MAKING A PINION GEAR FOR A 8" 3JAW CHUCK

petcnc

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With my new (to me) 14”X30” SLOTTA lathe came as an extra chuck, an 8” 3 jaw ROHM chuck. The chuck had definitely seen better days and, as I had no need for it, I left it aside and forgot all about it.

Rohm8 a.jpg

The biggest issue with it, apart from the abuse by some "hammer lover" owner, was that one of the 3 pinion gears was missing making the chuck a very good paper weight.
The inside of the chuck is in good condition. There is no rust whatsoever but the condition of the existing two pinions is very poor. They are pitted like they have spent their life underwater.

ssIMG_20201128_005906061.jpg

Although there is no need to use it at the time, as it requires a back plate that I do not have, and as Covid 19 forced me to spend plenty of time in the shop, I decided to kill some time in trying to make a new pinion for it.
First some measurements to make the blueprints of it.

ROHM 20 part1.jpg

Apiece of scrap steel in the chuck and the fun begins

ssIMG_20201129_174048275.jpg

It needed some careful machining though to bring it within dimensions and specs!!!

ssIMG_20201129_194252553.jpg

Then I needed to make a cutter for it. I intended to use my mini mill flycutter so I had to make a single point cutter from HSS
To copy the exact profile of the pinion gear, I used hot glue gun, I filled the space in between teeth with hot glue, when solid I removed it. I cut it vertically (using a razor blade) and copied the profile to the HSS.
Minor corrections made with a dremel disk.

IMG_20201129_194603988.jpg

Then I put the blanc to the mini mill and using the 4th axis I wrote a simple gcode to make the cut using the fly cutter and the bit I had made.

ssIMG_20201130_235554160ss.jpg

It was not an easy job for the mini mill! It struggled to make the cuts although I used very light passes(0.1 mm per pass) and very slow speed. To make the full depth for the 12 teeth took hours.
At the end the pinion gear was ready.

ssIMG_20201201_231043867.jpg

Time to test it on the chuck.
Naturally I had to make the securing pin also that was missing as well.

ssIMG_20201201_231118555.jpg

After testing time to cut the unnecessary steel off the back and create the square hole for the chuck key.
I can tell one thing for parting on a lathe: Rigidity is the key to success. With my mini lathe I could never part a piece successfully. I even made a spring parting tool to ease the job (full story here). With the new lathe it was just another job for the machine that was done as it should!
To make the 11mm square hole first I drilled a 10mm hole then I bored it to 11mm.

ssIMG_20201202_005401336.jpg

Then I took it to the mill where with the help of a 3mm end mill (and some g-code) I made the Square hole.

ssIMG_20201211_163020062.jpg

Sq hole on the spot!

ssIMG_20201211_165003207.jpg

On the chuck it performs OK.

ssIMG_20201211_165946455.jpg

And it looks ok also.

ssIMG_20201211_171755622.jpg

Now I have a working chuck that I cannot use because:
a) there is no back plate for it
b) I do not have the set of outside jaws
c) I do not need it for now.

I had a great time in fixing it though! :dancing banana:


Thanks for reading.

Petros
 
Last edited:
Excellent save @petcnc !!!!

it's ok to make something work that you do not need- soon you may wish to make a backplate.
if you can make the pinion, you can make a backplate! :encourage:
if you have a working chuck, you'll find a use for it if you think long enough :grin:

keep up the great work!
 
it's ok to make something work that you do not need- soon you may wish to make a backplate.
if you can make the pinion, you can make a backplate! :encourage:
if you have a working chuck, you'll find a use for it if you think long enough :grin:

MiKe of course I can make one!
The thing is that I will make it when I will need to use the chuck! So I must first make the backplate, then I must put the chuck on it, then I must make all adjustments needed, then... I can use it to hold the part that does not fit to the 6 1/2" chuck that is on the lathe now.
Lots of fun eh?
 
the fun never ends, if you are doing it right!
you are doing it right!!! :)
 
This is a very cool fix. I love the use of glue to make a copy of the gear profile for copying to HSS. Very neat trick.


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I don't remember where I saw it, but an alternate solution is to fill with wax/paraffin to "copy" the profile.
Either way really neat fix, hadn't seen this thread before.
 
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