Re: [CAD_CAM_EDM_DRO] Re: CNC power supply question

On Saturday 06 March 2004 11:19 pm, caudlet wrote:

> > > 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.

Ok, my ambitions at least at this point are nowhere near this large -- a
square foot would be nice, but not all that necessary for the kinds of
things I envision doing to start with. (Circuit boards, mostly.)

> > 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.

What I'm envisioning as a starter setup is to use the mechanicals (and motors,
though with my own electronics driving them) from a scrapped printer,
wide-carriage model. This would give me left-right axis (whichever one
you're calling that) and I'd have a sliding table going toward/away under it.
The mechanicals that were formerly involved in moving paper vertically would
be adapted to z-axis, somehow.

> > 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.

Most definitely.

> 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.

Ok.

> > > 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.

How about a pointer to that info?

> 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.

Plasma? I don't think I'll be going _there_ for at least the forseeable
future...

> 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.

Ok.

> > > 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".

I'm in there, and also have subscribed to as many of the Yahoo groups as
appeared to have any applicability to this stuff as I could find...

> 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.

Yeah, I'll start there and work my way up...

> 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.

I haven't looked at what the complexity of such a project would involve, the
cost is enough to put me off of it... :-)

> 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".

I will be starting out with the idea of something that'll run under linux,
which I'm gathering will tend to narrow things down considerably.

> 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.

I did take a bit of machine shop in high school, so I'm not a complete
stranger to this stuff, but that was also a *long* time ago, and I've not
used most of what I learned back then in the interim.

> 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.

Yes.

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

Oh, I've been scrounging stuff for ages, and have plenty of parts on hand,
it's just nailing down some of the ideas and deciding on some of the details
of things that's getting to be the focus now.