Lathe Chucking Depth

[MaverickNH]

On my 4in-4jaw 7x16 lathe chuck, the inside jaw depth is about 1-3/4” from from front jaw face to back. When chucking up round stock, would I be thinking right to figure pushing a workpiece further back than the rearmost jaw contact point gains nothing as far as grip strength and alignment accuracy? I’d be using a cut-off saw to make a workpiece 2” longer than the outer chuck jaw face for my project, and want to “waste” minimal 1” brass round stock.

From the other perspective, what’s the minimum chuck jaw contact that is advisable for safe holding and accurate alignment? I’m sure there are factors involved (jaw pressure, material, lateral cut depth, tool pressure, etc.) but is there a “rule of thumb” to consider, like 1/2 the jaw length?

On an outside jaw configuration on this chuck, the length from the back of the jaw step to the front of the contact area is ~5/16”, so that’s a given.

Plenty of basics to learn as a newbie!

BRET

 

[RJSakowski]

I like to minimize waste as well. Here is another thought. If you make the stock longer than necessary, your waste piece will be suitable for another project whereas a 1" piece of waste will be less likely to be useful. I will either cut the stock so I can insert it as far as possible into the chuck or cut it for around 3/4": to 1" engagement in the chuck jaws. The length left over from the original saw cut also plays in.

 

[RickKr]

I agree with RJ. Or, depending on how long it is, maybe not cut it all. If a piece isn't going to stick out the back side of the spindle, sometimes I put the whole thing in there. It will wobble, but the spindle contains it and depending of the diameter/mass of the stock and beefy-ness of your headstock, doesn't affect much.

If I'm concerned about the stock wobbling in the spindle, I insert spacers along the length to help keep the workpiece centered and not flopping around in there. Case in point is bamboo rod making, where I need to turn the ferrule stations on the butt ends of tip sections, or the butt end of butt sections for the reel seat filler. I previously lined the spindle with 1" ID PVC pipe and then slide cork rings (used in making the grips) that have been reduce in diameter to match the PVC pipe along the rod section at about 1 ft intervals to keep it centered and stable. When a workpiece sticks out of the spindle at the rear, it gets supported/captured by a workstand of some sort, otherwise it will whip and disintegrate. Had that happen with the PVC pipe liner, before I shortened it - er... it got shortened...

 

[MrWhoopee]

Every situation is different, but just as a general rule, I would try to have an amount equal to the stock diameter held in the chuck. As the amount in the chuck is decreased, the leverage exerted against the jaws increases, forcing them to cock outward and reducing the contact area. If I am making more than 1 part, I will "double-end" it. Cut the stock long enough to make 2, plus enough for cut-off and facing. Make the first part, flip, make the second, then part off.

 

[markba633csi]

You want as much jaw contact as possible and as little "stickout" as you can manage consistent with not springing the jaws or having the part tear out of the chuck and perhaps breaking the cutting tool. Experience will show what you can get away with but it's sometimes hard-earned.
I go "out on a limb" fairly often but I know what the limits are on my machine. You can take more risk if you are only taking light cuts with a sharp tool.

 

[RaisedByWolves]

You want as much jaw contact as possible and as little "stickout" as you can manage consistent with not springing the jaws or having the part tear out of the chuck and perhaps breaking the cutting tool. Experience will show what you can get away with but it's sometimes hard-earned.
I go "out on a limb" fairly often but I know what the limits are on my machine. You can take more risk if you are only taking light cuts with a sharp tool.

Put the feral kid back, lou Reed looks horrible in that pic.

Then again, who am I to talk, Im coming from the Netherlands today.