Chuck help

[rafe]

I've done that too and not out of laziness but out of necessity.I had a 3 jaw for my SB but no 4 jaw at that time, however I did have a 4 jaw off of a small atlas that I made a threaded shaft for and it worked perfectly for what I needed to do on more than one occasion , I have since gained a nice 4jaw and it usually stays on until I have to use the 3 jaw ...well not have to prefer to

 

[Walt]

Are you sure of that?

I'm have no actual experience to draw on, but if what you are saying is true, how can a 4-jaw chuck be used to compensate for runout in the first place?

 

[kd4gij]

My, you ARE lazy! The problem with this is you cannot gain the major advantage oif the 4-jaw over the three-jaw, being the ability to center the work dead-on. The setup you have pictured will suffer from any TIR of the three-jaw no matter what you do to center the work in the four-jaw. A lazy setup, yes, brilliant, no. :nuts:
Really now, how difficult is it to thread the 3-jaw off and thread the 4-jaw on???

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To answer the original question of how big a chuck will fit, the answer is in how big a chuck is practical. An 8 inch diameter chuck is the limit of practicality on these lathes, be it a 3-jaw, 4-jaw, or 6-jaw. Anything bigger than 8" in diamater will be grossly excessive.

A 10" diameter 3-jaw chuck with an appropriate backplate will weigh about 60 to 80 lbs and will be gripping the work several inches out from the end of the spindle. This will amplify any TIR in the system and will detract from the accuracy oif the lathe.

The abor the 4 jaw is on was made in that 3 jaw. It is stamped for jaw 1. The runnout on the 4 Jaw is less than .001. The job at hand was a 2min job bore a 1 1/8 off center hole to 1 1/4" for the boring bar you see in the pic. For bigger jobs the 4 jaw gets screwed on the spindle. That 8" 3 jaw is to havey to take off for what I was doing at the time. Works for me.

 

[wa5cab]

OK. Makes more sense, now.

On the root issue (chuck weight), do you have a way in which to hold the 8" chuck when you install or remove it? If not, and if the chuck weighs too much for you to comfortably support with one hand as you remove it but not too much for you to pick up and carry (NOTE: in the latter case, the chuck is too heavy for the spindle of an Atlas), here's a cheap and dirty solution.

Get a piece of 4X4 wood (treated fence post works well) and cut it about 4" to 5" longer than the width of the ways. Run the chuck jaws into the center and out of the way. Place the 4X4 on the ways and center it up front-to-back. Slide it up against the face of the chuck, hold it there firmly with the right hand, and with the left hand and a pencil scribe the arc of the OD of the back of the chuck body onto the side of the 4X4. Cut the arc out with your bandsaw and clean it up a little with sand paper. Place the 4X4 on the ways and slide it under the chuck. If too tight, thin the 4X4 a little with your belt sander.

To use, slide the 4X4 under the chuck and unscrew the chuck until it is clear of the spindle. Slide the 4X4 a little way down the ways and then lift it and the chuck using both hands. Hold it against your chest so that you don't dump the chuck onto your toes as you walk. To reinstall the chuck, reverse the process. A good application of paste wax on the arc in the block will help keep oil from soaking the top of it but not rub off onto the chuck during use as paint would. Same for the bottom that slides on the ways. You can paint the sides and ends. If you want to get fancy, cut about 2-1/2" height out of the part of the bottom that doesn't slide on the ways. That will reduce the top-heavy problem when carrying and reduce finger-pinch probability.

Robert D.

 

[kd4gij]

Thanks Robert

I do have a cradle like that to help when changing the chuck. For a quick simple job the 4 jaw works just fine as in the pic. It does get mounted on the spindle for real work. I was just enlarging a offcentered hole on a rectangle block witch is theboreing barr holder for mmy qctp. took all of 2 min. not worth swaping chucks twice for. Just another way to skin a cat.

I didn't mean to hijack the op's thread. Just posted the pic to show that an 8" chuck works fine on the 12" atlas craftsman lathe. Chose that pic becouse it showes the size deffernce between 6" and 8" chuck.

 

[wa5cab]

That makes sense.

RD

 

[Andre]

By the way, I recommend a 4 jaw scroll chuck. More gripping area than a 3 jaw and you can grip square stock. And I know what your thinking......but you can grip hex in a 4 jaw!