Gear Depthing Tool

[Mogens KildeParticipant @mogenskilde92996]

Hi All

 

After making my dividing head, I have now made a depting tool

 

 

Next job will be making a wheel and a pinion to test my tools

 

Regards

Mogens

[Mogens KildeParticipant @mogenskilde92996]

[Geoff TheasbyParticipant @geofftheasby]

Now then, this raises a question which has been bothering me for a while.

Why do clockmakers use a depthing tool?

 

Most model engineering is so precise, the more accurate the better, and yet it seems that clockmakers have to hand-fit every spindle and shaft by reference to how well the gears fit together.

 

Can’t you make the holes in the right place, make the wheels and pinions to the drawings, and have it all fit together nicely as intended?

 

Regards

Geoff

 

 

 

 

 

[RJWParticipant @rjw]

 

Sorry folks, there seems to be a word limit or something, as my reply won’t appear in full,

Will try again later.

John

Edited By RJW on 05/04/2011 21:28:47

[Tony JeffreeParticipant @tonyjeffree56510]

Posted by Geoff Theasby on 05/04/2011 15:23:17:

Now then, this raises a question which has been bothering me for a while.

Why do clockmakers use a depthing tool?

 

Most model engineering is so precise, the more accurate the better, and yet it seems that clockmakers have to hand-fit every spindle and shaft by reference to how well the gears fit together.

 

Can’t you make the holes in the right place, make the wheels and pinions to the drawings, and have it all fit together nicely as intended?

 

Regards

Geoff

 

 

 

 

 

Geoff –

 

In clockmaking, the objective is to get a good “running fit” between each wheel/pinion pair. In an ideal world, yes you could predict the appropriate centre-to-centre distance to achieve that for a given pair; however, in a world where you are making your own wheels and pinions and the PCD of the resultant object may not necessarily be precisely what it should, you need to use a depthing tool in order to figure out precisely what C-T-C distance you need for the components that you have in hand.

 

There’s a saying in clockmaking – “if it rattles, it will run” – what you are aiming for isn’t the perfect backlash-free fit, because in all probablility, the resultant friction will be way too high and the clock won’t run. So a clockmaker will err on the side of a loose fit, which will help reduce the gearing friction. Bear in mind that the drive train of a clock involves a massive gearing up; the cord that suspends the driving weight in my long-case clock is wrapped around a barrel 16 times to give 8 days of running, so 1 turn of the barrel represents 12 hours of running, so the escape wheel (which carries the seconds hand) rotates 720 times for each rotation of the barrel. Introduce any unnecessary friction into that system and the clock won’t run.

 

And of course, given that the drive train is always being driven in one direction, any backlash in the train that may result from your “rattling” fit is of no concern whatever.

 

Regards,

Tony

[Geoff TheasbyParticipant @geofftheasby]

Thank you, Tony. That helped a great deal.

 

Regards

Geoff

[Richard ParsonsParticipant @richardparsons61721]

One of the reasons why clockmakers use depthing tools is the type of gear wheels used.

Firstly whilst Involutes are sometimes more often Epicycloids and Hypocycloids are preferred.

Secondly the clock gear wheels are very often much thinner than an engineer would use. In my English Regulator in the ‘going train’ they vary from 1/16” (1.6mm) to 3/16” (appx 4mm) wide. These wheels drive/are driven by pinions or in my case lantern wheels. A lantern wheel is two disks joined by round bars. In my case these bars also rotate in their brass disks and are held in place by hardened steel disks which acts as end stones

Making my regulator I was very careful to drill, ream and burnish the bearing holes as well as turning and burnish the pivots to the correct engineering running fits. I built the darned thing up and it would not run. I got the odd ‘tick’ out of it and once a ‘tock’. I spent 4 weeks checking everything again and again and found nothing. I dumped the thing in a box where it stayed for about 6 months. I mentioned the problem to a clock maker i knew. He said ‘your fits’ are not right. I pulled out my pocket note book and showed him. He muttered ‘God these are MUCH too tight. I broached the bearing holes with tapered broaches and burnishers. I ‘topped’ the wheels skimming up to 0.007” (0.18mm) off them. I rebuilt the clock. To my surprise (and horror) the blooming thing ran. That was 12 years ago. It is still running and I hope that when it is loose enough I will be able to fit the double pulley loop on to the drive weight and make it a 14 day clock.

Now i will use a deapthing tool!

Edited By Richard Parsons on 07/04/2011 17:39:33

[Mogens KildeParticipant @mogenskilde92996]

Hello All

 

Thank you for the kind words.

 

I’m also very happy about the latest replys, for a moment I thought that my work on this tool was a waist of time, but now I’m more comfort again.

 

Mogens

[Stephen BensonParticipant @stephenbenson75261]

I wanted to reply to this thread but I can not add pictures, I can add pictures if I create a new thread but not to an existing thread what am I doing wrong I am using Chrome

[YouraTParticipant @yourat]

Hi Mogens.

 

Nice depthing tool – is it to your own design, or another?

 

How did you ensure the parallelism required ?

 

Cheers,

 

Youra.

[Mogens KildeParticipant @mogenskilde92996]

Hi

 

I made a special fixture for my mini mill

 

 

 

Mogens

Edited By Mogens Kilde on 18/05/2011 15:27:29

Edited By Mogens Kilde on 18/05/2011 15:28:04

[Stephen BensonParticipant @stephenbenson75261]

I did not want to upset anyone as
you have beautiful depthing tool which would be great for clock repair as well as clockmaking however I did not want somebody thinking they need to buy or make a traditional
depthing tool like yours to make a clock from scratch.
In most cases it is easier to
make the pinion as separate item and then fit it to the arbor later (I use 601
Loctite retainer ). The reason being that you can cut more than one pinion at
once and it is much easier to harden and temper the pinions if they are off the
arbor.>>

I prefer lantern pinions on my clocks
as I believe they offer lower friction but there are many that hold the reverse
view so the only work in progress clock I have at the moment has
lantern pinions.

I
have added enough views so that anyone could make one there several designs of
this tool mine is based on a John Wilding design modified so it can be mounted
in a vice.

Sussed the insert picture problem I had to scroll up to find the insert picture popup 

 

Edited By Stephen Benson on 18/05/2011 16:47:12

[YouraTParticipant @yourat]

I made a very similar tool when I constructed my first (and, it has to be said, thus far only) clock – also a Wilding design – the Egg Timer. Lantern pinions also.

 

http://picasaweb.google.com/youra.turceninoff/WildingEggTimerConstruction

Your vice mounting modification is a good idea – I may need to copy…

 

I still like the idea of making a depthing tool to the ‘old pattern’ as it were – but a fabricated version rather than one based on a casting seems the way to go.

Edited By YouraT on 18/05/2011 17:02:41

Edited By YouraT on 18/05/2011 17:02:59

[NJHParticipant @njh]

Hi Guys

 

Here is my variation on John Wildings theme!

I have added a “fine adjuster” as I found that tightening the moveable arbour sometimes changes the adjuustment and the need for three hands is reduced!

 

 

 Not any way near your standard though Morgens!!

 

 

Regards

 

Norman

Edited By NJH on 18/05/2011 19:16:15

Edited By NJH on 18/05/2011 19:17:38

Edited By NJH on 18/05/2011 19:18:04

[roy entwistleParticipant @royentwistle24699]

Remember that in a clock the wheels are driving the pinions which is not how an engineer would design it but thats the way things are. Also remember that a lot of country clocks were made by the village blacksmith who by tradition wouldn't measure anything. Things were made to fit each other.

Roy

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