I can confirm this. I don't have the skill to do it myself, but I've
watched better machinists than I do some very fine injector drilling and
Roxanna's "peck drilling" technique with lots of coolant, works. Better
than CNC, from what I've seen, or at least fewer broken bits wind up
sticking out of the injector holes.
If at all possible, design the injector blank so that the face will be
perpendicular to the drill at the point of contact. Look closely at
stream quality when doing water flow testing. Also, don't be afraid to
discard an injector that looks iffy under water testing. You lose a lot
less work throwing away a bad injector at the start, than finding out
you've made a bad engine.
John Schilling
On 8/13/2020 12:36 PM, roxanna Mason wrote:
As a 50 year machinist, beginning the trade in high school, I've drilled a few holes/orifices in that time. The trick is to continually clear the flutes by 'peck' drilling.
No more than one hole diameter plunge at a time. And of course coolant. The drill will not wander with proper technique. If you have the luxury of an EDM that's great like a 3D laser sintering machine, more the better. But at the amature level, you don't need high tech, only patience and technique by practice.
BTW, the CC can be drilled too with axial/longitudinal passages from injector to nozzle convergent section.
K
On Thu, Aug 13, 2020 at 11:57 AM Tyler Adkison <tyler.adkison@xxxxxxxxx <mailto:tyler.adkison@xxxxxxxxx>> wrote:
I've considered trying to drill a hyperboloid chamber, but trying
to drill those types of holes is something that sounds easy but
certainly isn't. Honestly, even just getting the drill bit aligned
well enough that you drill to the exact point you desire is a
challenge. I think you would need a rather nice EDM machine to
drill this on a hobby scale. That said, it's certainly an
interesting idea and it's not impossible to do.
On Thu, Aug 13, 2020 at 11:47 AM Henry Spencer
<hspencer@xxxxxxxxxxxxx <mailto:hspencer@xxxxxxxxxxxxx>> wrote:
On Tue, 11 Aug 2020, ken mason wrote:
> Jon, one other fabrication technique that is unique and
worthy of
> mentioning because it's viable even on a small scale and has
flown 100's
> of times to orbitthat being the RM-81 Agena rocket engine of
16KLbF,or
> 71KN. The nozzle shown in the pic is drilled from a solid
billet at a
> hypoid pattern... the cooling hole density is greatest at
the throat
> just where the heat flux is greatest. The Agena nozzle is
made from
> lightweight easy to machine/drill aluminum which
conveniently has good
> thermal conductivity.
Not a hypoid (that's something else), but a hyperboloid. See
attached.
(Credit:
<https://divisbyzero.com/2010/03/20/making-a-hyperboloid-out-of-skewers-and-rubber-bands/
<https://urldefense.com/v3/__https://divisbyzero.com/2010/03/20/making-a-hyperboloid-out-of-skewers-and-rubber-bands/__;!!LIr3w8kk_Xxm!5f2Ky5J7-0n2oAtHObZ8ORPtWIVeM2loLfQQxJ3WcQmJWm_H-52Fr-drpqLO-EE6AshJO9Ps1w$>>)
A bunch of long straight drilled holes, at an angle and an
offset from the
nozzle axis, outline a fairly nice nozzle shape and can serve
as cooling
passages for it. The trick is accurately drilling long holes;
"gun
drilling" is the generic term for this.
And of course, if you can do that for the nozzle throat, you
could go
whole hog by drilling passages in a cylindrical chamber and a
conical
nozzle extension, with the ends matching up to the throat
passages.
I'd say aluminum is an under-appreciated material for
engines. You really
have to cool it well, because it loses strength so rapidly as
it heats up,
but its thermal conductivity is far better than steel's, which
helps.
(Not as good as copper's, admittedly, but it's also rather
lighter.)
Henry
