Definitely over-engineered rod ruler

[Rick Kirchner]

Yesterday when the big one hit I was out in the garage trying to finish this gizmo. Got it done later in the day.

I'd been working with Steve Lathrop on some setup issues with my car and it always had a certain amount of asymmetry. I got obsessed with trying to get both sides as near equal as possible, starting with baseline measurements of the control arm assemblies, pushrods, etc.

I had a Coleman rod ruler, and what I found was a considerable amount of slop that allowed the moving "tower" to rock as much as 3/16 in either direction. I took some of this out by layering thick plastic on the bottom of the device that carries the tower, but still had (in my opinion) too much slop. No matter what I did I had a hard time getting consistent measurements, so I set about building a better rod ruler.

In the end the only parts of the coleman that remained were the two towers.

I took a BK12 ballscrew assembly available on Amazon for under 50$. Went to the surplus area of Industrial Metal Supply and picked up a few pieces of architectural grade aluminum angle for $12 (and that stuff is a pain to work with compared to 6061 or other engineering grades - it's pretty gummy and the bit walks a lot starting holes). You can buy Starrett Stick-on measuring tape for $6 on Amazon.

The result is still a little prototypey. After getting the initial design tabbed up I realized I'd really like it to be "right hand drive" and not to have to look over the assembly to read the scale, so at the last minute I had to flip some stuff around. If I ever get a 3-d printer I'd print the stuff I made out of aluminum angle that holds the towers. My milling capability is worthless (grizzly combo machine) so I had to keep those designs pretty rudimentary. Essentially made with a "poor man's mill" (bandsaw and disc grinder).

Well - there's no lengthwise slop in this thing at ALL - I mean it would take a dial indicator to find it. There's a small mount of rotational slop that I will address with a piece of plastic that attaches to the traveller and rubs on the support frame. I'm also going to fit a small hand wheel or a square drive on the end so it can be quickly moved with a drill. I suppose if I wanted to be really boss about it I'd put a small reversible 115 motor on the end along with the hand wheel for fine adjustment.

I've seen similar takes on this idea. I just had a creative itch to scratch.

[Chris Livengood]

Really cool project!

I'd bet that single ball nut has something like .002" of backlash, luckily it's not under much (if any) load. So the backlash won't be too apparent.

You can always repack the ball nut with slightly larger balls to reduce backlash if necessary.

[Rick Kirchner]

At one point I ran the screw too far out and dropped most of the balls, and then got it all jammed up putting them back, so after a few you tube videos I took everything out, cleaned it, put vaseline in there and put all 51 balls back in- 17 per track - by hand. Don't want to do that again....

[Chris Livengood]

Repacking ball nuts is something I've unfortunately had the pleasure of learning. I'm pretty good at it these days but it's not something I enjoy.

[Steve Demeter]

I am guessing that this device is what Carroll Smith would call a precision adjustable trammel bar?

[Rick Kirchner]

yes

[swiftdrivr]

Pretty darn cool!