Floating Head Switch?

Does any one have a picture of what a floating head W/probe switch looks like.I have an idea but I think it is wrong.The way I have it now is as follows. When the Z-axis probes down to find the top of the material, it will go down till the torch tip touches the material?As soon as it touches the floating head will make the probe switch (it will be NC or NO ?) It will continue until it reaches the set probing distance? Then it will back away to the material surface? Then it steps back whatever distance I have set for the pierce height?

Does this sound correct? I,m new and I don,t know what to do. :drowning:

There are some pictures on the CNCMANUALPLASMA yahoo group and on CandCNCSupport.

The basic concept is that the tip touches the material wich moves the torch holder and torch upwards. A switch (roller type lever switch work good) is mounted so that as the torch holder does move up it rolls past the switch and the switch is activated. The switch is hooked to the Z home input. At the point the switch is activated, the tip is actually sitting on the surface and you have run past the actual zero point. The home move will back the Z up some but not enough to actually leave the tip at precisely the top of the surface. That is where the switchoffset value is used. It is the net value between where the swtich is tripped minus the home "backoff" and the actually Z distance to move the tip to just (.005 or less) above the material

Here is how to calibrate it:

Make sure Homing is working on the Z axis and it moves in the right direction (down) on a home move and hits the switch and stops. You should be able to reach over and slide the torch and holder up with your hand and manually trip the Z home and see it in the Diagnostics page of MACH.
Now load some material and hit the reference button for Z (next to the DRO). The head will move down, push the torch holder up, the torch holder strikes the roller of the switch and the switch stops the Z axis. Next without moving the Z, hit the Z Zero and zero the DRO. Now, carefully jog Z up until you can just slip a piece of paper between the tip and the material. Read the value on the Z DRO....that is your "switch offset value". Do the calibration a couple of times to make sure it's repeatable.

There are two ways to use the value. If you are NOT using SheetCAM and it's special THC300 Plasma POst or the MP1000THC post (both do automatic "touch-n-go"), then put the switch offset value into MACH3 in the Homing/Limits (Home Off) as a NEGATIVE number. Thus when you home the DRO for Z will show you are actually below the plate and compensate the Z axis that amount. It does not automatically back off to zero but when you tell it to retract it adds the distance to the move.

The other way. is to use SheetCAM, and simply open the post and find the "Switchoffset = xx" statement in the post (where xx is a number) and put your value for switchoffset there. From that point on it will stuff that value in the g-code and automatically back the head off to true surface zero and reset the Z DRO.

Either method works. Just do do both!

The advantage of using SHeetCAM and the listed posts is that it puts in the Z reference moves for you and has a distance traveled value (default 20 inches) that is used to trigger a new reference move before pierce. Most THC's not under control of the toolpath software simple reference every pierce since they don't maintain an actual Z height. Using the Sheetcam and triggred reference approach you only reference every "X" pierces. You still get the advantage of being able to cut warped and buckled material but without the delay of probe-pierce, probe-pierce, etc.

The type of swtich (NO or NC) does not matter since you can use either as a a Home swtich. Most common is NO.

It's the actual movement UP of the floatinghead that trips the swtich. It can be .020 of movement up to an inch as long as it says consistant and you can put it in the switch offset value.

I have a mechanical drawing of a floating head (soemwhere) and I will try to get it posted on my support site.

Tom Caudle
www.CandCNC.com

"Either method works. Just do do both!"

I meant to say: "Either method works, Just DON'T do both!"

Ok . Thanks again torchhead!

Torchhead could you give me a sample program to show me how this should work.It doesn't have to be a part or anything .I just want to see how to program all of my z-axis moves. I figured out my touch off distance it is .1166
.

I figured it out, I had to cut and paste this into the macros for the M3:

rem modified 02/04/2004 by Jim Cullins
Option Explicit
Dim TorchHeight, SwitchTravel, PierceDelay,TCutHeight
PierceDelay = getUserDRO (1001)

code "g31z-1"
While IsMoving()
wend
TorchHeight = GetUserDRO(1000)
SwitchTravel = GetUserDRO(1002)

TCutHeight = (getUserDRO (1003) + SwitchTravel)
code "G92Z0"
code "G1Z" & (SwitchTravel + TorchHeight)
While IsMoving()
wend
DoSpinCW()
code "G4 P" & (PierceDelay)
code "G1Z" & (TCutHeight )
TorchHeight = 0
SwitchTravel = 0

This does a reference on every pierce. That works but on a decorative piece with 50 pierces it is a waste of time. The THC post in SheetCAM has an automatic reference that will only reference Z every 500mm (default) of XY movement. It does the Z reference in g-code so the stock M03 macro is used for everything. Since one of the advantages of using MACH to control Z is it's knowing the height at all times, you can do multiple non-referenced pierces as long as the metal is flat in the area.

I urge you to consider upgrading to MACH3 and to the development version. We have found and solved several THC bugs and issues that are present in MACH2; one as recently as last month. I found that if you use an aggressive Input Debounce parameter (>500) to debounce the noise off inputs in MACH it also effects the response loop of the UP and DOWN inputs and causes the THC to do a vertical "sawtooth" cut with overshoots. Looks like a basketball going down the court! In severe cases it can cause the torch to loose arc. The latest development release has the debounce setting ignored by the Torch UP and DOWN input signals that are used by the THC300

There are other small problems that have been solved as well.

I tried to download Mach3 today with no luck.I did the re-boot,but it kept locking up when I would try to open it afterwards.

i havent got to the sitch yet but here is the one im working . this is just my opinion but if your kinda new at this stuf as i am. i would highly recommend dealing with Tom over at candcnc he is a great guy and offers awsome products
John
st.louis

hehehe, your table looks like mine. Partially cut material, tools everywhere, some instructions, and a Garage door. My kind of people.