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My Pocketwatch

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ProfessorGuy

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#1
I did geometry and trigonometry for 2 weeks, culminating in publishing a series of tables on the "Shop-Made Tooling" forum. I filled more than 10 sheets of paper with diagrams and formulae, and created several spreadsheets.

math1.png

I finally came up with some firm decisions for my train. And that means after many years of planning, building my shop (check the "Our Shops..." forum), and getting familiar with the tools on small projects, I have begun construction on my spring detent chronometer pocketwatch.

Every journey begins with a single step. This is step one (of a million):

step1.jpg

This chunk of steel is going to be a specialized tool. I don't own a lot of expensive equipment, so even this simple cut will take some hand work. Get the hacksaw and cutting oil and get to work:

handcutting.jpg

Some rough grinding to put a 5 degree cant on the front edge, and drill a through hole also tilted 5 degrees. It is now a cutter base.

cutterbase.jpg

The angle makes the tool insert hang out over the edge, giving relief to the insert as it cuts. The insert, which becomes the second tool I've made for my watch, has 5 machining steps. The radius of the top end is to within 0.01mm.

cutterinsert.jpg

It drops into the base, the relieved tip can now etch a radius of exactly 0.59 mm. The radius it cuts will be the inside curve of a second cutter. That cutter will cut the teeth of the center wheel of my watch.

cuttercutter2.jpg

That's right, this is a wheel cutter-cutter. It makes a wheel cutter, which makes a wheel. Every wheel has its own cutter-cutter and cutter!

Still a little work to do. I trimmed the shoulder from my cutter insert so it could sit flat on the stage of the cutter base. It is critical that the insert not move during the cutting process--the tolerances here are pretty damn tiny--so it must sit nice and tight.

Also, I should clean up the base to guarantee it is flat, for that all-important support. Here the milling vice is mounted on the tilting table set at 5 degrees:

millingtool1.jpg

Polish the insert, then off to the high-tech hardening station. If you look carefully, you'll see the tiny insert wrapped in iron wire ready to be dipped into the bowl of icy cold New Hampshire water. Wrapping it assures control as the red-hot piece goes into the water--it must enter vertically so as to not distort the dimensions.

hardeningtool1.jpg

The hardened insert must be polished before tempering. I use a piece of hard, dry ash wood from a tree that grew outside my shop, sharpened and charged with polish.

polishingtool1.jpg

Into the bed of brass chips, which I collected last time I had to part a piece from a 1" brass rod (the largest diameter I've ever turned). The handy steel vessel was made by hand by my son!

temperingtool1.jpg

You may have laughed when I called the hardening station high-tech. But when you see my tempering furnace, you will understand I wasn't being ironic.

temperingfurnace.jpg

Yes, that's the woodstove that heats our house. Since there's a fire going from November to April, and since I'm cheap as hell, I'm going to try to temper in there even though I've never tempered steel in my life. Oh well, what could possibly go wrong? I rake out some coals and place the brass-filled steel dish on them. Then I watch. I was looking to bring it to straw, but I figured I'd take anything short of dark blue. When it looked to be darkening, I grabbed the vessel with a regular leather glove and quickly put it onto the stone hearth to cool (and quickly removed the glove). Took all of 3 minutes. Let's be generous and call it dark straw, good enough!

Finally, the tip is polished off with 2000 grit sandpaper (the base piece itself is the polishing jig), so it is razor sharp. Here's the tool completed and mounted in the toolholder of my lathe (note the straw-ish color of the insert):

tool1complete.jpg

Next step, make a wheel cutter!
 

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brino

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#4
I am "watching" too.

Thanks for sharing this!

-brino
 

mzayd3

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#5
Wow! You are an inspiration to the rest of us. I'll be watching with interest.


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ProfessorGuy

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#7
I tried a spring wire cutter. I would use my cutter-cutter to cut around the end of a small diameter rod in the lathe, turning the end of it into a cutter. To make a cutting edge, I'd cut away half of the diameter. But the cutting tip is only 0.39mm wide, so that makes the cutter only 0.195mm thick. That's not much meat for a cutter. Would that work?

One way to find out! I've read that a lot of cutters prefer to grub out most of the space between the teeth with a general cutter, then finish it with the perfectly sized gear-cutter to get a good shape without having to push a lot of metal out of the way. If I make a grubber--basically a too-narrow gear-cutter--I'll be able to get rid of most of the material between the teeth, and find out if a thin cutter like that can work.

I'll make a grubber to take out 0.30mm of the brass between the teeth (the final space will be 0.39mm wide). If that cutter can survive the process, then obviously the bigger final gear-cutter will have no problem.

I made a new steel cutter base. I hand etched a v-groove along the top, then glued the 0.3mm rod into the groove. I polished off the top of the rod to make a flat cutting surface and rounded the end:

grubbertrial1.jpg

The scale of this thing makes it seem unlikely this will work:

grubbertrial2.jpg

Install the grubber (or trial gear-cutter) into a fly cutter. Let me reiterate, this blade is small:

grubbertrial3.jpg

Set up to cut a partially parted wheel:

grubbertrial4.jpg

There will be 80 teeth, so each cut is 4.5 degrees apart. It looks OK, but why did I grub out only 2 teeth?

grubbertrial6.jpg

During the 4th cut, I heard a 'ping' and the cutter was sheared off:

grubbertrial5.jpg

Fail! OK, that was just one way to make a cutter. Time to move to plan B.
 

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ProfessorGuy

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#8
Plan B involves making a disc cutter and mounting it eccentrically in a mandrel.

That means I'll need a mandrel. Those are cheap, but in for a penny....

I made a mandrel. It has a stepped diameter so that it will fit into a through collet. My through collets go up to 5mm, the collets above that are stepped and can take only about 10mm of material.

For a first try, I think it looks quite pretty:

mandrel1.jpg

It takes a 40 tpi #4 allen head screw. Two soft brass washers for good grip:

mandrel2.jpg

Now for another try at a cutter. First shape some steel in the lathe:

cutter1.jpg

And I get to try out my cutter-cutter. It is used to shape both sides of the symmetric cutter:

cuttingcutter1.jpg

Hey! The cutter-cutter worked! I guess the tempering and sharpening was sufficient. It'll need an eccentric hole for mounting on my pretty mandrel. For those old time machinists, I apologize beforehand. I parted off the cutter above, then found I had absolutely no way to drill through it. The edges are cutting surfaces which cannot be dinged--so no vice. Ut-oh. OK. On to try #2:

eccentricdrilled.jpg

That huge hole accommodates the tiny #4 screw of the mandrel. This entire cutter is less than 1/4" in diameter. Some filing with a safety edged file and the cutter surface (and the shape between the teeth of the gear) becomes clear:

cutter2.jpg

Unfortunately, I didn't drill the hole deep enough. Yes, I'm very smart and I know how big a millimeter is. But I managed to blow this. Trying to clamp it to finish the hole completely destroyed this cutter. Let me stress how tiny these pieces are.

I keep a little set of shelves in my shop. It is my museum of failures. Plenty of exhibits on display (there are a dozen screws in one of the bags):

failshelf.jpg

The failed cutters get their own shelf:

failedcutters.jpg

Since I am using up only about 1 gram of steel on each attempt, I can keep this up for another few thousand tries. Stay tuned.
 

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David S

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#9
Hi Professor. I work on clocks so am keeping track of your and Wagner's Thread.

I often have to make a clock wheel or replace teeth. To cut the spaces on a rotary table I use 1" diameter jeweller's slitting saws. They are available in various thickness's. I think the thinnest that I have is 0.008" (.2mm). I have a selection and I stack them on the arbor to get the desired thickness. You can take full depth in one pass and I find very much faster than multiple passes with a single point cutter.

Save the single point for the final pass??

David
 

ProfessorGuy

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#10
To cut the spaces on a rotary table I use 1" diameter jeweller's slitting saws. They are available in various thicknesses. I think the thinnest that I have is 0.008" (.2mm).
25mm diameter is far too large to fit between the collet and tailstock while cutting the pinions, and it is the steel pinions rather than the brass wheels that most require the pre-cutting. So for wheels and pinions, I'm making my own cutters (and pre-cutters where necessary). However, when I get to the escapement, I believe it must be made with slitters.

You can take full depth in one pass and I find very much faster than multiple passes with a single point cutter.
Neither how many passes nor at what speed I am able to cut are considerations here. Unlike a tradesman, I am trying to make one watch and how long it takes matters not a bit.

In The Artificial Clockmaker, published 1734, William Derham espouses clockmaking as an avocation: The country gentleman may fill the vacant hours with delight in Mechanical Studies and Exercifes: To whom it hath been an Innocent and vertuous Diverfion.
 

brino

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#12
I keep a little set of shelves in my shop. It is my museum of failures.........The failed cutters get their own shelf
That's a neat idea.....not to torture the maker, but more like trophies of what I tried and learned did NOT work.
When I see some of my old failed parts I realize how much I actually learned from the attempt.
However there is no way that all of MY mistakes could be smuggled out in a pocket.....

Thanks again for sharing all this effort and for the fine close-up pictures!
-brino
 
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atlas ten

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#13
I'm following this too. I too have a collection of broken thinks but mainly auto parts. I'm thinking about trying a wooden escapement for my first clock. Not sure were to even start with clock making.
Jack

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TommyD

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#14
I like your attitude about making your cutters and use of your time, a real craftsman. Nice work.

I used to live in Bristol, CT and have seen and fixed some old time tooling used way back when Bristol was the clock making capitol.
 

Nick01

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#15
I second Tommy D ^
Just the fact that you took the time to create your own cutter from scratch when they're readily available online in most common watch sizes speaks to your dedication and craftsmanship.

I'll be following this thread as well and hopefully learn a thing or two from you as I undertake my clockmaking projects.
 

savarin

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#16
Just found this thread, excellent work. Subscribed.
I also attempt to make as much as I can but not in the micro catagory:immersed:
 
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