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Turning Slender Journals

Started by Peaky 556, Jul 11 2020 18:38

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Peaky 556

Hello all of you lathework experts (if only, a rare breed nowadays), how would one best approach the turning job pictured?  It would be made from 5mm silver steel, and accurate parallel turning of the smaller journals I foresee to be a problem with my ancient (and well-worn) "Ideal" lathe.  Whilst I would hold the workpiece in a collect chuck and pop in a tiny centre-drill into the ends, use a revolving centre, highest speed and plenty of suds, I can just imagine them deflecting into little 'barrels'.  I'm talking of maintaining a diameter to within a hundredth.

Of course I might be predicting problems that aren't there.  Any views please?


Andy B

Tim,
A roller box and take it down in one pass.

Andy

Peaky 556

Thank you Andy, I couldn't remember the name of the tool, but neither have I ever come across one.  Do you have one?

IanT

It's quite a long slender part.

For shorter (but thin parts), a watchmaker would use a pivot runner to make 'points' at each end - and then turn it between female centres. A pivot runner can be as simple as a hardwood block with an inclined 'V' shaped groove filed in it. The work is spun in the chuck and a file used to make the point. After turning between centres, the ends are cut or filed off. On small diameters, this is much simpler than trying to centre drill the work. However, this is too long & too slender for that I think.

Box tools are normally found on capstan lathes but can also be fitted to the tailstock. They do not always have a through hole however.

I would use my "small diameter work steady" which is very similar to the design by Malcolm Wild. It's a combined toolholder and work steady, so both move together. A cylindrical guide is drilled the initial diameter of the work piece and that guides the part past a cutting tool (held at the centre of the guide hole) to make the cut immediately behind it. I've got one which (I think) was sold by Chronos at one time but I couldn't find them when I looked just now.

Hemmingway do a casting for the Myford 7 series lathes, that is a kind of small moving steady - which is very similar in concept. If you need a better idea of what mine looks like, I'll dig it out and take a photograph for you.

If you are in a hurry and cannot wait - you could also try 'inching' the work piece out of the chuck 'bit by bit' and turning it down in stages (e.g. always working with very little overhang/outstick). This works but is not ideal, although using a collet chuck helps.

If the 5mm part had been quite a lot shorter, you could also possibly have cheated and drilled it 3.2mm and then loctite'd a suitable length of rod into it - but it's far too long to be able to drill it straight with that size drill.

Hope this helps give you a few ideas!

Regards,

IanT
Nothing's ever Easy - At least the first time around.

cabbage

Tim,
Would you like to borrow my small lathe?

Regards

Ralph

Peaky 556

Hmmm...
Thanks all, some interesting suggestions there. I don't have a roller box or travelling steady
Another could be to insert two pieces of 1/8" journal into drilled holes and Loctite them in place.  Eccentricity is a predictable outcome though...
I might just try and turn in one piece in my wobbly lathe first (and might knock on your door Ralph thank you), taking the approach of dividing the journal into three distinct sections: for the wheel, the bearing, and the outboard crank.  Wish me luck!

cabbage

To me this looks awfully like SM32(?) When I was doing that I used a 1/8" stainless shaft and would bore the brass sleeve for the gears to mount on. Then I would grub screw the sleeve to the 1/8" shaft.

But then I am lazy!!!

Regards

Ralph

IanT

This video shows how to make a small diameter steady/cutter Tim. I have something similar to the commercial version he shows at the beginning.

https://www.youtube.com/watch?v=yDrXDVB1ABI

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Peaky 556

Thanks for all help.  I may be spared the embarrassment of trying and failing to make this in one piece as the client has decided to adopt Ralph's sleeve methodology by making one to fit around his own 1/8" diameter axle.  When I receive the sleeve I shall assess it carefully and see if I can build it into a gearbox for him.  Mental note: don't tighten the gearbox grubscrew tightly and distort the sleeve!

Peaky 556

Ian, regarding your later post, that travelling steady looks very useful.  The question in my mind is whether the bronze bush needs to be a very close fit on the shaft, as I'm guessing that the more rattle the worse the diameter control whilst cutting.  I also think I would need a better tool post in order to precisely get the bush on the headstock centreline.  I'd like one of the "cup and saucer" style of toolpost to give infinite control of tool height, rather than the packing method I have to adopt at the present.  There is a more pressing need however, and that is to rebush the headstock bearing and eradicate vertical freedom.  The penalties of an old lathe, I'm having to nurse it through the 21st century, having been made in the first part of the last century!

PS, I also enjoyed the follow-on video by Joe Pieczynski on one-step turning of a half inch bar down to a wire of 30 thou! :

https://www.youtube.com/channel/UCpp6lgdc_XO_FZYJppaFa5w

IanT

It needs to be a 'running' fit - allow the part to turn but not move away from the cutter. A drilled hole to match the part is usually sufficient. The guides are made to suit the job but I only have about 3 or 4 I think, I don't really use it that often.

Joe Pie is one of my YouTube favourites, he really knows what he's doing and explains it all in simple terms the viewer can understand. There are some other people on there that don't meet either of those criteria I'm afraid. 

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Jon Nazareth

Ian

That's a coincidence!  Where did you buy yours from and will it fit a Myford quick change tool post?

Jon

IanT

I'm pretty sure it was Chronos Jon.

I couldn't find it when I looked recently - and yes, it fits a QCTH and is therefore height adjustable.

Regards,

IanT
Nothing's ever Easy - At least the first time around.