Author Topic: would this be an acceptable way to mount small work pieces in a lathe...?  (Read 6660 times)

Offline jonogt

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I'm just getting into machining, and one of the things I've found sort of annoying is that quite a bit of the material is unavailable for turning because the chuck is in the way.  This is only an issue for me because I'm on sort of a budget and only want to use the amount of material I'll actually be turning. 

what I have in mind is getting a piece of steel stock, like 1" dia by 8" long, and turning the front half of it down to where I can put standard half inch male bolt threads on it.  When I want to turn a part, I'll put it in the chuck and drill/tap it for matching half inch female threads.  Then I'll just put the male threaded piece I made in the chuck and screw my work piece on to it.  Since I drilled it on the lathe it will be true, the direction of the threading will keep it tight, and the only waste will be the short portion that I drilled and tapped.

The setback I can think of is the work piece might get screwed on excessively tight, but this could probably be remedied by putting a rubber grommet or something in before screwing it on.

What do you guys think?

Offline Bernd

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #1 on: February 24, 2009, 09:33:37 PM »
jonogt,

Have you ever heard of the term "turning between centers'?

This method allows you to used the length of material that is required by the job. What you need to do is to center drill both ends and then put the part between centers in the lathe to turn you part.

This is just one method. You will probably get many different answers here.

I realize that it may be difficullt to visualize what discribed above so will do a set up and take some pics. Check back in a day or so.

Bernd
You can't fix "STUPID".

bogstandard

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #2 on: February 24, 2009, 09:48:47 PM »
Hi J,

That is perfectly feasible, and I think a method that wood turners have used for a long time.

The only problem is accuracy. Unless you use a collet chuck system or four jaw independant chuck and clock, every time you reinsert your mandrel back in a three jaw, it will wobble slightly, because you can never get it back in exactly the same position it came out from.

Also, for perfect concentricity of the original threaded hole for the stud, it would need to be bored and single point internally threaded. There are a few easier ways to obtain a concentric screw thread sticking out of a block of metal.

Maybe if you really wanted to go this route, remove your chuck and purchase a blank end arbor to fit into your spindle nose (very cheap), then drill and thread that for holding the parts.

There is another way, and that would be to buy a set of soft jaws for your chuck (if you can get them for your chuck, they are not too expensive). These allow you to bore a very shallow but high grip recess for mounting thin or short parts, and is a very easy way to obtain super accurate tolerances on very thin or short parts. I use this method a lot, and if you precut your piece parts fairly accuratley to begin with, very little wastage.

John

John

Offline jonogt

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #3 on: February 24, 2009, 10:11:05 PM »
thanks for the replies guys,

Bernd I think I mostly get the idea... the workpiece is basically "pinched" between the tailstock and headstock in a position far enough from the chuck that the tool has full length access to it, right?  I assume the tailstock end would be held by the live center?  But what holds the headstock end?  Is it a mandrel similar to what I described, but with more of a spur deal instead of threads?

now that you've mentioned the concept, I have seen parts in the shop that look like they may be used for this process.

am i on the right track here?


Offline Bernd

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #5 on: February 25, 2009, 09:54:30 AM »
J,

John has found an excellent explination of what I mean. And you were very close to the answer. A dead center is used at the headstock end so it revolves with the spindle and a driver is used. But you need to center drill both ends first.

Thanks for finding an answer so fast John.

Bernd
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bogstandard

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #6 on: February 25, 2009, 11:38:38 AM »
Bernd,

Rather than trying to interfere with your post, it is easier to direct to a web description. Then the person gets the answer straight away.

John

Offline jonogt

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #7 on: February 25, 2009, 02:16:56 PM »
Does this
http://www.jjjtrain.com/vms/lathe_functions/lathe_functions_11.html
portray it correctly?  The images in bogstandard's link look like they match this, but I havn't seen any mention of using a catch plate and lathe dog yet.  The procedure i'm visualizing is:
-> Chuck up your work piece and center drill each end,
-> Remove the chuck from the headstock,
-> Install the dead center and catch plate (or face plate with appropriate bolt holes),
-> Slip the lathe dog onto your work piece and mount it between the headstock's dead center and tailstock's live center,
-> Put the lathe dog in position to solidly contact the catch point on your catch/face plate,
-> Tighten the lathe dog's set screw against your work piece and firm up the pressure being applied to it by the centers.

* Slots would be used instead of bolts in holes if using a bent-tail lathe dog *


Is this correct, or is there a way to do it without the lathe dog and catch plate?  Is it standard for face plates to have room in the middle to install a dead center?  Is there any way to do this procedure with a 3-jaw chuck instead of a face/catch plate (for the sake of not having to change them out)?

thanks again for the help
-Jon

Offline sbwhart

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #8 on: February 25, 2009, 03:32:15 PM »
John

To do it in the three jaw all you have to do is turn up a dead centre in your three Jaw and drive the carrier off one of your Jaws.  :thumbup:

Stew
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Location:- Crewe Cheshire

Offline jonogt

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #9 on: February 25, 2009, 06:45:42 PM »
sounds like a plan  :clap:  The turning i wanna do in the near future will be almost all brass and aluminum, so do you think I'd be fine just making it out of pretty cheap mild steel, or should I get something tougher?

Offline SPiN Racing

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #10 on: February 26, 2009, 02:12:53 AM »
My two cents from someone who has ZERO experience before the last 6 months or so.

Im not sure what you are making..... But I have spun several different types of metal with no experience beforehand other than a vague notion. And what I found out is this:

Stainless Steel, a bitch to Turn and get smooth when you are new. (like me) (But Im stubborn so I do everything I can in it.. and Im getting better)
Regular Steel, Easier to turn, will turn smoothish.
Iron.. like cast. Easy to turn smooth.. not shiny.
Aluminum.. easyish.. but its softer, so it can be easyish.
Brass... turns like hard balsawood, or something. And is REAL shiny if you are a little careful. Easy to turn.

In my small experience turning relatively thin metal.. that is hard.. Like a rod of 316 Stainless that is 1/4 inch diameter, 6 inches long, and trying to get fancy with it is difficult, as the metal deflects. So... keep things like that in mind.

Im in no way an expert. But its what I saw from a very new guy perspective. And I am certain I dont always turn the right speeds etc. I am becoming more and more aware of the how simple things are.. yet how many incredible variables there are to cut a piece of metal properly.
SPiN Racing

Offline sbwhart

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #11 on: February 26, 2009, 03:15:55 AM »
John

The dead centre will be fine out of mild steel, it's doing nothing just sitting there supporting the stock, the dead centre at the other end has to contend with friction from the rotating stock and needs to be hard and lubricated with a bit of grease, or better still get yourselve a live centre, that rotates with the work. :thumbup:

You havn't said what sort of tools your going to use, for what your planning to do I'd suggest you just use High Speed Steel  HSS you can get hold of square and round blanks of this stuff quite easy from the suppliers, and its very cheep,  and grind your own tools up, some where on the Forum there should be some information how to do it, you'll learn a lot by grinding your own tools don't be afraid to experiment a bit angles and radiuses on the tools it'l show you what works and what doesn't.

One safety tip always wear safety glasses,

Have Fun

 :wave:
Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire

Offline jonogt

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #12 on: February 26, 2009, 12:54:18 PM »
ah yes i should we have a few HSS ones that are more specialty shapes (i beleive some are for boring) but I havn't looked at them much.  All my access to this stuff is in my college's student shop, in case it seems weird that I have all this stuff with little clue what i'm doing.

SPiN racing it sounds like we are a bit similarly minded lol.  I've approached most tools for the first time with little more than youtube videos and internal monologue logic on my side, and after I'd done a few successful operations without maiming myself, I figure out the finess of it thru trial and error.  i havn't lost any limbs or extremities yet, so I guess it works allright.  Most past experience is woodworking though, and I'm being a lot more inquisitive with this machine stuff because i know it can mess you up bad (and they revoke student shop privelages if you mess somethin up  :wack: )


sbwhart, there is a very nice live center available that i'll use, so that won't be an issue. and yes I always have some safety glasses on when playin with this thing.


the only specific thing i'm planning on making right now is a model steam engine... other than that i'm just wanting to learn how to do this stuff properly.  i'm sure i'll have other project ideas stem off in the process (-:


Offline sbwhart

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Re: would this be an acceptable way to mount small work pieces in a lathe...?
« Reply #13 on: February 27, 2009, 04:24:55 AM »
Hi John

Looks Like your getting some good guidance from your college, look forward to seeing the progress on your steam engine.

Cheers

and have fun

Stew
A little bit of clearance never got in the road
 :wave:

Location:- Crewe Cheshire