New build – input/comments appreciated

[Clive S]

If we agree that the purpose of limit switches is safety and prevents the machine from exceeding its working area - why then is it not required to have limit switches in both ends of each of the axes? (ok Z is a little different).

This is because they use a target at both ends ie the switch will travel with the gantry and so will hit the target at the end of travel in either direction.
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Re point 3 It is the homing that give the ref points for the soft limits.
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re point 4 After you have homed the Z you then move Z down to a ref point (say top of work piece) and then Zero it on the dro so now the machine or should I say the controller knows where zero is and can work out the depth of cut.

[Neale]

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Re point 3 It is the homing that give the ref points for the soft limits.

It is really useful to have reliable, accurate, homing switches so that you can quickly set up reference positions when you switch on each time. Picking up accurate positions from one session to the next is difficult without this, whether you use hard limit switches or not. I don't have home switches on my current machine and it's a pain.

[njhussey]

It is really useful to have reliable, accurate, homing switches so that you can quickly set up reference positions when you switch on each time. Picking up accurate positions from one session to the next is difficult without this, whether you use hard limit switches or not. I don't have home switches on my current machine and it's a pain.

I'll second it being a pain not having homing switches....

[ngundtoft]

Thanks for clarifying this Clive. Obviously (now that I understand it) you can use the same switches for both limit positions. I see now that it is also what JAZZ writes - just wasn't clear to me.
So, since I am not using slaved motors, I should have 3 limit switches.
So even though JAZZ only uses 3 (+1) switches, it sounds like it is a very nice feature to also have the home switches - or can you also use the limit switches for this purpose? I sounds like it is the same position (0,0) + Z?
I can see the advantage in using the top of the work piece as reference, so that you don't have to measure the difference between a fixed reference point and the work piece surface. How do you do it in practice - do you need a manual rotary control or can you do it from the keyboard (without damaging anything)?

[routercnc]

This is often a point of confusion for beginners so don't worry. Keep asking until you get it. Once you have the machine and software in front of you it makes even more sense.

Jazz only has 3+1 (roving) switches but still has the home and limit function. They are just shared from the same switch. In terms of Mach3 (or whatever software) you are either homing an axis (so a switch detection means you are at the home point) or you are manually moving / gcode cutting (when a switch detection trips the e-stop for example). You are never doing both at the same time.

I think from what you are saying in your posts you also need to understand the difference between 'machine coordinates' and 'work coordinates'. This also trips up beginners so make sure that also makes sense. Machine coordinates are where the machine is in absolute space and are set to 0,0,0 by going to (referencing to) the home switches. When you are ready to cut you need to go over and down to the corner edge of the workpiece and set the local work coordinates to 0,0,0. This will be at some machine coordinate absolute location such as 100,100,-50. You can switch between looking at machine and work coords in mach3 on the DROs to see where you are on each axis system. The work coordinate locations can be set using a touch probe, or a piece of paper between flute and workpiece using the jog function (e.g. 0.1mm increment movements) until the paper is just trapped.

Now the machine knows where 0,0,0 home position is (in case the job goes wrong and you need to reset, or you need to stop the job to go home). It also knows where the workpiece 0,0,0 is so all the cutting can take place where the work is on the bed.

Have a read of the manual, ask more questions and eventually this will start to make sense.

[JAZZCNC]

Machine coordinates are where the machine is in absolute space and are set to 0,0,0 by going to (referencing to) the home switches.

Every thing neil says is correct but just want to clear up something that could confuse or be taken wrong by a beginner. Neil says "Absolute" space but this is very different to absolute positioning mode G90 used with-in G-code.
Absolute positioning mode doesn't refer to absolute space but rather it moves an absolute distance in inside the WORK coordinate system. Compared to Incremental Mode G91 which increments by a commanded distance.
ie: G90 X150 would move 150 units away from Work zero. G91 X150 would Increment 150mm from the absolute position so if your at G90 X150 then with G91 X150 you'll end up at X300 absolute work coordinate.

One other slight point I'll make for new folks which I know confuses them is that the Work Zero doesn't have to be on the corner of the Work piece or material. It can be any where you want it to be on the material. Where you located the Zero coordinate in the CAM softare in relation to the part will mostly dictate where on the material you actually place the WORK zero.
ie: For instance if your part was circular like a Wheel for instance then you'll most likely locate Zero at the centre in CAM which means you can't loctate WORK zero on the Corner of material.
In practice often you'll be cutting out of much larger piece of material than the actual parts size so will job to any location that the part will fit within and knowing the Programmed Zero point on the part choose point in that area.


Now to use one switch for Both homes and Limits you need to turn off Home SW safety option in genreal Config. This will tell Mach3 to ignore the Limts while the Machine is Homing.
Your also better to turn on Auto Limit over ride in the setting screen. This will allow you to reset Mach3 and drive off the switch. If you don't turn this on you will need to include a Limit override Switch in your Wiring to knock out the limits while you reverse off the switch.

[routercnc]

Every thing neil says is correct .

Was me not Neil but agree with you on use of the term 'absolute'.

I ran without homes and limits for several months, then added some switches (but never got round to wiring them up) and one day jogged into one and smashed it to pieces and banged into the end stop. Makes you realise how powerful these machines are and to keep your hands out of the way.

Just got round to adding limits and homes so should be OK now.