Anodisers broke a stud in a high value part...

gregormarwick · Oct 18, 2019

They screwed in a stud in order to suspend it in the tank. One of six parts, value is ~£6k each, the other five are fine, unplated in the one same hole so they clearly used the same method on all six.

The part is fully plated so presumably they sheared it off during removal rather than insertion. It's sheared off cleanly about 1mm under the surface.

Sheared off during removal means it's well stuck.

Hole is tapped M5 helicoil. No idea if they used an appropriately threaded stud, but the others are not obviously messed up so I assume it is.

32µin RMS surface requirement on the face around the holes, so wary of mechanical means of extraction.

Anodise is type 3 class 2 hard, as per MIL-A-8625, black dye, dichromate seal.

I don't have any edm, and am reluctant to push this part out to any of our nearby places that do...

Is there any chemical method that will not affect the anodise?

TIA for suggestions...

Milland · Oct 18, 2019

Bugger. Well, if you're feeling brave...

Can you refixture the part with the stud vertical, then mill a 1mm W x 4mm long "X" into the top of the stud, perhaps a mm or so deep? Then cut a small socket (good hard steel) so the end has the right prongs left to engage the slots in the stud (very close fit is best).

After using a penatrating oil on the stud and letting it sit for a while, try to back out the stud. If you take a thin sheet of Al and make a "mask" that can be clamped over the hole it'll protect the surfaces if the tool slips or breaks.

Is the stud also Al? If so could it have induced a locking interface with the part due to the anodization process? You'd think the others would have done the same...

Radar987 · Oct 18, 2019

The stud is either aluminum or titanium. Probably aluminum because it snapped like a twig. It ain't coming out chemically. Machining it out is your best bet.

Lesson for next time: provide provisions for hanging a high dollar part. Preinstall your own titanium hardware.

gregormarwick · Oct 18, 2019

Milland said:
Bugger. Well, if you're feeling brave...

Can you refixture the part with the stud vertical, then mill a 1mm W x 4mm long "X" into the top of the stud, perhaps a mm or so deep? Then cut a small socket (good hard steel) so the end has the right prongs left to engage the slots in the stud (very close fit is best).

After using a penatrating oil on the stud and letting it sit for a while, try to back out the stud. If you take a thin sheet of Al and make a "mask" that can be clamped over the hole it'll protect the surfaces if the tool slips or breaks.

Is the stud also Al? If so could it have induced a locking interface with the part due to the anodization process? You'd think the others would have done the same...

Kind of hard to gauge the material of the stud tbh from what little of it is exposed, I did a couple of scratch tests on it and it seems pretty soft, but not aluminium soft. Mild steel of some description at best guess.

I think if I put it in the mill I will probably just try to machine it out at the thread minor and see if I can pick the threads out, then retap.

I can't see any visible threads in the exposed section of the hole, and it's sheared off deep enough that I should be able to see at least the start of the thread. Looks almost eroded...

I don't know much about the process of anodising, so at a loss as to what mechanism caused the stud to be stuck in there...

gregormarwick · Oct 18, 2019

Radar987 said:
The stud is either aluminum or titanium. Probably aluminum because it snapped like a twig. It ain't coming out chemically. Machining it out is your best bet.

Lesson for next time: provide provisions for hanging a high dollar part. Preinstall your own titanium hardware.

Sorry, you posted this while I was typing out the above post.

Titanium could be a possibility from the apparent hardness. It's not aluminium. Also the part is pretty big and heavy to suspend from a single M5 STI stud made out of aluminium, pretty sure they would have broken more than one if they'd tried that...

We've worked with this anodiser for years and a few botches aside, they do pretty good work. They've never asked us to preinstall hardware before, and I don't know enough about the process to get it right anyway.

Cole2534 · Oct 18, 2019

Any other coplanar studs? That could form the basis to attach a subplate and use a mag drill to remove the stud if it's not easy to fit into a mill.

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Larry Dickman · Oct 18, 2019

the ol left handed drill trick might work here

jz79 · Oct 18, 2019

gregormarwick said:
Sorry, you posted this while I was typing out the above post.

Titanium could be a possibility from the apparent hardness. It's not aluminium. Also the part is pretty big and heavy to suspend from a single M5 STI stud made out of aluminium, pretty sure they would have broken more than one if they'd tried that...

We've worked with this anodiser for years and a few botches aside, they do pretty good work. They've never asked us to preinstall hardware before, and I don't know enough about the process to get it right anyway.

it must be Ti (grade 1 or 2 most likely, alloyed Ti don't work well for anodizing), there simply are no other options really, apart from aluminum, which you say it isn't

I can't say for hardcoating, but about TypeII parts I anodize on Ti threaded studs - at first I made the studs with long thread, this was problematic because some of the acid is leaching into the threads and partial oxidizing occurs (both Ti and Al oxidize in the bath), and sometimes the stud would be difficult to unscrew, a "sticky" feeling, like stainless/stainless galling

so the fix that worked for me was to make the stud with 1-2xD of thread, thread it in till the end, the end of the thread on the stud, when tightened to deform the Al around it, forms sort of a seal not allowing any acid to leach into the thread, no "sticking" issues since

a thread sealant might work for through holes if there is a risk of acid leaching in from the other side, but I can't suggest one, haven't tested any, resistance to caustic etch, deox and sulfuric bath can be an issue

I suggest for the future to discuss how the parts will be fixtured to avoid costly mistakes

daryl bane · Oct 18, 2019

Seems at 6K for the part, could EDM /spark erosion not be used? I am ignorant of the process, so maybe this is not an option?

Milland · Oct 18, 2019

daryl bane said:
Seems at 6K for the part, could EDM /spark erosion not be used? I am ignorant of the process, so maybe this is not an option?

If Gregor can set the part back up, he might as well try to cut the stub out. One thing to watch for is that if the (presumably) Ti has bonded itself to the Al, then there's a risk of it tearing sections of the thread out as it's removed.

Sometimes I try to have the customer take uncoated parts and handle anodize or plating on their own. Not my problem if things go wrong...

JCByrd24 · Oct 18, 2019

Larry’s got it, left hand drill. Stud should be relatively loose it’s not like it’s corroded in there. Left hand drill will often walk it right out. I start small and then jump up in size to encourage the drill to grab. On an expensive part of you can hold it in a machine and get it on center all the better but I’ve done these by hand if you are worried about the anodizing.

This job is the difference between a good manual repair machinist and a CNC operator. It’s routine for the former.

MichaelP · Oct 18, 2019

Drill a hole in the stud (preferably, using a left hand drill since it can be sufficient to unscrew the stud if you're lucky). Then tap a left hand thread inside the stud and use a left hand screw to unscrew the stud.

If you do it accurately, yet are not successful, you'll still have an option to drill the stud out as you mention in your post #4.

Guest · Oct 18, 2019

Agree with left hand drill. Of course use a spot drill first as close to center as possible.

gregormarwick · Oct 18, 2019

Thanks for all the replies!

I've removed my fair share of broken studs, and my gut feeling is this one is not screwing out of there.

Got some more pressing things to attend to first, but plan is to put it into the mill and helical bore out to minor diameter, and see what it looks like then.

Milland's point of galling/cold welding in the threads is my biggest concern, but if I mill out the minor and pick out the threads hopefully it will be salvageable.

as9100d · Oct 18, 2019

Have you contacted the anodizer? In my industry we will issue a C.A.R for the non conforming part and make the vendor answer for the issue. I can send you a blank form if you like.

I would maybe negotiate a substantial discount on the next batch of parts. They may give you $1000 credit or more possibly? Still have to fix the part but at least you are getting paid to fix it in a round about way.

gregormarwick · Oct 18, 2019

as9100d said:
Have you contacted the anodizer? In my industry we will issue a C.A.R for the non conforming part and make the vendor answer for the issue. I can send you a blank form if you like.

I would maybe negotiate a substantial discount on the next batch of parts. They may give you $1000 credit or more possibly? Still have to fix the part but at least you are getting paid to fix it in a round about way.

Thanks, but not sure what it would achieve tbh.

I could certainly document the event with an NCR/CAR but it wouldn't have any meaningful effect.

My experience with anodisers is that they have very slippery shoulders when it comes to responsibility for bad work.

Also these guys are one of two places within a workable distance for us and we run a lot of work through them, and they quite frequently pull out the stops for us to put a rush job through on time.

Better to let it slide with them, and maintain an amicable relationship...

Milland · Oct 18, 2019

gregormarwick said:
Milland's point of galling/cold welding in the threads is my biggest concern, but if I mill out the minor and pick out the threads hopefully it will be salvageable.

Unless there's some chance it could discolor the anodize, I still think dosing the stud/hole with a good penetrant oil before trying to remove it would help. Even some light heat (like from a hot air gun or household portable heater) should expand the Al a bit more than the Ti and encourage seepage of the oil.

as9100d · Oct 18, 2019

gregormarwick said:
Thanks, but not sure what it would achieve tbh.

I could certainly document the event with an NCR/CAR but it wouldn't have any meaningful effect.

My experience with anodisers is that they have very slippery shoulders when it comes to responsibility for bad work.

Also these guys are one of two places within a workable distance for us and we run a lot of work through them, and they quite frequently pull out the stops for us to put a rush job through on time.

Better to let it slide with them, and maintain an amicable relationship...

I would issue the NCR/CAR anyways and explain that you want to find a solution so that it doesn't happen again. Making the point that you want to help, not put blame on anyone. Thats an awful high dollar item to possibly ruin with no accountability.

Mud · Oct 18, 2019

barbter said:
Gregor,
Give it a go with say a 3mm (ish) L/H drill so you still have a reasonable sidewall.
Tap in there a 3.2mm (ish) A/C torx driver (on a socket end) and see if it wants to unwind?
If not, you gotta try a stud extractor, but I always liked the torx first, as a stud extractor gives a second "go".
Good luck

Snap On has these neat mulitspline extractors, they engage the full length of the drilled hole and don't taper to cause a wedge effect to make the bolt tighter.

eKretz · Oct 18, 2019

Those look like the Ridgid extractors I've got. My favorite kind of extractor, bar none.

Anodisers broke a stud in a high value part...

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