TITANIUM  ATTEMPT
Welding The Seat-Tube/Bottom-Bracket Joint

18 February 2008,  by James Morikawa

 It's February 18,  2008.   I did my the first weld on the Ti-frame I'm attempting to build — the Bottom-bracket/Seat-tube joint.  It was a good learning experience.

I need to mention that I not an authority of Ti welding.  This is my first Ti-frame attempt.  I lack much hands-on experience.  Only time and doing Ti-frames will overcome that.
These are personal notes on my first attempt at a Ti-frame.

Below is brief summary of my progress.

I cleaned the weld parts by doing a wipe-down with "Windex",  and a clean rag.  Then I did a second wipe down with Acetone.   After cleaning the parts,  I wire-brushed the weld area with a fine stainless-steel brush,  then did another acetone wipe down.  I  inspected and made sure the weld zone was free of lint.  Because I did use my abrasive belt-miter to miter the tubes,  I did file the miter lightly, prior to cleaning — this was to clean off any grit that may have gotten embedded in the Ti.

                       After prepping (cleaning) the parts I mounted them onto the frame jig.  I was                          After doing the tack-welds,  I removed the parts from the frame-jig and mounted
                     careful not to touch the weld areas with my hands.  I installed the internal purge                        it on my welding fixture — where I completed the weld.   I welded  without Pulse.               
                     devices and let the tube/BB purge for about 5 minutes,  at 5 CFM Argon flow.                    The machine set at 100 amps,  DC straight polarity,  Hi-freg start,  3 second  preflow,
                                                            I then did my tack welds.                                                                                                           and 10 second postflow.

Anyway,  I feel OK about this weld.   The weld-penetration is good.  There is a slight weldment undercut on the bottom-bracke side.  I made sure there would be no undercut on the thinner seat-tube side.   I ended up not using any filler rod.   Due to the thickest of BB, I found myself  "fusion welding" — I was getting good penetration and build-up, and it didn't seem necessary to add filler. This is the reason for the slight undercut on the BB side of the weld,  and it's barely noticeable.  I feel OK about doing this because of the BB's thicker walls.  It also allowed me to run the weld effecting a lesser HAZ (Heat Affected Zone).

I going to have to cold-set (straighten the alignment) of this weld.  This seat-tube has a bad curve to it, not caused by the welding   I should have checked the tube before I mitered it.  There also a minor mis-alignment between the BB, and the seat-tube — I believe caused by welding distortion.  I have to put things back into alignment.

My build philosophy:  Build it straight as I build.  Keep things aligned or correct any mis-alignment as I build.

The Bottom-bracket mounting,  purgeing, and heat-sink sleeve did it's job.  I think it's going to be a keeper.

It's been a learning process.  I'll probably be altering the way I do things as I progress and improve.  I'll post a few more pictures before I end this webpage.

     CLEANING STUFF:
 That middle jar of acetone — I let the tube miter sit in it for a couple of minutes.  Rags have to be clean with minium lint, and can be washed later.   Windex works as a cleaner.  Learnt this stuff from various Ti-builders.

 WIRE BRUSHING:
 Used a fine bristle stainless-steel wheel, 1/8" shaft Dremel brand is what I used.  Small enough to brush the internal edge of the miter.  Has to be stainless-steel.

 INTERNAL TUBE PURGE:
 Simple set-up made out of a rubber plug,  brake-line tubing,  and automotive vacuum tubing.  There's a tiny little vent hole at the top of the rubber plug to aid in venting.

I'm ending here,  I'll write more as I progress on my first Ti-frame attempt.  

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