Atlas /craftsman Back Lathe Specific Turning

[Round in circles]

My 1943 Sphere back lathe is nigh on the same as a 1943 Atlas 10 inch

I recently spent the massive sum of about $ 9.00 USD on a three ,Yes three caliper set , which are an internal pair. an external pair and pair of dividers.

Now for this magnificent sum one can only imagine the quality of them . The good news is that the arms/legs are a quality steel , the riveting is reasonable & the pivots & spring clams are fantastic ...... so far so good .

Now for the crud stuff ...... The screw threads and adjusting nuts are obviously some sort of Brutish standard American /Chinese Indonesian guess work for even with the naked eye you can see the thread form and bar wax & wane along the 5 inches of each threaded rod . On looking in the adjusting nuts I can easily see that the thread is a taper thread like a gas seal thread.
End result is that once each instrument is opened more than 1/2" there is no grip to stop it flying out to the maximum width .

So I'm now having to consider do I turn some bar down to 1/8 inch or so x 5 inch length and try to lathe cut a thread or hand cut the thread with a die or do I purchase precision threaded rod and make my own quick adjusting nut arrangements .
So far I've chickened out on turning any thread forms on the lathe for I've got a various tap & die sets.


Going down to 1/8 in steel bar on the old lathe over 5 inches must surely have a lot of problems ...... sadly I don't have any centre rests or followers .
If anyone has successfully turned long fine threads on one of these old machines would you be kind and pass on you experiences please ?
If anyone has done it on a different manual lathe you're also most welcome to add your views.
Thanks
Dave

 

[Inflight]

Without a follower rest, I think you'll encounter lots of trouble at that diameter for a length of 5 inches. I'm sure you could make a follower that fits a Quick Change Tool Post and still permits proper threading.

Show us a photo of what you come up with.

Matt

 

[pdentrem]

You can make a follower rest out of wood or metal. With such a fine thread, a couple passes will likely do it. Use a freshly sharpened tool and good lube, but you likely know this already.

 

[John Hasler]

You can make a follower rest out of wood or metal. With such a fine thread, a couple passes will likely do it. Use a freshly sharpened tool and good lube, but you likely know this already.

I like the idea of wood or plastic for a special-purpose follower rest. Thanks for the idea.

 

[pdentrem]

There is one thing that still bugs me. It is the error in the leadscrew over the length of the thread. I ran into this in just 3" of thread. All leadscrews have some error, the question is how much. Comes to cost of the precision demanded.

To fix this, I basically did a rough pass and then ran a self made die, made with the tap used to make the long nuts, to finish the leadscrew threads that I was making. They are the collimation bolts for the telescope that I finished just last weekend. The long threaded section at the top is what the lathe made. On close inspection the threads have a repeating pattern that caused the long nut to bind at regular intervals. The lower one is after running the die over the roughed out threads on more of the same material.

The die is not pretty, it just looks that way! Quick and dirty, never to be reused again, maybe.
Pierre

 

[gr8legs]

Although it would be an interesting lathe challenge, why not just get a suitable length of all-thread and use that as a starting point? McMaster has threaded rod in standard gauges all the way down to down to 0-80 size.

Stu

 

[wa5cab]

First, you described these as an inside and an outside caliper. Neither are self-reading or calibrated so the "precision" of the thread pitch is immaterial. As Stu suggested, It would be much cheaper and much quicker to simply buy an appropriate diameter and pitch of threaded rod, and matching knurled thumb nuts. McMaster probably isn't a viable source as shipping would cost more than materials. But surely there is a UK equivalent. Always remember that the ability to do something does not equate to a requirement to do it. Or to put it another way, don't make something that you can buy much quicker and cheaper, especially if whether or not you can successfully make it with existing equipment is questionable.

 

[Round in circles]

After I'd made the original post I made a cup of sweet milky coffee ,watched one of the , " Discovery , How it's done " programmes on catchup TV & I came to the same conclusion Robert.

So in the very early hours of the new day , I had a look on eBay & found I can get 3 mm & 4 mm precision thread in 8 " long hard grade stainless steel ( Model aircraft control rods ) The cost was slightly more than the " Expensive " calipers for 4 off 3 mm x 8 " long plus 2 off 4 mm x 8" long rods.
I'll make my own quick adjusting nuts and locking cones for the rodding myself ......... which in itself should be an interesting project in precision thinking & working .

The rods are due in by Monday afternoon , so now I have my next POTD job planned , now I only have to fit it into the list of about 17 other "POTD Priorities ".