Feedscrew thread die/thread chaser

[Wes K]

I have an Edison Opera which uses the same thread as the model D & up Standards and the Firesides, but it has some bad spots that a die would likely clean right up.
Has anyone made a die/thread chaser for Edison feedscrews? I know Ron Sitko was selling some new repro feedscrews a few years ago, so I am hoping someone out there can help.

[Wes K]

Correction:
the Opera feedscrew is right-hand thread, so it is the same as the A & B Standards.

[JerryVan]

Many feed screws use a "buttress" style thread form, as opposed to a "V" type thread. If the Opera screw is a buttress type, finding a die will be impossible, without having one custom made. Often, a very fine file, ground to a sharp knife edge, can be carefully used to file away burrs and rust damage, assuming the damage is not too extensive.

https://en.wikipedia.org/wiki/Buttress_thread

[Curt A]

I bought this set for just this purpose. It has two diamond rotary files that can be used on any threads to repair them. They are made for rotary tools like a die grinder, but my intention is to use them hand held against a feedscrew while it is installed and running on a machine. I haven't had time to try it, but it appears that it would work well...

https://rotarythread.com/collections/ki ... tarter-kit

Screenshot 2023-06-30 at 2.57.20 PM.png (185.42 KiB) Viewed 727 times

[Inigo]

I'm not an expert, but after what I've read herein, the thread of the opera feedscrew has a special asymmetric shape. These tools with 60 degrees angle at both sides seen that they could spoil the feedscrew irreversibly... I wouldn't use that.
I've read here or in Reiss's Compleat Talking Machine, that a surplus half nut can be used to pass it along the feedscrew to detect bad spots, and then use manually a thin file to repair bad spots locally

[Wes K]

Thanks for all the replies. A member of the board got in touch via PM and has offered to loan me a thread die that was made just for the Opera feedscrew.
Before that message arrived, I read thru the above replies and took a closer look at my feedscrew and had reached out to a die maker for a quote.

The Opera feedscrew is 5/16"-50tpi, just like the A, B & C Standards, but that is all they share in common.
The Standards have a symmetrical 'V' shaped thread. The Opera has a buttress thread. The wear on my feedscrew and half nut made it very difficult to see (and I was using the loupe I use when working on pocket watches!!). It only became obvious after I pulled a feedscrew out of one of my Standards and began looking at them side by side.
The OD of the Standard screw (tops of threads) is 0.312". The Opera screw in the least worn place I could find is 0.302"

I think the thread chaser is the only chance of hope for reviving this screw.

Wes

[JerryVan]

If anyone wants to pursue having special taps & dies made, here is a source I used once. They did a good job.

https://www.widell.com/index.html

[phonospud]

This is just my opinion but being a tool and die machinist for over 40 years, it’s my belief that the only proper way to fix a damaged lead screw is to chase the thread in the lathe with proper profiled tooling.
This actually isn’t that difficult and any competent machinist worth their salt can do it.
Getting a die made isn’t cheap and how many times will you actually use it?
It’s less than an hour’s worth of work on a lathe including grinding a tool to suit the buttress thread.
This is provided your lathe has the capacity to cut the thread pitch you need.
If you’re not a machinist, it shouldn’t be that difficult to find one. Trying to hand finesse a damaged thread by hand with a grinding tool wouldn’t be my go to method. The chances of just making a mess of it is quite high I would think.
Do it right the first time, the second time might end up in needing a replacement.
Just my 2cents

[MarkELynch]

Phonospud,

Could you guide us on the proper way to accurately align the feedscrew of the lathe with the existing thread on the part being chased? Getting the two in sync would be very important so as not to overcut the existing thread.

Thanks for your expert guidance.

Mark

[phonospud]

It’s very straightforward. If you have the knowledge and background of running a lathe.

With your damaged feed screw in the chuck, indicated true and supported with the tail stock center:

Set your cross slide to be parallel with the lathe’s axis, or 0° on some lathes.
Have your pre-ground formed tool set to center in the tool holder.
Set your lathe threading gearing for the correct pitch of the feed screw, and engage your threading half nut.
With the lathe’s headstock in neutral, manually rotate your chuck, or collet system forward to take up all the slack until the carriage moves in the desired direction.
Bring your tool in with the cross slide and adjust your compound slide carefully left or right so that the tool is engaged into the thread and carefully adjust cross slide depth to the point where you’re barely cutting anything.
Record your depth position, or zero out your cross slide and retract tool.
Now you are synchronized with the the damaged lead screw.
I don’t recommend disengaging the half nut if your lathe is significantly worn. Reverse the lathe and keep the half nut engaged until you are finished chasing the thread.
Don’t go to full depth in one cut, and if you aren’t confident enough to run the lathe under power, just hand turn the chuck through the damaged areas.
I would not chase the entire thread either. Only the damaged areas. I would not go to full depth unless there’s evidence of damage still, then go to with in a thou of full depth or a half thou over full depth, carefully.
Use cutting oil for at least the last cuts.
Lastly, always ensure that the apron is following the thread accurately with the tool close to the work before committing to cutting. Careful checking as you go will ensure accurate results. Run your rpm’s slow, under 60rpm if possible. Don’t get in a hurry.
NEVER change rotation direction without retracting the tool from the thread!!! Retract tool then reverse direction past your starting point then return the tool to the required depth. Lathes are only synchronized in ONE direction, when you change rotation you loose all the gear’s tension, so don’t reverse your lathe with the tool in the thread!!!

Hope this helps.

Cheers,

Darren J Wallace