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        Rant Set screws - why wont they EVER come out?

#1 JetPlaneFlyer Jul 17, 2012 04:27 AM

Set screws - why wont they EVER come out?
 
I've just rounded off yet another couple of shaft retaining set-screws (grub screws to those of us in the UK) while attempting to remove a motor shaft:mad:
I'm using a new good quality allen key but yet again I'm going to have to drill the screws out (which is always a bit of a worrying job). Is it just me, am I doing something wrong?

Maybe i should heat the part to soften any locking compound before trying to shift them?

Steve

#2 aeromaniac Jul 17, 2012 04:48 AM

Quote:

Originally Posted by JetPlaneFlyer (Post 22186285)
I've just rounded off yet another couple of shaft retaining set-screws (grub screws to those of us in the UK) while attempting to remove a motor shaft:mad:
I'm using a new good quality allen key but yet again I'm going to have to drill the screws out (which is always a bit of a worrying job). Is it just me, am I doing something wrong?

Maybe i should heat the part to soften any locking compound before trying to shift them?

Steve

Most likely poor quality grub screws, ( its grub screws for us in Australia too lol)

#3 JetPlaneFlyer Jul 17, 2012 06:05 AM

Quote:

Originally Posted by aeromaniac (Post 22186335)
Most likely poor quality grub screws, ( its grub screws for us in Australia too lol)

I guess you re right but they must be poor quality on most brands of motor because I have the same trouble often.

#4 jackerbes Jul 17, 2012 06:22 AM

Quote:

Originally Posted by JetPlaneFlyer (Post 22186285)
I've just rounded off yet another couple of shaft retaining set-screws (grub screws to those of us in the UK) while attempting to remove a motor shaft:mad:
I'm using a new good quality allen key but yet again I'm going to have to drill the screws out (which is always a bit of a worrying job). Is it just me, am I doing something wrong?

Maybe i should heat the part to soften any locking compound before trying to shift them?

Steve

Was it a straight ended hex wrench or a ball ended wrench? The ball ended ones have a severely reduced engagement and area simply work like small metal cutting tools. Especially so on a grub screw that has a locking compound on it.

Ball ended wrenches are OK for advancing screws to initial contact or removing previously loosened or lightly tightened screws but not for removing tightened screws.

On the screws with a locking compound applying heat to relax the locking compound is the secret. For red #271 Loctite the release temp is 482F/250.

Applying heat can done with the pin point flame of a cheap butane micro torch. Direct the focus of the heat (a point just beyond the visible flame in a dimly lit room) at the screw for 5-10 seconds, it will not be enough to damage the motor, shaft, or the finish on the aluminum parts.

Another way to apply heat in is to use a spare 1.5mm, straight shanked, hex wrench to apply the heat. Hold the wrench in a small pliers or hemostat and heat the end until it is a bright red cherry red heat (1450F/790C) and then stick it in the hex socket. Leave it in place for 5 seconds or so and then quickly remove it and replace it with an unheated hex wrench and remove the screw while the locking compound is still softened.

A 1/16" (0.0625") hex wrench is just slightly larger than a 1.5 mm (0.591 mm) hex wrench and can often be forced or driven into a damaged or stripped 1.5 mm socket to save the day. The best choice for the savior wrench is one of those short 1/4" hex drive Allen. Those are usually hardened to just short of the point of brittleness and it also gives you a larger 1/4" drive for applying turning force.

Good luck with the drilling out of damaged grub screws. They are usually hardened to the point where that will not work. My favorite last desperate ploy for removal is to use a Dremel tool and a #409 abrasive cutting disc to cut a narrow (0.025"/0.64 mm) slot across the center of the stripped screw and then remove it with a close fitting straight screw driver. Using the screw driver immediately after cutting the slot will often find any locking compound present softened from the heat of the abrasive cutting process.

The abrasive cutter will cut into the shoulders of the threaded hole on each side of the screw for a short distance on each side, that damage is unavoidable and should leave you with a functional threaded hole. Do not view the visible damage as shameful evidence of the work of an inept mechanic, instead view it as evidence of miracle save performed by a knowledgeable and skilled machinist. You were the victor, wear you wounds with pride!

Good luck with it!

Jack

#5 hoppy Jul 17, 2012 07:15 AM

Hint -
Just grind off the rounded parts of your hex wrench using short applications to the grinding wheel with a dip in water in between. The ends get rounded in short order even when the screws come out.

#6 flypaper 2 Jul 17, 2012 07:40 AM

Many yrs ago Allen screws were hardened and almost impossible to strip. Another trick is to hit the end of it with an appropriate sized punch. Serves two purposes, drives the rolled out corners back in and loosens in the threads too.

Gord.

#7 ernie b Jul 17, 2012 07:45 AM

I use my soldering iron and put the tip(old tip, not my good tips) at the junction of the wrench and the grub screw, wait about a minute and then turn it out, I have yet to have this method fail.

Ernie

#8 JetPlaneFlyer Jul 17, 2012 08:58 AM

Thanks for the tips guys. I was using square ended allen wrench, not ball ended. It seems that heat may be the key, at least next time.

The comment about drilling being difficult is spot on. I've done it before but this time the grub screw seem especially hard and I've already took the point off four HSS drills and not got down to the shaft. I've ordered a few cobalt drill bits to try, hopefully they will get the job done.

Having now removed half of the screw by drilling I've no option but to persevere with the drill. If that fails the last desperate option is to try to drift the shaft out with the remnants of the screws still in place, the big risk there is that I deform the rotor housing in the process.

The motor is only a week old, it was second time out that I did the shaft, and it's not a cheap motor either:censored:

#9 zeroback Jul 17, 2012 10:17 AM

I find chrome plated Allen keys more durable and better fitting...for future reference.

#10 Bare Jul 17, 2012 11:10 AM

'possibly' due to crappy grub screws,
but it's IMO far More likely that your Allen wrenches are the crap element. Especially incriminating when it happens on more than one grub screw. A tight fit into the hex hole IS critical.
Quality varies dramatically on those wrenches.. more so than in the screws actually..something I've learned over the years.

#11 ernie b Jul 17, 2012 11:30 AM

Quote:

Originally Posted by bare (Post 22188653)
'possibly' due to crappy grub screws,
but it's imo far more likely that your allen wrenches are the crap element. Especially incriminating when it happens on more than one grub screw. A tight fit into the hex hole is critical.
Quality varies dramatically on those wrenches.. More so than in the screws actually..something i've learned over the years.

+1 :)

#12 flypaper 2 Jul 17, 2012 11:51 AM

Get the genuine Allen wrenches and you won't have any problem with quality or hardness.

Gord.

#13 JetPlaneFlyer Jul 17, 2012 12:48 PM

Quote:

Originally Posted by Bare (Post 22188653)
but it's IMO far More likely that your Allen wrenches are the crap element. .

Yeah, that's what I thought, so I got some brand name chrome vanadium allen wrenches.... No improvement whatsoever, in fact one of the cheapies is a tighter fit.

#14 t.edwards Jul 17, 2012 01:32 PM

Quote:

Originally Posted by hoppy (Post 22186882)
Hint -
Just grind off the rounded parts of your hex wrench using short applications to the grinding wheel with a dip in water in between. The ends get rounded in short order even when the screws come out.

This is a good thing to do even with new hex wrenches. The end is almost never a good hex because the ends are sheared to length. Grind them back slightly to get a good sharp hex all the way to the end and you're ahead of the game

#15 AirBornOne Jul 17, 2012 01:51 PM

Is there an issue of using imperial sized wrenches in place of metric sized (or vice versa) ?
Another proof these are indeed 'Set' screws: [QUOTE] ... to assume a fixed or rigid state, as the countenance or the muscles./QUOTE]
Skies
J


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