Small Allen screw too tight to get out...

[basinstreetdesign]

You've probably all seen this:

I'm trying to repair an HP 1741A scope and I have to take the front knobs off to get one of the internal boards removed.  But the set screws that are used on HP & Tek scopes are very small.  They are .05 inch guys and can be very stiff to get turning.  Well a few of them are VERY stiff.  So much so that they are rounding my only Allen key.  And the screw sockets themselves are getting rounded.  I've heard that drilling it out a bit and then using an "easy-out" will do the trick.  But try to find one that small...  I don't think that's going to happen. 

Any suggestions?  Any advice is well appreciated.

[jcw0752]

Hi,
Sometimes when this happens to me I will dremel disk off the end of the allen wrench in order to get a fresh end. Try putting a little WD40 on the screw and let it sit for a while before you try again. You can also heat the screw slightly by putting an old allen wrench into the set screw and then heat the allen wrench so that heat is conducted to the screw. I usually use a solder gun to provide the heat. Be careful not to melt the plastic.  When you do try to loosen the screw again do not turn the allen wrench smoothly and easily but twist it in pulses stopping your torque just before the wrench rounds. Sometimes this provides an impulse force that better frees the set screw.
John

[tautech]

For the Timebase shaft remove the collars inside and withdraw the shaft out the front.

Which other assemblies do you need remove ?

[mrpackethead]

Sounds like you need a better set of hex keys.     Decent ones will not burr off like that!

[Falcon69]

if you've rounded the allen screw for the screw (not the wrench), then use a small dremel cut-off disc to put a slot on the screw head, then try using a precision regular screwdriver to back it out.

Alot of those screws have a lock tight compound on them, and they are hard to get out.

If that doesn't work, drill a smaller hole, rethread it with a left hand thread, screw (with left handed threads) in another screw with a hex head on it, and use a wrench to back it out.  When you tighten the screw with left handed threads, it will forse the orginal screw to thread counter-clockwise, backing it out.

[David Hess]

I just had this problem with the 0.050" set screw holding the fan in a Tektronix 465.  My solution is to take a sacrificial 1/16" hex wrench and grind down the flats slightly until it fits tightly enough to be tapped in.  It is difficult to see but the photograph below shows the result.

[Falcon69]

careful doing that however with a tapered grind like that. I've broken set screws in half doing that, then they are impossible to get out, as when you turn the set screw, the two pieces start to act like a compression fitting against the hole/threads they screw into. Kinda like how a one way bearing works.

[dcarr]

Don't know if this will work for allen screws, but it works great with phillips:

Buy a tube of valve grinding compound at the local auto parts store.  Dip your screwdriver/wrench in this prior to attempting to loosen the screw.  The gritty compound greatly increases the torque you can exert before the tool starts to slip.

David

[David Hess]

We just had this discussion over on TekScopes@yahoogroups.com and these were also recommended:

https://www.kctoolco.com/wera-135060-0-05-x-25mm-hex-bit/
http://www.miponline.com/store/mip9000.html

The 1/4" drive bit would not have worked in my case because of lack of clearance and I prefer grinding up inexpensive 1/16" hex wrenches anyway.

[tautech]

Specmaster had similar problems in this thread:
https://www.eevblog.com/forum/testgear/hp-1740a-on-the-bench-help-please/

In the end he broke the knob and dealt with the remaining boss.
The other option is to sacrifice the knob and get another from Sphere.
http://www.sphere.bc.ca/test/hp-parts/hpparts7.html

[Bushougoma]

I rarely use the L shaped hex keys anymore. The hex tools I use are made by Integy part number INTC22301.

They make quick work of removing knobs on old Tek gear and the tips are replaceable if need be. The handles are color coded the silver one is .05 and they do sell them separately.

I originally bought these because I had a stubborn knob on an HP 5316B counter that wouldn't come off. I stopped when I felt the L shaped hex key slipping found these and the hex screw came off like it was nothing.

[Alex Eisenhut]

Manufacturers should use Bristol drive for tiny set screws.

https://en.wikipedia.org/wiki/List_of_screw_drives#Bristol

I found one in some Tektronix plug-in and once I found the right key it worked perfectly.

[duak]

A camera repairman friend recommended using lighter fluid or, in a pinch, gasoline on fine threads because it evaporates cleanly.  WD40 contains some oils that leave a sticky residue that has to be cleaned off when done.  I've never tried it on an hp knob so don't use too much until you confirm it is safe.

Cheers,

[basinstreetdesign]

I rarely use the L shaped hex keys anymore. The hex tools I use are made by Integy part number INTC22301.

They make quick work of removing knobs on old Tek gear and the tips are replaceable if need be. The handles are color coded the silver one is .05 and they do sell them separately.

I originally bought these because I had a stubborn knob on an HP 5316B counter that wouldn't come off. I stopped when I felt the L shaped hex key slipping found these and the hex screw came off like it was nothing.

Thanks for this, Bushougoma.  I'll keep an eye out for them in Canada.  Getting them from the 'bay would cost me about CDN$55 for the sake of one screwdriver, so I think that's out for now.  Maybe if nothing else pans out...

As for grinding down a larger key to get one that JUST taps in probably would result in my other keys ground down to a nub and never a usable hex shape.  WD-40?  Why make it more slippery?  I just might try the valve grinding compound, though.

As for just sacrificing the knobs (there's two at risk, here) and grinding off the bushing, and ordering new ones from whoever, well that's out for sure.

The knobs that are giving me trouble are the Volts/div knobs, both of them on the HP 1741A.  I want to get the vertical amp board out so I can get at the CHOP/A/B/ALT switches.  They're buried under the vert board.  The ALT button is sticking too far out for some reason and I cant use it.  I need to get that switch working again.  BTW: the real reason I opened this scope up is the delayed sweep doesn't run.  So I guess I'll attack that until I can fix the knobs and the ALT button.

[David Hess]

As for grinding down a larger key to get one that JUST taps in probably would result in my other keys ground down to a nub and never a usable hex shape.

I have done it with a file before but what has worked best for me is to securely mount my Dremel as a small fixed grinder with the flat end surface of a grinding wheel.  A cutoff wheel will work also.

https://www.amazon.com/Dremel-85422-Silicon-Carbide-Grinding/dp/B00004UDKE
https://www.amazon.com/Dremel-Aluminum-Oxide-Wheel-Point/dp/B000683PCG

I like the inexpensive L shaped hex keys because I can always grind the end off to true it up.

[alsetalokin4017]

if you've rounded the allen screw for the screw (not the wrench), then use a small dremel cut-off disc to put a slot on the screw head, then try using a precision regular screwdriver to back it out.

Alot of those screws have a lock tight compound on them, and they are hard to get out.

If that doesn't work, drill a smaller hole, rethread it with a left hand thread, screw (with left handed threads) in another screw with a hex head on it, and use a wrench to back it out.  When you tighten the screw with left handed threads, it will forse the orginal screw to thread counter-clockwise, backing it out.

I'd love to see the video of someone doing either one of these with a tiny 0.050 setscrew recessed down inside the knob which is mounted on the control shaft up against the front panel of the scope ....              


basinstreetdesign, get thee to thy nearest RC helicopter hobby shop, where you will find individual WIHA branded 0.050" Allen key tools similar to the Integy tools shown above. Should cost about 5 dollars for the one you need. Will it work? Maybe... try the valve grinding compound trick.

[HighVoltage]

There is a simple trick that has worked for me each and every time:

Instead of using a hex tool, use a tapered torx bit (Most of them are tapered)
If a tapered torx with hand handle will not grip either, use a short torx bit and pliers to push the torx bit in to the screw. At the same time apply torque with a wrench and push the bit in with the pliers. I have special soft pliers to not damage the knob.

This way I have removed the most difficult hex set screws, every time!

[VK5RC]

I have an ancient bottle of Penetrene, the classic technique was that and heat,  don't know if they still make it.
50/50 Acetone and Auto Transmission Fluid said to be pretty good (what plastic knob!!!)

[basinstreetdesign]

basinstreetdesign, get thee to thy nearest RC helicopter hobby shop...

Thank you very much for this.  I found the Integy drivers at a shop in town.  I just bought them and used the .05" one.  It worked like a charm on the screws that were rounding my cheap keys.      Also allows me to clean the front panel.

Thanks also to Bushougoma for recommending this brand. 

I fixed the button issues and am now trying to figure out why the delayed sweep wont run...

P.S.  The set still cost me CDN$60

[TheSteve]

The price sucks but they will come in handy over and over, as time goes by you'll wonder how you survived without them. I've had a nice set of hex drivers for 15 + years simply because of RC car and helicopter assembly.

[KL27x]

https://www.amazon.com/Chapman-MFG-1313-Standard-Spinner/dp/B0000WSYWE/ref=sr_1_2?ie=UTF8&qid=1512016589&sr=8-2&keywords=chapman+hex+key

The case looks cheap, but it's actually just right.

I love this set. One day I'm fixing something and my GF sees and instantly recognizes it. If you believe her, all the aircraft mechanics use these. She worked at an airline for many years managing mechanics scheduling.

You can't reverse the ratchet. You have to flip it over. But it's smaller profile for getting into tight places and it has higher resolution ratcheting than the sub 10.00 garbage you can get in similar form factor. That and the bits are stellar. I have used the 0.05" hex before and I'm amazed they make screwdrivers this small, lol. And I'm surprised how well it actually works with a good bit and screw. Plenty of torque available. Two of these screws are the only thing holding the breech and back of the barrel to the receiver on a Crosman 1377 / 1322. Got off my butt and took out a family of tree rats a bit ago, after my GF started threatening to call the overpriced exterminator.

First time I looked at this screw, I thought it can't possibly be a driver head. That it was a rivet or something. When it fit and worked, it felt a little bit like magic.

[Cubdriver]

I'll second that - Chapman makes good stuff.  I got this set in 1984 when I started working at National Semiconductor.  33 years later ( ) I'm still using it.


(And somehow have lost only one bit - the small flat blade, which I rarely have call to use.)


-Pat

[cncjerry]

Heat is your friend.  Most of the time the issue is loctite or the equivalent.  The first thing to do with a tight setscrew is to heat it up with the tip of a soldering iron (assuming it's stuck in metal).  Anyone that has built and flown RC Helicopters knows this trick and they would vibrate out just about anything that wasn't sealed with loctite.   Heat will break loctite as well as superglue.  Also, superglue is a great substitute for loctite but you have to make sure you have all the oil off the mating parts.

Another trick if you can't get in there with a soldering iron is to use a small butane torch to heat the wrench while turning.