CNC (computer numerical control) machining allows the production of custom precision parts for scale models. The author worked with a company called HLH Prototypes in China to CNC machine custom side frames for a scale helicopter gearbox. Within 10 days of submitting the 3D CAD file, the author received the finished parts, which fit perfectly and worked well in the assembled gearbox. CNC machining makes it possible for hobbyists to economically produce small batches of complex, high-precision custom parts for scale models.

1. ;
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TEXT A PHOTOS BYJIM RYAN
e recent y d scussed how
regujar modelers could
use the revo ut onary
techno ogy of 3D printing
to produce custom parts
for scale mode s camera dTones and
0ther model fg applicat ons. 3D printing
s ndeed a game changer but there are
st I compofents that, owing to strength
or to erance requ rements, need to be
'nacl l.d o r. o'ai r r L^ o olre
metals. [,4achin ng prec si0n components
s a cha eng ng art form, and tools
w th the necessary precls 0n can cost
thousands of dollars Fortunate y,lust
as 3D pr nting al ows us to bypass the
expense and comp exlty of hav ng p astic
parts nject on molded, custom CNC
machin ng makes it pract cai to pr0duce
p-.. ..or -reL.l o"r-. to,oLl . a
spec fications.
78 N4odelAirplaneNews.com
HLH Is managed lry JafiL.s
Murphy, who rElo<ated lo
Chlna h 2008. Ihe compary
has morc than 2O0 emplo!'ees and
provlde5 a wlde rdn8e of ma(hhlng and
rapld-prototyplng processes.

2. WHAT IS CNC MACHINING?
CNC (Computer Numerical Control)
machiningtakes in a family ofprocesses
that use computer controlto operate
milling machines, lathes, and other
equipment. Instead of manually running
the machine making toolchanges, and
repositioning workpieces, operators
generate "toolpaths" on a desktop
computer, effectively telling the machine
not only what shape to cut but also what
cutters to use and how quickly to operate
the CNC machine then cuts the parts
with little operator involvementi some
machines can change cutters or evenload
fresh workpieces automatically. Once the
tool pathis generated, the machine can
produce anynumber of copies
With the growlng influence of rapid
prototyping in the industrial world,
there are a growing number of suppliers
ar ound rhe world who use CNC machin.r g
and otherprocesses to quickly and
efficiently produce one-off or small
batch prototypes. I recently started using
one of these suppliers HLHPrototypes
(hlhprototypes com), to produce custom
components formy scale helicopter
mechanics. The process is easier and more
affordable than you might expect:My
custom gearboxparts were less than 5100,
andl could order smallbatches for less
thanSS0per set
OVERVIEW OF }ILH PROTOTYPES
HLH Prototypes is a rapid-prototyping
supplier in Shenzhen Chjna.It provides a
broad array of manufacturing processes
jncluding CNC machining 3D printing,
inlection molding andvacuum casting. lhe
company was founded in 2001 and now has
more than 200 employees lhey currently
operate more than 40 CNCmachines,
along wir h 3D printer s. va.uum casting
machines, andinjectionmolders.HLHis
managed by lames MurPhY, a natlve of
!tl
Larg€ CNC machlnes can handle a wld€ range ol workplec€s and materlals. When machlnlng metal, a <onstant
tlood of cuttlngfluld/coolant ls pumped over the workplece to rcduce cutterwearandlmProvesurfacefinlsh.
t,l
NOVEMBER 2015 79

3. CNC Machined Parts
the United Kingdom who moved to China
in 2008. the compary has a strong online
presence, and it typically turns around
quote requests overnight.
GETTI G STARTED
'lhe first step, of course, is to draw your
components in 3D CAD (Computer-Aided
Design). Rhino is my personal favodte 3D
design application, but therc are many
other options, including open-source ard
web-based products.
[,fy prcject was to build a 42-degree tail
rotor gearbox for a scale Huey helicopter.
Because I was using parts from Align
T-Rex 600 tail units, the flrst step was to
carcfully measurc the stock side plates
and draw them in the CAD environment.
'fhis 2D computer model was then
mirrored at a 42-degree angle to get the
basic layout for my new side plates, the 2D
design was converted to a 3D solid, and I
was ready to email my design for quoting.
Because HLH'S business model
emphasizes speed, its pdce quote includes
the cost for international FedEx shipping.
If you can wait a tew days Ior your parts,
you can save a Iittle on shipping costs, the
terms are 50% down, with the balance
due on completion, and HLH commonly
completes small prctotypes in one to two
weeks.
Based on calEfrrl measu*ments ot
the stock Allgn tall udt, I dr€fl rry
42-degEe slde lram.s uslng Rhlno,
tnylavo te 30 dGslgn proararl- I then
emall€d the 3D model to HLH. Hces
are typlcaly quoted ovemlghL My
custom aearbox parts rrere less than
S1O0. and I could oder small betch.s
Ior less rhan S50 per set.
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My completed slde fr.mes errlt edvla FedExFn lo daysaftcr ordfflrE. Ihe rdls€d bosses aEund
the saew holes dlo/ morE poslB,€ allgment.nd wouH bc lmpracdcalwlthout C C technoloBr.
the ball beadng! were r p€rfcct press-fit.
80 ModelAkplaneNews.com
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Above and below: Cl{C maclinlng rEkcs lt posslbh to Drodue
complex parts wlth mlnlmal dlEct labor. HLH can Erydy .try
number of parts, lrom slryle unlt! to thousands. You <an s€e
hundreds of product ex.mples ln HLH'S Fllckr album.

4. '
RESULTS
My sales representative kept me posted onmy order status
and provided tracking info when my parts shipped.Ihad
mypartsin handjust 10 days after placing my order, which
is impressive. Sohow did theylook? Thephotos speakfor
themselves. l was pleased that all tool marks had been buffed
out, and the dimensional accuracy simply could not have
been any better.'lhe assembled gearboxruns silky smooth
and Iooks as good as any commercialproduct. I can foresee
using HLH's services for allsorts of future projects, such as
retractable landing gear, scale rotorheads, and custom gears.
lhe possibilities are neariy endless. +
82 ModelAjrplaneNews.rcm
',:
!r Here are lust a few of HLH'S fle€t ot machtnes. fte company
op€rates more than 40 CNC machlnes ln a range ofstz€s tn addtton
to 30 prlntlng, Inlecdofl moldlng, vict um castlnt, and lr,ke EDM
(electrlcaldlscharge machlnlng).
.,;,I After CNC machlnlng ls complet€d, parts go to post-
6nlshln& wheE remalnlng tool marks are buftud our.
HLH canalso pmvlde hlgh-gradepollshedfnlshes.
palndry, oranodlzlngat an addltlonal cost.
-l: ir,: r. Ihe ass€mbled 42-d€gr€e gearbor
Iooks as good as any commerclal product.
Gearlash ls permanently set and
requlres no adjustment. lvlth CNC
machlnl.rg, lt's posslble for retular
modeleE to d€slgn and produce
pre€lslon custom ass€mblles
pl- Q, o
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