What are the limits on length when turning bar stock
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  1. #1
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    Default What are the limits on length when turning bar stock

    I need to turn an accurate end on a long piece of 3/4” bar stock on my 10EE. If the bar stock is supported by a 2J collet a couple of inches from the end, how long can the bar be without potentially causing damage to the collet or the spindle bearings? I.e. at what length do you need an outboard support?

    I’m open to the idea of making something to support the bar stock at the back end of the spindle. I haven’t seen any commercial collet systems or chucks that attach to the rear end of the spindle, but it seems like it would be a pretty simple thing to make, e.g. a bushing that is a tight fit to the spindle, possibly with setscrews to adjust concentricity.

    Another possibility is to make my own outboard support. Can it be simple? e.g. a tripod made from pipe with an adjustable V-support, like the one I use for my cutoff saw? If you have any pictures of a stand you like, please post them.

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    I've seen something like the tri pod setup, but they mount lathe's steady rest to it. Or a steady rest from something else.

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    Had about 2 ft of inch thickwall tube out the back of my Smart & Brown 1024 last week. Wobbling about as much as I'd care for but not rattling. A fair while since I had 3/4 bar out the back but maybe 18" would be quite enough without support.

    My support system for collet held work uses bored to size plastic bushes about an inch long held onto the back end of the collet draw tube by a permanently fitted flange with a large nut from the plumbing rescue department screwed on. The nut has an internal flange to hold the bushes against the fitting. Needed half a dozen sizes over the years. Made from nylon, delrin or whatever else is in the offcuts department.

    Within reason it works well enough with all stock I have room to feed up the collet. Say 4 ft ish so maybe 3 ft out back in larger sizes fitting my 5C collets. Will make another for my spindle if the need arises. 15 years and counting!

    Clive

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    I have a few different turned to size PVC tubes that I use. When a long piece is hanging out the back of the spindle, I just run a piece in the entire length. I'll use one inside the other if need be. Its quick, holds my stock tight and is cheap. I feel safe with it a good 24 inches past the spindle end. If its longer than that then you'll need a support stand. Don

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    simple thing to make, e.g. a bushing that is a tight fit to the spindle, possibly with setscrews to adjust concentricity.
    A bush from anything (hardwood, plastic) that fits the bar and the spindle bore back there has worked for me over many years

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    Quote Originally Posted by Don's Engine View Post
    I feel safe with it a good 24 inches past the spindle end. If its longer than that then you'll need a support stand.
    For those who are smarter than me, at some point the length sticking out the back reaches a point where it suddenly becomes a one-bladed propellor spinning at 1000 rpm.

    It'd hurt if you walked into that ... or were standing there when it suddenly decided to do that 90* bend.

    2' sounds good to me, much more than that maybe not

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    Quote Originally Posted by EmanuelGoldstein View Post
    For those who are smarter than me, at some point the length sticking out the back reaches a point where it suddenly becomes a one-bladed propellor spinning at 1000 rpm.
    3 ft of 3/4 nylon showed me that trick.

    "Look Dad I can almost touch the floor!"

    Once was enough thank you.

    Clive

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    Quote Originally Posted by Gobo View Post
    Maybe the tripod setup is not the best plan;

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    Thanks for the suggestions, Clive, John and Don. A plastic bushing it is, maybe with something on the end of the spindle to stop the bushing from walking out.

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    Be extremely careful to avoid whipping. I got to investigate a fatality due to it. Employee was working alone on Christmas Eve and chucks a 1-1/4” bar of stainless with about 3ft hanging out the back of a CNC slant-bed lathe. The victim was found bled to death with his arm ripped off. Nobody knows exactly what happened, but the theory is that the victim tried to grab the bar before it bent to the full 90 degrees. Nobody knows why he was working on the bar, because it was not standard production. The back end of the lathe was quite trashed and the machine ended up being scrapped.


    Sent from my iPhone using Tapatalk

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    For my Hardinge DSM-/DV-59 I have successfully used an ad-hoc outboard support made from one or two V-stands for pipe and a length of DOM tubing with slightly larger ID than my bar OD. Lashed the tubing to the V's, and lined it up with the spindle bore by eye. No issue with bars 6' long (fully enclosed in the tubing) and 1500 RPM. "Slightly larger" maybe 1/4", no more than 1/2".

    Notice that in that video, the bar is not even touching the roller stand. Totally different situation than being captured inside a tube, the tube being bound securely to one or two 50 lb tripod stands.

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    If you're careful with the speed you can have plenty of stickout. I once had to part off a bunch of small 1026 DOM (needed *all* of it) and so I ran whole sticks with the outboard end supported in 2x4s with holes drilled then held up on saw horses. You just have to be careful with the speed and patient.

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    First off unsupported and contained shafts sticking out of the back of the headstock is a huge safety issue for many reason, but mainly that the bar can start to whip. Operators have been killed and machines destroyed by doing this. Look up critical speed of rotating shafts and you can figure what safe speed you can run a shaft of certain diameter and length. When supporting the shaft it needs to be support like a steady rest supports shafts.

    You might consider removing the tailstock and supporting the shaft with the steady rest, and depending on the length of the shaft the unsupported length might be acceptable speed you need to turn it.

    Most of all research and plan out how to turn you shaft safely.

    John


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