Chainstay dimple tool and a couple questions about it.

[alexwetmore]

This may be useful to this thread. Sometimes I need to add a secondary dimple to the outside profile of the drive side chainstay for chainring clearance. I've been meaning to put this one together for some time, and this latest 29+ project which is a Rohloff build (Rohloff requires 135mm rear spacing, so 73mm BB shell width was a must) had me looking for a little extra room for that drive side chainring to chainstay clearance.

You can pretty easily make a 150mm Rohloff by modifying a TS left side extended length axle plate (even on the CC/DB/QR hub).


Drill it out for a QR, thread on a spacer, and you can add 15mm of offset.

Did you consider offset chainstays like on the Pugsley?

I'm impressed by the smooth shapes of your manipulated stays, the pocket in your form does a great job of supporting the shape. I do wonder about how well almost flattened chainstays do with lateral loads though.

alex

[alexwetmore]

You can pretty easily make a 150mm Rohloff by modifying a TS left side extended length axle plate (even on the CC/DB/QR hub).


Drill it out for a QR, thread on a spacer, and you can add 15mm of offset.

Offline a friend did point out the difficulties with getting good disk alignment with this approach. I've only played with it on a rim braked tandem. There isn't much room on a Rohloff to play with spacing out the disk since the shift box gets in the way.

The Salsa approach of using a "fat" left side slider to simulate an offset rear triangle is one approach, but heavier than just offsetting the rear triangle.

[fortyfour]

Did you consider offset chainstays like on the Pugsley?

I did not because there is enough to handle just keeping a frame IN alignment. Additionally, I've never really liked the looks of an offset rear triangle. That's just my own sensibilities.

[Tristan]

Offline a friend did point out the difficulties with getting good disk alignment with this approach.

If the frame is IS it should be pretty straight forward to space the disc adapter inwards. A bit harder on a post-mount.

[bencooper]

I've built wider Rohloff hubs by boring out the TS axle plate - did one recently for a 145mm OLN tandem, and machined a custom Speedbone to go inboard of the disc mount. Worked well.

Though it will invalidate the hub warranty.

My preference is to build an offset rear triangle - a bit fiddlier to build, but a better solution overall I think.

[afwalker]

I've just been using a trailer ball hitch in a 2 ton press:)
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Seems to work ok, handles loads pretty fine and gives a smooth dimple, I made an oak channel that just fits the chainstay to keep the stay from spreading out.
cheers
andy walker
Walker Bicycle Company | | Walker Bicycle Company
Flickr: afwalker's Photostream

[Jussi Kettunen]

Inspired by Kris's desing, I made these. Nowhere as nice as I wanted it to be but works very well.
5" diameter round die is old cam belt sprocket with teeth grinded off and backing die is made out of birch.
Next time I need to under bend the first bend even more, I ended up having more bend than I thought.

[afwalker]

Yeah, these benders and dimplers are nicer than my decidedly low tech approach:)
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I hope to make something like Kris' dimpler, that is sweet!
cheers
andy walker
Flickr: afwalker's Photostream
Walker Bicycle Company | | Walker Bicycle Company

[bencooper]

This is what I mostly use for dimpling - I call it the Dingus:



It has the big advantage that can be used on built frames.

[Tristan]

These photos were on the Serotta flickr site explaining the Pronto's construction.
9195694104_ec67d5ecc4_b.jpg9195694064_11ede24fd8_b.jpg

[DevinL'Ecu]

Love it.

"Yeah, looks like the dimple should be about here." Clamp- done.

[Tristan]

Wouldn't it effect the alignment of the frame?

[Bill Bryant]

"Wouldn't it effect the alignment of the frame?"

I use a very similar chainstay dimpling tool based on a Vise-grip. I got the idea from Albert Eisentraut.
As you infer, I was worried at first about alignment, but after measuring it on several frames, no change at all.
I like how one can dial in the depth of the dimple; some bikes need more than others.
An easy, effective tool; been using it since the late 1970s with total satisfaction. Albert really knows his stuff. (Duh!)

[Jussi Kettunen]

Wouldn't it effect the alignment of the frame?

With my limited experience I would say yes it does effect the alignment of the frame. On one frame I did add small dimples on the chaintays, even with the dummy axle in place rear spacing ended up being 132mm and before the dimples it was 135mm.
That's why I prefer to do all the dimpling before the tubes are welded or brazed in.

[jclay]

Just adding my two approaches to the library for reference.

At about 1/2", the aluminum one is too thick and makes the dimple wider than I'd like. The steel one is 1/4" wide and makes only a slightly narrower dent. I may sharpen its leading edge.

Attachment 67438

[jclay]

A little more info on the chance it might be useful to others. Many sorted this out long ago but until recently I always ended up with adequate clearance; that being due to longish stays and 584 or 559 rims with only modestly wide tires. In any event, I made another chainstay dimpling die and brazed it to the same piece of angle. You can see the lengths in the photos. The longer one is from 1/8" mild steel, the shorter from 1/4". They both work but I prefer the results of the longer one. The wooden form prevents the stay from changing dimension in the vertical axis and flattening on the back. I thought I'd need to bend the stays around the die a little for adequate fat tire clearance (for ~42mm tires) but it doesn't appear necessary, at least for this 559 frame. A little dimpling goes a long way in the clearance dept.

Attachment 67501

Attachment 67502

Attachment 67503

Attachment 67504

[bencooper]

For reference, a new improved version of my indenting tool:

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