chuck on... you don't want any ice to form on the arbor

turn it over, tap it lightly and let it sit for 4 hours...

this will be a great bond and as straight as it can be

jeffe

Jeffe, I am almost totally naive about machining, but I always enjou hearing you pro's discuss solutions to machining problems. That process you descibed just sounds damn interesting. I am hoping to be able to minimize the work schedule in 6-10 years, and then maybe take some machining classes.

I was an engineering minor in school, so I'm not totally blind......but,
Is there a book or two you guys might reccomend for a rookie to read on machining, just to understand the lingo etc.?

Regards--
Don

go get a copy of the machinist handbook

Somewhat along the subject; I have read sveral
references that tell to tighten a chuck from all the key positions. Looking at a chuck and trying this I can find no difference???.
Good luck!

Debee,
sounds like afair bit of runout(.100")
a small amount of it may be attributed to normal variation one gets in a 3jaw setup, is it a serialised number chuck? Jacob make different grades,with different tolerances of manufacture. Also, do you know the history of that chuck?, someone may have used it to machine laterally with endmill cutters,putting unhealthy strain and wear on it. Jacobs are purelly for plunge cutting,anything else requires specified collets.

The chuck in question is a Jacobs 34. While it's not Jacobs top of the line, it's not Taiwanese junk either. I feel it's worth a salvage attempt.

The chuck came on a Clausing 15" press I picked up recently. The spindle runout on the drill is less than I can accurately measure, so therefore, I am focusing on the chuck/arbor relationship. If I had to guess, I'd say it took a hit during shipping as it was mounted in the spindle at the time (not the best arrangement). I don't know the history-the chuck doesn't look abused- clean, no burrs or rust. As an aside, I have a well abused Jacobs 14N that runs true in the drill press- but I have delegated that to lathe use/abuse...

I've seen the morse taper wedges in the MSC catalog but I don't know how to use them... I will continue to listen to any suggestions...

DeBee,

Look in the Yellow Pages in your area and find a small machine shop. Take your chuck to them and ask if they can remove the chuck from the arbor...and ask if you can watch them do it. If you’re like me you will learn far more from watching someone do it than you will ever learn from written instructions.

Once apart it should be fairly simple to find the culprit with a dial indicator.

.100 is almost .125 which equals 1/8th inch! Junk the chuck. I would NEVER trust that chuck again. Especially where pricision gun work is concerned.

DeBee

You might want to read this FAQ page.

http://www.jacobschuck.com/support.asp

Jacobs chucks are nearly bulletproof with reasonable care. If you press it apart, clean it and be sure the jaws are in the correct order, it may fix your problem. If not, get a new arbor. My preference is that the American made ones are well worth the extra cost.

I would never put an arbor on with the temperature difference suggested earlier. That might distort the chuck body and destroy the chuck. They were made with a class of taper that is self and designed to be mounted with a hammer blow. They usually stay nicely if the arbor and chuck are clean.

I was always taught to tighten all three holes as well. I never did figure out why. My logic tells me it should make no difference, and it may be just a carry over from when chucks were designed differently. Just because I don't understand why, it doesn't mean it isn't true, and I find myself doing it the way I was taught.

The 34 is a very good chuck, I would not through it away. A bit of effort should fix this. Good luck

Roger

Should have said "self holding taper"

Roger

this is another resource page that may help. Roger

http://www.beautifuliron.com/jacobs.htm

Here is the best reason I have heard for tightening a chuck with all 3 holes-

Due to the geometry of the teeth in the chuck, one position will give you more leverage than the other two. Unfortunately, no one knows which hole it will be, so the only way to be sure is to tighten all three of them.

Whether it is true or an old wives tale I don't know, but it makes more sense than anything else I've heard.

Great links. It was worth downloading Adobe Acrobat to see the pics...

.100 was eyeballing it. It was off enough to be clearly noticable at a glance. I'm not yet ready to trash the chuck- but I may demote it to screw polishing jig if it doesn't start running true...

Good Tip: Tighten the chuck with all three holes. Every so often, you get to learn something on this site.

Attempting disassembly and cleaning of the chuck- will post results good or bad...

the jaws are worn out in the chuck. a #34 is not a ball bearing type chuck, which means you can't really tighten it as much as you need to sometimes and drills will slip in the chuck wearing out the jaws. you can buy a rebuild kit for about $40.00. i really don't recommend it though. save up the money and buy a jacob's ball bearing chuck. you'll never buy an other plain bearing chuck again.
don't buy the machinery handbook. if your just learning it won't help you. it's really just a reference book with too much needless crap. make friends with a machine shop. they'll probally give you a copy. i buy one every couple of years and give my old copys away.
if you want a good book to get started get a subscription to "the home shop machinist" magazine. i've owned my own shop for 10 years and thought i new it all. i got one of my custormers a subscription for christmas last year cause he was interested in the trade. it got sent to my po box by mistake. i had to get him something else cause i kept all the magazine's my self. good stuff.
also agree with the poster about just cleaning the the taper and slaming it home. starter fluid works the best to clean.

Mark; Thanks that makes at least some sense.
Now I can sleep nights.
Take Care!