> professional machine shop has a good many more things to be concerned
> with. Among them are efficiency, productivity, material costs,
> competitiveness...
YES ! Agree 100%.
>
> It's a common misconception that tolerances amount to "how badly the
> thing can be made." Tolerances and allowances are needed to ensure fit
> and function of independently manufactured parts.
>
Also.
> I retired as Chief Technologist in one of NASA's largest machine
> shops, after a career as machinist, metrologist, tool and instrument
> designer. The largest part of my job was to advise on the
> manufacturability of parts and assemblies. Any time I saw a design
> with 10 micron tolerances, I required a detailed tolerance analysis to
> demonstrate the need.
Sometimes.
It is very true that apparently it was common practice at one point for
guys with cad to just spec very tight totally unnecessary tolerances.
I just dont see it anymore, these days.
I think everyone moved on.
>
> Reliance on tight tolerances to achieve fit and function is a hallmark
> of bad design.
Yes !
>
> I have installed an inexpensive pair of DRO's on my mill and found
> them entirely satisfactory. Details here:
The key is the first part;
Efficiency and productivity and competitiveness.
No-one here is going to be either efficient or productive by machine
shop standards.
What takes someone here (like me) say 40 hours (my set of 48 wrenches
might take that much) can be knocked out in around 2 hours on a modern
machine (horizontal mill, multiaxis, or several multi-axis turning centers).
Using a big machine (rotary transfer multiaxis) could do them in maybe
10 minutes, with a 6 hours setup time.
The real point is that the investment is effort is far more than the
additional cost in making it as good as possible, and much more than
using the best possible material.
In making a unique, superb, object, from the best materials, I am
actually getting about 6x more payback from my efforts (however modest
they may be), with a minimal increase in additional effort (maybe 5% in
my case).
If I spent the time, and made the wrenches so-so from mild steel, 2
years from now I would have rusting, dinged, sloppy, poor homemade
tools, essentially worthless.
Instead, for a weeks work, I will have a set of aerospace quality tools
worth at least 5000$, for 1000$ in materials, that will never rust, are
unlikely to fail in my use ever, and will appreciate in time.
They will also be a fantastic calling card demonstrating the quality and
productivity and competitiveness I bring to everything.
They will also asolutely, totally, 100% certainly bring in many times
the materials cost in new work and sales, just from the looks, wow, and
demo aspect alone.
I do not conder the inside mics, gage blocks, or whatever tools I need,
to be part of the cost of producing them. Just the materials.
Most things we make cannot and should not try to compete with mass
produced lowest-cost stuff.
It´s just not worth it.
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