So in my incessant thrifting I came across a pair of Big Blasts and immediately had a great idea for one: I wanted to cleanly integrate a nice turret capable of rear loading.
One problem is that I have limited access to a machine shop, so I opted to do most of the build using 3-D printed parts.
The end result is a Big Blast reminiscent of Ryan McNumbers rear loading AT3ks
- 3-D Printer
- 3" 1/4-20 or 1/4-28 bolt
- 1/4" washer
- Nylon insert locknut for the 3" bolt
- Small strong spring-- I got mine in a spring assortment bag years ago
- 8 barrels of your choosing 5/8" OD I used some PETG 5/8" OD 1/2" ID CPVC works too, but I would bore it out so it's not so tight
- Marble-- Mine was from slingshot ammo and the OD is 0.540" so try to get one close to that
- Spring 9657K286-- I believe that is the part number
- 1/16" thick neoprene washer-- most hardware stores carry these
- Super Glue
- Amazing Goop
Here is the link to the GrabCAD folder. There is a SolidWorks model of the whole turret, and .stl and .step files for the 3-D printed parts.
When you are printing these I found that the holes for the barrels in the base and spacer were not that accurate diameter-wise.
My solution was to print them close and use a 5/8" reamer to do the final sizing.
I would do a test print of the the spacer or part of the base, and then adjust the hole sizes as needed.
Building this is pretty self explanatory, and the pictures do a pretty good walk through, so I'll let them do most of the explanation.
- I used 7" barrels, but use whatever you want
- The turret will fit snugly in the shell, so be careful not to remove too much material.
- I super glued the barrels in place, but feel free to use whatever glue you want.
- Print the turret base so the junction to the BBBB tank is down then you should be able to avoid any supports in the internal air passage
- You can also do any other sort of mods you want i.e. pump relocation, trigger replacement...
For the turret base you will see better performance if you do some after treatment of the print such as a vapor bath. This will seal the layers together well, and prevent leakage from the internal air passage.
I used PLA which is not easy dissolve but I did a vapor treat using tetrahydrofuran. This stuff is nasty, if you aren't trained to work with it DO NOT!!!!
Another safer option is just to paint the internal passages with a durable enamel paint, like nail polish or modeling paints.
For ABS prints acetone is readily available (Nail polish remover) and not as dangerous, but still use caution. You could even just apply it to the internal walls of the air passage using a cotton-swab.
Questions, comments, concerns?
Edited by louiec3, 30 July 2018 - 08:05 PM.