I admire you guys, this thread is a perfect example of why I could not built a scratch-built airplane. Problems like this would consume all my thoughts.

Normalizing is moderately important on most carbon steels, although 4130 is still fairly mild so it can be welded easily. Normalizing is air cooled with 4130. Annealing can be done with the kaolite method mentioned above (slower cooling). However, full annealing can induce a small tensile strength loss compared to normalization. In either case, you will likely be fine.

A couple of things that helped me with harder carbon steels like 4130 were:

1) filler rod material. Too hard or soft and the weld line cracks at the weld margin (too hard) or at the centerline (too mild). You can use a dye penetrant to detect these defects really well,and it is cheap insurance. If you are used to welding really mild steel, cracks can be a surprise at times.

2) preheat. My first TIG welding on a fuselage was in a colder garage, and preheating for clusters really helped make a difference.

Normalizing requires the entire part to heat soaked to 1650 degrees. Stress relieving is 1100 degrees. I used tempil sticks....they're available for many temps. It's like a crayon. Mark the part prior to heating. When the mark turns black you've hit the temp. Lincoln and miller have the heat treating specs and the correct methods for welding 4130 tubing.. I didn't use the tempil sticks....much on my fuselage. Wing strut mount clusters, wing mounts and tail spring cluster. Couple other clusters prior to welding...they got hot enough...I didn't do narrow high heat fast beads...which are far more likely to crack.

In my limited experience of welding gear and fuselages both with gas and tig, I have never seen that kind of metallurgical failure as seen on your tail post, ever.
I looked through this thread and saw no mention of the kind of filer rod that was used ie 4130 rod is a no no.
Watch this video, This guy is one of the best welders on youtube, he explains in a no nonsense fashion that's easily understandable. I find his videos to be a great teaching aid.
And one observation I can offer is this, Just because a guy may have years of experience tig welding on race car frames, or whatever, does not make him qualified to jump into small diameter, thin walled aircraft welding. It's a different ball game, that takes time to adapt, even for the most experienced welders.

My tail post failure looks just like the other embrittlement failures I've read about caused by too quick of cooling. There is a picture in one of the Beartracks (Bearhawk news letter) that shows this failure on a test piece, this pic is grainy so you can't gain much from it but it does seem to represent the same thing that happened to me.

ER70S2 was the filler that was used on the fuselage and it is one of the correct options. Bob designed the fuselage for gas welding with RG60 rod.

I'm going to stress relieve a few critical areas, grind out and redo a couple welds then move on.

Sidewinder wrote:Watch this video, This guy is one of the best welders on youtube, he explains in a no nonsense fashion that's easily understandable. I find his videos to be a great teaching aid.

Damn, that was awesome. That guy was stacking dimes and making it look effortless.

Great instructional video.

Sidewinder wrote:

That's a pretty good trick with the pulse on the gap filling. I've used pulse and spray arc filling gaps with GMAW but often get burn through and MORE gap to fill. Really good video. I've subscribed and now I suppose I've got to start shopping for a TiG machine.

When we were building BH 357 we were not sure whether to stress relieve or not so we did some T joints and tested them by putting them in a vise and bending them, almost like your tail post test. Very quickly we found that when we did not stress relieve after a couple of pulls the tube cracked right at the heat affected line. With the stress relieved joint we could totally deform the tube with totally rude bending and twisting but it never cracked. We took the joints to 800*f and then wrapped with KAO wool or Fiberfax material. We TIG welded the frame and used 309 SS for a filler rod. The frame was completely intersection drilled with 1/8th holes then we used a refrigeration vacuum compressor to remove all the moisture , then filled the frame with nitrogen and installed a pressure gauge. This eliminated the need to oil or linseed the frame and we could check the gauges as part of our preflight inspection. No oxygen no rust. No pressure no fly. 11 years and 1500 hrs and the pressure gauge still goes up and down with the temperature change.
That is what made us comfortable. What makes you comfortable may vary.
KenW

Great info there Ken. Thanks

Got the new post tacked in place. Wing formers going on. Slowly starting to gain some ground.

ER70S2 was the filler that was used on the fuselage and it is one of the correct options. Bob designed the fuselage for gas welding with RG60 rod.

When I first started to tig, I went to a sprint car chasis builder and watched. They were tig welding with RG60 . After reading up on it, ER80-S- D2 is the best rod for aircraft 4130.

Just a thought, since you acquired the fuselage second hand don't forget vent holes. Nothing like having a nice blowout on a weld when you don't need it. I can hide vent holes easy on new construction but when I'm doing an extensive repair I go ahead and drill vent holes where needed, easy to close up when its time. I use RG45 for ox/acet and have used RG60 for tig. I mostly use er70s2 now. All a matter of preference.

Only took a week to get back to building the vertical stab. Glad that tail post deal is over.

Looking good Whee,

It's all visual progress at this stage, enjoy it!

I've been working on the front H-stab mounts for a couple days. So frustrating that I can't work on it very long before I move to something else. Think I about got it.

Let me know if you need closeup photos of anything.

Thanks Z. I've been scouring your and Battson's photos and have been able to find most of the stuff I've needed.

whee wrote:Thanks Z. I've been scouring your and Battson's photos and have been able to find most of the stuff I've needed.

I've leaned on Battson quite a bit for photos, so I know how it is

Got the front brackets in and just needed to make the cross tube that connects the front of the H-stab. Was nice to have something easy to do.

image by whee8e, on Flickr

I use a step bit to drill the top of the tube because they are rigid and don't wander when starting the hole. Then I swap to a regular bit and drill clear through the tube.
image by whee8e, on Flickr

image by whee8e, on Flickr

image by whee8e, on Flickr

image by whee8e, on Flickr

Nice whee!

Pick up a set of center drills. They are a very thick shaft drill bit that looks kinda like a countersink but they are designed to do just that: get the hole started with no deflection.

Step drills are great too, I use them extensively for drilling larger holes by starting with a small pilot hole and enlarging it.