Three or four start thread ?

[blacksmith]

Hi, Is there anyone out there in the land of Oz who can cut a 3 or 4 start thread for a flypress? Make most of my machinery but this ones got me stumped !
The shaft would be approx 35mm x 450mm long with corresponding female thread cut in a bush.
It's a pretty steep pitch ,about 50mm in one revolution.

If there's any lathe guru's who are up for a challenge I'd be pleased to hear from you as I only bash hot steel around , definitely not a precision engineer

Thanks

[Stustoys]

Hi,
What thread pitch (or what lead) were you after?

Stuart

[blacksmith]

About 50mm per revolution.,if that makes sense. think it's an Acme or square thread.

[Kody]

Cutting a four start thread is easy to do. It's no harder that a two start thread. I could do it for you but my Myford Super 7 is not up to the job. A much bigger and robust lathe is needed that can cut a thread of 2" Lead. Such a "long" lead needs solid gears to drive the carriage. To locate the four threads, simply "drop in" every half inch on the thread dial. A lead screw of 0.5" pitch would make it a very easy job to do.

[RayG]

Hi Blacksmith,

I think there might be two threads overlaid one fine left handed and one coarser right handed, I will go and look at my flypress and double check.

Regards
Ray

[Bryan]

Ray, that's something I'd like to see. Can you post a pic?

[RayG]

Hi Blacksmith,

On mine it's a 4 start right hand square shouldered thread for the press. And the depth stop is on a finer pitch left hand thread overlaid on top of the 4 start right handed square thread.



Hope that makes sense.

Regards
Ray

PS Hi Bryan, I must have cross posted with you, I went to take the picture at the same time as you asked.

[Bryan]

Way cool!

[blacksmith]

That's the one Ray.
All I got to do now is get someone to cut it. Local machine shops won't touch it for some reason.

[RayG]

Hi Blacksmith,

I just did a couple of quick measurements, on mine it's 1 3/4" diameter, the 4 start thread is 2" pitch, cut 1/4" wide square profile, so it ends up being equal spacing.

The left hand thread for the depth stop would be cut first and then the 4 start last.

The problem is going to be to find someone with a lathe that has a lead screw that can do that 2" pitch, on mine the coarsest thread I can do on my lathe is 3 tpi... nowhere near it.

Maybe someone on the forum has a lathe that can do 2" pitch?

Regards
Ray

PS.. A CNC lathe would do it..

[.RC.]

There is a possibility the thread was milled rather then cut on a lathe....

Would not be very cheap to do either way....

[PDW]

There is a possibility the thread was milled rather then cut on a lathe....

Would not be very cheap to do either way....

That would work for the screw and is how I'd do it. Pretty simple job really. The nut is a different matter, not sure how to tackle that one. My big Monarch will do 2 tpi on its standard set of gears.

PDW

[.RC.]

It is 1/2 TPI isn't it? 2" lead ?

You would want a BIG lathe to cut a thread that coarse on especially since it would be a 6mm wide cut... My Purcell lathe has 1/2 TPI on the thread plate but I fear something would break cutting a thread like that.... You would want something like a 25"+ swing lathe to do it... With a big leadscrew...

[RayG]

Hi .RC,

I think you are right when you suggested milling it, a CNC mill with a 4th axis for the rotation, would be the way to do it. Same for the nut, CNC mill with thread milling capability.

Maybe when I finally finish the CNC conversion...

Regards
Ray

[.RC.]

Buying threaded rod from the US would be another option... I doubt whether anything like that would be available here...