Anyone with experience with Jacobs Rubberflex collets?

I have a Jacobs Rubberflex collet chuck for my 10K, and have a question about runout. With the chuck mounted on the spindle, the taper where the collets seat runs true within tenths, nearly perfect, but some of the collets exhibit quite a lot of runout when holding work, others are good to very good. None are as good as the taper itself. Any idea why this is happening? Do the collets wear out? I know Jacobs no longer makes these, and I have no idea how old my set is. I have made every attempt to be sure the collets are clean inside and out, as well as the chuck taper. The rubber on the collets appears in good shape and is still flexible. Any info will be appreciated - thanks.

Using these can be a little tricky. There are two series of these, 500 and 900 series. I have both, but primarily use the 900's. Each series requires its own chuck. The predominate issue is if the piece you are trying to hold is shorter than the depth of the collet, the piece may cock. The collet must be fully loaded from the front of the collet to the back of the collet. In the case of a short piece that does not extent on the same diameter across the depth of the collet, you are supposed to use a rubber plug behind the piece at the back of the collet. These plugs are usually included with the collet set and come in various sizes. The use of the plug allows the rubber within the collet to compress equally, as the piece is clamped.

Something you may also want to keep in mind when trying to cut a thread on Steel parts is a) have full collet engagement if possible and b) use a live center if possible.

Recently I was cutting a thread on a steel part in which I had full chuck engagement and only 1 1/2” stick out. I was halfway into cutting the thread so I was only infeeding 0.002” and not using a live center. The v form engagement was enough surface area to overcome the elasticity of the collet and the side force of the cut pushed the part instantaneously off center and grabbed the insert. Broke the insert, knarffed up the part and made for an unhappy camper!![emoji35][emoji1]

I evaluated what had just happened and remedied the problem by adding a live center. I started over with a new piece of bar stock and had no problem finishing the thread the second time.

The Jac chuck and collets are a very handy tool to have but its usefulness and limitation is the elasticity of the collets. Not as rigid as 5c but has more size range per collet and can hold delicate work nicely. Just make sure you support the end of your work if you plan to take heavy cuts.


Machine on!

My 10K has a model 50 Jacobs Rubberflex chuck that stays on it 95% of the time. The only time I've experienced any runout to speak of is if the work piece is long enough to need support at the other end. On pieces too short for full collet contact, I always use the rubber plugs like has been mentioned above by steve-l.

Thanks for the replies. After reading the replies it occurred to me that they are 'rubberflex' after all!! Duh. Fooling around with the chuck and collets this afternoon I found that the worst runout occurs with larger, longer and heavier workpieces, which makes sense. I was able to eliminate most of the runout on these larger pieces by lightly bumping them with a dead blow hammer. The smaller collets all run pretty true, within .001 -.003". Learn something new every day. Fortunately I have 5C and 6K setups when more rigidity is needed, but the wide range of the rubberflex collets is great for odd sizes, and it's nice to know there's nothing wrong with them.

Thanks again for the replies - sometimes my brain needs a shove in the right direction. Heh, more often than not! :-)

In case you don't have this..note step 5...

http://www.wewilliams.net/docs/The Operation and Care of the Jacobs Model 50 Collet Chuck.pdf

iwananew10K said:

In case you don't have this..note step 5...

http://www.wewilliams.net/docs/The Operation and Care of the Jacobs Model 50 Collet Chuck.pdf

Click to expand...

Thanks - I do have the instructions. I think I mentioned that the taper runs nearly dead true with the chuck mounted on the spindle.
I do appreciate everyone's willingness to help and offer advice - this site does rock.