wheel building - too tight, too soon
 

Hello! I'm building wheels for my bike. Part because my bike has steel rims, that render it basically breakless... and because I want to learn how to do it.

It's a 27" rim (Schürmann 630-16) with a Quando hub on the front and a Maillard hub on the back. All very cheap, I know, but it's I could get.
Spokes are stainless steel. I forgot to ask in the shop which size they gave me (I left everything in the shop to me measured).

I started with the front wheel, 3-cross. The pattern is okay, I already more than triple-checked it. but the spokes are already very tense even with some threads to go. Is this normal? Sheldon gives as an example for the initial tensioning, turning the nipples until the threads disappear -- I can't do that using a screwdriver, there's just too much tension already.

I can still squeeze them, but not that much...
Should I start truing the wheel or is it possible I'm not seeing this right?

Not possible to tell for sure what's wrong - too many variables. Spokes could be too short, you could be crossing more spokes than you think (can be easy to miss the 1st cross) or you could be lacing to the wrong holes. The first step is to take the parts back to the shop or call them to recheck the spoke length. You can also measure the spokes yourself, and can even determine the correct length on your own if you want to take the time to learn how. Google Sheldon build wheel - everything you need is there, from how to measure a spoke to spoke calculator links and wheel lacing instructions.

Your spokes are probably too short. Whether it's because someone miscalculated,m or because you changed the cross the effect is the same.

As a guideline consider once you pull all the slack out of the spokes, there's only 2 turns or so left to full tension. So if you're showing more than 2 threads odds are you still will be when the wheel is at full tension. Showing thread is only a cosmetic consideration, but it probably means that when you're finished the spokes won't be reaching into the heads of the nipples, and that is a problem.

It's up to you whether you continue, or pull it apart and start fresh but for future reference, I start aligning, focusing on radial errors, as soon as I transition from taking up slack to adding tension. When exactly that happens is a judgement call but you want to align as soon as possible, but aligning while there's slack is pointless.

Based on your remarks you are starting from scratch (with hub and rim) and don't have the original spokes? Given that, you need to measure the rim (ERD) and the hub. There's plenty of info around the internet on how to do both. It's easy but if you can't make this part happen maybe you should turn the wheelbuilding over to a shop with a reputation for building good wheels.

Given the OP has the hub and rim already laced up, determining proper spoke length is a simple matter of adding 4mm (or whatever puts them into the nipple heads) to the current spoke length.

If you are setting the spoke tension using a screwdriver on the nipple heads, you can't get it nearly high enough. Get a proper spoke wrench and work on the square drive faces of the nipples. You may be surprised how easily the nipples still turn.

You only need to engage 3-4 turns on the nipples to achieve 90% strength. Trueing the wheel with a spoke wrench will add at least another 2-3 turns. Wheel should be fine.

Unless the spoke is threaded into the nipple HEAD, you have a weak joint.
2.2 turns = 1MM.

so it seems I was being a extra cautious.. I took it to the shop (to use the truing stand) and, slowly but surely, brought the wheel into true and tensioned it. There are still some spokes not fully threaded (one or two threads left), and there are some discrepancies in tone. The guy in the shop said (he just touched a few spokes) the tension was ok, but I'm not happy.. everything should have the same (or closely) tension, right (front wheel)?

The rear wheel has the axle inverted... the guy was probably using the right side of the axle as a spacer for a single/fixie... so I need to fix that first.
Thanks for all the replies ;) these are my first wheels, it's always nice to hear some ideas, as to build a troubleshooting database

That's irrelevant as long as there are at least 3-4 good turns for engagement. Feel free to experiment using a tensile testing machine.

With brass nipples you are probably right. Aluminum nipples have a tendency to shear at the head/shank intersection if the spoke threads don't thread into the head.

I know Furballi is an an engineer, so this isn't for him, but for others who might read this.

I don't want to belabor the point, but standard practice is for the spoke to engage the head by 2-3mm. This is not arrived at by accident but is based on a century of experience.

Yes, a brass nipple has a tensile strength of 80% of the spoke in the shank area (Furbali's assertion, accepted at face value), but that only tells a part of the story. Since the brass is notched in a number of places, especially at the rim line by the threads, this means that there'e be notches at the fulcrum of any bending moments. These will lead to premature fatigue failures. (the type of brass typically used for nipples isn't especially suited to repeated bending stresses)

Nipple breakage at the rim line is a well documented phenomenon in both brass and aluminum nipples, though far less so in steel nipples. We don't have to reinvent the wheel here, the CPSC conducted extensive research when they formulated the first bicycle standards. They focused on nipple failure because of a number of cascade failures of wheels leading to injury, and mandated a standard that short (not into nipple head) spokes with brass nipples generally failed, though those with steel nipples passed. Fully threaded spokes and nipples (2-3mm into the head) pass easily regardless of nipple material.

It's always tempting to shortcut standard practice or rules of thumb, but before ignoring them you need to consider why folks have done things a certain way for eons.

Now if the Op wants to ride this front wheel based on Furballi's advice vs. following well established practice he's free to do so.

Since I can't really be sure, I'm just going to the same shop where I bought the spokes and ask them to critic my work. They are renown for their quality, so I guess I can trust their advice.

I was dumb and didn't ask neither the size of the spokes, nor the material of the nipples...

That's a good idea. If they did the calculation ans sold the spokes, you might ask that they check their own work, and maybe see where you or they went wrong.

Yep - "The first step is to take the parts back to the shop or call them to recheck the spoke length." You weren't dumb - you've done this once. The shop has done it enough they should know to double-check their work and inform you of the length they are giving you. It's simple to just include that on the receipt.

I would also take it to the shop for an inspection- but before I did (if I were you) I'd have a quick check to see where the spoke ended up in the nipple. If it's up to tension and the spoke isn't close to the slot, something is wrong. Once the threads are hidden in the nipple it about 3 1/2 turns to reach the slot. As you said in your op there were still threads showing when it felt tight. There is no way you could make up for that discrepancy in spoke length. Read FBinNY's response and follow the advice.

Well, you got part of it right, but it doesn't apply to spokes and nipples. Typically it is understood that for maximum strength of a fastener you only need thread engagement equal to the diameter or the screw. Not so when talking about spokes and nipples. You need to have engagement equal to the (spoke) diameter beyond the seat of the nut (nipple.) This will put you close to the screwdriver slot. Below the seat of the nut (nipple) and you have a weak fastener. Anyone know the difference between an engineer and a wheelbuilder? Wheelbuilders don't think they are engineers.

Perhaps you can educate me about the physics of failure mode on the brass nipple. Show your work with concrete data or there will be no point assigned to your hard work. While it is true that the wall thickness of the brass nipple is thinner than most nuts, I have never seen nipple failure on steel wheels that have crossed my path. And yes, a few wheels had short spokes (about 3-4mm from the end of the nipple). A weakened fastener does not translate to a defective fastener. Often, it is the thin-walled steel rim that gives in.

A weakened nipple is exposed to over 1M stress cycles in ~1500 miles. If the nipple does not fail in high-cycle fatigue during this period, then it should, in theory, last forever. The other major variable that could result in pre-mature brass nipple failure is corrosion due to storage at the beach.

The fact that you've never seen failed brass nipples isn't evidence that they don't fail. It's only evidence of your lack of experience.

As I pointed out in an earlier post, nipple failure when spokes end short of the rim is a well documented phenomenon. No new research is needed since it was researched extensively and exhaustively. May I suggest searching for the supporting research that the CPSC used in creating their first bicycle standards over 40 years ago. That would be a place to start if you care to learn, or you can base your conclusions entirely on your personal experience.

The nipple may fail due to corrosion, undesized wall thickness and/or inferior metallurlogy (cheap no-name junk import), or damage by a spoke wrench! Cut a DT Swiss brass nipple in half and measure the effective cross-section area using an optical comparator. Now use basic strength of materials to calculate the allowable safe load.

There have been a tremendous advance in material science and manufacturing technique over the last 40 years. Do you still rely on engine design protocol from the 70s to build a modern direct-injection gasoline engine with 12:1 compression ratio?

Thirteen years ago, I helped a friend build a wheel with spokes that were at least 2.5 mm short at the rear (both side) using straight DT 2.0 mm spokes. The wheel held up like a champ even after 4 years of use (before it was sold to his friend).

Have it your way. I don't care. But arguing about the specific cause, doesn't change the simple fact that nipple failure happens when spoke are too short.

I said in my first response that I wasn't trying to convince you, just posting what I knew. This is a forum, you post your opinion, others post theirs and readers can choose what to believe.

As far as I'm concerned this thread has achieved dead horse status. But anyone interested can find more here. Plenty of links to work your way through. Happy hunting.

Again, poor metallurlogy could be the root cause of the nipple failure. You have not provide any scientific data to support your claim. Your assertion is based on data taken 40 years ago on spokes that may be vastly inferior to modern stuffs from DT and other top tier manufacturers.

Like trying to communicate with an ex wife. She needs the last word, to convince herself that she is always right.....

Are all of your spokes the same length?

You have two different hub brands and drive side vs. non drive side spokes. You could have 3 different spoke lengths. Are you sure you're using the right ones?

Let's flip that on its head, canyou prove that modern nipples are superior to old ones? If not, the safe thing to do is assume they aren't and build wheels accordingly.