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Tips needed on this TYPICAL pot metal tonearm
http://forum.talkingmachine.info/viewtopic.php?f=2&t=34033
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Author:  briankeith [ Tue Feb 06, 2018 5:07 pm ]
Post subject:  Tips needed on this TYPICAL pot metal tonearm

Typical Columbia pot metal frozen tonearm - tried freezing it, Kroil oil, Mouse Milk aviation oil, froze then heated only the mounting base - still won't budge an inch LOL. Goes up and down fine but ZERO left to right at the motor board mounting flange. Reproducer came off just fine for a rebuild. Tips?

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Author:  De Soto Frank [ Tue Feb 06, 2018 7:27 pm ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

First tip: be patient.

Harvey Kravitz (phonofreak) might have some wisdom...

I have rescued one or two of these.

This is the first-generation cast Columbia arm / base, with the limit screw for the arm, and another one for the motorboard flange.

I would remove the limit screw from the motorboard flange, and soak some Kroil in there, same from the underneath side of the same joint.


If there is any trace of movement in that lateral joint, you are a big step ahead.

I would fasten the motorboard flange securely to the work-bench using the factory screw holes, then GENTLY try to work the arm from side to side, looking for any trace of movement between the elbow and the flange.

If there is, just keep working it back and forth, gently, repeatedly... while you're watching TV or similar.

If you find yourself gaining more range of movement, flood joint with more Kroil / PB Blaster, and keep working it.

If the elbow starts to work up and out of the flange, then try to work it down again, and keep working it sideways and up & down.

If you get tired, flood it again with solvent, and walk away for the night, or an hour or so.



If you get no perceptible movement at all, if you can get some dry-ice (WEAR HEAVY GLOVES!), take a small-ish chunk, and hold it against the elbow, while working the arm laterally. After 20-30 seconds, remove the dry-ice, and try to move arm again, as things come-back to room temp.


The most recent one I worked-on was the later cast arm, where the arm is secured to the elbow via an internal snap=ring, and will not separate for ANYTHING. Up & down was stiff, side-to-side was very stiff.

I was able to flip the arm upside-down and flood with Soft-Scrub abrasive cleaner, as a lapping compound, and work the joint around. It took a LONG time, several episodes over several days, but it finally loosened-up enough to drop / swing under its own weight. I flushed the cleanser out thoroughly, oiled it up, and it has been okay since.

Patience is critical.

These can be buggers.

Reproduction elbows are available, but quite pricey.

Author:  Phonofreak [ Tue Feb 06, 2018 8:15 pm ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

Frank, you took the words right out of my mouth. I couldn't explain it any better, or so eloquently. :mrgreen: :rose:
Harvey Kravitz

Author:  De Soto Frank [ Wed Feb 07, 2018 10:11 pm ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

Thanks for the kind words, Harvey !


I don't know which models and for how long, but the last Columbia arm I worked on (pre WW I "Jewel" or "35", the softscrub lapping treatment ), the motorboard flange was cast-iron or steel: it was very magnetic. I doubt the thin layer of nickel plating would impart enough magnetic property to be able to hold a magnet.

Which is to say, that if steel / ferrous, the flange itself should be "stable", and the pot-metal elbow would be the culprit... and also that the flange could take some heat, as opposed to the pot-metal elbow.

I will check-out a few of my Columbia machines to see if I can ID that flange material.


:coffee:

Author:  briankeith [ Thu Feb 08, 2018 10:34 am ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

I'm still working at it - so far no luck.... BUT at least I didn't pulverize the elbow... (yet) :lol:

Author:  De Soto Frank [ Thu Feb 08, 2018 11:20 am ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

I might have tried a process of "thermal shock" to see about breaking mine loose: alternating between boiling water bath and ice-water bath.


I think that might be a more risky approach ?


I'd hate to see you destroy the elbow.


On the set-ups were the tone-arm has a limit-screw, the arm is brass, the elbow is pot-metal, and there are "bayonet lugs" or "ears" on both pieces. Removing the limit-screw allows you to swing the arm to vertical ( 12 o'clock ), and the a wave-spring should pop it out of its seat it the elbow.

The weak spot would be the ears on the pot-metal piece.



On set-ups where the arm has no limit-screw, and is secured by an internal snap-ring, both the arm and the elbow are pot-metal.


Keep after it. Take frequent breaks. ;)


:coffee:

Author:  De Soto Frank [ Thu Feb 08, 2018 11:23 am ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

Harvey, and others - Have you ever carefully run a hacksaw-blade in the throat of the elbow, carefully cutting an axial slot through the pot-metal neck, allowing some flex / relieving pressure of the swollen pot-metal ?


I've used this trick on machinery to remove stuck bushings...


Sounds almost like an act of desperation, but might not be as bad as crushing an elbow from repeated torque ?

Thoughts ?


Frank

Author:  briankeith [ Thu Feb 08, 2018 11:35 am ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

Yes, the limit screws have been removed. The arm is back in the freezer after two days soaking in Kroil....

Author:  De Soto Frank [ Thu Feb 08, 2018 11:39 am ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

They are buggers.

In the 1920's, automakers used die-casting (pot-metal) to make all sorts of complicated parts: vacuum-tank tops, generator end-frames, and carburetors to name a few.

The alloys were problematic, and warping / crumbling was a problem in short order.


Many cars from the 1920's are sidelined due to decaying pot=metal parts for which there are not yet replacements.

Author:  JerryVan [ Thu Feb 08, 2018 1:28 pm ]
Post subject:  Re: Tips needed on this TYPICAL pot metal tonearm

You can try penetrating oil, but it won't make the pot metal elbow any smaller or any less tight. It's not "stuck" in that there's old, dried oil, rust, or anything like that.

The elbow must be pressed out. Don't try pulling or rotating, it will only break. Remove the retaining screw, or any other retaining means. Turn mounting flange over and look inside. You'll see the end of the elbow down inside the flange. You'll need a piece of metal, or hard wood, that will fit closely to the hole in the flange. The metal should rest squarely and evenly against the end of the elbow, but slide easily in the flange. Place the flange, upside down, in the open jaws of a vise such that the flange is supported by the jaws. You're not looking to clamp this in the vise, you just want to support it. Probably should put a towel over the vise jaws first to help protect the flange's top surface. While a helper is holding everything nice and even over the vise jaws, hit the piece of metal with a rawhide or rubber mallet to push the elbow out of the flange. It's best to not use a steel hammer here, unless maybe you're using hard wood instead of the metal piece to drive the elbow out. The shock of using a steel hammer may cause the elbow to shatter. Start with soft bows, then work up as needed to remove the elbow, keeping in mind that you're also hitting against the cast iron flange of the base.

- Of course, it would be best to use an arbor press to do this, but most folks haven't got one at their finger tips.
- As for finding a metal piece that fits nicely within the flange piece, go through your socket wrench set and look for a socket who's outside diameter may be just right. (Surprising how often that works!)

Once it's apart, you can have the base flange inside diameter opened up until the elbow fits nicely. The hole can be enlarged in a lathe, or carefully using a drum sander on your drill press and hand drill. In other words, you can re-use the elbow!

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