[Coco] [Color Computer] [coco] Coco CNC

[Gene Heskett]

On Monday 12 February 2007 01:10, David Roper wrote:
>Hi George,
>
>I don't have a clue what you're talking about, but it was an interesting
>read, none-the-less!

So let me explain some of the acronyms.

>Kind regards,
>David
>
>George's Coco Address wrote:
>> Okay!
>>
>>  I've been working on my Coco powered "Tiny CNC" machine this weekend.

CNC=Computer Numeric Controlled.  Every part you make is identical to the 
last one if the tooling doesn't break or wear.  A text file tells the 
computer where to run the motors to.  Just re-run the program for the 
next identical part.

>>  Whew!
>>
>>  What a task! I discovered that the axis designations were all messed
>> up.
>>
>>  (You learn a LOT when working in a machine shop)
>>
>>  All three were wrong. X, Y and Z were wrong. So I renamed them and in
>> the process, I lost the driver(B09 driver) for the REAL Y axis.

X is normally the left to right motion of the table the piece to be carved 
on is attached to.

Y is normally the to/from, or across the width of the moving table motion.

Z is normally the up/down motion of the carving spindle, so that one can 
do 3d carving.  On bigger machines, the spindle is rigid in the castings 
and the same effective motion is done by raising or lowering the table 
itself, called the knee.

>>  No problem, I thought. Just rename the X or Z axis driver. Well, it
>> didn't work. After two days, I discover several problem with my
>> hardware that proved that the port for the Y axis was wired
>> incorrectly, the cable that connected it was also wired incorectly and
>> the software to correct this error is now lost.
>>
>>  No matter about the software. I repaired my mistakes with the
>> hardware and now the software to drive the servos works correctly. I
>> can swap the cables to each of the servos and it works correctly.
>>
>>  Since I've been working at a machine shop, I was forced to buy some
>> precision instruments such as a dial caliper. My old vernier caliper
>> was not acceptable at work.
>>
>>  Hmm. I really can't see any accuracy difference except for the fact
>> that the dial is easier to read.
>>
>>  Anyway..... Math always works......
>>
>>
>>  All three lead screws are 32 TPI. The three servos are 200 steps per
>> inch. Doing the math, this comes to 6400 steps per inch, or precision
>> to .00015625.
TPI=Threads Per Inch of the screw.
>>
>>  Not bad, but not as good as what I work with at my job.
>>
>>  I've learned that offsets and HOME are important. (I did have trouble
>> figuring into this on my coco)
>>
>> FINDING HOME:
>>  Originally and even now, I use brute force to drive the axis into a
>> mechanical stop. The stepping motor would stall there and hum until
>> the software stopped driving it. At that time, I set the software to
>> assume it was HOME. Actually, it works! However, it isn't elegant. So
>> I'll add some micro switches to the sytem to fix this. Besides, I can
>> move that switch to a more convenient place for each project.
>>  My coco takes a long time to step these motors to where they are
>> supposed to be. Basic09 is a lot faster than RS Basic, but it doesn't
>> hold a candle to ML. .....Someday, maybe!
>>
>>  I envy you folks that can "whip up an ML program".
>>
>>   So far, I can move each of the three axis from home to the limit and
>> back and my dial indicator reports a return of exactly zero. This
>> implies that my stepping motors, power transistors, software and math
>> are working correctly. The only problem is finding home. The micro
>> switches will take care of this.
>>
>>  Backlash on each of the three axis are different. The Y axis is only
>> about two steps on the stepping motor. This is incredible!. However, I
>> took extreme care to minimize backlash when building this thing. I
>> won't go into detail on how I did this until later.
>>
>>  I've learned at work, that extreme brute force and extreme mass of
>> machinery is important to get the results necessary. Heavy metal is
>> good! However, it's expensive. The machines that I work with cost a
>> TON of money. We're talking 600 thousand dollars for a small one. My
>> first 4k coco was $300 and took a couple of pay checks to pay for it.
>> So, I won't expect to do what those monsters can do. I just want to
>> make some small gears, sprockets and pulleys. Later, I want to do some
>> 3D stufff, small things.
>>
>>  More later....
>>
>>
>>
>> George

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
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message by Gene Heskett are:
Copyright 2007 by Maurice Eugene Heskett, all rights reserved.