Another learning module

[Chunky]

Like the last one, this learning module is to help me. It is not intended to verify whether anyone else knows what they are doing. It might not even be a good way for me to learn but at this point in my struggle I think it might. The module I posted before didn't have an arc. What I hope you vets will do is to write a gcode for it. Then I can study it to see why you did what you did. Thanks for your time. arc a and arc b

[ger21]

First thing, is that the origin (0,0) is usually at the lower left, not the upper left. But here's the code with the origin the way you have it, upper left.

Looking at it again, with out knowing the location of the endpoint, and the radius of the arc, it's not possible for me to give you the exact g-code. I'll give you something close.

The top of the workpiece is usually Z= 0, so the firs tjing you do, is lift up the tool to clear the workpiece.

G0 Z0.125 (lift tool 1/8 above work)
G0 X6.25 Y4.25 (move tool to start of line)
G1 Z-.3125 F5 (plunge 5/16" @ 5" per minute)
G1 X12 F10 (move to the start of the arc at 10" perminute)
G2 X18 Y10.25 I0 J6 F10

The last move makes an arc with a 6" radius to position X18,Y8.25. The I and J specify the centerpoint of the arc relative to the start of the arc. I is the X, J is the Y. The center of the arc is 12,10.25. The start of the arc is 12,4.25, so the I =0 (12-12) and the J =6 (10.25-4.25).

This is not exactly the way you show it, but hopefully it will help.

[Rekd]

Originally Posted by ger21 First thing, is that the origin (0,0) is usually at the lower left, not the upper left. ...

That's a matter of opinion.

I make my targets against the sold jaw in vise operations. That's the back on the kurts. Also, on fixtures, when using locating pins, I put them to the back when possible because it's easier (safer for operators) to push the part against the pins instead of pull them.


As for arcs, I wrote this up for one of my classes when teaching them arcs on a HAAS.

Arc Definition Using I & J Two lines of code define arcs: Line #1 = Start Point. Line # 2 = Direction, End Point, and Arc Center. Start Point: - Can be any legal move to position the tool, example- G0, G1, G2, and G3. Direction: - Is defined by G2 for CW motion, G3 for CCW. End Point: - Can be X or Y or X, Y or neither X nor Y. Only use X or Y if the end point is different than the start point (start point and end point are the same on full circles). In G90 mode, X & Y are absolute distances from part 0 to the end point of the arc. In G91, it is an incremental distance from the start point to the end point of the arc. Arc Center: - Is the same for both G90 & G91. It is the direction (+ or -) and distance from the start point of the arc to the center point of the arc. The direction along the X-axis is defined by the signed value of I, & the axis is defined by the signed value of J.

HTH

[Chunky]

I think I was told before about the proper starting place. I won't make that mistake again (left lower corner). The steps you laid out help me to see how something other than a straight line is executed. The need for this may seem ridiculous for many observers but it will help me a lot. I will study it thoroughly. Thanks

[Chunky]

The next step for me (working backwards) is to revise the diagram showing 0/0 where it belongs and then show what the g-code (by ger21) looked like when it existed as a graphical tool path (my term- probably wrong).

[Chunky]

Whoa! I suspect there's some good info in there but I'll have to dissect that carefully.

[cyclestart]

Chunky
CNC convention places the machines xy origin at lower left. Rekd is talking about offsetting the origin
to a position a given distance from machine origin by using a code such as G54 or G92. In my
opinion no matter where you shift the origin, x0,y0 remains lower left. Any move from this new
offset origin towards the machine origin now becomes a movement in the negative direction.
Learn your movement codes first and the concept of offsets will be easier to understand.
For now I would stick with the concept of x0,y0 is lower left.

From the origin (overhead view)

X movement right +
X movement left -
Y movement up +
Y movement down -

The thing to keep in mind is that you can place x0,y0 at any position on your part.
For instance, if you place X0,Y0 at the top right corner of your part all points on this part
will be X- , Y- .

[Rekd]

Originally Posted by cyclestart Chunky CNC convention places the machines xy origin at lower left...

??

I haven't done my CNC conversion yet, so haven't considered that, but every commercial CNC machine I've ran has the X0 Y0 in the back right.

[ger21]

Rek'd, I don't think any commercial routers are back right. Ours is actually upper left.

Chunky, disregard this and make it lower left. You'll find that virtually all CAD programs use lower left, which makes it easiest to set up your machine that way.

[Chunky]

I hope you guys will suffer through one more for me. This time I have written the code by looking at what you've done. The one thing I've not really addressed with my questions is what part of the tool is used for determining its position. I can't imagine it would be anything other than the center. But I'm about to see. Will you please look at this pic and see if the gcode is correct. Thanks. DIAGRAM

[Dave's_Not_Here]

Originally Posted by Rekd ?? I haven't done my CNC conversion yet, so haven't considered that, but every commercial CNC machine I've ran has the X0 Y0 in the back right.

... so where is X0,Y0 when you face the mill from behind...?
... and where would X0,Y0 be if you faced your monitor from behind...?

... the right hand doesn't know what the left hand is doing....

... go get'um Chunky....!

Dave leaves to get a popcicle....

[ger21]

Originally Posted by Chunky I can't imagine it would be anything other than the center. But I'm about to see. Will you please look at this pic and see if the gcode is correct. Thanks.

Use the center of the tool. Your code is perfect.