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I'm hoping for a little help from some of you fabrication experts... I've been working on making the mandrels for my (electronic) cylinder machine, but machining them to the exact taper, parallelism and within (ideally) +/- 0.001" has been really difficult. The quotes that I've received from machine shops (who are even willing) have been $1,000+. I turned one on a Southbend lathe, out of aluminum, and it took me 16 hours. If anyone has any good tips, I'd really appreciate it.

Thank you,

Don-

You could use wood, or plastic instead.... It must be much cheaper and easy to work out. You lose the mass regulating flywheel effect, but I feel that a solid metal mandrel is a luxury not in line with the not-too-expensive idea... Plastic could bed a good option. You could make one and use it as a mould to make moulded production mandrels in plastic resin. Although precision centering the hole in the mandrels could be a nightmare.
Making plastic sleeves to be inserted in the primary mandrel could be expensive to produce too, because of the fine precision you need on both the inner and outer surfaces, to avoid any wow... Not easy!
Maybe the best solution is to produce machined plastic mandrels on the lathe, one (or two) each time. The lathe precision work is there, but material and time costs would be cheaper.

Why not use original phonograph mandrels?

Inigo wrote: Wed Mar 16, 2022 4:46 pm You could use wood, or plastic instead.... It must be much cheaper and easy to work out. You lose the mass regulating flywheel effect, but I feel that a solid metal mandrel is a luxury not in line with the not-too-expensive idea...

I'm currently 3D printing them out of ABS and truing them on a custom lathe, but the results aren't ideal. Current 3D printer technology makes parts +/- 0.020", which is far too sloppy to use without machining. My design is partially hollow, so I can fill them with something heavy, but this is still far too light, even using high-speed motors. And these are the issues of being an inventor

Inigo wrote: Wed Mar 16, 2022 4:46 pm You could make one and use it as a mould to make moulded production mandrels in plastic resin. Although precision centering the hole in the mandrels could be a nightmare.

Yes, exactly. I can make a mold of one, but making a mold with all three planes critically aligned.... AND not change by more than +/- 0.001" while pressure-casting is "difficult" to say the least.

Andersun wrote: Wed Mar 16, 2022 5:06 pm Why not use original phonograph mandrels?

That would work for a normal sized cylinder, assuming it hasn't shrunk or was missing plaster (Blue Amberlols) but finding any other mandrel size is nearly impossible, especially for a machine which I plan to produce in some numbers...

And the option of no mandrel? I mean, like these other phonographs that have a much steeper cone at each end, which you adjust and catch the cylinder ends? For that to work you'll need an end gate with one of the adjustable cones.... A different arrangement, but seems much easier to make. The issue is that you loose the fast and easy feeding of the cylinder to play, putting the user in need of more work to adjust and play a cylinder. Not so comfortable.
For cheap these would have to be made of machined wood or plastic. You'll need a source of massive plastic bars of adequate bore, to cut a cylinder, center it and then machine out the surplus to make the sloped mandrel... Sounds not easy to center...
Ufff....! Not easy!

Don - Do you have drawings prepared for the mandrels? I have access to machine shops internationally (if your ok with that) which are typically ⅓ the price. Let me know!

Aaron