Perplexed...not sure how to finish, or start over....

[medic29]

Good evening. First let me say, I'm not much more than a beginner. I have enough knowledge to allow me to get into trouble. I have tinkered around and made some things in my shop and have been successful in most of those projects, albeit they probably took me significantly longer than it would someone else with more knowledge and experience.

I have a tailstock for my Monarch 10EE lathe in which the screw for the tailstock seems to be slightly bent and thus does not allow the tailstock to function very well; I can only extend the spindle about 1.5 inches. So I decided to make a new screw for the tailstock. The most daunting part of this process for me when considering this was cutting the acme threads, mainly because I had never cut any before. I had performed single point threading many times, but never had the need to do acme threads. So below is a picture of what I need to make.



I apologize for the size of the picture, I'm not sure how to make it smaller.

Anyway, after evaluating everything I decided I was going to need tailstock support at a minimum and since I had the tailstock for the 10EE tore apart I figured using it was out of the question. I still have my first lathe which is an old Southbend 9A and I have a steady rest and follow rest for it. After some investigating and thinking I decided it might be best if I turned this project between centers. Something else I had never done before, but have seen it done. I found the center of each end of the stock I planned to use and set it up between the headstock and tailstock. Then began taking cuts and went through the process of aligning my tailstock on the 9A. After finishing this I set about to make the stock for the different sections of the screw.

Today I went out and got to work and made a lot of progress...until I ran into a snag. My snag may be the result of my order of operations. My plan was to work on turning down the end of the stock to size that was closest to the tailstock. Then using the steady rest close to the middle for support and using the follow rest I would cut the acme threads. This process went okay. I had to move the steady rest to gain enough room to perform the threading, so it wasn't as close to the work area as I wanted, but everything seemed to turn out okay.



My next plan was to reposition the steady rest over to the area of the threads (maybe not the best plan, but hey, I'm learning). Then I was going to turn down that central disc to size (1"). Then I was going to turn down the last section from the disc area towards the headstock, about 3.5 inches. Then I was going to part it off. This is where I ran into my problem. I couldn't get the steady rest close enough to that area where the central disc is because the steady rest would hit the saddle and I couldn't flip the steady rest around because it has to sit a certain way on the lathe bed. So when I tried to turn that central disc area I got all kinds of chatter regardless of speed/feed and/or tool I used.



I was thinking I had seen someone who was turning between centers take the item out and flip it, but I'm not sure if I can actually do that. If I can, then I would have to take the dog off the one end and switch it to the other end and I fear that would screw something up, but I'm not sure.

The cool part at least, my threading is good, it screws into the tailstock spindle for the 10EE, but....I'm only halfway there with the lathe work and I'm not sure how to finish it. Any ideas or suggestions would be very appreciated as I sit here speculating my next step.

Thanks again,
Rick

 

[Just for fun]

Your work looks great so far. I am a beginner also and I have never turned between centers but from what I understand moving the lathe dog (If you have one to fit) will not cause a problem. Your centers are not going to move right? Turning your part around shouldn't cause any sort of problem.

Hanging out to see what the experienced guys have to say.

Tim

 

[OTmachine]

High Speed Steel tool bit, preferably something with cobalt in it. You could hold the threaded end in bored to fit soft jaws or a collet. My .02

 

[medic29]

High Speed Steel tool bit, preferably something with cobalt in it. You could hold the threaded end in bored to fit soft jaws or a collet. My .02

And switch from turning between centers? Would that change the concentricity by placing it in a collet?

Sent from my SM-S911U using Tapatalk

 

[Aukai]

4 jaw with soft jaws, or an ER collet to hold it now that the threads are done? The 4 jaw would get you back to zero,,,, no?

 

[mmcmdl]

Swapping the dog and machining will not change a thing , although the part may stress relieve itself and move a bit . I did years of large shaft work on lathes and cylindrical grinders in the past . Never had major issues other than introducing heat into the part while machining . Looks good so far though !

 

[brino]

First, this was a very ambitious project for a beginner...... Good for you!
There is no better way to learn than to jump in and swim.
And in this case since you are NOT modifying the original, what do you have to lose?
Also, you have done a fantastic job!

Being able to flip the work end-for-end is one of the benefits of turning between centres.
The drive dog could be clamped onto the threads if you use some sacrificial wrap (aluminum sheet scrap).

Grabbing the threads directly in a collet should cause no damage.
If using a chuck to grab the threads, bend a piece of aluminum sheet around each jaw first.
Re-centering the work in the 4-jaw could be done if there is enough length at the small end to grab it and check for centre.

Brian

EDIT:
Not to discourage your current project, but have you considered straightening the original?
I have never done it, but I believe there's some good info out there and right here on this site too....

 

[MrWhoopee]

I would definitely grab it by the threads up close to the shoulder. Use a collet if you have it. If not, make an aluminum split bushing or use copper or aluminum shims in the 4-jaw to protect the threads. Concentricity, while important, is not extremely critical. It won't affect the alignment of the tailstock quill.

I would have tried straightening the original. Considering the small diameter, it wouldn't take that much.

 

[OTmachine]

And switch from turning between centers? Would that change the concentricity by placing it in a collet?

Sent from my SM-S911U using Tapatalk

First, check the runout of the threads o.d. with the part between centers. Most 5C collets run within .0015” T.I.R, better ones,(Hardinge), will be within .0005”. Since you turned the whole assembly between centers, the threaded section should be concentric and good to hold by. In this application, I believe that you could reduce the finish size of the chattered diameter by .001 and still function properly. This would cancel out the minimal off concentricity of the collet. Other than that, a 4-jaw with soft pads would work.

 

[medic29]

I would have tried straightening the original. Considering the small diameter, it wouldn't take that much.

How would I got about trying to straighten the original? I did place it in a collet chuck and turned it in the lathe to find the high area, but wasn't sure where to go from there since it involved the threaded area.