New build – input/comments appreciated

[Boyan Silyavski]

Boyan you are going Way over the Top with your idea of a Z axis.! . . . You need to read the man requirements.!!
Using 20mm Steel isn't required for cutting Wood and will actually lower the machines performance due to having high inertia and affecting accleration/velocity. Or increase costs by requireing larger motors or Servo's.

The Z axis has drawn will be perfectly fine for cutting Wood even with 3Kw spindle on it.

Ok. But...


The way i have drawn it is from 40mm aluminum that weights 6.6kg

Simplified plate 150x500x20mm aluminum is 4kg, steel is 12kg. Not so much weight, for what will bring as rigidity. A couple of welded short bars more at the raised sides and as i like to say- will reap through aluminum like butter even fully extended.

Ok, i will stop drinking Monster Reaper. Too much energy drinks...

[JAZZCNC]

Ok. But...
Simplified plate 150x500x20mm aluminum is 4kg, steel is 12kg. Not so much weight, for what will bring as rigidity.

That's a cost 3 x weight increase for ridgidty gain that isn't needed in the first place. Then you add in the hidden cost's of lower acceleration which for a Z axis, esp if doing 3D or relief work is quite important. Then if you really need that acceleration it's a move upto Servo's and the extra cost there.!!

I agree 200m travel is excessive in most cases and 150mm covers 98% of work and tools used. But Reaping thru Aluminium at full extension like you say would be foolish thing to do and the cost for the less than 1% time you really have no choice is very high.

It's a simple fact that you can't have ridgidty without it costing something.!! . . . . Money or performance. Wood's etc needs higher performance so can live with lower ridgidty.

[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?