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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 4:01 pm 
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Perhaps take another look at the original problem, the binding of the outer scale against the panel...
Sometimes when the obvious solution is not obtainable, you need to look at less obvious solutions.
How much clearance do you need to eliminate contact?

Rather than moving the dial on the shaft, can you bend the ring scale slightly to obtain enough clearance?
This could be a possibility if the distance required is small.

What about moving the innards of the generator frequency control bracket slightly to move the shaft and dial outwards/away from the front panel?

Of course, you may want to exhaust all options for loosening the set screw before moving on to other alternatives.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 4:54 pm 
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processhead wrote:
Perhaps take another look at the original problem, the binding of the outer scale against the panel...
Sometimes when the obvious solution is not obtainable, you need to look at less obvious solutions.
How much clearance do you need to eliminate contact?

Rather than moving the dial on the shaft, can you bend the ring scale slightly to obtain enough clearance?
This could be a possibility if the distance required is small.

What about moving the innards of the generator frequency control bracket slightly to move the shaft and dial outwards/away from the front panel?

Of course, you may want to exhaust all options for loosening the set screw before moving on to other alternatives.


Paul, I've considered that, but frankly I don't trust my mechanical skills to the point that I might really screw up the skirt--make it so cockeyed that things are worse and not better.

Along the lines of johnnysan's suggestion, I'm going to try to devise a means of applying a constant force rather than trying to rely on sporadic brute force.

I'm thinking about drilling a hole in the end of a length of thick oak dowel that would fit onto the exposed (short) arm of the allen wrench, to gain leverage (akin to Phillip's suggestion above). Then I can try to find some combination of vise grips and metal tubing that further extends the arm and can be wedged into an angle that applies a turning force to the wrench.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 5:04 pm 
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I have used a hollow shaft nutdriver many times for added leverage on an allen wrench. Anything with a small ID and hollow that's stiff enough should work.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 5:19 pm 
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Screw it (not) :roll: leave it be...
The Allen screw probably has cracked. Such screws are hardened and only a tougher than average drill bit will cut...
Slip a piece of your favorite, tough, but thin 220 sandpaper between the skirt of the knob and the dial, sandy side toward the knob. You know the drill, sand until happy, blow out the dust and call it done...

YMMV

Chas


Last edited by Chas on Feb Fri 02, 2018 5:39 pm, 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 5:25 pm 
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Just a quick comment on allen wrenches. There allen wrenches, and there are cheap allen wrenches. If you use a cheap one, it's likely to round off in the hex, bend, snap, or do any number of unpleasant things. Make sure you use a quality tool.

One other idea ... if you can obtain an "easy out" of sufficient small diameter, you could try that if all else fails. Be advised though, this is a last resort issue as it will destroy the hex socket in the setscrew. The plus side... it allows considerably more force to be applied.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 5:50 pm 
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Location: Potomac, Md.
pixellany wrote:
Is this the style you have?
Attachment:
200CD_dial.jpg

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....;)


Mark, I assume it's the same, since your photo shows a 200CD. The case for heat, made by several on the FB vintage test equipment page, was that it might help the PB Blaster work into the threads.

I've tried the hammer.

See toward the end of the thread for the approach I'll try later today.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 5:54 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Potomac, Md.
Chas wrote:
Screw it (not) :roll: leave it be...
The Allen screw probably has cracked. Such screws are hardened and only a tougher than average drill bit will cut...
Slip a piece of your favorite, tough, but thin 220 sandpaper between the skirt of the knob and the dial, sandy side toward the knob. You know the drill, sand until happy, blow out the dust and call it done...
YMMV
Chas


May wind up doing that, but knowing me I can't see how I'd avoid scuffing up something I don't want to scuff up, and not accomplishing what I want to accomplish besides.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 7:08 pm 
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Avery wrote:
pixellany wrote:
Is this the style you have?
Attachment:
200CD_dial.jpg

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....;)


Mark, I assume it's the same, since your photo shows a 200CD. The case for heat, made by several on the FB vintage test equipment page, was that it might help the PB Blaster work into the threads.

I've tried the hammer.

See toward the end of the thread for the approach I'll try later today.

All 200CDs are not the same in this regard--I don't recall any details, but it's out there in Googlespace....If it is like mine, loosening those set screws will not allow you to move the disk in and out. For that, you will need to adjust something inside.

I'll try to find something about the different mechanisms...

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 7:12 pm 
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pixellany wrote:
All 200CDs are not the same in this regard--I don't recall any details, but it's out there in Googlespace....If it is like mine, loosening those set screws will not allow you to move the disk in and out. For that, you will need to adjust something inside.

I'll try to find something about the different mechanisms...


Sheesh. So I may have been wasting my time. But the disk is attached to the knob, and the knob's position on the shaft is set by the setscrews, no?

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 7:23 pm 
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Location: Sunbury, Ohio 43074
I'd look around for a shaft stretcher. They can be found in Home Depot, next to the wire stretchers, and the wind shifters :-D

Seriously though ... you may have better luck adjusting something inside the instrument... perhaps enlarge some mounting holes and use washers to allow a bit of shifting

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 7:34 pm 
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Location: Albuquerque, NM 87123
Avery wrote:
pixellany wrote:
All 200CDs are not the same in this regard--I don't recall any details, but it's out there in Googlespace....If it is like mine, loosening those set screws will not allow you to move the disk in and out. For that, you will need to adjust something inside.

I'll try to find something about the different mechanisms...


Sheesh. So I may have been wasting my time. But the disk is attached to the knob, and the knob's position on the shaft is set by the setscrews, no?


No, the knob is separate (look at the picture posted by pixellany). The dial is mounted with a large washer held on by 4 screws. Once you remove that you will see how it's binding.

PLEASE!!! DON'T try anything like sanding or bending metal. You also can't move the internal structure of the variable capacitor or the gear mechanism (which is cast iron). Once you loosen the dial plate the fine tune knob has to come out (it just pulls out). Be careful with the dial light crystal as it can be broken.

PLEASE..... Get a good set of allen wrenches.


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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 7:54 pm 
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Okay, Johnny. I didn't want to bend or sand anyway. And I won't look for the answer inside. Finally, assuming my 200CD is the same as Mark's, I'll keep trying to loosen those darn setscrews.

A few minutes ago I found a short length of wood with a hole about the size of the allen wrench conveniently drilled in one end. It's been slipped over the short end of the engaged wrench, torque applied, and it's being held in that position by a spring clamp on the back side of the front panel.

We will see what happens.

Meanwhile I discovered that I CHIPPED THE KNOB during my hamhanded machinations. Damn! My part unit 200AB has the same diameter knob. If it can come off more cooperatively than the one on this unit, and if the design is the same, then I'll sub it for the one I chipped. If not, I'll see if I can epoxy the chip back in place--if the knob ever comes off, that is.

I really appreciate all the tips I've received, especially from Johnnysan, who has direct hands-on expertise. John, the wrench hasn't broken or bent yet. If it does, is there a high-quality allen wrench provider that sells in single sizes?

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 8:01 pm 
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OK...
I can't find anything about different mechanisms---maybe I was hallucinating (it certainly would not be old age.....;) )

Here is a picture of the shaft end where the disk and dial mount:
Attachment:
200CD_dial-shaft_SM.jpg
200CD_dial-shaft_SM.jpg [ 22.7 KiB | Viewed 500 times ]

The disk is mounted with 4 screws--and slips when you loosen the screws (this is how you set the low-end frequency calibration--see the manual)

The knob goes on the shaft in the center (1/4", i think). When you remove the knob. you still have the disk fastened to the hub with no axial adjustment.

SO---i think the only axial adjustment is inside

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Fri 02, 2018 11:44 pm 
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Hey Pix, yeah, you're right! Pulling the main knob won't do anything.

The shaft of the vernier is supposed to float in and out from the panel. There should be a coil compression spring around the shaft behind the rear vernier drive wheel that pushes it against the rear of the dial plate. If you remove the vernier knob and the top drive wheel, you should be able to push the shaft in toward the panel.

Is the vernier shaft bound up? Does it turn freely? Does it move in freely? If not, try some PB Blaster on the bearing for the vernier shaft. Once it's free, put some oil on it. There may be an oil port on the casting behind the front panel.

BTW, epoxy works well for gluing bakelite knobs back together.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Sat 03, 2018 12:25 am 
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FWIW - I use Kroil or SiliKroil penetrating oil on this kind of job. With heat applied to the allen wrench, plus time for the oil to soak into the warm joint.
-Chuck


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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Mon 05, 2018 4:08 pm 
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I used to have a part time job stripping equipment. Heat often works when nothing else will. The set screw is steel and the collar is brass, they have different coefficients of expansion so they move against each other. That little shift will break corrosion, galling etc. and allow a bit of lube to seep in. I've had setscrews that would snap a good wrench feel finger tight after heat and lube.

If it were mine I would insert spray liquid wrench, insert allen wrench, twist with pliers and apply heat with a pencil flame propane torch. Maybe use a piece of aluminum to protect the dial. I would be very surprised if this did not loosen the screw and leave the rest undamaged.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Mon 05, 2018 7:05 pm 
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K7MCG wrote:
FWIW - I use Kroil or SiliKroil penetrating oil on this kind of job.

Kroil is the industry standard penetrating oil.
It's what we use when rebuilding machinery.

- Leigh

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Tue 06, 2018 2:56 pm 
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Transmission fluid / acetone mixture is old as the hills and works. But as noted the acetone makes it not suitable with plastics nearby.

Because 'allen' screws are VERY hard standard drills and easy-outs just polish the finish. Left had drill bits same thing. IF an allen is really stuck cutting tools just polish the surface. I have in a couple of instances used up a LOT of bits and finally removed enough material but the result is messy and usually also chewed up the threads at least some.

Carbide drill bits work. But are brittle and hard to use freehand.

The conversation here suggest the dial had been warped. Judicious application of force to 'unwarp'??

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Tue 06, 2018 10:39 pm 
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Oh, my head...

1. Mark (pixellany) is right. Even if I managed to remove the frozen set screws, that would not permit me to reposition the shaft, as I thought I'd be able to do.
2. I managed to break off a piece of the knob while attempting to loosen the set screws with a reverse thread screw extractor.
3. PB Blaster judiciously applied to the shaft of the tuning capacitor and to the shaft of the vernier drive, followed by a series of small amounts of sewing machine oil, freed up both to a considerable degree. There is still some minor scraping, but it is tolerable.
4. I repaired the knob so it's hard to tell it was broken unless you're looking for it.

but...

5. The power transformer primary seems to be open. Checking across the AC plug with the switch on shows infinity, and yes, the fuse is good. I'll check beyond the switch later to see if that's the problem, but if the transformer is blown I'm not spending more time with the unit, which is too bad. It's beautiful inside. But it will become a parts donor.

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 Post subject: Re: Ideas, please, for loosening setscrews on HP-200CD main
PostPosted: Feb Wed 07, 2018 1:16 am 
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Greetings to Avery and the Forum:

If your power transformer primary is open, that will be the first one I have ever heard of. However, I have a couple of HP 400 VTVM's and a 200-CD.... all of them have flakey on-off switches. The internal grease dries up and the toggle flips but the internal slide does not move. Usually, this is detectable by feel. The cure is to set the instrument on its back and dribble some WD-40 or light oil into the spherical bearing at the base of the toggle handle. Operate the switch a few times and apply more oil. Do this a few times and the switch will usually recover.

Good Luck,

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