Slow cooking - R100/7 twin-disc conversion at last

[Ken in Oklahoma]

. . . I made a wooden carriage for the dial indicator and as I move it up and down along the stantion tubes, they deflect ever so easily. What I'm saying is that I have to be careful to not put any pressure on the tubes that could deflect them in the direction I'm measuring. That makes me think there could be some compliance in the tubes even when they're captive within the lowers. Of course, the axle is the link that ties all this together. It is also the factor that makes it so we can't measure to find what we want to know about the stantions.

I had a spare lower triple tree with a destroyed steering stem. So I used that with a dial indicator as the basis for a tool to measure the difference in spacing, top to bottom, between the fork legs. (Duane had brought his tool to an earlier rally.) Unfortunately the tool can only measure the difference in one direction, but with the use of a glass plate to check the parallelism between the tubes it gives you a good evaluation. It was fun to watch how very little lateral pressure on one of the fork legs results in a big swing on the dial. (The indicator had 0.001" resolution marks on the face.)

With such an indicator one could ensure that the fork legs are parallel to begin with and then watch what happens when the upper triple tree is installed and tightened, as well as what happens when the axle is inserted and tigtened, and also the stock fender mount/fork brace. And you could also watch what happens mounting a San Jose fork brace or similar such device.

I haven't done any serious work with my shop made indicator, but it having one would would serve to give a person a lot of confidence about the "accuracy" of the whole fork. What to do if the indication is inaccurate is a whole other discussion. (Which Duane and Randy Glass have undertaken to our benefit).

During the Rally at my place I could dig out my indicator and anybody with a pre mono-lever airhead (I think) could take a look at their forks (after pulling off the fork sliders) Meanwhile the rest of us will look on, carbonated beverages in our hands, as we offer our wisdom and advice.


Ken

[ME 109]

Is glass flat to within 0.00000"?
I doubt it.
While a very small twist is 'feelable' with rocking glass, is it the forks, is it the glass?

[Ken in Oklahoma]

Is glass flat to within 0.00000"?
I doubt it.
While a very small twist is 'feelable' with rocking glass, is it the forks, is it the glass?

I doubt it too ME109, but it's the only game in town. And way better than nothing. One could go with a precision granite block flat, but they're pretty hard to hold against the fork legs. And with a thin section of granite I reckon it would be prone to deflection from pressure, perhaps much like glass. Plus a hunk of flat granite would be a hell of a lot more expensive.

Perhaps use two different (unrelated) pieces of glass and see how they compare? The same deflection "feel" in the same location?

I'm guessing that the variances in fork leg parallelism that matter on the road would be detectable by a piece of glass. Of course it goes without saying that the thicker the glass the better. And I think we're talking about plate glass as opposed to window glass. But then I don't really know my glass from a hole in the ground. (Sorry! It had to be said.)

Or were you typing tongue-in-cheek and I was a tad slow on the uptake?


Ken

[ME 109]

Or were you typing tongue-in-cheek


Ken

Ken.........I had only just finished my breakfast.

I flip the glass over, and rotate, to judge the amount of twist in the glass. That is with a laminated 6mm glass.
Then I can get an idea of where things are at.

[Major Softie]

Is glass flat to within 0.00000"?
I doubt it.
While a very small twist is 'feelable' with rocking glass, is it the forks, is it the glass?

It's supposed to be around .1mm -.2mm in 24" (according to someone on Practical Machinist who checked - yes, I go there too, but only to learn, as I have nothing but questions to contribute). That is 4 to 8 thousandths in 24 inches, or about 1 - 2 thousandths when checking a fork.

Not as flat as a ground granite plate, but pretty flat.

[ME 109]

Is glass flat to within 0.00000"?
I doubt it.
While a very small twist is 'feelable' with rocking glass, is it the forks, is it the glass?

It's supposed to be around .1mm -.2mm in 24" (according to someone on Practical Machinist who checked - yes, I go there too, but only to learn, as I have nothing but questions to contribute). That is 4 to 8 thousandths in 24 inches, or about 1 - 2 thousandths when checking a fork.

Not as flat as a ground granite plate, but pretty flat.

One might also consider where the glass is from. I'm sure that as in most things, there are lesser qualities.

[Chuey]

My glass plate, 1/2" thick, is not flat. I hadn't thought I should say that, as I thought it may be heresy and I wouldn't want to be accused of that.

I really want to fit an upside down fork to one of my bike projects.

Chuey

[SteveD]

When I checked mine, I used a hardened glass chopping board. I ran a steel ruler along it as a poor man's test for flatness. It seemed flat to me, so I happily used it.

[Ken in Oklahoma]

Isn't it interesting that with all this talk about the flatness of glass we're talking about flatness of a liquid? At least as evidenced by the pieces of glass in ancient cathedrals that are thicker at the bottom than the top.



Ken

[barryh]

I think the jury is still out on glass flow but just in case better make sure to use a piece that's not older than the bike.