Making The Thumb Screws

[RWL]

First I had to grind a small threading tool since my regular threading tool won't reach close to the shank of the screw. I turned down a piece of brazing rod to around 0.103", which itself wasn't easy without support on the outboard end. Since I had plenty of brazing rod, I thought I'd try threading it without outboard support to see if it would work. As expected, it didn't, and the screw bent. Photos below. I need to come up with some way to support the far end of the screw. I don't know if I have a tiny center drill that will put a hole in the end of the screw.

 

Photos of the failed attempt below.

 

 

[Geoff Wooff]

I guess that if you had thousands of these to make you would get a Die made ,so I am assuming you just need a couple of them. So, why not start with a larger diameter rod of machining grade Brass or Nickel Silver . Chuck it and centre drill it,turn down the length needed for threading but leave the centre drilled end to be the tail support whilst you thread cut. Then trim off the fat end and voila!

 

I know how tempting it is to use what you have laying around but Brazing Rod might not be an ideal alloy for this purpose.

Edited July 15, 2015 by Geoff Wooff

[David Hornett]

AH, yes, get the right dia, brass bar: approx 15mm across,

 

Tool down to the right dia for the threading die, (approx 10mm of thread.

 

Lock the die in the tailstock, or hold it by the hand tool

 

With model still in chuck cut the thread using the lathe to turn the model through the die (The thread does not need to go all the way because there is also the lather which sits on a collar.)

 

Knurl the other end of the bar.

 

Part off.

 

I made my first half dozen from an old brass bearing drift.

 

 

Hope this helps

 

David

Edited July 15, 2015 by David Hornett

[TJPearson]

How about the following solution?

Tap out the screw plates to 6BA which is 0.110" dia X 47.85 TPI, just opening the threads up slightly.

Then you can use a 6BA Die to cut your thumbscrew threads.

Does involve the purchase of a tap and die, I know, but then you have them for any future jobs.

 

Shalom

 

Timothy

[Geoff Wooff]

Maybe we need to read through RWL's previous topic where he is trying to decern the original thread size used on Wheatstones and Lachenals... hence his wish to thread cut them on the lathe.

[DDF]

I can't see if you have got the topslide set over @ half the thread angle.If not it would be worth a try as you will only then be cutting on one side of the tool so there is a bit less drag as you feed in on the topslide.You could also make a temporary back steady from hard wood and clamp it to the cross slide put a vee notch in at centre height and keep it against the rear of the job. Brass or nickel would be easier brazing rod is rather hard and springy.Best of luck David.

[TJPearson]

Sorry, I hadn't picked up the previous post, just trying to be helpful.

DDF is right offsetting the compound slide to half the thread angle will mean the tool only cuts on one face, plus if you do this, you can also put top rake on the tool to further help reduce the cutting pressure.

Wishing you success.

 

Shalom

 

Timothy

[Dana Johnson]

Gotta be careful with top rake cutting brass it doesn't take much before it wants to dig in. As others said, set the compound rest at half thread angle, use the cross slide to back out and return to the same number for the next pass. All feeding is done with the compound rest parallel to one side of the thread. On small diameters, sometimes I leave extra on the end and chuck a rod of delrin or similar stuff with a hole the right size for the stock in the tail stock drill chuck. A little oil in the hole for lube. You don't thread at high speed anyway. It gives some support and can help keep the stock in line better than a center. You may need to repeat the finish pass a few timesto account for the deflection, though you'll never get all of it. Makes you appreciate watchmakers!

Edited July 15, 2015 by Dana Johnson

[RWL]

I was successful today in making a prototype screw that threaded part way into the nuts on the Edeophone. Using a die would be the easiest way to make a handful of these screws. At someone's suggestion I tried a 3-48 machine screw in the Edeophone and it fit well even though it's about 0.010 undersize. Unfortunately I don't have a 3-48 die. I used some tailstock support with a quickie "female center". There wasn't enough room for the quick change toolpost, so I had to revert to a lantern style tool post. Photos below.