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Thread: Chrome Moly 4130 Motor Mounts - Prefab Parts?

  1. #21
    Aaron Novak's Avatar
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    Well, unfortunately it is all copyrighted otherwise I would scan and post the documents here. The gap does indeed help quite a lot in forming 100% penetration weldments, although it does make welding seem more difficult for the novice, which is what I believe welding machine companies push it.

  2. #22
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    I sure wish I understood this gap = better penetration thing. The tube that's most difficult to get penetration on is the one that continues through the cluster and the gap does nothing for that one as far as I can tell. Brimm and Boggess says to use a 1/32" to 1/16" gap "depending on tube size" for expansion which doesn't ring true -- welding causes things to shrink, not expand. Of course that was written when gas welding was the most common method but still......

    I'll continue doing what I've been doing for the last 40 years until I understand how an on purpose gap helps the integrity of the joint.

  3. #23

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    It isn't about tube size, but rather the gap is dependent on thickness. Or if it can be welded on both sides or if only one side is accessible. Gap is an alternative to v grinding for full penatration in one pass. For example two 1/16" plates edge welded should probably have a 1/16" gap. Two 1/8" plates about 1/8"gap or if thicker use a V grind.
    Don't normally need a gap for very thin tubing.
    These are just my general comments. Every weld is different.

  4. #24
    Aaron Novak's Avatar
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    Quote Originally Posted by cwilliamrose View Post
    I sure wish I understood this gap = better penetration thing. The tube that's most difficult to get penetration on is the one that continues through the cluster and the gap does nothing for that one as far as I can tell. Brimm and Boggess says to use a 1/32" to 1/16" gap "depending on tube size" for expansion which doesn't ring true -- welding causes things to shrink, not expand. Of course that was written when gas welding was the most common method but still......

    I'll continue doing what I've been doing for the last 40 years until I understand how an on purpose gap helps the integrity of the joint.
    It was never for expansion, but actually it does help with contraction and "locked up" stresses. Although many times to the confusion of others, authors of welding texts will interchange the two. So tell me, when you are welding a cluster, are you doing keyhole welding?

  5. #25
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    I guess not since I had never heard that term before. I looked it up and I still don't know how that type of weld is accomplished. One source says "USING A STIFF. CONSTRICTED ARC" whatever that means.......

  6. #26
    Aaron Novak's Avatar
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    Quote Originally Posted by cwilliamrose View Post
    I guess not since I had never heard that term before. I looked it up and I still don't know how that type of weld is accomplished. One source says "USING A STIFF. CONSTRICTED ARC" whatever that means.......
    Keyhole welding is you are using enough heat to cause the edges of the material to melt, pull back, and recombine on the back side of the weld pool. If you were to stop welding it would would like a keyhole sort of. When doing tubing work as in a cluster, the edge of the tube should pull up about 1-2x metal thickness and form a half keyhole. Otherwise think of it and simultaneously making and filling a hole, or half hole as you weld. 95% of the failed welds I cut apart look pretty, but are in fact just fillets sitting on top of the tube. Oh as a stuff constricted arc is formed by ( in the tig world ) a fairly blunt tungsten grind, high amperage and moving quickly.
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  7. #27
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    Interesting. I use a pretty pointed grind, more like a regular sharpened pencil than a golf pencil. I don't weld fast when doing clusters for several reasons mostly having to do with having to start and stop a lot to change positions. I don't weld super fast when access is more open either. I see guys on YouTube really moving fast but that's not something I'd be successful with, even when I was younger and could see the puddle better.

    I wonder what a cluster weld would look like when you stop like the image in post 26? There's generally only one edge and with my normal fits there's little if any gap. I should play with that and see what I learn.
    Last edited by cwilliamrose; 09-23-2018 at 03:48 PM.

  8. #28
    Aaron Novak's Avatar
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    Quote Originally Posted by cwilliamrose View Post
    Interesting. I use a pretty pointed grind, more like a regular sharpened pencil than a golf pencil. I don't weld fast when doing clusters for several reasons mostly having to do with having to start and stop a lot to change positions. I don't weld super fast when access is more open either. I see guys on YouTube really moving fast but that's not something I'd be successful with, even when I was younger and could see the puddle better.

    I wonder what a cluster weld would look like when you stop like the image in post 26? There's generally only one edge and with my normal fits there's little if any gap. I should play with that and see what I learn.

    Oh I know what you mean! One of the disadvantages of tig on 4130 is that every stop/start usually has some areas of the HAZ that are really hard, yet when welding a cluster man its difficult to keep moving. I know before I do something critical I will weld up a bunch of samples, section, polish and etch them to check for penetration etc. Even after all these years I still like to double check myself and improve with every project. We all have room to improve

  9. #29

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    Hi: I am an aircraft mechanic and certified Non Destructive Testing Specialist (x-ray weld Inspector) with 40 years of experience. I don't usually comment on forums like this, unless I see a problem that is personal safety related. In the case outlined here 'welding an aircraft engine mount' - unless you are a certified AIRCRAFT welding specialist (either AWS or CWB), you should not be welding any LIFE CRITICAL components. You could be risking not only your life, but any passengers, or innocent bystanders on the ground, when you fall out of the sky. If you intend to continue with this folly, at least go out and buy the best Ballistic Recovery Parachute you can find, plus no passengers and no flying over populated areas.

    Every certified aircraft engine mount was designed by an aeronautical engineer, a welding engineer, as well as a level 3 welding inspector. Each has a specific area of expertise. It starts with the computer design and testing of the mount and they will use stress analysis to make sure there are no weak spots in their design. Then a welding jig will be designed and built by the welding engineer and level 3 weld inspector, as well as the weld procedures, which a certified aircraft welder will follow to the letter. The procedure outlines the specific filler rod, the amperage settings, the speed and angle of the welding process etc etc etc. It follows with dozens of trial and error tests to make sure the welds will hold in the most impossible situations you can imagine. All this preparation before they even begin to weld the mount.

    Welding is never as easy as it looks, especially on LIFE CRITICAL components. My recommendation - find a certified aircraft welder, who has extensive hands-on experience with this exact type of welding, as well as an approved weld procedure and welding jig. It does not matter how much it costs, if the end result is you do not kill yourself or others. OR the BRS is your last resort. I worked for two years in a helicopter search & rescue squadron - I carried more than my fair share of body bags.

  10. #30
    Sam Buchanan's Avatar
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    Quote Originally Posted by nixrox View Post
    Hi: I am an aircraft mechanic and certified Non Destructive Testing Specialist (x-ray weld Inspector) with 40 years of experience. I don't usually comment on forums like this, unless I see a problem that is personal safety related. In the case outlined here 'welding an aircraft engine mount' - unless you are a certified AIRCRAFT welding specialist (either AWS or CWB), you should not be welding any LIFE CRITICAL components. You could be risking not only your life, but any passengers, or innocent bystanders on the ground, when you fall out of the sky. If you intend to continue with this folly, at least go out and buy the best Ballistic Recovery Parachute you can find, plus no passengers and no flying over populated areas.

    Every certified aircraft engine mount was designed by an aeronautical engineer, a welding engineer, as well as a level 3 welding inspector. Each has a specific area of expertise. It starts with the computer design and testing of the mount and they will use stress analysis to make sure there are no weak spots in their design. Then a welding jig will be designed and built by the welding engineer and level 3 weld inspector, as well as the weld procedures, which a certified aircraft welder will follow to the letter. The procedure outlines the specific filler rod, the amperage settings, the speed and angle of the welding process etc etc etc. It follows with dozens of trial and error tests to make sure the welds will hold in the most impossible situations you can imagine. All this preparation before they even begin to weld the mount.

    Welding is never as easy as it looks, especially on LIFE CRITICAL components. My recommendation - find a certified aircraft welder, who has extensive hands-on experience with this exact type of welding, as well as an approved weld procedure and welding jig. It does not matter how much it costs, if the end result is you do not kill yourself or others. OR the BRS is your last resort. I worked for two years in a helicopter search & rescue squadron - I carried more than my fair share of body bags.
    Thousands of welded experimental aircraft have been flown that were not built by certified aircraft welding specialists.......

    I consider every weld on my aircraft to be life critical.
    Last edited by Sam Buchanan; 10-09-2018 at 08:13 AM.
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