How do I engrave numbers...

[slp_prlzys]

Hi,
I'm trying to engrave numbers on flat piece of round wood,
about 2" in diameter, I'm having trouble centering the numbers.
I export the text as dxf and import to Mach2 demo,
but it seems that it always start at lower left. I could move the axes
to set my 0' to the center of the piece, but it has no effect
on the generated gcode during import.
I just need to put a sequential number 1-12 on 12 pieces.
I'm thinking that if somehow I could start in the center of the piece,
the result wont' be too off centered.

thanks.

[High Seas]

Maybe give this a try. May be a kludge - but might get the job done.
Open MS Paint
Pick a number - say 8. Pick a font, Say Engravers - or what ever you like.
Type the number - save as a monochrome BMP.
Import the BMP into MACH2, USE the Spiral cut - It will start at the lower left, but then drive to the middle of the number and cut in a spiral. If you figure out on a "test pass" where that is (the center), then you could set up a jig on the worktop to hold the pieces in the same place for the other 11 numbers.
As I said a kludge - but works around learning all that Gcode and re-reading the MACH2 manual! Jim

[slp_prlzys]

my pc choke 3x with the bmp conversion,
I thought I'd give dxf another try, and success not perfect but
it works, I draw a circle with approximately the same diameter as the
pieces and put a number in it. I then try to import it in Mach2 and I run
a cycle with nothing ON on my cheesy cnc router, I watch the lines
scrolls and find out that the z- axis is only moved once when it's started
to create the circle, I then edit the code, so it doesn't touch the piece while
creating the circle, and voila! a not too off centered number 1, 11 to go!
It's much easier to zero the machine, too.

thanks for the help.

[HuFlungDung]

I suspect that you need to find a way to offset your part center coordinates from the machine's home position. Normally, when a machine is powered on, it assumes the current "power up position" is X0Y0Z0 until a homing routine (or maybe built in parameters in the software setup of your cnc controller) has told it otherwise. Even after the homing routines are completed, this might commonly place your machine home at all zeroes, and zero the displays.

So you can set up a work offset in a couple of ways. This work offset is the distance from where the tool tip is when the machine is at homed position, relative to some important reference point of your part. For round parts, the most common reference point would be the center of the circle representing the perimeter of your workpiece. For simplicity's sake, I would recommend that you make your autocad drawing with the center of the part's circle at X0Y0 on the autocad coordinate axis.

The distance from your machine home to the part center would be entered (somewhere) in your controller's work offset registers. Usually, this would be in the G54 offset register. You would also have to place a G54 command near the beginning of your program to inform the controller about using the offset with the program.

The other method is to "fake it" by using a G92 command. If Mach2 sticks to convention, then the G92 command is used to rename the current position of the machine with new coordinates. Most cnc people do not like to use the G92 command though, because there is no handy way of cancelling the effect it causes. By contrast, a G53 command cancels a G54 work offset.

I know this may all sound like goobledy-gook to you. But, maybe if you read the help files for Mach2, you might see some of this stuff mentioned

[slp_prlzys]

It's a little bit deep for beginners like me, but I'm learning
tho rather slowly, thanks to guys like you.
On page 83 of Mach2 manual describes how to make an offset, but
I notice that offset is basing it's new position to the original which is
still on the lower left. I can't use the center of the piece as the
reference for the offset because that's where the first plunge would be if I did.
the simplest thing I could do I think was to engrave the number on the table,
and position the piece by eye, that way even if the width of the numbers changes,
there's still a good chance for it to be centered, for beginners like me improvising
seems to help a bit

thanks.

[HuFlungDung]

I know it sounds complicated, but most of this stuff, you have to read the method, then figure out what that means, one piece at a time

Just to add a bit more to your confusion, but maybe to attempt to make it clearer, a cnc controller works in multiple coordinate systems: one "real one" and countless "imaginary ones". The "real one" is the machine's coordinate system, which is the first one it "knows" upon powering up, or homing.

After that, all the other workpiece coordinate systems are imaginary offsets from the real one. However, we speak of each of these imaginary coordinate systems just as if they were the only real one, at any given moment. The cnc controller keeps tab in the background about how much this imaginary coordinate system is shifted in relation to the "real coordinate system" which it derives from the servo encoders, or the cumulative pulse streams sent to the steppers.

When I say use the center of your round part as a reference point, this is because you have to locate the part center somewhere so why make it an absurd random location, when a logical one would do? There is no need to actually call for any Z motion at the reference point. Your lettering might begin in the X- Y+ quadrant, work its way towards the X+Y+, then retract the tool, move down a line to the X-Y- quadrant and begin cutting again whilst working its way towards the X+Y- quadrant.

You would need to know whether your cnc is working in G90 (absolute coordinates) or G91 (incremental coordinates). Since you are already getting some kind of results, you may already have this sorted.

[slp_prlzys]

thanks,
I'm beginning to understand the coordinate system,
I see that I could 0 any axis anywhere on the table, but I'm still
partial on the machine coordinate, and the offset, I'm going to read
more , there's a possibility that I'll do a second set of the pieces if
it actually works.
I'll post my progress on the offset thing.
thanks again.

[Aksess]

you can use desk engrave it has 3 buttons align left, center, right you can align it center and just 0 your machine in the center of where you want to carve