New build – input/comments appreciated

[ngundtoft]

Great input - thank you.
Silyavski your idea, with some kind of threaded screw to adjust the belt tensioning, sounds good. I will find a way to implement that.
As for Z-axis extension (and stiffness) I think I will stick with my 220 mm. I agree with JAZZ that you can do with less by moving the bed up or Down, and I have decided to implement some way to do that. But I will mainly be cutting wood, and for that I don't think it will be a big problem. When cutting aluminium, I think it is ok to raise the bed to a position where the spindle plate is moving around its center position and that will be sufficient. Spindle motor will be 2,2kW.

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I am not quite certain about the limit and home switches.
The limit switches/sensors are there to define the absolute outer limits for the gantry/spindle.
I expect that means that you must have limit switches in both sides – 2 for X-axis, 2 for Y-axis and presumable just 1 for the upper Z-axis?
The home switches define a central point on the bed, including a middle position on the Z-axis?
That is a total of 8 switches/sensors if I am correct?

[routercnc]

Don't really need to do it like that. You need limit on X and Y on furthest away point only. For the other end the limit switch function can be shared with the home switch ( so only one near side limit / home switch needed per axis)
That makes 5 in total. You can add a Z lower limit if you want but not everyone does that.
As you can gather from that your home position is then in the nearest corner (0,0) on a graph paper not the middle. All movement and cutting is done at positive X and Y coordinates and since Z zero is at the top home then cutting is done in the negative Z

[JAZZCNC]

That makes 5 in total.

I'll name that tune in 3 switches.!! . . . Lol (Ref to Uk Tv program called name that Tune for those out uk)

You can share the Home and Limit function using just one switch. Place that switch on the moving parts and trigger with a Target and you can bring the switches down 3 + 1 for home if slaved motor.

This is my prefered way has it saves wiring and less switches to go wrong.

Also you can have the Home Zero Position a set distance away from the physical switch trigger point. So if you want Home in the middle of the table you still can. Why you would I don't know but you can if required.

[Boyan Silyavski]

I'll name that tune in 3 switches.!! . . . Lol (Ref to Uk Tv program called name that Tune for those out uk)

You can share the Home and Limit function using just one switch. Place that switch on the moving parts and trigger with a Target and you can bring the switches down 3 + 1 for home if slaved motor.

This is my prefered way has it saves wiring and less switches to go wrong.

Also you can have the Home Zero Position a set distance away from the physical switch trigger point. So if you want Home in the middle of the table you still can. Why you would I don't know but you can if required.

I always forget that. Have to write it down. Again i have bought a ton of switches for my new machine and was just at the point of wiring them.

So you define start and end trigger or you define just one trigger at one end of travel?

Thats sth i don't understand. Have to read again the mach 3 manual obviously.

[ngundtoft]

I am confused - apparently I am lacking some basic knowledge about the limit/home switching concept (but I am new to all this, so trying to learn).
Basically I can follow the mail from routercnc, which corresponds with my understanding. But when JAZZ limits the number of switches to 3 , I get confused and have some questions:

• 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).
• I did not really mean that the home position should be in the centre of the bed, it was mainly to distinguish it from the limit switch position. If you always work from the nearest corner (0,0) - as described by routercnc - then the limit switch position and the home position is the same, and what would you need the home position for? Or rather - it only makes sense to use the same switch for both purposes.
• Soft limits are set up in the SW as I understand it. But what are the reference points for these soft limits? Asking because you sometimes get the impression that you can almost manage with these soft limits and omit the mechanical limit switches.
• I can see that there is not much purpose for a normal limit switch on the lower Z-axis, since the tools will vary in length. But how does the router know the cutting depth? I think I saw a video (Obiwan?) where the spindle was moved to a certain (X,Y) position and then lowered (Z), until the tool made contact to a reference point (or activated a switch), to give a reference position. Is this the way to do it - or are there other ways?

[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.
.
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.

[Christian Knuell]

Hi,

• 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).

Seeing it from this perspective you'd be right - but my personal opinion is that limit switches are not only unnecessary but even give a deceiving sense of security they cannot provide:

• If a machine can be damaged by chrashing into its axis limits it is just a crap machine...
  (OK - not talking about professional high speed machining centers where you have tons of material accelerated to very high speeds - but even there a limit switch is just the last line of defense - position feedback will stop those machines way before this could happen)
• A machinist not noting the workpiece will require machining outside its limits is just a crap machinist... ;-)
• If the machine looses steps the workpiece will most likely be damaged anyways...
• And limit switches do not detect step losses - a machine may ruin anything including tool changers or sensors within its work area without the limit switches taking any note of it. Which is also why a machine should never ever run unattended.
• So basically: if you really need security you need position feedback.

What sometimes makes sense is reference switches to automatically home the machine. But even though they can make life a bit easier in some situations they are rarely necessary:

• Usually you clamp your workpiece just anywhere on your machine and need to touch it off anyways because your machine has no eyes.
  
  • In this case knowing machine zero is absolutely pointless - it is just a set of numbers without any meaning for the actual machining process.
  • Only in case of step losses it can safe you a little time to get back to the correct workpiece zero - if your workpiece isn't destroyed anyways which will most likely be the case... And a machine losing steps regularly enough to make you want homing switches is again just crap or badly set up ;-)
  • But even in this case you can usually just touch off again (if the reference edges are still available)...
  
  
• Reference switches are only necessary if you have things like tool changers, tool length sensors or fixed clamping devices on your machine.
• And: if the switch isn't precise (or a chip gets in between) machine home will also be imprecise accordingly. Many cheap homing switches are much worse than touching off the workpiece. I program CAM Software and I came across quite some people unnecessarily referencing after every toolchange and wonder why there are visible marks on the finished workpiece that wouldn't be there if they just kept X and Y (or at least used proper limit switches with good repeatability instead of the cheap stuff they bought).

Christian

[JAZZCNC]

Seeing it from this perspective you'd be right - but my personal opinion is that limit switches are not only unnecessary but even give a deceiving sense of security they cannot provide:

I agree upto a point but here are some cases they are required. Servo's for instance will just take off at full speed if there positioning system fails or gets interupted. So in this case they are very much required.

Also with small fast router machines it's very easy to jog from one side to the other which can result in banging into end stops etc often. Esp when first learning. Again I agree a machine that breaks with just a small limit crash is Crap but enough of this banging and eventually damage will occur so best avoided and for just a few sheckels more is it really worth not having.??

What sometimes makes sense is reference switches to automatically home the machine. But even though they can make life a bit easier in some situations they are rarely necessary:

[LIST][*]Usually you clamp your workpiece just anywhere on your machine and need to touch it off anyways because your machine has no eyes.

• In this case knowing machine zero is absolutely pointless - it is just a set of numbers without any meaning for the actual machining process.
• Only in case of step losses it can safe you a little time to get back to the correct workpiece zero - if your workpiece isn't destroyed anyways which will most likely be the case... And a machine losing steps regularly enough to make you want homing switches is again just crap or badly set up ;-)
• But even in this case you can usually just touch off again (if the reference edges are still available)...

[*]Reference switches are only necessary if you have things like tool changers, tool length sensors or fixed clamping devices on your machine. [*]And: if the switch isn't precise (or a chip gets in between) machine home will also be imprecise accordingly. Many cheap homing switches are much worse than touching off the workpiece.

This I mostly Disagree with.!!

Homing switches are THE most useful thing you can put on your machine. I'll give examples to why.

Only yesterday I was cutting parts in large expensive sheet of aluminium when the cutter broke. The part wasn't damaged but it was my last cutter so the Job was stopped. The corner of the material where I choose Work Zero had been cut away. So how without Home switches do I get back into absolute position when my reference point is gone.?
Yes I could go back into Cam and choose some hole to re-reference from etc but this all costs time and effort. Home switches provided resonable quality remove all this hassle.

Example #2 Same large piece of material and Large Job with multiple parts nested into material. So large I don't have time to do in one sitting. Again Zero ref has been cutaway. Home switches allow me to pause the Job or break the Job into smaller jobs and still quickly get back into position.

There are other examples like power cuts or PC crashes etc that back the need for Home swithces but again for the small cost it's silly not having them.
The only thing is that if you need high accurecy homing then you need Good Home Switches. I find even your Cheap Chinese Proximity switches are more than good enough for 99% of Routers or DIY'ers using Milling machines.

So for the Small cost and the fact Limits and Homes can share the same switch it's Stupid not to have them.!!