The person in question imports metals for race cars, aircraft grade
steel and aluminium tube, but sells a lot of material to the local home
aircraft builder market, the local sport aircraft chapter seem to think hes
great, so I was very surprised when he told me he was getting a plasma
cutter especially for cutting 4130 steel plate, so thought I had better
check with someone more learned than me in these things, heat and aircraft
grade metals are not a good combination in my opininon.
Chris Johnston
North Richmond NSW
Australia.
----- Original Message -----
From: "Brian Kraut" <[email protected]>
To: "KRnet" <[email protected]>
Sent: Saturday, August 26, 2006 1:23 PM
Subject: RE: KR> WAF Plasma cutting
>I am not a structural or materials engineer. I design electronics. I
>would
> think that engineers working for an aircraft manufacturing company would
> know more about it than I do, BUT it sounds a little fishy to me. They
> may
> be doing the equivalent of shot peening, but as far as I know that is only
> a
> stress relieving treatment and will not change the hardness and therefore
> the brittleness of the metal. Of course a lot of what is acceptable and
> what is not depends on the safey factor that is designed into the part to
> begin with. There are also different methods of plasma cutting using
> oxygen
> or nitrogen and they do not each leave the same edge on the part.
>
> It all boils down to my stock answer. If you don't know for sure that it
> is
> O.K. then use a method that you know is O.K.
>
> Brian Kraut
> Engineering Alternatives, Inc.
> www.engalt.com
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Larry H.
> Sent: Wednesday, August 23, 2006 12:15 AM
> To: KRnet
> Subject: KR> WAF Plasma cutting
>
>
> Brian, I know someone who is making all of the 4130 fittings which
> includes
> wing attach for an aircraft mfg company. All of the parts are being
> plasma
> cut by computer and then the parts are being tumbled to deburr. The
> tumbling
> process is the normalizing effect. Their engineers think the parts are
> fine.
> What do you think about this practice?
> Larry H.
>
> Brian Kraut <[email protected]> wrote:
> Absolutely not. Plasma cutting leaves a very hard edge. I have had
> several
> 4130 parts plasma cut including my lower gear attach fittings for the KR
> and
> the seatbelt attach fittings and canopy latch parts for the Stang. I did
> some finish machining on some of the parts and the edges were hard as
> rocks
> and needed carbide tools to cut them. Hard edges mean brittle edges.
> Brittle edges mean the high liklihood of cracks starting. The parts I have
> plasma cut are sent to a heat treater to be normalized when done, but if
> you
> are not getting that done don't do it for structural parts. Same applies
> for laser cutting. Water jet is O.K.
>
> Another problem with plasma and water jet depending on the thickness is
> that
> they both cut with a taper and sometimes also a slightly rough edge. If
> you
> do water jet and have the bolt holes cut you want to have them done
> undersized and ream them to finish the holes.
>
> Brian Kraut
> Engineering Alternatives, Inc.
> www.engalt.com
>
> -----Original Message-----
> From: [email protected] [mailto:[email protected]]On
> Behalf Of Chris Johnston
> Sent: Tuesday, August 22, 2006 6:56 AM
> To: KRnet
> Subject: KR> WAF Plasma cutting
>
>
> Can you plasma cut the wafs without affecting the metal??????
> Are the tailplane hinge ply backup plates glued in place or just held on
> by the nuts and aluminium backup plates?
> The plans state the inner hinges have two bolts, does this mean the
> outer hinges have only one bolt per hinge half?
> Can you use two bolts on the outer tailplane and elevator hinge without
> weakening the spars too much?
>
>
>
>
> Chris Johnston
>
> North Richmond NSW
>
> Australia
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>
>
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