I bought a Shimano dynamo hub, 3N72, and a pair of XM317 rims. The spoke calculator says that I need 261.2 spokes for the front wheel. When I plug my Deore LX rear hub in I get 264 for the right and 265.6 for the left.

What I want to know is if I can use the same 262 or 264 spokes for all of these. They are a lot cheaper in bulk.

Calculators vary as to the assumptions that they make.

If you used a good one and its assumptions match the measurement method of your spoke manufacturer, you will most likely be unable to tension the front wheel with 264's and possibly even 262's (spokes will be undertensioned even when screwed all the way into nipples), and you'll have rear left spokes engaged with the nipples barely halfway if you use 260's there.

Your typical nipple has 9 mm of thread and you want to engage as much of that as possible without going over.

The safe answer is no, you need the correct length, though there is some tolerance but not that much. From the numbers you've provided it appears that you're planning a significant contrast in lacing patterns. Are you lacing the front with fewer crossings? Just curious. Of course there are several online calculators available.

front vs rear hubs have different flange diameter and width, so why so surprised that spoke ength front vs rear are totally different ?

tho it would be kinda interesting to see a front hub with flanges oversized just right to cancel width differences so spokes come out same as rear
would probably only be consistent for a specific rim erd.... not worth it I guess, less you choose a sunringle cr-18 559er as the model....

for rear hub, use a 7spd freehub body with 135mm spacing, drive and non drive spoke length differences become negligible

That's pretty much what I think too. My rule of thumb is plus or minus 1 mm will work fine but I don't like to exceed that. Building up a wheelset is a fair amount of work. I don't like to risk either the time or extra cost that's involved if I fudge on the calculations.

No, there are not fewer or different crossings, just different hubs. Both front and rear will be 3x. Dynamo hubs are very large flange. I'll take the advice and buy two different lengths, or maybe 3. Only the front is going to be built at this point anyway. That will be a completely new wheel. The rear has a dent in the rim, but is still rideable. I wasn't actually going to replace it except that I found someone selling pairs on eBay for only a little more than I was finding single rims at the online retailers.

danscomp sells individual spoke in 1mm sizing's.

As does Universal Cycles: https://www.universalcycles.com/shopp...p?category=198

I would simply buy the correct length spokes. It'll save you a ton of frustration.

Back when I was learning to build wheels, we used the same length spokes for both sides of the rear wheel, then cranking on the right side spokes to get the correct offset. This was a total pain.

The answer depends on the specific spokes and nipples, whether you are using double wall rims, and how well you know the spoke calculator.

If we agree that the ideal height of spokes in nipples is 1mm below the top, or at the bottom of the screwdriver slot, we have about ±1mm tolerance between the spoke being too short and not engaging the head properly, and too long and extending beyond the top.

With double wall rims there are no consequences to spokes extending beyond the top of the nipple, but the ability to do that depends the thread length of the spokes and nipples. Some combinations will run out of thread and jam at close at 1mm beyond or less, other combinations allow much more.

I generally look for spoke/nipple combinations that allow threading to 3mm or more beyond the top of the nipple (check this before lacing), and calculate the length to end at the top of the nipple. This expands my working tolerance to -2mm/+3mm or a range of 5mm which would easily allow building with the same length -- IF the calculator is on target, or I knew how far off and could compensate.

In 95% of my builds I use the same spoke for front and left side rear, and a different spoke for the shorter right rear. I don't have o do this because of length issues, but do so because I use different gauges for the tighter right side spokes.

That's a fine idea.

What combinations would those be which don't involve a spoke machine putting longer threads on?

It's usually not a question of spoke length. Just about all the spokes I use have 10mm of thread, which is plenty, since only 3mm of engagement is necessary or beneficial.

However nipple thread length varies greatly. Somewhere, MrRabbit has a list of pairings showing the overrun range.

More nipple thread makes it easier to lace up a wheel since the spokes engage sooner, and the wheel can be laced before there's any tension. Some (lousy) builders also use this extra thread as an excuse to err to the short end of spoke length in calculations ending up with spokes well short of the heads of the nipples.

Less nipple thread allows more overrun. I look for 12mm nipples with about 4-6mm of thread relief in the flats, which combined with 10mm of spoke thread means 3-4mm overrun possible at the head. Sometimes, I can't find what I need, or need more than normal overrun, so I'll put a 2mm drill into a vise and drill out more thread. This is a slow PIA process and not worth it based on what nipples cost, but I'll do it if/when necessary.

Sure, but which ones?

DT are out - their 12mm nipples have 8mm of thread measured from the top, and allow 1.5mm of overrun using DT spokes with 9.5mm of thread. Wheelsmith claims the same 8mm of thread but asserts it's "33% more than our major competitors" with those going unnamed.

I'm still using an old stock of DT nipples from when they were made by Dubied in Neuchatel. These have about 6-7mm (never measured exactly) of thread, so they give me 3mm of overrun with Wheelsmith spokes, or spokes I threaded myself on a Phil machine.

I wish I could help more, but I'm old school and don't track all the details, only the rules by which I decide what matters. If/when I need more nipples, I'll check out what's available and (hopefully) find something I like. That may be hard because the old nipples were made on screw machines and have larger well shaped heads, and very square cut wrench flats, whereas most of the other stuff I see smaller button heads and formed wrench flats that don't go all the way to the corners.

If the front and rear wheels have the same number of crossings and the same number of spokes I don't understand why the calculated spoke lengths are shorter for the front wheel than the rear. Most rear hubs have longer diameter flanges.
Am I missing something?

You might have missed that the front is a Dynamo hub. I didn't look up the specs, but it's reasonable that the flange would be larger than a rear, plus flange separation might be less. Neither confirming nor denying, just listing a possibility.

Yeah, OK, that could explain it. I've never seen one of those.

You can see how large the flanges are. The rear is a typical small flange hub, so there is a big difference.