Turning A Long Oval Bar Into A Round One ( Help Please )

[Round in circles]

I'm nearly finished making the mount for a fixed steady rest . The travelling one I'd hoped to mount on my lathe is too problematic for my little garage workspace tooling to solve at present .

I want to turn a 19 inch long 17 mm dia round bar from a free cutting hot rolled steel 20 mm rough blank but the blank is at least 1.5 mm out of round .

I understand about mounting the bar between the centers , having turned a couple of shortish test bars without a steady , but I due to the length of this bar I want to ensure it is not going to flex once it gets turning .

How do I used the fixed steady ?
.
Do I set the bar up between centers , turn a short section to just above above the required thickness say 3 inches from the chuck , then put the steady in place on this turned part , moving along another 3 " turn another place for the steady and doing a final one another 3 inches along .
Then turn the bar from tail stock to the chuck to the right dimensions where I'm able to do such a thing .

Finally moving the fixed steady over to a correctly dimensioned area and finish off the whole bar to size ..... or it is better done differently ?

 

[JimDawson]

What you really need is a follower rest. This is somewhat like a steady rest but attaches to the carriage and contacts the work just to the right of the cut to support the work.

from : https://en.wikipedia.org/wiki/Metal_lathe
By Unknown - Burghardt, Henry D. (1919), Machine Tool Operation, volume 1 (1st ed.), New York, NY, USA: McGraw-Hill, LCCN 20-026190., Public Domain, https://commons.wikimedia.org/w/index.php?curid=12190205

 

[Round in circles]

Thanks Jim ,
I have a follower rest , at present I can't fit it to the cross slide dovetail on the carriage as I don't have the corresponding dovetail slide or any " bolt on lips ." to do it .

Even if I did have them I'll still have to do a lot of modifying to the female dovetail slider & steady I have to get it mounted on the dovetail as the steady . Forwould be about three inches too tall for it to be any use in its present form .
Plans are afoot to chop some metal of it & locate a suitable female dovetail , for I don't want to try drilling & tapping the headstock side of the carriage & fabricating a bolt on mount to locate it there .


That's why I asked the question above ........to try and do it differently but still have a good outcome .

 

[JimDawson]

The only other thing that comes to mind is to use your steady rest. Turn a bit, then move the steady rest over a bit, then turn a bit more. You might want to loosen the tailstock center a bit while using the steady rest, but I'm not sure about that. Maybe it would be OK snugged up, a little experimenting would be in order here..

 

[kd4gij]

What is the bore of your spindle? What I have done is using the tail stock, stick the part out of the chuck 6" turn that, bring it out another 6" turn that. then flip the bar and do the same thing on the other end. once it is all turned I extend it all out use 80 grit emery to blend it all in then 120 grit to polish it.

 

[kd4gij]

Or here is a flow rest that fits a QCTP. I red a write up on here awhile back where they used this idea but modified it to use the threaded hole on the side of some QCTP.
http://www.frets.com/HomeShopTech/Tooling/MiniFollower/minifollower.html

 

[stupoty]

A tool post mounted steady like a "turning box" used on a capston lathe might be an option..

I recently made a long'ish shaft from some hot roll steel, about the same size your starting with.

I used very sharp cutters basic knife edge grinds with very small radius, if i started to get chatter i used a verticle shear tool to take very small passes and remove chatter marks then went back to regular tool.

I used abrasive roll (25mm wide) to even out variations in the shaft to bring it to a reasonable tolerance for its purpouse.

I have started a follow steady side project now

Stuart

 

[Round in circles]

Or here is a flow rest that fits a QCTP. I red a write up on here awhile back where they used this idea but modified it to use the threaded hole on the side of some QCTP.
http://www.frets.com/HomeShopTech/Tooling/MiniFollower/minifollower.html

Nice one , I didn't know such a beastie as a double tool holder existed for QCTP's ..

" Oh to have a decent milling machine and a much bigger Man Cupboard to put it in ..... Dream on Davey ...... Santa ain't real & even with the biggest tin of Germolene that hole will still be there " .

 

[Round in circles]

What is the bore of your spindle? What I have done is using the tail stock, stick the part out of the chuck 6" turn that, bring it out another 6" turn that. then flip the bar and do the same thing on the other end. once it is all turned I extend it all out use 80 grit emery to blend it all in then 120 grit to polish it.

Unfortunately it's too big to go through the spindle at present .
Happily I've been able to do a bit more on making the mounting plates to bolt the fixed steady to.
Tomorrow if all goes well I may even have it on the lathe.

I've rethought things wrt how to do the bar .
Perhaps it's better using an extra along bar that can have the first inch or so at the chuck end & the tail stock of it sacrificed with a grinder . With this over length bar unsupported bar free turn between two centers around the mid point at a slow speed using auto feed , tickling it with a fairies feather duster sort of cuts a thou at a time , to get about an inch wide turned round but well over size round section . Then set the follower up on this turned area , now turn the headstock end to size as it will be around 8 1/2 inches of supported work , then turn the tail stock to size . Then move the steady to the left and turn the remainder to size.

If I do 0.0187 thou auto feed on the final finishing cuts of each stage I dare say things might work out well . I can always face of the bar ends easily once it is to the diameters size as it will then go through / inside the headstock . I'll just have to remember to keep my pencil & note pad handy so I actually write down what I do & what measurements things are .

 

[Round in circles]

A tool post mounted steady like a "turning box" used on a capston lathe might be an option..

I recently made a long'ish shaft from some hot roll steel, about the same size your starting with.

I used very sharp cutters basic knife edge grinds with very small radius, if i started to get chatter i used a verticle shear tool to take very small passes and remove chatter marks then went back to regular tool.

I used abrasive roll (25mm wide) to even out variations in the shaft to bring it to a reasonable tolerance for its purpouse.

I have started a follow steady side project now

Stuart

Can we have pictures of your follow steady project in this thread please Stuart

I seem to recall I may have a threaded hole going spare on the side of my QCTP as well .. I'll have to check that one out that's for sure .