New build – input/comments appreciated

[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.

[JAZZCNC]

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

Doh I blame coolant fumes.!!

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.

Ye try snapping a 12mm Carbide cutter by hand.!! . . . Even a small machine will snap one like a carrot.!!

[ngundtoft]

Thanks - lots of really useful info. I know a lot more about limit/home switches now.
So 3 switches it is. Based on the above, I cannot really see why you would want to use separate home switches - unless you want some very special home position?
And let us switch tune. I have updated my model with a single Nema 34 motor for the Y-axis and an adjustable mounting flange, as suggested by Silyavski. Is 20T pulleys/idler pulleys ok for this, or should you choose larger ones?

[JAZZCNC]

Is 20T pulleys/idler pulleys ok for this, or should you choose larger ones?

Yes they will be fine arranged like this with nearly half the teeth engage. Don't want to go too large other wise the extra interia starts to affect things.

[ngundtoft]

I have been thinking about how to design a holder so that you can route dove tails at the end of boards.
This is not a function I will be using every day, so it should be simple and it should not compromise the machine in other ways.
I read the thread by EddyCurrent and how he has done it. It looks good and stable and I am sure it works very well.
However, I don’t want this function to interfere with the precision of the bed, so I am not too happy with the removable plate. Also, for handling, I find it somewhat impractical to have this opening in the middle of the machine. All that is needed is a jig that will hold the work piece in an accurate and repeatable position. So I was thinking of placing it at the end of the machine, as shown in the model. You simply fasten the work piece with one or two clamps. I may have to extend the cantilevers/ rails to get sufficient overhang for the spindle or alternatively reduce the length of the frame, since this machine is already getting fairly large.