Here you will find all the settings for printing a strong lower that has a good fit and finish. Slicing is a very important step in making a strong and functional part. Settings will depend on your printer and the filament you are using. Below are a couple videos on the subject. I’ll also through in some quick reference farther down the page.
In this video I go over all the basics of slicing an AR-15 lower. Keep in mind that this is an older video, so some things are out of date. But all of the basics are still valid.
Slicing is also important for other parts like Stocks. In this video I’ll go over the details of printing a strong light weight stock. I recommend similar settings for Pistol Grips. But like to use four walls and 25% infill.
Slicing can broken up into two categories. Filament Settings and Print Settings. The first is filament specific settings like nozzle and bed temp. The latter is more mechanical settings such as layer height and print speed.
The single most important step when slicing is proper print orientation. Many of my designs come with built in support, which should make the print orientation obvious. The proper orientation for the Super Lower is with the bottom of the mag well against the bed. The flat bottom of the lower should be on the bed. Any other orientation will result in a weaker lower or improper support. Stocks are printed with there matting surfaces against the bed. The part of the Stock Neck that goes against the Lower should be printed facing up, and the butt end of the stock should be facing up while printing.
Getting the right nozzle and bed temperature is very important. Head over to the Filament page for more details. Fan Speed and Flow are also important. But these will have to be tuned as you go. You want enough fan speed where you get good overhangs, but no more. Flow should be adjusted until the plastic is slightly over extruding. This insures maximum layer bounding. See the end of the first video to understand what this looks like.
Print settings are equally important. Bad print settings will result in a broken lower. Things such as layer height, line width, wall count and infill type are some of the settings that need to be set. The nozzle diameter you use will have a large effect. I recommend sticking with a 0.4 MM nozzle. All of the settings listed here assume a 0.4 MM nozzle is used.
I always print with 0.2 MM layer height. It is the optimal balance between print speed and layer bonding. Larger layers will cause significant loss in layer bounding as well as a less detailed print. Finer will never hurt, but the return is small below 0.2 MM.
Wall count and infill are two of the most important settings. I recommend three walls and 100% aligned rectilinear infill. It is critical that the infill angle is adjusted so that the infill runs the length of the lower. Do not use less then 100% infill, it will result in slightly lower print times and worse layer adhesion. Of course this only applies to high stress parts like lowers. When printing Stocks and Pistol Grips less infill will work fine. I like Gyroid or Honey Comb infill for these types of parts. You can use as few walls and as little infill as you think you can get away with on non critical parts. As as it does not break in the field you are fine.
Line width is an interesting setting. The wider the line the more it is pressed against the lower layer. This results in better layer adhesion. But as the lines get wider they press less an there neighboring line in the same layer. Resulting in poor side to side adhesion. I have recommended wider line widths before. But I now recommend 0.5 MM for lowers. Use a narrower line on the outside wall, so as to get better print resolution. 0.45 MM is a good option. To save weight when printing low stress items like stocks I use 0.45 MM lines everywhere.
Scaling and setting the XY Size Compensation are also important. You will probably need to print several lowers before you get these settings perfect. After installing the upper, If you notice a gap between the front pin plates and the lower body, you problebly need to scale your print a little. By measuring the gap, you can calculate how much you need to scale. I normally scale my prints by 100.3% on X and Y axis. Scaling on the Z axis is not normally needed. With a perfect printer this would not be needed, but all printers have some error. XY Size Compensation is different from scaling. See the above video for an in depth look. Basically it shrinks (or expands) all surfaces on the part be a given amount. If parts are fitting tightly, and your scaling is set properly, then you may want to adjust your Size Compensation. Start with a small negative number like -0.03 MM.
There are some miscellaneous settings that can matter. Turning on “Print Thin Walls” will insure thin sections are printed properly.
That’s about all! There are more details in the above videos, so I highly recommend you watch them!