Help with TD-160 tuning/suspension (both subchassis and motor spindle).

Ok, all signs point to a warp in the outer platter...it is a slight dish warp of sorts, where if laid upside down on a flat surface, pushing down near the warped area will slightly lift the other side of the platter. Pushing down in the good areas does not do this. The sub-platter and spindle look good and show no signs of trouble.

Unfortunately, if this somehow happened in shipping, I have no recourse for damages because I've had the table for too long now and just now noticed it. No damage whatsoever to the rest of the table though...

So the options are to try and have the platter straightened back flat on top, or find another platter. Since I'm on the hook for the bill, I obviously want to go with the most economical option.

Who would I call? There is a good amount of aerospace industry in my area, so there may be some machine shops or fab shops worth trying? I just fear it will be expensive to fix. But I'm also afraid of a replacement platter being damaged in shipping and being back to square one.
 
Obviously, I'm not in a position to recommend anybody on your side of the world. But I wouldn't be too worried about getting a warped second hand outer platter. This sort of damage is pretty unusual, and is unlikely to happen during transport. Personally, I'd be more worried about getting the old one back in perfect shape for a reasonable fee. Mostly because I don't have shops of that caliber around here.
 
Ok, I'm back with more questions.

I haven't tried every source yet, but I've had one shop turn me down so far (they did not see it/I asked over the phone - maybe they assumed it was something thinner/lighter?).

So the zinc alloy is fairly soft on these? Can it be straightened without heat?

I'm wondering if a flat surface and a rubber mallet might suffice? With careful strikes on the bottom side of the platter while laid with the flat side down?
 
I've never had to adjust any of these thick zinc cast platters. But I have done similar jobs on thinner aluminium ones, e.g. a Thorens TD-124 top platter which i got from an error of ±2 mm to ±0.04 mm - from junk to perfectly OK. It should be doable, but you won't get there the way you describe.

I would suggest something like this: First you need to know that your work surface really is plane. Check it with rulers along all sides and diagonally. Locate and mark up the fault line across the platter. The trick your plan is missing is that you must be able to bend the platter a smidgeon further than where you want to get it: when you bend it, it will recoil a bit afterwards. If you just try to do the job over a flat surface, the rebounce will never allow you to get where you aim. You need to place a thin strip of cardboard, plastic or something similar along the fault line, to "bend" the platter over it. The strip cannot be metal or anything hard enough to leave marks on the soft zinc alloy of the platter, and of course must be thin enough to not allow for an over-compensating while you work. I would start without any hammers or mallets, instead trying to massage the platter in shape by hand. That way you can apply the force over larger areas, with a smaller risk of cracking the alloy. Don't expect to get it right at once - you probably will need to work on it for quite a while.
 
Flat reference surface is definitely needed here. Good table saws with a large iron top plate are generally decent enough but confirm first with a known good straight edge.
 
So I'm back with an update...

I called around but couldn't find anyone in my area to take on the job - so I caved and bought another platter online (I still held onto the original in hopes of possible future repair).

The new platter is definitely a significant improvement in flatness, but I can tell it's not absolutely dead-on perfect (but it's close). It sits flush with the sub-platter and all looks well when playing a record on it, but a very small amount of wobble can be seen with the platter inverted (though nothing like the video in my previous post). FWIW, my suspension adjustment is likely not 100% spot-on.

I guess I'm wondering...is this an acceptable platter, or should I send it back?

Another FWIW - the new platter has improved the speed performance to be more accurate (both measured and to my ears).
 
Since we don't have any measurements I can only give a very vague answer, but I wouldn't be concerned about what you describe. Most of the "uneven" platters I've seen only appear to be so, due to uneven surface finish along the edges. As you describe it, the small deviations will get evened out in practical use by the rubber mat and the warps on the LP:s. Avoid the rabbit hole of audiophile perfectionism, if possible.

If you still worry, try the top side of the platter on some flat surface you have around; e.g. a glass table or suchlike. (If you use a glass table, clean up any grime before rotating anything...)

If you find some high point(s), try rotating the platter a bit, to see if it follows the rotation. If not, it is in the table. If it does, you could try measuring the gap with a feeler gauge. Or just ignore it all, and listen to the music.
 
tothmes said:
Or just ignore it all, and listen to the music.
Click to expand...
That's what I was hoping to hear, lol.

If there really is a deviation, it's maybe like 0.25 to 0.5mm? One of my other tables uses a thinner cast aluminum platter with similar imperfections, but it has zero effect on playback that I can measure or hear. So I decided to quit worrying about it.

I guess maybe I should just double check my suspension adjustments with a spark plug tool and carry on with the music then?
 
Is it flat on top? Thats really the only thing that matters. If the bottom edge is a bit off, that won't affect playback at all. Unless the top is really off, it won't have much effect either honestly.
 
It may be the case that the position of the outer platter WRT the hub is not optimal. I have seen many platter and hub decks that have a sweet spot, Here's how you do it. Draw a line across the join at the hub. Try a little tapping , sometimes you can find a faint rattle. Rotate the platter a little maybe 20 deg and tap test again also check normal running to see if it improves. You will almost certainly find a sweet spot where the platter hub interface is a best intimate fit.. Once you find that point erase your original sharpie mark and draw a new one across the joint.
That one is your reference.

One UK manufacturer used to mark the best fit with a small punch mark on the platter and hub. Line them up and you were golden.
 
I suppose if you really wanted to get nutty with it, some valve lapping compound and a lot of time to mate the inner to outer platter could make that a non-issue. Done proper it wouldn't have a "sweet spot", the two faces would both be flat and parallel to one another. Still has the potential of an alignment for best rotational balance sweet spot though.
 
You must log in or register to reply here.
Back
Top Bottom