CNC Shaper

On 17 Oct, CAD_CAM_EDM_DRO@yahoogroups.com wrote:

> From: Paul <Paul.Corner@...>
> Boy, do you have this disease real bad...
>
> And I thought a BP Series II + Boxford CNC lathe squeezed into a single car
> garage was bad enough - AND I'm off to buy a Grizzly at the weekend to CNC.

A single car garage - luxury !

My "machine shop" is 7'x10', and has a Shoptask, Burke HMill, my AAMCO
7" shaper, compressor, 4x6 bandsaw, floor-standing drill press,
hydraulic press, arbor press, parts washer, small sandblaster, 6' long
bench and enough storage for all the tooling accumulated by a truly weak
and addicted man.

> But CNCing a shaper... Why ? <g>

I bought the shaper on a lark, really. One issue or other of HSM, there
was a picture of something done on a shaper, and it had a truly lovely
finish. I mean, great !

That same day, in our local paper, was an add for a small shaper,
perfect shape, really good price. This I took to be a sign. <G>

Two hours later, I'm making room.

Well, it turns out that a shaper is a pretty cool thing. Cutting inside
keyways is a classic use, but cutting dovetails is a use not commonly
thought of, and the shaper does a fabulous job of that. And does with
a cheap toolbit. ( I hate to think of what bit dovetail cutters sell
for .. and how long those delicate edges last )

Cutting timing gears is another use - just grind another cheap toolbit
until it precisely matches the profile of an existing gear.


Now, why CNC ? Well, small shapers are slow. And while even small
ones do have a power crossfeed, there is a very limited range of feed
rates. On mine, there are really only two rates.

The feed systems on small shapers is a ratchet arrangement. Mine has
been modified from the original, with a larger COARSER gear used.
This gives less range than the stock setup, but the small stock gear
wore out quickly, according to some reports.

Also, a person only wants to move the table on the return stroke,
meaning that you only want to use the power feed in one direction.

Finally, there is no kick-out mechanism to stop the feed at any point,
either at the end of the work OR AT THE END OF THE TABLE TRAVEL. So
while shapers work slowly, you do need to keep an eye on them.

So, adding a stepper to the crossfeed leadscrew AND a sensor to detect
when the shaper is at the beginning of the stroke will allow me ( with
some clever software ) to control the feedrate and the distance
travelled.

This is a useful enough modification. But a person REALLY wants to do
the same thing to the downfeed. There is no power downfeed on these
little guys, meaning that you must manually turn the crank .. and do
so with the ram swinging back and forth, timing your twist to end of
the stroke, trying not to overtwist, and so on. It's a pain.

A mechanical feed could be rigged up somehow, I guess, but would suffer
from the same problems as the crossfeed. Put a stepper on that one as
well.

Well, now that we have a stepper on both axes, we can cut more complex
shapes. Recently, I had to make a mount for an acme nut. ( I made a
larger table for the Burke ) To clear the table, though, the mount
needed an unusual shape. Basically, the piece looked like

------
/ \
/ \
/ \
______/ \______
| |
| |
| |
|________________________|

Only the diagonal edges were not diagonal, they were curved, to clear a
semicircular recess in the bottom of the table. To make it, I started
from a square block, scribing the curved shape on one end. I then went
to the shaper and "carved" the metal away, down to the line. I was
careful, and I bet that I was within .020" at the end of it all.
Still, it was a long time standing in front of, and leaning over, the
machine.

Now, if there were steppers of both leadscrews, this would just be a
fire it up and let it go proposition.

> And were you going to use EMC ?

No, I'll probably use CNCPro. Even though I'm a Linux guy at work,
CNCPro is what I use at home, and is one of the best purchases I've
ever made. VERY happy with the performance, so much so that I just
can't seem to get around to setting up EMC. Every time I want to get
serious about it, some other project comes up.

One thing that Mr. Yeager added to CNCPro a long time ago, partly, if
not totally, at my request ( now THERE'S customer service ) is the
ability to define a parallel port pin as either EStop OR PAUSE.

Initially, I wanted to use the PAUSE feature as part of my
hardware backlash compensation device. Conversion to ballscrews put
that project on the backburner, but the pause feature remains.

So, we have a sensor to detect the end/beginning of the RAM stroke that
RELEASES the PAUSE input and then use really low feed rates. Should
work.

What does work ( on the bench, anyway ) is a home brew program wherein I
define the number of strokes and the steps per stroke. Since the
accelerations are small, the max speed low and the steppers essentially
unloaded ( as opposed to when milling ), the code is fairly easy. This
can't be used for gcode, but should work nicely as a feed rate
controller.


Alan

--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta