screw cutting made easy

Do you know this threading attachment ? The tool is stopped and withdrawn just before the shoulder. This attachment is almost completely contained on a toolholder set in the toolpost. It’s not as efficient as the “single tooth dog clutch” but far easier to make and few costumization is necessary, whichever lathe you use. The result is like the one obtained on a CNC lathe, the tool is withdrawn always at the same place, no circular groove is made!
Video:

**LINK**

Sorry I've made a mistake for the video link (while this attachment is of some interest)

Here is the good link: **LINK**

It's only an auto-retractor, (I think)

big pain 1 is setting up the changewheels

big pain 2 is picking up the threadstart

big pain 3 is stopping at a shoulder which won't happen unless the unit is used in a lathe which has a leadscrew clutch/drivetrain disengagement system

(BTW that video looks like a CNC machine...but it's usually edited before each pickup for some strange reason, so it's 6 videos sellotaped into one video)

Edited By Ady1 on 15/06/2013 17:56:58

Some answers:

Big pain 1: 2mm lead is standard from the gear box.

Big pain 2: I use the thread dial indicator after each infeed so the delay for starting the cutting pass. From the infeed increasing you can see that there are not 6 videos sellotaped, only the 2 last (slow speed) are such.

Big pain 3: The tool is stopped and withdrawn (this is the purpose of this attachment) on a standard lathe. The result is like CNC.

This attachment was (is?) commercially available, called "Snap Tap" from a Swedish company (now Seco tool I think).

People may be less confused by looking at this link

On the video explanation there is a link to some bucket pictures.

Looks interesting. One could perhaps make a holder for the stop bar that clamps onto the tailstock barrel to simplify and provide easy adjustment.
I also found your first miss-link interesting and so simple it's worth a try too.

Edited By Bazyle on 16/06/2013 10:20:01

Thanks Bazyle,

A picture is worth a thousand words.

Mike

Pity the video doesn't show the machanism in action stopping and retracting the tool instead of a close up of the thread being cut otherwise it could be a thread being cut by any means. Bit of an Emporer's new clothes situation.

Thank you to Bazyle for the links.

I'll give more informations on the snap tap attachment. in the following days. The principle of function is very simple but confusing. I've made my own attachment and discovered that there are many hidden traps in the conception. It's almost impossible for an amateur to make a copy of the genuine as no adjustement is possible. Here is a first photo:

New video showing the home made attachment at work : **LINK**

Jacques, fascinating bit of kit, looks complicated!. Have you seen the flip up type of threading tool holder that John Stevenson and others designed ?. Another way of screwcutting. I made one to JS ,s design which works a treat . Ray Behner ( I think thats the correct spelling) in the US made an automatic releasing toolholder, you can see it on the PM siite. Cheers.

John, my humble apologies about the flip up toolholder. I didnt know , but good on you for sharing the design with others.

Roger no need to apologise to either of us.

Previous to both of us working on our respective version Mike Cox came out with a version on the 7 x 14 lathe forum.

When, in a post i asked the question why it had not been done this way before someone pointed out a swing tool patent from about 1905 so like most things, nothing is new.

John, (Bogstandard)Ive just read through your post again, and cant help see the other point of view about making a tool like Jacques describes, or the Ray Behner one. Id love to have a go at making the latter one, just for pleasure of doing it . I might never use it much, indeed Ive got a HLV-H for threading as well, but to be able to construct something and enjoy doing it , is all I care about!. Ive plenty of time to do it as well.!Each to his own .

Cheers.

Edited By Roger Williams 2 on 19/09/2013 23:38:50

I'm afraid I differ with Bogs as well as I screwcut loads of threads, even if I have a die of the right size.

95% of my threads are metric, my machine and gearbox is metric so setup is very quick.

Screwcutting ensures the thread is square to the work even if you finish off with a die

Having seen bogstandard's intresting video is there anywhere we can find details of his and John's screwcutting attachment thanks.Graham

Jacques, I mentioned Ray Behner in the US, if you are interested, type Auto Retract Single Point Threading on U tube, and have a look. Perhaps someone can kindly put the link in for me !!!!!!!

Regards, Roger.     PS, another one by The Daumen called the Altered threading tool.

Edited By Roger Williams 2 on 20/09/2013 14:54:04

A near relative of the "Snap-tap" attachment has been descrtbed in "Model Engineer" (no photo, only sketches). Try to find in which issue!

J Maurel

Looking at the photos from Jacques first post, how is the HSS tool held in place ?

BobH

 The problem with this tool (15° rake angle) is that it must be of the spring type for the tool not to plunge in the work as the chip is very wide for the last cuts.

J Maurel

Edited By John Stevenson on 20/10/2014 22:47:10

You'll find a near relative of the snap tap in ME issue N°4177 (sept 2002) title: A high speed thread striking attachment. The problem is : what happens if the feeding force is more than the spring one?

J Maurel