Homing / Zeroing you Z ?

[TrickyCNC]

How do you all do it ?

I've tried various methods, with unpredictable results.

The best method I have found so far, is to manually jog to the surface, until nearly touching. Then set my jog to 5 thou increments. Place a piece of paper between the surface and the bit, and jog down till the paper gets pinched, and wont move. Then I jog down another 5 thou and home.

It still seems a bit hit and miss though. Especially when trying the onion skin method.

Is there a preferred way ?

I've heard about the touch off in ger's mach3 screen... how does that work ? can I do something similar with EMC2 ?

Thanks
Rich

[jckstrthmghty]

Mach 3 runs a vb script that waits for a signal from one of the inputs. In this case it's "probe". This is similar to setting up limit switches or your e-stop. You run one lead as a touch plate and one lead to the router ground or bit. Seems complex but very easy once you understand the basics. Many examples for mach 3 but not so experience with emc2.

[ger21]

Z Home and zero are usually two different places.
Most have Z Home at the very top of the Z axis travel.

Z zero is usually the top of the workpiece.

I used to do it like you, but used .002" increments, and called it zero when the paper was pinched.

The electronic method is much faster, and should be more consistent.

I don't know what the EMC guys do.

[Walky]

I usually use either the paper method or the "flashlight method" (I don't remember seeing anyone else using this one): use a small flashlight almost parallel to the table, so you cast an enlarged shadow of the bit (and the gap). This of course depends a lot on the material, so you can actually see the shadow. I want to make a touch plate eventually, though.

[PaulRowntree]

Even if you don't have the controller running the approach, a simple PCB touch-plate, battery and LED with manual control with 0.001" steps make the Z zero'ing very reproducible.

[TrickyCNC]

how does a touch plate help for zeroing to the work surface ?

[louieatienza]

The easiest "manual" method I found is to just hand-tighten the collet nut such as the bit won't fall out, but can still slide a little. Then drop your Z down until the bit touches the material, and go a little more so the bit actually slides into the collet a small amount. Zero the Z, then you can finish tightening the collet nut with your wrench. Depending on teh job, you might find that getting close, then PULLING the bit down to the work, might be easier, for example, with a long bit.

Another way: Shut off your drive box, and manually drop the Z down. You'll feel and hear the bit touch the material. Turn on the drive and Zero the Z. Will get you to within one step, which is pretty close depending on your screw pitch.

There are times when I have to machine a board with an uneven surface, but want an accurate thickness relative to the back of the board; for example rabbeting the edges for a groove. Or I have boards of different thicknesses that I need to be the same thickness at the edge to insert into a tenon. Once I surface the spoilboard, I'll zero the Z out to the spoilboard, then go into the MDI and move the Z up to the nominal thickness of the boards, then zero it out again.

You can do the opposite, if you have a workpiece where you cannot mar the surface. I get a scrap piece of ground aluminum plate of known thickness, and zero out to that. Then I go into the MDI (after moving the cutter away from the piece) and bring it down the thickness of the plate and re-zero.

[louieatienza]

I have no homing or limit switches on my machine. I have a safe Z set up for rapids and a park Z when the job is finished. Normally, for sake of job speed, you want the safe Z as small as possible, and I normally have it at .05". But if you have fixtures, clamps, or screws that protrude above the work you may want to set your safe Z to clear them just in case! Your park Z can matter too, if you are working with thicker pieces. If it's set too high you can crash your carriage and lose position, then watch in horror as teh bit plunges down and ruins your workpiece before it even starts! I've made a habit of scanning through the gcode in the editor just to make sure I don't run into problems.

[ger21]

Just for clarification for Mach3 users.
What Louie is calling Safe Z is NOT the same as Mach3's SafeZ function. It's more commonly called the clearance plane, or retract height.

The easiest "manual" method I found is to just hand-tighten the collet nut such as the bit won't fall out, but can still slide a little. Then drop your Z down until the bit touches the material, and go a little more so the bit actually slides into the collet a small amount. Zero the Z, then you can finish tightening the collet nut with your wrench. Depending on teh job, you might find that getting close, then PULLING the bit down to the work, might be easier, for example, with a long bit.

Another way: Shut off your drive box, and manually drop the Z down. You'll feel and hear the bit touch the material. Turn on the drive and Zero the Z. Will get you to within one step, which is pretty close depending on your screw pitch.

There are times when I have to machine a board with an uneven surface, but want an accurate thickness relative to the back of the board; for example rabbeting the edges for a groove. Or I have boards of different thicknesses that I need to be the same thickness at the edge to insert into a tenon. Once I surface the spoilboard, I'll zero the Z out to the spoilboard, then go into the MDI and move the Z up to the nominal thickness of the boards, then zero it out again.

You can do the opposite, if you have a workpiece where you cannot mar the surface. I get a scrap piece of ground aluminum plate of known thickness, and zero out to that. Then I go into the MDI (after moving the cutter away from the piece) and bring it down the thickness of the plate and re-zero.

I think if you spent an hour wiring up a touch plate, you'd smack yourself in the forehead for doing it the manual way for so long.

[PaulRowntree]

how does a touch plate help for zeroing to the work surface ?

My plate is a 2"x2" piece of double-sided copper PCB, total thickness=0.060". One side has a soldered wire to make the circuit, which is just a 9V battery, a current limiting resistor, and a connection to ground. Put the plate on top of the work, then approach until the tool touches the PCB, and lights the LED. Usually it is reversible within one step. Set Z to be 0.060", and you're away!

Just for caution's sake, I test the circuit before use by touching it to the tool. As others have said, work pieces without a flat area pose other problems ...

Cheers!

[CarveOne]

how does a touch plate help for zeroing to the work surface ?

An Auto Tool Zero button script like Gerrys 2010 screenset is installed, or Greolt's, or Big Tex's script is installed into Mach3. You measure the touch plate thickness and put that value into the script to compensate for the plate's thickness. You set the plunge rate value that you want. Save ane restart mach3.

Then you place the touch plate on the top surface of the material under the router bit and connect the ground lead to a convenient place on the router bit or other point that connects through to the bit. Some people have a permanently wired ground connection.

You click on the Auto Tool Zero button in Mach3 and after a pause it will lower the bit down to the plate's surface, set the Z axis DRO to 0.000 and retract to whatever retract height you set in the script.

Makes the zero setting very easy. However, if contact isn't made with the plate surface, it will attempt to push your router out of the mounts.

[CarveOne]

I think if you spent an hour wiring up a touch plate, you'd smack yourself in the forehead for doing it the manual way for so long.

Yeah, I'm in agreement with what Gerry just said.