# Milling Welds



## Nick Hacking (Aug 25, 2018)

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


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## BtoVin83 (Aug 25, 2018)

Did you touch the electrode to the puddle?


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## Norseman C.B. (Aug 25, 2018)

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 ..........


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## BtoVin83 (Aug 25, 2018)

oops sorry, mind old tired mind read MIG and thought TIG. Nevermind


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## P. Waller (Aug 25, 2018)

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


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## Nick Hacking (Aug 25, 2018)

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


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## Nick Hacking (Aug 25, 2018)

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


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## BaronJ (Aug 25, 2018)

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.


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## Nick Hacking (Aug 25, 2018)

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.



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


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## BaronJ (Aug 25, 2018)

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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## markba633csi (Aug 25, 2018)

Seems like a job for Mr. Dremel tool (and his friend, Mr. Abrasive point)
mark


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## BaronJ (Aug 25, 2018)

Hello Mark,

I suspect that he might need something a bit heavier than a Dremel.  I was envisioning something like a 30 mm X 12 shaft mounted stone.  Since he has got it in the mill vise, it should be an easy job.  If he can get a flat surface he might be lucky and it is not as hard under the skin.


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## Winegrower (Aug 25, 2018)

I think the weld likely quenches rapidly and forms martensitic hardness material.   You have to heat this way up and let it cool very slowly, maybe stick it in dry sand.   Then it can be machined.   Usually.


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## projectnut (Aug 25, 2018)

You're lucky all you had to do is plug a few holes.  Several years ago we rebuilt the deck at our cottage.  It's on the side of a hill so from the floor of the deck to the ground at the farthest point from the house it's 12 feet in the air.  The building inspector didn't like the old style railing and showed us the building code that now required less than 4" between the balusters.  We went to a local fabricator to get prices for a new railing and almost passed out.

For 9 sections 8' long and 3 sections 6' long plus a gate the company wanted nearly $5,000.00.  I decided I could make it for far less so the project began.  All the welds were done with a Miller Syncrowave 250 mig welder. Everything went well with the fabrication and I thought I was finished.  That's when the wife decided she didn't like the look of the welds where the balusters met the top and bottom rails.  She wanted a finished radius on all 4 sides top and bottom.

I built a fixture on the mill to support the sections and went to work.  If I recall correctly there was over 1,000 inches of weld that had to be radiused and contoured.  At first I tried some in house brand HSS ball end mills from Enco with absolutely no luck.  They bounced around like they were made of rubber, and rubbed off more material than they cut.  I returned them and bought some Niagara brand HSS ball end mills.  They cut the welds like butter.  I think I used 2 end mills for the entire project.  I might have been able to do it with one, but didn't want to take the chance I'd break it.

The bulk of the work was done on the mill with the final polishing and blending being done with a high speed grinder and twist lock deburring and polishing disks.

Here are some pictures of the mill fixture, the welds before starting, the sections on the bench prior to finishing with the deburring disks, and the final installation.








I think if you purchase some high quality end mills you'll be able to cut through the weld without any problems.


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## BtoVin83 (Aug 25, 2018)

To get back to my original question if you have contaminated the weld with the tungsten electrode then the weld is harder then the hubs of hell.
I built some chipper blades and needed them hard so used acetylene tungsten powder rod on the edges. The only thing they are good for is making small grinder wheels out of big ones.


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## Karl_T (Aug 25, 2018)

I've done a HUGE amount of this over the years.  6013 stick then MIG are the best for welding. Grind smooth if at all possible.  Top quality HSS is better than carbide here for the milling step.  FWIW drilling can be a problem as the drill will deflect away from the hard area. Mill drills are your friend here.


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## JimDawson (Aug 25, 2018)

Maybe you're just turning too fast?  30 to 40 SFPM might be a good place to start with HSS.  1/4 inch solid carbide end mills (router bits) are available at Lowes and Home Depot, and you can get them on the weekend


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## Firstram (Aug 25, 2018)

I love to see peoples reaction when cut steel with a carbide router bit!


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## Chuck K (Aug 25, 2018)

Isn't the piece you welded made of cast iron?  I don't know anything about myford lathes, but I would have chosen silicone bronze with the tig or just brazed it.  I've never mig welded cast.


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## 682bear (Aug 25, 2018)

Being a lathe cross slide piece, I would guess that it is cast iron... if so, it may be difficult to machine with pretty much any type of end mill... not impossible, but difficult... I would try carbide, but wouldn't be surprised if it chipped the teeth off the end mill.

I agree with Chuck... silicon bronze/ tig brazing would have been my first choice...

-Bear


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## Nick Hacking (Aug 26, 2018)

Thanks to all of you. Plenty of suggestions for me to try.

I think that the proper name for the part that I've been working on is "compound rest" - it's the top-level sliding component that holds the tool post.

I know that the part is easy to machine because it used to have a central spigot (terminology?) which fits into a depression on the cross-slide on a Myford 7. My lathe is an odd Myford/Drummond which was adapted (by an expert - not me!) to have a Myford 7 type headstock - but it still has a standard Myford/Drummond carriage. My cross-slide is flat so I had to take off the nubbin, spigot, bump thing to get it to fit on my lathe. It came off easily with a few cautious passes of the HSS end mill.  

The reason that I'm working on a second-hand part from eBay is so that if I do bugger it up, I haven't wrecked my lathe: I can still use the original compound rest and tool post. I'm not a _total_ idiot (opinions do vary on this point).

I've bought a Dixon-type QCTP - it mounts to my old Sheldon with no modification other than a top spacer for the nut and I've used that set-up very successfully. The plan is to have a suitable compound rest for the Myford/Drummond which can carry the QCTP so that I can move it from machine to machine. Now that I have the QCTP, I plan to copy the tool holders on my mill and, when my skills have improved a bit, then to copy the body so that I'll have one for each lathe.

I deliberately didn't put all of this detail in my original post because the core problem is that I have a difficult-to-work weld. I can see that everyone is wondering "Why did he do this stupid thing?" - and now you know. There was method in my madness.

Jim Dawson: that has to be the easiest step to try. I'll put on a new HSS cutter and turn the speed down.

Firstram: carbide end mills are on their way to me from the magic that is eBay. If plan "A" doesn't work then I'll post my reaction here.

BaronJ: I think you're right about the Dremmel. I'll see if I can find some suitable grinding tools for plan "C". I confess that I didn't know that such things existed.

Winegrower: I'll put annealing down as plan "D" but, if BtoVin83 is right, that I've contaminated the weld with tungsten, then I suspect it may not help.

To go back to PWaller's post: if all else fails, I suppose I could simply mill out a new body for the compound rest from a block of steel. If I do this, would it be best to use a steel that can be case-hardened? I've never done this before but I do have an oxy-acetylene torch and buckets of sand and water. What could possibly go wrong? 

Thank you again, to all of you, for taking the time to post your suggestions. I promise that I'll post back with a progress update in due course. It's all learning, I suppose, and knowledge is power.

Kind wishes,

Nick


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## Firstram (Aug 26, 2018)

Nick, I was reiterating what Jim D said, you can grab a carbide tipped router bit for wood and get the job done.  Take it easy on the DOC and feed rates and you'll surprise a few people by "routing" steel.


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## Nick Hacking (Aug 26, 2018)

Firstram said:


> Nick, I was reiterating what Jim D said, you can grab a carbide tipped router bit for wood and get the job done.  Take it easy on the DOC and feed rates and you'll surprise a few people by "routing" steel.



Thanks,

Sorry: I completely misunderstood. I presumed that you meant there would be alarming sparks and shards of hot metal, not that I'd be pleasantly surprised! I have a wood working router somewhere - I haven't used it for ages - but there is a box of tools for it. I'll go and see if any of them is carbide tipped. If not, it's back to eBay.

I still cannot find those grinding bits that BaronJ mentioned. All a trawl of eBay throws up is a mixture of Dremmel-type tools and pepper mills.

I shall get off my rear end, go out to the workshop and see if I can make any more progress.

Kind wishes,

Nick


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## Nick Hacking (Aug 26, 2018)

I am out in the workshop now, on my old laptop.

Progress! I swapped the cooked bit for a new-looking cutter that's rather smaller (7/16) and I turned the speed down to 500 rpm. I've been taking slow, shallow cuts and it is working. I think that I was simply going too fast. So far, Jim Dawson seems to have had the answer.

Next, I need to find out if it is possible to resharpen cooked HSS bits...

Thanks again for all of the advice.

Kind wishes,

Nick


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## JimDawson (Aug 26, 2018)

Congratulations !



Nick Hacking said:


> Next, I need to find out if it is possible to resharpen cooked HSS bits...



They can be resharpened, but for small bits (<1/2 inch) it's not really worth it IMHO.  They are pretty inexpensive to buy new.


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## Cadillac (Aug 26, 2018)

Carbide will have a tendency to shatter or chip on a rough intermitant cut like a weld. Best bet is hss and take it easy.  
 A lot of times I will use a angle grinder and leave the weld a little proud then mill the last bit to save on your cutters.


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## BaronJ (Aug 26, 2018)

Hello Nick,

Look here:
https://www.dumoretools.com/mounted-points/quarter-inch?osCsid=bmaf6doou52amo410e9fkahcl2

Near the bottom of the page.


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## Nick Hacking (Aug 26, 2018)

Thanks once more to everyone. I am now back in my study, having a cold beer to celebrate: the hole has been moved. I was going to mount the bolt that holds the tool post by cutting threads, but although I have some taps of about the right size and some dies similarly, I don't have taps *and* dies in the correct combination, so I went for an interference fit: I turned down the end of the bolt until it was _just_ too large to fit in the new hole, heated the compound rest body with a propane torch until the hole expanded and pushed the bolt into place. Everything is cooling (slowly!) now and I don't think the bolt is going to be coming out in a hurry.

If it all goes back together, I'll post a couple of pictures to show what I've been up to.

BaronJ and Firstram: I'm going to get some grinding tools and carbide router bits to add to the tool stock, along with some new dies. One cannot have too many tools.

The problem with the Bridgeport, I think, is that it often lets me get away with bad practice because it's so capable: obviously throwing more oomph at the problem isn't always the way forward.

Here, in the UK, it is a bank holiday tomorrow: I think I might just have another beer and bask in my success.

Kind wishes,

Nick


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## Nick Hacking (Aug 27, 2018)

Here are two photographs: one showing the QCTP mounted on the unmodified top slide of my Sheldon, the other showing it fitted to the modified Myford ML7 topslide which I've bolted to the (unmodified) cross-slide of my adapted Myford-Drummond. I'm sorry: I do find the top-slide / cross-slide nomenclature confusing. I'll get my head around it in the end.



Do excuse the mess and clutter in the background. I think it may be time to tidy the workshop and clean the lathes.


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## ericc (Aug 27, 2018)

I have heard that MIG weld can be hard.  That can be useful.  For example, an article I read recommends it for build up of repaired anvil edges if you dont have the correct rod.  For machinable welds, 7018 is good if you keep a tight arc and the weld stays clean.  Your multipurpose welder should be able to handle 7018, and it is a cheap way to go (no gas).  Annealing also helps.  One thing that helped me get through some hard metal is a cobalt lathe bit rigged up in a homemade toolholder which spins it like a flycutter.  Keep the feed rate real slow, since only one "tooth" is cutting.


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