I'm Going to contradict myself now..!!! . . . If your not going straight across with the belts then I wouldn't bother has it's very complicated and messy with belt that long winding around the machine. Keep it simple else stay with Slaved Motors.
Yes the belt approach is much more reliable and gives great piece of mind your always in sync. But not if the setup is overly complex it's needing constant attention and with belt this long threading around the back I fear it may cause trouble.?
So I'd say either change the design and keep it more direct or keep with slaved motors which if properly tuned and connected to good drives don't give too much trouble.
I don't know if you've seen my long running build thread, Which ive only just started :-) ut this is what I am planning on doing with the motor, It will clear the gantry and bed just.
The first image is showing the belt and bearings, the second is showing it with a 50x25 channel housing the belt and also holding the motor and idler bearings. I may have to use a larger channel but I wont know until I get to that bit.
The Following User Says Thank You to Lee Roberts For This Useful Post:
I am back.
I have not been able to post mails, because my thread suddenly disappeared. Lee has been very helpful and has recreated most of it. However, there are still some drawings/pictures missing. JAZZ can you please mail the very instructive gantry pictures again and CharlieRam can you also please send your nice drawings again?
Anyway, I agree with JAZZ, I was not too happy with the very long and complicated belt in my (now missing) drawing. The drawing from CharlieRam is a much better Construction, from a mechanical point of view, but, (as JAZZ also points out) I do not like that it blocks the end of the bed if you need to route long structures.
Previous drawing with long, complicated belt:
Drawing where I have put back the extended cantilevers at the top of the machine and moved the now longer, ballscrews, and crossed the belt over directly between them. The bracket serves as cover for the belt, and the motor/idler-pulley assembly goes on top of it, so that it doesn't block the end of the bed.
I would go even further and make it so that the belt is tightened by some screw that moves the motor up and down. Additional plate that slides or sth similar.
As for how far the Z should extend is suggest you contemplate this screen snip and read post #8 where i am trying to explain the benefits of properly designed Z axis
The idea is to achieve maximum Z extension with minimum effort and maximum rigidity as a result, using the spindle body to make Z super stiff.
is more than enough for more
My advice is to understand this/about the Z/ and check your design backwards from there. 150mm Z travel is more than enough for all purposes.
The Z on the picture will extend 200mm with 3kw spindle , but that would seriously question a beginners design. As a precaution the plate should be 20mm steel or 30mm aluminum and reinforced with side braces /against front back deflection/ exactly where the black line is especially at the yellow area. Of course another design problems will arise from such an extension so you have to make sure left/ right you dont have any weeak element on gantry, gantry sides, ball screw mounts, etc.
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.
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...
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.
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.
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?
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
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