Tube butt gauge
 

After many years of trying to measure the butt transitions of frame tubes with the "sight down the inside and note the light reflections" method I decided to make a tool to do this. My designs adds almost nothing to the previous designs posted on the interweb. I have included some notes with the shots about the tool's nature. I will say here that when you think you can measure a thousands of an inch you really need to how important, or repeatable it is. Over the many thousandths (as displayed with the dial indicator) of a butt change it's easy to see where the butt changes are. More shots on this Flicker link. Andy.

http://www.flickr.com/photos/7319558...57594353980745

http://bikeforums.net/attachment.php...hmentid=244193http://bikeforums.net/attachment.php...hmentid=244193

tube gauge
 

Half the reason to post the shots is for personal pride. The other half is for future builders and the archiving of info. Along this second reason I'll add some comments now that I've spent a little time checking tubes. First the gauge is REALLY sensitive to things that can disrupt the read out. Like vibration, tube centering, as stated in the Flicker shots the weight of the tube flexing the support rods, the friction between the dial point and the tube, even body heat unevenly applied to the dial holding tube will flex it. Second the wall thickness measurements are not consistent with the claimed specs, even with a correction factor for the tube's weight bowing down the tube support tube. Now i know that paper claims are worth the paper only but still had hoped that the gauge would read out a close measurement. Third, the butt differential (through the transition portion) is pretty close to claimed specs. If I were to do this again I would suspend the dial from a tube/beam that ran beneath the tube support tube. This lower beam would be more stable/massive and the dial support arm that would extend up and over the tube support arm would also be stiffer. Both would reduce the dial's tendency to move and read out a changing amount. The tube support tube/arm would be also stiffer, maybe a solid beam instead of a tube. This gauge will be useful to establish the butt points, as I make pretty small frames sometimes this will be helpful. Andy.

Very nice, Andy. I have found my gage to be really frustrating to use because it's too flexible. I haven't really been motivated enough to rebuild though. I did add some stiffeners. Was the indicator clamp homemade, or did you scavenge it from something?

I may just copy Jamie Swan's version, which is a rod with a ball on it held in vee blocks and an indicator stand. This would have half as much flexibility as my current gage

I love homemade tools, the ingenuity behind the design, the skill and precicion in building it... plus they are fun to build. Nice work. But let's not confuse the newbies to the point they think they need such precision. For my needs 1/4" +/- is close enough.

I locate butt transitions but use a simple snap guage. The only limitation is length. The reach is limited to roughly 10cm into the tube. However I've never seen a tube that was intended for a specific location, and frame size that didn't have adequate butt length. Short cut from the short butt end and finish cut from the other end.


Still, I like to locate and mark the butts. It's especially helpful if you are using a "top tube" as a "downtube" for instance. Or one want's to keep the butts as short as possible for the sake of saving weight and knowing butt length helps with tube selection. Not sure of the necessary butt length, but I think as long as it's within 1/4" of the HAZ it's fine.

There is the issue of butt lengths when using lugs versus other joining methods. Again, select the proper tubes for the application.

Don't wanna run out of butts. But no one like big butts.

http://bikeforums.net/attachment.php...hmentid=254577Butt gauge version #2. I was not happy with #1's flexibility and size. So #2 is different. Here's a Flicker set ling for more detail and a tease shot for this post. BTW i'd be willing to sell #1. Andy.
http://www.flickr.com/photos/7319558...7594353980745/

These things are cool, but for those who do not need one often enough, normal measurement systems with dial indicators and other normal shop stuff will make this measurement. So I have a metal table with a vise. Place wrench in the vise, so as to create an extension that will have a rounded bump on it. I place my dial indicator over it. I place a tube with one end on a V block and feed it in so it rides up over the wrench end. As the tube rises and falls the dial indicator will make a measurement. And there are many other similar set-ups. And they are rock solid. Ties up some space so if I needed this set-up often enough a tool would make sense.

pics are required.

Jamie Swan posted a picture of his, which featured a metal rod, some vee blocks, and an indicator stand. Thinking about copying it because mine is too flexible. It works, but it's annoying

Here's mine.

Made from square aluminum stock and bolted together. You set the point in the thicker butt so that there is no play, but not tight enough to scratch the tube. Then you slide it forward until you can rock the tool a little, meaning you're somewhere in the transition. Not accurate by any means, it's simply used to confirm whatever are the specs of the tube. It takes some of the guess of sighting the transition through the tube and gauging its distance with a rod.