Milling Welds

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Nick Hacking

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H-M Supporter Gold Member
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Jan 22, 2017
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Dear All,

I have a project which involves moving a small hole in a piece of steel. The part is fairly easy to work so I assume that it's mild steel.

I thought that the best way of tackling this would be to fill up the hole and then mill a new one in the desired position. I dug out my MIG and plugged the hole with weld until the weld was proud of the original surface. After some time to cool (no quenching or anything like that went on) I popped it in the machine vice on my mill and set about it with an HSS endmill. The cutter seems to be having a very hard time removing material - even with light cuts. Unless I keep the tool drenched in coolant, it starts to glow at the end, which I think is A Bad Thing.


Previously I've always attacked welds with an angle grinder: I've never tried to machine a weld before today. Do they tend to be very hard? Should I be using a carbide cutter?

Sorry if this is an idiot newbie question, but I rather hoped that this is what the forum is for!

Kind wishes,

Nick
 
If the part is not likely to warp you could post heat it to draw some temper out and soften it some
That being said carbide is your friend when milling weldments ..........
 
The first question you must ask is, is the part worth repairing at this point. If 8 hours of labor have already been spent making it then fixing it may be worth it. If the off position holes were drilled during the first operation it may be less costly to start again.

I welded closed eight 10-24 tapped holes in a part several weeks ago after the last person to work on it broke a tap in one hole, each one of these parts had 22 man hours labor up to that point, it was worth doing so and the positions were not critical to its function.

The first mistake is the least expensive mistake, if you work in a job shop the last person to work on a part has the most pressure not to bugger it up.

You're IT
 
Rumbled!

I didn't post all of the details because I didn't think they'd matter. Until you made me realize that they probably did.

More complete story: I have a new TIG which does AC and has a pulsed mode and can iron shirts and make coffee. Well, perhaps that's a slight exaggeration, but it has loads of settings. I blame This Old Tony on You Tube: he made me buy it. Well, I haven't had much of a chance to try it out, so I thought I'd fire it up and put it through its paces. Much touching of tungsten to the outer wall of the hole occurred and, after filling my lungs with ground up thorium and tungsten one time too many I got fed up and switched over to the old MIG.

Do you think that's the issue?

I'll see if I can buy a small carbide cutter on eBay. I have a few big carbide cutters - but they will not fit into the space that I need to machine: it's a lathe carriage and it has side-walls.

Kind wishes,

Nick
 
Sorry, that was a reply to BtoVin83.

Thanks, P. Waller: I think it is worth saving. It's a carriage (or do I mean top slide?) from an old Myford 7 lathe that I bought on eBay to fit to a modified Myford/Drummond lathe and I need the bolt for the tool post to be in a slightly different position.

I've bunged up the hole with weld quite successfully: now I simply need to machine it to be flat and level with the surfaces, then make a new hole for the new toolpost bolt.

Kind wishes,

Nick
 
Hi Nick,

Did you make the weld well proud, let it cool and then grind almost flat. That should have got rid of the hard skin. If not you will have to anneal the slide and risk having to repair the distortion, though it has probably distorted already from the welding.

The right way to have done that job would have been to make a press fit plug, possibly with a smear of locktite as a lubricant and fixative, then machine as needed.
 
BaronJ said:
Hi Nick,

Did you make the weld well proud, let it cool and then grind almost flat. That should have got rid of the hard skin. If not you will have to anneal the slide and risk having to repair the distortion, though it has probably distorted already from the welding.

The right way to have done that job would have been to make a press fit plug, possibly with a smear of locktite as a lubricant and fixative, then machine as needed.
Click to expand...

Thanks,

The gap between the sides isn't small enough to admit my angle grinder, so I went straight from welding to milling. The surface of the weld pool has now lost the top layer of scale - it was argon shielded, so there wasn't much scale at all to start with - but the cutter has managed to take some material off. It took forever, the tip got very hot, and the cuts are not getting any easier.

When my time machine comes back from the menders I will, of course, fill the hole with a plug and fix it with locktite. Here and now, I'm stuck with a lump of weld that needs to be made flat and smooth :)

I'm coming to the conclusion that only a carbide cutter can save me.

Kind wishes,

Nick
 
Hi Nick,

You have already said that you have tried a cutter. Just replace it with a grinding stone, the type that have a shaft that you can put into a chuck.
 
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