DIY Turntable

[c2cthomas]

Hello All - and Thank You for the warm Welcome!:cheers:

J7 - I have seen your floppy drive scheme on the web during my search for DIY TT projects. Very inspiring!! Grrrrreat! :notworthy: I will fur sure be checking into that a bit closer as the motor drive section of my project.

Part of my inspiration is from the Altman TT site http://www.altmann.haan.de/turntable/ but I'm sure that most of you are more than familiar with his work. There are several sites that show photo's of completed DIY TT's but most of them do not go into the details of how to get it done. So my hat is off to Herr Altman for his project and helpful how-to's.

Looking at something like this for a tonearm http://www.freewebs.com/stereobass/funwithtonearms.htm

Then of course is the business of the platter, spindle, plinth, bearings, bushings etc.

My goal is to make up something that can pieced together using tools commonly available to the typical DIYer and of reasonable cost - say less than $500 US including a decent cartridge.

The attached is a concept drawing off the top of my head and show just for the sake of showing you what I'm thinking. If things develop along I'll open up a thread on the project and we can all toss in there.

In this concept I am using the wheels and bearings from some roller skate wheels as shaft bearings. The intention being to utilize the rubber of the skate wheel as mechanical isolation from the chassis. The thrust bearing will most likely be traditional ball and plate for version one but this version does show a magnetic thrust bearing in the base of the unit. You might also notice that I choose to drive the beast with a belt (magnetic tape) from a drive platter positioned between the spindle "isolation bearings" (?) :whistle: The reasoning here is that I have always felt that imparting the drive force onto the end of a shaft presents a number of problems that can be overcome by driving from a position that is more firmly fixed to the chassis. The same reasoning is used in the drive motor in that the drive pulley will go up to a ball bearing and be supported against side thrust and tilting etc.

Just some things to play around with and I'm looking forward to the chase!:der:

[j7]

good drawing there thomas
and the bearing idea is very good

roller scat bearings will be great...try and get them with no greese inside just oiled and they will spin much freeer

any pictures please post them up

bw
j7

[The Professor]

are roller bearings a good idea in a TT?

Aren't they more prone to noise? would they not sound noisier than a point source and so negate the magnets?

your idea is a sound one Thomas, but try replacing the bearings with a sleeve and bush arangement and retain the magnetic thrust plate. (by all means use a compliant surround for the bushes, however it could move around too much due to magnetic thrust not having a self centering action like a trad single point.) Keep it simple is my philosophy, anyone who heard Simons DIY TT or J7's Floppy deck will attest to that.

Welcome BTW

[c2cthomas]

are roller bearings a good idea in a TT?

Aren't they more prone to noise? would they not sound noisier than a point source and so negate the magnets?

your idea is a sound one Thomas, but try replacing the bearings with a sleeve and bush arangement and retain the magnetic thrust plate. (by all means use a compliant surround for the bushes, however it could move around too much due to magnetic thrust not having a self centering action like a trad single point.) Keep it simple is my philosophy, anyone who heard Simons DIY TT or J7's Floppy deck will attest to that.

Welcome BTW

Thank you for the feedback!! The drawing above was simply a first effort rushed to paper so I could keep track of my thoughts (an important concern at my age :rolleyez:)

The spindle bearing idea is my humble attempt to isolate the shaft from transmitting bearing and chassis vibrations to and from the platter. Just some ideas on reducing rumble to a low level. Bushings have been around forever and are a tried and true technology, but I still get uncomfortable about metal to metal contact and materials changing size due to temperature and friction variations. Rumble has always been one of my major concerns when it comes to TT's but method's to reduce it can lead off to a long and winding road of ideas and best practices.

These type of bearings are round ball bearings made from various materials - usually stainless steel - and not the roller type bearings. If I can devise a poor man's magnetic bearing I might use that but all of the magnetic bearings I have seen are very large and very expensive. I have a great deal of experience with permanent mag's so I get tempted to use them - but they do introduce some other considerations and concerns of their own - and the goal here is to keep things reasonable in terms of cost and complexity. If price and technology were unlimited I could come up with a great many Goldberg looking contraptions but I find the fun for me is to boil those things down to a simple and reliable design. Simple - reliable - reasonable cost (a relative term) easily repairable and maintainable are skills I learned as a Quality Control geek - Repair Tech - Production Chief etc. in my previous life - before becoming a lazy old retired bum looking for interesting ways of getting into mischief. :p

[zharca]

Hi Thomas,
welcome - a real interesting project.
I must admit I'm not convinced by ball bearings for a turntable. They're actually designed for very different kinds of work like thousands of rpm under big loads and will actually be noisier than a nicely made plain bearing at turntable speeds. There's also a lot to be said for introducing a bit of oil drag into a turntable bearing to damp flutter.

I do really like the idea of supporting the shaft either side of the drive, it solves lots of problems.

I think that for the length of shaft you'll need perhaps starting with a precision ground tube (like they use for air bearings) of about 15mm would give the stiffness you need and a nice bearing surface without being really heavy.

Jeff

[j7]

needle rollers may be better than normall ball bearings

[c2cthomas]

Hi All

I've been sitting in the corner reflecting about things and have refined things a bit. The rev. 2 drawing using a traditional ball and plate thrust bearing, and rubber (?) isolation for the shaft bushing. I'll need to scheme up a method for lubing the shaft bushing as there isn't a cup up there to have a reservoir of lube in and I'm reluctant to use a grease bearing - but this is still the mucking about stage so no worries (yet). I will also play around with the roller skate ball bearing idea as well as the suggested roller bearings - I mean where is the fun in all if this if we can't screw around with things 'eh? :eek:
On the other hand - I used to work around things that went KA-BOOM :explode:- and doing things other than a well documented procedure was rather frowned upon :nutkick:

I have added some iso cones for things to sit on - but there are some decisions to be made there. I am also still considering the use of a magnetic thrust bearing but that might go into the upgrade or tweak section. I do intend to make the unit upgradable for those that wish to do so with different motors, platters, tonearms etc., but need to settle down and prove out a sound basic design 1st.

Now on the Ruth Goldberg side of things i suppose that I could use some of the technology from noise canceling headphones and put an electromagnet surrounding the shaft to cancel out vibrations. I don't know if that would actually do any good but it could serve as a great line of BS with which to impress the easily baffled and confused. :rotfl:

[Chops54]

Bushings are best, period. Roller bearings, needle bearings etc are all far to noisy.If you don't like metal use PTFE of something like Linn do. The only bearing I've seen that may be better than a steel shaft in bushings is the one used in the Well Tempered turntables which uses four flat plastic fingers edge on to the shaft and a ball bearing in the bottom which is free to float around and self centres. A very interesting idea.

[c2cthomas]

Hi Si,

Thanks for that - consider it a done deal about the bushing- I'm assuming Sintered Bronze is your fav material for this. I am also tempted about using a bushing fashioned from iron wood as I could fit it to the rubber isolator tho. It won't be hard to give both of those a try and see what happens. Still lot's to take a look at and play with - it helps keep the mind young. I'm thinking a .500 inch (12.7 mm) hardened steel shaft for the main works as there are all sorts of off the shelf hardware available for that size and it should be robust enough to resist any bending or warping over time.:cheers:

[Chops54]

Hi Si,

Thanks for that - consider it a done deal about the bushing- I'm assuming Sintered Bronze is your fav material for this. I am also tempted about using a bushing fashioned from iron wood as I could fit it to the rubber isolator tho. It won't be hard to give both of those a try and see what happens. Still lot's to take a look at and play with - it helps keep the mind young. I'm thinking a .500 inch (12.7 mm) hardened steel shaft for the main works as there are all sorts of off the shelf hardware available for that size and it should be robust enough to resist any bending or warping over time.:cheers:

Sintered bronze is good. I like oilite bushings, similar to sintered bronze but porous and hold oil well. These guys keep a good stock http://www.bearingboys.co.uk/Oilite_Bearing_Bushes_-1011-c
In the States, McMaster Carr and such keep this sort of thing.

If you want to be really adventurous try an air bearing and a magnetic support. Nothing will wear out and no bearing noise either. I've thought about it many times but there's a lot of work involved.

[zharca]

Bearing quality is probably the most important factor in a turntable because it defines all of the measurements of quality. If the bearing isn’t right you can spend hundreds of hours working up the idea and still be disappointed.

I think the real challenge of this design will be to get the kind of precision you need to align two bearings to really close limits and keep them aligned with temperature changes etc. And humidity changes, too, if you’re using wood. After all, we’re talking about 0.005mm clearance with about a 4 micron finish for a good bearing bush.

Maybe the bottom one has to be mounted with a bit of float so it can self-align, like the end bushing of some electric motors?

[c2cthomas]

“Sintered bronze is good. I like oilite bushings” – Yes, of course oilite bushing – I should have been more specific and thanks for you spotting that Si.

Air bearings? Ahhh yes – but there you go spoiling my fun as I intended to approach this subject as a tweak or upgrade to the basic model. I have wanted to do a linear arm using an air bearing and know of the many problems this design aspect presents. Obtaining pressurized air that is free of moisture and contaminates such as dirt and oil is not as easy as one would think is it? I’ll have more to discuss about air bearings and linear arms as the project develops but I will give you a bit of a clue as to what I am considering – CPAP.

“Bearing quality is probably the most important factor in a turntable because it defines all of the measurements of quality.” I absolutely agree with this – as I’m sure we all do. This concern is why I am addressing it first and without a workable solution the rest of the project will go right down the crapper. I’ve repaired, overhauled and tweaked my fair share of TT’s back in the day. Later on in life I worked as a tech in a PMEL lab (Precision Measurement Electronics Lab) and gained some experience around things that needed very precise mechanical adjustment and alignment. That was before we began using solid state sensors, digital signal processing and computer monitors as readouts so one needed to have a delicate touch and the patience of a saint. Damn – talk about things that were temperature and humidity sensitive - the 3 axis gyros could be real buggers!

“Keeping the bearings aligned with regards to temperature” – a proper wood such as cedar (ply of course) looks to be considerably more stable than aluminum http://www.engineeringtoolbox.com/linear-expansion-coefficients-d_95.html but I had completely overlooked any consideration for humidity. :wall:

Living near Nashville Tennessee should present me with some resources to tap as we have a number of people who make and repair wood body musical instruments (primarily guitars – but “fiddles” as well) and perhaps I can find a helpful craftsperson that will enlighten me as to the proper sealing of wood in order to resist the effects of humidity. I do know a bit about the subject from building up speaker cabs out of MDF (I might make the basic platters out of that – but not structure) and plywood but there is a great deal more tolerance to be had there. Trying to keep the upper and lower bearing aligned to a high degree of precision will require pulling a fat bunny or two out of my technological top hat, which on occasion slips down over my ears when my brain shrinks (like now).

The suggestion about using a self centered bearing is well put zharca – and well taken – Thank you! I have seen these in use but it was in a high rpm situation so I’ll need to look into low rpm uses. A couple of things spring to mind (hint).

[Chops54]

This is turning into a good thread :) Mechanical engineering is something I enjoy very much.

The idea of a self aligning bottom bearing is a great idea. However I'm fast becoming convinced that one long bushing is probably best, maybe with a groove like a rifle barrel cut internally to allow oil to get from top to bottom. It's a trade of I suppose. Less surface area with two bushings means less noise but one long bush gives good alignment. You pays yer money ;)

I'm also considering magnetic lift on my new deck, but only sufficiently to take the load off the thrust bearing. I'm a closed loop believer and I'm not happy with the thought of losing the mechanical connection twixt platter and subchassis.

[zharca]

Yes, the one bearing makes life easier and I suppose that if you get the position of the drive belt and the platter right then the forces balance out the same as two.
But hey, it's nice to try out something new, especially when someone else does all the hard work :D:D:D

The actual DIY making of bearings has been discussed a lot. Perfectly possible with home workshop gear providing you have a LOT of patience and only want one of them!
Interesting thread here:
http://www.diyaudio.com/forums/showthread.php?t=70115

and I once did an idea to make a nicely accurate bearing on "hobby" type gear:

http://www.diyaudio.com/forums/showthread.php?t=81637&page=4
but never got round to it.
I have five nice bits of journal-sized aluminium bronze sitting in a drawer if anyone wants one...........

Oh, and Conrad Hoffman (diyaudio, Vinyl engine) has done a lot of work on air bearings for his linear tracking arm project. Very knowledgeable guy.

[zharca]

double post!
Boy, am I dumb. Missed the obvious. If we want to rotate the platter and drive ring together then we turn it inside out. The shaft stays still and the journal turns. It's then all one long structure with a bearing area at each end. Alignment problem goes away, both journals finished together. Thrust ball at the top or magnets at the bottom. Couple of flanges on the outside of the journal to locate the platter and drive ring.


http://www.audiomods.co.uk/images/twobearing.jpg

Job's a goodun. trouble is, I kinda think I've seen it before......

[cat's squirrel]

double post!
Boy, am I dumb. Missed the obvious. If we want to rotate the platter and drive ring together then we turn it inside out. The shaft stays still and the journal turns. It's then all one long structure with a bearing area at each end. Alignment problem goes away, both journals finished together. Thrust ball at the top or magnets at the bottom. Couple of flanges on the outside of the journal to locate the platter and drive ring.


http://www.audiomods.co.uk/images/twobearing.jpg

Job's a goodun. trouble is, I kinda think I've seen it before......

isn't this like the Michell bearing?

I like the idea of constraining the flywheel top and bottom, lets you have mass where you want it, and not in the platter, where you don't need it (in this design). I had a similar idea, with roller skates (and a tone arm design) until I found out they were not fixed axles :( A rotating mass ontop of a bearing is bound to have more gyration/precession.:dunno:

[Chops54]

double post!
Boy, am I dumb. Missed the obvious. If we want to rotate the platter and drive ring together then we turn it inside out. The shaft stays still and the journal turns. It's then all one long structure with a bearing area at each end. Alignment problem goes away, both journals finished together. Thrust ball at the top or magnets at the bottom. Couple of flanges on the outside of the journal to locate the platter and drive ring.


http://www.audiomods.co.uk/images/twobearing.jpg

Job's a goodun. trouble is, I kinda think I've seen it before......


The Clearaudio bearing is just like that Jeff except that the bearing sleeve runs top to bottom intead of the two lands.

[c2cthomas]

Sorry for my absence but I have been busy trying to figure out just how to transition the basic concept into something that might actually have a chance of working. That involved looking up materials that can be found at the local hardware store or via the internet and not cost a precious amount if building up a basic model.

To prove out that the parts fit and discover unforeseen bugs and got-cha’s I intend to do the prototype primarily out of MDF, HDF, BB ply, etc. The acrylic platters and gold plated doodads – for those that feel a need for them - shall have to wait until things get ironed out.
The key to this concept is to keep as much of the mass as low possible (at least two thirds) and thus in the lower drive platter with the idea being to improve stability.
In this sketch I have included opposing magnetic rings located at the bottom of the unit with the purpose of relieving the thrust bearing of as much weight as possible while still keeping the ball in firm contact with the end plate. The magnetic ring might not work out – it would be much easier to do with two smaller neo’s mag’s facing each other dead on but I’m going to give it a go just to see if it can be made to work. Stationary magnets are one thing but getting two magnets that are rotating to play nice with each other can get interesting. Still – with a bit of magnetic shielding around things to control the fields it might work out in the end. On the other hand, if those assemblies start fighting with each other it could result in instabilities and a high degree of wobble or rocking motion being introduced.

I’ve also been busy welcoming our 16 year old Granddaughter from Australia into the household as my wife Susan and I have been awarded custody of her care. Two days here and she wants to get a metal stud put into her tongue and I can only imagine what will be coming next with the boys sniffing about. 16 years old – going on 25. At least she is good natured and bright and a pretty good young person all things considered. On the plus side – I now have a pair of good young female ears to listen to my speaker tweaks!!