I have been working on the TALOS missile launcher for the OK City, and ran into some unexpected and annoying problems. Here is an image of the CAD model I am working from:
Attachment:
TALOS launcher CAD model small.jpg [ 116.32 KiB | Viewed 883 times ]
I am still working on the launcher body but I have completed a first pass at the missiles and launcher arms:
Attachment:
Launcher arms and missiles small.jpg [ 116.38 KiB | Viewed 883 times ]
The arms are just sitting on the missiles at the proper location, but I need to add some locating pins and sockets for fastening them together. Even at a small vertical step size the slots in the rails and the lugs on the missile do not mate (the lugs are extremely small).
The arms must slip into openings on the sides of the launcher body and then be fastened together.
Attachment:
Launcher arms small.jpg [ 118.5 KiB | Viewed 883 times ]
Slots on the arms and lugs inside the launcher body will limit the angle of rotation from horizontal to +55 degrees - the highest launch angle for the missiles.
To get the port and starboard arms to mate and lock together I devises a "lock and key" mechanism:
Attachment:
Launcher arm key small.jpg [ 109.29 KiB | Viewed 883 times ]
This is where I had the unexpected problem. The starboard arm has the "key" and it usually prints correctly (I have printed these things several times now) although there have been a couple of failures. But the hollow "socket" in the port arm has failed several times. Here is an image from Chitubox showing the default supports the program adds:
Attachment:
Port launcher arm default supports small.jpg [ 113.79 KiB | Viewed 883 times ]
Because the bottom of the cylindrical interior arm is pretty thick (3 mm) I thought it would be fine for supporting the upper part of the opening (remember this things prints upside down so the supports are on the bottom of the part). But when I printed at 0.05 mm and 0.03 mm vertical steps this is what I got:
Attachment:
Port arm key hole bad small.jpg [ 116.1 KiB | Viewed 883 times ]
The opening "caved in" and it has a oval cross section (instead of circular). All of the half dozen parts had this failure to some extent, and this was the worst example. Obviously the key wasn't going to fit in this lock!
Then I added extra supports to the Chitubox default set:
Attachment:
Port launcher arm extra supports small.jpg [ 133.95 KiB | Viewed 883 times ]
Notice the additional internal support and several supports that are above the maximum diameter of the arm. Here is the result:
Attachment:
Port arm key hole good small.jpg [ 101.07 KiB | Viewed 883 times ]
So the extra supports did the trick - mostly. However, even with all the supports some of the prints of both the port and starboard arms have had the ends of the cylindrical arms squashed a bit to oval cross section on the side with the supports! Apparently the part is separating from the supports near the end of the cylindrical arm and this allows it to "droop" while printing. The attachment points are sized "Medium" with a 0.80 mm contact diameter according to Chitubox. Maybe I should use "Heavy" supports or larger contact size?
I am using the default motion timing for the Anycubic Photon Mono printer (lifting speed = 240 mm/minute). I wonder if the force of lifting the printed parts through the resin is breaking the attachments?
****
Another issue is apparent over exposure during curing. You can see the white flaky patches in places. From what I have read this indicated over curing.
I was using a 300 Watt photocopier exposure bulb (mostly white light with some UV) that I used for exposing photo etch. It took about 30 minutes to get a good cure. However, this incandescent bulb burned out, and I noticed the replacements have only a 20 hour life expectancy.
I ordered a Tresbro 20 Watt LED UV lamp with 405 nm wavelength. The adds said it was a "200 Watt equivalent" but of course the marketing morons fail to tell the luminosity (lumens) of the lamp.
https://www.amazon.com/dp/B085NMPW7B?ps ... ct_detailsI read several articles on line saying that the 2-4 Watt UV lamps used to cure fingernail polish could cure resin in 1 to 5 minutes (thicker parts may take longer), and there were a number of 4 Watt versions of this same lamp. I cured these parts in a bottle of water for 5 minutes and then another 2 minutes upright and 3 minutes inverted on the turntable. Apparently that was a bit too long!
So that is my latest adventure in 3D printing. If anyone has suggestions for proper support or information about how to know the correct curing time I would appreciate it.
Phil