Re: CNC power supply question

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Roy J. Tellason"
<rtellason@b...> wrote:

> On Saturday 06 March 2004 02:47 pm, caudlet wrote:
>
> > Sit down and decide what kind of machine you are building or

retro-

> > fitting.
>
> I guess for retrofitting this isn't that hard, but for building

something

> from scratch?
>
> > Determine the type of machine and work envelope.
>
> By "work envelope" do you mean the largest bit of material that the

machine

> could handle?

Exactly. To cut a piece 4' X 4' you have to allow for enough rails,
screws and room to move the cutting head in that area. It has to be
at least wider and longer than the width/length of the carriage. A
little room for safety is added so you can add a limit say one or two
inches past the fartherist cut and still stop the machine in time to
prevent a crash. The "envelope" is 4 X 4; the total movement area is
slightly larger.
This is just one example of a lot of terms I see being tossed

> around in these groups that I'm not familiar with, so mostly I'm

guessing...

>
> > Is it to be moving table or moving gantry.
>
> What are the tradeoffs? Seems to me that moving table would be

more

> complicated to build, but again I'm guessing.

General statement: Moving table designs are typically less
complicated to build and run than moving gantry. Moving table
designs take the form of moving both X & Y one stacked on top of the
other (good for small engraving and mini routers), A moving Y and
fixed X gantry with the X moving back and forth; one of the more
popular designs for work envelopes up to 2 or 3 ft. Since you are
just sliding the work under the cutter the amount of torque is less
than moving a gantry and its components. The down side is that the
moving table has to move double the distance (i.e.) the rails have to
be twice as long since it moves the same distance on either side of
the cutter.

For this reason larger machines tend to go to the moving gantry.
There are exceptions and moving bed machines of 20 ft or more have
been constructed. They eat up a lot of square ft.

>
> Taking a look at a web site with a bunch of different kinds of

machines (take

> the crankorgan site for one example), there's not much there that

would tell

> me which of these would be more suitable for what kind of task. Or

which

> would be that much harder or easier to get going with.
>
> > What kind of drive approach will you take: rack and pinion,

toothed belt,

> > ballscrew, acme screw, etc)
>
> For me I'm guessing (again) that the first thing I build is

probably going to

> use threaded rod from the hardware store or home center. :-) I

don't see

> where I can justify spending the money on some of the

alternatives, or at

> least not yet.

Ah, a learning experience. There have been several projects
documented on these pages using threaded rod and drawer slides to
provide linear motion. I think it's important that you build
something...anything...and if your budget is low then use whatever
you can to do it with. You will learn a lot from the experience and
your next machine will profit from your learning.

>
> > Decide how fast you want it to go
>
> How do you decide this? I was surprised to see in one of these

groups a while

> back that routinnng-type tools need to move at a certain minimum

speed

> (depending on the tool and the material?) or you end up burning the

material

> instead of cutting it. Where do you guys learn this stuff?

Same place you learn not to touch the white wire and the black wire
on the socket at the same time: experience in the school of hard
knocks. Read the lists and monitor the answers to questions but in
the end you are your best teacher. As to the speeds. You are
right. There are minimum and maximum cutting speeds for different
materials using different bits. These are published tables and
formulas and we are discouraged on this list from talking about
standard machining factors. I can give you some general things to
think about. You route most wood at speeds from 30 to 70 IPM using
smaller routers but speeds as high as 100 IPM have been mentioned for
light cuts. Plan your router to do at least 70 or 80 IPM or you will
be limited as the type cuts you can expect without burning the bit.
Things like plasma need even faster cutting speeds. Small metal
cutting mills can get by with much lower speeds.

In every design there has to be a starting place. In this field its:
1) What do you want to cut/make (material and geometry)
2) What is the biggest piece you want to cut
3) What is the fastest speed you need to cut the things in #1)

A forth is how much are you expecting to spend for 1, 2 and 3. 4 may
require a re-think of 1 or 2.

>
> > and roughly how much you think the moving parts will weigh. In

other words

>
> Me, I don't have too much trouble with the electrical/electronic

side of

> stuff, it's all of this machine-shop stuff I'm needing to learn.
>
> Any suggestions on that?

The best source of learning machine shop stuff is to join several
general purpose machining groups like JobShopHomeShop. Pick up a
copy of Guy Lutards "The Bedside Reader" series (there are three).
They are easy to read and entertaining while getting you to start
thinking in machinist terms. The DIY-CNC group is a less constrained
group of hobby cnc'ers that like to discuss not only building your
own CNC machine but other related topics, like how to use it after
you have it built. Even routing wood requires some understanding of
machining concepts like "feed and speed".

The important thing is to get started. If all you can afford is
something made from all thread, cheap draw slides and old motors form
a broken printer then so be it. Too many guys see their first
project as a 5' X 10' 5 axis super router capable of carving great
works of art with a .0001 accuracy only to get discouraged at the
complexity and cost of a machine like that.

There are minefields along the way. Then there is the second most
asked question; one that has dozens of correct answers..."what
software should I use".

Being from the electronics world you have one piece of the multiple
skillset puzzle in place. On the other hand you will have to learn
some of the simple (simple to a person that has done it many times)
machining and mechanical issues. There is no magic book on how to
build what you want. There are some fine articles in various places
but think back about how you learned electronics. There was not one
source that taught you all you know. You learned the basics from a
book or in class but you learned how to solder by doing it. You
learned the distinct smell of a circuit where a component got to hot
from having fried something. I don't remember a single class in EE
that taught me as much as the first 6 months in the real world.

Now, get started planning and sketching ideas and scrounge, scrounge
and barter until you have some components to start you project!

Happy cutting ~(:-)#