Re-grooving Files and Tongs

by Jamie Hall on May 21, 2010

Annealing the tongs

I’ve been doing some work on our tongs at work, so I thought it was worth posting about it. I decided to do this because of my historical work – it’s nice to see that my efforts are starting to spill through into the real world. In this case, it’s two sets of tongs that I’ve re-grooved, but the same principle applies to files.


Armed with a cold chisel, I wanted to solve the problem we have with the tongs not gripping that well. We only really use them for wire drawing, and the teeth had become too smoothe. The tongs are antiques; one pair is from an old Derby firm of traditional jewellers that closed in the 70’s. My dad suggests that they are soft iron that has been cast and then forged, with the grooved tool face hardened after cutting.

The tongs

The first step was heating the tongs and letting them cool slowly, in the hope of softening the metal (first image). I then opened the tongs up as far as possible, and placed them into a vice (second image). It was quite an effort opening them up – one jaw had gradually gouged a lip into the other, preventing them from opening far; that had to be ground off with the flex-shaft. If you look at the expanded image, the grooves are a very clear cross-hatch pattern, and you can even see the slope of the grooves – they run in the other direction to a file, but they are otherwise similar.

Re-grooving

Using the chisel and a claw hammer (the other hammers are too good to damage this way), I started cutting the grooves (third image). The chisel was certainly making a difference – the metal left behind was bright-cut by the tool. The first pair of tongs I did had wider grooves, and were much easier to do than the pair pictured – this might be a matter of how fine the chisel was. One useful technique I found was to apply pressure slightly more on one side of the chisel, which seemed to move the leading edge along the existing groove. But that wouldn’t have been an issue if I’d had a wider chisel, which would have allowed me to go each groove with a single strike.


I have some files that might benefit from this treatment, but I’ll need to purchase a wider chisel for the purpose, and make sure that the cutting edge is a fine as possible. I’d like to have some ability in this area because it was the only way to make files in history, as far as I can see. In Anglo-Saxon Crafts, Kevin Leahy describes some files found in a 7th century grave in Lincolnshire; these have a simple pattern of grooves that run perpendicular to the length of the tool – by the late medival period, pictures of files seem to suggest that they had the modern crosshatched pattern. In any case, there was no other method than hammering or chiselling to achieved the desired surface.


UPDATE: Make sure you check the comments section of this post, as there is more information there than I’ve supplied in the article.

{ 5 comments }

Lynn June 25, 2010 at 03:19

Nice… I wonder how fine of a file you could re-work? Would probably depend on the chisel… do they make small chisels?

Anyway, enough rambling. Great post.

Jamie Hall June 25, 2010 at 09:07

In principle, you could re-work a file as fine as the chisel you have. In practice, I think a lot of modern files would be difficult – they have a lot of teeth, and to do it well, the teeth all need to be cut at the same angle. Anything thin would be deformed by the process.

Thanks for your comment, Lynn.

Torsten September 20, 2010 at 13:49

Nice article!

For the files… it is actually quite simple and easy to produce very fine files with medi-eval techniques (as described by the German monk Theophilus Presbyter in his work De Diversis Artibus from the 11th century).

For the tools you need:
– an asymmetric shaped chisel (edge sharpened only on one side).
– a little anvil placed upon a pole
– a strong cord or leather strap with loops at the ends (for placing your feet to fixate the workpiece)
– a hammer
– some round steel rod
Materials:
– a raw, uncut file forged from soft iron (and cooled down slowly, as you did with the tongs)
– some fat (pig or cattle is easy to come by)
– some thin (goat) leather
– some thin linen (or hemp) thread
– some clay
Main Process:
The raw file is placed upon the anvil which is in front of your seat. Then strap is placed over it and you place your feet in the loop-holes, thus holding the raw file in place. You then start to cut the teeth using hammer and chisel (early medi-eval period cutters would start near the handle, late medi-eval cutters near the top). With a little excercise you should be able to cut 2-3 teeth per millimeter. When working on the file, you will notice that the workpiece will move on the anvil in just the right direction to make the next cut.
From time to time you may need to adjust the workpiece or straighthen it – you should also draw the steel rod over the cut teeth from time to time in order to adjust the angle of the teeth. If you are working on a somewhat larger file, you may also to re-fatten the surface form time to time.
Hardening:
Now, the cut file is still soft – heating it up and plunging it in water will do not much good, because of the low carbon content, so carbon must be added to the surface first…
Apply a layer of fat on the file’s surface. Wrap the file in well fatted thin goat leather (one layer only, you may use different leather, but since goat leather is very flexible, it is suited best for the task) and fixate the wrapping with linen thread. Finally, apply a layer of clay and let it dry (just like pottery) for a couple of days – take care that no cracks develop during the drying process (the clay is used to keep the oxygen off the carbon and the iron; theoretically, you would not need the leather, but it prevents contamination of the file by sand from the clay).
When the clay is dry, put the file in a furnace and heat it up. At good forging temperature, the carbon from the fat (and the leather) will wander into the surface of the file (about 1 mm per hour). After enough time has passed to let sufficient carbon find its way into the iron of the file, pull the file out of the clay, quench it in cold water and temper it.

I used the above method to produce a couple of files for working with silver and bronze. They work nicely although I’m extremely far from being an expert file cutter. The files are also always an eye-catcher when I’m working in a museum or a similar place to show how people did their stuff in the middle ages. :)

Jamie Hall September 20, 2010 at 15:20

Thanks for your comment Torsten, that’s really helpful information. I’ve studied book III of Theophilus quite a bit, but I’ve not got a workshop set up yet, so I haven’t been able to follow many of the procedures as he instructed.

The info about the assymetric chisel is really useful – I’d been wondering how to get the best angle on the teeth. Do you know much about the angles that the teeth were cut at? Most of the archaeological finds for that period show teeth perpendicular to the length of the file, whereas from the renaissance onwards they are usually diagonal or cross-hatched, just like modern files. But if diagonal works so well, surely someone must have tried it earlier than the 15th century.

Do you have a website, blog, twitter…etc?

Torsten November 22, 2011 at 08:26

My apologies for getting back to you so late…

About the angles of teeth cut into files:
As far as I know, until the early middle ages, the teeth were cut perpendicular. Diagonal cuts were introduced during the Viking age as finds from Haithabu (near Schleswig, Germany) indicate: Those finds are dominated by the perpendicularly cut type, but also include files which have been cut using a diagonal angle (Source: Petra Westphalen, “Die Eisenfunde von Haithabu”, Neumünster 2002, ISBN 3-529-01410-9).

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