You spin me right round

[jjgoertz]

Had been thinking about buying myself a turntable and that turned into me building one from scratch. Of course I've already spent more on this project than I ever would have buying one, but that's just part of the fun.

I found a piece of live edge curly maple to use as the plinth:



And I am using end grain maple and walnut for the platter. It's 1.125" thick and the grain is fairly consistent so hopefully it stays fairly flat. Where the tape measure is sitting will be about the edge of the plinth, approximately 18" x 20"



The bearing assembly I'm making will be tall enough to hang below the 2" plinth, so I made this base to hide the feet, the bottom of the bearing assembly, and house the motor controller. The base is a piece of baltic birch edged with walnut.







I looked around me and constructed a rudimentary lathe.



And on the underside of the platter I have routed a fairly substantial groove to fill with lead shot to add some inertia. The wood platter weighs about 2.3 pounds and this is about 5.3 pounds of lead.





The drive system is going to be a brushless camera gimbal motor. Initially this will be open loop speed control, but if that isn't consistent enough I'll be adding some hall effect sensors.



I will be building a passive linear tracking tonearm but all I have to show on the tonearm so far is this 8x10mm carbon tube that fits my headshell.



This is going to be a fairly lengthy project, but hopefully fun. And maybe by the time I'm done I'll actually own some vinyl!

[emilime75]

Wow, super cool project.

[Brian Steele]

FWIW, I don't think the platter needs to be that heavy. It's more about weight distribution. Some pretty good turntables I had some experience with many, many years ago had pretty light platters, but the weight was concentrated on the edge rather than the center.

[Millstonemike]

FWIW, I don't think the platter needs to be that heavy. It's more about weight distribution. Some pretty good turntables I had some experience with many, many years ago had pretty light platters, but the weight was concentrated on the edge rather than the center.

+1. A disk's moment of inertia (rotational inertia), I, is the integral of r²dm; r=0 to radius . Thus, mass towards the outer edge of a disk creates more inertia than mass towards the center.

This is why figure skaters are able to increase their angular velocity (spin rate) simply by pulling in their arms. Some mass has moved towards the center while rotational inertia is conserved (mostly) thus increasing the rate of spin.

I have to ask ... will the loose lead shot be a stable mass? Is it's mass uniform around the disk?

BTW: Very nice looking build, love the wood & craftsmanship.

[skatz]

Seems like it would take quite a bit of torque to get a platter that heavy rotating, are those motors up to it?

[jjgoertz]

+1. A disk's moment of inertia (rotational inertia), I, is the integral of r²dm; r=0 to radius . Thus, mass towards the outer edge of a disk creates more inertia than mass towards the center.

This is why figure skaters are able to increase their angular velocity (spin rate) simply by pulling in their arms. Some mass has moved towards the center while rotational inertia is conserved (mostly) thus increasing the rate of spin.

I have to ask ... will the loose lead shot be a stable mass? Is it's mass uniform around the disk?

BTW: Very nice looking build, love the wood & craftsmanship.

Hence the lead in the perimeter and not in the center. The motor I have is bigger than what is really needed for the job so I'm getting the inertia ratio up so the platter isn't as affected by small variations in the motor speed.

It won't actually be loose shot in the final product, it'll be epoxied in place. I will have to do a bit of balancing after adding the initial mass.

I haven't actually built the bearing yet but the friction should be low enough that a smaller motor will just take longer to get up to speed. Laterally it's going to be two teflon bushings and vertically will be opposing magnets. The magnets will have their steel casing between them and the cartridge, plus about 4-4.5" of minimum separation to the cartridge.

[Æ]

It won't actually be loose shot in the final product, it'll be epoxied in place. I will have to do a bit of balancing after adding the initial mass.

Beautiful workmanship. My initial thought was exactly about balancing and how you'd manage that!
I have a DIY turntable on my very back, way back burner. I added lead shot to the plinth to give it more mass.

[---k---]

Wow. Beautiful craftsmanship. I'm curious how you so perfectly achieved the check board stain pattern.

[mattsk8]

Beautiful craftsmanship sir!! Looking forward to following your build, looks like a very fun project .

Wow. Beautiful craftsmanship. I'm curious how you so perfectly achieved the check board stain pattern.

That isn't stain, those are individual blocks of maple and walnut glued together.

[Face]

Beautiful work!

[---k---]

That isn't stain, those are individual blocks of maple and walnut glued together.

That is what I originally thought. But, then was like no that is impossible. Too difficult... So impressive.

[jjgoertz]

That is what I originally thought. But, then was like no that is impossible. Too difficult... So impressive.

So I didn't actually do the glue up for the platter because I don't own a table saw or a large plane, but the method is relatively simple. You rip long strips of your two woods, in this case about 6 strips of each, glue them up into a long striped board, then cut that board across the grain into a bunch of pieces of a length that equals the the thickness of the end grain board. Then glue those strips together with an offset to get the checkerboard pattern. After that you just need to get everything smooth and apply a finish.

[Æ]

So I didn't actually do the glue up for the platter because I don't own a table saw or a large plane, but the method is relatively simple. You rip long strips of your two woods, in this case about 6 strips of each, glue them up into a long striped board, then cut that board across the grain into a bunch of pieces of a length that equals the the thickness of the end grain board. Then glue those strips together with an offset to get the checkerboard pattern. After that you just need to get everything smooth and apply a finish.

Almost seems a shame to make the platter so attractive, since it will be unseen whenever you are playing a record. If you decide to use a platter mat that will also cover up the beauty. Had you thought about recessing the center of the platter just a tiny bit to accommodate the label thickness of a typical LP?

[jjgoertz]

Almost seems a shame to make the platter so attractive, since it will be unseen whenever you are playing a record. If you decide to use a platter mat that will also cover up the beauty. Had you thought about recessing the center of the platter just a tiny bit to accommodate the label thickness of a typical LP?

Had not thought of cutting a recess. I'm going to use a felt mat, so that would probably make the recess unnecessary, right?

[jjgoertz]

Made some pretty good progress in the last two days. Started by getting the live edge plinth cut to length and flattened.



Put a 1/2" radius on the straight edges then I played with the layout a bit.





This morning I started with a coat of a 2lb cut of de-waxed amber shellac. This is the first time I've used shellac and I am super happy with how it brought out the chatoyance.



And then it got the first coat of poly. Really excited for how this board will look once the finish is completely smooth.



Then I worked on gluing in the lead shot. This ended up being much harder than anticipated. My plan was to pour the epoxy into a cup of lead shot, mix it up, then spoon it into the groove. As it turns out epoxy and lead is an extremely viscous mixture and that combined with the exothermic reaction kicking off the glue a little faster than I expected and it was a real pain in the tuckus to fill. My recommendation after doing it would be to put the lead in the groove first, then use a low viscosity casting resin and pour it over the shot and let it run down on its own.



Finally I got to work on the tonearm carriage. It's 3mm carbon plate with a 10mm OD carbon tube.





Attached the bearings and got to playing around with the carriage. It's riding on a hard anodized aluminum shaft that's meant for linear bearings. Friction is nice and low, you only need a couple degrees of slant to the rod for the carriage to roll either way. I will probably swap out the shoulder bolts for nylon ones to save some weight once I find some of the right length. Current weight is 48 grams.