Coventry Diehead

[PeterBParticipant @peterb58166]

I bought a 5/16 Coventry Diehead off e-bay recently and after some servicing and adjusting I am almost ready to press it into use.  However, it came with only one of the 4 screws that hold the front face-plate on – ie the plate that secures the die-cutters in place.  
The screws are countersunk and about 10mm long, but they are some weird thread.  Its about 5/32 dia (or 4mm) but no imperial or BA thread size appears to fit.  So I suspect its a metric non-std size M4 x 0.6.   The long adjusting screw with its knurled head and knurled lock-nut appears to be the same thread. 

Can anyone confirm the thread-size  – and also advise where I might get some spare screws please? 

 

Thanks in anticipation, Peter

[PeterBParticipant @peterb58166]

Screw sizes

[JasonBModerator @jasonb]

I would have thought it unlikely they would use non standard screws, the metric pitches for M4 are 0.5, 0.7 and 0.75. Are you able to give a more exact pitch in tpi or mm.

 

0.6mm is not far of 40tpi at 0.635 so it could be 5/32×40 or even a non prefered american thread such as 8-40 UNS.

 

Jason

[David Clark 13Participant @davidclark13]

H There

I doubt it is metric.

More likely to be imperial.

regards David

[JasonBModerator @jasonb]

Try this company company, they do repairs and recons so should be able to help with screws.

 

Jason

[PeterBParticipant @peterb58166]

Thanks for the inputs, especially JasonB for his link to Wisemans.  They were very helpful and confirmed that Alfred Herbert Coventry Dies were deliberately made with obscure threads so that they could control the market for spare parts.  He declined to say what the actual thread was (“drawings not to hand at the moment”) but was happy to sell me some at £1.61 each and £8.75 each for the adjusting screw – without locknut.  (All this before post and VAT).  He did say that the threads were usually imperial/UNS specials – rarely metric.  I measured mine and M4 x 0.6 is as close as I can get – which is 42.33 tpi.  I tried a 40 tpi gauge and its too coarse, 44 is too fine. 

 

Either way, its now in use and is a mighty fine bit of kit – the quickest and most accurate way to make threads in my view. 

 

Regards,

 

PeterB

[david greggParticipant @davidgregg87136]

iIf you are using a diehead can you tell me how the dies should be fitted The dies are all numbered so they must go in  the proper order , Do you fit them going clockwise or anti clockwise  in the diehead 

[PeterBParticipant @peterb58166]

David,

No problem.  You simply start anywhere with #1 then proceed clockwise with the rest in numerical order.  And you are right, it is essential that they go in sequence.  And don’t mix dies from different sets. 

 

A further tip, if your die is larger than the 5/16 variety, it will likely have a little lever on it marked plus (+) and minus (-).  This should be set accordingly to give an initial cut of approx 3/4 depth, followed by a second cut to full depth.  It can take a bit of trial and error with a piece of spare MS rod to get the overall setting correct for a perfect thread that a nut will run down by hand without being over loose.  But once set and lock-nutted, that’ll be correct for the life of that die set.  When I’ve finished I run a piece of folded wet and dry paper in the thread grooves to polish-off any high-spots. 

 

Do persevere, its worth it in the end.  Oh and do use a quality thread cutting lubricant such a Rocol. 

 

Best Regards, Peter B

[David Clark 13Participant @davidclark13]

Hi There

I ttink you go aniti clockwise when using left hand dies.

regard David

 

[bernard towersParticipant @bernardtowers37738]

Further to the discussion about 5/16 diehead front screws I had a discussion with the nice man from Wisemans today and when he found out I was a Model Engineer said he would ring me back ha ha, but he did and told me the price of the screws and said he had the works drawing in front of him and the screws were 0.155 x 42 Wh !!. So if anybody is desperate away you go!

[BazParticipant @baz89810]

Make them a bit slack and over the short length required you may get away with 5/32 x 40 ME. Easy enough though to screwcut, it going out to the workshop to check because it is chucking it down but I am sure Myfords QC box cuts 42 tpi.

[mark costello 1Participant @markcostello1]

Working in a screw machine using Geometric chasers once in a while putting the chasers in sequence would not work. Boss showed Us to take and put the chasers out of sequence, instead of 1-2-3-4, He would change it to 1-3-2-4. Or moving the chaser blocks around 1 hole for the start position. Some times they were fidilly but eventually He got them to work. Did not think it would work but it did.

[bernard towersParticipant @bernardtowers37738]

sorry baz only 40 and 44!

[Phil PParticipant @philp]

Posted by bernard towers on 02/08/2023 16:35:11:

and the screws were 0.155 x 42 Wh !!.

I wonder if they sell chasers in that size ?

Phil

[Robin DuftonParticipant @robindufton85682]

Posted by Baz on 02/08/2023 16:53:29:

Make them a bit slack and over the short length required you may get away with 5/32 x 40 ME. Easy enough though to screwcut, it going out to the workshop to check because it is chucking it down but I am sure Myfords QC box cuts 42 tpi.

If you're going to do that you might as well put an M4 tap in the hole and use M4 screws. Having had a 1/4 die head I can't see why the body would be hardened and prevent doing it.

Edited By Robin Dufton on 03/08/2023 19:33:30

[Anonymous]

Posted by Robin Dufton on 03/08/2023 19:32:09:

…can't see why the body would be hardened…

All of the smaller Coventry dieheads have hardened bodies.

Andrew

[Anonymous]

Posted by Robin Dufton on 03/08/2023 19:32:09:

…can't see why the body would be hardened…

All of the smaller Coventry dieheads have hardened bodies.

Andrew

[bernard towersParticipant @bernardtowers37738]

Well done Andrew!

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