homing vs 0,0,0

[planeflier]

I am fairly new the CNC realm and have built a router and my questions is regarding homing the machine is this suppose to be the same as 0,0?

Do I use the same homing point as my 0,0? I have set up guides on my machine in the X, Y directions and machined them with my router to help align my raw material stock. If I put this on X, Y home and X=0 and Y=0 then which ever size cutter I use I will remove ¼” if using a ½” cutter etc from my alignment rails.

Then if I run a program with two different cutter diameters how do use alignment rails without cutting them?

Any help would be greatly appreciated.


Planeflier

[HuFlungDung]

A lot depends on the capabilities of your controller.

Typically, the machine home does not correspond to the part home (or reference point) for the reasons you state.

Work offsets are most commonly employed to provide a temporary shift of the machine home position to a new location. This shift is called up after the X and Y values for the difference in position between the two reference points have been inserted into a table of work offsets, commonly beginning at G54 and continuing up to G59 (the first 6 standard work offsets lie in that range).

So what kind of machine controller are you using?

[planeflier]

I am using a hobby cnc controller running Mach 2 & 3 and sheetcam as my g-code program.


The reason that I have been using rails is because I typically machine both sides of my parts and this helps align for machining on side 2. My router has the ability to cut 40" x 50" x 7".

Thanks for the help HuFlung

Planeflier

[Geof]

The technique used on commercial CNC routers to avoid cutting the alignment rails is to use retracting pins, not rails. In your context you could have rows of holes that you insert wooden pins into, align and secure the part and then remove the pins before machining.

[HuFlungDung]

You should be able to use work offsets then.

If I might suggest something to preserve your fence rails, would be to use some thin spacers between the fences and the stock during setup. Say some 1" wide by 1/8" thick strips that you could leave laying there if the cutting is happening at a greater height. Or, just use the spacers for setup, clamp or screw the part to the table, and remove the spacers. Then use a work offset of X1 Y-1 (I have no idea what sign you would use, so adjust accordingly) in your G54 table. This offsets the program so the X0Y0 for the part is now located 1" right and 1" towards your belly from machine home.

I hope that makes some sense. Call the usage of the G54 in your program by placing a G54 command near the beginning before the first programmed XY move.

[planeflier]

Thanks for the tips guys. I like the idea of using pins simple an effective. I will also try the offset setup.

[turmite]

planeflier you may well be like me and not want to learn the G54 offsets that Hu told you about, but it is something that will be of long term use. I don't use too much flat stock is the reason I have not really worried with it, but if I were to need to cut a bunch of flat stock you can bet I would learn it in a hurry. Also don't forget that Mach3 has tool compensation. I don't know how you are doing your code but it might be something to look into as well.

Mike

[planeflier]

Turmite I use sheetcam to write my g-code.