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Chain Stay miter template

Some questions about chain stay miter template generation...

1. I think there was a problem with the CS templates in pre version 8.0? I am now running version 8.0, are the CS templates working ok in this version? When I look at the miter templates for my chain stays the drive side template is different to the non-drive side? I dont understand why this is the case as both stays are identical and symmetrically attached to the bottom bracket shell?

2. What is the dimension "R" for a single curve (symetrical) chain stay? I was looking for somewhere to enter the large dimension of an oval stay and I think this might be it?

3. In my design I know the dimensions of the chain stays (16mm x 30mm) and I know the approach angle to the bottom bracket shell is 110 degrees and of course I know the diameter of the BB shell. Is there some way to generate a miter template based on these critical dimensions and not have to derive the other measurements that are asked for in the chain stay section?

Thanks in advance

Lachlan

Chain stay miter template

I've attached a screen capture of a typical chain stay miter template below. To the right, I've overlapped the two templates so that you can observe the difference between them. You are correct that the drive side and non-drive side templates are different, but this is only because the stays themselves are symmetric but not identical. In the view where the two templates are overlapped, you can see that each template has a side which is mitered deeper than the other. The side that is mitered deepest is reversed when you compare the stays. This is how it should be.

Chain stay miter templates

Prior to version 8.0 BikeCAD only generated a template for the drive side. Back then, you could use the same template but wrapped with the back side of the paper facing out on the non-drive side. However, this only worked if the stays were symmetric.

The "R" dimension refers to the radius of the curved stay. If this is not clear, I would recommend turning on the auxiliary view of the stays and trying a very large value for "R" and then a small value like zero, and observing the difference.

While BikeCAD doesn't actually allow you to directly input an approach angle for the stays, it does calculate that value for you and does generate the miter template based on those very numbers.

Thanks Brent, I knew I must

Thanks Brent, I knew I must have been missing something!
I think it would be really helpful if the BikeCad program could generate a miter template based on a simple approach angle as I find it is really difficult to accurately determine the dimensions needed i.e. the radius of the bend in the stay etc and feel like there is alot of room for measurement error and therefore miter template error?

Chain stay approach angle

Be aware that the radius of the curve in your chain stay has no effect on the approach angle.

Also, while BikeCAD doesn't actually display the approach angle, it does display the chain stay miter angle, which is a function of the approach angle. Approach angle = 90 degrees +/- miter angle.

You seem to already know the approach angle you want (and therefore the miter angle). While it may be a shame that you cannot simply type in your desired approach angle, you can display the miter angle and then tweak the chain stay geometry until the miter angle displayed reflects the required miter angle.

Great, sounds like I can

Great, sounds like I can achieve exactly what I want with existing capability, will try tonight.
Thanks again for the quick and informative response.
Cheers,
Lachlan

CS template too small

Hi Brent,

I am finding that the chain stay templates are too small for the actual stays. The stays are 300mm x 16mm oval (confirmed by measurement) but the templates seem to be about 1.5 to 2mm too "short" i.e. when the template is wrapped around the stay the two ends do not meet leaving a 1.5mm to 2mm gap. I ensured that the printer settings were correct so not sure what might be the problem?
Thanks for any assistance provided.
Locky

Template for oval chain stays

I'm not sure what the 300mm dimension is in your stays. The taper length perhaps? If you are going to define an oval cross-section for your stays you'll need to enter a value for both VF and HF as defined in the chain stay diagram in BikeCAD. For reference, the diagram is shown below:
Chain stay side dimensionsChain stay auxiliary dimensions
The next thing to be aware of is the fact that the BikeCAD miter templates assume a perfectly elliptical cross section. In practice your oval shaped stays will probably not be a perfect ellipse. This could cause your templates to come out a little too small or a little too big. You may consider inputting slightly larger or smaller values for VF and HF in order to compensate for this.

Hi Brent,

Hi Brent,
sorry, I meant 30mm and was referencing the large dimension of the oval chain stay. I figured it was probably something to do with the fact that the stay is not a perfect ellipse as you have explained. I will play around with the VF/HF values until I can get it right.
Cheers,
Locky

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