Author Topic: Grub Screw Extraction  (Read 1042 times)

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Offline Peaky 556

Grub Screw Extraction
« on: Jan 13 2021 19:32 »
Good evening all,
Can I ask if anyone has been successful with removing something as small as a M3 socket head grub screw that is jammed in a brass hub?  I think I’ve had a bad batch of screws, as two have failed in quick succession, characterised by the key (1.5mm) rounding off the hole as it was being tightened onto a shaft.  I’ve managed to loosen them slightly to be able to remove them from the shaft, but even with now no preload on them they seem to have jammed well and truly.  Maybe the screw has fragmented and the action of turning the hex key has driven the fragments into the brass.
Thank you,
Tim
Facebook.com/AppleTreeRailway/

Offline Andy B

Re: Grub Screw Extraction
« Reply #1 on: Jan 13 2021 21:30 »
Tim,
Is the object with the hub (a gear?) now separated such that you can drop it in a container of liquid on its own?
And are the grub screws mild steel (not stainless?)
If so, I'd try Alum. I've used in successfully to remove the broken off end of a drill in brass.
Plenty of references on how to do it on t'interweb. Alum is easily available on ebay, etc..
You'd be welcome to a few grams from the bag that I have, but Derbyshire police may not consider it an essential journey for you to pick it up!

Andy

Offline John Branch

Re: Grub Screw Extraction
« Reply #2 on: Jan 13 2021 22:33 »
Tim,
I have every sympathy with you over this event.  I have been drilling, tapping holes and (ahem!) screwing bolts and grubscrews at a great rate over the past couple of weeks, and have experienced a larger than usual series of broken drills and taps and smoothed off socket heads, and hex keys with rounded edges.  Some of this is due to my natural and increasing clumsiness, but I think that the quality of such items from the new "workshop of the world" is sometimes questionable.  With grubscrews I now go into the shaft with a clearance drill, and get metal to metal in shear rather than rely on the clamping force to transfer the drive.  Roll or split pins can also sometimes be used.  I did not get this trouble with UK sourced BA sizes.

 How can we be sure of decent quality when buying these items?

John

Offline IanT

Re: Grub Screw Extraction
« Reply #3 on: Jan 14 2021 08:54 »
With small (non-ferrous) item like this - Andy's Alum method is probably the easiest & best.

Larger items can sometimes be drilled out but it becomes very fiddly as they get smaller (at least without spoiling the thread). A small CNC machine could probably do it - I've got an article on using one to repair very small watch parts and I don't think the work involved could be done manually (at least not by me).

Btw - if the grub screw is 'soft' and being driven onto a hard shaft, it may deform the (threaded) end and make it very hard to then unscrew. Turning a 'pip' on the end (or using screws that already have one) avoids this problem but takes time and needs a small accessory. It's just a short piece of brass rod, drilled and tapped through. The grub screw is screwed in (from the back) to protrude from the front and then a second screw is put in to lock it in place. It's easy to hold & modify it then and although this takes time, it can be a good investment sometimes. I've had this kind of problem on some of my machine repairs and it can be a real pain.

Broken taps/drills in cast iron or steel really need an EDM machine to remove but I've used a 6mm diamond tipped 'core' drill recently (in cast iron) to remove a broken tap, then plugged the hole and re-drilled & tapped it. It's VERY annoying when this happens!!       

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline Chris_P

Re: Grub Screw Extraction
« Reply #4 on: Jan 14 2021 09:04 »
"How can we be sure of decent quality when buying these items?"

Whilst it's very hard to be assured of quality when we buy it might be comparatively easy to test each screw in a suitable blind hole in a piece of appropriate scrap material before actually using it in a critical component.  If it fails then little is lost. We could get into a debate about potential plastic deformation and weakness in second use following over stressing in first test but I doubt this is a real issue for modeller's purposes where an if in doubt use a different screw (after test) approach should be fine.

Offline 753

Re: Grub Screw Extraction
« Reply #5 on: Jan 14 2021 10:05 »
I have fitted a couple of Slater’s motor / gearbox units to locos recently. The drive spur gear comes a small grub screw and key which I think is to small to get any decent torque without the risk of striping the flats of the grub screw.
I drilled the gear out to take a 6BA grub screw, it also helps if you can spot drill the axle to take the screw tip thus less torque required.

Mike

Offline Peaky 556

Re: Grub Screw Extraction
« Reply #6 on: Jan 14 2021 12:36 »
Thanks all, it’s obvious there has been a lot of frustration out there (and probably swearing) from similar calamities.  For my problem I will add that I also tried the next size up of Imperial Allen key (1/16”) but that wouldn’t grip either, nor would the depth of socket allow my screw extractors to grip.  The screw was black, so I took it to be a high tensile steel like a grade 12.9 “Unbrako”, but I’m probably misled there.  The remainder of the batch has gone into my rejects tub (rapidly filling with dodgy ballraces, motors, eccentric shafts, non-threaded nuts etc!).  I have a batch of stainless grub screws to try in future, from Boltbase whose products I generally find pretty good.

I will look into your Alum suggestion, thanks Andy.  I probably won’t call though, nor arrange to meet you and swap small packets of white powder for bundles of notes, or other suspicions may be aroused 😂.

On the matter of design features when using grub screws, I always file a flat on the shaft.  Not quite so good as the ‘pocketed hole’ method but easier on small diameter shafts.

I’ll continue having fun 🤔
Thank you,
Tim
Facebook.com/AppleTreeRailway/

Offline Peaky 556

Re: Grub Screw Extraction
« Reply #7 on: Feb 12 2021 16:33 »
Evening all,
I’m about to order some Alum but this name seems to encompass a family of similar salts containing Al, Potassium and sulphate.  Can anyone advise a particular formulation on the basis of chemical knowledge or experience with dissolving steel items?
Thanks,
Tim
Thank you,
Tim
Facebook.com/AppleTreeRailway/

Offline IanT

Re: Grub Screw Extraction
« Reply #8 on: Feb 12 2021 17:38 »
Potassium Aluminium Sulphate will remove a steel part from non-ferrous parts I believe Tim. It's about £6 on Amazon - and it may take a while.

I've only used mechanical means up till now because (unfortunately) I've only broken taps and drills in steel or cast iron parts. For a "soft" (grub) screw you might be able to drill it out if you can guide the drill sufficiently for it not to 'skid off' - or a carbide end mill will almost certainly cut a grub screw out using a vertical mill.

For broken HSS or some hardened parts this approach may not be possible. I've tried using special stud 'extractors' etc but they are (frankly) quite useless. More recently however, I've used a 8mm diamond-coated 'core' drill to drill out (& around) a broken tap in cast iron. It cut both the surrounding cast iron and some of the tap too, leaving a hole that I could then simply re-drill (and plug) before re-drilling and tapping. It wasn't very fast though, was messy and needed some patience. I think I got it from Arc Euro Trade...

Mmmn - I've just checked and they are on clearance (I'm sure I paid a lot more than this though)  :-(

 https://www.arceurotrade.co.uk/Catalogue/Diamond-Tools/Diamond-Drills/Diamond-Core-Drills

EDM is probably the best solution for this problem but I don't have access to it.

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline John Candy

Re: Grub Screw Extraction
« Reply #9 on: Feb 13 2021 09:39 »
Assuming the grub screw has not split, which I would have thought unlikely, being constrained by the thread/bore, my plan of attack would be :-

1) Try soldering the key into the screw, if possible using a RSU on the highest power setting (this concentrates the heat at the joint ...... it will be hot enough to make the joint glow red, if held "on" for long enough). Otherwise heat the key with a butane microflame torch until the solder flows.

2) If that fails, clean-up the solder paint residue, then, using "industrial grade" thick cyano, put a small spot into the screw hole and force-fit in a length of rod (preferably steel) with end filed to square or hex section.

3) Alternative to (2) this step depends upon the length and gauge of screw : Drill out the core of the grub screw and tap to take a cheesehead steel screw and again use cyano to fix the screw. Put a drip of penetrating oil down the bore and use a miniature mole grip to turn the screw head. If this fails use superglue release fluid to remove the rod or screw before moving onto (4).

4) Last resort, very carefully using progressively larger drills in small increments, open out the drilled hole until the thread collapses, avoiding damage to the threaded bore.

Over the years, I have had a number of cases where Allen keys have failed to release screws  most recently, the screws which hold Slaters wheels to axles, where the screw had been "Loctited".

May sound tedious but doesn't take long, if you have the tools to hand.Combinations of the above methods have always worked for me and have left the threaded bore undamaged.

John.
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline cabbage

Re: Grub Screw Extraction
« Reply #10 on: Feb 13 2021 11:11 »
Tim, you asked for a chemist? The EDM is probably the best bet but having read "Build your own EDM machine" - even I am not that crazy... BUT you could try reverse electroplating in which the grub screw is etched away and the iron deposited on (say) a copper cathode. You would need a high current low voltage 0-12v supply and Ferrous Sulphate (cabbage fertilizer!).

A similar system is used to derust tools.

Regards

Ralph

Offline Peaky 556

Re: Grub Screw Extraction
« Reply #11 on: Feb 28 2021 15:41 »
Ralph,
I was really asking for advice on which compound to choose within the wide family of powders on t’internet claiming to be “Alum”.

I did pick one that seemed to have the elements Al and K, and ‘sulphate’, in the description, but on arrival it seemed to be aimed more at cooking from the packet.  My brass gears have been sitting in a shallow bowl of saturated solution for over a week now, and, despite regular stirring, I’m disappointed to report that no dissolution of the steel seems to have taken place.
 
Does anyone have both a positive experience and a reliable supplier of this seemingly mythical wonder powder?
Thank you,
Tim
Facebook.com/AppleTreeRailway/

Offline John Branch

Re: Grub Screw Extraction
« Reply #12 on: Feb 28 2021 16:59 »
Tim,
Have you seen this?  It's from Wikipedia.  It seems that the word Alum refers to many very different compounds used for a huge number of purposes. The bit that refers to your problem is below:-

"Alum in the form of potassium aluminium sulphate or ammonium aluminium sulfate in a concentrated bath of hot water is regularly used by jewelers and machinists to dissolve hardened steel drill bits that have broken off in items made of aluminum, copper, brass, gold (any karat) and silver (both sterling and fine). This is because alum does not react chemically to any significant degree with any of these metals, but will corrode steel. When heat is applied to an alum mixture holding a piece of work that has a drill bit stuck in it, if the lost bit is small enough, it can sometimes be dissolved / removed within hours.[33]"

looks like you are in with a chance if you get the right stuff.  Best ask for potassium aluminium sulphate or ammonium aluminium sulfate rather than alum.

John