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 Post subject: Ideas, please, for loosening setscrews on HP-200CD main knob
PostPosted: Feb Thu 01, 2018 9:19 pm 
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Location: Potomac, Md.
I'm digging into a 200CD audio generator that's been sitting on the shelf. I want to move the frequency control knob out a bit because the edge of the dial skirt is binding against the inner part of the vernier drive. Don't worry if you can't visualize it--the important thing is that I need to loosen the two setscrews holding the knob in place in order to do that. The setscrews take a 5/64" Allen key. I have one with a long shaft that makes it all the way in. It's a long way.

The setscrews won't budge.

I have tried every trick I could think of. Dribbled PB Blaster down the shaft of the wrench onto the setscrews. Waited a few minutes and tried to loosen them. No luck. Reapplied penetrant, let it sit overnight. No luck. Tried a quick clockwise move (tightening) followed by steady force in the other direction. No luck.

I might have better luck with a T-handle, but all the Allen sets seem to start at 3/32, which is too big. I can see why--5/64 is pretty small. A T handle would make it easy to apply too much force and snap it.

Several members of the Vintage Test Equipment FB page advised applying heat. I'm not sure why that would work, since it would expand the setscrew, and I can't heat the setscrew directly without melting the knob. I've also been advised to heat the wrench, and use that to transfer heat to the setscrew. How would a thin shaft retain and transfer enough heat to have any effect?

Very frustrating.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Thu 01, 2018 9:35 pm 
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Location: Canandaigua, NY
I've never had one that stuck. I doubt you could get much heat into it via the wrench. Probably better luck dipping the wrench in liquid nitrogen and shrinking the screw a bit. I'd grind the end of the wrench so the edges are as sharp as they can be, maybe stick a rod in the hole and rap it a bit, then go for broke with the wrench, no pun intended. If it strips out, you'll have to drill it, and that might be a project in itself to get a drill long enough or extend one. Maybe best to live with the position error?


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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Thu 01, 2018 9:44 pm 
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Location: Potomac, Md.
Hmmm, where'd I put that liquid nitrogen... :?

I wouldn't mind leaving it alone if the problem was minor position error. But the problem is that the dial won't turn smoothly because the edge is binding up on the inner bushing of the vernier drive.

I do NOT want to turn it into a parts unit because I can't get a couple of setscrews loose!

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Thu 01, 2018 9:53 pm 
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I've never had to resort to it, but I'd try the heat. I think the idea is to get the set-screw to move a little with respect to the threads via thermal expansion, and hope that breaks it loose. I'd heat the allen wrench with my Weller soldering gun while applying torque.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Thu 01, 2018 10:00 pm 
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you could try heating, or even cooling, any part of the screw/shaft/knob/etc assembly, perhaps multiple times. Heat gun on medium, freeze spray, alternately applied. Or randomly applied. Heat one part, cool the other.

usually for this kind of thing I'll fiddle with it for a bit and then get out the sawzall, 16lb sledge, or acetylene torch :roll:

Seriously tho, heating/cooling might eventually loosen something enough to get the setscrew to budge. I'd give that a shot first. If not, it's drill time.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Thu 01, 2018 10:39 pm 
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You'd be surprised at how much heat you can transfer through the allen wrench to the setscrew, I have done this several times using a standard Weller 140 watt gun. You have nothing to lose, just be careful to use a good allen wrench so as not to strip out the recess in the screw.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 12:43 am 
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End of allen wrench should be totally fresh like stated above. Long end of the wrench into the hole. Then grab the small end of the wrench with old fashioned pliers and slowly twist/crank. If the set screw gets messed up, try to find metric size that's close. Sometimes the wrenches with the ball on the end work better - sometimes not


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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 2:24 am 
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Location: Albuquerque, NM 87123
I have worked on many of those 200 series HPs, and the problem of frozen set screws is not new. I have found that only the L shaped allen wrenches will work and often a steady consistent force will eventually cause the set screw to break loose.

If the shafts will not turn freely you may need to use a propane torch to loosen them.


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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 3:22 am 
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Quote:
Sometimes the wrenches with the ball on the end work better - sometimes not


Sometimes the ball breaks off - then you're really in deep doo-doo :(

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 3:36 am 
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Location: Potomac, Md.
Johnnysan wrote:
I have worked on many of those 200 series HPs, and the problem of frozen set screws is not new. I have found that only the L shaped allen wrenches will work and often a steady consistent force will eventually cause the set screw to break loose.

If the shafts will not turn freely you may need to use a propane torch to loosen them.


I've given up for the night. I used a soldering gun to heat the allen wrench while it was engaged, gave it a couple of sharp tugs when done, nothing. Let it cool, tried again, nothing.

The shaft turns freely. It's the skirt that's the problem, scraping on that inner vernier bushing. All I need to do is more the knob out maybe 1/16 inch or less.

I'm losing what little is left of my hair.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 3:42 am 
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majoco wrote:
Quote:
Sometimes the wrenches with the ball on the end work better - sometimes not


Sometimes the ball breaks off - then you're really in deep doo-doo :(


That's why you want to use a new fresh wrench. If you exert enough force to bust a ball :mrgreen: that's too much force.
Sometimes the bottom of the set screw hole is tapered too much - that's when the ball type work the best.
I used to repair/maintain/calibrate SMT machine feeders. Everything was put together with set screws. I'm sure I've loosened and tightened over a million. I always got 'em out one way or another.


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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 3:46 am 
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Location: Potomac, Md.
mgrant wrote:
majoco wrote:
Quote:
Sometimes the wrenches with the ball on the end work better - sometimes not


Sometimes the ball breaks off - then you're really in deep doo-doo :(


That's why you want to use a new fresh wrench. If you exert enough force to bust a ball :mrgreen: that's too much force.
Sometimes the bottom of the set screw hole is tapered too much - that's when the ball type work the best.
I used to repair/maintain/calibrate SMT machine feeders. Everything was put together with set screws. I'm sure I've loosened and tightened over a million. I always got 'em out one way or another.


Well, you're only a few kilomiles from me. Want to stop by tomorrow and take care of this critter? I'll cover all expenses up to at least 10 bucks.

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Avery W3AVE


Last edited by Avery on Feb Fri 02, 2018 4:21 am, edited 1 time in total.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 4:13 am 
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Johnnysan wrote:
If the shafts will not turn freely you may need to use a propane torch to loosen them.

Yes, the lubrication turns to glue :-(

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 4:32 am 
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How come no one's suggested WD-40? You've got nothing to lose by trying it in the setscrew shaft, Avery.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 4:35 am 
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Is this the style you have?
Attachment:
200CD_dial.jpg
200CD_dial.jpg [ 48.17 KiB | Viewed 439 times ]

If so, heating the set-screws will cause them to be even tighter in the brass bushing. For heat to work, it has to act to increase clearance

Stuck screws are freed up by some combination of heat, chemicals, and force (which could in turn be shock). For example, stuck brake drums are classically removed using a torch + a hammer.
I would be tempted to insert the allen wrench and then tap on it with a small hammer. Can't hit it too hard or you will bend something.

If you have a different style, I'm clueless....;)

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 4:37 am 
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+1 to fifties---you can add WD-40 to my procedure

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 4:49 am 
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fifties wrote:
How come no one's suggested WD-40? You've got nothing to lose by trying it in the setscrew shaft, Avery.

He's already tried PB Blaster. I doubt WD-40 would do any better.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 5:17 am 
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Greetings to Avery and the Forum:

Please find following a comparison test of various types of penetrating oils / fluids.

http://3cyl.com/mraxl/TomsTips/penetrating_oil.htm

As you will see, by far the best is a 50-50 mix of automatic transmission fluid and acetone.

Be careful with this; the acetone will do bad things to the knob plastic and the ink markings on the dial.

Other than this, differential temperature, mechanical shock and a high-quality allen wrench that can handle lots of torque are your best options.

Regards,

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 5:22 am 
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Just looked at photos of HP-200CD. Yeah, it's easy for me to say "do this, do that", but you're the one sweating bullets over it.
So these set screws might have blue or red thread locker on them. Heat is supposed to loosen that but you don't want to melt the knob. I guess you could spray more PB Blaster in there and give it couple weeks. Besides what I wrote earlier, the only other thing I can think of is to grab the shaft behind the face plate and try to lightly rock the knob back and forth. It might release some tension on the set screws. Of course you don't want to booger it up.


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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 11:02 am 
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Location: Albuquerque, NM 87123
Trust me, no amount or type of lubricant will get into the threaded portion of the set screw. The long L shaped allen wrenches are the only ones that will work. One thing I should have mentioned is that trying to tighten the screw then loosening sometimes works better. If the OP doesn't have a good set of allen wrenches then now is a good time to get it.

I have worked on many of these.


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