Saw Sharpening

Coupla' tips on dealing with an old saw…

  • When doing the initial jointing, check the shape of the blade; it may be concave, or you may want a "breasted" saw. Realising your saw is the wrong shape after you've done a lovely sharpening job is extremely irritating.
  • The best ever time to clean, derust and polish the saw is just after you've done the first (probably major) jointing. The teeth will be stubby and blunt, and less likely to interfere.
  • When tightening saw nuts to fix up a loose handle, use clamps or a vise to close the handle together, and just use the nuts to hold it together. Asking old and/or brass saw nuts to generate the closing force may be an "ask" too far.

Full Instructional Texts

Old Instructional Books

Some Saw Sharpening files in the UK

One of the pre-requisites for sharpening saws is files. I recently purchased every file labelled as slim or extra slim from Axminster Power Tools. These are marketed as Swiss made, but the brand is actually Vallorbe.
(23 Oct 2006) I'm blind - they're Grobet brand, but Vallorbe and Grobet are brands from the same group anyway.
The quality appears pretty good - I had previous bought a 10" bastard file which was most effective, so I thought I'd try their saw sharpening files.

The file widths (i.e the side of the triangle) are as follows:
4" 5" 6"
slim 5.6mm 6.4mm 8.1mm
extra slim 4.5mm 5.6mm 6.6mm
So, sadly, there appears to be size overlap between the slim and extra slim ranges. On my maths, the TPI to be handled by each size are:
4.5mm 5.6mm 6.4mm 8.1mm
13 TPI 10 TPI 9 TPI 7 TPI

The other limitation of the saws that can be handled is the gullet radius generated by the file. This is hard to measure, so I filed some notches in a piece of scrap saw stock, and photographed it with 1/64" divisions from a ruler in shot. After a bit of montage work, I have the picture on the right. The notches are in the order 6-5-4, with the slims above the extra slims

I'm afraid those gullets look a little generous to my eye.

saw sharpening file notches

(16 Jul 2004) I've also tried ordering the Vallorbe needle files in the hope of getting finer gullets. Sadly, the gullets so created were actually larger than those created by the 4" and 5" extra slims.

Update 23 Oct 2006; to get files capable of handling smaller teeth, I bought the 2 smallest sizes from Classic Hand Tools. These turn out to be the same Grobet files I already had from Axminster (see above) but in smaller sizes. The edge sizes are 4.5mm and 5.5mm for the 4" double extra slim taper and 5" double extra slim taper respectively. Priced at £4.95 and £5.45 we may want to rattle Axminster's cage to stock these sizes.

Illustration of some of the issues to be faced during teeth reshaping

The oft-quoted advice when saw sharpening is to joint the teeth, and then file away half of each shiner (flat top) on each pass; this is perfectly valid for sharpening, but more judgement is required when reshaping - unless you're going to remove the teeth more or less completely and retooth.
  • perfectly filed teeth
  • a few rounds of bad sharpening
  • the consequent shape
  • jointing - with "shiners" indicated
  • what you'll see looking down
  • the best possible job (easy on a computer!)
  • the (imperfect) result
saw teeth during reshapings

Controlling Fleam

Whilst aligning a file against a single bevel gauge on the bench top is OK, I find referencing the file against multiple lines easier - if the file is not in alignment, it's quite glaring. I simple place a suitable piece of paper against on the bench top, flush against the vise jaw. For the common good I present a number of ready-to-print reference images, at various "likely" angles, as a tiny (5K) PDF file and the postscript file that generated it.

(See also controlling rake)

Filing new teeth

In the age of the high resolution printer, marking out teeth by hand is crazy. Simply print the tooth pattern you want, and glue it on the saw.

For the common good, I have generated uniform teeth templates 12" long, from 6 to 20 TPI, ready for use. Here's the PDF file. The chosen page is printed out, folded at the apex of the twin tooth sets, and glued to the saw plate, leaving teeth marked on both faces of the plate.

The postscript program can also make incremental tooth patterns; the instructions for doing this are in the Postscript file. It needs to be put through a PostScript interpreter, invoked as

 ps2pdf "-sPAPERSIZE=a4"

Cleaning near the teeth

When cleaning a saw blade, there is a clear difficulty near the teeth. If you have not had to do a major jointing (rendering the teeth pretty harmless) the cleaning medium (probably wire wool or wet 'n' dry paper) will tend to snag on the teeth, which is most inconvenient, to say the least. If using wet 'n' dry you may also damage the teeth; in short the teeth and the abrasive need to be kept from one another.

This can be easily done by making a "tooth guard". This is one of the best devices I know in terms of functional return versus difficulty of manufacture. It is no more than a piece of scrap wood, say 1/2" x 1" cross section, and 6" long. The key part is a tiny rebate, of around 1/8". The guard is simple pressed again the teeth, which are thus unable to interfere with the cleaning - indeed, the guard also acts as a fence, making using the abrasive so very near the edge of the saw a trivial matter.

device to protect teeth

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