[Fred Rezfield]

hey i was wondering
is it gonna show after you machine a WELDED hole? a filled up hole?say 1/2" hole that was filled about 1/2" ??
and which weld is best? TIG?stick? MIG?

[tweake]

done properly i doubt it will show.
jump on Instagram and check out "tig happens" he just put up a pic recently of one of his engine head repairs that was fully machined. you can't see where the repair is.

personal preference for me is tig, mig then stick.

[cj737]

It depends entirely upon the base material and filler material. If you are welding cast iron and filling the hole with nickel rods, yes, it will show. If you are filling a cast aluminum hole with 4xxx series filler, yes, it will likely show.

I’m with Tweake, generally I’d prefer to TIG fill a hole. All depends upon size of hole, depth, access, etc.

[Fred Rezfield]

ok excellent and how would you do it?
have a piece inside the hole first then weld? or just fill up with rod?

[BugHunter]

How structurally sound does this need to be? For a 1/2" hole I'd probably make a plug in the lathe that would have nice big tapers on the ends so I could get full penetration from one side, then hit it again from the other side. It is going to show if you know what to look for. If you can't make a plug, just back it up with a sheet of clean copper and start filling. Flip and do the other side to finish it off. If'll have some issues still on the back side if you don't flip it and fill in the very edges, since they'll almost certainly not knit in. If they do, you probably got it too hot.

[tweake]

ok excellent and how would you do it?
have a piece inside the hole first then weld? or just fill up with rod?

i don't think i've done a straight hole, most of mine is usually cracks or broken bits.

the catch with aluminium is you need to get the arc in there to clean. if it doesn't clean then you can get porosity. also with tig you need space to be able to get rod in.
so you would generally grind out the hole. this is also why you would not fit a plug in the hole.
the other option is to use mig. however i don't know if you can weld over the soot ok or if it would need a scrub on every pass. also its not a case of just aim down the centre and fill. you need the arc to work the sides so it gets cleaned by the arc.

[Fred Rezfield]

it's a blind hole
what do you mean "get the arc in the hole to clean"?

how about melting the rod? the welding rod....
or maybe some special rods for brazing

[tweake]

it's a blind hole
what do you mean "get the arc in the hole to clean"?

how about melting the rod? the welding rod....
or maybe some special rods for brazing

as you know the you need the cleaning action of the arc to break up the oxide layer. but that only works on areas it reaches.
with a crack the arc doesn't always go down the crack and clean the sides of the crack. that can leave oxide in there and cause the repair to crack later on. hence grind it out before welding.
a hole can be similar, just need to make sure you get the etching zone around the sides as you fill.
depending on size you may need to open up the hole so you can get in there.

if you just pour molten aluminium down the hole you end up with oxide layer trapped in there, which might show up when machined and also can cause cracking depending on what its used for etc.

the special aluminium brazing rods are zinc based (afaik). not really meant for filling holes, especially anything that will be machined.

[cj737]

If it’s a blind hole, do as Bugs suggested and machine a plug and insert it. Leave it short of the overall height, and weld the top closed and covered. Machine back flush. There may be a slight variation in the color of the material, but in time the oxide layers should blend them together.

I have even gone so far as to thread the hole and the plug, used Green LocTite and then machined flush. It all depends on the application, part, repair, etc. Why don’t you provide some greater details and pictures so you can get the best answer the first time instead of us speculating and flinging spaghetti on the wall…

[tweake]

If it’s a blind hole, do as Bugs suggested and machine a plug and insert it. Leave it short of the overall height, and weld the top closed and covered. Machine back flush. There may be a slight variation in the color of the material, but in time the oxide layers should blend them together.

I have even gone so far as to thread the hole and the plug, used Green LocTite and then machined flush. It all depends on the application, part, repair, etc. Why don’t you provide some greater details and pictures so you can get the best answer the first time instead of us speculating and flinging spaghetti on the wall…

it depends a lot on the application.
for shallow holes the time to machine a plug, heat/shrink fit it and weld closed, is more than just drilling it out with a countersunk bit and welding it back up.
plus blind plugs are a weak point in critical work or in things that get very hot.
however for deep holes where welding is not suitable, plug or thread is the way to go.

[BugHunter]

it depends a lot on the application.
for shallow holes the time to machine a plug, heat/shrink fit it and weld closed, is more than just drilling it out with a countersunk bit and welding it back up.
plus blind plugs are a weak point in critical work or in things that get very hot.
however for deep holes where welding is not suitable, plug or thread is the way to go.

I wasn't talking about making some precise plug if that's what you mean. I'm just talking about taking a length of aluminum 1/2" bar and angling a roughing tool, bevel the end and clean it up, clean off the outside surface, and cut it off. Put back in the lathe and bevel the other side with the same roughing tool. Done. Probably would take all of 90 seconds to make it. throw it in the hole with a copper backer plate and weld away. It'll easily get full penetration if you don't make it tight to the parent part, or if it is sorta tight, make sure the bevels are deeper so there's very little "root" to dig into. If that makes sense.

I also assumed this wasn't some part of a safety harness for a tower climber or anything. I figured more on the lines of stopping a water leak or some such.

[tweake]

it depends a lot on the application.
for shallow holes the time to machine a plug, heat/shrink fit it and weld closed, is more than just drilling it out with a countersunk bit and welding it back up.
plus blind plugs are a weak point in critical work or in things that get very hot.
however for deep holes where welding is not suitable, plug or thread is the way to go.

I wasn't talking about making some precise plug if that's what you mean. I'm just talking about taking a length of aluminum 1/2" bar and angling a roughing tool, bevel the end and clean it up, clean off the outside surface, and cut it off. Put back in the lathe and bevel the other side with the same roughing tool. Done. Probably would take all of 90 seconds to make it. throw it in the hole with a copper backer plate and weld away. It'll easily get full penetration if you don't make it tight to the parent part, or if it is sorta tight, make sure the bevels are deeper so there's very little "root" to dig into. If that makes sense.

I also assumed this wasn't some part of a safety harness for a tower climber or anything. I figured more on the lines of stopping a water leak or some such.

it makes sense on big holes to fill with material first. small ones not so much.
its probably quicker to drill the hole out and weld it all back up before you can even find suitable sized stock to fit in the hole.

if its a long hole your never going to get weld all the way in, and non critical application, then loosely plug it and weld the ends. more critical application needs tight fit or threaded.

[BugHunter]

If I'm looking to anneal as little as possible, then I plug it to try to hold the heat down as much as I can. Anything that goes above about 800F is going to soften up so if I can keep that area smaller, I generally do it. But I agree, it really depends on how critical the repair is as to how you want to go about it. 1/2" dia x 1/2" depth, yea, probably just grab some rod and stuff it in there. It just happens I have 1/2" alum rod sitting out handy all the time.

[Fred Rezfield]

it will always show
i tried this a few times even if there is no contamination it will show.

[sbaker56]

Tig for sure, and it shouldn't show if properly welded with the right filler, depending on the aluminum alloy you happen to be welding, 5356 could be a better choice as it won't discolor/oxidize as weirdly as 4043 can but it depends on the alloy. If it'll be anodized or exposed to anything remotely alkaline 4043 is definitely not suitable. If you've ever done a cut and etch on aluminum, 4043 leaves a dark grey almost black weld nugget in comparison to the base metal, while 5356 takes a better polish and a longer etching time to be easily distinguishable as 5356 doesn't discolor in the same way.