Welding Tips and Tricks

The question is I have a .062 4130 plate with a 8740 bolt that had been mig welded to it for a pulley to operate off of. I feel like this is going to be really brittle and a very weak weldment to say the least about it so I opted to investigate implementing a stainless steel bolt of 316 or 304 alloy. Famous head marked THE stainless bolts. There's not a lot of information on the web about it but it seems that 309 L or an inconel Rod would be best for this application and to keep the heat very low as possible . Any recommendations or suggestions on this would be greatly appreciated in advance ..... thanks.

SS bolts are generally soft and might not be a good choice if the pulley has much stress. Does the pulley use bearings?

Poland308 wrote:SS bolts are generally soft and might not be a good choice if the pulley has much stress. Does the pulley use bearings?

I second that most stainless bolts are only a Grade 2... Could it be a bolted connection with a shoulder bolt (especially if it uses a bearing)

The reason I wanted to use stainless is for Corrosion Protection and the pulley does have a sealed bearing. I'm just afraid of a Nas bolt being welded it has become very very brittle in the haz and I would expect it to break. Maybe I would be better off using a grade 5 quarter 28 shoulder Bolt and weld with er70s-2 after sanding off the zinc near the weld area...

Dip the entire bolt in acid to remove the plating to ensure you get a good clean weld.
You can then cold galvanize after the fact if you want to offer it some higher degree of protection.
What does it need to be protected from?

Just weather or actually caustic materials?

I have welded stainless using the 309 but never in a stress related situation.
At most to secure a body panel or such nothing that is exposed to high torque etc. It was done mainly for the looks of the stainless bolt.

I'll wager the application is a control cable pulley in an airplane, and I'd be careful about coloring outside the lines here. The softness of a SS bolt is not my bigger concern; The dissimilar metal weld with the require low heat input is, since the bolt (and the weld) will be loaded in shear, not tension.

I agree with your concern about the MIG weld, and for the same reason. I think I'd use a standard grade 5 AN bolt, TIG welded, and maybe a light PWHT with the torch on the back side of the weld. Then, a good cold galvanizing, and install the pulley with a good coat of a corrosion inhibitor like NO-OX-IDE A on the bolt.

I'll dig out my EAA books and see if they have a specific recommendation (I know one of them covers control systems in detail).

[EDIT] That was a waste of time... The only example I found was for a rudder balance cable pulley that was bracketed on both sides with a through-bolt.

Steve S

Yes you are right... more airplane stuff. The pulley deflects a cable run of 25 or so degrees. Even calculating the load as a tangent force it would be less than 65 to 85 lds force at the rare moments it would see that kind of stress. Surely a factor of 4 for safety it would be secure.... plus it is behind an inspection plate. So it will have my eyes and hands on it every 25 hrs and at every annual inspection. I am going with cleanup of the grade 5 bolt and tig welding to the plate. I know the mig welded hardened bolt is flying on a lot of kit/plans built planes similar to this... but I wont trust it. Thanks for the help. It will get a coat of this on it when done
http://www.univair.com/paint-dope-fabri ... rimer-kit/

I have only found 2 ways to remove it after a week cure.... torch or grinder. No chemical we have would touch it. Plus being inside the wing it will be subject to only condensate moisture....

Why not just weld a 4130 boss on the backside of the area the pulley is to be mounted to, ream to the nominal size and use a NAS 1300 series bolt of the correct grip length, fitted from the pulley side, and use a self locking tension nut.

You could machine a spigot on the boss for the inner race to butt up against and save having a spacer ?

I would love to do something like that...issue is that where the pulley bracket needs to go the main spar is where this plate gets riveted onto. No other holes allowed at that area. No back side access of anything.

Welded a grade 5 plain- uncoated 1/4-28 bolt to this today. I cut a radius with a fly cutter so the head would lie flat on the curve of the .060" bracket. Tricky to stay small with a puddle and keep things going good.... still had a bit of push through on the back side after trying to keep amps to a min. Clamped in a jig I had under the table to try and keep it's shape.

That looks really good. What kind of airplane is it?
I have plenty of experience building ultralight kits but never anything that needed to be registered as experimental. Is it dope and fabric?
This is the only photo that I have of any of them. I only have it because the baby in the seat is 17 now and she recently found it in some of her stuff. Her dad sent it to me.

Looks like it turned out well.

Nope. That machine had been crashed in North Carolina before I bought it. Sam fixed a bit of the structural aluminum on the rear end and then I recovered the entire plane. I bought a $30,000 Skyboy with a Rotax 912 before I got around to painting this plane and I eventually sold it back to the guy who designed it.
That Skyboy was supposed to have been registered experimental but I never did any such thing. It would do 103mph flat out and weighed close to 650 lbs. It also held 15 galons of fuel. All of those things put it well outside the specifications for an ultralight trainer.
The Freebird in the photo above had a 70hp 2 Stroke International, 3 cylinder engine on it. I could not keep the exhaust gas temperature down on that beast. The manual called for .170 main jets and it was still overheating with .185 main jets. I took it back to the factory and the tech who tested it told me that it appeared to breathing fire because someone had polished too much metal off the intake ports (2 stroke piston port engine). He wound it up and sucked the propeller guard cage right off the ground and destroyed my prop blades in the process. He then told me that it was more than likely producing around 85hp instead of the rated 70hp. The only way that I was gonna be able to keep the temperature down would have been to put .205 main jets in it and that would have likely lead to catostrophic detonation.
When I realized all of that crap I just said screw it and plunked down the cash for the Skyboy. Damn! I sorely miss having that kind of money......

It is a rag and tube bird. Avid flyer- similar- kitfox. Tons of mods and upgrades to make it not just new.

jumpinjackflash wrote:It is a rag and tube bird. Avid flyer- similar- kitfox. Tons of mods and upgrades to make it not just new.

Kitfox...awesome fun. My Dad has built a Rutan Long Ez as well as a Vans RV6. Been all over Oz in them.


Kym