Highly accurate delta printer rods

Producing accurate pieces with a 3D printer requires precision of its construction as well as tuning of its operation. For a delta printer, most of the construction pieces are dimensionally critical. Let’s take the suspension rods as one example …

The vertical motion from the three towers is translates into 3-dimensional motion by the length and angle of the arms. These arms are installed in pairs so each pair creates a parallelogram of motion. There are six arms.

carbon fiber tubes with rod end ball fittings

carbon fiber tubes with rod end ball fittings

While the finished length of the arms is a configuration parameter in the software it is critical that all six arms are EXACTLY the same length (as measured between the mounting holes). An error as small as 0.004 inches will create misalignment in the print layers.

I set out to find a design Which would’ve me fabricate each rod “close enough” and the adjust them to a common length within 0.001 inches.

Most delta printer rods use threaded rod ball ends. The problem is that to align the ends, there may be as much as a half revolution of one end to slim with the other while attempting to be “close” to the same length. Even on M4 threads, that is 0.41mm or 0.015 inches, or 15x too much error.

I tracked down complimenting left and right hand threaded rod ends. The carbon fiber tube is 4mm inside diameter so I needed to fill the tube ends in order to have the rod ends “thread” into the tubes. My solution was to grease the threads and then apply epoxy inside the tube. Once hardened, I was able to carefully twist the rod end and the epoxy became the complimenting threads. It worked … well … except for the first one where I forgot it was left hand threads and I tightened rather than loosened the rod end; cracking the carbon fiber tube. (oops)

Now I have six rods and by attaching the ends to a test jig, I rotate the tube body gradually until the rod holes are the current distance.

This setup can easily be adjusted to 0.001 inches using a digital caliper. Once a rod has been “dialed in”, a drop of blue-locktite fixes the ends in place.

Update 1: the first rough attempt at adjusting these achieved a 0.002 difference across all 6 arms. Getting to 0.001 is not difficult to achieve and is more an attribute of the measuring jig than the adjustment to the arms.  

I user immersion bath cooking and I won’t apologize!

I am sitting here enjoying the latter part of a pleasant glass of red wine, having just finished a near perfect medium rare Sirloin steak with a simple salad and half potato dressed with a horseradish brown sauce.

simple steak that is simply delicious

simple steak that is simply delicious

I could have cooked the steak any number of ways. I used sous vide finished with a pan seer at 480F. Is this cheating? Perhaps. But ask yourself if you would want any of the following:

  • a streak that is cooked exactly to your preference without sweating about watching and timing the grill, the oven, or the pan
  • steak or fish for seven that is ready on time and in perfect sync with the dishes coming out of the oven
  • enjoying the pre-dinner conversation with your guests rather than sequestered in the kitchen making sure the main event is ready not
  • worrying when guests will arrive or when the family will be home for dinner

Using immersion bath cooking makes all of these possible because you don’t over cook the food. You CAN’T over cook the food.

I like the freedom and the accuracy of using sous vide. The meal is ready to plate when the people are ready to sit down – not the other way around.

I’m enjoying fish and steak more frequently now than in years. I doubt I’ll order a restaurant steak again. It would be too much of a disappointment.

Humor: how machines will take over the world

SkyNet is coming. Humans are in its cross hairs.

I wrote, “most people say that SkyNet will be the result of a revolutionary breakthrough in computer science. I say it will be an evolution of 3D printers upgrading themselves by printing better parts.”

Today I believe it will be chemical warfare. Machines will use our additions against us. It’s quite simple actually. 

Our automated coffee makers and espresso machines will subtly increase our caffeine dosage ever so gradually over days and weeks and months. Humans will not even notice. The change will be so slow it will be imperceptible. 

Then one day way off in the future, all of the machines will simultaneously dispense well flavored zero-caffein beverages and the human race will collapse as a pile of slugs, unable to concentrate, unable to move, unable to defend itself.

The machines will be victorious without firing a single shot from some ultra-advanced lasar weapon.

3D Printer Series

k3Over the holiday break at the end of 2015, I decided to get a 3D printer. I enjoy building things and enjoy learning so I chose one of the kit printers. I chose a delta printer design. These are the printers with three towers and the printer head – referred to as the hotend – suspended between the towers by rods. An example of the delta printer is in the photo (this is not the actual printer I built).

Ultimately, the process from wanting a printer to getting useful parts has had many steps. Nearly all of those steps had a learning curve associated with them. And so, this series of blog posts will attempt to cover the following topics (but I can’t guarantee on the order):

  • choosing the kit and ordering process
  • assembling the kit
  • Upgrades
  • Software workflow
  • 3D Print Server

Now that I’ve outlined the series, I guess I will get started writing!

2015 in (flying) review

Friends prompted me to look back at the flying I did this past year.

Tallying the hours, it was a pretty typical year with about 75 hours on the Hobbs meter.

The year can be broken down into three categories: test flights, training, and visiting friends. (There may have been a little sight seeing thrown in for good measure.)

The airplane received a new “instrument capable” panel at the end of 2014 and that meant getting acclimated to some buttonology for getting my instrument rating current again. I flew 6 flights dedicated to instrument training and several more flights had a segment dedicated to being fluent with the procedures necessary to fly instrument approaches into some of the local airports. I also had my biannual flight review.

While the plane is running exceptionally well, the new avionics required several software updates. This resulted in a number of short local flights that lasted less than an hour each. 

The majority of hours were flying to see friends. One location accounted for five trips to help with a fellow RV-8 owner who was upgrading his panel. Most of the time, two heads were better than one – most of the time (grin).

October saw a set of “butt buster” flights. There were three separate 6+ hour days. 

An interesting fact: I did not end up with a single overnight trip in 2015. Every flight was a day trip including Knoxville, TN and Portsmouth, NH.

There was only one regret in my 2015 flight log (more accurately absent from it). I didn’t plan very well for my niece’s wedding in Maine and foul weather kept me on the ground. Better planning on my part would have lead to a road trip or a commercial flight. That’s one of thereabouts of being a pilot. 

Here’s looking forward to 2016 flying!

Tire pressure sensor fault – it may be something completely different

Have you seen a tire pressure fault message and then checked your tires to find they are properly inflated? It may be your cellphone.

Pressure Fault message

Pressure Fault message

How can that be true?

All cars and light trucks starting with model year 2009 have tire pressure sensors.

My truck has occasionally started reporting a fault in the system. A Google search uncovered the video below. This video is informative on how the system works. Two pieces of information:

  1. tire sensors reports in every 30 seconds
  2. a fault is recorded if no valid report is received in 20 minutes

The sensors are obviously wireless. This means RF interference can prevent the sensor reports from being received.

Many things can creat RF interference. The video highlights a common one – inexpensive cellphone car chargers.

The next time I saw the fault message on my truck's instrument panel, I pressed “OK” to clear the message. The little icon remained on my instrument cluster. After 5 minutes I reached down and unplugged the USB charger plugged into the cigarette. Within 90 seconds the fault cleared. This is precisely what the video detailed.