There has been a lot of discussion on 3D printing lately so I thought people would enjoy seeing one way we are using it on 4329. We are attempting a gear drive for the first time and wanted to check the hole center to center distance tolerance on our drive side test part prior to ordering all the gears from VEX. These were printed on a ZPrinter 650 and are made out of a composite material.
At the scale where your test results are useful (in the thousandths), this must be very sensitive to dimensional inaccuracies. How did you ensure that your printed gears were scaled correctly?
Did you do this?
I think he just 3-D printed the spacers…the gears look like the aluminum VEX gears.
A good question. We basically just printed them at the highest resolution possible with the smallest layer thickness possible. From other parts we’ve printed in the past, I’m confident that when the prints were completed, they were very accurate. The ZPrint software does a great job of managing this automatically for us.
However, we didn’t apply any kind of hardening / finishing agent to the parts, and they are vulnerable to being damaged as part strength is fairly low coming right out of the printer. So we’re definitely taking these results with a grain of salt, but it was a nice activity to show some of the students how the gears will integrate with the drive too.
The gears & tube shaft parts are 3D printed here. The bolts are real but are not the ones we are planning to use for the real drive.
A big thanks to Madison from 488, Allen from 3847, Jeff from 1986 & Akash from 11. All of you have either helped us directly or inspired us by providing public CAD models & discussions on Chief Delphi.
I assume a sponsor printed these for you? Seeing that printer is a $60k piece of hardware.
And since otherwise wouldn’t the cost of the plastic be as much if not more then the vex alum gears (which are pretty cheap). Printing on a Dimension I have access to, mostly for none FRC related projects, the plastic runs $7 in^3 before discounts…
Yes. I work for The Boeing Company in the Immersive Development group. There’s a great publicly released video of our printer in action here: http://www.boeing.com/Features/2012/09/bds_3d_printer_09_11_12.html
Cost really wasn’t a factor on these prints. On occasion when there is room in the print volume and we don’t have any additional models to print, we’re allowed to print demonstration parts or, in this case, parts that may benefit the robotics team. Boeing mentors work closely with the high school students and we are looking to bring technologies & practices that Boeing engineers get to use on a daily basis to the students on the team to help inspire them.
Here’s another picture with a test part we had made by our new sheet metal sponsor -
I had the same thought. Assuming you don’t know the manufacturer’s tolerances on the gear tooth profile, how can you be sure that this reflects the actual fit of parts chosen (essentially) at random off the production line?
Generally, gears of that size will still have reasonable involute contact without binding or substantially reduced load capacity (with less or more backlash), even given a few thousandths of an inch of variation in centre distance—so this was likely to “work” pretty well, given the constraints of the test.
Also, if it wasn’t possible to measure the centre distance directly with the tools available, wouldn’t it have been been more accurate to 3-D-print a pair of gauge pins to fit the mounting holes and measure between them (accounting for their diameters)? That way you’d be testing against a simple dimensional tolerance (which you presumably established during design), rather than a functional constraint (which is kind of tough to evaluate under the circumstances).
Either way, as a demonstration of the 3-D printer’s ability to produce intricate parts, it appears to have been a success.
This isn’t how we will actually be validating our production part’s dimensions & tolerances. Our students will be learning inspection methods and comparing the physical part to the CAD model and/or drawings.
I just wanted to post a photo of one of our students inspecting a part at our sponsor’s facility from this weekend. It was an awesome learning experience for everyone involved.
We plan to do a full write up & reveal of our practice drive design and build by the end of December.