Building a Plinth for Lenco L75

Looks like a productive weekend! From whatever I have read, sintered bronze
is good for bearings because it has pores which retain oil.
 
I came up with a few variations for the bearing design. I shared with a few fellow forumers for feedback and viability. Thanks, guys, for your valuable feedbacks.

The critical parameters - in my opinion, and as per feedbacks from others seems to be:

1) accuracy of machining the parts - since the accuracy of the mating between the bearing and the bushing will decide how quietly and smoothly it operates.

2) length of bearing and bushing assembly: the stock bearing has about one-and-half inch length. This is sufficient to support the 8 lb platter without undue stress on the bushing, which is the softer of the two mating surfaces (the other being the bearing which I think is made of hardened steel). I have decided to arbitrarily use about 4 inch length.

3) design of load bearing part: the stock bearing has a conical cutout at the bottom of the bearing into which the 5 mm ball rests. Below the ball is the thrust pad. Below the thrust pad is the steel "coin" that provide further mechanical support to the pad above. Finally below the "coin" is a circlip lock. This arrangement is good enough to prevent oil leaks from the bottom.

When the ball is inside the cone, about 1 mm of it visible, meaning about 4 mm of the ball gets "immersed" into the cone. The roof of the cone is cleverly extended to act as a reservoir for the lube. No need for sintered bronze.

4) Lubrication: I wanted to avoid using a ball as the interface for the bearing and the thrust pad. This is mainly to simplify the design. So I rounded the bottom of the bearing. My thought was to use a stainless steel as thrust pad and bottom support. It will be threaded as I could not come up with a design that will be leak proof without the use of additional rubber bushing. The rounded portion of the bearing will sit directly on the stainless steel pad. The lubricant would now assume greater importance as it needs to lube hardened steel and stainless steel. My thought was to use (for the bottom of bearing) a mix of lithium grease and sewing machine oil (or compressor oil, if I can source it locally), to obtain a viscosity/consistency higher than sewing machine oil but definitely lower than grease. For the vertical portion of bearing-bush contact, I thought regular sewing machine oil will be better as it has low viscosity. Also, I have been reading up on lubes and the conclusion seems to be that there is no such thing as a universal lube. Each turntable has a different recommended oil.

After 3 iterations and variations, I decided to simply copy the stock bearing design, with the only difference being a thicker bearing diameter and longer spindle. If my regular machinist turns out a good job, other designs shouldn't be difficult to implement.

I have put the design on paper, right down to every last dimension. I will go meet my lathe guy today or tomorrow. Cutting off a 100 mm section of the brass pipe (16 mm inner diameter and 25 mm outer diameter) this morning was hard work. Now I know just how hard brass is. Hoping that this works out well.

After all this, I did an image search for the (in)famous Jeremy bearing and the design of the load bearing part closely resembles what I came up with. The difference being that the Jeremy bearing's rounded bottom is narrower than my design. I guess this is a validation that my design will work as there are already lots of Jeremy bearings doing duty on Lencos worldwide. I won't be able to replicate the bling factor of his designs, though:)
 
I did the deed - went and met my lathe guy. I grossly underestimated the experience, knowledge, wisdom and age of this guy. Here's the plan after nearly half an hour of discussing with him and showing him the sample:

1) The brush bushing I bought is NOT good enough. The hole is a bit oval when examined closely. So it is decided now that he will source a solid rod of brass and he will bore the required hole himself.

2) The bearing will be of steel. After machining it to shape with some slack, it will be hardened at a metal specialist.

3) The hardened bearing will be buffed and polished to size for a close fit at another specialty shop. The negative after-effect of this step will be an ugly conical hole on the spindle.

4) The bracket will be machined from stainless steel.

5) The bottom cover-cum-thrust pad will now be brass (plan was to use stainless steel). A 2 mm or so thick "coin" of stainless steel between bearing ball and brass bottom will be the actual load-bearing thrust pad.

6) The outer surface of the brass bushing will get a fancy plating - chrome or gold-coloured. This is as much for cosmetics as it is for protection.

Expected turnaround time is a week. No quote yet as cost of materials is not yet known. Also cost of hardening and buffing not known yet.
 
The negative after-effect of this step will be an ugly conical hole on the spindle.
That's opportunity, put diamond or any stone with will decorate it. :) ( and could be some audible effect :p)
 
That's opportunity, put diamond or any stone with will decorate it. :) ( and could be some audible effect :p)

I checked the spindle of my TD 124 and there is some sort of a hole! So things are not too bad as I thought:lol:

PS:
Today I got Veedol AP-3 "Premium Lithium Based Grease". 50 grams, Rs 30.

Also, I got bearing balls (steel). Brand is "Professor". Ludhiana made. From a bicycle repair shop. 144 pieces, Rs 30. Size is 6.35 mm. Stock ball is 5 mm, btw. I have tried 6.5 mm ceramic ball and it works well. The platter goes up by unnoticeable amount when using 6.5 mm ball. Also, the conical cutout at the bottom of the bearing is large enough to fit 6.5 mm ball too. Reason I bought the bearing balls is because the current one has worn out of shape. If I had not been fiddling around with the bearing and studying it closely, I wouldn't have noticed it.

Try this: take out the ball and dry it well using tissue paper. Roll it between two (dry) fingers to feel if it is perfectly rounded or is worn. There shouldn't be any edges in the ball. If you can feel edges, it needs to be replaced. Confirm with visual check. Ideal replacement is 5 mm (for L75) steel ball if you can source it.

I was also hell bent on getting SAE 30 or 32 compressor oil. The first shop I checked at had SAE 60 or 62. He directed me to a nearby shop but the second shop didn't have it and instead directed me to go look for it in a pretty far away part of town. I obediently went there but it was a complete wild goose chase. Came back empty handed, tired and irritable. Lessons learned: don't trust Google Maps for directions. Not too much, anyway.
 
A W.I.P teaser shot:)

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The flange or bracket to mount the bearing assembly to the top plate is machined from a billet of steel. The cut-out (like in the original) is yet to be milled. Also, the three screw holes are pending.

Similarly, the thrust plate cum bottom is also machined from steel.

Both bracket and thrust plate are threaded for mating to the brush bushing.

The bushing is machined from a brass rod. The hole for the bearing is bored with a special drill bit.

From what I could see, touch and feel, the fit and finish of bracket, bushing and thrust plate is A1.

Only the two bearings (one for one-platter operation and second one for stacked platter operation) have to be given their final shapes, then sent for tempering to harden them. Post that, they go to a buffing specialist who will polish the bearings for correct dimension and impart a shiny finish.

I have decided to forego electroplating of the brass parts as I am afraid it will interfere with the inner dimensions. The outer surfaces will be buffed. Can we use varnish spray can to retain the shine on the outer surfaces? Varnish is for wood, right? Will it stick to brass and steel?
 
Solid aluminium would be quite a plinth. There was a 124 sold by a gentleman in NCR a couple of years ago, with a plinth machined from a billet of solid aluminium. It would be a very interesting experiment to try something similar for the L75.

This 124 and plinth is currently with the infamous Lakhwant Singh. Saw a pic of it on his facebook page.
 
Lakhwant Singh. Saw a pic of it on his facebook page.

Sometime ago, he had a very nice Micro Seiki (DDX 1000, IIRC) and a 401 in very good shape. I have stopped informing others about it as his prices are usually not digestible.
 
Here's the finished product:

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I have fitted it to the turntable and it is playing smoothly.

Lube used: lithium-based grease liberally around the ball bearing and thrust pad, and then some sewing machine oil squirted on top of that; the spindle is liberally oiled with sewing machine oil, then slowly inserted into the bushing. Spillover oil cleaned off. It rotates smoothly. The bearing ball used is of 6.35 mm diameter, stainless steel. Lube to be checked and changed after some days of play.

Areas of improvement: spindle diameter (7.15 mm) where the record is inserted is slightly larger than optimal and record needs to be pushed down with a bit of force. This can be corrected by further buffing. Spindle hole on the platter is 7.25 mm. 0.1 mm tolerance is a bit too tight in this case:)

Next test: extra long spindle version of bearing to be tested with multiple platters. Platter donor for testing will be a poor G301.

Will do A/B with stock bearing after some days of play.
 
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