# Mounting Chinese chuck on a Chinese Lathe



## Tomc938 (Nov 2, 2021)

As I mentioned a few days ago, I got a 4 jaw chuck for my Craftex 9x18 lathe.  The lathe backing plate has three holes, and the chuck has four.  The alignment boss lined up very well, as did one hole.  I was a little concerned that one bolt holding the chuck on might not be sufficient. ;o)

So I was faced with the question of drilling 3 extra holes on the lathe backing plate, or 2 more in the lathe body. In the end I decided to make the 2 new holes in the chuck body as it would fit in my milling machine better that the lathe backing plate and spindle. It is worth mentioning that the bolts are not located with much precision - the boss aligns the chuck.  The bolts are to keep the chuck from coming off and killing the operator.

The first challenge I would have would be locating the 2 new holes on the chuck.  I could mount my rotary table and attack things that way.  But it is probably more precision (and hassle) than the two holes are worth.

Fusion 360 is really good at making circular bolt patterns with quite high precision, so I modelled a ring with three holes to see how well it would line up with the existing 3 jaw chuck.  The ring (and a collet wrench I was prototyping are below)   It lined up right on as far as I could tell by eye, and there was plenty of slack from the clearance holes in the backplate.







I was concerned about how I would get the template to line up with the back of the chuck properly.  A small alignment error around the perimeter would make for a larger error on the location of the holes.  Then I realized that Fusion can make circular patterns with 4 AND 3 evenly spaced holes - on the same ring!  So I modified the model to include both bolt patterns on one ring and increased the height of the shoulder around each of these holes.  Now I can bolt the pattern to the four holes on the back of the chuck and use a transfer punch for the two holes I need to drill and tap.  Below is a picture of the template alone, and then it mounted on the chuck.







I'll need to make a 9 mm transfer punch, drill and tap carefully, and I think I'll be off to the races! 

I will be out of town, and busy for the next few weeks, but I will keep you posted on progress.

If you see any glaring issues I overlooked, please chime in.  A second (and 3,4,5) set of eyes and perspective is appreciated.

PS:  BY the marking on the back of my chuck, I think it was made in San Fransisco - American quality! (Or someone with the initials SF, and a cheap engraver, was responsible for quality control - Chinese quality!)


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## Susquatch (Nov 2, 2021)

I think I smell a personal 3D printer in my future.......

Anything I would have done different would probably have been mathematically superior, but inferior in actual practice to your 3d template approach. I think it's cool! Let us know how it turns out.


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## gerritv (Nov 2, 2021)

I personally would drill a new 4 bolt pattern in the back plate, carefully aligned inside the 3 hole pattern; you need to consider the overall balance of the assembly when spinning at 2000 rpm. Also if you inadvertently mess up the backplate the replacement cost in not as high.


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## Tomc938 (Nov 2, 2021)

gerritv said:


> I personally would drill a new 4 bolt pattern in the back plate, carefully aligned inside the 3 hole pattern; you need to consider the overall balance of the assembly when spinning at 2000 rpm. Also if you inadvertently mess up the backplate the replacement cost in not as high.


Not thinking this would be the case with my lathe:  The backing plate is a solid piece with the spindle.  





The question of balance is a good point.  Was thinking about it, but didn't come up with anything.   Filling the unused holes with a "headless bolt" should help with the out of balance issue.  Something to think some more about.


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## whydontu (Nov 2, 2021)

Forest for the trees? My guess the big offset hole in the spindle mounting flange is going to have more balance effect than a couple of unfilled bolt holes. However, headless bolt? Busy Bee B2227 uses 8mm fasteners, a few socket set screws would do the trick.

 I use these, but I’m sure you can find them at other sources:









						McMaster-Carr
					

McMaster-Carr is the complete source for your plant with over 595,000 products. 98% of products ordered ship from stock and deliver same or next day.




					www.mcmaster.com


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