Klarinet Archive - Posting 000544.txt from 2005/06

From: "Keith" <100012.1302@-----.com>
Subj: Re: [kl] metal clarinets
Date: Mon, 27 Jun 2005 05:53:04 -0400

Ormondtoby

> Keith wrote:
>
> > Cost - the mould is more expensive but the subsequent operations
> > cheaper.
>
> I wonder whether this is true?
>
> Molding machines are rated in terms of "tons of clamping
> force", which means that a certain amount of clamping force
> is required to hold the two halves of the mold together while
> the molten plastic is pumped into
> the mold. If the mold halves separate, then plastic oozes out of the
> old instead of filling the mold cavity completely. Presumably a mold
> that is twice as long requires a much higher clamping force
> (twice as much?).

True. Yes, approximately twice - controlled by the projected surface area of
the component.
>
> I've seen injection molding machines in action. They can be huge - as
> large or larger than an automobile --- in order to supply
> sufficient clamping force over the entire platen which holds the mold.

Yes.

>
> There's also the matter of cooling, which must be engineered in order
> that each part cools and shrinks evenly. Slow cooling means longer
> cycle times, which translates directly into hourly production
> costs because it controls how long an expensive machine must
> 'do nothing'
> while the mold either cools or is removed from the machine
> and a different mold inserted for the next part.
>
You are right that cooling time is significant. But for a longer part of the
same cross section the cooling would not be significantly different, since
the cooling is essentially radial.

> I don't know anything about extrusion, but I presume that a
> longer extrusion with variable diameter faces similar 'extra
> production costs'.
>

You can't extrude parts with a variable diameter.

> Machining one less tenon + socket and applying one less cork
> may be a relatively minor saving compared to the operating
> cost of a larger & slower machine.
>

Machining costs are generally huge compared with moulding costs **provided**
that you are making a lot. Even including cooling times you would mould a
complete clarinet much faster than you could machine a tenon and socket and
fit a cork. And the moulder will be operated by a relatively unskilled
operative, unlike the machinist.

So the mould would cost maybe $50,000 and the machine $500,000. As long as
you make 100,000 clarinets, this is a mere $5.50 of the cost. For this you
will get about five minutes machining/corking/fitting, less the cost of two
other parts, the tenon reinforcement and the ring. And you have one less
setting up operation for the drilling of the holes. (You can't mould-in
holes that are anything other than in-line or 180 degrees apart.

But if you make ten clarinets a year, moulding is unlikely to be cost
effective!!!

So if I were running a low-end clarinet-making company, I would plan to
dominate the world market with 100,000 a year, mould in one piece, design a
sexy cool mini-Wiseman cylindrical case also made in quantity, and tell my
marketing department to sell the superior virtues of one-piece instruments
and cases that look like something hitech rather than a fusty parent's
briefcase.

Keith Bowen (wearing retired engineering professor & company technical
director hats)

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