View Full Version : Jacobs rubber flex

07-15-2009, 09:00 AM
How can you tell what model a Jacobs rubber flex lathe chuck is? Seems like there are 2 different styles of collets availible. I see no numbers or indication of a model on the outside of the chuck.



07-15-2009, 09:51 AM
Jacobs made two lathe sized collet chucks. One was similar to a Jacobs drill chuck and used a key to tighten, the other, larger one had a handwheel to tighten much like a Hardinge Sjogren chuck.

Both use the same collets, which is an eleven piece set covering the 1/16"-1-3/8" size range. They are J910 through J920.

Jacobs makes several Rubberflex collet series for tapping heads, I believe there are three or four different series, each fitting a different chuck.

Forrest Addy
07-15-2009, 11:57 AM
Well stated JC.

07-15-2009, 12:00 PM
I am asking about the large hand wheel tightened chuck. I see on ebay the 9XX and a 500 series. I think I need/ want the 900s.

At work we have both the Jacobs and Hardinge with the steel collets. 5C? That Hardinge can be a real bear to get open! Where as the Jacobs is not so hard to get open but occasionally spins apart if you stop the spindal quickly.

Thanks for the help!


07-15-2009, 12:13 PM
You want the J900 series collets. The handwheel chuck has a locking feature to prevent opening when stopping or running in reverse. There is a locking ring on the chuck, outside of the nose piece which retains the collet, that should be pushed in after the chuck is tightened.


07-15-2009, 12:45 PM
Speaking of J900 chucks, what is the thread on the nosepiece supposed to look like? I received a Rubberflex chuck with my "new" old lathe, and the threads on the nosepiece are very thin, almost akin to wood-screw threads. Is my chuck badly worn (doesn't seem like it otherwise), or are the threads supposed to be like that? How do you get that funky interlocking split retaining ring off to dissassemble and clean the works?

07-15-2009, 12:59 PM
Jacobs made two lathe sized collet chucks. One was similar to a Jacobs drill chuck and used a key to tighten, the other, larger one had a handwheel to tighten much like a Hardinge Sjogren chuck.

There is/was a third collet chuck using the 9xx collet series, a lever action collet chuck. For reference, the chuck numbers were as follows: "91" was the handwheel model, "92" was the lever action and "96" was the key operated.

They also had a set of steel collets for the series with hex and square. I've seen one set on eBay in the last 5 years, so they're pretty rare.

07-15-2009, 12:59 PM
The thread is square. It should be the same width as the space between the threads.

To remove the split ring, push the locking ring in and pry between the locking lugs to spread apart. The ring can then be removed. The chuck can be dismantled by lifting the parts off. In the sleeve, there is a hole with a snap ring to retain the bearings. Remove this and the bearings to clean. There are 33 1/4" ball bearings, when reassembling, do not add more than 33 balls as it will jam the chuck. Lube the balls and race and the internals with light machine oil when reassembling.

07-15-2009, 08:44 PM
Thanks for the info! The chucks at work coming apart when you stop the rotation just go to show how worn out all the tooling we have is. I have dissasembled and replaced the key on both of them several times in the last 20 years. Second time I did it I made half a dozen keys and we/I need to make a few more soon.

I like the Jacobs so much more than the Harding thast I bought 1 for my own shop at home!

Thanks again!

Rich Carlstedt
07-15-2009, 11:56 PM
Hey Jim
Let me ask you this.
My Rubberflex chuck is really loose and rattles when running.
The collets are straight as an arrow, but the rattle bugs me.
Do I take it apart and grease it to stop the rattle,and/ or do I replace the balls ?
Thanks my friend

07-16-2009, 08:40 AM

Cleaning and greasing might help, as well as replacing the ball bearings to tighten things up. Too few ball bearings might also make for a rattle, make sure it has 33. The lock ring has spring loaded detents in it. If they are gummed up, it might allow things to flap around and rattle too.

The only other place I see for a source of rattling is if the hand wheel is floating around too much. There is a washer behind the retaining ring to take up thrust, a thicker one or a plastic shim behind that might help if that is the case.

I have only had mine for a few months now, but so far it looks like it will be my second most used chuck. I am very pleased with it's accuracy and repeatability as well as the wide range of holding capacity.

07-16-2009, 02:52 PM
This is a super chuck with only one drawback. Under extreme torque the blades in the collets will flip sideways. Example, using a large diehead or using it to torque up a pipe fitting. For normal turning operations they are able to grip in between sizes better than other collet chucks. Peter

07-16-2009, 03:31 PM
I also like my Rubberflex very well, and it does not rattle. Just for rough work, I generally keep my 3 jaw mounted, but the Rubberflex is sure nice as long as you have sufficient length to grasp in the collet. Frankly, those little rubber plugs for short pieces are just not ideal.

07-16-2009, 06:44 PM
We have several rubberflex collet chucks for our lathes at work. A couple that fit the big American lathes but we also have 2 that fit the Monarch
10EE's. I'd say that on the little 10EE's they get used 75% of the time or better. They are just so useful and run very true.

07-18-2009, 04:37 PM
Wasn't there a smaller Jacobs Rubberflex chuck made for SB 9" lathes? It might have been a Moel 50 or maybe Model 950. AIR, all of the collets came in one box/case and there were 10 or 11 of them.