Die diameters and holders

[derek hall 1Participant @derekhall1]

Hi,

Happy New Year everyone.

I have an arceurotrade  sliding tailstock die holder containing 6 metric and 4 imperial sized holders for different sized die diameters.

I am very happy with the kit except that the ID of the die holders are almost the same nominal ID as the die itself, this leaves no room for slightly expanding the die. Interestingly there is no coned grub screw fitted in the die holders to facilitate this!

I have been reading an article that GHT wrote back in the late 1970’s where he described making a very similar set. However, he measured the dies in his collection and found that the 13/16 dia and 1 inch diameter dies were within a tolerance of 0.000 to – 0.003. He therefore bored out the housings in his kit to around 0.015 (15 thou) larger than the die diameters. Obviously this would create enough “space” inside the holder to allow the die to be slightly expanded if needed. This seems logical. I have also measured the ID of some die stocks that I have that are also slightly larger than the dies I have.

So I have decided to bore out the holders I have in my kit to around 15 thou larger than the die, following the expert advice of GHT.

So my question is though, what is the tolerance of the typical OD of a die (metric and imperial)?, I cannot seem to find this anywhere other than “nominal” sizes.

My kit includes holders for 16 mm dia, 20 mm dia, 25 mm dia, 30 mm dia and 38 mm dia. My kit also includes the imperial set, these being 13/16″, 1″, 1 5/16″ and 1 1/2″ dia. holders. Sorry to mix up imperial and metric, but am I right in assuming that any housing to contain any dia should be slightly larger to accommodate any adjustment i.e. “expanding” the die? (I am talking about “split” dies here).

I am going to modify the holders and replace the fitted cup point grub screws that are ineffectual in expanding the die and fit coned stainless steel grub screws that engage in the “split” in the die for the purpose of “wedging” (expanding) the die.

Interestingly, GHT in the same article, had 4 die adjusting grub screws at 90 degrees around the holder, instead of the more traditional 30 – 0 – 30 degrees, one of these grub screws was coned the other 3 were cup point and simply used to compress the die slightly.

Any comments would be welcomed.

Regards to all

 

Derek

 

[JasonBModerator @jasonb]

The only issue I see with boring out by 15thou is the die will then sit 7 1/2 thou out of true to the lathe axis

I seem to remember reading a Dormer atricle that did not mention opening up a die, only compressing it to get a looser fit.

[DC31kParticipant @dc31k]

Starting point:

https://cdn.standards.iteh.ai/samples/7527/671f054ac2104eedb76af5d5cdd7f98c/ISO-2568-1988.pdf

(Note2, page 2)

which is very wishy-washy…

[JasonBModerator @jasonb]

The f10 for precision dies works out as this which is under nominal

Regarding not expanding dies, page 271 of Dormer threading pdf applies. Also note that the do more unspilt dies than split ones so you can’t adjust them anyway.

 

[EmgeeParticipant @emgee]

As Jason says the die will be off centre with the normal 3 screw die holder, possibly why GHT suggests 4 adjusting screws, that way the centricity of the die could be maintained.

Emgee

[derek hall 1Participant @derekhall1]

Hi

 

Thanks all for your feedback!

It was very interesting Jason that Dormer specifically say not to expand the die, yet other sites seem to promote the adjustability of the split die although Presto do not explicitly say do not “expand” a split die it does seem implied that it is permissible.

In my apprenticeship days it was taught that the split die could be adjusted within the constraints of a die stock and I have used that method for 50 odd years and not broken a die yet.

For some reason the offset holes in the 13/16: holder in my set do not coincide with the dimples on any of my 13/16″ dies, so I am going to modify the holder to comply with GHT’s method of having 4 adjustable screws as Emgee mentions – although this all seems a bit overkill…!

 

Thinking about this, maybe using just the die stock method (i.e. not using a lathe – GHT refers this as “garden engineering!) relies on no guiding from the tailstock, so the 7 1/2 thou becomes irrelevant and the user just ends up with a dodgy drunken thread !

Thanks for all the replies

[Rod RenshawParticipant @rodrenshaw28584]

I can’t see any problems with boring out the die holders as Derek proposes. It used to be a fairly standard practice to expand dies slightly to get a “first cut” on difficult materials and also be able to adjust the fit to pre-existing female threads. Derek can experiment with additional and differently positioned adjustment screws and report back. The additional holes will not do any harm, even if they don’t prove useful.

Also, re the points about concentricity and drunken threads. My tailstock die holder was made by Arrand and it’s in two halves, one which slides closely on a mandrel which fits in the tailstock taper and the other which holds the dies. The two halves ( perhaps “ends” would be a better description) are held together with 3 screws which are left a little slack, there is no attempt at concentricity, the 2 halves functioning rather like a floating reamer holder. This lets the die find its own centre on the workpiece to be threaded.

What the die holder does do is hold the die square to the centre- line of the lathe, but not necessarily concentric. My own understanding of a drunken thread is one which is not properly formed because the die was not presented square to the work at the beginning of the threading operation.

This tooling seems to work well for me. i was once told that a tailstock dieholder has to have a little slack in it somwhere because the hole in the centre of a die is not necessarily concentric with its outside diameter, though modern dies may be better in this respect than older examples.

Rod

 

[Ramon WilsonParticipant @ramonwilson3]

I wrote about this many years ago when I first experienced the same issue. I had made a carefully turned tailstock die holder that the dies fitted in to prevent the exact issue that Jason raises. I very quickly realised that A, the tolerance on the die to allow expansion was too tight but on relieving the bores to alleviate that soon realised that B the die was now off centre. I have been somewhat perplexed ever since how a tailstock die holder can actually indeed be used with expanding dies 🙄

My solution at the time and one I still use to this day was to make several die holders of circular shape of around 60mm-21/2 diameter and about 5/8 thick with a knurled outside. These were bored to fit the various die diameters with sufficient tolerance to allow expansion. The conventional tailstock die holder as intended was made redundant at an instant but was pressed into further service by fitting a spring behind it and using it to apply pressure to the die holders which by that nature can now float. I have no idea how many threads I have cut using this over the years but must be in the high hundreds if not more. For most BA sizes the die holders are held by hand but it gets a bit of a strain up toward 1/4 diameter so there are tommy bar holes drilled in the periphery to help at this stage. The only factor that is critical is to ensure the back face of the holder is in the same plane as the back face of the die holder bore – I did mine by holding them on a mandrel

I’ve never seen it described other than my original text which is so long ago now I have no idea where that was.

I don’t think I have any images of this but if the above’s not sufficient or clear enough I can soon take some

 

Best – Tug

[David George 1Participant @davidgeorge1]

When making acurate threaded parts at work we would use a coventry die head, or ocasionaly thread roll die, or screw cut the thread and maybe use a die to cleaan up a cut thread if nessesary. Only threads which were not needed to be true were mae like this perhaps a stud with clearance were cut with a die which had clearance in the die holder to allow us to expand the die and recut to finnish.

David

[JasonBModerator @jasonb]

It’s also interesting to see that Dormer say their unsplit dies are suitable for use on lathes and in small diameters can be used by hand. The split dies they say are for “threading by hand”

A floating holder as Rod mentions would alleviate any concentricity issues. Although a diestock may present the die square on to the work if it’s a small slender part it will deflect that 7 thou so you will be threading a bent rod.

A bit of shim opposite the split in an oversize die holder will help keep things concentric and allow for expanding the die. An alternative might be to us ea boring head to open up the dieholder but not take any metal off the edge opposite the central screw.

[Ramon WilsonParticipant @ramonwilson3]

Here you are – just found these two pics in the Waller Engine file so must have described them on Home Model Engine Machinist.

 

 

 

 

That should explain it better. I should perhaps add that apart from the very first attempt to use that die holder as intended it has never ever been used as a die holder just purely as a back support.

[Howard LewisParticipant @howardlewis46836]

Hopefully, the Tailstock Sliding Die holder body will be loose fit on the arbor, so that it can then float, and self centre onn the work, (Aided by a chamfer on the end of the workpiece)

I made myself Sliding Tap holders, reamer holders, using ER collets, and ensured that the bodies were also  a slack fit on the arbor, to allow them to float and self centralise.

Howard

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