# Putting a Chuck on a Dividing Head



## silverhawk (Apr 18, 2020)

When you attach a chuck to a lathe, you have to machine the backplate on the lathe to maintain concentricity.  It is an absolute must.  I needed to put a chuck on a dividing head.  That means that I can't machine it on the lathe, because it has the potential to end up with the chuck center line offset from the dividing head center line.  Simply put, you have to machine the backplate on the device it is to be used for.  I searched the 'net and didn't see much, so I attempted to do it myself.  The only back plates I could find that had a 1 3/4-8 TPI thread were for an 8" diameter chuck or a 6" diameter chuck.  I ordered the 6", having to cut it down to a 4" for the dividing head.  The come slightly oversized to be machined.

Taking a 6.25" back plate to be used on a 4" chuck, you need to hog off a lot of material.  Also, I needed about 3/4" of overall depth, and this back plate is 1.25" deep.  I used the lathe to break down as much of the outside surface as I could.  You _must_ leave it oversized, because you will still machine the plate on the device it will be used on.  So, after the lathe, I'd removed a bit of material.





After removing that, I could put the backplate on the dividing head backwards.  This would allow me to face off the rear surface that mates up against the dividing head.





Once that is surface is machined, I pulled the backplate off and turned it around.  I could then machine the outside edge down to match the chuck.  In this case, the chuck was 3.948", and at this point the back plate was 4.250" in diameter.  I machined off 0.030" using the mill.  You must be careful here.  As the end mill rotates, the direction where it meets the backplate _must_ tighten the backplate instead of loosening.  The speed of the dividing head is minimal, so we don't need to worry much about having it round.  It's nice to do, though, for a finish.





With the outside edge, you can now machine the mating surface for the chuck.  This should be done very slowly - it is the same principle as doing it on a lathe, but the part isn't rotating, and you are taking it off with an end mill.  Remember, when you take off 0.125", it removes twice that because it takes the 0.125" off the other side, so it's really taking 0.250".  Take your time.

After the boss for the chuck has been cut, you can surface the boss so it is deep enough.  At this time, you can rotate the dividing head and drill your holes for mounting the chuck.  I flipped the back plate again, so that the indexing-side surface was on the outside.  This allowed me to bevel the rear flange for clearance on the screw caps.





With that complete, it is now time to pull the plate off and install the chuck.  That completes the installation of a new chuck to a dividing head, and will allow me to make another attempt at cutting a gear.


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## Lo-Fi (Apr 19, 2020)

Great write up! The back plate on my dividing head needs similar attention as I suspect that kind of care was not taken by the original owner. 

Will you be posting up your gear cutting escapades?


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## silverhawk (Apr 19, 2020)

Lo-Fi said:


> Great write up! The back plate on my dividing head needs similar attention as I suspect that kind of care was not taken by the original owner.
> 
> Will you be posting up your gear cutting escapades?


I will. The gear I need to cut is a 40 tooth spindle gear for my heavy 10 that works with the collet closer. I'd already made one gear but used the wrong pitch cutter. It took way too long with the 4 jaw independent chuck to set up, so I opted to redo the chuck. 

My next attempt will be to try and clock in the first gear to see if the right cutter fixes the tooth angle. If that fails, I will cut a new blank from cast iron (start from scratch).

joe


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## silverhawk (Apr 19, 2020)

Just a reminder to ALWAYS be aware of the rotation of the end mill. If the side of the end mill in contact with the plate rotates in the directing of loosening, the plate WILL come loose and end up with end mill marks all over it. 

joe


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## Lo-Fi (Apr 19, 2020)

silverhawk said:


> ...plate WILL come loose and end up with end mill marks all over it.



And likely break an end mill! A sage warning. 

Looking forward to the gear cutting, it's one of my favourites jobs on the mill. Quite relaxing when you get in a rhythm.


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## silverhawk (Apr 22, 2020)

Here's the end result.  This was posted over on the POTD, but here we go here to tie up loose ends.  I managed to clock in my gear, cut it slightly deeper (I had it about 0.005" shallow), broach the keyway, and install it to my SB10L.  First, get the gear axially centered on the dividing head :







Next, use the mill to ensure you have the dividing head clocked in using the gear :






Then center the cutter on the gear body :






Then free the gear from the chuck and turn it until you have it timed with a cut along with one of the holes on the dividing plate, and re-center on the dividing head axis (this ensures we are perfectly lined up).  Now you can establish the proper depth of cut.  I marked the slot with a sharpie on the end as well as the gear teeth grooves so I knew I had it right.






Then, took some 1.75" CRS and milled a 3/16" groove into it so I could use the 1/8" broach to cut the keyway.






Check the fit for the broach :






Slice it off in the bandsaw, file all of the edges off for a free sliding fit, and check again :






Broach it in the press, and then have what appears to be a successful gear :






However, the proof is always in the pudding, so it was time to install it and see for real :






It works great!


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## Flyinfool (Apr 22, 2020)

I was going to starting on a similar project of setting up a 3 jaw for my rotary table. I was planning to do all of the machining on the lathe. I was going to start with a disc of cast iron 8 inch dia x 1 inch thick. 
First is to face the back plate and turn the register to fit the chuck. 
Second drill the chuck mounting holes and mount the chuck to the back plate semi permanently.
Third was to put a piece of steel the biggect that will fit thru the chuck in the lathe chuck and turn it o give perfect registry to the spindle and then mount the rotary table chuck and back plate assembly onto the shaft using the jaws of the RT Chuck to be able to face the mounting surface to desired thickness, turn the OD and turn the register to match the rotary table. Am I missing something here? My thought was that this method will put the center line of the jaws square and on center with the table.


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## silverhawk (Apr 22, 2020)

Flyinfool said:


> I was going to starting on a similar project of setting up a 3 jaw for my rotary table. I was planning to do all of the machining on the lathe. I was going to start with a disc of cast iron 8 inch dia x 1 inch thick.
> First is to face the back plate and turn the register to fit the chuck.
> Second drill the chuck mounting holes and mount the chuck to the back plate semi permanently.
> Third was to put a piece of steel the biggect that will fit thru the chuck in the lathe chuck and turn it o give perfect registry to the spindle and then mount the rotary table chuck and back plate assembly onto the shaft using the jaws of the RT Chuck to be able to face the mounting surface to desired thickness, turn the OD and turn the register to match the rotary table. Am I missing something here? My thought was that this method will put the center line of the jaws square and on center with the table.


If you can do the entire mounting plate without removing it from a lathe chuck, you can ensure it is concentric and perpendicular to the table. That assumes that the table surface is perpendicular to the rotational axis of the table. If you know the table is flat (put an indicator on the outside, top edge of the table, rotate it all the way around, and ensure it is not high or low), it should be close enough to put the adapter plate together this way.

If you want it perfect, you can mill it on the rotary table. Install it to the rotary table and use an end mill to surface and cut the register for the chuck. 

I had to do it on the index head because it was threaded, and I didn't know if the thread was aligned to the axis properly. I wanted it right on the money, so it was a must. 

joe


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## BGHansen (Apr 23, 2020)

I had a similar problem on my Tormach centering up the 4th axis.  I ended up using either a small 4-jaw on the rotary table to dial in work or a mounting plate for the 3-jaw.  The 4-jaw is more of a pain as I have to dial in the work every time.  The 3-jaw isn't too bad, slap it on tell the machine to rotate it while it gets tapped into place with a brass hammer.  Once dialed in, it's a lot quicker swapping out parts.

I've got an L&W small dividing head and a Japanese 8", had planned on making set-true type chuck backing plates on them but you have a better solution.

Bruce


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