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Posted by Youra on May 2, 2008, 4:46 am
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Hi all.
<apologies for x-post, but both groups seem appropriate....>
I'm building - and learning much from - my first 'clock' - the John
Wilding weight driven egg timer - from the original HJ articles.
I'm a little stuck on a 'missing' dimension in the drawings - the tip
width of the teeth in the 48-tooth ratchet wheel. In the text, this is
not really described - other than saying a small 'witness' should be
left - I was thinking that something around 0.02" (0.5mm) might be
appropriate - or would more (or even less....!) be better ?
I'm making a custom cutter to cut the teeth, to this is quite an
important number......
It's very possible that it's better described or specified in the
later re-print as a separate project in his book, but I don't have a
copy......
Advice, pointers and hints gratefully received !
Thanks,
Youra.
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Posted by Tony Jeffree on May 2, 2008, 5:32 am
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On Fri, 2 May 2008 01:46:21 -0700 (PDT), Youra
><apologies for x-post, but both groups seem appropriate....>
>
>I'm building - and learning much from - my first 'clock' - the John
>Wilding weight driven egg timer - from the original HJ articles.
>
>I'm a little stuck on a 'missing' dimension in the drawings - the tip
>width of the teeth in the 48-tooth ratchet wheel. In the text, this is
>not really described - other than saying a small 'witness' should be
>left - I was thinking that something around 0.02" (0.5mm) might be
>appropriate - or would more (or even less....!) be better ?
>
>I'm making a custom cutter to cut the teeth, to this is quite an
>important number......
>
>It's very possible that it's better described or specified in the
>later re-print as a separate project in his book, but I don't have a
>copy......
>
>Advice, pointers and hints gratefully received !
Youra -
I suspect that you are about an order of magnitude too big there - I
would go for something nearer 2 thou, possibly less.The point of
leaving a witness is just to ensure that you don't end up with a wheel
that is undersized - what you do is to cut the wheel blank to the
correct OD, then coat the cut edge with a marker pen so that the
witness is obvious when you cut a pair of adjacent tooth spaces. You
adjust the depth of cut so that the witness is only just visible; at
that point the depth of cut is correct. If you leave a witness that is
too wide, the depth of cut will be too small. This probably isn't
really a big deal on a ratchet wheel, other than that the tooth shape
won't look quite right if the depth of cut is too small; on a gear
wheel if you get the depth wrong it will change the pitch diameter of
the wheel, so the centre to centre distance between it and whatever it
meshes with will be affected.
Regards,
Tony
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Posted by Youra on May 2, 2008, 7:56 am
Please log in for more thread options > On Fri, 2 May 2008 01:46:21 -0700 (PDT), Youra
>
>
>
>
> Youra -
>
> I suspect that you are about an order of magnitude too big there - I
> would go for something nearer 2 thou, possibly less.The point of
> leaving a witness is just to ensure that you don't end up with a wheel
> that is undersized - what you do is to cut the wheel blank to the
> correct OD, then coat the cut edge with a marker pen so that the
> witness is obvious when you cut a pair of adjacent tooth spaces. You
> adjust the depth of cut so that the witness is only just visible; at
> that point the depth of cut is correct. If you leave a witness that is
> too wide, the depth of cut will be too small. This probably isn't
> really a big deal on a ratchet wheel, other than that the tooth shape
> won't look quite right if the depth of cut is too small; on a gear
> wheel if you get the depth wrong it will change the pitch diameter of
> the wheel, so the centre to centre distance between it and whatever it
> meshes with will be affected.
>
> Regards,
> Tony
Tony - many thanks for the reply.
I think I see what you say - however the depth of cut is clearly
specified (1/4"), so I had been planning to set up the wheel in a
dividing head on the milling machine, and cut each space in one go -
that's why the tip thickness is so important - adjusting it will
adjust exactly how I make the ratchet wheel cutter (I think) as the
vertical part of the tooth is not on a radius of the circle segment
that makes up the curved bit.
I'll do some more sketches and see if I can simplify it any further in
my own head...
Cheers,
Youra.
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Posted by Tony Jeffree on May 2, 2008, 8:15 am
Please log in for more thread options On Fri, 2 May 2008 04:56:28 -0700 (PDT), Youra
>> that point the depth of cut is correct. If you leave a witness that is
>> too wide, the depth of cut will be too small. This probably isn't
>> really a big deal on a ratchet wheel, other than that the tooth shape
>> won't look quite right if the depth of cut is too small; on a gear
>> wheel if you get the depth wrong it will change the pitch diameter of
>> the wheel, so the centre to centre distance between it and whatever it
>> meshes with will be affected.
>>
>> Regards,
>> Tony
>
>Tony - many thanks for the reply.
>
>I think I see what you say - however the depth of cut is clearly
>specified (1/4"), so I had been planning to set up the wheel in a
>dividing head on the milling machine, and cut each space in one go -
>that's why the tip thickness is so important - adjusting it will
>adjust exactly how I make the ratchet wheel cutter (I think) as the
>vertical part of the tooth is not on a radius of the circle segment
>that makes up the curved bit.
Youra -
I think you are talking about the escape wheel (not a ratchet!), in
which case, if the tip of the tooth is too wide it may interfere with
the proper operation of the escapement.
What cutter does John recommend in the article? It looks like a pretty
conventional recoil escape wheel from the pics I can see on the web.
Making an escape wheel cutter of the right shape is going to be
interesting...
Regards,
Tony
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Posted by Youra on May 2, 2008, 8:33 am
Please log in for more thread options > On Fri, 2 May 2008 04:56:28 -0700 (PDT), Youra
>
> I think you are talking about the escape wheel (not a ratchet!), in
> which case, if the tip of the tooth is too wide it may interfere with
> the proper operation of the escapement.
>
> What cutter does John recommend in the article? It looks like a pretty
> conventional recoil escape wheel from the pics I can see on the web.
> Making an escape wheel cutter of the right shape is going to be
> interesting...
>
> Regards,
> Tony
Hi
Yes - it is the same shape as an escape wheel - John refers to it as
the ratchet wheel in the article though - the escapement proper is
made up of the single pin escape wheel crank and the pallet arm
slightly higher up the mechanism - in most of the pics on the web, is
the thing that's just above the egg marked '6' at the top of the dial
ring.
He doesn't recommend a cutter - the article originally had the radial
cuts done with a slitting saw on the mill/dividing head, all the
curved edges of the teeth marked up by hand and then cut with a hand
saw and filed to shape - I thought I'd give making a cutter to suit
the teeth a go, based on the instructions in "Making Clocks - workshop
practice vol33" - it looks relatively straight forward <gulp>.
I may rough them out by hand and use the cutter to finish them off,
mostly so the cutter lasts for all 48 teeth !
Your point about interfering with the action of the suspended lantern
pinion that mates with it is very well made - I'll try and keep below
0.005"....
I'll post some pictures with links when I'm done - unfortunately a
specific radius cutter I've ordered to make the form tool with hasn't
arrived in time to be used over the BH weekend, so it won't be for a
couple of weeks yet.
Thanks !
Youra.
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>
>I'm building - and learning much from - my first 'clock' - the John
>Wilding weight driven egg timer - from the original HJ articles.
>
>I'm a little stuck on a 'missing' dimension in the drawings - the tip
>width of the teeth in the 48-tooth ratchet wheel. In the text, this is
>not really described - other than saying a small 'witness' should be
>left - I was thinking that something around 0.02" (0.5mm) might be
>appropriate - or would more (or even less....!) be better ?
>
>I'm making a custom cutter to cut the teeth, to this is quite an
>important number......
>
>It's very possible that it's better described or specified in the
>later re-print as a separate project in his book, but I don't have a
>copy......
>
>Advice, pointers and hints gratefully received !