Hand-filing a square accurately

I am studying watchmaking via the British Horological Institute's Distance Learning Program. The practical lessons of the first year involve a lot of filing and precise measurement. I've made some hand levers, a small try square from gauge plate, and a hardened scraper. I scored well on those assignments. But now I'm working on the next assignment and I want to squeeze out some improvement on my accuracy when filing squares.

The assignment requires filing a piece of 1.5mm brass into a piece 1.2mm thick, 25mm wide, 30mm long.

I dealt with the thickness by filing it on a cork pad -- this kept it level with the file, and then I finished it page of sandpaper. I measured the accuracy using my micrometer. It was averaged to 1.20mm, with only 0.02 deviations, so I was happy enough.

The edges, 25x30mm, I feel like there is another tier of accuracy I could get to, but my current techniques don't achieve it.

Here's a range of the tools I employ:

My approximate technique is:

1. Decide on master edge, file it roughly flat.
2. Hold it against my try square edge to see how flat it is.
3. Try to eliminate the high spots using either (a) needle file (b) my stainless stick with some sandpaper glued to it (c) or drag the entire face across a sheet of sandpaper. The needle file seems to round the edge, as the file flexes a bit. If I drag (c) the piece, I have to do it unidirectionally (pull it perpindicular towards me), otherwise when i push it away from my i build up a slightly different angle). The "sandpaper stick" does ok for small patches, but it's tedious to reapply fresh sandpaper after it degrades.
4. Recheck the edge flatness with the try square, repeating step 3-4-3-4 until it seems "straight".
5. Then I start doing the same process with the adjacent ends, using the try square taking data from the "master edge".
6. Finally wrap up the opposite side of the master edge using one of the other sides as the datum for the try square. [this seems most dodgy -- accumulated square errors as i work from master to side to the oppositeMaster]


The results? It's pretty darn square. It's just that the try squares never are light tight and the light crack results are very hard to repeat. I even think that micro grit messes up the reading. The try square has 1mm thick blades, and the base is a heavy ground block. I bought a preisser bevel square with narrow, unnicked edges and i have trouble getting consistent light-tightness measurements using that too though.

I feel like the last few percent perfection on this is limited by me: 1) not using the try square or bevel square well enough (are their tricks tips to using them?) 2) my last bit of micro-finishing work not quite fine enough. (but I think any micro-finishing effort is doomed if i am not exactly where the high spot is, so perhaps issue #1 is most important to deal with first?


Any advice on how to get closer-to-light-tight accuracy and squareness on tasks like this?

Thanks

First, you could improve your measuring tools. A used but in good condition vintage micrometer would have considerably better accuracy than your vernier calipers. And there are many listed on eBay for not much.

A really square square would also help---like a granite block purpose made and widely available. In the size you need also cheap. Use spotting dye to compare your square to a granite (or steel) square on a small granite surface plate. A small plate is about 25 dollars and will last you your career. Spotting dye will be much more sensitive and repeatable than the "light crack test."

But, most of all grab a few books on metrology and find a metrology mentor--tool and die maker---near you.. There is a ton written about solving this problem. If you work at it some and get some decent guidance, you will get amazing results. You have already demonstrated a fair bit of patience and attention to detail necessary to get to the next level.

Incidentally, I am presently reading Daniels' Watchmaking. Fascinating stuff and a beautifully written and illustrated book I am sure you are familiar with.

Denis

karavshin said:

I feel like the last few percent perfection on this is limited by me: 1) not using the try square or bevel square well enough (are their tricks tips to using them?) 2) my last bit of micro-finishing work not quite fine enough. (but I think any micro-finishing effort is doomed if i am not exactly where the high spot is, so perhaps issue #1 is most important to deal with first?


Any advice on how to get closer-to-light-tight accuracy and squareness on tasks like this?

Thanks

Click to expand...

Gotta love that file handle..

You could use engineering blue to mark your high spots, and just work on getting a consistent blue transfer.. If you don't have blue, you can use lamp black.

How good are those squares? Do you have access to a surface plate?

Ray

dgfoster said:

First, you could improve your measuring tools. A used but in good condition vintage micrometer would have considerably better accuracy than your vernier calipers. And there are many listed on eBay for not much.

Click to expand...

Ooops, yeah, I forgot to include that. I was using a small 25mm vernier micomenter to measure the thickness. You reckon I should use a vernier for the width and length, too?

dgfoster said:

A really square square would also help---like a granite block purpose made and widely available. In the size you need also cheap. Use spotting dye to compare your square to a granite (or steel) square on a small granite surface plate. A small plate is about 25 dollars and will last you your career. Spotting dye will be much more sensitive and repeatable than the "light crack test."

Click to expand...

Love this idea -- makes tons of sense. Thanks.

dgfoster said:

But, most of all grab a few books on metrology and find a metrology mentor--tool and die maker---near you.. There is a ton written about solving this problem. If you work at it some and get some decent guidance, you will get amazing results. You have already demonstrated a fair bit of patience and attention to detail necessary to get to the next level.

Incidentally, I am presently reading Daniels' Watchmaking. Fascinating stuff and a beautifully written and illustrated book I am sure you are familiar with.

Click to expand...

I have a a book from Mitutoyo that is interesting and "foundations of the mechanical accuracy" (about jig borer development) that is staggering however many orders of magnitude beyond me. ahaha

(yes, the Daniels book is similarly staggering)


thanks

What a joke.

So this school is charging you hundreds of pounds so you can file blocks "accurately"? Over here in the USA we call that a scam.

First, a salute to you on pursuing such a challenging discipline.

In addition to the glorious history of British (and Chinese, given your location) horology, you stand heir to perhaps the most powerful, precise, and efficient languages on earth. To that end, I must protest that one cannot file a "square", that is, a two dimensional shape with equal, straight sides each at right angles to its neighbor. If the sizes of the sides of your 3D object were equal, you would be filing stock to a cube shape. Given the unequal sides, you are filing to a cuboid shape. Alternately, a right rectangular prism shape.

I'd 'a let "cube" pass without comment (cuz a cube is 3D), and a "rectangle" might have gone unmentioned (cuz a rectangle has unequal sides), but "square" is wrong on two counts!

Just given you the business. Filing a cuboid is old school, but once you've done it you've figured out a lot of problems and know a lot of techniques. I wonder if the lay public has any appreciation for all the subtleties that this "simple" task requires?

Good luck, and be proud! You're not just filing a square, you're filing a cuboid!

John Welden said:

What a joke.

So this school is charging you hundreds of pounds so you can file blocks "accurately"? Over here in the USA we call that a scam.

Click to expand...

In other parts of the world it's called learning a traditional craft...

Ray

I would add to my kit a small angle plate and a surface gauge. Then you can scribe layout lines on both sides of the piece to help guide your filing efforts.

You should ask over here National Association of Watch and Clock Collectors Message Board what you need is a filing block but these can get expensive and maybe not easily found in your area?

karavshin said:

Ooops, yeah, I forgot to include that. I was using a small 25mm vernier micomenter to measure the thickness. You reckon I should use a vernier for the width and length, too?
<>
(yes, the Daniels book is similarly staggering)

Click to expand...

Yes, use the most accurate tool you can come up with. Whatever dimension you are trying to hit you should use a measuring method one order of magnitude more precise than that dimension. If you are going for .02mm (.0007" for those of us who live in a part of the world where we are so sophisticated as to never be scammed into learning an awesome traditional craft) you should be using a .0001" micrometer.

I think I would be filing first and then using abrasive films to lap to final squareness and dimension.

Good luck. I hope you post pics of a gleaming, highly accurate block completed to better than requested accuracy. Those same skills will transfer over when you want to make a couple of small precision squares etc from hardened (initially soft) tool steel.

It was really interesting to see the tooling Daniels and others use like special jig borers to elegantly solve, on a very small scale, machining problems that most PMers work to solve an a scale 100 times larger.

Denis

timeseeker said:

You should ask over here National Association of Watch and Clock Collectors Message Board what you need is a filing block but these can get expensive and maybe not easily found in your area?

Click to expand...

Hmmm. I couldn't even google to get a decent explanation of what a filing block was. Esslinger said a filing block was a piece of wood to protect metal being held in a vise. A guy on etsy was selling a rubber shoe like thing which is maybe similar to my cork plate for filing the the thickness? Perhaps there is yet another type?

karavshin said:

Hmmm. I couldn't even google to get a decent explanation of what a filing block was. Esslinger said a filing block was a piece of wood to protect metal being held in a vise. A guy on etsy was selling a rubber shoe like thing which is maybe similar to my cork plate for filing the the thickness? Perhaps there is yet another type?

Click to expand...

Yes sorry I call them a filing block but it's correct name is a swing tool, Horia is the only company that still makes it, but many older watch co did as well,you can find them from time to time at that online auction.

RayG said:

In other parts of the world it's called learning a traditional craft...

Ray

Click to expand...

Yeah sounds likes he really learning a traditional craft.

Too bad they don't even bother to show him the proper tools or technique. Scam.

I'm not sure that this would be considered a scam John. I worked in a German machine shop for five years (Hauni Hamburg) and some of the machinist told me that in their apprenticeship program they had to file a vise out of a block of steel. Acme threaded shaft and all. The only part they could "cheat" on was that the nut for the threads was just an engagement pin driven into a groove in the movable jaw. I never got around to asking them how they got a hole to start with but they said it was all done with files. Of course that's not all they are doing but the project was due at the end of their first year. These are some very fine machinist who really know what they are doing. I suspect all that hand work gave them a good "feel" for working metal, measuring and a lot of the tricks of the trade. I read a story once about some prisoners of war who built a working lathe during WW2 from scrap and you can bet they knew something about filing. I would equate this task that Karavshin was given with any seemingly mundane chore given a trainee in any trade that teaches hand eye coordination etc.

Most of these filing stories end in bullshit, I dont beleive that German vise story at all. A kraut I apprenticed with for a couple years said all they had to file was a little hammer head hammer and a tiny square. All I had to file during mine was an dial indicator holder(aka a big metal mustache) to use for aligning couplings. These stories usually go the way of guys who claim to measure to a thou with a ruler. You have to remember apprentices are paid by the hour and are expected to make the company money, dicking around letting 3-4 kids file something for 2 months would bankrupt a company.

Its a distance course in watchmaking the OP is taking, a mans gotta be given some sort of project to do I guess. Congradualtions on your learning project OP, I myself am fascinated by horology and have been thinking of trying my hand at one of John Wildings project clocks.

hickstick_10 said:

Most of these filing stories end in bullshit, I dont beleive that German vise story at all. A kraut I apprenticed with for a couple years said all they had to file was a hammer and a tiny square.

Its a distance course in watchmaking, a mans gotta be giving some sort of project to do I guess.

Click to expand...

It turns out that a true watchmaker (not a battery changer technichian) has to use hand filing, drilling, and burnishing techniques, to name just a few, throughout his career. It is an absolutely essential part of the job. That is as opposed to watch manufacturing done with high speed, mass producing machines which has its own cool factor. But it is entirely different and difference in the resulting watches are as different as a Ferrari and a VW Jetta. The Jetta is fun to drive and very practical. The Ferrari is on another level....

Denis

John Welden said:

Too bad they don't even bother to show him the proper tools or technique. Scam.

Click to expand...

He he... and apprentices today think that a file is something that you either zip, or upload to a cnc... now that's a real scam.

Ray

dgfoster said:

It turns out that a true watchmaker (not a battery changer technichian) has to use hand filing, drilling, and burnishing techniques, to name just a few, throughout his career. It is an absolutely essential part of the job. That is as opposed to watch manufacturing done with high speed, mass producing machines which has its own cool factor. But it is entirely different and difference in the resulting watches are as different as a Ferrari and a VW Jetta. The Jetta is fun to drive and very practical. The Ferrari is on another level....

Denis

Click to expand...

With watchmaking and horology I have no doubt as the scale of the work alone allows that, its the machinist (smelting the ore and filing it into a small engine) stories that I hate. The only proof I've ever seen was the japanese POW lathe, and even they had machine tools to complete it.

hickstick_10 said:

Most of these filing stories end in bullshit, I dont beleive that German vise story at all. A kraut I apprenticed with for a couple years said all they had to file was a little hammer head hammer and a tiny square. All I had to file during mine was an dial indicator holder(aka a big metal mustache) to use for aligning couplings. These stories usually go the way of guys who claim to measure to a thou with a ruler. You have to remember apprentices are paid by the hour and are expected to make the company money, dicking around letting 3-4 kids file something for 2 months would bankrupt a company.

Its a distance course in watchmaking the OP is taking, a mans gotta be given some sort of project to do I guess. Congradualtions on your learning project OP, I myself am fascinated by horology and have been thinking of trying my hand at one of John Wildings project clocks.

Click to expand...

No it's true! And the Wright brothers made a crankshaft for their engine on a drill press. They only used chisels and files..... ITS TRUE!!!!

So funny how humans can't resist believing in complete bullshit if it makes them feel good.

I truly love German MASTER machinist filing stories.

A filing rest is another way to file accurately. Here is a link to a thread on another forum with detailed info.

Homemade Filing Jig

These used to be very common in the heyday of small plain turning and watchmaker's lathes. I have seen several references in old books where they were used to file squares, hexes, etc. on the end of pieces while they were still mounted in the lathe.