[Coco] [coco] CNC coco

[Gene Heskett]

On Friday 08 February 2008, George Ramsower wrote:
> I learned a long time ago that cutting steel with an abrasive wheel is okay
>if the steel isn't very thick. On thick pieces, it is important to keep
>moving the part and get a cool spot. As the steel heats, it liquifies and
>causes the cutting wheel to literaly float over the surface..generating more
>heat and wasting time. If you were to work a square piece as if you
>drilling, ie: hit, get off, hit again, get off.... etc. it would work a
>little better. It's called "Pecking".

There are two ways to cut steel with an abrasive wheel.  For thick stuff, 
given enough wheel and power to turn it, say a 14" wheel turning 11-13k rpms 
with a multihorse motor, bear down until the fire turns from orange to white, 
at which point the spinning wheel is carrying fresh oxygen into the burning 
steel and you effectively have a very precise cutting torch.  Wheel wear is 
minimal after the first shot to get the cut up to ignition temperature.

Or you can peck and keep it cool so as not to damage the wheels binders 
although the wheel will still get dull in time & need a pass with the 
dressing stick to expose sharp abrasive edges.  Keeping the contact area 
small allows a greater per unit of area pressure for a given amount of power 
available.  Carried to the right extreme, you also get wheel wear that keeps 
fresh abrasive available.  I don't think I'm reaching that, not enough motor.

ATM, its been doing its thing, lights out for the last 3 hours, making a pass 
thru the groove already cut at around 30 thou a minute, then retracing and 
resetting 20 thou deeper to do it again, so the contact patch is fairly 
small.  And I'm still not getting enough wear to keep it sharp, darnit.

I made an AC ammeter to watch the motor draw so it would be using as much of 
the motor as was safe.  Feed speeds adjusted to peak at about 2/3rds of a 
blow fuse. :)

Silly Q though George.  Would I be ahead of the game if I had it pecking the x 
axis as it sweeps the y?  In and out about 2-3 thou at a good repeat speed?  
I could do that short distance 2 to 3 a second I think. I suspect I'd need a 
heavy flywheel mounted along with the wheel to supply the pulsing peak drag 
though.  With my current, and undersized arbor, the flywheel represents a big 
problem though.  It would also require a major loop rewrite.  And put a LOT 
of wear on the x screw.

Food for thought.  Moot if I wanted to spend 2 bills on a cutoff saw.  Which I 
just might do yet, this is getting to the point of boring. Emc says it will 
be done Monday, late... :(  If it blows another fuse, I buy the saw.

> Last year, I had to cut a four inch round stock with an abrasive wheel. It
>didn't take long to SEE what was happening. So I started rotating the stock
>as I was grinding through it and suddenly it was finished.
> Use a mill to finish the part after it's rough cut. Don't count on a saw to
>make a good part. Even a machine shop will cut off a piece large enough to
>finish it with a machine to make a good part. It is a lot faster and more
>precise.

Pretty much true, I expect I'll have to finish face this part with a bit of a 
dip in the center, say 2 to 3 thou, for crush room anyway.  That I think I'll 
do after drilling the pulldown bolt hole so I have a place to lower the bit 
into and then raise it back to the endpoint just outside the work.  Endmills 
don't always dig cut so clean.

When working in alu, I actually use my 12" bandsaw as a hacksaw, with a 4 tpi 
1/4" blade in it, I can cut a 5" thick block of alu at about an inch a minute 
and it doesn't seem to bother the blade, I done that lots.  But not steel, 
too hot, too fast, or not hot enough and fast enough.  You can cut steel with 
a bandsaw with a piece of packing strap for a blade if its moving 20,000+ 
feet a minute & has enough power.  Friction cuts that way just as well.

> I don't think my coco cnc machine can do this, unless it's about 1/4 inch
>thick... and our energy resources will last long enough or the sun doesn't
>burn out first.

We'll probably run out of oil first. :)

>George
>----- Original Message -----
>From: "Gene Heskett"
>
>> On Friday 08 February 2008, George Ramsower wrote:
>>>WOO:HOO!
>>
>> Join the club George.  I have a similar project under way.  Lacking a
>> power
>> hacksaw, I'm crazy enough to use a WhizCut abrasive wheel to cut off the
>> amount of a 2" sq steel bar that I need to make the clamp block for a
>> boring
>> bar, spinning it with that puny little motor on my micromill.  I blew so
>> many
>> fuses I hit the shack for a meter & enough stuffs to make an amperage draw
>> meter so I could see how hard the motor was working, and in about 10 hours
>> run time over the last 2 days, I'm about .85" deep with the cutting line
>> right now.  But its going faster since I found it cut better if I swept it
>> back and forth with emc, only cutting 50 thou at a time, which narrows the
>> cutting surface and speeds the overall cut.  A straight plunge cut soon
>> has
>> so much surface in contact with the wheels edge that I can only advance
>> about .002/minute.  But I should have pretty close to an optical flat on
>> the
>> cut surface, which will be the bottom, sitting on the lathes cross slide
>> when
>> I'm done, which is not the ideal as I'll have to make another pass and
>> dish
>> it in the center about 3 thou so it will crush into 100% contact when
>> tightened down.  I had to do the same with that Phase II quick change tool
>> post, otherwise it was just so much rubber sitting there.
>>
>> This is truly lights out manufacturing as once a cut pass is underway, I
>> can
>> leave and warm up my feet & get a fresh cuppa.  Sometimes one measures
>> progress with a micrometer?  :-)
>>
>>> When I started this project, it  was mostly an experiment. Now it's
>>>becoming a reality.
>>>
>>>I'm about to crash and burn... kuz I wus up all night, working out the
>>>software on this coco to make this machine work.
>>>
>>> I suppose it's the approximation of success that does that.
>>>
>>> Anyway... it's so cool to see the thing actually move around  the table
>>> as
>>>planned.
>>>
>>> After some sleep time, I'm going to actually make an automated machining
>>>process to finish the construction of the X axis.
>>>
>>> I'm tired. I'm turning it off and landing... It might not be a smooth
>>>landing but, if I can walk away, it's a good landing.
>>>
>>>
>>> Piper Cubs forever!!!
>>>
>>>
>>>Buenos Noches, amigos! Even if it IS almost luch time.
>>>
>>>George
>>>
>>>
>>>--
>>>Coco mailing list
>>>Coco at maltedmedia.com
>>>http://five.pairlist.net/mailman/listinfo/coco
>>
>> --
>> Cheers, Gene
>> "There are four boxes to be used in defense of liberty:
>> soap, ballot, jury, and ammo. Please use in that order."
>> -Ed Howdershelt (Author)
>> Neurotics build castles in the sky,
>> Psychotics live in them,
>> And psychiatrists collect the rent.
>>
>> --
>> Coco mailing list
>> Coco at maltedmedia.com
>> http://five.pairlist.net/mailman/listinfo/coco
>
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-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Davis's Dictum:
	Problems that go away by themselves, come back by themselves.