Remove stripped set screw on front panel knob - Page 1
Forum section: electronics / repair

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 22, 2020, 01:15:40 am
content: I'm trying to remove the knob from the front panel of an HP 8566A. However, one of the 2 set screws is stripped. I've attached an image showing the knob and the hole for the screw. If you'd like me to attempt to image the screw let me know. How can I remove this? I'm a bit nervous to take a drill to this. If possible, I'd prefer not to damage the knob. But, if that is necessary I expect the knob is probably replaceable.

author: jdragoset
author_rank: Frequent Contributor
timestamp: December 22, 2020, 01:38:34 am
content: You have not said if it is an Allen set screw.If it is, get a correctly sized easy-out (grind the end if it bottoms out), back the opposite side of the knob with some mass (so the knob shaft is not stressed) and drive the easy out with a small ball pein hammer before trying to turn the easy out.

author: xrunner
author_rank: Super Contributor
timestamp: December 22, 2020, 01:40:51 am
content: Yea it's tough. I restore test equipment and I've had to leave on knobs like that or risk destroying it to get it off - drilling the screw out and sweating it. If I didn't see a replacement knob I've just left it alone. If there are any jagged areas in there you can try sacrificing a small screwdriver to turn it if you can get some solvent down there for 24 hours.That knob + encoder is available on Ebay for $27.I don't know how bad you want it off ...

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 22, 2020, 01:56:45 am
content: Quote from: jdragoset on December 22, 2020, 01:38:34 amMy mistake. It is indeed an allen set screw. Size #4. About 150mil length. Thanks for the advice!

author: Miti
author_rank: Super Contributor
timestamp: December 22, 2020, 02:13:08 am
content: I have a Craftsman set with 15 sizes in inch and 15 in metric. If I were you, I would try the next size up from either inch or metric. Literally next size up, measured with a caliper. Maybe is not completely rounded.

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 22, 2020, 02:18:30 am
content: Quote from: jdragoset on December 22, 2020, 01:38:34 amI'm not too familiar with this process. Does something likehttps://www.mcmaster.com/5054A11/look like it would work?

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 22, 2020, 02:20:12 am
content: Quote from: xrunner on December 22, 2020, 01:40:51 amThat's a fair point. It is just for personal use and the reasons are purely cosmetic (cleaning the front panel). But, my perfectionism is getting the better of me. A $27 mistake doesn't sound too bad though. Anyway, thanks for the advice.

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 22, 2020, 02:21:19 am
content: Quote from: Miti on December 22, 2020, 02:13:08 amThis is one of the first things I tried and unfortunately I didn't have any luck. It's possible that I just didn't have the right next size up.

author: xrunner
author_rank: Super Contributor
timestamp: December 22, 2020, 02:23:39 am
content: Quote from: matthuszagh on December 22, 2020, 02:20:12 amIcompletelyunderstand.

author: bdunham7
author_rank: Super Contributor
timestamp: December 22, 2020, 03:19:05 am
content: You can try wedging a sharp Torx driver of the appropriate size in there and seeing if it will grip. Failing that, I have left-hand drill bits for difficult cases, but that takes some care.

author: Runco990
author_rank: Frequent Contributor
timestamp: December 22, 2020, 03:28:50 am
content: I'm an HP test gear whore....so am extremely familiar with the dreaded set screws.What has worked BEST for me after much grief and trial and error:Heat up the set screw with a fine tip soldering iron and THEN try a filed down to fit allen key.Most of the time they come right out when they will absolutely NOT without heating them first.Good luck!

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 22, 2020, 03:33:05 am
content: Quote from: bdunham7 on December 22, 2020, 03:19:05 amI tried the Torx driver technique to no avail. Good to know about the drill bits.

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 22, 2020, 03:34:24 am
content: Quote from: Runco990 on December 22, 2020, 03:28:50 amThanks for the advice. I assume heating the set screw damages the RPG?

author: Runco990
author_rank: Frequent Contributor
timestamp: December 22, 2020, 04:02:48 am
content: Sorry... the RPG?Heating the set screw makes it expand and then contract. This often breaks it loose and then lets you extract it without a lot of force. Don't overdo it, or you'll melt the knob. Just get the set screw hot for a few seconds and then try.

author: matthuszagh
author_rank: Frequent Contributor
timestamp: December 22, 2020, 04:10:17 am
content: Quote from: Runco990 on December 22, 2020, 04:02:48 amSorry, the whole knob assembly (saw RPG in the manual, so that's what I though it was).I got you now. That makes more sense. Thanks!

author: jdragoset
author_rank: Frequent Contributor
timestamp: December 22, 2020, 03:40:48 pm
content: Maybe this one.https://www.mcmaster.com/easy-outs/socket-set-screw-extractors-6/

author: tkamiya
author_rank: Super Contributor
timestamp: December 22, 2020, 04:52:46 pm
content: As far as I can remember, the rotary encoder has mostly plastic internals. If I were to do this, at this stage, I will be making decision as to if I want to destroy the knob in order to remove it without hurting the rest. I can nibble away at the plastic knob to expose the brass collet and set screws. At that point, you can dremel your way in. The whole front has to come out before you can change it out. It's pain in a butt to do that.

author: langwadt
author_rank: Super Contributor
timestamp: December 22, 2020, 05:31:27 pm
content: dissolve the steel screw with alum or acid?

author: tkamiya
author_rank: Super Contributor
timestamp: December 22, 2020, 05:57:13 pm
content: How do you do that in reality? The knob, thus the whole collet, is stuck on the front panel. It will take an incredible luck to pull that off (ha!) without damaging the rest.... Let me actually look at one of mine to see how they are actually mounted. I'm curious now. Somehow, I recall seeing very fragile piece of construction in there.

author: Runco990
author_rank: Frequent Contributor
timestamp: December 22, 2020, 06:07:10 pm
content: Geez, I just "RE-looked" at that image. No, you cannot get a soldering tip in there. That only works for the small knobs that you can see the set screw. But keep that in mind for the next one.The best shot is to file a slightly larger key at a taper and tap it in. Then try to turn it. It has to be a tight fit.I bought an entire cheap set just to "make" HP set screw extraction tools.You'd think they used an impact gun to put them in.Now if you already stripped it... all bets are off. May HAVE to drill it out.

author: David Hess
author_rank: Super Contributor
timestamp: December 22, 2020, 06:49:18 pm
content: Quote from: Runco990 on December 22, 2020, 03:28:50 amFiling down a slightly larger Allen wrench to fit what remains of the set screw tightly has always worked for me. I have never needed to heat the screw up.Another recommendation I have seen is to put cyanoacrylate glue on the end of the Allen wrench before inserting it into the worn screw.

author: Microdoser
author_rank: Frequent Contributor
timestamp: December 22, 2020, 06:54:28 pm
content: Mechanics have access to some quite strong metal glues/fine metal fillers.I would think about putting some on the end of an allen key nearly the right size, waiting until it is really cured, then carefully trying to put *just* enough force to undo the screw.

author: tkamiya
author_rank: Super Contributor
timestamp: December 22, 2020, 07:10:08 pm
content: I took one of mine and looking at it closely. Actually, took it apart to see how both the rotary encoder and the knob is made. Yes, one pair was sacrificed in name of science and just pure curiosity!The knob is unusually heavy. Cutting into it showed it is mostly made of metal. It is a machined and plated brass pressed into a plastic. Front gray/creme circle is a thin aluminum which you can pop off once it is removed. Shiny ring visible from front is NOT a plated plastic like in cars from 1980s but it is part of aforementioned plated brass piece. Drilling into it will be a significant effort.Shaft of the rotary encoder appears to be made of a stainless steel. So drilling THROUGH it while it is still on the panel is close to impossible. Drilling the set screw out may be possible but then burr and all that will likely cause it to bind even harder. Getting that off will require too much prying force for the rotary encoder to survive.If I were you, I'd stop right there and not attempt to remove the piece just for cleaning....

author: tkamiya
author_rank: Super Contributor
timestamp: December 22, 2020, 07:11:17 pm
content: I have pictures but forum is not allowing me to upload them. Weird!

author: Gregg
author_rank: Super Contributor
timestamp: December 22, 2020, 08:00:12 pm
content: Before screwing it up with heat or glue, try a left hand drill bit.

author: james_s
author_rank: Super Contributor
timestamp: December 22, 2020, 08:06:29 pm
content: Quote from: bdunham7 on December 22, 2020, 03:19:05 amFunny, that is almost precisely what I was going to reply with.

author: richnormand
author_rank: Unknown
timestamp: December 23, 2020, 12:02:43 am
content: I had good results with this on a Tek 7D20.Hex set screw was damaged from previous whatever (eBay purchased). Completely stuck and hex driver would then slip.Tried a Torx but it is really seized.Made a thin plastic square with a slot to the middle to clear the shaft and holding nut to insert under the knob and protect the faceplate in case I have to go medieval on it.Orient the plugin so that I can let some "Liquid Wrench" in the hole overnight, repeat the day after. No dice.Used a generous dose of "Super Cold" spay with a thin tube in the hole and waited for the whole area to freeze over. After about 5 minutes used a hair drier to warm the assembly quickly.On the second trial the Wera Torx got a good grip and got it. No damage to the front plate either, only a new set screw.Good luck with it, hope this helps.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 23, 2020, 01:42:26 am
content: I have had good success with a couple of drops of "Weasel Piss" on stubborn set screws - works better than Liquid Wrench and similar products.Be careful about spilling this on plastic though.

author: David Hess
author_rank: Super Contributor
timestamp: December 23, 2020, 04:46:16 am
content: Quote from: tkamiya on December 22, 2020, 07:11:17 pmI have the same problem with the forum all the time now.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 24, 2020, 11:54:22 am
content: I've had this problem a few times too. There is one thing to try before doing anything that will further round out the allen key hole.This trick comes from realizing that the grub screw isn't actually 'seized' (ie corroded in, where corrosion products have greater volume than the original metal, so the threads are seriously locked in.) Nor is it spalled (metal graunched off the threads, making a jam.)It's more likely just very tightly screwed in, ie there's a force where the grub screw tip presses into the shaft, and an equal force spread out over one side of the threads in the knob. That's ONE side of the thread, not both. Hence if the shaft could be magically removed (so no force anymore) the grub screw would turn freely, even with a rounded out allen key hole.But the thing is, you don't have to remove the shaft _entirely_. You just have to make it not quite so large, right where the grub screw touches it.And that is easy!For this you need a small pin punch (flat end), that fits in the grub screw hole. Best if it is a close fit, so the end rests on the top of the grub screw. Then arrange some side support for the knob, that can take a strong force without damaging the plastic. Scrap piece of wood, use a hole saw to cut a hole that pretty closely fits the circumference of the knob. Cut one side off so you have access to the grub screw hole. Get this support resting against something solid, or in a vice, take up shaft sideways slack so the bearing sleeve doesn't take the impact...Now whack the grub screw downwards into the hole, with a sharp impact from a small hammer on the pin punch.The aim is to drive the grubscrew end slightly into the shaft, deforming the shaft metal (typically brass) just a little bit. This relieves the screw pressure. It will also break any adhesion between the grubscrew and the knob threads.It's surprising how small an impact will work.Now the grub screw will be loose, and easily backed off enough to remove the knob.If you still have trouble turning it enough to remove the damaged grub screw entirely, once the knob is off you can turn the grub screw *inwards* more easily, till it falls out the central hole.

author: aqibi2000
author_rank: Regular Contributor
timestamp: December 24, 2020, 02:00:08 pm
content: Remember to make sure whatever you insert into the allen hole is FULLy BOTTOMED out.Make use of the Russian precision tool (hammer) with support on the other side of the knob to ensure all is well.

author: SilverSolder
author_rank: Super Contributor
timestamp: December 24, 2020, 05:13:44 pm
content: The hammer needs to be very light for this to work, it seems to me. Sounds a good idea.

author: james_s
author_rank: Super Contributor
timestamp: December 24, 2020, 06:15:26 pm
content: Another trick that can work in some situations, jam a torx bit or even a hex key in there, then fill the gaps with baking soda and use a syringe to dribble a bit of cyanoacrylate (super glue) in there to saturate the baking soda. It cures quickly into an incredibly hard substance, a trick I first learned to use as a filler while building model airplanes I've since used it in a handful of other applications. Of course you have to be very careful not to get any of the glue on the threads of the thing you're trying to get out, so best not to fill it all the way up to the brim.

author: TerraHertz
author_rank: Super Contributor
timestamp: December 25, 2020, 02:53:27 pm
content: Quote from: aqibi2000 on December 24, 2020, 02:00:08 pm"a small pin punch (flat end), that fits in the grub screw hole" - Actually I worded this poorly. I meant 'fits in the threaded hole in the knob'. The pin punch should sit on the top of the grub screw. The grub screw should be hardened steel, and should not deform.You'd be hard pressed to find a pin punch small enough to fit down the hex socket on the grub screw, and if it did then it would probably be too thin to transmit the required force.Re hammer size: I use a small tack hammer, with quite a sharp, fast hit. You only need to make a tiny deeper dent in the brass shaft where the grub screw is already dinked into it.

author: Runco990
author_rank: Frequent Contributor
timestamp: December 25, 2020, 05:13:10 pm
content: The punch method makes sense, I'll have to try that one next time I have a stubborn grub screw.Really hate those things.

author: cncjerry
author_rank: Unknown
timestamp: December 25, 2020, 11:26:26 pm
content: I think the best way to get it loose is with heat as previously mentioned.Take a tool, either hex or torx that fits snuggly in it, cut the 'L' part off and clamp it in a high wattage soldering iron. It doesn't need to be perfectly centered in the soldering iron but the tool needs to be clamped tightly in it. I had an older, high wattage iron with a large set screw in it for holding the tip. Once it gets hot, you might be able to twist it out with the bit in the soldering iron, should be able to at least break it loose. But if you heat it up it should come loose more easily with a modified easyout or another wrench.Prior to doing this, apply aluminum tape they use on HVAC tubing to protect all the plastic parts. If you have room, you might be able to stick a small tube cutoff down in the hole to protect the plastic around the hole in the knob.