Metalwork for my Covid project (Part 1). Caution large pictures.

[dmills]

New 400mm vacuum capable lathe platter (Three components), motor drive plate and motor mount have just turned up.

IMG_20200814_222109.jpg

This thing has a hollow shaft from below that provides the suction, and has extensive milling on the reverse side that will be filled with a polyurethane resin loaded with bentonite to damp any resonances (Yes, those steps are a harmonic residue sequence). Between the two major components you are looking at 40mm of thickness.

IMG_20200814_135040.jpg

The bronze dohicky in the centre can be rotated to select different disk diameters for the suction. It still needs a little elbow grease with some sandpaper as it appears that I forgot to tolerance the thickness to be just less then the void it sits in, the silly thing seems to work until you nip the screws down whereupon it jams solid!
I have a centre spindle for it, but that also needs a little visit to the metal lathe (another tolerance snafu, no big deal to sort out).

That whole thing rests via a set of kinematic V blocks on three M20 (Enormous) ball ended screws thru the motor drive plate which can be used to trim the assembly to level. Amazing how it adds up, there is about 12kg of metal there, just glad I didn't make the top bit out of 303 stainless!

Now I need to get this servo amplifier that I am using for the direct drive motor to actually behave itself properly... The motor itself seems to be fine, but I am having a terrible time with the servo amplifier. Still, 18N/m of torque, and a 100k count per rev resolver, it should hopefully be worth the fight.

Next up, sheet metal, more Pu resin and filler, the cross slide and its reduction gear.

[tragwag]

looks great! would love to get a VR worthy version, for my SP10

[trailerparkjesus]

looks great! would love to get a VR worthy version, for my SP10

YES me too

[dmills]

I would worry about the SP10 bearing with that much load on it, as well as the little issue of getting the vacuum port out.

I am working on a bearing assembly for it as the motor I have has just a little too much rumble when heavily loaded, current thinking is a pair of Nd ring magnets to take most of the vertical load, with either an oilite or Iglidur plastic sleeve bearing at the top and the usual single ball on a hard plate at the bottom to force vertical alignment. Finding a machine shop that wants to make the spindle part in 303 or 304 is proving annoying, mostly because of the tolerance requirements and the fact it needs to be heat treated to be non magnetic, cold working those steels makes them martensitic which with the strength of the magnets in play would make assembly a pain.

While it is provably NOT possible to build a fully non contact passive magnetic bearing, it is possible to build one having only a single contact point (The ball at the bottom), I am trying to avoid going there because my sketch of the thing looks expensive on the magnetic components side and tricky to assemble (Lots of fields that will fight you when it comes to putting the thing together).
If needs be I know how, but frankly there is a point of diminishing returns and low frequency rumble is something that some lathe electronics introduces deliberately anyway (Depth of cut control).

[dmills]

isolated assembly.png

Just ordered the sheet metal for the above assembly.
This mounts on vibration isolation to the machines main frame, with the drive motors slung under it on another isolated plate.

In this version, I have gone all in on the 'do not make what you can buy on ebay' school of design, to the point that the platter main bearing is actually an automotive wheel bearing assembly, which seems to be surprisingly satisfactory in the prototype lashup.
Because I lack the ability to ensure that the axis of rotation is sufficiently close to 90 degrees to the travel of the slide, the slide is on a sub assembly with a pair of kinematic balls and a 100tpi adjustment screw so the thing can be dialled in with a dial indicator after assembly.

The cross slide is (at the moment) a pair of NSK precision cross roller rails, with an (yuck) Ball screw (Yea likely to be replaced with a lead screw, but I got bigger issues), the saving grace is that at 4mm per turn it is going to run REALLY slowly.
There is a 50:1 strain wave gearbox with the ball screw connected to it by a slipping clutch such that a manual fast winding handle can be fitted behind the strain wave gear.

Motor wise, it is going to be direct drive, I have a suitable BLDC, the only reason it is not literally DD (as in bolted directly onto the motor) is that there is some bearing noise when you do that, cross slide is a Technic integrated driver BLDC, simple and quite capable of the ~60RPM or so that the input to the strain wave gear will need, drive for that is a 3M HTD belt.

The yellow bit at the front is mount for an Ortophon AS-309 300mm playback arm, annoyingly a 230mm arm is not easily compatible with a 400mm platter (Just not enough space when you set the stylus overhang correctly). I had not thought that one out!

It is all 5mm mild steel, being as that is cheap and easily laser cut by an on line service for not much money, but it does mean that I am not sure it is going to wind up lighter then a VMS....

Swan neck and cutting head suspension next (Also the motor mounting plates).

Progress of a sort.

[symatic]

awesome stuff!

I'm waiting on my Presto platter being modded for a new bearing system, the original was shot.
But it's also a big 12kg chunk of metal. Your cutouts to avoid resonance is really interesting.

great work

[dmills]

Yea, not sure that is really working right, but it was a nice idea, might just be that the Pu resin is showing too much of an impedance mismatch to the ally, needs investigating.

I am thinking that the next version might do the constrained mass damping thing, but get what I have to work to some extent first before I start on improvements.
I am loving how cheap laser cut metal is, all that sheet steel, plus the lower platter for just over a hundred bucks!