I am a frame builder AMA

If this is correct Merckx's bike at that time was on 265. If that's good enough for cornering when racing, with clearance required for wide pedal and cages, does a rando bike really need a higher BB (I understand it'll be just fine)?

I like my BB low. Nothing wrong with that. I am just saying 270 aint that high. Also depends on the wheel base. My cargo bike suffers badly from pedal strike, but it isn't a problem if you know it's a thing

My cargo bike suffers badly from pedal strike

Those flat MTB pedals need a lot of clearance don't they. Now you'll know for the next one!

Yes for sure. BB is at 265mm I think. Turning with such a long wheel base seems to mean I get quite close to the ground. SPARKS have been made ;-)

AS @PhilDAS says, I think if I find a correctly dimensioned 4130 straight tube I should be able to make it work with some off the shelf headset parts. The trouble with a 44mm HT is that it doesn't leave much room for the rear brake hose to wrap around the steerer.
I asked a Chinese CNC company and they quoted me $220 for a fully custom machined headtube which will just take the drop-bearings. Not crazy expensive once you factor in the cost of headset cups etc. Obviously, it's expensive if you fuck it up and have to order a second one...

A second one would be cheaper if you ordered them at the same time though... Half the cost is in the set up

Yes, most definitely. Time for a list ;)

haha im keen, sounds cool

Haven't properly dimensioned it, but it'd be something like this.

1 Attachment

Had a call with TBA yesterday to discuss my course which was generally positive, as in they're willing to help with my ideas but not take responsibility if they don't work (fair enough).
I might abandon the wishbone in favour of concentrating on the headtube as the key feature and not messing that up.
As a backup headtube option, I was looking for just some plain gauge tubing that might come in a suitable diameter and wall thickness, i.e. 58mmOD, 2mm wall. Anyone know of a good source?

What's your vital dimension?

LASAero don't do 4130 that large, Aircraft Spruce do 2 1/4" or 2 1/2" but choice of wall thickness is pretty limited at that diameter.

Ideally, the finished piece should have 62mm OD, 55.95mm ID at the ends. I can machine the outside to remove some weight in the middle of the tube.

2.5" x 0.12" wall thickness from Aircraft Spruce is pretty damned close?

Talking headtubes, what's the deal with mitreing a downtube to meet a tapered headtube?

Having only done straight headtubes it seems like doing a tapered one will be hella difficult but maybe I'm over thinking it?

yeah they look awkward. Ive wanted to do one for a bit but havent got round to it. Also are there tapered heatsinks out there for tiggin?

Is it boric acid that some people use as flux?

I knows its something acid!

I tried it a while ago and wasn't overly enamored but fancy trying it again just for dipping my rods in.

Yep, that's the stuff. Matt swears by it. Never tried it myself.

Cheers.

Just grabbed some off ebay.

I remember when I was trying to make a paste with it it just didn't want to go where I wanted it to. Hopefully it sticks to a hot brass rod ok!

A drop of washing up liquid helps.

I find it a right faff to wash off. Not sure if money saved on it, works out cheaper than time trying to get it off. I probably bake it on a bit much.