More Testing - 3D Printed Gears

I finally needed to print a functional gear. Driving my RC car in the snow was a bit too much for the main reduction gear (My 3D printed A-arms seemed to hold up fine this time). Snow got into the gear (due to a very poor design that left the gear exposed) and was turned to ice by compression from the pinion gear. The built up ice seemed to push the motor out of the correct meshing distance. The motor then proceeded to grind away most of the teeth.

The snow was deeper than this in most spots. I took this picture after the car had already stripped the teeth from the main reduction gear.

I put the car in the bathroom to wait for the snow to melt. The electronics avoided the water for the most part, so the only damage  done to the car was the stripped gear.

This is the slot in the bottom of the chassis that leaves the gear exposed. The replacement gear is already in the car at this point. I managed to get a face full of gear teeth after a second or two of run time. I didn't have the car on the ground, so the forces on the gear teeth shouldn't have been too high. The gear teeth seem to have shattered. I think this is due to warpage in the gear after it originally printed. The portion of the gear teeth touching the support material had significant warpage. I found this was a problem in my early gear tests, but I decided to try running the gear anyways. I increased the spacing between the pinion and the reduction gear to compensate for the wapage and prevent binding. I also post-cured the gear, which increases the strength and hardness. The post-cure also made the gear more brittle which would explain the shattered teeth.

It's hard to get a good image of the gear without removing it from the car which takes a while. I didn't want to take apart the car until I had a suitable replacement ready to test.

I tried printing with my black resin instead of the clear resin. I had hoped the black resin would have less warpage than the clear resin.

The gear in the bottom left is the original gear. The bottom right is my new replacement gear printed in the black resin. The top two gears are spares that I printed, but didn't release from the support material.

I used a machinists square to visualize the warpage on the gear teeth. The majority of the gear has gear teeth that are square to the faces of the gear, however a small portion (~20%) has slanted teeth like these. This makes it impossible to have a proper gear spacing without binding. I will keep trying different orientations and possibly different gear geometry to avoid this waparge, but for now I may have to order a replacement set of gears for my RC Car.

New Machine - Form1+ 3D Printer

After thinking it over for a few months I decided the usual FDM type 3D printer I was building (the kind that squirts out plastic like a hot glue gun) wasn't going to meet my needs. I just moved and no longer have access to mills, lathes, or other metal working equipment aside from my trusty file and hand drill. I decided a 3D printer was the only way to continue my projects without making a mess in my apartment. After looking around at the different available 3D printers I came across the Formlabs Form1+ printer. This printer uses SLA technology. SLA printers use a photosensitive resin that solidifies when exposed to a light source. The resin in this printer cures with a UV laser.

I need a printer than can make parts with fine details, high accuracy, and decent strength. Although I'd love a printer that could make metal parts, however I'm a few orders of magnitude away from being able to afford one. I decided to settle with a printer that makes plastic parts. The FDM printers (like the one I am/was building) are nice because they have become very popular. The popularity has driven down the material costs which makes the printers very affordable. There is also a large number of users who have lots of great tips and tricks for getting high quality parts. Unfortunately the nozzle design in an FDM pritner limits the minimum features size. The fusion of layers through heat also tends to leave voids which causes very different properties depending on a part's orientation in the printer. This can make "engineering" grade parts difficult to make.

The SLA printers have only recently become available to hobbyists, so there is not a very large number of users. The material is somewhat proprietary, so it costs 3-5 times more than an FDM printer for a given volume of material. The quality from the SLA printers can't be beat by the FDM printers. The laser curing technique is able to make much finer details in the parts. I expect to be printing gears that are 32 and maybe even 64 pitch. The parts are also solid, so the material properties are going to be the same regardless of the part orientation. There should also be fewer voids in the parts, which will make "engineering" grade parts easier to produce.

Here's the printer in all its glory. I personally find the printer aesthetically pleasing. It also fits well on my bookshelf.

Here's the setup for my first prints. These parts are shock spring mount replacements for my rc car. The original ones no longer fit properly due to my machined replacement parts not being the exact same geometry as the original components.

The printer readout is pretty cool. It tells me the remaining print time and the number of completed layers. The remaining time is exact and can help me schedule my time around the printer so I can be as productive as possible.

This printer is upside down compared to FDM printers. The table rises out of the resin to grow the parts. It's a pretty neat concept and seems to work well.

Here are the final parts after removing the excess resin with isopropyl alcohol. They came out perfectly first try. I'm sure more complicated parts or parts with tighter tolerances will require some test parts, but parts like these take nearly zero effort to make.

Overall I'm pretty happy with the printer. I have more project ideas than ever now that I can make parts without labor. I'll be running test parts for things like gears and press-fits. For now I'm not going to finish the 3D printer I started making. The FDM printers can't make the parts I want to make. It is a good XYZ CNC platform, so I should be able to use it for another project some time in the future.