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MMD > Archives > April 2017 > 2017.04.21 > 06Prev  Next

SLS vs. CNC for Manufacturing Complex Parts
By John A. Tuttle

If you're going to be having a significant number of complex metal
player parts manufactured, might I suggest having the prototype
made using Selective Laser Sintering (SLS).  While the prototype can
be made on a CNC (Computer Numerical Control) machine, the cost of
having just one part made can be quite prohibitive.

As an example, the part in this picture (see: nylon-frame-1.jpg),
an Ampico A transmission frame which was made out of nylon using SLS,
cost me $55.00.  To have just one of them made out of aluminum using
CNC, the cost would have been $460.00.

The primary advantage of having the prototype made using SLS,
besides to low cost of production, is that you can verify that
everything associated with the part is going to fit and work properly
(see: nylon-trans-2.jpg).  And, if things don't fit properly, slight
adjustments can be made in the CAD file, and another prototype can
be made to verify that the changes 'will' work, without spending
a ton of money.

Unfortunately, with regards to this particular part, having the
part made out of nylon, using SLS, for actual use in the piano proved
to be unsatisfactory.  The two main reasons were strength and surface
roughness.  With regards to surface roughness, you can see how rough
the surface is in this picture (see: nylon-frame-3.jpg).  The sliding
valve surface has to be perfectly flat and smooth.  While the surface
can be lapped* to get it air-tight, it's a royal pain to lap nylon down
to 1200 grit.

With regards to strength, the problem is the lever arm.  It's not
strong enough, and it bends because of the tension of the spring that's
used to hold the sliding valve tightly against the surface.  As can be
seen in this picture (improper-posit-1.jpg), the guide pin for the
sliding valve isn't engaging with the hole in the valve as it must
(see: proper-posit-1.jpg).

In closing, this is the only part that I've had made out of nylon and
the SLS process.  It's my understanding, although I haven't personally
investigated the matter, that parts can now be made out of metal using
the SLS process.  However, I easily found a really neat web page about
"DMLS" at: 
Here again, what I noticed is that surfaces that have to be smooth and
flat do (at this point in time) require post-production machining.

*lap : (a): to dress, smooth, or polish (as a metal surface) to a high
degree of refinement or accuracy; (b): to shape or fit by working two
surfaces together with or without abrasives until a very close fit is

John A Tuttle
Brick, New Jersey, USA

 [ Nylon Ampico A Frame - full size

 [ Nylon Ampico A Frame - close-up

 [ Sliding Valve not properly engaged

 [ Sliding Valve properly engaged

 [ John, Thanks for sharing this new technology and your first experience
 [ using it with us.  I found the video link near the end of your article
 [ to be fascinating. Did you find out the cost for making the same part using
 [ SLS with various metals ?  --Jody

(Message sent Fri 21 Apr 2017, 18:36:43 GMT, from time zone GMT-0700.)

Key Words in Subject:  CNC, Complex, Manufacturing, Parts, SLS, vs

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