Bottom Bracket Post

[ToddFarr]

If there is that much heat distortion can you rely on the thread faces? How does Joseph Ahearne hold the frame up? does the insert rest on the tower?
Where did you get your V-blocks? Are they high enough to hang the stays over the table?

[Luke]

This is my home-job version of affixing the BB shell.
Not as good as some of the others...but it worked for me.
It was a pain in the ass to take apart, so I eventually went to using just the plate side insert with the single bolt during the build phase.

016.jpg
023.jpg

[afwalker]

Luke,
So that's like 1 1/2" diameter brass, how tall is the lower post?
cheers
andy

[shand]

I think I touched on this in another thread a while back but I have a question for the folks using a BB post for alignment (I use the HT).

How do you handle the fact that throughout the build process, the bb shell will vary, in either roundness, parallelism of the faces or if you face the shell after tacking or brazing, variability in length?

Assuming you have a blueprinted shell with parallel faces, you tack the frame in the jig, you pull the frame out of the jig and check on the alignment table (referenced off the shell face on the BB tower). Now, you braze the frame, if you're sure the shell hasn't distorted, then you're good to go and you can check alignment again knowing that the centreline of the frame above the table is the same. But if you need to correct for any distortion by facing the shell (at least one side) surely the centreline of the frame is now at a different point above the table?

Does anyone account for this or does this method (BB post) only work if you know you're not screwing with the accuracy of the shell during the build process?

Steven

[e-RICHIE]

I face the shell once, when the part is grabbed and ready to use in a frame. Most times I don't even do this;
I trust the faces and measurements as they are delivered from the casting house. Never, as in never ever,
would I face a shell during or after a frame or sub-assembly is brazed.

I think I touched on this in another thread a while back but I have a question for the folks using a BB post for alignment (I use the HT).

How do you handle the fact that throughout the build process, the bb shell will vary, in either roundness, parallelism of the faces or if you face the shell after tacking or brazing, variability in length?

Assuming you have a blueprinted shell with parallel faces, you tack the frame in the jig, you pull the frame out of the jig and check on the alignment table (referenced off the shell face on the BB tower). Now, you braze the frame, if you're sure the shell hasn't distorted, then you're good to go and you can check alignment again knowing that the centreline of the frame above the table is the same. But if you need to correct for any distortion by facing the shell (at least one side) surely the centreline of the frame is now at a different point above the table?

Does anyone account for this or does this method (BB post) only work if you know you're not screwing with the accuracy of the shell during the build process?

Steven

[Andrew R Stewart]

Why must using the shell's face mean that the rest of the frame has to be referenced to it? As I have tried to explane a few times my use of the shell is more for whipping then for a measurement point. I do try to insure the shell is square with the ST and DT, to a degree. But after that the main triangle's parallelness is measured by comparing the slope of both the HT and ST. The same slope over the same distance along each tube is my goal. The ST is very close to being parallel to the surface plate (a few thousandths to a hundreth over about 10") when the shell is mounted onto the post. Then the HT is measured over the same length via a rod and cones through it's center. Jack stands are placed under the HT ends before the rod/cones are placed to maintain the HT's height off the surface. The same jack stands will be placed under the proper tube ends to support and whipping needed to get the HT and ST parallel. I will flip the frame over and repeate a couple of times, seeking the average. I don't do the rear triangle aligning on my surface. Andy.

[shand]

Why must using the shell's face mean that the rest of the frame has to be referenced to it?.

I realise if you're not aligning the rear triangle off the table in the same was, then that's not an issue. My concern was that by using the shell face as a reference then as soon as you put any heat (ok, a lot of heat) near the shell, then you're going to start chasing your tail.

I like the fact that in my system (referenced off the headtube), I have a known frame centreline that sits off the table that never changes through the build process. This makes alignment of the rear triangle really easy.

[steve garro]

IMG_3776.JPGIMG_3775.JPGIMG_3774.JPG

I think I touched on this in another thread a while back but I have a question for the folks using a BB post for alignment (I use the HT).

How do you handle the fact that throughout the build process, the bb shell will vary, in either roundness, parallelism of the faces or if you face the shell after tacking or brazing, variability in length?

Assuming you have a blueprinted shell with parallel faces, you tack the frame in the jig, you pull the frame out of the jig and check on the alignment table (referenced off the shell face on the BB tower). Now, you braze the frame, if you're sure the shell hasn't distorted, then you're good to go and you can check alignment again knowing that the centreline of the frame above the table is the same. But if you need to correct for any distortion by facing the shell (at least one side) surely the centreline of the frame is now at a different point above the table?

Does anyone account for this or does this method (BB post) only work if you know you're not screwing with the accuracy of the shell during the build process?

Steven

Sure - but, the headtube distorts as well - your facer/chaser tells you that - check it with a square and you'll see it distorts.
The best thing is to find a sequence that works for you with repeatable results every time and stick with it.
You can drive yourself crazy, but at the same time it's a hell of a cool challenge.

I recently tried to make a frame as straight as possible, REALLY sweat it - just to see what I could come up with.
Here are the three measurements i sweat, and how they came out.
The ST was high 1/2 the thickness of the .6mm to the left.
The HT was high to the left *just* enough to not let the height gage slide onto the HT
the center of the rear axle was a little snug, and as off as you see.
The fix = hard yank to the left CS and call it good for the day.
Nice fuckin' bike.
- Garro.

[ToddFarr]

What's the process/tooling for going off the Head Tube?

[shand]

What's the process/tooling for going off the Head Tube?

I have a 5ft x 4ft granite surface table. The end tube is supported in a pair of bench centres. I use either cones or inserts depending on what I'm doing. The cones are quicker and more versatile for different headtubes but the inserts work better for resisting twisting forces if I need to tweak anything while it's on the table.

This puts the frame at a know centre height and the BB is supported by a post. The post has spacers to enable me to adjust the height so that the shell is a known height above the table. I normally use 73.5 or 68.5mm shells but I have additional shims if I'm using a shell that's a different size. I also have a go/no-go gauge that slided inside the seattube. Again this sits at the frame centerline. I also do the rear triangle at the same time. I have a gauge that's mounted at the centre height that lets me check dropout width and dropout spacing and I use a tall square on the table to check the relative height of the to dropouts.

I'll try and get some pics tomorrow when I'm back in the shop. You can see some of it in the (terrible) pic below:

alignment.jpg

[Andrew Drummond]

If there is that much heat distortion can you rely on the thread faces? How does Joseph Ahearne hold the frame up? does the insert rest on the tower?
Where did you get your V-blocks? Are they high enough to hang the stays over the table?

Todd,
I think the threads are pretty reliable - the inserts don't just engage two or three threads, they go in pretty far, and they're a close fit on the post - so they're parallel and coaxial. The inserts hold the frame up... I wish I'd taken a photo. Maybe there's one on Joseph's website. My V-blocks came from Victor Machinery Exchange, but they're available everywhere - they're just cheap cast iron, less than $30 a pair on ebay. Not exactly $500 Suburbans, but close enough for framebuilding. By themselves they're not quite tall enough to get the rear dropouts far enough off the table, but I put a 1-2-3 or 2-4-6 block underneath. A piece of cold rolled flat bar is probably good enough, though. I should mention that the V blocks are on their sides, to maintain the centerline using tubes of different diameters.

Andrew

[ToddFarr]

Andrew,
I guess I'm not quite understanding this part:

"I should mention that the V blocks are on their sides"

I'm trying to picture how you could put them on their sides and still support the frame?
Thanks,
Todd

[Andrew Drummond]

The tubes are clamped into the v-block, with a ratcheting clamp or a toestrap or something. I don't have a photo of my setup right now, but here's Dave Kirk's old fixture - the V-blocks are used the same way.

kirk.jpg

[illcomm33]

So I have been watching the thread and asking a few questions on the side. Thanks for everyone's contributions/guidance/suggestions etc. (Especially Todd!)

I am not sure about the steel so before I spend $22 on ebay I wanted to make sure this would do the trick.
4140 Steel TGP bar end 3" round 4 3/4"
$(KGrHqNHJEwE92gJ2C6gBPiIM9uEoQ~~60_35.JPG
Gameplan is to purchase the steel and tap it completely for an all-thread rod (to mount/bolt to underside of the phenolic table, and then to a steel handle (McMaster Carr: Steel Handle with Nylon Ball Knob Double Offset, 5/8"-11 Threaded Hole) to cinch down the BB. (I would also need a heavy duty washer style part like Todd used)
steel handle.jpg
A) Is the 3" diameter ok and the 4 3/4" height sufficient (slightly taller than a few of the ones here but not overly excessive?)
B) Is the 4140 a good steel choice? I have very limited, like zero, experience with steel hardness/durability/etc ratings. It seems the 303 mentioned my be too soft?

Here is the post I had on MTBR about the phenolic table. It has pictures of the step by step process.
Phenolic Science Lab top for alignment table? - Mtbr Forums
It was said to be flat.

[Andrew R Stewart]

ck Ilcomm33- As I see it the size of the steel plug you're considering is fine. You'll want to make sure no post/chainstay interference can happen, maybe bevel the top end a bit. You could use a hardened washer on the top surface if you are worried about the hardness, or do so some time in the future if there is some wear over time. If I read your plans correctly it seems that you're going to thread the plug all the way through it. That's a lot of effort. You could only thread a short portion of the length and have a through hole for the rest of the length. Once tightened down onto your flat surface there should't be any movement. Or as I did, use bolts on either end and only thread enough to have the bolts tighten well. Do a little home work as to how high off the surface you want the framw tubes to be. What vertical devices will you use and their ranges? Will you have machinist's jack to support the frame during the cold setting? How about vee blocks? What about the rear triangle alignment? Andy.

[Andrew Drummond]

illcomm33 - it's been a while since I've seen a phenolic table in person. How hard is it? Do you plan to use the BB post to do any cold setting? If you do, you'll want as big a base as you can get, if you're bolting it to something that's softer than steel - you don't want the post to put a dent in the table when you wrench on a frame. 4140, by the way, is a great choice if it's not annealed. I looked up the auction, and the seller doesn't specify hardness, but I'd guess it's been heat treated if it's TGP (turned, ground, and polished - close tolerance OD) shafting. And $22 shipped is a good deal! I'd probably avoid using 303. It's relatively soft and can't be hardened by heat treatment (through a thin, hard layer can be deposited, but that's more for wear than strength, and is $$).

Andrew

[ToddFarr]

With every ones input and how this thread is progressed, I decided to make REV2 of my bottom bracket post. Originally when I was looking into making it I had not done much research, and figured all I needed was a post that would hold the bottom bracket. After some playing around I determined it would be nice to have a bigger handle (making clamping a bit easier for really manhandling the bike), a slightly bigger base (like most are suggesting), and an insert at the top instead of washer (if I can keep tolerances tight enough this will help square the bottom bracket up of the thread faces, and not rely on the BB face so much).

1. Handle - I went with the cast handle originally because it was cheap and pre-tapped to what I wanted. I also went with McMaster since I order from them like 5 times a month for my job. Being a machine builder I have a ton of resources for these types of parts. This time I decided to do it right and find something I really like. One of my favorite suppliers is Elesa out of Italy. They do a great job of finishing their components, they look polished and complete. I finally settled on Part # GN 99.7 which I was surprised to find out is only $14.11

2. Slightly Bigger Base, I went to 3" or 75mm whichever I can find for less, automationmaterial.com is down right now so we will see what happens. I am also planning on using a heat-treatable material or something with a bit more wear resistance that my last 303 BB Post

3. Out of the same material type I will be machining an insert that will help square the thing up a bit better, I also went to M16 threaded rod which will be more stiff than the 1/2" I was using before.

Anyways, here she is.



Exploded

[Will Outlaw]

Wanna make two? Maybe a second with the base tapped for 3/8-16 that'd fit my new table perfectly.

You know, for practice. :-)

[ToddFarr]

Yeah,
I can make 2. That qualifies me for free shipping from Elesa so thank you!

[Will Outlaw]

Yeah,
I can make 2. That qualifies me for free shipping from Elesa so thank you!

Shot you a pm.