welding 4130

[dedgemon]

Hmm, well I'm just barely removing scale and paint (the tubing has some cheap paint on it for color code). I would think that removing 7 thou of 4130 would take quiet a while. I guess I'll have to try it on a piece of scrap and mic it. :-)

For what its worth the "50 grit" doesn't really seem to equate to 50 grit in the sandpaper world. That would have pebbles in it.

[sjt]

All three colors are available from the local auto part store "A-Line Auto Parts".

They are a great help with 4130 and welding.

[dedgemon]

Since Paul commented on how much material the green bristle discs might be removing I thought I would sanity check it. When I clean off an area of the tubing prior to welding, the goal is to just knock off the scale, paint, whatever until we see bright shiny metal. I cleaned up a tube and put a caliper on it. I can't even measure a difference from the uncleaned side to the cleaned side. I think we're good !

[alaskabearhawk]

All I said was to be careful. Depending on how it is used it does remove material quickly.

I did check with 3M about the designation of 50 Grit on the green wheel and here's the exchange:

Don V: Thank you for contacting 3M where we apply science to life. Can I start by asking for your full name, company name (if applicable) and your zip code?

Paul: Paul xxxxxxxxxxxxxxxxxx

Don V: Hello Paul, how can I assist you?

Paul: Scotch-Briteâ„¢ Rolocâ„¢ Bristle Disc, 2 inch, 50 grit, 07524

Paul: It says "50 Grit", on other literature it says "50 grade".

Paul: How is that number determined? It certainly doesn't have the same grit, or coarseness, as 50 grit sandpaper.

Don V: Grit and grade would be considered the same. Some industry call it grade, some call it grit. The number is determine by how deep the scratches are left after using the wheel.

Paul: So how does that equate to other products? I use the green Roloc, but on the 2x72 belt grinder when rough fabricating parts I have a 60 grit belt. The green disc is in no way as aggressive as the 60 grit belt.

Don V: Paul, the two have very different blends of mineral, The green belts generally will have a mixture of aluminum oxide blend with ceramic which will cause it to cut faster and more aggressive. Bristle disc are designed to cut similar to a coated abrasive without doing much damage to substrates. Generally used for removing coatings or deburring.

Paul: It just seems odd to use the same number value to describe the different products.

Paul: You would think the grit designation would be a constant, not a variable in relation to each application.

Don V: Correct, there is also lots of variables such as speed, pressure, tool design, backing material, etc that plays a big role on how abrasives are supposed to cut and what they are designed to do, example the bristle disc generally designed for removing coatings, deburring, blending, it removes the coatings at a rate a 50 grit would but does minimal damage to surface you are working on.

Paul: Sounds good. thanks...

[Chris In Milwaukee]

Don V: Thank you for contacting 3M where we apply science to life. Can I start by asking for your full name, company name (if applicable) and your zip code?

That was quite an interesting exchange. One might actually say impressive :-)

[dedgemon]

careful we are 😊

funny conversation. The type that drives engineers nuts. Sounds like you found a good guy there though.

[nichzimmerman]

More generic welding questions:

1) When a welded joint isn't air tight, do you re-weld it? I recently put polyfiber's tubeseal in my tail post and when I walked in the next morning, there was a puddle of oil on the ground and the tail wheel attach bracket was soaked with oil. By the time that area is welded, it's quite a hunk of steel and my poor little torch (Meco w/ #4 long tip) apparently didn't get the job done...or maybe it was the operator. Re-welding this area would probably require a bigger torch/tip than I own.

2) Is there a secret to obtaining air tight welds other than good penetration and uniformity?

[Bdflies]

I think the short and dirty answer here, is; "Yes, reweld it." Can you see the spot that's not sealed? Did you simply miss an area, or is there an area of cold-lap? I'd say a missed area isn't too bad, but cold-lapping (weld metal laying in the joint, but not properly fused into a homogeneous structure) is quite bad. Find the problem, thoroughly degrease it, grind out the old weld and do it over. There's a lot going on, at the tailpost, that creates a big heat sink. This is where the TIG process shines. The downside, can be access with the TIG 'torch'. You might have to borrow a bigger torch, if you're limited to oxy/acet welding.
This whole building process is an adventure! Sometimes you have to assess something you've done and re-do it. I've got a stack of scrap aluminum to prove it.... As to the "secret", the secret is that you'll be a much better welder when you're finished than when you started.

Bill

[mike 427]

I turned a piece of 4130 bar to size to fit inside the tube about 1/2 inch with 1/2 inch out for threads.then drilled and taped it to desired thread an welded it in place with a small tack weld 1/4 inch back from main weld onto piece inside. On the weld question .sounds like you flame is to short and your holding it to close,that causes popping.

[Glenn Patterson]

The only way that I know of to get an air tight weld is to drill a tiny vent hole so the gases do not build pressure in the tube to pop the last of the weld then fill the small hole. I have managed a lot of high pressure pipe installations & repairs where the welders regularly use a wire wheel to remove mill scale or the slag after a pass then lay the next pass. The welds are xrayed and there are no issues from the wire wheels showing up in the weld. Welds pass with the odd little speck here & there as long as they are within a size and count on the xray to pass the inspection code for the service. A couple of tiny minute specks here and there will not compromise properly laid down welds on a cluster as the welds will far and away exceed the strength required for the joint.