Taylor Hobson’Trutaper’ mystery solved [?]

This topic has 3 replies, 3 voices, and was last updated 27 June 2026 at 22:34 by Bazyle.

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27 June 2026 at 21:44 #853765
Michael Gilligan
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@michaelgilligan61133
By letting ChatGPT do the donkey-work … I think I have probably found the underlying truth.

The taper wasvery closely measured by Charles, at 2.14° … but there is no obvious reason why Taylor Hobson would have choosen that slope.

Here, I think, is that reason … Manufacturing Convenience !

Quote from ChatGPT

The exact value 2.143° corresponds almost exactly to a taper of 1:13.333 on diameter (3/40), which is the sort of neat fractional ratio an engineer might deliberately choose.

QED ?

MichaelG.

.

Ref: https://www.model-engineer.co.uk/forums/topic/taylor-hobson-pantograph-engraver-model-d/
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27 June 2026 at 22:07 #853770
Nigel Graham 2
Participant
@nigelgraham2
That’s a “neat” ratio?
27 June 2026 at 22:12 #853771
Michael Gilligan
Participant
@michaelgilligan61133
Yes, Nigel … in the sense that it’s one that can be quickly and accurately set, using Jo blocks or whatever.

MichaelG.
27 June 2026 at 22:34 #853773
Bazyle
Participant
@bazyle
A few years ago on an unrelated forum there was a particular measurement accurate to a tenth thou we were trying to understand and many weird theories sort of fitted the numbers. I expected it to be a round figure something like cosine(13) from memory but no end of fiddling in Excel would give me that round figure. However then I realised that as it was designed in the ’30s they did not have Excel working to 20 decimal places – they just had 4 figure tables. When I did the calculation ‘inaccurately’ with my school sine tables book bingo; spot on.
So round figure 3/40 looks very plausible, not least because they would have drawn it fitting easily on a 4ft wide drawing board and then set the angle with 0.45 blocks and a 6in sine bar. edit no that’s wrong but can’t be bothered to work out the cosine.
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Taylor Hobson’Trutaper’ mystery solved [?]

Taylor Hobson’Trutaper’ mystery solved [?]

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