Help - Machining slim rod on the lathe

[Wongster]

Hello guys,

I've not been doing much for several months now. With the market quieten down, I may be back in the shop more often.

Recently, a foreign student doing his PhD in Singapore approached me to help him with some small parts for a micromouse. The initial parts are rather simple; enlarging a couple of gear hubs and turning down small sections of a steel pin that act as wheel shaft he bought off the shelves. Due to some amendments in his drawings, he is asking if I can help him to fabricate the shaft according to the new requirements.

This is how it supposed to look like:



The ideal metal to use would probably be stainless but I'm testing with aluminium at the moment.

Ok, after boring you folks with the background: how should I go about turning this? I would be starting with probably a 100mm long piece. From my past experience doing a similar job which I didn't quite complete, the stock would flex like crazy, even between centers. I tried using the follower rest but don't know how to go about with 2nd and subsequent passes.

Appreciate any sharing of how you would approach this.

Have a blessed day.

Regards,
Wongster

[EdK]

It depends on the accuracy you need but I would get some 4mm stock, maybe drill rod (bright steel), and chuck it up in a collet and turn the ends. Or you could make a quick and dirty tool post grinder with a Dremel type tool and grind the ends to diameter. I'm sure the experts will chime in and correct my errors.

Ed

[Wongster]

Thanks Ed. You're right. Getting right size rod and just machining the ends would make more sense.

Regards,
Wong

[Mayhem]

Hi Wong,

You adjust the follow rest prior to each cut and take a second pass every now and then without increasing the depth, to try and counter and flex. Each end will need to be done in a 4-jaw chuck to decrease the risk of them being eccentric to each other.

[stevec]

That seems more like "wire" to me than "shaft". Why would you start with a 100mm piece?
I'd start with a 70mm piece of 4mm stock, (approx. .157" Dia. for our U.S. buddies) and machine the ends with the material projecting from the chuck (or preferably collet) as little as posible. If the 3mm x 8mm (.118" x .315) ends are actually to be drilled and tapped M2.50 (.098") I would say it's an impossible job.
The 3mm Dia ends tapped 2.5mm would have a wall approximately .25mm ( .010") That's feeler gauge thickness!

Boy! alotta people posted while I henpecked out my response.
Did anybody consider the size? Mayhem what size 4 jaw chuck would hold 4mm D. rod?

[Mayhem]

A small one Steve This is where a little lateral thinking comes in and I should have elaborated...

I know my 400mm 4-jaw won't touch anything below 25mm, so if I needed to do that I would turn up a split bush and grip it that way. As you say, a collet would be the way to go but not everyone has those.

[Wongster]

Thank you all for chimming in.

Steve, the 100mm was because I started the trial piece with a 9.6mm dia aluminium rod which I have available. One end went into the jaws of the 4 jaw automatic chuck (or is it called scroll chuck?) and the other end on the revolving centre. I'll get hold of 4mm dia SS to ease the process. On the M2.5 he wants at the end of the 3mm dia section, they were on the off the shelves axle he bought. I don't know if it makes sense at all as I read that the tap drill for M2.5 is 2.05mm. With the threads cut, it does leave a very thin wall... I'll give him that feedback to see what he says.

Mayhem, what I can't get in my thick skull after I tried using the follower rest on the sherline a couple of years back is the setting of the "fingers" after a cut. The "fingers" will hit the shoulder created by the previous cut. If I do a series of cut, I'll have several steps around the thickness of the "fingers". I think I may be using the follower rest wrongly. Yet to take the follower rest for the Proxxon lathe out of its box except for photo taking when the lathe first arrived...

Regards,
Wong

[stevec]

Wong, usually 4 jaw chucks have independently adustable jaws, Three jawed chucks employ a scroll that moves the jaws simultaneously. I have no idea what your "automatic" chuck is. A pic would be interesting.
I have never been able to maintain precision using a follower rest. Actually both my lathes follower rests attach to the headstock side of the saddle so if used for normal turning (toward the headstock) they should be called leader rests, not follower rests.
I'll wager that Brian of "minimal clockmaking" would have some opinions/advice.

[Wongster]

(03-14-2013, 10:34 AM)stevec Wrote: Wong, usually 4 jaw chucks have independently adustable jaws, Three jawed chucks employ a scroll that moves the jaws simultaneously. I have no idea what your "automatic" chuck is. A pic would be interesting.

Steve, it is a scroll chuck with 4 jaws. Mine is a Rohm. Got to know that there is such from Sherline. I've never taken it apart and so won't know what to show in the pic. Will try to figure it out and post.

[stevec]

Wong, well I learned something new today, I'd never heard of a 4 jaw scroll chuck, 3 & 6 yes.
Does it look like this?
http://us.roehm.biz/typo3temp/pics/IM000...b2127e.jpg