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Using a metal lathe safely


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Hi Folks,

Last year I purchased a pair of brass pedestals for my Smuggler project.

They were turned on a lathe at the factory but the surface was very rough so I decided to polish them on my mini metal lathe.

I tried three setups, two of which turned out to be unsafe, so I've decided to share my experience.

The first setup was the most unsafe.  The three jaw chuck has it's jaws protruding slightly.  Also, the live center isn't touching the workpiece so it could come off the machine and fly around the room

I immediately got whacked in the middle finger on my left hand right on the tip of my finger.  If that wasn't bad enough, I play guitar and bass all the time and my fingers are sore anyway.  Thankfully, there was no blood or broken bone. 

The second setup was better but still not perfect.  I was still using the three jaw chuck, but reversed the jaws so they didn't protrude as much.  Also, I used a piece of threaded rod to secure the workpiece.

The third setup is the best.  I used the threaded rod as in setup #2 and used a jacobs chuck which is much smaller.

The bottom line is: think through your setup, turn the machine over manually before turning it on to identify any dangers, run it on the slowest speed the first time.

In the end, my pedestals look great, but I could have injured myself in the process.

Be careful with your power tools!

Jamie

 

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Edited by Jamie Peghiny
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I'd advise a little caution in using a drill chuck to hold a workpiece in the headstock of a lathe.  Such chucks are not designed to take lateral forces and could result in either inaccurate work, or worse, failure of the chuck, if overloaded.

 

If you cannot mount it securly in a 3 jaw chuck, then use a 4 jaw, failing that, a centre plate.

 

The same would apply if trying to carry out a milling operation in a pillar drill.

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Using a 4 jaw check would have been a better option from the start. But like the person also said, it is best to think things out before hand, and if possible try and do it on a practice piece first, which he wasn't able to do with this project. Look on the web would also help in trying to figure out the best way, and then last but not least when you are not sure "ASK HERE OR ON THE WEB" and someone is sure to post the way to do it. The project in hand was not something that needed to be done right at the moment so you could have waited to see if someone would have replied back with an answer. It is good that you didn't get hurt with the first setup, someone must have been looking out for you. I have been lucky in the past with some thing I have done on a wood lathe, and later when I really look at the way I did it. I ask myself why did I take a chance doing it that way when I know better, but we all learn and sometime we learn the hard way. I been lucky in things I have done.

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I agree with what was said above, a jacobs chuck is fro drilling, which only involves axial forces, not for turning, which involves mainly tangential forces.

 

Your second set up is the one that would normally be used in turning. A general rule is that a part should only protrude 3x the diameter, if unsupported by a tailstock. If the part is longer, one should center-drill it and use a life or dead center in the tailstock to support the outboard end.

 

Personally, I am not so fond of 3- (or 4-)jaw chucks because of the risk you mentioned, namely to be caught by a jaw. Most turning work I do with collets. On the other hand, if you keep your hands well off the headstock, you should be ok.

 

wefalck

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In theory, a 4-jaw chuck can be centered perfectly. In the above case this would be an overkill. The pillars on which a model rests are not really pieces of precision machinery. The issue of centering perfectly is only really relevant, if you have to say turn a piece in the chuck to machine the end that was originally in the chuck, or if you have pre-cast holes or something like that.

 

Otherwise, the procedure of centering is just like that: centering by eye, turning slowly (perhaps with a dial indicator touching the piece), losening one jaw, tightening the opposite, turning by hand, and so on. Very tedious. I very rarely use a 4-jaw chuck for turning round material.

 

As I said, collets are really the best option for our purposes. Unless you really do high-precision machining, collets allow you to re-chuck material. There are also now jaws sticking out. The downside is that the maximum diameter is rather restricted, depending on the size of your lathe.

 

wefalck

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Grant,

 

I thought about that too, but the price put me off ($80-100.00US). -I saw a cheap Dial Indicator at Harbor Freight for about $15.00US.

 

And yes, you get what you pay for. But this one seemed to have pretty good reviews, and will probably be good enough for me. It will beat using a lathe bit on the toolpost to center the chuck.

 

Thanks,

 

Harvey

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Well try Grizzy.com for some of your stuff, used them for years. One step (I think) above harbor freight but still low cost. Check this out for dial indicator and base. $19.50

 

http://www.grizzly.com/products/Magnetic-Base-Dial-Indicator-Combo-President-s-Special/G9849

 

That said, happy that all is ok enough for you Jamie to be able to type in your warning to everyone. That's good!!

 

Wow where did you find the old Unimat? That's cool, a great tool that was rebuilt into a interesting piece of plastic "stuff" with a little metal of course. Unless they have redone the line in the last few years of course. Enjoy that unimat and don't try to hurt it with your fingers again, those unimats can only take so much. Keep your fingers out of them and they last longer LOL.

 

I guess that I should note that I just walked away from making a pile of aluminum shavings with my sherline lathe. Spent the last hour resizing a piece of bar stock while working on finishing up a sander that I started a few years ago. Someday I'll finish that sander. Need the sander for the wood for the HMS Triton cross section that I'm trying to start.

 

Later 42rocker

Edited by 42rocker
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A self-centering 4-jaw chuck is only useful, if you work a lot with square bar stock. It does not replace an independent 4-jaw chuck. The point about the independent one is, that you can center round, square of rectangular material to any point with (near) zero run-out. With self-centering chucks you are at the merci of their production tolerances (which can be pretty large for stuff in the 100€/$/£ price range).

 

wefalck

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For precise centering with the 4 jaw chuck you do need either a dial indicator or a "wobbler", I'd opt for the former.  However, for ornamental turning you may well be able to get away with using a centre in the tailstock as a guide.  You will need to know where the centre is of the workpiece is, this is easily determined with a circular item, forgive me if you know already how.  Measure the diameter of the item, then set the radius onto a pair of spring dividers.  Touch one point to the workpiece edge (anywhere) and carefully (this can be fiddly) scrib an arc, repeat this a further two times and there the lines bisect is the centre.  Then put the item in the chuck, slide up the tailstock and carefully adjust the jaws until the centre point is on your determined centre.  This will be fine for ornamental work and even forms a good starting point for using the DI  for the final set-up on more precise work.

 

Self centering 4 jaw chucks are nice to have, but their use is limited and an independant 4 jaw chuck does everything they can, and more.

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