How does the router know where to start?

[chuckknigh]

This may seem obvious to some of you, but it's not to me.

I now (basically) understand the construction of a router table, and all 3 axes. I have a clue about bearings, mounts, etc. I understand how the controller software drives the stepper driver card. However, there is one little detail that is nagging at me.

How does the router know where to start cutting? Basically, how does it "zero" itself?

On most printers, if the cartridge is replaced, the printer head does a little dance and resets itself to the top left corner of the paper -- everything is keyed off of this spot.

Similarly, on my old plotters, the paper would dance a little, as would the plotter head, and it would establish a starting point off of which all plotter commands were keyed.

How is this done on a homebrew router? I've heard mention of limit switches, but have no idea what that means...or if that's what does it.

Thanks for any insight you can provide.

-- Chuck Knight

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[balsaman]

To start, all the axis are sent home by a home command. Each axis eventually hits a switch when the axis is at home and the software sets the axis to zero (or some other number as chosen by the operator).

I home my machine, the axis get set to x=0, y=12, z=3 (cutter to the far left, back, and up). This allows for easiest access to the table for placement/clamping of stock.

The machine just goes from there.

Another option is to forget home switches and just move (jog) the machine to the corner of the stock and manually set the axis' to zero.

Eric

[chuckknigh]

So, in other words it's keyed off whatever is the starting position. If you don't make accomodations to identify the starting position (i.e. limit switches) it just starts at whatever the "current" position is...

You mention jogging the machine -- that's basically setting it by hand?

Just want to make sure I got it right.

THANKS!

-- Chuck Knight

P.S. I really don't intend to offend with these nagging little questions -- they're just questions I have not found answers for, and this forum seems the proper place to ask them.

[WOODKNACK]

Yes jogging is set manually by yourself. meaning you move the machine by the software to where you want to start it. Or by crank handles on the machine. Then you zero it out in the software.

[normalus]

Hello, this question bothers me too. So if i want to engrave round wooden object, how it is possible to adjust by hand it directly in a center of the round object??

[RossMosh]

Hello, this question bothers me too. So if i want to engrave round wooden object, how it is possible to adjust by hand it directly in a center of the round object??

Several ways to do this.

1. Create a table with guides along the x and y axis. Put the object against the guides and using the software you should be able to center everything easily.

2. If the object is ordinary, you can simply cut the shape out of a piece of scrap then plop your piece within the hole.

3. Lightly cut the exterior of the shape into your spoilboard and then using that as a guide, clamp down your piece.

If you're doing a lot of cutting into supplied pieces, it's worth looking into adding guides to your machine. It allows you to align things very quickly.

[normalus]

Thanks for quick replay. I need cnc milling machine for engraving wooden round objects from maybe 6mm to 50mm or more in diameter. i dont need it to cut. Im looking now to buy cnc machine for small projects, but i need it to be precise. I have no idea how much i need to pay that i was happy with results.

can you tell me a little more about "adding guides to your machine"
sorry for my english.

[ssutton]

Keep in mind that in Mach there are "machine coordinates" and "work coordinates". The machine homes to the machine coordinates, these are absolute positions on your table that should represent the full working envelope of the machine. Then, you have work coordinates, these are where you can type in a position. Say that in machine coordinates that Mach indicates that you machine is at X 24.000 Y 24.000. If you have a 4'X4" machine, this is in the middle of the table. But, you can type into the "work" coordinates a value of X 0.000 and Y 0.000, now you can run a job from that location and your G code will drive the machine based on this position and NOT the machine coordinates. You can place material anywhere on your table and set your work coordinates to work from there, however, keep in mind not to start a job in a place on your table where your G code will attempt to exceed the working envelope of your machine. If you have soft limits enabled, Mach will warn you of this.

Scott

[normalus]

Maybe someone could tell me, is it worth to buy small cnc from china? cuz if not, i dont know where to look if not on ebay.