A Copernican View of the Turntable System

Concrete armpod indeed!
Why not Audpulse?

Here’s the design:-
A sand and cement mix (3:1 or 4:1 is fine) is available in any hardware store in small plastic bags.
Now for the mould…..select any hollow metal tube section from 100mm diam. (4”) to 150mm diam. (6”) cut to the height required at the seller’s yard.
This metal tube will become the ‘finished’ external surface of the Pod (permanent formwork) so select the material and finish you wish to achieve.
Stainless steel may be linished or polished, copper or brass can have a clear sealer applied, aluminium can be anodised natural or black or can also be powder-coated any colour or painted in an automotive workshop with 2 pack polyurethane to any colour.
A PVC tube from plumbing suppliers is really cheap, but as the concrete cures, it emits quite a lot of heat and the danger becomes one of ‘buckling’ the softening plastic mould?
That’s why ‘wall thickness’ of the hollow tube should be reasonable. Not less than 1mm I should think?

Place the tube on a flat surface lined with heavy weight plastic building sheet (we don’t want the bottom face concrete to stick) and add water to a quantity of the sand and cement mix.
We do not want the mixture to be wet and runny as the higher the water content, the greater the shrinkage and we don’t want the concrete separating from the metal mould?
A nice, dry mix will be perfect to pour into the mould.
Screed off the top of the mix level with the top of the mould, with a metal or wood ruler edge and then place a weight on top of the mould till initial cure has occurred…..we don’t want the concrete to slip out from the bottom edge of the mould?

After 24 hours, initial cure has occurred and the mould can be lifted off the plastic sheet and placed anywhere for the final cure to take place…….30 days is ideal but 21 days may be OK if you are in a hurry.
Now for those who have a tonearm that is all surface fixed, place the tonearm base on the top surface of the finished pod close to one edge (this is for 9” arms which possibly won’t get close enough to the turntable edge if the arm were located in the centre of the 6” diam. Pod) and mark the location of the holding screws. Drill these positions to accept standard plastic plugs and hammer these into the concrete.
Do the same in the base of the pod for the 3 screw-in spikes which you can source from various suppliers.

Voila…..your armpod is ready!

Now here’s the good bit…….for those with vintage tonearms or modern arms which have VTA towers or DIN connectors underneath the arm…..you need to position block-outs in the permanent mould BEFORE pouring the concrete mix.
The phono-cable block-out can be another metal (or plastic) tube (12mm or 1/2” diam.) which will extend from top to bottom of the mould (the cable will exit under the armpod) and be permanent.
The VTA block-out will be made of Styrofoam (cut to the correct size and depth) and taped to the inside face of the metal mould (the cutting of the Styrofoam need not be super accurate or beautiful but needs to be OVERSIZE.
The Styrofoam will be burnt out of the mould after curing of the concrete and we don’t want to be hacking concrete out of the mould because the VTA tower ‘misses’ by 2mm?

Most vintage arms rely of nuts to clamp the arm between a turntable ‘baseboard’.
In this situation, you can either…..finish the concrete lower in the mould to accommodate a 1/4” metal plate cut to size or…… even easier…..add the 1/4” metal plate to the top of the finished armpod and fix IT to the concrete via screws into drilled plastic plugs.
This metal top-plate needs to be drilled for the VTA tower and fixing nuts as well as the holding-down screws…..but this should be a piece of cake for any metalwork shop or indeed any DIY hobbyist at home.

Now for the comments and barbs……..
What do you think?

Halcro,
Makes sense as an inexpensive DIY solution. May not be as pretty as the DaVinci solution but there is no reason why it cannot be made reasonably pretty. The question I would have is how one can make really decent Micro-Seiki-like armbases to fit in the middle of the top plate, and have the top plate look really, really good.

The only way I can think of it is to make a very fine liquid "top" by turning it upside down (so top is down) on wax paper and pouring only the first 2-3 cm (with a styrofoam blockout for where the top plate and VTA tower will be). Then after that is done and mostly dry, pour the rest in around the blockouts and let dry. The first layer on wax paper, if wet at the very bottom, should create a super-smooth surface which can be finished as one likes.

T-bone,
Not sure I follow you on the tip-up and down bit?
If you want a glass smooth finish on the concrete?.......that is normally achieved by steel trowelling which is why I suggested screeding of the top surface with a metal flat edge as in a steel rule.
This will be equivalent to a steel trowel.

Otherwise, a machined metal top-plate to fit on top of the concrete, ensures a "really really good" finish.

Yes, you are probably right. The nest way to deal with the top is have a full-width metal top-plate.

T_bone, Why not use an actual M-S armboard (if you are using an M-S tonearm)? I think reproductions are made.

Halcro, You are obviously an architect. (I already knew that.) But doesn't all cement shrink to at least some degree whilst it is setting up, no matter how low the water content? And wouldn't even a small amount of shrinkage cause the inner cement cylinder to pull away from the walls of the metallic tube? Thus, could the cement cylinder become loose and actually fall out of the tube?

By the way, this issue of "shrinkage" was covered in a Seinfeld episode.