Engine mount tube thickness?

[FoxbuilderWill]

How did you make your own donuts? What material etc?

Also have some questions about annealed vs normalized 4130. From what i can see ACS 4130 steel plate is annealed, and i haven't looked into it for sure but I think the round tubing might be normalized. I'm not going to weld the mount personally i'll have someone else do that but if some of it is normalized and some is annealed what then? Even if it is all normalized do you have to heat treat it after?

[jrevens]

Hi Will... FWIW, normalized 4130 is considerably stronger than the annealed condition. Many welded steel aircraft structural components are fabricated from 4130 N, but it is not normally re-heat treated after welding. It is usually good practice to stress-relieve a structure that has been arc welded (TIG or MIG) after welding, usually with an oxy-acetylene flame. This seems to be ignored by some fabricators. The need to do that varies with the design of the structure.

[David47]

Hi Will... FWIW, normalized 4130 is considerably stronger than the annealed condition...

Agree with everything John says above. Any good welder who knows his stuff will also be able to stress relieve by flame heating the welded area and then using chalks/colour charts to determine temperature levels required to stress relieve. In 2016 while at Oshkosh, I asked one of the demonstrators at one of the weld workshops whether they stress relieve after welding. Simple answer was no, which was unfortunate because that was a conversation stopper. I don't understand why some don't do this. The inbuilt stresses resulting from the welding process can lead to grief later on if you don't stress relieve. I only deal with a particular qualified aircraft welder at my airfield because I know he does this as standard practice.FWIW.

[HighWing]

How did you make your own donuts? What material etc?

I used urethane rubber - the type used for making rubber molds. It comes as a two part liquid that cures after mixing. I had to make molds for getting the shape I needed.
I dont remember the shore hardness I used.