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 Minumum stem length/clamping area DIY tiller

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SpiderMonkey Posted - 03/29/2019 : 11:40:42
I'm starting to hack away at the steering and I wondered what the experts here thought on tiller stems. I'm going to make a DIY flipit, and I've got some CF steering spacers from China in various lengths. I plan to build the flipit onto the front of these while putting a pinch bolt assembly (M6) on the other side.

Almost every stem I've ever seen has 2x M6 for pinching the steerer tube. My NoCom's stem is a single M6 and that was always plenty sturdy (after I'd rebuilt them with t-nuts and used assembly paste) for tiller steering. This project, as with that one, has CF steerer tube and CF stem/clamp interior.

I cut a 30mm length of tube for the stem since that's the height of the flipit on my Azub, and it looks short-ish to me. I'm wondering if 30mm (minus 2-3mm for steerer tube top clearance), so say, 28mm of height x 88mm of circumference will be enough clamping area. (~25 cm^2)

I could easily make these 50mm high, with a pair of M6 screws for clamping, but that feels like overkill.

8   L A T E S T    R E P L I E S    (Newest First)
warren Posted - 03/31/2019 : 17:46:02
With 2" overlap and ample clamping you generally don't need the assembly paste.
SpiderMonkey Posted - 03/30/2019 : 14:31:59
I haven't seen those 1-bolters. Good to know. Maybe they want 2 bolts on a lot of the stems to try for more even pressure or something, or they figure riders are going to throw too many spacers underneath and not have enough clamping area. Putting a set screw all the way through makes sense (but then I'd have to make sure I had the thing straight!).

I bought a cheap-ish (https://www.aliexpress.com/item/2017-full-carbon-fiber-riser-mountain-bike-road-bike-bicycle-stem-carbon-fiber-new-arrival-ultra/32786685828.html) Chinese CF stem that I was going to cut to use for the basis for my flipit, but now I think it's too nice to wreck (and my wife wants me to build her an upwrong…)

I suppose I should just go ahead and build as planned. Worst case scenario, I need to build another. (My "Carbon Fiber" spacers that I bought to build the flipits on turned out to be carbon-wrapped only, glass inside. I figured that would be the case since they were so cheap, but the multi-meter showed they don't conduct any juice at all on the cut edges.)

TVM Posted - 03/30/2019 : 12:41:09
Yes, I made that one. 231 g's total weight.

Set screw goes from front to back, through the carbon tube, tapped into the AL stem.

The question is "how short"?

IMO it could be a 1/4" tall if you had a way to prevent slippage.

"2 bolt stems".
Have at least half a dozen factory stems with 1 bolt.
Both off-road and on.
I buy up close-out stems to use for donors.

If they have 2 bolts, I cut them in half.
Twice as many parts, half as much weight.

If I tried to use a "2" stem on most of my builds, I would be looking at it instead of the road.

If 1 1/8" is good enough for Bacchetta???

SpiderMonkey Posted - 03/30/2019 : 11:54:31
Did you machine that flipit from alum, John?

I like that design, but I'm need something that'll be angle adjustable and that might be trickier to rig with that design. I'm also only worried about not rotating, since no one leans on a tiller like on regular bars.

Is this on a carbon steerer? With a set screw?

(PS, I tried to get hold of you to commission 2x M1s a few years ago. Turned out I didn't need 'em, so good for my wallet we didn't get in touch. ;) )

Warren, do you use carbon assembly paste on yours? I measured my NoCom tube clamping and I'm only clamping to about 30mm of steerer there. It got a lot better when I used that grit paste.

(All bets off when Kamil's nut tore off it in the field in Iowa, but it was easily mended with a hose clamp from the corner store and a hunk of inner tube from the nearest RAGBRAI trash can.)

warren Posted - 03/30/2019 : 08:36:30
I usually use 2" to clamp to a CF steerer.
alevand Posted - 03/30/2019 : 07:18:00
Maybe that's why they have two screws, for clamping force.

Tony Levand
TVM Posted - 03/29/2019 : 17:02:14

1/2" in front to 5/8" in back.

The Bacchetta "flip-it" is only a little over 1" tall.
Must be enough?

The biggest thing (for me) is having enough clamping force to "not rotate".

I run a set screw.

Had one customer bitch and whine and complain and then bitch some more that I "cut it way too short"
Used the Bacchetta with one spacer.

IMO on a low racer with hardly any line of site over the top.


Yeah MIKEY, you would be that customer that wanted to run a TALLER stem??????? WTF?

SpiderMonkey Posted - 03/29/2019 : 13:52:53
Most of the other stems in the house I see are 40mm minimum, so maybe there's my answer. Just make 'em 50mm, two screws, and not worry?


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