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Is it just me, or are there others wondering what these
machines are intended for?

How can the apparent goal of self-replication (of a largely metalic
machine) be
accomplished by squirting layers of hot-melt plastics? Or
carving foam??

They're fascinating to watch .. but other than
rapid-prototyping (making plastic models of things), and/or
as a conceptual challenge, of what utility are they for
getting -real work- done??? Or is that not the point?? Is it
all really academic for you folks? Engineering student toys,
in other words. That's how it sounds to me, so far. Maybe
it's enough to get it built and moving, with little thought
as to what can actually be -done- with the thing?? A useless
robot, in other words. But utility may not be the point. In
which case, why is the whole thing relevant here?

Things have to be really beefy to do heavy, yet precise, work
in steel, and I don't see how eliminating mass is going to
work at all for us home- shop types doing metal. Plastic
bearings wouldn't last long at all, either.

Yes, I know a tripod is a very strong structure. And I do get
the concept of the things. But, there has to be mass
somewhere, doesn't there?? How can a decent spindle holding
real milling cutters hang off spindly legs?? Or is there a
'scale' thing here I'm not getting?

I DO admire those who think out-of-the-box, tho. And I sure
hope you smart folks can come up with a revolutionary
home-built, -useful- for everyday work, machine.

Ron Yost .. looks at his quaint mill and lathe and ponders
the universe.

Something else for you to ponder -


Rapid prototyping in itself can be real work, the ability to quickly come up
with a few mockups is quite handy. One use for these machine is for
jewellers, carving stuff out of wax, then casting it out of metal.

A hexapod has more degrees of freedom than a normal mill, they come close to
the abilities of a 5-axis one. Consider an engine block with angled ports,
on a normal mill you'd need to tilt & rotate the block to drill or polish
them, but a hexapod can do it without moving the block.

I've seen pictures of very hefty hexapods, so scaling isn't a problem. Look
at how fast normal mills are today compared to 20 years ago.

The mill & lathe combination in the workshop probably won't change anytime
soon, you don't need a hexapod to drill a few holes in a bit of steel.
Inertia plus the fact there's nothing a hexapod can do that a normal mill
can't means there won't be a rush to replace them. A bit like 4-cylinder
engines vs rotary ones. If the rotary was 10 times as good, then we'd all
have them. A little better or just the same means 'why bother?'

Be careful about dismissing something as a toy, history is littered with the
remains of those who made that mistake, from steam shovel makers about
hydraulic diggers, to mainframe computer makers about personal computers.

Tony

Speaking of which. I think the reprap machine could make strong structural
elements out of that plastic if they laminated it with some glass fabric.
With a 90deg rotary table they could make fiberglass tubing.

Is it just me, or are there others wondering what these machines are
intended for?

How can the apparent goal of self-replication (of a largely metalic
machine) be
accomplished by squirting layers of hot-melt plastics? Or carving foam??

They're fascinating to watch .. but other than rapid-prototyping (making
plastic
models of things), and/or as a conceptual challenge, of what utility are they
for getting -real work- done??? Or is that not the point?? Is it all really
academic for you folks? Engineering student toys, in other words. That's how
it sounds to me, so far. Maybe it's enough to get it built and moving, with
little thought as to what can actually be -done- with the thing?? A useless
robot, in other words. But utility may not be the point. In which case, why is
the whole thing relevant here?

Things have to be really beefy to do heavy, yet precise, work in steel,
and I don't see how eliminating mass is going to work at all for us home-
shop types doing metal. Plastic bearings wouldn't last long at all, either.

Yes, I know a tripod is a very strong structure. And I do get the concept
of the things. But, there has to be mass somewhere, doesn't there?? How can
a decent spindle holding real milling cutters hang off spindly legs?? Or
is there a 'scale' thing here I'm not getting?

I DO admire those who think out-of-the-box, tho. And I sure hope you smart
folks can come up with a revolutionary home-built, -useful- for everyday
work, machine.

Ron Yost .. looks at his quaint mill and lathe and ponders the universe.

Jim,

Geckos require 16milliamps to work, the parallel port delivers 10
milliamps per pin. The reason why geckos will work ok with 10
milliamps is because the tolerance of the optoisolators used. So you
just have to be lucky enough to a set of geckos with optoisolators in
the right range. This is the main reason why you should get a
breakout board that buffers the signals.

Arturo Duncan


--- In CAD_CAM_EDM_DRO@..., "Jim Dubois" <jdubois@...>
wrote:

I have a problem with Gecko drives not working, I am assuming I

have

done something stupid or have overlooked something....or will a PC
parallel port not actually "sink" the required 16ma? I have used
the parallel port for control of many drivers, but for what ever
reason the Geckos are not working. This is my first effort with
Gekos....

I have replaced a set of IMS drivers on a formerly functioning
controller with new out of the box Gecko 201 drivers. I have +65
vdc, tied to a chassis ground, I have +5vdc for the common terminal
on the drives, also tied to chassis ground. The parallel port,

also

grounded properly, is communicating with the controller as I can
turn on and turn off the aux devices, ie spindle, coolant and the
like. The power light is "on" on the drives, the motors "lock".
Current setting on the drives is at default, 7 amps. No connection
to the "disable" connection. There are no limit switches or other
complexity...just a 3 axis controller with 2 aux's and the aux's
work.

I have checked out the controller with a different computer, no
change. I have verified the +5vdc to common stays steady. I have
not been able to verify the TTL signals, no scope or logic trace
tools in house. But, it worked with the IMS...so...I would think

it

would work with Gecko.....

any thoughts? do I need a parallel port interface card to drive

the

Gecko's?

yea! that is smoking right along...dont put your finger in the way! cul
brian f.

Hi guys,

Haven't posted in awhile...been busy this summer with other
projects. I just disassembled a HP7550A pen plotter and cut down
the carriage to make a lightweight Y axis for a laser engraver. The
plotter was all of $15 purchased locally, and includes two very nice
pittman servos with encoders. They are pretty small, but actually
have quite a bit of power. Of course there are little forces with a
flying lens laser engraver, but perhaps they could be used to move a
camera for a 3D digitizer or something similar. I am driving them
with a Pixie P100 step/dir to analog converter (www.skyko.com)
hooked to an Advanced Motion Controls 12A8 brush amplifier (a bit
overkill).

Here is a quick video of the carriage moving at 2640IPM running on
Mach3. The carriage actually takes 4000 steps to move 1 inch, but I
have set the step multiply in the Pixie P100 to 4x. With Mach3
outputting a max of around 45khz, this gives me 1000dpi resolution
and the 2640IPM travel speed (fairly fast, no?)



-Rick

Hi, Folks:

While searching the net, I came across a version of EMC designed to work
with a small Linux called PuppyLinux.

I've downloaded it and am starting to play around with it. I'm wondering -
is anyone else on this list using that particular version? If so, what are
your experienes.

I'll be using this software with a HobbyCNC 4AUPC motor drive and a Sherline
model 2000 mill.

-- Carol & Jerry Jankura
Strongsville, Ohio
So many toys.... So little time


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afogassa wrote:

Hi Peter,
I do have deskcnc and it's good enough for this, but water jets needs a good cam that can look way ahead and predicts what is going to happen and than starts to adjust the feed rate before it gets to a corner or radius to compensate for Jet lag doing that manualy would be a pain if not impossible.
Got a quote from PEPs and it runs at 10K US$ (ouch !!)
I've being thinking about getting a working G code, than work this out on excel to adjust the feed rate.

Why would the CAM be doing the lookahead? Why can't the CNC control
handle this? Normal lookahead, only worrying about machine acceleration
is done in the CNC control, as the acceleration is constant (a property of the
machine) and doesn't scale with feedrate override.

I think EMC could be adjusted to handle this. It would need a different
acceleration parameter for cutting vs. non-cutting moves, and that cutting
value would need to be changed for the material and part thickness.

Jon

--- In CAD_CAM_EDM_DRO@..., Peter Renolds <prenolds@...>
wrote:

I don't think you need any of that 5 axis (or 4 axis)

complication -

plasma cutters have all the same issues about a curved cutting

profile

through thicker material. Remember the KISS motto... You have to

limit

your feed rate to give the waterjet time to cut through. As you

will

only cutting 2D profiles, you need something that can convert a

DXF

profile into G-Code. Rasterfratz works for me for 2D cutting and
engraving letters converted from true-type fonts. You will need a

CAM

package that supports lead-in so you can cut a clean edge after

you've

penetrated the material.

Cheers, Peter

Hi Peter,
I do have deskcnc and it's good enough for this, but water jets
needs a good cam that can look way ahead and predicts what is going
to happen and than starts to adjust the feed rate before it gets to
a corner or radius to compensate for Jet lag doing that manualy
would be a pain if not impossible.
Got a quote from PEPs and it runs at 10K US$ (ouch !!)
I've being thinking about getting a working G code, than work this
out on excel to adjust the feed rate.

fogassa

Yes, that is part of the tool changer - the tool magazine. It holds 38
tools.

Chris



--- In CAD_CAM_EDM_DRO@..., "Graham Stabler" <eexgs@...>
wrote:

The new picture on the group page looks cool, whats happening to the
left of the spindle, I think I can make out a chain but not a cable
chain, is that part of a tool changer?

Graham

Some stuff I didn't have time for this morning...

On 8/31/06, Graham Stabler <eexgs@...> wrote:

--- In CAD_CAM_EDM_DRO@..., "Dennis Schmitz"

When using mach I set up secondary axes, these were the actuator
postitions which were defined in terms of the primary axes using the
equations function. The quantization error is no more of a problem
than it is for a normal machine thought the positional error will tend
to grow as you move from the sweetspot.

Sorry, I'm not familiar with Mach because I don't own a copy.

On the other hand, you do need to develop a transform for your own

machine. It might seem daunting to delve into the matrix math

I sometimes wonder if I am talking to myself. I have posted a link to
my kinematics page at least twice. You don't need matrix maths you
can calculate the lengths or base positions directly using pythagorus.

I'm not sure why the distinction. It's still the same number of
operations. Matrices are just an easy form to work with in code as
well as conceptually. Of course I spend a large part of most days in
Matlab, so I might be biased.

For example if you take a triaglide, you know the position you want
the table to be in, the points on the rail where the carriage should
be are given by the intersection of a sphere with a line. i.e. the
possible positions of the struts other end with the rail. You will
get two solutions but you can ignore one. Also if you keep the
equation in its most general form you can account for rails not being
parallel etc.

I find the matrix to be a more general form, probably because I'm used to it.

PLEASE have a look at my page, you will see that ball joints aren't
even needed.

I saw the stuff about the clevis, but I think the ball with self-lubed
plastic bushing is a simpler design. In any case you're right about
what's required, if you're making a 3dof platform and parallelograms,
you only need a universal joint since there is no twist to account
for.

The other crucial thing is the gearbox for the servo arm. It's a lot
different than mill screws, and probably more expensive. I'm still
pondering that.

Again see my page, there is a cool way of getting high gear ratios
using a belt.

Bottom line, I think triaglides and deltas have real homebrew
possibilities, I've done the ground work, please run with it. BUT
hexapods specifically don't fit the bill for reprap or most homebrew.

Fair enough. I wasn't suggesting a hexapod for reprap anyway, but a delta.

True enough, but I was thinking about straight-line movements and
non-linear resolution in cartesian coordinates. A straight line
movement through the range would have stepping.

Graham,

Let me second that -- your site is excellent. In fact, your site was one of the reasons why I started working on my design (which is a "triaglide with vertical rails", as per your diagram).

Mike

Alan Marconett wrote:

I don't think you need any of that 5 axis (or 4 axis) complication - plasma cutters have all the same issues about a curved cutting profile through thicker material. Remember the KISS motto... You have to limit your feed rate to give the waterjet time to cut through. As you will only cutting 2D profiles, you need something that can convert a DXF profile into G-Code. Rasterfratz works for me for 2D cutting and engraving letters converted from true-type fonts. You will need a CAM package that supports lead-in so you can cut a clean edge after you've penetrated the material.

Cheers, Peter

afogassa wrote:

Dennis Schmitz wrote:

Not really. Since CAD models are built in a cartesian coordinate system,
somewhere along the way you need to translate into a motor space. Whenever
you translate co-ordinate systems, you get quantization error at the encoder
(or step) resolution.

In the cartesian axis case, I don't think quantization error is a given, because the step resolution can match the coordinate system resolution. In my case, for example, steppers are 200 steps/rev, and leadscrews are 10TPI. That gives a quantization of 0.0005".

So, as long as I specify coordinates in 0.001" increments (which is what I normally do), there's an exact representation in motor coordinates (and no quantization error).

Mike

HI Graham,

*I* looked at your site! I've been back a few times, for that matter. I
like the Hexel platform, and would love to make a working model of it. Not
sure if I could work out ALL the kinematics, but it would be a good
exercise. What is the stuff that looks like links (copper colored) down ON
the table?

Alan KM6VV
P.S. It's OK to talk to yourself; it's when you start ANSERING yourself
that you want to worry about!

<SNIP>

The new picture on the group page looks cool, whats happening to the
left of the spindle, I think I can make out a chain but not a cable
chain, is that part of a tool changer?

Graham

--- In CAD_CAM_EDM_DRO@..., "Dennis Schmitz"
<denschmitz@...> wrote:

Not really. Since CAD models are built in a cartesian coordinate system,
somewhere along the way you need to translate into a motor space.

Whenever

you translate co-ordinate systems, you get quantization error at the

encoder

(or step) resolution.

surely you get quantization error of this sort even if you don't
translate between co-ordinate systems.

Graham

The point is that you don't really need to know how the transforms work to
use them, and that people shouldn't be put off by the bit of robotics math
because under the arcane terminology, it's pretty easy.

Not really. Since CAD models are built in a cartesian coordinate system,
somewhere along the way you need to translate into a motor space. Whenever
you translate co-ordinate systems, you get quantization error at the encoder
(or step) resolution.