COVENTRY DIE HEADS

This topic has 6 replies, 4 voices, and was last updated 10 September 2020 at 11:34 by Nicholas Farr.

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9 September 2020 at 13:22 #494868
noel shelley
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@noelshelley55608
Coventry Dieheads. The chaser cutting face rises at an angle, do all sizes use the same angle and what is it ? Not the rake angle! Does anyone have a height gauge for 3/4" and 1" dieheads, the graduations would span 70 to 150, or have any ideas as to making one ? Herberts book states that a different height gauge is needed for each size of diehead yet I have seen one that does all sizes up to 1/2".When was the "new Type" grinding fixture first produced ? Which edition of herberts "The Book of the Coventry Diehead" covers their use ? It will be higher than ed 19.

Many thanks Noel
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9 September 2020 at 13:22 #19939
noel shelley
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@noelshelley55608
9 September 2020 at 15:09 #494899
Anonymous
As far as I'm aware the angle stays the same, as it controls the transition from cutting to guiding. I don't know the value of the angle.

I have LH and RH height gauges for 3/4" and 1" dies. Height gauges vary; I've got one for 1/4" and one for 1/2" but the values overlap slightly. So presumably one or the other would also do for 5/16" and 3/8" dieheads. In theory it should be fairly easy to make a height gauge. One just needs the angle, the spacing of the ticks and one reference point from a known good die.

I don't know when the new grinding fixtures came in; I'd hazard a guess in the 1960s. They're not in my Ed 22 version of the handbook.

Andrew
9 September 2020 at 18:40 #494939
noel shelley
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@noelshelley55608
Dear Andrew, I had it in my mind that it could be 2.5* ? I have spent part of the afternoon researching this and the spacing give or take a little appears to be 1/16", this being found after measuring a gauge for 1/4" & 5/16 plus another for 1/2". Could you check this fact from your larger gauges ? Are there 2 gauges to cover 3/4" and 1" or is it one large one and what numbers does it cover ? Simple sums seem to indicate that the angle is 2.7* On your largest gauge could you measure the hight at 120 or 150.

Many thanks, Noel
9 September 2020 at 19:20 #494949
Clive Foster
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@clivefoster55965
Noel

I have a hard copy of the 23 rd edition of the Coventry Die Head Manual which does not mention the new type grinding fixture and a rather poor PDF of the 25 th edition which does.

So 25 th and later editions will certainly cover the new type grinding fixture. Maybe 24 th too but without sight of one its impossible to know.

I hoovered up a set of all three old style grinding fixtures for £ "very little" many years ago from someone who neither knew nor cared what he had. Hafta say I wasn't sure at the time either but I've always been a sucker for cheap almost unobtanium!

Never managed to luck into the height gauge. Which is annoying as all my die sets are still good enough not to need resharpening except for a couple with a broken front tooth or two. As I read the manual grinding those back to useable condition requires the gauge. Sigh.

Clive
10 September 2020 at 10:01 #495024
Anonymous
The RH & LH gauges are marked for 20mm, 3/4", 1", 2-1/2" FT and 3-1/2" FT dies. The numbers run from 50 to 145 on both gauges. I also have a RH gauge for 1-1/4" dies where the numbers run from 70 to 145. A die marked 77 is pretty close (±1) on both RH gauges. So I surmise that the numbers are linear across the complete range of dies, at least in the sizes we are likely to use. The height at 120, measured with gauge blocks, is 0.359".

I measured the angle on two gauges with a clinometer. I got 2°55" and 2°52". I'd agree that the markings appear to be 1/16" apart, as measured with a rule.

Andrew
10 September 2020 at 11:34 #495048
Nicholas Farr
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@nicholasfarr14254
Hi, this scan below is a copy from a PDF of; The book of the Coventry Diehead 24th edition. the only other mention is how to use it. I don't know if it is the one you a looking for though and there doesn't appear to be any angles quoted.

Regards Nick.

Edited By Nicholas Farr on 10/09/2020 11:37:24
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