A (relatively) simple general purpose rotary turntable. Intended for any of those, "Hmm, I'd really like to spin this around" type of projects, with the various mounting interfaces on the top surface aimed at providing flexible mount options to interface to these various tasks.
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There are V-grooves on both the Base and the Table to serve as the bearing races, and these are filled with 3/8" steel balls (or, if you play with balls as much as I do, you may want this bad boy, which I recently discovered with great glee). The grooves are sized to fit 34 balls in total, but you can use less if you'd like. However, it will be a little more noisier and less smooth, but not like you're looking for air bearing performance from your 3d printed rotary table...I hope :) The bearing is preloaded (and parts held together) with sets of 20x3 disk magnets (3 on each side).
The table has locations for a variety of mounting options, as shown in the below. These interfaces are:
- 3x M3x5.7 Heat set inserts on a 25mm circle
- 3x M4x8.1 Heat set inserts on a 50mm circle
- 3x M5x9.5 Heat set inserts on a 75mm circle
- 3x M4x8.1 Heat set inserts on a 100mm circle
- A 'Maxwell clamp'-style kinematic mount on a 100mm circle, sized for between 3/8"-1/2" (9.5-12.5mm) diameter balls. The contact points and preloads are provided by 6 of these 12x6x3 bar magnets.
- 3xM3x5.7 Heat set inserts on a 125mm circle
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Assembly Tips
First and foremost, KEEP TRACK OF YOUR MAGNET POLES! Few things more frustrating that waiting for the parts to print, the glue to dry, your fingers to separate...and then floating mount.... Don't do it, definitely a check thrice, glue once situation.
Once everything has had plenty of time to cure and dry, I clean the surfaces of the kinematic mount magnets to ensure there's no left over CA muckin up ma mount. I just take some of those long q-tips, sorry, "Cotton Swabs", and some acetone and dip, wipe, repeat until there's no residue left and I've got nothing but nice, shiny neodymium.
Paper Towel Adapter
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If you really want to flex your love of determinism, have I got the paper towel holder for you! This paper towel holder adapter uses the kinematic mount points of the turntable. Finally, a paper towel holder with a central axis that's stable despite CTE differences...amma right???
Curious about the...interesting...shape of the towel holder itself? There is actually a reasoning behind the bizarre choice of contour. There are two functional (or allegedly functional) drivers for this geometry. The first is that I wanted to try to define the contact regions with the paper towel tube, so the concave regions top and bottom result in two lines of contact with the paper towel roll at those two heights....for those precision engineering nit-pickers, yep, it's overconstrained....paper towels ¯\_(ツ)_/¯ The second reason is to introduce some compliance to account for variations in paper towel roll sizes (at least within a range), since a full roll has quite a bit of hoop stiffness (resistance to growing in diameter...ish). So as you can see in the cross section below, the contact regions have a variable thickness.
The original plan, and the first version I made, was for this to be a TPU component, but I've since printed it in PETG and it works just dandy. The TPU version does have a much better 'feel', in my opinion, but I'll gladly take the printing speed of PETG over the slight increase in enjoyment when swapping paper towel rolls. But if you want to really showcase the 'compliant mechanism' aspect, TPU is definitely the way to go.