What's special about spoke nipple washers?

Question

The last couple of wheels I've built have been all from reused parts. One was to convert my unicycle from 24" to 20" largely as an experiment, and the one that I'm currently working on is for the junk bike I keep near work.

For the unicycle wheel, I found my spokes were about 1mm too long nominal, plus measuring error, and ordered a bag of (round) nipple washers. They were 0.5mm thick, and I'm not sure if the were strictly needed in the end.

For the 26" wheel, the spokes are more like 2mm too long, so I reckon I'll run out of thread before the wheel is fully tensioned. I'd like it built quickly. Ordinary M4 washers are dirt cheap and available same-day. New spokes are probably more than the bike is worth (even cheap ones) but what really puts me off is the several days delivery time. So I'm considering using 1 (or even 2 on the drive side) M4 washers (0.8mm thick) under each nipple. They seem to be a good size for both nipples and rim. The extra thickness is good but obviously adds weight - not an issue on a bike made of gas pipe.

Am I missing something? Are round nipple washers just thinner and harder to obtain than normal washers (I know there are other shapes for narrow rims). Is it just about weight?

Answer 1

This is a really short answer:

I use brass washers in this type of scenario which deform to the rim shape and the nipple. This was the recommended type of washer in one of the books I read when learning the subject, possibly Brandt's book or another similar.

The wheels where I have had to do this have built up nicely. Using washers is good anyway as the nipple turns more easily under high tension than it would against the plain rim surface.

Answer 2

The washers need to fit the rim. If the part of your rim where the spoke holes are, i.e. where the washers will sit, is not flat, your washers will sit on two points rather than on a flat face. As a result, the forces from the spokes are entering the rim via these points. This will either deform your rim, or your washers, but my guess is you will deform the rim.
That does not sound like a good idea to me. I would expect early failure of the rim. You might want to bend the washers, ideally to the same shape as the rim inside, or bent somewhat more, which would mean the force is distributed over a line rather than over two points. Keep in mind that the topmost spoke at any given position carries most of the combined weight of bike and driver for that wheel (~70% on the back, ~30% on the front wheel) plus any impulse from bumpy roads, so the forces are by no means negligible, and if the rim breaks, it will be while you are driving, so you risk injury.
Also, depending on your rim, your nipples might protrude too far inwards, making damages to the inner tube quite likely.

You may want to shop for a cheap wheel, which might actually be cheaper than a set of new spokes, or search for cheap spokes on ebay.

Answer 3

The best way is not to use washers at all, save your money for a threading tool, it's about the same price. Perhaps from an online hobby shop where they make very small bolts. It may be difficult to find a 1.7mm one, perhaps post a thread to ask where to source them.

If you spin the threading tool onto the ready-made spoke thread, it will glide on easily, and when it gets to the end you can turn another 5 times for an extra mm of thread, maybe just jam the elbow of the spoke very loosely in a vice. and then cut of 1mm at the top with a sharp pliers before unscrewing the threading tool through the new cut.

Chances are you wouldn't even need to rethread them if it's just 1mm, they may have 2mm extra thread to start with.

Answer 4

#1: Do not use a die on spokes. They are rolled...Spoke rollers are not cheap, but it's the only way to make spokes that last.

#2: Washers, especially varying amounts of washers between spokes is not a good idea. You'll have wheel wobble when you go past ~30 km/h.

#3: Using washers is legit in some cases. In fact, sometimes better - provided that you have washers made from softer material then the rim, and equal amounts of them across each spoke.

#4: Wheelbuilding is the most serious thing about bikes - do not do it in a rush, you'll regret it later. Take time to buy properly sized spokes. You don't need to go fancy like Sapim or DT Swiss. I used fancy spokes. I used dirt cheap, simple spokes. Not a huge difference if you have correct length, proper tension and great wheel truing.

Happy riding!