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Thread Rolling

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Involute Curve16/03/2015 10:42:22
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328 forum posts
86 photos

I'm looking for advice on thread forming, I have all the taps and dies I think I will ever need, I also have a couple of die heads with various sets of jaws, However I use a lot of stainless bolts and also some Titanium ones, I am looking at the feasibility of building a dedicated CNC threading machine for bolts, probably based around a small ish Capstan or Automatic lathe, however I want to form the threads rather than cut them so thread rolling would appear to be the answer, max size will be 12mm.
So do any of you have experience of thread rolling and or thread rolling heads etc.


TIA

Shaun

Capstan Speaking16/03/2015 10:56:40
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177 forum posts
14 photos

Wow, sounds like a money pit at every level.

Forget automating a capstan and look at an old EMI-MEC Sprint.

You can still get rolling heads from people like Rotagrip. It needs neat cutting oil for best results.

You'd be better off buying them from someone who does this. In any event you need to be looking at 1000+ for it to be worth doing.

John Stevenson16/03/2015 10:59:10
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5068 forum posts
3 photos

You will need some serious HP for stainless and Ti for thead rolling so this might limit the machine you want to use.

You could use progressive heads for stainless but I'd imagine that Ti will work harden that fast it will have to be a one pass operation.

David Jupp16/03/2015 11:23:19
701 forum posts
17 photos

I've had threads rolled on 3/8" stainless thick walled tube (304 & 316), for use on 2000 bar pulsating duty. I didn't handle the direct liaison with the local contractor who did the job, but I can contact the person who did.

I do recall that there were 2 common styles of rolling head - one type used rollers, the other worked more like a plough.

It took a bit of trial and error to find size to machine the tube OD to to give correctly formed threads.

Same process was (still is) used for much larger size tubes (typically in low alloy steels).

Oompa Lumpa16/03/2015 11:24:33
888 forum posts
271 photos
Posted by John Stevenson on 16/03/2015 10:59:10:

You could use progressive heads for stainless but I'd imagine that Ti will work harden that fast it will have to be a one pass operation.

In a nutshell. I remember the first time I tried to knurl some Titanium, learned a valuable lesson there. Cut knurls like the Quick work but other than that, not a chance. Not unless you were using some very serious pressure. I would imagine threads would be just as challenging.

graham.

Involute Curve16/03/2015 12:35:51
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328 forum posts
86 photos

To be honest I figured that it could be a nightmare and require a lot of power, some of the bolts I use cost silly money, I can already make them for less using standard methods, I just don't enjoy doing it, I enjoy paying for them even less, I use a lot of Titanium and stainless bolts, I do more and more work on race bikes and drag racers, 500 quid for bolts on a single is not unusual, I have a small thread rolling machine for motorcycle spokes and surprisingly it easily threads Titanium, this is a long term project which may never happen in the mean time Ill keep my eye open for an automatic lathe with the above in mind.

John Stevenson16/03/2015 13:49:58
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5068 forum posts
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How about thinking outside the box. ??

Andrew Johnston16/03/2015 14:33:22
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4941 forum posts
560 photos

Rolled threads tend to have better fatigue resistance than cut threads. Using the wrong thread production method can, and has, had fatal consequences.

Andrew

Capstan Speaking16/03/2015 14:48:31
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177 forum posts
14 photos

I once saw someone make an adaptor for a centre lathe where it bolted to the rear toolpost mount and held a Coventry Die Head.

This allowed rapid production of small quantities in a cost effective manner.

High load applications of the product should be tested for safety.

Involute Curve16/03/2015 14:48:36
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328 forum posts
86 photos

JS, I've actually seen one of those in action, very fast in operation, I've also seen a spoke threader of this type, cuts and threads a spoke as fast as you can blink.

this is the type

https://www.philwood.com/products/tools/spokemach.php

I actually contacted them with a view to buying formers, however they only do them in imperial sizes, I'm still looking at this option which to me is the more interesting method, I could easily automate this.

jason udall16/03/2015 16:06:05
2012 forum posts
41 photos
Roll boxes are expensive..and the rolls when I last bought some 900 quid..though they can be reground. For about 300 quid...
They do last well...around 4k threads per grind.

Fantastic if your machine has the grunt..doing 14 mm thread at 800 rpm..
And you have never lived until you have seen one tear the end off a 20 mm bar of en 16 t iq...
jason udall16/03/2015 16:08:45
2012 forum posts
41 photos
Oh some way of "cocking" the rolls is needed...
And the starting diameter makes a BIG difference to the resulting thread.
Adam Harris21/09/2015 16:43:33
438 forum posts
19 photos

I have a Fette thread rolling head (triple dies) for size M6-10 threads, that has been used on a 3hp colchester lathe. I have no experience of using this head and know it is a very expensive piece of kit that I do not want to damage! Firstly I am not sure if you set up the carriage on a free sliding basis to have the workpiece pull the rolling head onto itself (after manually pushing the carriage/head onto the chamfered end of the workpiece), or if you drive the carriage/head onto the revolving workpiece by the leadscrew.... Any advice before I try would be most welcome! Secondly, is a 3/4 hp Myford powerful enough for thread rolling, or is it only possible on something like the 3 hp colchester? Thanks

Adam Harris21/09/2015 16:49:24
438 forum posts
19 photos

I can see that the dies spring apart when the motion of the carriage is stopped so then the workpiece cannot pull the head any further onto itself - how is this best performed on a manual lathe? Do you set up a stop for the carriage so that when it hits the stop the workpiece forces the dies to spring apart?

 

 

 

Edited By Adam Harris on 21/09/2015 16:50:46

jason udall21/09/2015 17:16:37
2012 forum posts
41 photos
My experience is with cnc usage

That said I would feed in at "screw cutting" feed ie just as if screw cutting.
..too fast with thin the threads..too slow will attempt to stretch the base metal...
Our Fette rolls disengaged when the spindle reversed and disengaged the coupling...
As to HP..well I have seen bar sheared off in half inch threads.. ( careful with the start diameter of you thread..)..
We threaded at 1500 rpm for m6 with a 15 hp spindle..
Didn't rpm didn't drop but then again tight servo control..so.....
jason udall21/09/2015 17:20:58
2012 forum posts
41 photos
Don't fear...manual thread rolls even exist for off machine work..
In fact thread rolling "taps" exist..
All this means that a 1/3rd hp bench operative can do it.. so just a matter of torque.
Adam Harris21/09/2015 17:33:50
438 forum posts
19 photos

Thanks Jason but I still don't really understand how it should be done on a manual lathe - do I feed the head onto the workpiece with the leadscrew engaged at tpi screw cutting feed (as if cutting) which is very slow? The Fette you tube videos show the head moving extremely fast (but nowhere do they show or explain the head-carriage-bed set up....

Adam Harris21/09/2015 17:51:24
438 forum posts
19 photos

As I look at the mechanism it makes me think that the carriage should be free floating and one should set a carriage stop along the bed to determine the length of the thread (at which point the dies spring apart as the head is pulled forward from its shaft which is clamped to the stopped carriage). In terms of engaging the head onto the chamfered workpiece , I am wondering if best to push steadily to initiate a bite or to slam it more forcefully. Have I got completely the wrong idea?

Edited By Adam Harris on 21/09/2015 17:51:47

Michael Cox 121/09/2015 18:19:58
519 forum posts
27 photos

I have often thought about trying to make a simple tool for thread forming. In essence it would be a little like a conventional scissor type knurling tool but with the rollers threaded at the required pitch. It would be used like a knurling tool but with the leadscrew engaged and change gears to suit the required pitch. Has anyone seen or made such a tool?

Mike

David Clark 121/09/2015 18:27:51
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3357 forum posts
112 photos
10 articles

Thread rolling, as far as I remember, was done very fast. We used a capstan lathe with the roller box in the turret.

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