A simpler method of repairing broken saw nut screws!

[bentontool]

Hello again Brothers,
Whilst out in the shop yesterday, I was working on the restoration of a well-used "Jackson"/Disston carcase saw. One of the screws was snapped-off at the post, and the split-nut was MIA (missing). Note the plate has been filed many times; there is a curvature near the handle, which I had already started sanding.
So, I reviewed several several postings on this website (and followed their links) in order to see how I was going to tackle the repair. Frankly, I found most of the recommendations to be perhaps more difficult than necessary.
Below is a far simpler solution to repairing the broken screw post. I have also attached a few pics on how I made the split-nut, which can be done by anyone with a drill press or a mill. Aluminum and brass tend to machine well with woodworking tooling.

First, file the end of the screw flat. Then file a notch on the broken post. I used a worn-out saw file. It still cuts brass well (save those worn-out files!). Grind the screw end to fit the notch.

Mount the two halves in a vise and solder together. The result is on the right (after cleaning-up a bit). The alignment is not perfect, but it works. I will probably try to straighten it out. The brass should bend easily.

Here is a close-up shot of the solder joint. It is quite strong.

I then found a piece of 0.127" brass plate in my scrap bin. I used a 1/2 inch plug cutter (designed for wood but cuts brass easily) to cut the split-nuts. Caution: do not try to do this with a hand drill. I used a mill, but a drill press will work well. I made a few extra split-nuts for next time. Drill & tap for the appropriate size (in this case, #21 drill & #10-32 tap).

I then simply used a fine hacksaw blade to cut the screw slot. I cut it off-center on purpose... I have seen this on older saws with split nuts, and (IMO) it adds a bit of nostalgia/hand-made appearance.

The last step is to file the split nut to proper size, and file the taper (if it has one). I simply made a mandrel from a hardened steel cap screw with the head ground off. You can lock the split-nut in place on the mandrel with a nut or two.

Done. Easy by comparison...

 

[Phill05]

Well done just one thing missing your (initials)

 

[ChaiLatte]

There is one slight correction to your figure: No 10 (3/16" or 4.8mm) is close to M5, not M6.

 

[spanner48]

M6 ???

I have measured 20 split-nut sawscrew threads from my 'spares' collection. All are around 3.6mm OD [range from 3.4 to 3.9] and are for 90% 24 tpi [1.06 mm pitch], with 10% being 26 tpi [0.98 mm pitch].

Oddly, these are NOT BS Whitworth threads, but much coarser, lying between 1/8" BSW at 3.175 x 40, and 5/32" BSW at 3.97 x 32. Again, close to,but MUCH coarser than M3.5, at 3.5 x 36 tpi

Saw plate screwholes vary from 3.7 to 4.1 mm diameter. Using either Nº 10 or M6 would require significant reaming out of the plate holes – as also the drillings in the tote.

From what I can see, there are ten missing split-nuts for each broken sawscrew. So, to keep things as original as possible, the key is making replacement nuts which will screw onto the existing screw ends without disturbing them. That means getting 11 mm or 13mm brass rod, drilling and tapping it as deep as practical to 3.5 x 24, and cutting off 2 mm slices. And that means a 3.5 x 24 taper tap.

Obviously, domed-nut sawscrews are significantly larger. But they rarely need replacement