Thread: Filling holes in metal, what techniques are available?

Hi,

I'm currently working on an object (a helmet) formed from sheet metal (ordinary mild steel) about 1.5mm thick. It has a few drilled holes in it which I want to fill. I was wondering what the best techniques were? I've had some ideas.

1)a)Is it possible to do a quick spot weld into the hole in some way to bung it up?

1)b)If this is possible can a reasonable home-made job be done using say a blow-torch and oxy-acetylene welding rod or is that too dangerous/won't get hot enough?

2)Is it practical to use car body soldering techniques to do simple repairs on deep scratches (too deep to polish) and could body soldering be used to fill holes in some way?

If it helps I'll post a picture of the job up if anyone thinks that might help? Thanks.

Chris330
Is the helmet going to be painted? The reason I ask is because the answer will have a bearing on how to fill the holes. ie if no, then what ever you use to fill the holes will need to be a similar colour to the parent metal.
How big in dia are the holes?
If they are only small, yes an oxy welding set up could be used, BUT if you are not skilled in the use of one, I would recommend that you get someone who is to do the job. It would be quite easy to end up with more damage to the helmet than what you started with. 1.5mm thick is quite thin when you start putting heat from an oxy on it.
Finding someone with a Tig or even a Mig welder would be a far better option than an oxy. Granted, someone skilled in welding thin materials with oxy would have no problem, but its a skill you lose rapidly if you don't do it regularly.
A good place to look for help would be a car body repair shop that does old car restorations. If the holes are small and few , I don't think it would cost very much to get them repaired. You might even be able to pay with beer.
If you decide to go this way if you make a backing plate from a NON ferrous metal like copper, brass or aluminium it will take less time for the welder to do the job.
The idea is you get a lump of metal that is at least 6mm thick, (the thicker the better) that is a fair bit larger than the hole. clamp it securely to the back of the job so it is under the hole. has hard against the job as possible. you want the minimum gap between the edge of the hole and the backing metal. The welder can then fill the hole using the Tig or Mig by welding from the edge out onto the backing plate. once the weld has cooled, remove the backing plate. being non ferrous the weld metal won't stick to it.
Have a talk to the welder and ask what they want.

Hope this helps

bollie7

Hi Chris
You raise more questions than answers.
What diameters are the holes?...this makes a difference!
Are you looking for a polished metal finish? Natural mild steel look? or a painted one?

So looking at your suggestions:
Think about how car panel repairs are/were done.

Big holes are harder to fill and probably need a patch ...welded in flush.
Small holes are OK and medium ones are best worked from the outside edge toward the centre.

Spot weld. It is possible to spot or Plug weld small holes. MIG is probably best.
If you uses a Stick welder it can be done but often ends in a bigger hole. The rod would have to be absolutely vertical and jabbed/puddled over the hole. I have done this successfully but it sometimes blows out.
Perhaps others may be able to help with technique.

Blowtorch and Oxy rod: Do you mean Liq. Propane gas torch( LPG) or Oxy/Acet.?
LPG wont melt/fuse mild steel wire..the rest of the metal helmet acts as a heat sink.
You need concentrated spot heat sufficient to melt/fuse both the puddle of parent metal and the mild steel filler rod. Therefore Oxy/ Acetl. is the go.
The result can be metal distortion requiring plainishing and re shaping. you would also need to grind away excess filler metal.

Soldering: Low temperature lead solder can be used. LPG may provide enough heat. Car panel beaters used lead-wiping to fill/level repairs before the advent of plastic fillers.
Depending on the hole size you may need a temporary backing plate to stop the lead falling through until it sets. So use Stainless or Alu. or some metal which is incompatible with solder ..so that it does not stick.
Lead wiping could also be OK to fill scratches but is is still a different colour to the base metal of the helmet. ( if it is being painted ...does not matter) Acids can further dull the shiny lead finish.

Hard Soldering/ Brazing: It is also possible to fill with Brass rod, Silver solder ( alloy), or other hard solder rods. Again needs Oxy/ Acetl. for best results. Same problems re heat distortion and may need temporary backing plate. Also much different colour than base metal. Not so good for filling scratches.

Another option is to use an Epoxy ( full of metal filings) so that you get a dull metal effect. These "plastic metals" are often available at Bearing suppliers.

I strongly suggest you find a scrap of similar thickness mild steel and PRACTISE practise, practise. (yes, the Verb ..Practise, has an S instead of a C )


PS sorry I did not read your previous post re a polished finish. So please ignore the useless bits of info

Hope this helps
Cheers
Bob

Hi Chris,
I will have another go at your problem.
Sorry about the useless options but did not read your previous post about wanting a polished finish.
Bollie also slipped in an answer whist I was typing mine. We both say the same thing about a backing plate when fill welding.
Also from an antique value scratches may be a positive factor.

Here is another solution but it may be harder to source.

For the holes I would fill with weld as described using the same mild steel. The repair will polish out and basically disappear.

For deep scratches there is this obscure option.
I have an attachment which fits to an oxy/acetl handpiece/torch.
It is basically a small gravity hopper fitted at the mixer between the handpiece and the tip. When triggered it feeds very fine (mild steel) powder/dust into the gas stream. This hits the flame at the tip and becomes molten. You are therefore spraying molten metal onto a redhot surface where it binds with the base metal. The end result looks like sandpaper but can be polished out to a smooth finish of the same base metal.

I use it for spraying hard-facing onto tools or building up worn keyways, oval holes in castings etc etc.
It does require a large tip and a fair bit of heat ( read distortion?)
Works better on heavier castings than sheet metal.

These were available in Australia and made by CIG (Commonwealth Industrial Gases..now taken over by BOC ...a British company??). I reckon an engineering firm in the UK may know of similar BUT most places would not have this.
Maybe a google search on "metal spraying" might bring up a firm that does this type work? Very much an industrial environment.
They will have the knowledge/skill...Try and talk to a superviser/manager and set them a challenge.
I have mine because I have done restoration work on vintage sports cars etc where parts are unobtainable and need to be rebuilt or recast.

I would be careful about overheating the helmet.

good luck
Bob

Wow they really are the best and most detailled replies I could have ever hoped for thanks alot that's great! I printed off the replies from both of you and read through them closely and I've come back with the following observations.

1)The helmet will not be painted and as such anyhting that will not remain in relief with the existing finish's appearance is a no go.

2)The holes are no bigger than 6mm in diameter.

3)I will as recommended avoid oxy welding due to the potential damage to the helmet as it is quite thin. I can remember doing a welding course at uni and the oxy-a gas went through the metal frighteningly easily.

4)I need a non-ferrous backing plate to make a seat for the spot weld.

5)I need a typical mild steel weld repair which I can polish out to near perfect relief. I suppose I could get minor scratches repaired this way too if I was prepared to put in the filing and then sanding work afterwards (I am )

6)I've decided against chasing the spray metal option even though it is very appealling in it's unusual-ness!

Thanks very much for clearing all this stuff up for me it's been much needed. I do know someone who can spot weld some repairs for me so that should be that sorted.

I have two remaining questionswhich I'm sure you guys can help me with!:

1)Is there a specific 'grade' of file I would need to use to get the welded repairs down to before the P80 grit sandpaper takes over? I've rubbed out alot of imperfections on the helmet already with P80 and it does a good job but it would never cope with some of the deeper filing scores my regular files make. What 'grade' (is there such a thing?) of file should I take the repair down with just before handing over to the P80 grit to make sure the P80 can get the file scores out?

2)There will be in the fairly near future the need to do some filling in a brass part. The filling will be used to fill in the gap between two brass plates which are clamped together leaving a gap probably a mere half millimeter wide. Can I use a LPG torch to solder some brass into it or will this method bugger the finish of the surrounding brass and/or suffer the same temperature issues mentioned above with regards to oxy-a welding?

I'll post some pics of the job up over the weekend and then periodically as it improves so you can share in the pleasure of the job as it comes on

Another way to fill the holes , make sure they are round , buy a 6 mm (or what ever size) bolt and cut with a hacksaw flat shims from it a little thicker than the plate thickness and solder these in the holes

Probably a Mill cut File.

Originally Posted by Ashore

Another way to fill the holes , make sure they are round , buy a 6 mm (or what ever size) bolt and cut with a hacksaw flat shims from it a little thicker than the plate thickness and solder these in the holes

Lol that's a brilliant idea!! Many thanks mate

I'll also ask about a Mill Cut file thanks pipeclay.

Hi Chris
The Internet is your friend. Do a search on Hand Files and look at Wikipedia or an Engineere suppliers site. You will see reference to the range of metal files and their Gradings from coarse to fine.
Forget the coarse, Bastard cut etc... too savage.
Second Cut is still fairly coarse whereas smooth, mill cut are at the finer end.

Best visit an enginering supplier or big hardware store and "feel" the blades.
Remember a new sharp file (even a fine one) will cut well and this cut can be varied by the mount of grunt you apply. Light sweeping strokes to finish.
You have the advantage of time.. so steady it goes.

When using ( sanding) paper ..glue it to wooden strips to make hand files.
Files pick up the high spots whereras rubbing with paper by hand can also abrade the area surrounding the bit you wish to file..still leaving a high spot.
Also paint the area wth a dark felt tip pen. You will soon see where the cutting occurs as it brightens up.

(SorryI did not get back earlier but I have been working a couple of 18 hour days to help an architect get some fabrication details right ..prior to an "opening" of a new venue last night)

Cheers Bob

Another way to fill the holes , make sure they are round , buy a 6 mm (or what ever size) bolt and cut with a hacksaw flat shims from it a little thicker than the plate thickness and solder these in the holes

A simple cheap and effective technique!
Mark another one up for the old fellas!

Originally Posted by Knotaclue

Hi Chris
The Internet is your friend. Do a search on Hand Files and look at Wikipedia or an Engineere suppliers site. You will see reference to the range of metal files and their Gradings from coarse to fine.
Forget the coarse, Bastard cut etc... too savage.
Second Cut is still fairly coarse whereas smooth, mill cut are at the finer end.

Best visit an enginering supplier or big hardware store and "feel" the blades.
Remember a new sharp file (even a fine one) will cut well and this cut can be varied by the mount of grunt you apply. Light sweeping strokes to finish.
You have the advantage of time.. so steady it goes.

When using ( sanding) paper ..glue it to wooden strips to make hand files.
Files pick up the high spots whereras rubbing with paper by hand can also abrade the area surrounding the bit you wish to file..still leaving a high spot.
Also paint the area wth a dark felt tip pen. You will soon see where the cutting occurs as it brightens up.

(SorryI did not get back earlier but I have been working a couple of 18 hour days to help an architect get some fabrication details right ..prior to an "opening" of a new venue last night)

Cheers Bob

Back when I was an apprentice it was drummed into us that a new file had to be "broken in" by first using it on brass, copper or aluminium. Apparently this makes the file less likely to break the tips of the teeth off when using it on steel later. If this still applies I have no idea. You would hope that the advancements in materials technology over the last 34 years would have made it down to the humble file but, still, might not hurt to file a bit of brass with a new file first.
Another thing, if you start filing the high spots on your helmet. When you buy any files buy a "file card" and use it to keep the file clean. (file card is a special wire brush for cleaning files, not sure what it would be called in the UK) When the teeth on the file get clogged up with metal (called pining) the metal can scratch the filed surface pretty bad. ( the size, depth and length of the scratch increases in a direct proportion to how close you are to the final finish)
hope this helps
bollie7

That's great! Thanks Bob and bollie for some top info, I reckon I've got what I need thanks to this thread now to do a really good job of this that's very helpful

I've took some pics too I'll post them up as soon as I can work out how to!