cutting these threads

[kd0afk]

How would one cut threads on a classical guitar tuning machine so that the thread has no relief and with no cnc? Would I use a retractable tool holder and plunge in when I engage the half nut?

 

[kd0afk]

Forgot the photo.

 

[sssfox]

The only way I can think of doing it is to hand-turn the lathe spindle.
A spindle crank would come in handy.

I'm not nearly coordinated enough to advance the cross slide the right amount on a consistent basis for this type of work..

I imagine they cut them with a hobbing machine.

Steve Fox

 

[kd0afk]

The gears are definitely hobbed and i didn't even think of hand cranking. Go nice and slow for a.really smooth cut. I'll bet there is a machine made just for doing this. Might be an interesting project to build a hand crank worm cutter. Might be a good selling point.

 

[MuellerNick]

These threads were whirled. Unless you do heve a whirling head for your lathe, you can't do it.
Only option would be a live tool in your lathe and mill it.

Nick

 

[dave-in-england]

I have the same tuners on my own guitar.

I can definitely say that these spindles are made on a special purpose grinding machine, with a thin, pre-shaped grinding wheel.
You can see that the thread does not run off the end of the shaft, the grinding wheel is retracted before it reaches the end of the shaft.
This is probably about 10 T.P.I. pitch, with an odd shaped form.

Even if your lathe has such a rare option, you would have a lot of trouble pulling the turning tool out instantly at the end of the thread.

Maybe a less stressful visit to Ebay ??? Ha Ha.

 

[MuellerNick]

Who on earth would grind threads like these?
If you know how whirling works, it is obvious how easy it is to start and stop a thread in the middle of any stock.
The end of a whirled thread has a radius of at about 5 to 10 times the thread's Radius. That radius is convex, but you could make a straight disengaging path of the tool if you care.


Nick

 

[fltenwheeler]

Who on earth would grind threads like these?
If you know how whirling works, it is obvious how easy it is to start and stop a thread in the middle of any stock.
The end of a whirled thread has a radius of at about 5 to 10 times the thread's Radius. That radius is convex, but you could make a straight disengaging path of the tool if you care.


Nick

Hi Nick

I can find videos on new CNC thread whirling. Did they make older machines (non CNC) that would do it?

Tim

 

[MuellerNick]

Whirling, works om manual lathes to. It only requires a whirling head and low spindle RPM.


Nick

 

[kd0afk]

I think I'll try finesse before I guy a whirling head.

 

[kd0afk]

Why not use a retractable cutting tool that runs along a plate and the ends of the plate curve outwards so that when the cut starts and ends it is eased in and out of the cut consistently. I think that would work.

 

[Woodster]

It could be done with a copy turning attachment and a milled profile.

 

[Journeyman]

If it is for a guitar it would probably be easier to get a new set of tuning heads from a luthier. On the other hand as an exercise it could be made in two parts:- cut the thread as normal working from one end of a bar. A hole up the middle for the thinner shaft and then silver solder / loctite a fat washer on the open end. Finesse the ends of the thread / worm with a file. Voila... Merry Christmas

John

 

[abby]

If I had to make them I think I would cut the thread in the lathe , enough length for a dozen or so.
Drill through and part off to length .
Make separate parts for the spindles and silver solder the assembly together.

 

[dman]

i'm not sure how they do these but i'm sure it was once done on special machines. they may have been wirled but i don't know anything about wirling, but notice the helix plunges to a point gradually and retracts to roughly match the shape of the gear? this would be difficult to do with a lathe. they may have been hobbed.

but if you dont care for reproducing the part exactly and would settle for function over form you could use the grooves as your relief and grind your own threading tool. there should be enough surface that i don't think the end of the thread will catch on the hooks that hold the piece in.

 

[napoleonb]

Not sure if it would work but using the same method for creating wormwheels, when you make a hob and put it in the spindle of your lathe and the workpiece attached to your qtcp, reverse this procedure and making a hop which looks like the gear on which you wind your strings and put that in your qtcp.

Seems like an awfull lot of work but its the only easy way I can think of making it in one piece and being able to duplicate.

Another trick which should work is using the headstock and put it off centre and cut the thread half-way, making it conical to the inside. Mind your cutting angle! and then reverse the headstock the other way. I've seen tapered injectionmold spindles been made this way, even with changing pitch (running in from 2 sides with an overlap)

 

[mcostello]

I have a South Bend Lathe with a low gear speed of 40 rpm and a Dial Indicator for a stop. Stopping exactly would not be hard. Starting exactly would be another matter without making a ring around the part.

 

[MuellerNick]

Stopping exactly would not be hard.

May not hard for you. But hard for the tool and the lathe. Imagine what happens after a few passes when the tool hits the wall (left by previous passes).


Nick

 

[n4zou]

I would put a 10:1 ratio reduction gear box on the motor. This would provide a spindle speed of 5.5 RPM if the lowest speed without the 10:1 box was 55 RPM which is common on most lathes. It would be very easy to start and stop thread cutting at that speed. You might even get bored waiting for the start of the thread to turn the compound dial so you can start each cut. Backing it out at the end of the cut would be even easier.

 

[mcostello]

Yes that did happen, must be vigilant. Darn half nuts jamb up pretty quickly when that happens, I did know that not everyone has the luxury of a slow speed, but then I have the luxury of a top speed of 800,it's all a compromise somewhere.