Bottom Bracket Post

[Erasmus]

Well if you're going to do two... Three couldn't possibly be that much more work... ;-)

[ToddFarr]

Erasmus,
We will see how much time the first 2 take, and if I have enough material. I want to build bikes soon, and it seems I spend most of my time making tooling.

Anyways,
These babies showed up in the mail today.



Hopefully I'll have some time to work on the posts this week.

[illcomm33]

Well done Todd!
If your frames are as desired as this BB post you are off to a good start.
I also PM'd about adding my name to the waiting list. (Without convenient access to to any machining tools (lathe/mill) I decided to hold off on trying to fabricate one of these. Plus yours looks better. ;)

[Erasmus]

Understood. Keep us posted how the finished product turns out!

[ToddFarr]

If there is much more demand I might send off a quote to have 20 of these posts made up by my local machine shop I use for my business. I get really competitive pricing, I'll let you guys know what comes of it.

Here was last weeks project. It took a heck of a lot longer than I expected. It jumped to the top of the priority list because I needed it to work on my latest build. It works amazing as a lug stretcher. There is a thrust bearing under that handle that make clamping so simple, and the coarse threads make it less than 1/4 turn for clamping/unclamping.

[ToddFarr]

Just got an E-mail back from the company I am going to have heat treat these posts. $0.40 per pound, and he's saying 50-53 HRC. That's a lot cheaper than I thought it was going to be, and the hardness should allow for many years of use!

[Mark Kelly]

Well if you are going to make twenty, I'll have one.

Post pricing and payment details as soon as it's sorted.

[ToddFarr]

Spent tonight cutting away massive amounts of material

[illcomm33]

You the man Todd! That looks great. Keep us posted through the steps.

Travis

[ToddFarr]

Thanks Travis, I appreciate it. I should have another update this afternoon. The taper isn't as smooth as I'd like it but it's pretty tough to manually feel that little handle on my lathe. I also went and did a .0025"/min finish pass on the main surface, put a dial indicator on it and I have less that 0.0005" of run out which is pretty good for my old clunker lathe.

-Todd.

[Andrew R Stewart]

Todd- Run out between the base and the shell's face contact (the top) was a concern of mine, as well as the long term wear. So I had my post surface hardened then ground, both top and bottom. My post does not have a stepped section that goes up into the shell though. With a solid tightening of the shell onto the post I don't see any shell shifting on the post so the need for a stud/step going into the shell is a questionable need, IMO. Andy.

[ToddFarr]

Andrew,
Good insight, I mostly added the stepped sections as insurance. I didn't want to have to worry about it shifting during cold setting. I also made the tolerances tight, my hopes is that if the shell face is out of line (due to tacking/brazing) the steps will hold the thread faces if it wants to tilt when it's clamped down.

[RCP FAB]

Let me know when you are taking orders.

[Andrew R Stewart]

Todd- Not to be a downer, but unless the step is a slight press fit into the shell's threading I don't see how it will locate the shell very much. But then i'm splitting hairs. Which makes me wonder if the stud had threads... Andy.

[ToddFarr]

My thought was that if the tolerances are tight enough any angular movement would be compensated by the contact of the thread faces against the inserts against the threaded rod since those parts remain rigid. They are not a press fit, but they are a super close slip fit. You can slid them in the shell with just the tiniest bit of resistance. Either way a nice feature of the inserts is that I don't have to support the frame when clamping it down. I put a full frame on it last night and without even clamping it the frame held suspended and want to twist or lay down on the table just because of these contact areas. You are probably right and they are more of a luxury than an necessity.

[cardinal]

On an old table at Bike Gallery I got a BB pretty stuck on a post like that. The fit was close and the BB was warped just bad enough to make me cuss. A non-brazed BB shell fits nice and tidy, but think about the worst case and design for that.
I'd have to go with Andy on thinking twice about the step.

[ToddFarr]

Good point and thanks for the insight. Like I say in most my threads I have very limited experience building bikes (working on #2 right now), and I appreciate the input and advice from those who have more experience then I do. That being said maybe the step idea is a better in theory than in practice, I might leave it but take a few more thousands off for worst case. I really do like being able just to slide the bike on there and it supports itself until I clamp it down.

I will also say although I don't have many frames that I built I do have a ton of frames I've been collecting and restoring/rebuilding. That being said every single one of them (28 frames) fit on the post without a hitch. And being a machine builder by trade, I know for a fact never to force anything.

With all this constructive criticism I have however decided not to offer these to anyone. I don't want to be responsible for someone getting a BB stuck on this post. Maybe you can learn from the discussion here and design and build your own.

-Todd

[echelon_john]

One other point about the step: I'm not sure about others, but I'll often leave chainstays a little long; same for the DT protrusion into the BB shell. This all gets ground out and cleaned up, first with a die grinder, then with the thread chasing tool. But in the interim, it's really handy being able to throw the thing on the alignment table to check this, that or the other dimension during the construction process. Having a close-fit step would mean that you couldn't put it on the post until the BB was essentially chased.

On the other hand, I've been thinking along the lines of using the threads as the reference, rather than the BB face. To that end, what would you guys think of a design where, essentially, the frame screws down onto the post by its BB threads, then the frame & post could be rotated on the table for positioning, and locked down from the underside via a threaded post and toggle that would sit below the plate? Obvious concern would be continually loosening and tightening the post onto the plate/block. Thoughts?

[ToddFarr]

John
I'd say rather than having to swing the bike around a bunch you could make a threaded insert that sticks out a known amount after it's inserted, and then slides down over a turned post. The threaded insert and the post base make contact instead of the shell face and the post base.

-Todd

[Curt Goodrich]

Not to pile on but I'd turn down the post a bit. Relying on the threads is a fine idea in theory but IMO it makes the build unnecessarily slower with no tangible benefits. If one has to chase the threads every time you want to put the frame on the table, one might be less inclined to use the table and that's a step in the wrong direction.