Author Topic: Wheelbuild woes  (Read 369 times)

Wheelbuild woes
« on: September 24, 2020, 09:41:36 am »
Last night I finally got round to attempting to build a dynowheel - my first wheelbuilding attempt of any kind - and had a bit of a faff getting it laced up. I'm building it up 36h x 3; the first two sets of spokes went in fine, but rotating the hub in order to get the third and fourth sets in was tricky - the fact that I was using spoke washers may have made this more tricky. I think one flange may have rotated more that the other, which meant that it was very hard to pull the spokes across enough to engage with the nipple for the latter spokes. In the end I had to resort to cranking the tension on the adjacent spokes to try and pull the rim in enough to get engagement, then backing everything off again. Whilst I eventually got the wheel laced up, it looks like the rim is inclined at an angle as to where it should be. I don't think this is a pringle - the rim seemed reasonably true before I started - and if I've visualised the geometry correctly, this could be the result of not having rotated the spokes enough on one side of the hub. The side-to-side run-out is about 3.5cm.

I don't *think* I've made a lacing mistake - the pattern all looks OK, and the spokes all went in eventually - so am I better off unlacing and having another go, or should I just start trying to tension and true the wheel and hope that the spokes will rotate in the flange as the tension is upped?

Re: Wheelbuild woes
« Reply #1 on: September 24, 2020, 09:57:55 am »
3.5cm is a HUGE run-out. Do not expect any amount of tensioning to result in a rideable wheel! If you are sure that your lacing pattern is correct, maybe some of your spokes are longer/shorter than the others? I would definitely check all spoke lengths first.

A


Re: Wheelbuild woes
« Reply #2 on: September 24, 2020, 10:42:00 am »
This usually means (if you lace one side at a time, which I do) the first spoke of the second side has gone in the wrong hub hole.  It should be almost exactly parallel to a spoke on the other flange, but offset by one hub hole and two rim holes.  You have to hold the hub just right to be able to see it properly.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: Wheelbuild woes
« Reply #3 on: September 24, 2020, 11:16:38 am »
Looking again at the wheel, it looks like something has gone wrong; though all the crossings, parallel spokes etc. seem to be in the right place, there's a section of the wheel were instead of the spokes going left-right left-right into the rim, they go left-left right-right  ??? 

Have de-laced the wheel, and will have another go this evening...

Re: Wheelbuild woes
« Reply #4 on: September 24, 2020, 11:17:35 am »
Rule n°1: if it ain't working out don't insist. In this case if your third and fourth sets won't go in without brute force and ignorance it's time to stop, take it apart, check the lengths and positions of everything and start again - before you have put a terminal kink in the rim. I am a skinflint who regularly builds wheels (only for myself) with mismatched components (as in salvaged scrap!)and this happens. Above all never insist!

Possible areas of error: 1 the measures of rim, spokes or hub are quite simply wrong. It happens. Measure everything yourself to be sure. Look up in wheelbuilding manuals or on the net how to measure spokes (don't ask me, I never know). Don't trust the word of anyone, particularly not internet databases or salesmen.
2: You don't say what the hub is. Some dynohubs (I think all disc brake dyno hubs) are not symetrical. Have you got the hub the right way round?
3: The holes in the rim are offset from the centreline. Have you got the rim the right way round? (I have always built right side of the rim for right side of the hub - I assume this is correct, it works for me. If not I have been wrong for half a century. I have often wondered if the wheel would be stronger with right going to left to increase the angle a bit but I don't think I am going to try! Anyway the spoke lengths would be wrong  :facepalm: )
4: I get all the spokes in before putting any tension on anything. Just three or four turns on the nipple to make sure it's threaded. Done this way all the spokes should be well loose when put in place. If not something is wrong!
5: Everyone has his own way of lacing up a wheel. My way is to start with the narrow side (least dished side, as in drive side on a rear, disc side on a front disc) putting the spokes in from  the outside. Then for the same flange I put in two spokes inside going out and crossed correctly. These two spokes will give me the flange hole for the spokes on the other flange (either leading or trailing to give the right direction at the valve hole). The first set of spokes on the second flange go from the outside in (which is why there are only two spokes on the opposite flange, to make putting them in position easier). Finally it's just a question of finishing off the remaining flanges on which the spokes go inside out - which makes life easier. If you get to the last set and they are too short then something is wrong somewhere; time to stop and start again, or give it a rest and come back two days later when all will be fine.
6: don't forget that the holes on the two flanges are not face to face. One side will lead the other (by half the distance between two holes usually. There are some strange radial wheels which don't follow this exactly). Pass a spoke through one hole and if it is parallel to the axle it should hit the other flange between two holes. You need to have the spokes leaving the hub in the same direction from the twp flanges with the flange holes correct, leading or trailing, otherwise you're doomed!   

Re: Wheelbuild woes
« Reply #5 on: September 24, 2020, 04:47:47 pm »
After initial re-lacing, radial run-out is ~1 mm, and side-to side ~6mm, which seems much more reasonable. I think the dish will need tweaking slightly, but this seems like a much better point to be starting from.

Thanks all.

Re: Wheelbuild woes
« Reply #6 on: September 24, 2020, 04:56:00 pm »
ideally you will work out what you did differently before, and learn from it. 'Mystery problems' have 'mystery solutions' and are not learning opportunities!   

Did you take a photo of the first lacing attempt?

cheers

Re: Wheelbuild woes
« Reply #7 on: September 24, 2020, 05:06:59 pm »
I *think* I put some of the leading spokes one hole out; looking from a distance the pattern looked correct, but as I said, going round the rim the left-right pattern of spokes was out. By the time I thought 'I should have taken a photo of that', I'd already removed half the spokes...

Lesson learned is perhaps 'don't try lacing for the first time when tired and with less than full concentration'...