Finding tube dead center for rivnut install,,,

[dlui]

https://www.amazon.com/Milescraft-13...690633437&th=1

similar idea to the Stein, just have to measure distance between holes manually

[AngryScientist]

Thanks all. Some good ideas here. need to determine where my FD clamp will be located and then I'll do some drilling.

[MikeD]

Frankly, I would not drill holes in a good frame. The holes won't be reinforced and the frame tube could fatigue crack over time. They make clamp-on water bottle cage holders.

[AngryScientist]

Originally Posted by MikeD

Frankly, I would not drill holes in a good frame. The holes won't be reinforced and the frame tube could fatigue crack over time. They make clamp-on water bottle cage holders.

lol.

You're basing this recommendation on what now? Many many many frames have rivnuts for bottle cages, including a few high end customs i have in the shop here.

clamp on bottle cages mounts are a visual atrocity.

[windsurfer]

Use blue tape to tape the cage where you want it. Reposition as many times as necessary to get it exactly where you want it and then use a transfer punch to mark the locations of the holes. Might want to start with a center drill and then open it up to size so the bit doesn't wander.

[pinkshogun]

When I first got my riv nut tool i practiced on junky frames as the gun has a slight learning curve to it

[robt57]

Another thought, use a ruler with a V taped or cut on one end Or a piece of luan plywood etc.

Put the self centering V forward on DT or HT and use the straight other edge to mark a line center of Seat tube on your painters tape.

[marciero]

I've eyeballed things like this with good results. Eyeball-with-visual-aid, especially one that exaggerates misalignment, such as Dave Kirk's method with a long ruler. You would have the bottom bracket to sight but also the ends of the ruler would not be even if misaligned.

Another method that would exaggerate misalignment-sort of a riff on NHaero's idea- is if you had a threaded clamp of some sort, like an FD clamp but where the threads were radially inward such that they mimic the location of the threads you want in the seat tube. You could even make such a piece by drilling and threading an FD clamp. You could position this on the seat tube where you want it, then take a very long screw and thread it into it. It will be very obvious if the hole is not direct center because this screw will be canted off to one side. The longer the screw the more exaggerated the effect. In fact you might not even need that long of a screw. Once you get it located screw it in tight enough to leave a mark on the seat tube.

Edit: On reflection, this method would rely on the threads in the clamp being aligned radially, so drilling and tapping to ensure this is just a recasting of the problem...

You could use this as an aligment tool, along with a long screw, with the caveat that the alignment is a function of how much the clamp is tightened. The hole could be parallel with the top tube yet slightly to the right or left of top dead center, if that makes sense. I think this would also be obvious with a long screw. For better precision, if you need it, you could separate the two pieces- breaking the hinge if necessary, and just tape the front piece with the threaded hole in it to the seat tube.

[catchourbreath]

Word of caution my shop had the threaded style rivnut tool that worked really ****ty.

[MikeD]

Originally Posted by AngryScientist

lol.

You're basing this recommendation on what now? Many many many frames have rivnuts for bottle cages, including a few high end customs i have in the shop here.

clamp on bottle cages mounts are a visual atrocity.

Yeah well I had a Trek 1200 that had a front derailleur mount held to the frame via two rivnuts. The frame cracked around the seat tube at one of those rivnuts. I noticed afterwards that Trek switched to clamp-on derailleurs in later iterations of their frames. Maybe bottle cage rivnuts, since they're more at the center of the tube, there would be less stress there. If you look at quality steel frames, the inserts are brazed in, thus reinforcing the tube. Rivnuts aren't as good.

Read what Jobst Brandt said about this https://yarchive.net/bike/rivnuts.html.

[marciero]

Originally Posted by MikeD

Yeah well I had a Trek 1200 that had a front derailleur mount held to the frame via two rivnuts. The frame cracked around the seat tube at one of those rivnuts. I noticed afterwards that Trek switched to clamp-on derailleurs in later iterations of their frames. Maybe bottle cage rivnuts, since they're more at the center of the tube, there would be less stress there. If you look at quality steel frames, the inserts are brazed in, thus reinforcing the tube. Rivnuts aren't as good.

Read what Jobst Brandt said about this https://yarchive.net/bike/rivnuts.html.

Butted tubes would be thinnest in the center section, which probably includes the derailleur location. In any case I think the stress is coming from the bottle weight and impact stress from road, rather then where on the butted section the holes are located.

[MikeD]

Originally Posted by marciero

Butted tubes would be thinnest in the center section, which probably includes the derailleur location. In any case I think the stress is coming from the bottle weight and impact stress from road, rather then where on the butted section the holes are located.

There's bending stresses on the seat tube from pedaling; especially out of the saddle.

[marciero]

Originally Posted by robt57

Another thought, use a ruler with a V taped or cut on one end Or a piece of luan plywood etc.

Put the self centering V forward on DT or HT and use the straight other edge to mark a line center of Seat tube on your painters tape.

Nice. Simple and clever.

[AngryScientist]

the FD mount would have been riveted on, not rivnuts. similar concept but different product.

the rivets have a smaller diameter and much moire stress on them than bottle cage mounts would.

the problem with rivnuts is they may come loose eventually, but i have never heard of a failure at the hole. they would not be my first choice for bottle mounts, but in the case if this frame, they are by far the best choice.

[marciero]

Originally Posted by MikeD

There's bending stresses on the seat tube from pedaling; especially out of the saddle.

Okay noted. So additional stress at the hole locations due to that- wherever the holes are located.