ERD...Correct Method?

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NATURAL ANKLING
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ERD...Correct Method?

Postby NATURAL ANKLING » 3 Nov 2016, 3:13pm

Hi,
So after a few wheel builds and spoke length might be slightly out, even with all the best will in the world consulting tables.

What's correct way to determine correct ERD, Not the method so much but where you think ERD is :?:

Nipple contact point on rim.
Or
Point where the spoke end should be, this relies on the spoke profile and if you favour spoke end at bottom of slot.

May be they are same place near as damn it?

Also is nipple breakage due to too little insertion a real worry?

http://miketechinfo.com/ERD-measuring.htm

https://leonard.io/edd/howtomeasure
NA Thinks Just End 2 End Return + Bivvy
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Mick F
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Re: ERD...Correct Method?

Postby Mick F » 3 Nov 2016, 3:40pm

I use the "Two cut-off Spokes Method".

Take two spare spokes and cut off the hooked end plus a few inches. Superglue the nipples so that the spokes are flush with the tops of their heads.

Insert each spoke through holes diametrically opposite each other and fit them so they are nicely seated. Measure the gap between the cut-off ends.

Repeat at a few places around the rim.

Add the gap to the sum of the two spokes' overall lengths. That is the ERD.
Mick F. Cornwall

Brucey
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Re: ERD...Correct Method?

Postby Brucey » 3 Nov 2016, 3:49pm

The nipple seat is not where the spoke should finish if the spoke length is correct. To measure ERD, use measuring spokes/nipples (of the same type as you intend to use), finish the spoke ends in the nipples where you want them to finish and measure accordingly. This will get you within 0.5mm... simples...

However

a) some new rims are not quite round and
b) very many used rims are certainly not (but you can still measure them using another technique).

If you use spokes that are too short then there are several risks

1) if they are really short you may not have enough thread engagement
2) the threads may show out of the bottom of the nipples
3) the nipples themselves may break in half.

some of the above can be addressed using longer nipples, but not all. Very often there is (or should be) a 'set' in the spoke at the end of the nipple; it is important that the spokes are stress-relieved in such a way as you don't change the set angle in the spoke ends, else later in-service flexing at this point will shorten the life of the spoke.

If the threads show below the nipple, this usually means the wheelbuilder has screwed up somehow, but it doesn't actually make anything much worse than it is already; the bottom of the nipple has a tapered entry and there are usually some spoke threads beyond the point at which they are supported by the nipple.

cheers
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MikeF
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Re: ERD...Correct Method?

Postby MikeF » 3 Nov 2016, 8:04pm

NATURAL ANKLING wrote:Hi,
So after a few wheel builds and spoke length might be slightly out, even with all the best will in the world consulting tables.

What's correct way to determine correct ERD, Not the method so much but where you think ERD is :?:

Nipple contact point on rim.
Or
Point where the spoke end should be, this relies on the spoke profile and if you favour spoke end at bottom of slot.

May be they are same place near as damn it?

Also is nipple breakage due to too little insertion a real worry?

http://miketechinfo.com/ERD-measuring.htm

https://leonard.io/edd/howtomeasure
Depends on how slightly that is. If threads are showing outside the nipple I should have thought the spoke was too short. ERD to the bottom of the nipple slot seems to be a good starting point. I've measured this by first measuring the wheel diameter rim edge to rim edge, and then putting a nipple into a hole and using the "tail" of a straight vernier gauge to measure the depth of the slot below the rim edge. ERD is wheel diameter - 2x depth of slot of nipple. A spoke isn't needed to measure this way. I don't know if there are snags with using this method, but seems to work.
Possibly the ideal spoke length is one where the spoke reaches about 1mm above the slot. You could, of course, use the above method and measure to the top of the nipple if you want the spoke to reach that far, but a 1mm or so too long a spoke is then liable to bottom out on the thread. Alternatively measure both ways and take the average.

I'm not a professional wheelbuilder, but that seems to be fine to me, although I'm lighter than most men and my wheels have 36spokes so there may be overbuild.
"It takes a genius to spot the obvious" - my old physics master

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Redvee
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Re: ERD...Correct Method?

Postby Redvee » 4 Nov 2016, 1:28am

Mick F wrote:I use the "Two cut-off Spokes Method".

Take two spare spokes and cut off the hooked end plus a few inches. Superglue the nipples so that the spokes are flush with the tops of their heads.

Insert each spoke through holes diametrically opposite each other and fit them so they are nicely seated. Measure the gap between the cut-off ends.

Repeat at a few places around the rim.

Add the gap to the sum of the two spokes' overall lengths. That is the ERD.


Same here, only used this method on a rim I couldn't find the ERD of online.

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Mick F
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Re: ERD...Correct Method?

Postby Mick F » 4 Nov 2016, 8:21am

Redvee wrote:Same here, only used this method on a rim I couldn't find the ERD of online.
The problem with that, is that the stated ERDs are not necessarily correct. I had a "pair" of rims with different ERDs. Only a few millimetres, but different.

Best thing to do, is to buy your rims, measure them, then buy your spokes.
Mick F. Cornwall

Suffolker
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Re: ERD...Correct Method?

Postby Suffolker » 4 Nov 2016, 8:38am

Mick F wrote:
Redvee wrote:Same here, only used this method on a rim I couldn't find the ERD of online.
The problem with that, is that the stated ERDs are not necessarily correct. I had a "pair" of rims with different ERDs. Only a few millimetres, but different.

Best thing to do, is to buy your rims, measure them, then buy your spokes.


I've been bitten this way as well. I always measure ERD myself, using the "2-spokes" method, and then buy spokes accordingly.

mig
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Re: ERD...Correct Method?

Postby mig » 4 Nov 2016, 9:49am

do the positions hub drillings also vary?

Suffolker
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Re: ERD...Correct Method?

Postby Suffolker » 4 Nov 2016, 10:02am

mig wrote:do the positions hub drillings also vary?


In my experience, they can do, but not usually by much. However, when working out spoke lengths using the various on- and offline calculators (at least, the ones I have), the hub measurements involve taking a distance from the hub centre to the centre of the spoke holes in the hub, and that dimension then dictates spoke length based on the actual measurement relating to that particular hub.

As well as not taking "as read" supplied ERD's, but checking these myself on the rim to be built, if key dimensions on hubs are given by the manufacturer or someone else, I always double-check the ones in the hub I'm holding in my hand and about to build into the wheel.

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NATURAL ANKLING
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Re: ERD...Correct Method?

Postby NATURAL ANKLING » 4 Nov 2016, 10:17am

Hi,
I am sure all the good guys do this to.
Nipples also vary in length and profile.
I will take more care in the future.
Its relatively easy to build the same wheels you have built before with same parts / the second wheel, assuming the rims don't change.

Who's every built dished wheels and end up with nice spoke nipple engagement both sides.

Do spoke calculators advise ERD methods (that's screw the spoke all the way to top) when arriving at calculation?
Maybe I am not reading notes in the text.
NA Thinks Just End 2 End Return + Bivvy
You'll Still Find Me At The Top Of A Hill
Please forgive the poor Grammar I blame it on my mobile and phat thinkers.

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Tinnishill
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Re: ERD...Correct Method?

Postby Tinnishill » 4 Nov 2016, 10:33am

Is there any reason that I shouldn't find ERD by simply using a vernier gauge to measure the internal diameter of the rim and add a couple mm to cater for the thickness of the metal ? I am looking at buying the "Silverline Jumbo Vernier" (£15) which goes up to 610mm.

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Mick F
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Re: ERD...Correct Method?

Postby Mick F » 4 Nov 2016, 10:52am

Suppose not, but don't forget that there's more than the thickness of the metal to take into account.
If you're going to the trouble to measure accurately, why not use the Two Spoke Method?

Tell you what though, if I were to be making up a few wheels a year ................ which I don't! ............ I'd buy blank spokes and a thread roller. Who cares about ERD then? Just make the spokes to suit.
Mick F. Cornwall

Keezx
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Re: ERD...Correct Method?

Postby Keezx » 4 Nov 2016, 3:03pm

You will still have to calculate the spoke length.....

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Mick F
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Re: ERD...Correct Method?

Postby Mick F » 4 Nov 2016, 4:45pm

I've not done it, so I'm thinking off the top of my head here.
I reckon that I could fit blank spokes and mark them off where I want to cut. I wouldn't need any figures, just a good eye.
Maybe I would do them too long to err on the safe side, but cut off and re-roll the threads if required.

Dunno really, but I reckon I could do a wheel without knowing the ERD figure - or the actual spoke lengths to the millimetre.
Mick F. Cornwall

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Re: ERD...Correct Method?

Postby MikeF » 4 Nov 2016, 5:52pm

DavidNichol wrote:Is there any reason that I shouldn't find ERD by simply using a vernier gauge to measure the internal diameter of the rim and add a couple mm to cater for the thickness of the metal ? I am looking at buying the "Silverline Jumbo Vernier" (£15) which goes up to 610mm.
Yes in my view. It seems you would be just measuring the internal diameter of the rim.That seems to be about the same as using a ruler, so I don't know why you need to bother with a vernier gauge. If you are just adding an arbitrary 2mm you are not measuring very accurately anyway. Easy to be 2mm in error and buy the wrong spoke length. ERD takes into account the nipple heads so you would have to allow for that as well.

NATURAL ANKLING wrote:Hi,
I am sure all the good guys do this to.
Nipples also vary in length and profile.
I will take more care in the future.
Its relatively easy to build the same wheels you have built before with same parts / the second wheel, assuming the rims don't change.

Who's every built dished wheels and end up with nice spoke nipple engagement both sides.

Do spoke calculators advise ERD methods (that's screw the spoke all the way to top) when arriving at calculation?
Maybe I am not reading notes in the text.
Nipples are made various in length, but all my wheels have 12mm ones. Depends what rims you have; deeper rims need longer nipples but I haven't built wheels that need those.

Dished rear wheels need slightly shorter spokes on the drive side.

The ERD calculators seem to work for me, but I can't remember what I found the best. I think most assume the spoke is screwed to the top of the nipple.
https://leonard.io/edd/howtomeasure
You can usually buy spokes in increments of 2mm lengths so you may not be able to have exactly the right length of spoke. However if they are too long the threads will bottom out and you won't be able to fully tighten the spokes, whereas if they are too short there won't be enough thread in the nipple. I think that as long as it reaches the bottom of the slot it is OK.
Like most of us here I suspect, I only build wheels "occasionally", so I then have to recap what I did the last time. :lol: I suspect how good your wheels need to be depends on you - I'm neither a heavy nor powerful rider, but my wheels take quit a hammering on some sections of the so called NCN. :wink:
"It takes a genius to spot the obvious" - my old physics master