[ARC5] Stuck set screw

[John Hutchins]

get an old spline wrench from pawn shop or Goodwill.

Use heat.


On 11/18/2019 7:08 AM, Michael Hanz wrote:
> These set screws are rarely easy to remove after so many years of 
> being untouched.  The other problem is the short distance from the 
> screw to the control panel, which limits what you can get in there to 
> help.
>
> The single most effective way I have found to break it loose is to 
> emulate an impact wrench.  Sometimes you can use the L shaped Bristol 
> wrench for this, hitting it with a small hammer while holding it with 
> needle nose pliers applying CCW torque.  Protect the panel from wild 
> rebounds with some sort of cover - I learned that the hard way.
>
> If that doesn't work, by removing the plastic handle of a DS series 
> Bristol screwdriver, you can adapt it to an extension bar and use it 
> with one of the _small_ impact driver tools. (Yeah, I know, it pains 
> me to modify a good tool like that, but if you get desperate 
> enough...)   You also have to cut the spline down in length to a very 
> short section to reduce the torsional twist of the spline during the 
> jolt (a long spline absorbs the torque like a torsion bar), but 9 
> times out of ten it will get the screw out with one light blow.  Use a 
> _small_ hammer, not a 5 pound sledge.  I think sometimes they used a 
> drop of lacquer on the screw as a locking mechanism back in the day.
>
>
>
>
> If all else fails, the screws _can_ be drilled with an appropriately 
> sized _carbide_ drill.  The screws are usually hardened, but a carbide 
> bit will do it without working up a sweat.  If you use two drills, one 
> the outside diameter of the Bristol wrench followed by the second 
> being the minor diameter of the set screw thread, it will usually stay 
> centered.  Use medium speed, light pressure.  You still may have to 
> make some sort of adapter to connect the drill to the rotating 
> mechanism - unless the knob is close to the edge of the panel, 
> conventional chucks are usually too big and require tilting of the 
> drill to the point where it's not very helpful in getting to the 
> contact point on the shaft.
>
> If it's essential to get it out with minimal damage, there are firms 
> that specialize removing these and broken taps with EDM (electrical 
> discharge machines).  It will depend on how much you want to spend.
>
>           73,
>  - Mike  KC4TOS
>
> On 11/17/2019 2:08 PM, Waldo Magnuson via ARC5 wrote:
>> The set screw in the audio volume switch on a C-1254A control unit IS a Bristol set screw. The wrench fits tightly, I’ve used Blaster penetrating Oil but even with excessive torque the screw has not come loose. Any suggestions- heat/cold/drill?
>> Skip W7WGM
>
>
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