4" or 5". 4 jaw chuck for 7x12?

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Douglasr

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Which independent jaw chuck would be most useful on a 7 x 12 HF mini lathe? Opinions anyone, I am getting ready to purchase one of the two from LMS. I know the thru hole, on the 5", is a little bigger but it also weighs more. Being a newbie, is there a significant benefit of one over the other if you could only have one? Thanks
 
I bought the 4" independent 4 jaw with backing plate from LMS and it seemed huge on my mini lathe. I wound up sending it back because the adapter plate wasn't balanced properly and I could only cut at verry low RPM or my lathe would be dancing all over my bench. I called LMS and Chris told me to put some metal in the backing plate hole to bring it in balance. I figured I would never get it perfectly balanced by just tossing in some metal and sent it back.

I have a bigger lathe now, but if I were to get another 4 jaw for the mini lathe it would probably be the 3" just because it would bolt right to the spindle without an adapter and wouldn't seem huge on the lathe.

Chris
 
Hi,
I use 5'' chuck on my 7X12 on a backplate I made without problem!
To avoid balancing problems, as you can see I also made holes opposite to the ones needed.

petros

PC300373s.jpgPC300374s.jpgPC300375s.jpgPC300376s.jpg

PC300373s.jpg PC300374s.jpg PC300375s.jpg PC300376s.jpg
 
I thought the 5" was a monster and wound up swapping it for the 4". I'm pretty happy with that.
 
petcnc said:
It is a sweet monster that works beautifully for me!
Click to expand...
That's a very nice backplate on your monster.:)) Did you make it of iron? Did you do any balancing?
 
LEEQ said:
That's a very nice backplate on your monster.:)) Did you make it of iron? Did you do any balancing?
Click to expand...

Yes it was made from an old iron base of a microphone!! I cut it to an approximate hexagon drilled it mounted directly on the spindle and transformed it to a back plate for the 5" (12,5 cm) cheap 3 and 4jaw chucks I bought from Chronos. http://chronos.ltd.uk/acatalog/chinese_lathe_chucks.html.
I had to drill holes both for 3 jaw (3 holes) and for 4 jaw chuck (4 holes).
For balancing I did nothing more than drilling symmetrical holes (see photo).
The goal was to make sure the weight was even around the axle of the backplate to avoid serious vibration. With the 3jaw chuck on the backplate I have practically no vibration. With the 4 jaw chuck is a different story as the chuck is only balanced when I remove the jaws or when I center a piece using the dti.

Balance.jpg

Balance.jpg
 
I am considering re machining the back of my four jaw to fit the spindle without a back plate. The one that came with my chuck is pretty darn thick. The chuck is already taking up more real estate than I want to give up.
 
Might want to consider the weight that will be hanging on the spindle bearings. Lot of metal in a 5"
 
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