I was making grains one at a time with a mostly 3d printed pressure cast
I developed a spreadsheet to select Kn based on the "flatness" of a
symmetric burn profile.
It is discussed here: https://www.nakka-rocketry.net/design1.html
I was doing this mostly for initial characterization testing, however, it's
also nice for flight motors too.
To get consistent grains in both length and mass, I determined (mostly by
testing) the mass of propellant that gave me a finished grain length.
I would then pour my grains in the fixture over a tared digital scale to my
target grain mass.
The casting tube was left intentionally long, and then would be cut down to
I never fired any motors, but am confident in this process, as it yielded
very consistent results.
On Wed, Apr 14, 2021 at 10:45 PM Bdale Garbee <bdale@xxxxxxx> wrote:
William Schmiedlin <wschmiedlin@xxxxxxxxx> writes:
I'm making grains from Sorbitol, so the stuff is as hard as a rock.
It's actually not hard to saw KNSB. I've used a cheap manual miter saw
and box for grains up through 75mm. The trick I've learned is to use
water to lubricate the blade.
I use hot water to wash off accumulated propellant when the teeth clog
up, then let enough cold water run to re-cool the blade and leave it wet
when I go back to sawing. Helps to have a utility sink in my shop, I
At least here at high altitude, things dry off quickly after I'm done
sawing. Just make sure to clean and dry the saw before putting it away,
since the oxidizer in the propellant will make quick work of rusting
your saw if you don't...
Having said all that, it's certainly easier to just cast grains the
length you want them.