I've come across more than a couple of occassions recently in which I found myself wanting to controllably spin stuff while tinkering on projects. The best tool at my disposal for this task was my "little" 6 inch rotary table for my mill.

 While  it's certainly up to the task, it's a heavy little bastard! So to keep me from lugging it up and down the stairs from the shop to the 'lab', I decided I should take a stab at a DIY, lighter-duty variant. 


OnShape CAD files available to do with as you please here.

RotTable ann1Asset 2 100 314fd

The above image shows the major externally-visible components. The Base is a printed part that  provides not  only the structural support for loads from all of the other components, but also  is responsible for controlling the alignments of the motion components. 

On top of the Table is the kinematic mount, formed by bar magnets set at 45 degrees from the table surface (so a 90 deg V.) If you haven't come across this style of interface before, you can find general info if you give a Google to "Maxwell clamp" or "kinematic coupler."   I included a very similar coupler on my passive rotary / overkill papertowel holder build  , as well as a great many of projects in my day job over the years...they're just tops :) hopefully seeing the repeatability numbers down below will start bringing you around to sharing my fondness for 'em.

 One thing I decided to add that my machining rotary is missing is a power feed!  In addition to the hand wheel for manually driving the table, a DC motor can be coupled to the other side of the drive mechanism.  There also should be plenty of space to swap out this DC motor for a stepper, should I  decide  to down the line. 

 The Table is driven by a worm gear drive housed inside the base, as shown in the below image. The worm gear is integrated into Hub component, which attaches to the Table via three M5 fasteners.  Sandwiched between the Hub and Base is a needle thrust bearing.  This thrust bearing's counterpart is the main bearing  that is integrated into the surfaces of the Base and Table. V-groove channels in the top of the Base and the bottom of the Table form the bearing races, and the rolling elements are 9.5mm steel balls (aka 3/8 inch slingshot ammo....hey, it's quite round and damn cheap). 

RotTable xsec1Asset 3 100 92f41



 On the hand crank side of the table, a printed coupler sits inside the "hand wheel horn", held in place with a roller skate bearing (I used these. They're overkill for this, but they run really smooth.) The hand wheel presses onto the coupler with a light interference fit. It's really just intended as a close running fit, but with 3d printed parts it ends up being more like  a bit of an interference fit.


RotTable xsec1Asset 3 100 1877e


On the power feed side is a similar printed coupler, but with a d-hub  hole for engaging the motor shaft and no support bearing (the motor has a bushing that's serving the same purpose.) For a motor, I'm using one of these 24VDC, 150RPM motors.  Something a little faster might be nice, but I might worry about the wear on the worm. Plus I don't really need this thing to be  speed demon, so  I don't have any plans to swap it.

RotTable exp1Asset 5 100 48786





Measuring runout:

Just for the sake of making sure there's no uncertainty with what I mean by runout, allow me to elaborate...probably to much. Feel free to skim. When I say, "runout", what I I'm referring to is any movement of the Table, relative to the Base, other than the desired spinny bit. There are three types of runout that I want to measure on my rotary table:

 Radial Runout

Radial runout is the side to side movement. It is the error motion radially out from the rotational axis. The below gif is an attempt to show what I mean, but just imagine the base isn't floating all over the place. Apologies for the seemingly lazy animation...I say seemingly, cause it sadly took me a fair bit. So that's as good as you're gettin! 

Axial Runout

Axial runout  is error motion that is along the axis of rotation, or 'up and down' as I'd probably refer to it if just pointing at it and talking   ¯\_(ツ)_/¯.  But hey, in good news, my gif-making skills definitely improved a bit for this one. So by Axial I bet it's gonna be fuckin epic. 

Angular Runout

Ha, just kiddin, it's even shittier...Oh, right, angular runout. Yeah, that's the tip/tilt one. Basically either of the two rotations that you didn't request of the table.


Measurement Setups

In order to obtain the measurements I'm after, it will require nine sets of measurements. Each set of measurements will include measurements recorded at consistent intervals throughout the 360 degree travel of the table. So why nine? What seem like an extra six will (hopefully) make a bit more sense shortly, but they're going to help us make sure we're measuring our actual motion and not the surface/shape of the surface we're measuring.

The nine measurements will require the indicator/sensor being mounted in three positions. Or, if you're flush with cash, just get yourself three sensors and a nice frame for em...while you're at  it, send me a set too :) 

Position 1 - Low on the post, near to the mount face

Position 2 - 50mm up the shaft from Position 1


Position 3 - On top and centered on end of rod.


The remaining six measurements, are repeats of these positions at  each position of the kinematic mount. I'm using the kinematic mount here to perform a variation on the "reversal technique" to cancel out part geometry. If you aren't familiar, but are interested, or just want to see if I'm totally bullshitting you, you can find plenty of info out there by giving something like, "reversal technique metrology".  The kinematic mount allows us to repeatably position the test sample at 120 degree offsets.  I'll show below in the data analysis how I then used these offset datasets.



Mount Repeatability







No comments

Leave your comment

In reply to Some User