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Thread: Chrome Moly 4130 Motor Mounts - Prefab Parts?

  1. #11
    What settings are you using on your TIG for the tub welding? I have been trying to build an enbine mount and my practice welding is not very good.
    Thanks,
    Marty

  2. #12
    cub builder's Avatar
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    The washers are also commercially available from Aircraft Spruce at this link. Select Q&A under the part to get the specs on the two versions they sell. I use the washers and 4130 tubing of the correct spec to fit the bolts.

    -Cub Builder

  3. #13
    Aaron Novak's Avatar
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    Quote Originally Posted by TansAir View Post
    All done, and Thanks all for the helpful comments and suggestions!!


    I used the 4130 sheet to make the "washer". It was overkill with the .125" thickness, I should have just used .065" and it would have been fine, eh well.

    McMaster had nice hole saw, I went over size a little so that the resulting inner disk that drops out when done was closer to the 1.5" OD I wanted. The pilot drill was of course smaller that the 1/2" ID hole I needed, but easy to drill that out afterwards.

    I found the 4310 tube from ACS, .5"OD x .120 wall, .26" ID.

    Thanks to my trusty old Harbor Freight mill I was able to easily back drill (mill) thru the washer (after alignment by hand, with drill/mill not running). This made perfect fit for the 1/2" 4130 bushing.

    I made quick holding fixture from scrap 2x2 alum channel, then tack welded first, final welding later.

    Welding was done on my little HTP america TIG invertig welder (I love that little work horse). I used 100% argon shielding gas, and filler rod was ER70S-2.


    Enjoy the pics, maybe others can benefit so I share .. Thanks again guys!! Kevin

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    Ok, I was trying to figure out a positive way to say this, but instead I am just going to be blunt. That welding job scares me. The penetration is non-existent, the welds are not complete, and the heat input seems really erratic. The toes of some of those globs just are horrid. It looks like you were using away too little heat input. I would really really suggest you do some more practice, have you work inspected by someone competent and then re-do those parts. The design is good, however the execution I would not pass. Please realize I am saying this not to be mean, but instead as someone concerned for your safety. I would love to help you improve your welding skills if you need some pointers etc.

  4. #14

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    Looks like the bolt bushings are too thick. Makes it hard to get penatration of the thick bushing without blowing through the thin tube.

  5. #15
    Aaron Novak's Avatar
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    The thickness is not helping for sure, however with proper procedure and practice it could be done. The biggest error I see in hobbyist tig welding is lack of penetration. There is so much fear of burning through that they end with with these tiny looking welding sitting on top of the material, and the tig process by nature allows it.

  6. #16

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    Yes, the warnings about TIG penetration are in AC-43.13.
    The perfect fit up isn't needed or desired either.
    A gap that allows correct penetration is recommended.
    Last edited by Bill Berson; 09-21-2018 at 12:58 PM.

  7. #17
    Aaron Novak's Avatar
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    Quote Originally Posted by Bill Berson View Post
    Yes, the warnings about TIG penetration are in AC-43.13.
    The perfect fit up isn't needed or desired either.
    A gap that allows correct penetration is recommended.
    Oh for sure, that is standard practice in industry. Unfortunately there are some jokers that tell you to fit things up tight and use tiny welds, even though that goes against AWS specs , 43.13, the mechanics handbooks, etc, etc.

  8. #18
    cwilliamrose's Avatar
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    Quote Originally Posted by Bill Berson View Post
    Yes, the warnings about TIG penetration are in AC-43.13.
    The perfect fit up isn't needed or desired either.
    A gap that allows correct penetration is recommended.
    The other side of this is that gaps leave an exposed edge which the welder may try to protect by using less than sufficient heat. The weld gets wider because there's a gap to bridge but the penetration is not improved, it only looks that way because of the filler coming through the gap on the back side of the mating tube. The penetration on the 'main' tube (for example the longeron) is not enhanced in any way due to the gap being filled. The only way to get good penetration on both parts is to use the proper amount of current and good technique. Machine setup, tungsten grind, etc all play a role as well. Simply providing a gap does not insure a good result but can and usually does create more distortion in the finished weldment. There are no shortcuts to good welds and tight fits do not cause poor welds.

    I agree that the bushing used in this mount is too thick walled and that extra metal serves no purpose. Getting enough heat into that bushing while dealing with a poor fit would be quite difficult.

  9. #19
    Aaron Novak's Avatar
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    Quote Originally Posted by cwilliamrose View Post
    The other side of this is that gaps leave an exposed edge which the welder may try to protect by using less than sufficient heat. The weld gets wider because there's a gap to bridge but the penetration is not improved, it only looks that way because of the filler coming through the gap on the back side of the mating tube. The penetration on the 'main' tube (for example the longeron) is not enhanced in any way due to the gap being filled. The only way to get good penetration on both parts is to use the proper amount of current and good technique. Machine setup, tungsten grind, etc all play a role as well. Simply providing a gap does not insure a good result but can and usually does create more distortion in the finished weldment. There are no shortcuts to good welds and tight fits do not cause poor welds.

    I agree that the bushing used in this mount is too thick walled and that extra metal serves no purpose. Getting enough heat into that bushing while dealing with a poor fit would be quite difficult.
    Part of the purpose of the gap on butt type welds is to provide some gas coverage into the joint itself. It also allows the arc to reach between the two parts, something it cannot do when fitted up tightly. If gas welding the gap allows the heat to travel between the two parts. AWS D17.1 specifies the gap to use, FAA as well. Industry uses gapping. While it itself is not the root cause of this particular issue, it is by far the best practice.

  10. #20
    cwilliamrose's Avatar
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    I don't have access to AWS documents. I quick look at 43.13 did not lead me to anything describing gaps in anything other than sleeved repairs. I will say the thought of the arc going into the gap between parts or the argon flowing into the cluster, displacing the air and shielding the back side of weld seems unlikely at best.

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