Chainstay dimpler
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Matt Wilkinson
Sep 7, 2016, 4:01:39 PM9/7/16
to Framebuilders
Just wanted to share a solution I've found for dimpling chainstays.
The body of the large modified G-clamp held upright in the vice stops the frame from rotating by butting up against the left chainstay and so is hands-free with regard to the frame and gravity holds it in place. The turned brass thingy is recessed on the lathe to fit the clamp pad. The brass form is silver brazed into the thingy. The copper "female" form to preserve the back of the stay is cut from a piece of diameter bored out to 7/8" and linished to shape. Then silver brazed into a filed trench on the G-clamp.
All obvious perhaps, but this took a lot of stress out of the process for me at this late stage of the build. No more must I grovel around on the floor looking for that form that keeps falling out of the vice!
Matt Wilkinson
London, UK
Andrew R Stewart
Sep 7, 2016, 10:22:32 PM9/7/16
to Matt Wilkinson, Framebuilders
Matt- I keep a collection of posts with great framebuilding content. Yours
is the only one I’ve added to my file for a long time, thanks. Andy
Andrew R
Stewart
Rochester, NY USA
Rochester, NY USA
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Phil Smith
Sep 7, 2016, 11:33:38 PM9/7/16
to Framebuilders
Hi, sorry if this is a dumb question from a non-framebuilder--I assume this tool only works for the outside of the chainstays...have you considered a "reversed" version for dimpling the interiors?
Phil Smith
Los Angeles, CA
USA
Matt Wilkinson
Sep 7, 2016, 11:40:16 PM9/7/16
to Phil Smith, Framebuilders
Hi Philip, to be honest I hadn't considered dimpling the inside of the stays at this point but I'm sure I could make another part to make it possible. I will also make another seat part to add on to better accomodate oval stays.
Matt
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Mark Bulgier
Sep 8, 2016, 6:21:13 AM9/8/16
to Phil Smith, Framebuilders
Phil Smith wrote:
> [snip] have you considered a "reversed" version for dimpling the interiors?
Here’s my recently made indenter for tire clearance: https://flic.kr/s/aHskyV5FPK
Simple and crude, but I like the results, and it didn’t take long to make.
As you can see, I like the kind of crease that has a sharp line down the bottom of the indent, unlike Matt’s with a rounded bottom.
Sharp creases can mean stress risers, in many places on the bike, but I’m convinced that his is *not* one of those places. I think stresses flow away from the crease towards the parts of the stay that are farther from the neutral axis… or something. Fact is I don’t care all that much why it works, I just know it does, and I think it looks more bitchin’ that way.
I know it works because of all the frames made this way since, oh I don’t know, 1930s at least? Never seen one crack there. I’ve seen indented stays crack, but it was never near the sharp crease down the bottom of the indent. Most all Columbus SL and SP chainstays came this way (sharp crease) in the mid-70s and earlier, before round-oval-round became fashionable. Even the 1930s Barra aluminum had indents that look pretty much like this, and though they have been known to crack, I haven’t seen one crack there at the crease.
If I were to make this tool again I’d use a larger and/or higher quality clamp. Or not necessarily larger overall, just larger in the acme thread. On this cheap Chinese clamp, the threads feel kinda grindy at peak indenting force, like I’m doing damage to them to apply so much force. We’ll see how long they last. It’s a hobbyist tool for occasional use, not a production tool, so it may well outlast me.
For production* I prefer dedicated jaws bolted into a vise. Both the curved backing shape and the indenter can be rigidly mounted to the vise jaws, and an indicator/positioner rod can go out to the dropout, or the chainstay miter (or both?) to ensure the dents are always in the same place. Needless to say you should always do the indent before putting the stays in the frame whenever possible, so these C-clamp creations are just for frame modification on completed frames. I think if you find yourself frequently or always indenting stays after the frame is together, you're doing it wrong.
* by "production" here I mean low-volume, like in the range of one to fifty frame batches. I don't know how the big boys do it, automated machines using hydraulics no doubt. Load up the hopper, push a button and stand back. At Davidson (early '90s) when we had a stock MTB model called "Dirt" that used indented Prestige stays, I think I did something like 40 pairs in a half hour, and probably needed a rest after that. I seem to remember it was an aerobic workout. Doing them all day would definitely benefit from machine power.
Mark Bulgier
Seattle
> [snip] have you considered a "reversed" version for dimpling the interiors?
Here’s my recently made indenter for tire clearance: https://flic.kr/s/aHskyV5FPK
Simple and crude, but I like the results, and it didn’t take long to make.
As you can see, I like the kind of crease that has a sharp line down the bottom of the indent, unlike Matt’s with a rounded bottom.
Sharp creases can mean stress risers, in many places on the bike, but I’m convinced that his is *not* one of those places. I think stresses flow away from the crease towards the parts of the stay that are farther from the neutral axis… or something. Fact is I don’t care all that much why it works, I just know it does, and I think it looks more bitchin’ that way.
I know it works because of all the frames made this way since, oh I don’t know, 1930s at least? Never seen one crack there. I’ve seen indented stays crack, but it was never near the sharp crease down the bottom of the indent. Most all Columbus SL and SP chainstays came this way (sharp crease) in the mid-70s and earlier, before round-oval-round became fashionable. Even the 1930s Barra aluminum had indents that look pretty much like this, and though they have been known to crack, I haven’t seen one crack there at the crease.
If I were to make this tool again I’d use a larger and/or higher quality clamp. Or not necessarily larger overall, just larger in the acme thread. On this cheap Chinese clamp, the threads feel kinda grindy at peak indenting force, like I’m doing damage to them to apply so much force. We’ll see how long they last. It’s a hobbyist tool for occasional use, not a production tool, so it may well outlast me.
For production* I prefer dedicated jaws bolted into a vise. Both the curved backing shape and the indenter can be rigidly mounted to the vise jaws, and an indicator/positioner rod can go out to the dropout, or the chainstay miter (or both?) to ensure the dents are always in the same place. Needless to say you should always do the indent before putting the stays in the frame whenever possible, so these C-clamp creations are just for frame modification on completed frames. I think if you find yourself frequently or always indenting stays after the frame is together, you're doing it wrong.
* by "production" here I mean low-volume, like in the range of one to fifty frame batches. I don't know how the big boys do it, automated machines using hydraulics no doubt. Load up the hopper, push a button and stand back. At Davidson (early '90s) when we had a stock MTB model called "Dirt" that used indented Prestige stays, I think I did something like 40 pairs in a half hour, and probably needed a rest after that. I seem to remember it was an aerobic workout. Doing them all day would definitely benefit from machine power.
Mark Bulgier
Seattle
James Nachlin
Sep 8, 2016, 1:59:09 PM9/8/16
to framebuilders
Here's another take on a dimpling tool: https://www.flickr.com/photos/ericmonasterio/9480926151
Curtis Odom design, here implemented by Eric Monasterio.
Jim G
Sep 8, 2016, 2:01:33 PM9/8/16
to Framebuilders
I've made a tool similar to Mark's, but much cruder.
-Jim G
Matt Wilkinson
Sep 8, 2016, 3:17:30 PM9/8/16
to James Nachlin, Framebuilders
Nice. Perhaps I overthunk..
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Chapman Cycles
Sep 9, 2016, 2:00:38 PM9/9/16
to Framebuilders
I made this thing years ago. It's reversible so it can dimple for chainring and tire clearance.
Brian Chapman
Alex Wetmore
Sep 9, 2016, 2:13:44 PM9/9/16
to James Nachlin, Framebuilders
I use one that is just like that, except that I left the dimpler side replaceable (mostly in case I ever came across a shape that I liked better). It's nice that it does inside and outside equally well and is really quick to use. It's also really simple to make (Brian Chapman's design is really neat, but not as fast).
Another nice thing about the vise grip solution is that you can get perfectly repeatable dimple depth by setting the vise pressure on the vise grip.
alex
From: frameb...@googlegroups.com <frameb...@googlegroups.com> on behalf of James Nachlin <j...@nachlin.com>
Sent: Thursday, September 8, 2016 10:59:07 AM
Sent: Thursday, September 8, 2016 10:59:07 AM
To: framebuilders
Subject: Re: [Frame] Re: Chainstay dimpler
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rob perks
Sep 18, 2016, 5:14:45 PM9/18/16
to Framebuilders, j...@nachlin.com
Somewhere years ago I saw a tool that clamped at the BB Shell and pushed a large bearing (tennis ball large) towards the shell to make symmetric width between stays. I think this was being done in the BMX side of fabrication. Does anyone here recall that, and possibly have a reference?
Also, looking out of our general bubble to what the BMX builders are doing can me a fun diversion. Lots of creative ways to do similar things, but often in very different ways
framebuilder...@googlegroups.com
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Michael Catano
Sep 18, 2016, 5:22:55 PM9/18/16
to rob perks, Framebuilders, James Nachlin
Oh I like that idea very much.
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Steven Johnson
Sep 18, 2016, 11:16:41 PM9/18/16
to Framebuilders
I saw that too, on some website for builders in South Carolina. I remember it being a family team that would build bikes and painted.
The bearing was big.
Steven Johnson
Millersville,MD
Millersville,MD
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