I'm building my first wheel, and have got it laced and on the truing stand. I'm now trying to get the wheel dished correctly. Assuming that the truing stand is perfectly symmetrical, what is the need for a dishing tool? If it is the case that truing stands are not normally symmetrical (ie, the calipers are not perfectly centred to the uprights), then do I just set and check the dish with the special dishing tool, and then only use one arm of the calipers? (ie, the wheel, when correctly dished, will not sit in the centre of the calipers).

Thanks in advance!

To check the dish with my Spin Doctor (made by Minoura, I think) truing stand: (The centering line on the radial gauge was off center just a little.)

I used two pieces of masking tape on the radial gauge to mark the location of the two edges of the rim. I carefully flipped the wheel in the stand, and noted the difference in the rim position. I needed to move the rim halfway to the tape marks.

This is kind of tricky, since the two arms of the stand are self-centering, and could possibly shift a little. So I lowered the axle carefully onto the arms.

It worked okay.

As a final check, I clamped the wheel on the bike, then adjusted the brakes carefully so that both pads contacted the rim at the same time. (An easy way to check this is to clamp a dollar bill under the pads, pull from the folded middle of the bill, and slowly release the brakes. Both sides of the paper should come loose at the same time.)

Then I flipped the wheel on the bike, and checked that the brakes were still centered the same way.

If I was building more than a wheel every 4 years or so, I'd get a dishing gauge. (Or make one from lumber and a pair of bolts.)

The Spin Doctor stand. Two arms to support the wheel, a feeler for each side, and a radial gauge.

I've learned to be very skeptical of the accuracy of dishing devices built into truing stands. I never assume that they are accurate.

When building wheels I generally flip the wheel over periodically and true one side at a time. That's also how I check for true. I have a truing gauge that I use for 26" and 700c wheels but mine won't work on 20" wheels so I determine dish just by periodic flipping of the wheel on the truing stand.

Set 3 equal sized soup cans on the kitchen counter, like the point of an equilateral triangle.
Set the wheel down resting the rim on the 3 cans.
Measure the distance from the locknut to the countertop.
Flip the wheel over & measure again.
Adjust the spokes until the measurement is the same.

This, Andy

I just took a 2x4 and ran three screws into it: two outer ones spaced to touch the rim, and the third directly between them, to contact the axle nut. It costs nothing but 5 minutes to make from scraps. It's used just like any of the commercial dishing sticks, and you simply turn the center screw to adjust.

I use a dishing tool but often wonder why I bother. My stand is very good at measuring dish and the tool is just a check but I don't have to normally adjust from what the stand says. If you are worried that the stand isn't accurate (enough) and/or you don't have a dishing tool, you can always turn the wheel around in the stand to see if the rim is the same distance from both calipers.

I'm pretty certain that my stand isn't accurate, because I tested it with my nicest wheel (and no, not one I made myself ). One of the caliper arms was 3-4mm closer to the rim, even after flipping the wheel over in the stand. I have the Park Tools stand with self-centering calipers - it makes me wonder if something is wrong with the stand (I got it second hand).

I do this and slip a stack of dimes underneath to measure to the locknut (or the axle if you are sure it is perfectly centered). When you get to less than the thickness of a dime difference from one side to the other, life is good.

Thanks for this! Given that the instructions start with "Take 3 soup cans", it took me a moment to realize this was a serious answer

If I use this method, I was planning to use a QR skewer. The wheel in question is a rear wheel, so I am hoping a front skewer with nut will do the job.

If it's a TS-2.x, there's a procedure available from the PARK website to set them correctly.
Yours aren't.

I picked up my stand used and it HAD the same problem.
Now it doesn't.
I

A lower budget option is to use a stack of pennies

Thanks! I am pretty sure I have the TS2, so will see what I can do about adjusting it.

My version involves wood blocks and a screw driven up through the bottom of the work surface.

Kinda like DasPirate's setup.

assuming it is, flip the wheel over in the stand without changing any adjustments .. to the truing stand ..

Done that? see any differences?

even in stands that are not in adjustment-symmetrical, the side run out reference gap should not change ..

I tried this, with a good wheel. The left caliper arm remained in light contact with the rim, and the right arm remained 3-4mm off.

double check is do the same in the Bike , flip the wheel over .. then its probably adequate.

+1 Any equally sized objects will work

Park sells a centering gauge but they are kind of pricey. Minoura used to make a centering gauge that is simple and effective...you can see the gauge here ...but they apparently don't make that anymore. I picked up on ages ago but really seldom use it. Alternatively you could use a wheel that you trust but you probably need the dishing gauge to check the wheel first. Dinosaur/Chicken/egg.

I have the Minoura stand and the centering gauge. I still use a dishing tool.

This is exactly what I do.

I went with periodically flipping the wheel in the stand to set the dish. Thanks for all the replies, I learned a lot of useful info!

Here's the new wheel on its first ride - it worked perfectly.

Congrats!