1" tailstock die holder question

[steve-de24]

I'm making a 1" tailstock die holder for my Cowells lathe.

What diameter should I make the cavity which holds the die so that it allows for the split die being opened up to its maximum extent?

Thanks in advance,

Steve

[Jo]

Hi Steve,

Rewind a bit....How are you mounting your die holder? Around the outside of the tailstock or on a parallel in the taper in the tailstock? Think about the distance over the saddle.. I have a couple of the Cowells ones that fit over the tailstock but they are a bit short and I have to wind the saddle out of the way to use them.

As for the max diameter for the die hole: I would keep it as close to the die size as possible. Dies from different manufacturers have known to be different 1", like 25mm and 25.5mm    In theory your split die should have sprung inwards so if you measure the diameters across two directions you should find it is different. Tightening up the screw is just returning it to its correct diameter (i.e. actually round).

Jo

[steve-de24]

Jo,

Thanks for your reply.  The die holder will be an easy sliding fit on the outside of the Cowells 1/2" tailstock (it's got to be a loose fit to allow the die to be centred by the workpiece).  The size of the holder is dictated by the lump of scrap bin metal it came from, 1.5" dia by 1.625" long, I think it's EN8 or similar strength low alloy steel - it's noticeably harder to machine than my usual mild steel but my 5%Co HSS tooling copes with it ok.

As an exercise in making things to size I have so far bored it out so that my 8mm die is a nice push fit - it won't fall out if held upside down but doesn't require any great effort to push it out from behind. There was no need for me to do this other than I need the practice at doing that kind of thing!

But now the question arises how much more do I need to take out of the bore? As you suggested I measured my 8mm die and it is 25.27mm dia with less than 0.01mm difference between in-line or 90 deg to the slit. So much for me thinking that a 1" die was going to be 1" diameter.

I suspect that my solution is just to open it up to 25.4mm dia which should give me enough room for adjustment without too much risk of the carbon steel die going 'ping'.  Do you agree?

Thanks,

Steve

[Jasonb]

I was testing some new products the other day so went through quite a few dies checking their diameters and all were just a shade under nominal size so imperial 1" dies came out at around 25.2mm to 25.3mm and metric nominal 25mm dies were in the 24.8 to 24.9mm range. This was measuring both split and solid dies.

So I would say if you are using 1" dies then make the hole 25.4mm and if your metric die is metric OD then make the hole 25mm.

[steve-de24]

Jason,

Thanks for that.  But at 25.27mm OD my 8mm die wouldn't fit in a 25mm holder - it looks like I have an imperial size OD die cutting a metric 8mm thread. Has anyone got a Machinery Handbook  and tell me/us if there is a standard defining what the OD of a die should be - I couldn't find one on the web.

Steve

[Jasonb]

Dies for metric threads can be bought with either imperial or metric OD but ones for imperial threads are 99% likely to have imperial OD. You have a M8 with 1" nominal OD.

[steve-de24]

Thanks to both Jason & Jo for their help. I will have to remember to measure any future 1" metric dies I buy to see if they are 'Imperial metric' or   'metric metric' and be ready with a bit of shim if necessary.
Jason, does a similar situation exist for nominal 13/16" dies?

Regards, Steve

[Bluechip]

Thanks to both Jason & Jo for their help. I will have to remember to measure any future 1" metric dies I buy to see if they are 'Imperial metric' or   'metric metric' and be ready with a bit of shim if necessary.
Jason, does a similar situation exist for nominal 13/16" dies?

Regards, Steve

Yes and no. Not sure about 13/16" 'cos 13/16" is about 21mm ............. but I have some small metric split dies at 16mm OD nominal. Mine clock @ 15.88mm or close.  ( Threads are 1.4mm 1.6mm and, IIRC, 2mm ISO FINE !).  Rescued from the estate of a deceased friend. NO taps though ..... 

Dave

Just had a shufti ..... 1.4 x 0.2    1.6 x 0.2   2.0 x 0.25 

[Jasonb]

.
Jason, does a similar situation exist for nominal 13/16" dies?

Regards, Steve

Yes, you can get metric threads with 13/16" or 20mm OD and even smaller at 5/8" or 16mm.

Imperial ODs are 5/5, 13/16, 1, 1.312 &1.5 in the sizes we are likely to use and metric go 16, 20, 25, 30, 38 & 45 with 20mm often having two depth options of 5 & 7mm

I used to shim my odd few metricOD ones but now that I have bought a few more particulary metric fine all with 20 or 25mm OD I have made up a new double ended holder for them to fit my existing MT shaft.

[Roger B]

I have some also have some 12mm dies. A while ago I made a die holder to suit my range of metric dies. This is here:

https://www.modelenginemaker.com/index.php/topic,9229.0.html