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Old 1st Jun 2020, 2:23 pm   #1
knobtwiddler
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Default Removing Awkward Screw...

Hi,

I need to open an enclosure. However, one of the screws on the base plate (flat, sheet steel) is cross-threaded into a brass stand-off underneath (which goes into a PCB, with nyloc nut on top). When I try and unscrew the M3 Hex-head screw, the stand-off simply spins around inside the PCB, along with the nyloc on top. This means that the plate is effectively bolted to the PCB, thus preventing access to the enclosure as the PCB can only be removed (and the nyloc accessed) once the base plate is off...

My options (as far as I can see) are:

i) Get a Dremel and try and slice off the cap of the M3 screw. This will risk damaging the base plate, so not ideal - but I'm not exactly spoilt for options. I'm not sure I'll be able to get the Dremel cutter in-between the screw and base plate.

ii) Try and drill off the head of the screw. Start with an extremely sharp 0.5mm bit and go up, in the smallest increments possible. The drawbacks to this method are: firstly, it'll need clamping in a pillar drill (a whole chunk of delicate electronics). Secondly, the head will need gripping with fine nippers to prevent it spinning.

If anyone here has a tip, I'd be extremely grateful. The screw is stainless, which is an added complication.

Thanks in advance!
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Old 1st Jun 2020, 2:28 pm   #2
Scimitar
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Default Re: Removing Awkward Screw...

Quote:
Originally Posted by knobtwiddler View Post

If anyone here has a tip, I'd be extremely grateful. The screw is stainless, which is an added complication.
Grind off the head with a Dremel SpeedClic grinding wheel.
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Old 1st Jun 2020, 2:34 pm   #3
Radio Wrangler
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Default Re: Removing Awkward Screw...

Stainless can be a right begger to drill expect broken bits.

If using a dremel, grind the head off the screw. Go slowly and you should be able to save the panel. Protect things nearby from sparks and metal dust.

A new spacer would be easier than freeing the stub of the screw.

David
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Old 1st Jun 2020, 3:24 pm   #4
Jon_G4MDC
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Default Re: Removing Awkward Screw...

Is the screw countersunk or pan head?
Doh read it again! Hex head. I'm with David then. Grind it but it will get hot so the plastic won't like it.
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Old 1st Jun 2020, 3:36 pm   #5
The Philpott
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Default Re: Removing Awkward Screw...

Wot he said, ^^^

SS does not grind well and most of the energy goes to creating heat- it may be seen to turn blue just before it gets too hot!
Dave
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Old 1st Jun 2020, 3:50 pm   #6
vidjoman
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Default Re: Removing Awkward Screw...

Is there any way to get access to the nyloc nut? Could it be jammed with a screwdriver or even a loop of plain wire around it and pulled tight enough to remove the nut as you turn the screw. Just a thought.
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Old 1st Jun 2020, 4:23 pm   #7
emeritus
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Default Re: Removing Awkward Screw...

Axminster Tools used to do packs of second hand reground tungsten carbide small drills and burrs with 1/8" shanks, but they were't in their range last time I looked. They cope with stainless steel (and titanium). They were the only drills I found that would enlarge the holes in a stainless steel watch strap to take a larger size of watch bar.

Last edited by emeritus; 1st Jun 2020 at 4:46 pm.
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Old 1st Jun 2020, 5:27 pm   #8
BRASSBITS
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Default Re: Removing Awkward Screw...

pictures of the enclosure will help
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Old 1st Jun 2020, 7:18 pm   #9
knobtwiddler
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Default Re: Removing Awkward Screw...

Thanks, all - much appreciated.

There isn't much to see. It is a 300mm x 300mm sheet of powder coated steel. The cap-head screw is flush against it. The brass spacer is on the other side, in a dense nest of circuitry, which cannot be disassembled without removing said screw, thus creating a chicken and egg situation in that regard.

Maybe a Dremel disk, but instead of trying to cut the head off, damaging the enclosure due to the.flush nature, I could attack it vertically, milling an x into it??
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Old 1st Jun 2020, 7:30 pm   #10
David G4EBT
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Default Re: Removing Awkward Screw...

A tungsten carbide burr might do the trick.

I have a set for use with my Dremel and have found them very useful.

Better on stainless steel that HSS bits in my experience.

There's a set here which might have one or two in a suitable profile that might suffice:

https://www.ebay.co.uk/i/31287593895...b5054c5b135a6a

Hope that might help.

Every success in your efforts.
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Old 1st Jun 2020, 7:44 pm   #11
60 oldjohn
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Default Re: Removing Awkward Screw...

I wonder if it had Loctite applied as anti tamper. If you use a left hand drill bit it may unscrew as it heats up.


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Old 1st Jun 2020, 7:51 pm   #12
peterpiper
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Default Re: Removing Awkward Screw...

Have you tried freezer spray? .Heat the surrounding area with a soldering iron first then spray the screw head.

Peter
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Old 1st Jun 2020, 9:19 pm   #13
ronbryan
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Default Re: Removing Awkward Screw...

I suggest you clamp the chassis in a pillar drill, prevent the screw rotating with a slim BA style spanner on the hex head and use a carefully centred 3mm carbide 4 flute end mill to make a hole in the screw head the size of the bolt core diameter until it breaks off. Cool the end mill with a little paraffin on a small paint brush.

Ron
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