Re: [CAD_CAM_EDM_DRO] Re: How much accuracy is enough?

Ken,
You are absolutely correct in this statement.

HOWEVER; I will use my own hobby work as an example.

Once upon a time (etc) I was in college and as a ME student, was required
to take a machine shop course.
The course was built around the making of a "C" clamp out of highly leaded
steel and involved the use of the lathe, mill, shaper, and miscellaneous
hand tools to complete the course. Accuracy of the clamp was graded on a
tolerance of +/- 0.005"

I had one heck of a time trying to obtain that much accuracy. Now today, I
achieve that routinely and my GOAL
(read personal satisfaction is +/- 0.0005. WHY,

Simple. If I hone my skills on projects that don't require that level, they
will be available if/when I have a project that will require it. If I wait
until I need it, the project will be scrap. The first thing I had to learn
was SLOW DOWN. It is amazing how much temperature affects a work piece.
Measure it when it is still hot just after a cut and again after the
proverbial smoke break and you will see what I mean. Also, today; my tools
can be read to far more accuracy. Back in college, it was cheap mike that
was able to read to 0.001 (maybe) and today, I have DROs on my lathe and
mill that reads out to 0.00008"!

Again, I have to state this is my HOBBY read RELAXATION. I can go to the
shop and spend a whole day or evening just to make one piece and enjoy it.
Especially if I can hold to a degree of tolerance that a few years ago I
could only think about (or remember my Dad talking about as he worked in
the aerospace industry that required these tolerances).

To sum it up, as this is a hobby group, a tolerance of +/- 0.00001" MIGHT
be accurate enough for the challenge and bragging rights as I am NOT in a
production setup where time is money.

Who knows, maybe next year I can afford the tools to be able to measure
that accurately:-})
At 03:35 AM 3/12/02 -0500, you wrote:

>Chris raises some interesting questions regarding "how much is enough"
>and I have been asking myself some of those questions lately. Not just
>in relationship to CNC but in terms of general methods of work. Overall
>I am finding I err in many projects being too accurate strangely enough.
>I suppose the response might be, "How can you be too accurate?!! Surely
>it's better to err on that side?" True if you have all the time + $ in
>the world. I don't. All the additional time (and money in some cases) I
>spend on accuracy which is not required is wasted except in some
>sort of "inherent-reward for craftsmanship" or fulfilling some "aesthetic
>sensibility". We're not talking about types of commercial work where
>the QC requirements of the customer dictate regardless of "real issues"
>(translate: "We're GM! .... and you're not ... end of discussion.")
>The more accuracy you pursue, the more money and time you spend to
>achieve it, in the end does it really make a difference in terms of
>the functionality of the end product? (don't start your response to
>this with a lecture about pistons and cylinders, I know it depends
>on what you're making :-).
>
>The above leads up to the opposite side of another question I posted
>regarding "true cost of the ideal conversion project". How cheaply
>can someone get into this hobby/work and still be productive and make
>"real stuff"? Again, I know the above leaves out a lot in terms of criteria
>(required part fits related to function, materials typically machined,
>repeatability for multiple interchangeable parts, etc.).
>
>I have another reason for asking this in that I have a friend who works
>on footbridge and well projects in Kenya. It is amazing the effect that
>the implementation of hi-tech principals and materials in lo-tech, low
>cost scenarios can change people's lives. I'm wondering about a
>"cottage industry" implementation of lo-cost CNC set-ups in providing
>opportunities there and a plasma table made of mainly off the shelf
>components might be just the thing.
>
>Ken Jenkins
>kjenkins@...
>
>
>
> > Message: 13
> > Date: Mon, 11 Mar 2002 18:08:09 -0600
> > From: Chris L <datac@...>
> > Subject: Re: New Member to be has interest in home-brewing plasma table...
> >
> > Short and Sweet Version.............
> >
> > I Built my First CNC Plasma machine on the cheap because I needed something
> > quick. I used Cold Rolled Steel for Linear Rails and simple Cam
> Followers to
> > slide the carriages on it. Motion was provided by some very small stepper
> > motors using Belt drive to Rack and Pinion.
> >
> > Having Built a very qualified CNC Router already with the "more appropriate
> > components", I was a bit hesitant to use such cheap Linear Motion
> Techniques.
> > But, After using it a while, I am not sure that I would do it much
> different
> > next time.
>.
>. deleted
>.
> > Additionally, I gave some consideration to the necessary accuracy of a
> Plasma
> > Cutter. We're not talking Laser here..... The accuracy of any project you
> > typically use a plasma cutter for does not come into tight tolerances. I've
> > made some components for Automotive applications that just simply do not
> > matter if they are off a few thou. This is true especially if the
> components
> > get welded together. If the edge is smooth but off as much as .030 no one
> > would know. I've never measured anything off that much even with the cold
> > rolled rails.
>.
>. deleted
>.
>
> > Granted, My machine only cuts a 4' X 4' area. so if your building something
> > much longer you would have to make sure your rails are straight.
> >
> > I would also use the Rack and Pinion again...... No way any type of screw
> > could last a long time in this application. As long as the rack is
> placed on
> > edge so any Swarf can fall out you are set. Amazingly, I only use some 80oz
> > motors. She'll run as fast as 400ipm using a 36 volt supply. Obviously, a
> > little bigger motor couldn't hurt but these amaze me.
> >
> > Finally, I only have it set up for 2 axis. I can see that next time I would
> > plan for a 3rd Z axis and some type of software arc control. You do need to
> > have the material pretty straight and level to get a good job.
> Sometimes that
> > isn't so easy.
> >
> > So, as crude as it sounds, Plasma is one application where doing it the
> > "cheap" way just might be an excellent way for the hobby low volume user.
> >
> >
> > My experience in a nutshell......................
> >
> > Chris L

Bubba

OLDER THAN DIRT
Country Bubba
(Actually the inventor of Country and Bubba)

axtein@...
LaGrange, GA

http://members.dicomm.net/~axtein


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