Jig Chainstay Dimension

[ToddFarr]

Hello all,
Working on redoing the back end of my Bringheli jig and I have a question for the more knowledgeable.

When dealing with chainstay length how does a jig measurement factor in axle width? If you use a 120mm hub spacing vs a 130mm hub spacing is there some offset you use to determine your CS length, or is CS length measured as a bisect? For instance is it the center of the BB to the center of the axle measurement that is noted on frame spec drawings, or is that the dimension from center of BB to center of axle along the CS tube?

If its a bisect measurement I would just use the Pythagorean Theorem my BB drop & CS bisect lenght to figure out how far the center of the axle needs to be away from the center of the BB.

Is this the correct mentality? If not please school me. Also what do you find important in the rear end of your Jig?

Thanks for the help.
-Todd.

[e-RICHIE]

On my Bike Machinery Hydra fixture the chainstay measurement tells me the distance from the bb center to the rear axle measured on the ground (or on a virtual parallel). So when I set it to 420mm and then measure a bicycle after parts are on it, it will be about 430mm. All the distances for set-ups are typically virtual atmo.

[ToddFarr]

Richie,
Thanks again. Putting the numbers to it really helped me verify what you were saying.

So it is the virtual that we are after!!
Again I over complicated the situation thinking I'd have to figure out the different axle positions for different hub spacings.

(figured I'd post the image for future builders/searchers with the same question with Richie's numbers)



Anyways I would love to hear what all you guys like about your high end production jigs :) What works and what doesn't on the back end.
-Todd

[Dave Anderson]

I am not exactly sure what you are asking...Do you mean do you measure the CS length horizontally from center to center....in plane with the centerline of the frame?, or at the angle of the chain stay from center to center? or etc? It doesn't really matter how you get there as long as the bike matches the design/drawing in the end IMO.

The rear end measurement on a Bringheli is affected by the BB drop and so putting a simple horizontal scale on the jig doesn't work. I set BB drop and then measure from center to center as shown below. The outside end of my BB post extends out from the face of jig the same distance that the outside of the jig's 130mm dummy axle does, etc. It's easy enough to compensate for a wider or narrower axle.

Dave

[Eric Estlund]

Part of it is figuring out what you are measuring and how it relates to what you want to end up with- the numbers in isolation are just numbers and meaningless variables.

You mention redoing the back end of your jig. Why? What are you hoping to change? Improve? What lead you to these changes?

I'm a fan of being critical of your process, but I'd be hesitant about being overly critical without having a full process (not judging, just in general).

All jigs are just tools to hold the bits where you want them. More refined versions do it in a more accurate, more repeatable way.

[ToddFarr]

Dave,
I'm planning on completely redoing the Rear Assembly similar to what I've done on the front end. I was more so curious as to what the scales on high end jigs are measuring and what the chain stay length on the design drawing actually means. I mean isn't the ANVIL affected by BB drop as well? Seems like that behaves similarly to the Bringheli just with scales.
-Todd.

[ToddFarr]

Part of it is figuring out what you are measuring and how it relates to what you want to end up with- the numbers in isolation are just numbers and meaningless variables.

You mention redoing the back end of your jig. Why? What are you hoping to change? Improve? What lead you to these changes?

I'm a fan of being critical of your process, but I'd be hesitant about being overly critical without having a full process (not judging, just in general).

All jigs are just tools to hold the bits where you want them. More refined versions do it in a more accurate, more repeatable way.

My main goal is using the nicer anvil dummy axles to help keep the dropout in phase. Since the font end turned out so nice I figured I would try my hand at the back end, toolfree adjustments, quick repeatable setups, and scaled values.

[Eric Estlund]

toolfree adjustments, quick repeatable setups, and scaled values.

Cool- what adjustments do you want to make? What values do you want to be repeatable? What do you want the scales to measure, and how will you use this information? These are rhetorical- but once you have a clear vision of how this info will improve your method, the steps and changes needed to get you information you find valuable will make more sense.

[Dave Anderson]

Dave,
I'm planning on completely redoing the Rear Assembly similar to what I've done on the front end. I was more so curious as to what the scales on high end jigs are measuring and what the chain stay length on the design drawing actually means. I mean isn't the ANVIL affected by BB drop as well? Seems like that behaves similarly to the Bringheli just with scales.
-Todd.

Hi Todd,

Unfortunately, I don't know anything about the Anvil.

The Chain stay length on a drawing is typically the direct measurement from the center of the bb shell to the center of the rear axle along the centerline of the frame .......I set it as per the photo above. I know that it is set in a similar manner on other jigs, like the Marchetti, for example, as well, etc. If you design your frames in BikeCAD Pro it will give you the horizontal measurement for a given chainstay length and BB drop (or, of course, you could just measure it on a full scale drawing, or do the math, etc)...and in that case a scale would work, etc.

Dave

Rear End.jpg

[Eric Estlund]

Yup, drop and length pretty well locate the axle and bb centers. All of my measurements are on the center-line (bb, drop out and head tube), with hard contact points measured from there.

[Dave Anderson]

Todd,

PS: Your Bringheli mods have Rocked! so far and so I am anxious to see what you come up with for the rear!

Dave

[ToddFarr]

Thanks Dave!! Yeah I've been going through a machining kick. I've mainly been doing it to help my engineering. I'm finding learning and envisioning how to make parts helps me design components for manufacturability. I guess I should mention the reason why I've been making so much tooling lately is because I've been pretty tight on cash and haven't been able to afford to by tubes and lugs. However I am lucky enough to have a pile of scrap metal at my work and a lathe and mill at my disposal. In all honesty the parts have turned out better than expected. I set the jig up according to the dimensions off the drawing mitered the tubes to fit, pinned the front triangle and checked it over the drawing. It was perfect! I value all of your input Dave, Eric and Richie and all the other guys. You've given me lots to think about!
-Todd

[Jamie Medeiros]

You might think about making a dedicated fixture to tack chain stays. I find it easier this way and a bit more accurate. Mine is set up with a scale to measure center of bb to center of axle. I tack the chain stay, drop out, BB sub assembly then mount the sub assembly in the frame fixture at the desired drop.

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