37mm head tube with 42mm down tube

[waterlaz]

I have some tubing to build a fillet brazed tandem frame and my current plan is to have a 42mm downtube and a 37mm head tube.
The question is how to connect a bigger diameter tube to a smaller one. Currently I have two ideas:
1) Squeeze the end of a bigger tube.
2) Have the head tube pass through the downtube.

Which one of these two options would you recommend? Is there a third one that I'm missing?

Thank you.

[Jonathan]

I have some tubing to build a fillet brazed tandem frame and my current plan is to have a 42mm downtube and a 37mm head tube.
The question is how to connect a bigger diameter tube to a smaller one. Currently I have two ideas:
1) Squeeze the end of a bigger tube.
2) Have the head tube pass through the downtube.

Which one of these two options would you recommend? Is there a third one that I'm missing?

Thank you.

Squishing has been done for over 100 years with bikes. It's easy, cheap and quick.

The third option is to use a 44mm spec HT.

[Amaro Bikes]

Hello Evgeniy

As Jonathan said, you can ovalize the tube with your own force (if done properly) to fit your desired shape. If you haven't bought your downtube yet, I would recommend you to get any of the already shaped ones by both Columbus or Dedacciai which are built on full purpose tooling:
Columbus: SLFG12670GX or SLFG12670Y01 (HSS series) & ZONH12670112AF or ZONH12670112L (Zona megashape series)
Dedacciai: MTQ440K901

What I would definetly don't do is "insert" the headtube inside of the downtube.

[waterlaz]

Thank you.

What I would definetly don't do is "insert" the headtube inside of the downtube.

Is there any other reason except aesthetics?

[e-RICHIE]

Thank you.

Is there any other reason except aesthetics?

Are you asking about piercing the head tube so that the down tube passes though it?

[waterlaz]

The other way around. I want (not sure if I really want to) the head tube to pass through the down tube. Then I would close the end of the downtube with a thin plate or a piece of tube.

[e-RICHIE]

The other way around. I want (not sure if I really want to) the head tube to pass through the down tube. Then I would close the end of the downtube with a thin plate or a piece of tube.

Asking as a voice of reason and just plain curiosity, why are you using pipes with these dims? Is it a fashion thing? Did a client spec them? What are you trying to accomplish?

[waterlaz]

Asking as a voice of reason and just plain curiosity, why are you using pipes with these dims? Is it a fashion thing? Did a client spec them? What are you trying to accomplish?

I'm building for myself. It's just the kind of tubing I have.

[Nate Zukas]

This is in my jig right now for a 6'7" customer. 42mm DT to a PMW 44mm I.D. HT. A 44id HT can be had for cheap and and would be alot more pleasing to the eye and less trouble keeping that squished section in phase with your miters. Unless your height and weight needs a DT this large I would consider maybe a 35mm DT if you want to stick with your current HTsize. The HT pictured by the way is 280mm's long and the BB is a T47!

IMG_2199 by Nate Zukas, on FlickrIMG_2195 by Nate Zukas, on Flickr

NATE

[Nate Zukas]

Also if this is for a tandem frame, the 44mm HT will support a stronger zero stack headset for a straight steerer or an external 1.5 bottom cup for a tapered fork.
NATE

[Amaro Bikes]

It's just the kind of tubing I have.

Hi Evgeniy

As a general advice I will always say the frame tube choice should be a consecuence of your own decissions respect what you want to build, not the opposite where the tubes are the ones deciding for you. But as I can also understand sometimes this material choice might be very restricted due to several reasons and in order to give best possible advice, could you please give full details on your scenario?
-Joining technique? (Tig, brazing, etc)
-Type of frame? (mtb, road, city, etc)
-Tube availability seems to be a problem with you? any further details on what do you have access to?
-Why 42 and not 38 on DT? or as Nate/Jonathan said use a 44mm HT?

Cheers

[waterlaz]

I want to fillet braze a road/light touring tandem with an open frame (as in no lateral tube).
My plan is to have 35mm top tubes, 42mm down tube and boom tube, 31.7mm seat tubes.
Plus I have a pair of tandem-specific chainstays and MTB seatstays which I think should be sufficiently strong.
I also already have a 37mm head tube, which I bought when I planned to have a 35mm down tube.
Buying tubing from Nova or any other online store is not a very big problem except for the 1 month wait.

I'll consider a 44mm head tube. It's just that I have never seen one =)

[Jonathan]

I want to fillet braze a road/light touring tandem with an open frame (as in no lateral tube).
My plan is to have 35mm top tubes, 42mm down tube and boom tube, 31.7mm seat tubes.
Plus I have a pair of tandem-specific chainstays and MTB seatstays which I think should be sufficiently strong.
I also already have a 37mm head tube, which I bought when I planned to have a 35mm down tube.
Buying tubing from Nova or any other online store is not a very big problem except for the 1 month wait.

I'll consider a 44mm head tube. It's just that I have never seen one =)

So...one thing that comes to mind is if I was tackling what your doing is I'd set out to build a frame and fork or at least design a frame with a fork in mind. Forks imho, have as much bearing on what tube to use here as any other factor. My style is to let you fill in the blanks yourself and with that in mind I think you can probably figure out what your best option is. Btw, paragon makes a nice tube that is nominally machined for 44mm headsets. Be wary of the thin 44mm head tubes out there.

[Eric Estlund]

I'm not suggesting you use the bigger tubes, but mating large diameter tubes to smaller ones has been done for a long time. If you are interested in manually manipulating the materials do so with practice pieces and work on a repeatable method that gets you the results you are interested in. As most folks find, learning how to take round straight tubes and shaping them will result in a pile of stuff you won't use, but open up possibilities down the road.

[Amaro Bikes]

Hi Evgeniy

Reading your details and trying to make best possible set-up I would definetly go for a 44mm headtube, as to give as much front end strength and precise steering as possible, even more if you are thinking of discs.
For shipping times, you being in Ukraine, you could get it in Europe from Peter at Ceeway, they're nice cnc pieces for reasonable price and up to 220mm height, and as Nate said, you can even go for tapered fork with a EC44 bottom headset cup.
Attachment 90237

Regards