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Home✈️Aircraft🚁HelicopterHelicopter Main Discussion › Lets make this "Its CNCed" clear
09-02-2015 10:02 PM  4 years ago
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RM3

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Killeen, Texas - USA

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Lets make this "Its CNCed" clear
Ok just a rant,
Not a day goes by that someone somewhere pulls this bit about CNC parts somehow equate to quality.
I have been a machinist for the better part of 10 years and have been working with CNCs for about 3. I have just put together my own CNC mill just for fun...Others on this site have probably double or triple the experience and access to very nice 5 plus axis milling centers etc.

CNC does not automatically equate to quality.

the purpose of CNC is to make parts faster...the quality of the finished part is dependent not just solely on the equipment but on the quality of the tooling, programming, material selection, setup and inspection by the machine operator before, during and after parts completion.

That being said I have seen some beautiful parts made on old manual cast iron vertical mills and lathes.

rant over...
showing a preference will only get you into trouble, 90% of everything is crap...
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09-02-2015 10:04 PM  4 years ago
don s

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Chesapeake, VA

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Garbage in, garbage out?E820, Raptor G4N, X50F/E, E620, Forza 450, and some planks.
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09-02-2015 10:23 PM  4 years ago
Andy from Sandy

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UK

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A guy at my club is also pretty clued up on this stuff and thinks most of it is very poor where others think they are looking at quality.
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09-02-2015 11:53 PM  4 years ago
ICUR1-2

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Ottawa, Ontario

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💎Sustaining Member
I have always equated quality with time
spending time, paying attention
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09-03-2015 12:09 AM  4 years ago
fastflyer20

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N. Tonawanda, NY

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I have been around CNC machines for 30 years, owned my own mill and lathe for 20 years and worked in a screw machine shop for 14 years. I have seen all produce gems and scrap...Tom
CAUTION - my posts are based on my experiences, yours may be different.
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09-03-2015 12:13 AM  4 years ago
AirWolfRC

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42½ N, 83½ W

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Yup . . . a CNC can produce junk just as easily as a person can
. . . who do you think sets up and programs the CNC ?

A CNC can make junk lot faster . . .
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09-03-2015 01:08 AM  4 years ago
oldfart

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Vancouver, Canada

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There is also a big difference in the precision quality of CNC and milling machines available for big production commercial operations. There is a big difference in the precision of the parts that can be made with CNC machines made in China compared to those made in Switzerland for example.

There is also a big difference in the quality of the different metals that one manufacturer may use compared to that of another. The part for both may be CNC machined, but the metal used in one may be far inferior to that used in the other.
Phil
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09-03-2015 01:50 AM  4 years ago
Dingo07

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Irvine, CA - USA

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I think the disconnect is that a lot of people don't realize an operator has to program the CNC machine. Most probably think they just dump a CAD file into it and POOF, out comes the part - if it were only that simple!
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09-03-2015 02:03 AM  4 years ago
mr dan

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Stockton Calif

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Lets not forget the materials being used. No matter how well the layout and design is, the cnc machine cannot make a quality part if the material is sub par metals."R.I.P Roman" Citizen 0094 in the Nation
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09-03-2015 02:32 AM  4 years ago
whoamis

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san francisco, ca

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I think this started when CNC was the alternative to "plastic."

And not that killer carbon-infused plastic, but TRex 450 plastic.

Basically a synonym for "(anodized) aluminum."

But I think it's fair to point out that we should leap to quality conclusions, ever, based on an acronym, whether it's CNC, CF or ABEC.
oops, bounced it!
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09-03-2015 03:23 AM  4 years ago
Aaron29

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USA

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If CNC is well programmed and using quality stock, with proper fixture and tooling is kept fresh, it should be high quality.

However, there's a lot of ways to screw up: Bad design. Substandard alloy or material. Bad fixture. Worn out tooling.

Machinist basics still apply.

CNC just describes the process. Good or bad stuff can come out of a computer or a flesh and blood machinist.

Unfortunately in today's high quantity cut cost environment, cnc can be an attempt to push more product than a company should.

It's a tough call. Done right, it's every bit as good as a master machinist. Done wrong, it's pure sh1t
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09-03-2015 04:30 AM  4 years ago
RM3

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Killeen, Texas - USA

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...exactly...

just drives me nuts when I hear... "oh its top of the line cause its CNC"...
or " i prefer CNC parts..."

I think most that state this stuff couldnt tell the difference if a part was made on a haborFreight import, converted with cheap surplus parts to CNC run by a 20 year old computer and polished up on a buffer.
showing a preference will only get you into trouble, 90% of everything is crap...
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09-03-2015 04:34 AM  4 years ago
EEngineer

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TX

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Here's some examples of very high quality CNC machine work.

http://www.ronald-valentine-engines...Collection.html
Logo 600SXs, 800XX, TDR IIs
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09-03-2015 06:29 AM  4 years ago
TMoore

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Cookeville, TN

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Here's some examples of very high quality CNC machine work.
http://www.ronald-valentine-engines...Collection.html
Sorry to say but just about all of those engines were produced on manual and automatic equipment long before the advent of CNC. All the Cox engines were produced on standard production machines back in the day. The crankcases were extruded aluminum.

The term CNC (Computer Numerical Control) covers a lot of ground and can encompass a lot of different machine types and processes. There are no guarantees that CNC automatically equates to quality because "quality" can be a moving target. Plastic parts, properly designed and molded can take the place of machined parts in a lot of application. In the case of injection mold tools most of those are machined on CNC machines and oftentimes finished and polished by hand.

In my career I've seen as much or more scrap produced on CNC as on manual equipment. Trust me, when you run a 36 axis 8 spindle CNC Bar machine with a sub 20 second cycle time, you can make a lot of scrap quickly if you aren't on top of the process.
Part 107.
The only ZERO flight hour certificate in the world.
It's like getting a driver's license without the driver's test.
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09-03-2015 06:32 AM  4 years ago
EEngineer

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TX

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So you've visited his machine shop?

Nice place, isn't it?....
Logo 600SXs, 800XX, TDR IIs
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09-03-2015 06:55 AM  4 years ago
TMoore

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Cookeville, TN

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No need to go to his shop. If you have any experience in the custom metalworking business you can plainly see that there is nothing about those engines that require CNC processes and in fact the Cox engines as I said were never produced on CNC machines.Part 107.
The only ZERO flight hour certificate in the world.
It's like getting a driver's license without the driver's test.
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09-03-2015 07:01 AM  4 years ago
EEngineer

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TX

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You're correct with respect to Cox engines.

But you're mistaken if you think Ron's engines are not made with CNC tech.

Which is why I asked if you've visited his machine shop.
Logo 600SXs, 800XX, TDR IIs
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09-03-2015 07:02 AM  4 years ago
EEngineer

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TX

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You twisted Ron's engines into Cox engines.

Major differences, don't you know.

I thought you were a fellow engine collector. Perhaps I'm mistaken.

Cheers
Logo 600SXs, 800XX, TDR IIs
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09-03-2015 11:45 AM  4 years ago
Richardmid1

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Leeds, England

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CNC machines simply produce accurate parts faster. Quality comes from, well, the Quality Control, i.e. how regularly the parts are checked and how tight the tolerances are kept. A clone heli CNC part may have strayed slightly out of tolerance but kept. A Hirobo (for example) CNC part will not only be kept within tolerance but the tolerances on the drawing will be smaller, a Hirobo part that strays out of tolerance will be throw in the scrap bin.60% of the time, it works every time!
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09-03-2015 11:47 AM  4 years ago
Richardmid1

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Leeds, England

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Trust me, when you run a 36 axis 8 spindle CNC Bar machine with a sub 20 second cycle time, you can make a lot of scrap quickly if you aren't on top of the process.
Any pictures of such machine?
60% of the time, it works every time!
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