Hey all! I’m working on my own version of a tire dummy/fender bridge tool. I know a few folks have made or sell their own version of this tool, I’m trying not to step on anyone’s toes with this design.
My design parameters:
- Provide a reasonably accurate tire clearance model for go/no-go checking in the jig
- Accurately locate seat- and chainstay bridges for brazing
- Quickly adjustable without any additional tools
- Easy to set common wheel sizes without a ruler
- Available in a removable (hooked) or slide-on (clamp) configuration
- Bonus: tire models compatible with Cobra Stay Slayer
There is a minimal amount of secondary operations - I’d get the main holes tapped by Send-Cut-Send so it would just be the M4 tap + clearance holes for the clamp arms.
Bridge configuration with hooks:
Tire configuration with clamps:
1018 steel, 0.25"
Bridge position from axle:
BSD markings for tire gauge:
559, 584, 622mm
Markings for bridge:
M8 wing bolts
I’d love any thoughts critiques y’all have!
Looks great! I love the face.
Functionally, it passes the eye test. I have a few ideas that could make the assembly easier (or not required).
Petis Joints for dummy axle arms
I think you are one hole and T shape away from a Petis joint. This would allow you to swap arms between the hook and the clamps and make the assembly trivial. For the first run, you could always include those features, try the bolts out, and if it does not work, just weld up the arms.
Bending the dummy axle arms
I think you could get away with bending those dummy axle arms, instead of making them as separate pieces. Example:
The only rule you might get in trouble with is the U channel ratio:
Distortion at the bends might be a problem, but not a dealbreaker:
You could also bend this guy if you satisfy the minimum tab length:
These bending guidelines are from here: Sheet Metal Fabrication Bending and Forming Guidelines
Thickness and Material?
If you can bypass the need to weld, you might be able to use 1/4in aluminum to save weight. Or if you are able to use bent steel dummy axle arms, you might consider 3/16 thick steel to save some weight and money.
Another thing to consider is that send cut send won’t deburr ferrous (steel) parts. You can ask them if they can media-tumble your parts, which will save you a bunch of cleanup time.
Farr Frameworks has a spreadsheet of different tire dummys, sometimes even specific tires, their dimensions and their associated STL file for 3d printing.
Might be nice to design around that standard instead of laser cutting individual dummy tires. Assuming of course you have access to a FDM printer.
The link to it is in the description, you have to request access.
I love the idea of incorporating Pettis/T-slot joints! Even if I don’t use them in production, that would help with fixturing for welding everything up.
I’m not entirely sold on bending, but it’s an interesting idea to save on secondary steps! Maybe I’ll try that with V2 after validating this one.
I like the hook design! Easy on an off. Is there a way to incorporate a spring clamp, so it’s still easy on and off but a little more secure at odd angles?