First attempt at wheel build - FAIL
 

The spoke threads bottom out on the nipples and the wheel won't tension. The spokes are too long, right?

I used the spocalc spreadsheet and two online spoke length calculators - same length calculated by them all using published data for the rim and hub in a cross 3 design. (Salsa Semi 29r Disc and Surly New Disc front). Rounded up to the nearest mm (so says Sheldon) and ordered them.

Built the wheel and attempted to tension it. After looking at a floppy wheel for a while I measured the six spares I bought - all were 2 mm too long. I measured these from the center of the head of the spoke to the end of the threads. Then I measured the uninstalled set I bought for the rear - every spoke is 2 mm too long.

The cumulative error is 4 mm across the wheel diameter. Is the length that critical? Perhaps I should have rounded down rather than up (what the DT Swiss calculator does).

My spokes were cut to order using a DT Swiss spoke machine. How closely does the length of the DT Swiss boxed spokes compare to the indicated length?

-- Bradley

If the spoke threads are bottoming out in the nipples, yeah that 4mm across is that critical. Also check your lacing pattern very closely to be sure - you may have done a 2-cross instead of a 3-cross, or something else weird.

One idea if you're using long nipples is to try shorter ones. But too much spoke through the bottom of the nipple could poke holes in your tube.

That is not the way to measure spoke length. The quoted length of a spoke is from the end of the threads to the inside of the bend.

The most common cause of your problem is that the ERD you used is not the correct one. Always measure it yoruself, never trust specifications.

Show me someone who's never had spokes come out too long or too short, and I'll show you someone who hasn't built many wheels. Sorry it happened on your first wheels, but even if you do everything right it might happen again.

It's important that you use spoke calculators carefully, and make sure all the data you enter is correct. The direction to round will vary with the calculator, because some give you length to near the top of the nipple head, and some toward the bottom. It's good to stay with the same calculator because you'll get used to it's bias, and can factor it in.

Also be careful about data entered, for example rim diameters (ERD). I prefer to measure them myself, finding some mfrs. specs to be off. Mixing brands of spokes and nipples can also create surprises. Most spokes and nipples of the same brand will allow the nipple to thread until the spoke is about 2mm beyond the top, giving you some margin for error.

At this stage, I'd recheck all your data and recheck the calculation. Then I'd measure everything and see if you can discover where you went wrong. If everything is consistent, then make a note of how far off you came out, and factor that in next time. BTW- spokes are measured from the inside of the elbow to the end, not from the center of the bend. It's a difference of 1mm, but when you're at the edge of tolerance a millimeter is as good as a mile.

At 32 Hole 3-cross I get 292.50mm / 293.38 which rounds out to 292mm and 293mm.

At 36 Hole 3-cross I get 288.97mm / 289.86 which rounds out to 289mm and 290mm.

Those would work with 12mm nipples and probably be borderline okay with 14mm nipples...

What were your measurements?

=8-)

I got the same figures for the 32H and rounded up to 293mm and 294mm. Nipples are DT 12mm. I'll attempt to measure ERD tomorrow on a virgin rim using the DT nipples. The bit about measuring spoke length from the inside of the bend should be fine as long as the spoke length calculators determine spoke length from the periphery of the spoke hole in the hub to the ERD dimension rather than from the center of the hole. I expect they do because the hub's spoke hole diameter is a driving dimension.

One of the following probably happened:

A. You have the right size spokes - you just laced 2X instead of 3X without realizing it...

OR

B. The person operating the Phil Wood spoke machine mis-read the ruler - i.e., read the markings to quickly and place it at 298mm instead of 293mm when cutting and rolling.

("B" has happened to me at least a dozen times in 20+ years...often when someone was rushing me...)

=8-)

I measured ERD at two spots 90 deg apart on the new rim and got 606. Salsa claims 605. This was measured by taking two of the spokes that measure 295mm from thread tip to bend, inserting them into diametrically opposed holes and threading them fully on to the nipples. I pulled them tight and measured across the two bends, about 16mm.

The wheel is threaded as a X3. If it were threaded as a X2 there would be 10mm of spokes poking out.

I think I see what is going on here. If everything were perfect, ERD as specified and spokes cut to the ideal length, the wheel would go into tension just at the point that the ends of the spokes became flush with the ends of the nipples.

I rounded spoke length up and they were fabricated 1mm longer than spec so my spokes are about 1.5mm too long. With everything perfect I would need to be able to tighten such that about 1.5mm of spoke protruded beyond each nipple to tension the wheel. The spokes and nipples both have 9mm of thread; it is not possible to tighten the spokes to where there is 1.5mm protruding from the nipple - only flush or slightly beyond.

It seems to me that to allow for tolerances in spoke fabrication, and to allow tension to occur before the spoke protrudes from the nipple, spoke length should be specified as less than the ideal by perhaps 2mm. That still would allow 6-7mm of thread engagement under worse case tolerance stack up. OTOH, were these spokes cut to the requested length, and had I rounded down I think this wheel would have come into tension.

LBS uses a DT published wall chart like page, to lay the rim onto, got their help since my Sutherlands data
is missing a lot of rims made since that edition was published.

I have a DT spoke ruler, you hook the spoke over the hole in it.
zero is the edge of that hole


I found some Pop-rivet washers in aluminum same hole size as the one in the rims

maybe a kludge there, for your spoke overlength situation..

With this simple 1.5mm length error, and still no built wheel to show for it, you learned a whole lot more than you would have if everything had just fallen into place. Wheelbuilding is one of the best examples of an activity where you learn more, and a whole lot faster from your mistakes than from your successes.

Phil Wood and Kowa spoke machines cut 10mm of threads - and in your case 12mm nipples and 14mm nipples would have worked.

However you mentioned use of DT Swiss spoke machine? With 9mm threads? 12mm nipples might take up the slack and stop at the top - but don't think 14mm nipples will work.

Good Luck!


=8-)

Yup. An expensive lesson and I don't think it is over yet - I have to buy more spokes. :D

I was wrong. I check the site and they use a "Philwood spoke cutting and threading machine."

Another case of why I say to always round down.

Agree 99%

Some manus like Mavic aim exactly for the screwdriver flat. So as-is is fine with their ERDs. But most others aim somewhere between the screwdriver flat and the top of the nipple - so rounding down gets you right back to the screwdriver flat.

Recently when Sun-Ringle put out their MTX33's, they reported on the rim labels ERD's of 536 and 598. I knew right away when measuring and after building a dozen that someone had measured all the way to the top of the nipple. Called 'em, they already knew and had already corrected their documentation. (They still insist on 597mm for the 700c though...)

Luckily, rounding down on the first set of rims kept me out of trouble by a hair. I use 534 and 596 - as-is - perfect result everytime.

Also, rounding down makes the use of 14mm nipples more feasible as an option...

=8-)

Rounding down also helps offset spoke stretch, from my experience spokes that are double butted to 1.5 mm can definitely stretch on the drive side rear under normal high tension.