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Old 3rd September 2013, 12:03 PM   #851
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Default Found a Machinist, TD 124 restoration coming up!

First, looks like it's time for me to learn what the OEM clearances for all bushings & shafts should be, since I've got a machinist who asked!

I'm digging through the threads, through all that User510 posted on his site trying to find them, but if anyone knows them off the top of their head, well I'd sure love to gather all of that critical into into one place.

Ok, so here's where I'm at. I learned of a good machinist who has a nice shop set up out in the country about an hour from my house. He seems almost as intrigued by the project as I am, so we'll be working on it together, an evening here and there, likely starting this week.

In fact, the way we intend to proceed might net some interesting information for other TD 124 owners. I'll take a preamp, test record and laptop with me, so we can record before/after measurements each time we work on a part. While all I have for software is Audacity, that's enough so we can capture a waveform and spectrograph for every step.

Yesterday, I took the turntable out to him so he could get some idea of the drive train and decide what to focus on first. We confirmed that the idler wheel runs true when affixed to a lathe, but that the bushing I'd pressed in haphazardly was deformed, so first project will be cutting a drive pin and putting the second replacement bushing in - properly.

We'll take I.D. & O.D measurements of the bushing and the I.D. of the pulley so we've some idea of what clearance we should be obtaining once it's pressed into place. If the bushing's off, then no sense installing it and we'll look for some more suitable replacement. We plan on doing that as well for all replacement bushings.

The other piece we focused on yesterday was the stepped pulley, which I suspected had bad bushings as well, since we could see a slight shimmy in it.

Upon lifting it out, I noticed that what I'd earlier assumed was a small washer was actually a ring of grease that had turned to gum. Since last inspection this ring had broken up a bit, which is why I recognized it for what it was. I cleaned everything up, reinserted the pulley, placed a finger atop the shaft and checked for play. Sure enough, without that grease to lock things into place, it was very obvious the bushings were very worn.

I've not looked at the chassis close enough to know if the stepped pulley mounting assembly can be removed from the chassis, so studying that is on my agenda. Obviously if it can be removed, setting up to remove and replace the bushings would go a lot more smoothly.

I'll also be taking a tip from User510 (thanks Steve) and building a working jig so the chassis can be locked down safely and easily worked on underneath.

Been a long time coming, but looks like I'm finally getting into this project and have to say I'm pretty excited about it.
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Old 3rd September 2013, 12:35 PM   #852
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Default Stepped pulley shaft

Thanks to User 510 I got the answer to one of my questions, re: can the stepped pulley shaft be easily removed from the chassis? Answer, as posted at VinylEngine seems to be no.

"later design. Shaft is fixed solid to the step pulley itself. Shaft fits down into a bearing well (that is machined into the cast chassis) with two bushings and a thrust pad. Beneath the thrust pad is a threaded plug which can be turned one way or the other to elevate the step pulley."
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Old 3rd September 2013, 01:00 PM   #853
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Default Idler wheel washer question

OK, so all the washers beneath my 124's idler wheel are missing! Hopefully tracking down replacements won't be an issue, although I note the fiber washers are reported to be of varying thickness to aid in proper alignment. My question though has to do with what material people are using for the thrust washer. Also am I correct in thinking that the idler wheel bushing is a little proud, so just the bushing takes the weight of the thrust washer? Certainly looked that way on mine.
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Old 3rd September 2013, 07:19 PM   #854
volken is offline volken  Netherlands
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Quote:
Originally Posted by missouricatman View Post
OK, so all the washers beneath my 124's idler wheel are missing! Hopefully tracking down replacements won't be an issue, although I note the fiber washers are reported to be of varying thickness to aid in proper alignment. My question though has to do with what material people are using for the thrust washer. Also am I correct in thinking that the idler wheel bushing is a little proud, so just the bushing takes the weight of the thrust washer? Certainly looked that way on mine.
The idlerwheel runs on a white nylon washer from 0,5 mm thickness and 5mm ID -9mm OD.and for height correction one to three fibre washers !
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Old 6th September 2013, 04:58 AM   #855
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Kevinkr - Any comments on using Delrin rod vs G10 for making the tool? I asked my friend if he could machine Delrin and said no problem, but didn't ask about G10. Delrin's softer, correct? Would that provide any additional protection against deformation when inserting new bushings?

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Hi missouricatman,
I've never pressed out the bearings for the intermediate pulley, but I would imagine that you would remove the thrust screw and nut and using a custom machined piece of drill rod press them out. IMO you would machine the drill rod so that it has a step on it and the narrowed diameter would be enough to go through 2 X the length of the existing bushing so that it captures the second one on the way out. Press out from the bottom since that end is threaded..

I've attached a picture of the tool I use to replace the main bushings. There are a pair of nylon bushings still on it from the main bearing I posted about in a previous post.. This tool was turned from G10 and has a step. It is designed to allow bearings to be pushed out or extracted as required - the longer part is split and there is a wedge that can be inserted to force the tool to grip the bearing if this proves to be necessary - it has not been necessary so far.
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Old 6th September 2013, 04:24 PM   #856
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Not sure, but I suspect softer may not be better. I think the key is to have well machined, burr free surfaces to protect the interior surfaces of the new bushing.

I'm thinking a beautifully machined piece of stainless steel could be better. I don't think the G10 is going to be durable enough if service many more tables.

Let me know how you do with the main bearing bushings, I may be interested in some. Most I've encountered (eBay) fit too loosely in the bearing bore and are easily and distressingly displaced by hydrostatic pressure when installing the spindle. This does NOT happen with the OEM bearings, but only my low hour TD-124/II has original bearings.
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Old 6th September 2013, 05:57 PM   #857
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I'm still at a loss when it comes to the exact specs. for all this, in particular "pressed" I.D. for in each instance. It's this I.D. that that's critical as it assures clearance is right to allow for an oil film, a rock-steady rotation, and still keep drag to a minimum. For the life of me for all my reading, I've yet to find this info. Best I've come across was a mention by user 510 regarding his measurements of the clearance on an old spindle and old idler wheel bushing, the latter clearance I believe, he called "too sloppy". Barring finding anything more definitive, we'll use those and measurements of our own worn parts then do some seat-of-the pants subtraction to try and come up with optimal tolerances to shoot for, then compare that to what we are likely to achieve with the new bushings on hand. Man, I hate even saying that.

Kevinkr, I can see the advantages of stainless. I have in my head the design for a drive mechanism that came to me while thinking of the explosive impact hammer I use to drive nails through wood and into concrete.

Basically, it would employ a "gun barrel" to steady the bushing while being pressed and an inner stepped pin to push the bushing down the barrel and into the OEM part, all in perfect alignment. The clearance could be pretty tight on this outer barrel, tighter than than you could safely use if you were to try to steady the bushing by means of an inner pin, as that pin I.D. would have to take into account compression of the bushing from insertion into the OEM part.

Of course when I get to the spindle I'll let you know how it goes. I have two sets of main bearing bushings, both sourced from eBay, but different in that one set came as part of a kit supposedly purchased years ago. They do vary in length a few mm, but without OEM specs, I don't know which set is most accurate (hopefully one set is).

I had planned on trying to measure receiving shaft and bushings prior to insertion in part to try and avoid the slipping problem you've had, but also to try and gauge what the final clearance will be once the bushing is compressed. My thinking is if it's obvious from these measurements that once pressed in, the bushing will either slip or not provide proper clearance, there's no sense in proceeding. My hope then would be to see if my machinist friend feels he's up to speed on machining sintered bronze to give it a go.

Finally, on the continuing search for the perfect lubrication, I have on order a liter of Nye Oil 181b

http://productsearch.nyelubricants.c...OIL%20181B.pdf

While the general applications mentioned along with the specs did catch my eye, what led me to it in the first place was that Nye does market the 181b and many of its other synthetics as having been designed for use in sintered bronze. Obviously a liter's a bit more than I need, but the little vial they were willing to sell me was both cost prohibitive and insufficient so I guess I'll be happy with yet another oil on the shelf.
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Old 7th September 2013, 01:13 AM   #858
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Hi Kevin, MCM,

Kevin you mentioned "Not sure, but I suspect softer may not be better. ".

My Dad is a (retired) mechnanical Engineer, and many years ago, I mentioned that I noticed that most plain or sleeve bearings always seemed to have a soft material, (such as brass), and a harder material, (such as hardened steel.)

I thought this was curious, and would cause premature wear.
He said that is not true, that the wear is minimized in this kind of situation. He pointed out some examples, such as clocks, (steel shaft, and brass plates, watches, (ruby or diamond outer bearing and hardened steel shaft), etc. Every plain bearing I've seen supports this, can you think of a plain bearing that that doesn't follow this rule?

What my be interesting is if we could make the outer bearings of Lignum vitae or a synthetic jewel.



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Originally Posted by kevinkr View Post
Not sure, but I suspect softer may not be better. I think the key is to have well machined, burr free surfaces to protect the interior surfaces of the new bushing.

I'm thinking a beautifully machined piece of stainless steel could be better. I don't think the G10 is going to be durable enough if service many more tables.

Let me know how you do with the main bearing bushings, I may be interested in some. Most I've encountered (eBay) fit too loosely in the bearing bore and are easily and distressingly displaced by hydrostatic pressure when installing the spindle. This does NOT happen with the OEM bearings, but only my low hour TD-124/II has original bearings.
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Old 7th September 2013, 01:35 AM   #859
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I was of course talking specifically about the tool used to press in the new bushing. In this case a tool made of softer material does not seem like a big win to me if high quality machining is available for said tooling.

Obviously I agree with the other comments.. Maintained well these bearing assemblies are quite durable, unfortunately most weren't well maintained I suspect.
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Old 7th September 2013, 02:27 AM   #860
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agree 100%. Undoubtedly much of the work being done today to bring these treasures back to spec wouldn't be necessary if they'd been properly maintained throughout the years. But they weren't and so . . .
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