Thread: chuck weight size holding capacity ?

I'd do that with out giving much thought to it. 220mm dia in a 200mm chuck, Your only 10mm per side over the diameter of the chuck. With the jaws reversed, you still have a ton of adjustment screw holding onto the jaws. So you can grab it tight.

If you work piece can afford it, the one thing I'd do is face one end and clean up the O.D with a skim cut, first. Then turn it end to end to hold. That's no scarier than drilling a centre in, then you can face the end with tailstock support. It doesn't even have to be all the way across the face, just a big enough land to fit in your jaws. The O.D cut only needs to be a little longer than the depth of your jaws.

And once again, if you can get away with it, I'd turn a land, back close to the jaws, so you can use that to indicate off, when you end for end it.

A faced end going into reversed jaws is always better than a saw cut end, as the face bears on the jaws as well.

As you are only doing a 40mm bore. Most of your work is going to be drilling. Nothing is likely going to happen there as its pretty much all axial thrust, pushing the work piece back into the jaws.

Regards Phil.

I would do it and don't see a problem, make sure it's tightened up properly though.
To set it up bring your tailstock up to the face so it doesn't fall out while you dial it in.
As long as you keep the rpm down I don't see a problem with the lathe turning it, are you using HSS for the boring? In the situation it would probably be better as it will give a good finish at lower speeds.

Dave

Hi Lather,

What's the worst thing that can happen? It could grab and spin the work in the chuck, it's not likely to jump out and whack anything.

Still, I'd go slow and keep the speed reasonable.

Regards
Ray

As Phil says. I would additionally check, how many teeth of the chuck jaws engage with the scroll. If only two, be careful not to over-tighthen. If only one..... you really risk breaking that one jaw tooth out when tightening for such a heavy workpiece. Chris

Thanks for the tips,

was able to order 200mm o.d., 95mm long, 130mm was way more than needed, the weight is now around 24kg.

checked the swing over the cross slide, 220 is the limit on the stock lathe, though due to having modified the cross slides floating nut system ( which caused too much play) have lost about 6mm swing over the cross slide.
still need to counterbore the cross slide so the modified flanged dowel that bolts onto the brass nut sits below the level of the slides surface.

Originally Posted by Dave J

I would do it and don't see a problem, make sure it's tightened up properly though.
To set it up bring your tailstock up to the face so it doesn't fall out while you dial it in.
As long as you keep the rpm down I don't see a problem with the lathe turning it, are you using HSS for the boring? In the situation it would probably be better as it will give a good finish at lower speeds.

Dave

how tight is too tight, e.g. is the chuck key size (leverage) designed so that the chuck can't be damaged when tightened by ones full strength ?
whats a reasonable ft-pds torque for chucks ?

Originally Posted by lather

how tight is too tight, e.g. is the chuck key size (leverage) designed so that the chuck can't be damaged when tightened by ones full strength ? whats a reasonable ft-pds torque for chucks ?

I get into a lot of engineering companies. Often I'll see a 2 - 3 foot lenght of pipe on the headstock. Cheater bars.

I've never had the need. The small chuck key intended for my 3 jaw. That probably has a 10" handle, but its peened so it stays centered. But the one for the four jaw, has a handle probably 14 - 16" long, and its a sliding fit, much like a sliding 1/2" drive Tee handle.

I've never seen a maximun torque specified for a chuck. I'd almost take the lead from the chuck keys that have been supplied. A good rawnch on those with out doing in a foofer valve, thats tight.

I think you can almost tell by watching your indicator when you are dialing it in.If it still seems to move easily enough thats not tight enough. If it wont move and you have to back off an opposite jaw, thats getting tight

Phil.

Originally Posted by lather

how tight is too tight, e.g. is the chuck key size (leverage) designed so that the chuck can't be damaged when tightened by ones full strength ?
whats a reasonable ft-pds torque for chucks ?

There are no "torque specs" for this. It is left up to you to choose how you want to use or abuse your chuck. You got to balance how long you want it to last, versus your needs right now. The workpiece may be more worth than the chuck - if you need it to quickly make an urgently needed spare part for a harvester during harvest, the chuck may be utterly irrelevant pocket change.

If you buy a top quality 3 jaw chuck of say less than 0.05mm repeatability, you will know how how many days you had to work and save to pay for it, and you will no doubt look after it well. Overtightenig it a few times on one job is enough to ruin its accuracy forever, and reduce it to a cheap utility chuck! You certainly would not use it in a case where you have to ask yourself the question that you are asking us above.

I am assuming what you have is a low cost chuck, as they come standard with Chinese lathes. That is the right chuck to use when you are not sure, it's the chuck to learn what is ok and what is too much tightening. It will remain useful to clamp the "rough" stuff, like hot rolled steel rods and raw cast, long after the day you buy a more accurate chuck, or two.... large and small. There is always a need for an expendable utility chuck to clamp that odd chunk, or to part off some spacers. Not everything needs to be accurate.

Personally, even with an expendable chuck, tightening it full strength with its key is TOO much. Something is not right if you have to do that. Wrong clamping technique, or wrong chuck for the workpiece, or too much overhang etc etc. Chris