Jacobs #50 Collet Chuck for my Hercus 260

[cba_melbourne]

It arrived today with USPS Priority Mail, 16 days after I won the eBay aution. It cost AU$225 plus 72 for the postage. The chuck with collet set weighs 5.8kg without the package. Condition is excellent, there appears to be no wear, it definitely has not been used much at all. There is just surface discoloration from the thickened up protective oil, and some dust. I am sure it will clean up well. The mechanism moves freely and everything is as it is supposed to be. I am very happy.

The backplate adapter is for a threaded spindle nose 1-1/2x8TPI. Not sure yet what I do. I could bore it out and rethread 1-3/4x8TPI for the Hercus 260. Or make a new backplate and sell the original one, there is a drawing with the Jacobs chuck manual how to make a new backplate. Or modify an existing 260 backplate.

Here some pics how it looks right out of the box:

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Not bad, considering they stopped making these collet chucks some 15 years ago. No idea how old this particular one is, but could potentially be from the 50's.

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Interesting: yhe 0.1-0.2" collet only has four ribs, so its also suitable to clamp square stock. No idea why this is so though....


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Collets are almost unused. The rubber has not perished, no surface cracks. They were obviously properly stored away from sunlight.

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The three threaded studs that engage with the nosepiece are driven via gears by the large black handwheel. That makes for fast opening/closing of the collet. To firmly clamp down a workpiece, the three studs have an internal socket for an allen key.


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This is a link to the operation manual for this chuck:
http://www.wewilliams.net/docs/The%2...et%20Chuck.pdf
The chuck itself mounts with 6 allen screws to the backplate, and these are used to dial the chuck for minimum TIR when it is mounted for the first time.


Jacobs_500_series_collets.jpg
These are the dimensions of the 500 series Rubberflex collets as used with the model 50 collet chuck.

These chucks and collets do regularly pop up on American eBay, so are not hard to come by. They were very common in the US back at the times where manual lathes were in fashion, 50's to early 90's. Prices vary with condition, US$ 200 to 300 are common for this chuck with a complete collet set, one gets pretty much what one pays for. The main problem is that the rubber in the collets will perish if stored many years in sunlight or/and exposed to solvents. Affected collets show fine surface cracks in the rubber, just like an old perished tractor tyre does. New collets can still be bought, but cost from US$50 upwards each.

[cba_melbourne]

Some more pics of it disassembled. Before cleaning, all oil/grease and dust is left as it came.


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What looks like rust on the recessed screw at 2:30h, cleans off as dried oil in solvent.


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I believe this is the original factory oil. There are no metal chips to be seen. No wear marks even after cleaning. Looks like a new and unused chuck. Just been sitting around for a looong time. I would say it fits the description "shop soiled New Old Stock".

[cba_melbourne]

All parts are hardened and will not be scratched by a file - except the backplate adaptor.
This chuck is new and must have sat on a dealer shelf for a very long time.
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[cba_melbourne]

First thing I had to bore out the 1-1/2x8 backplate and thread 1-3/4x8. The material of this backplate does not machine well at all. It is made from some tough steel. A challenge to put a decent finish on. Especially on the thread!


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Next, the chuck body is bolted to the backplate. With a Nylon hammer it is set true, whilst the bolts are gradually tightened. This adjustment is pretty easy and fast. TIR changes by about 0.002mm after completely tightening of the bolts.

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A collet is inserted (10mm collet here)



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The cap goes on and is closed by rotating the big black handwheel. To firmly tighten onto the workpiece a hex key is inserted in any of the three leadscrews, this amplifies the handwheel force about 10-fold.


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The Hercus spindle nose does not use a registration to center the chuck. It completely relies on the threads themselves axially centering the chuck, and the flange face to put it onto a plane. I took the chuck off several times, cleaned both spindle nose and backplate, put it on again and checked runout. Every time, TIR was about 0.004mm. I would not have expected it to repeat as well as it does.

The quality of this chuck is well beyond the Hercus lathe, which does not even have a hardened spindle nose. But it will be a pleasure to use. I lubricated it with Super Lube Teflon grease, time will tell if this was a good idea.

By the way, there are two types of Jacobs Rubberflex spindle nose collet chucks. This is the smaller one. The larger uses a completely different mechanism.

[Tiptoeturtle]

It will be an idea to find out more about the bigger ones and perhaps locate instructions for it.

There is a miscellany of South Bend related documentation listed at:

http://www.wewilliams.net/docs/

Among other non-South Bend materials.

[cba_melbourne]

The bigger ones have Aluminium handwheels of diameter of 7.5 or 9". These are huge collet chucks. They also use a different size/type of Rubber-Flex collet. Not interchangeable.

Here the user manual for the larger chucks:
http://neme-s.org/images/Jacobs_Coll...llet_Chuck.pdf

This is an old sales flyer for the larger chucks:
http://neme-s.org/images/Jacobs_Coll...et_Chuck_B.pdf

This US seller seems to specialize in this old Jacobs collet stuff. Good to re-order a single collet if needed:
http://www.tools-n-gizmos.com/index.html

[Anorak Bob]

A great find and a great thread Chris.

Beautifully documented. Thank you.

Bob.

[oldtech]

First thing I had to bore out the 1-1/2x8 backplate and thread 1-3/4x8. The material of this backplate does not machine well at all. It is made from some tough steel. A challenge to put a decent finish on. Especially on the thread!


01_DSCF0278.JPG05_DSCF0282.JPG04_DSCF0281.JPG02_DSCF0279.JPG06_DSCF0283.JPG
Next, the chuck body is bolted to the backplate. With a Nylon hammer it is set true, whilst the bolts are gradually tightened. This adjustment is pretty easy and fast. TIR changes by about 0.002mm after completely tightening of the bolts.

07_DSCF0288.JPG
A collet is inserted (10mm collet here)



08_DSCF0289.JPG
The cap goes on and is closed by rotating the big black handwheel. To firmly tighten onto the workpiece a hex key is inserted in any of the three leadscrews, this amplifies the handwheel force about 10-fold.


11_DSCF0292.JPG09_DSCF0290.JPG10_DSCF0291.JPG


The Hercus spindle nose does not use a registration to center the chuck. It completely relies on the threads themselves axially centering the chuck, and the flange face to put it onto a plane. I took the chuck off several times, cleaned both spindle nose and backplate, put it on again and checked runout. Every time, TIR was about 0.004mm. I would not have expected it to repeat as well as it does.

The quality of this chuck is well beyond the Hercus lathe, which does not even have a hardened spindle nose. But it will be a pleasure to use. I lubricated it with Super Lube Teflon grease, time will tell if this was a good idea.

By the way, there are two types of Jacobs Rubberflex spindle nose collet chucks. This is the smaller one. The larger uses a completely different mechanism.

While the Hercus, Sheraton etc don't have a separate diameter on the spindle, the short unthreaded portion of the spindle after the threaded section forms a register. If you measure the od of the thread it will be slightly under the nominal dia and less than the unthreaded section. The chuck should be clearance overter the threaded section but a close fit on the short unthreaded section. Hope this helps.

[nadroj]

Actually, it's true that the thread and the shoulder-face on the spindle are the only things that centre the chuck on a Hercus.
I have an original Hercus-supplied chuck, direct fitted with no backing plate. When measured and compared to the unthreaded portion of the spindle nose, there is a gap. Checking on both my 260 and 9A, it's the same for all chucks and faceplates. Nevertheless, they keep concentricity quite well and repeatably.

Jordan

[cba_melbourne]

Actually, it's true that the thread and the shoulder-face on the spindle are the only things that centre the chuck on a Hercus.
I have an original Hercus-supplied chuck, direct fitted with no backing plate. When measured and compared to the unthreaded portion of the spindle nose, there is a gap. Checking on both my 260 and 9A, it's the same for all chucks and faceplates. Nevertheless, they keep concentricity quite well and repeatably.

Jordan

Yes, there was a discussion years ago about the registration flange on spindle noses. I was back then convinced that any serious lathe would have to use this to accurately center the chuck. But then someone asked me to measure on my 260. And sure enough, there is an air gap between the original Hercus supplied chucks and the diameter of the unthreaded portion of the spindle nose. Also, the argument makes sense that if this was indeed an accurate interference fit, it would in use not remain accurate for very long given the Hercus spindle is completely soft (unhardened).

I have to say that after owning this lathe now for a few years, I am very surprised how accurately the thread alone is capable to center the chucks. Especially given that the Hercus spindle nose thread is rather crudely cut, not precision ground as one might expect. That said, I still like the hardened spindle with precise short taper mount of my smaller EMCO lathe better - if only for the peace of mind that it will retain its accuracy no matter how much wear/use it gets.