What Is Runout - Wrist Twisters
 
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post #1 of 10 Old 11-27-2013, 10:26 PM Thread Starter
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What Is Runout

Continued from another thread:

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Originally Posted by str8ghtjacket View Post
What the hell is runout? Sry excuse my ignorance but that's a new one to me. I'm not a super techy guy so I'll like to know how that works?

Runout is what you do when you see Helen Thomas in a nightie in your bed.

Okay, all joking aside, I'm going to borrow one of the better explanations of runout as posted here: Explain runout please - Let's Talk ShopBot

Quote:




Runout has become a catch-all word for the sloppiness, flexibility, non-repeatability or just plain "poor quality" of a machine. Runout could mean many things to many people and the word is often thrown around as a bogeyman.

In the strict sense of the word, runout means the amount of deviation from the theoretical position.

The term can be applied to rotary or linear motion, static or dynamic. Because most folk who actually measure runout use dial gauges (as in the pics above), the measurements are normally static, or at hand-turned speeds.

It also stands to reason that if you push/pull, ie. apply force, to the shaft/carriage while measuring, that you will get a bigger reading of runout. (Somebody who wants to prove bad runout will push/pull rather hard - a machine salesman who wants to prove low runout will not push/pull at all)

Why the different readings depending on force applied?
- Because ALL machines are flexible and they WILL bend/deflect. (Cables are much more flexible than gear-rack teeth)
- Because there is often freeplay/backlash in a connection between parts of a machine and applying force causes the parts to move within this free range.

The other big cause of runout is a manufacturing defect, or damage. A bent shaft will not run "true" even if it was very stiff and had no freeplay. If a machined rail is not produced/setup straight then the rolling carriage will deviate from the theoretical straight line - ie. runout. If a 4-fluted router bit is put in a collet with a bit of dirt causing it to be held slightly skew, a dial indicator will get different readings from the flute edges - runout.

Can one achieve zero runout? No. Any machine that is doing the work it is designed for will bend and deflect. Normally these claims/demonstrations are made without applying loads and with measuring instruments of low resolution.

Is runout always bad? No. In the example with the 4-fluted cutter sitting slightly skew, it means that one of the flutes will take a bigger cut than the others as the cutter "wobbles". And the kerf will be wider than expected. For a single-fluted cutter, the only down side is the wider kerf. But, that wide kerf will be absolutely consistent in its width, and will be as straight as the carriage rails.

Is runout consistent? No. Aside from the fact that it is load dependent (as described above), it is also temperature dependant. A bearing that has a lot of clearance (backlash/freeplay) when cold, will have hardly any clearance when at the right running temperature - if it has been designed and installed correctly.
Okay, now that that's out of the way, the practical discussion of runout as it applies to this discussion. First, the Honda service manual page:


Runout is the amount of deviation from perfectly round or perfectly straight a rotating object is. In this case, we are wanting to find out how much 'warp' or 'out of round' there is in our wheel and rotor. You measure this using a wheel stand (though you can sometimes do it correctly on the bike and a dial indicator. Radial runout is 'warp' or how much the wheel rim/rotor moves left and right while rotating. Here is a video of a man checking his rear wheel's radial runout.

Checking runout of a motorcycle wheel - YouTube

1986 Honda Nighthawk 700S
2002 Honda 919
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post #2 of 10 Old 11-27-2013, 10:39 PM Thread Starter
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Axial runout is 'out of round' or how much the rim moves in or out in relation to the axle it's rotating on. It is measured the same way, you just point the dial indicator at the inside-facing side of the rim as shown in the lowermost of the service manual pictures above.

Runout significant enough to affect a bike's handling can actually be too small for you to find through just eyeballing the rotating object, but at other times it can be obvious. Here is a Gixxer exhibiting excessive radial runout on its entire rear wheel assembly:

2002 Suzuki Gsxr 600 rear wheel wobble - YouTube

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post #3 of 10 Old 11-27-2013, 10:42 PM Thread Starter
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Here's another example of *really* obvious radial runout:

Ducati Wheel Wobble - YouTube

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post #4 of 10 Old 11-27-2013, 10:43 PM Thread Starter
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Here's a bike showing axial runout on the tire (and possibly the wheel):

Out of Round Motorcycle Tire - YouTube

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Here's another example of axial runout:

Out of round? - YouTube

(Dammit, can we get a YouTube embedder setup that doesn't ruin the page layout if there's more than one in a post?)

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post #6 of 10 Old 11-27-2013, 11:01 PM Thread Starter
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Anyway, there's what runout means with regards to our 919s and specifically our wheels and rotors.

Our 919 wheels are lighter but not as sturdy as the old Comstar wheels or even the wheels on my 700 - just like our sportbike relatives, our wheels are surprisingly easy to warp, bend or dent by impact with road debris or even a perpendicular hit. It is always worth checking both axial and radial runout after running over something significant on the road or a crash (even if the wheels didn't contact anything - I've seen weird warping occur from transmitted forces on sportbike wheels). Likewise it is worth checking if your bike suddenly starts having weird braking issues like pulsing, juddering, etc., etc.

Hope that answers your question. If not, just ask.

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post #7 of 10 Old 11-28-2013, 04:54 AM
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Quote:
Originally Posted by CB700S View Post

(Dammit, can we get a YouTube embedder setup that doesn't ruin the page layout if there's more than one in a post?)
It's because the links were https, if you change the link to http it will format OK. I fixed em for you.

They plan to fix it as soon as the developers finish healthcare.gov

Great thread BTW!

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post #8 of 10 Old 11-28-2013, 06:36 AM
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They plan to fix it as soon as the developers finish healthcare.gov
2015?

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post #9 of 10 Old 11-28-2013, 06:54 AM
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Thanks CB700, great write up as always

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post #10 of 10 Old 11-28-2013, 06:54 AM
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2015?
Sure!

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