Lenco on a Mission

[ian]

Ages ago I got started using slate by trying to drive a Mission 775 platter and bearing with a Lenco motor.  It worked, sort of, but wasn't too stable  as the motor was supported from beneath using some foculpods.



Maybe it's the snow driving me mad but I keep staring at that beautiful 775 platter (heavier than the Lenco) and have decided to resurrect the project.  I've got a PTP motor mount from Peter and intend to use this to provide stability although I won't be using any other part of the PTP.

Some of you will remember the platter:



I think it's an alloy of lead around the rim, whatever, it is heavy!  Obvious difference is that the idler is going to run on the bottom of the platter rather than inside it if you see what I mean.  Now here comes the serendipity . The depth of the depression beneath a Lenco platter is approximately 25mm.




Which means the idler wheel is going to ride the Mission platter 25mm lower than the Lenco platter.  Now I happen to have some nice slate from an fire place hearth which is 25mm deep and also some 25mm ply to do a mock up to see if it works.  So can you guess what I am going to attempt?

Cheers, Ian

[hatehifi]

 

That platter looks awesome. Best of luck and I expect you are on to higher and better things once accomplished. Gut feeling speaking.

[nigel]

Which means the idler wheel is going to ride the Mission platter 25mm lower than the Lenco platter.  Now I happen to have some nice slate from an fire place hearth which is 25mm deep and also some 25mm ply to do a mock up to see if it works.  So can you guess what I am going to attempt?

Mount the motor/idler on the underside of the plinth? 

[jloveys]

Stacked platters. Put the Mission on top of the Lenco. LOL.

That's what I would do. Not you ? 
 

[willbewill]

Two layer plinth - motor mounted on bottom layer - platter mounted on top layer

[ian]

Mount the motor/idler on the underside of the plinth? 

Well done Nigel.  I am going to screw the motor mount under the first layer and fix the idler arm there too.  That will drop the idler by 25mm and therefore contact the Mission platter rim at the right height -  well that's the theory.

[jloveys]

Well, be assured that we will follow your adventures with great emotions...

   

Anything is possible...

 

[ian]

   Hope it doesn't self destruct!

[rfgumby]

I was considering that on that goofy two stacked opposite rotating affair.   No reason it shouldn't work.

Good luck Ian- 

[ian]

Saturday morning, snow outside so time to do some fettling on the prototype.

Hunt through the spares found an aluminium block and cut down idler given to me by Vic ages ago when I was playing with supporting the motor from beneath.  Here it is mounted next to the motor underneath the prototype board.



I've been careful to get the angles right so the idler is at right angles to the motor spindle and also a radius of the bearing.  So far so good. Right way up the idler sticks up nicely through the plinth.



Platter on.....



Aarghhh!  There's about a 5mm gap between platter and idler.  The trouble with trial and error building is that sometimes you come against errors!  In this case my simple calculations didn't account for the fact that there's a gap between platter and plinth

OK, don't panic.  Solutions?

1. In its original plinth the bearing is actually seated in a recess so the platter runs closer to the plinth.



So I could make a recess in the plinth to take the housing.  Possible just about (with my primitive woodworking skills) to do this on the ply but I don't fancy doing this on slate which is where this arrangement will end up.  Also that would mean The platter is going to be lower which will mean I would probably have to create a recess for the arm mounting.

2.  Recess the PTP motor plate underneath so the motor rides higher.  It will be messy in slate but hidden away so possible.

3. I could move the motor sideways so that the idler rides higher on the spindle.

4.  I could put a short and long spring in the nose end of the motor.  This will change the angle of the spindle but as this will be a fixed speed deck this may not matter.

OK, simplest solution to try is 4.....





........ and it works!  Lenco on a Mission lives!  It is now spinning quietly away and seems pretty stable.  This is the proof of concept.  I may look at solution 2 above later when the weather improves and I can get outside and start cutting some slate!

Any opinions on the spring swap solution?

[willbewill]

Ian - your builds are always really interesting and outside the box

I don't see a problem with the springs other than the idler is possibly touching the shaft at even more of an angle than usual?

[ian]

Hi Malcolm,
Yes that is my concern but thinking about it the angle varies quite a bit as you change speed up the cone so maybe not so important.  I've had it running for an hour or so now and it seems fairly quiet considering the bearing isn't bolted down!  What I have found is that there is a huge amount of torque with this set up, finger pressure tested.  Probably just a bit too tight but with this arrangement I have some room for adjustment with the spring nuts.  Tried playing with them a little and quite surprised at the difference in  noise transmitted to the ply which is acting as an effective sounding board at the moment!  This is quite encouraging as it does mean I will be able to tune in the motor with this arrangement.  Good thing is, with the PTP motor mount and Vic's idler arm mount, everything is totally stable which was never the case when I tried this before. 

It's started snowing again!

[ian]

Still snowing .

Bolted the bearing down and cut the plinth to the shape I'm hoping to do in slate.



Ignore the rough work this is a template for slate.  Also ignore the Sound Organisation frame - that won't be part of it!

The pencil mark top right is the place where a 12" Jelco would go (if I go down that route).  Now I've bolted the bearing down it is running very quiet

[mred]

Great project Ian, it has huge potential.
Is this a kitchen table project?....I would be castrated for such activity no matter what the outside temps 
Keep up the good posting.
Ed

[daiwok]

interesting, just wondering with the shape, would a rim drive work better and isolate the motor from the outside ? I know Vic did this in the past, but of course hiding the motor underneath makes it a very clean build.

Once thing I considered and still considering is having the bearing, motor and arm totally separate and independent which you could do before you go to do your slate.