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Quick question - Z-Axis movement method

Posted by John W 
Quick question - Z-Axis movement method
May 24, 2008 06:46PM
I am about to start building (already have a working cnc pcb driller) I really liked the elegance of arnie, as in this pic


where the vertical members are also the table bearings, which I understand is not without near perfect alignment idiosyncrasies.

Then the blog shows that direction was moved towards the current darwin design using 4 sets of studding as lead screws, which again seems overkill


The other option would be to use the 'lead screws' with 3 or 4 steppers then use an accelerometer to self level...


I guess it depends on the criticality of perpendicularity.

Apologies for thrusting what could be a contentious first thread out but thought it would be worth while discussion, at least for my learning smiling smiley


Edited 1 time(s). Last edit at 05/25/2008 06:27AM by John W.
Re: Quick question
May 24, 2008 08:13PM
I doubt anyone is going to buy 1000 accelerometers to get that price. Sparkfun.com sells one at a time fairly cheap (also at mouser.com)

Accelerometer $13
stepper motor 1 $30 stepper motor 2 $30 stepper motor 3 $30 stepper motor 4 $30

Stepper motor 1 $30, MXL belt +-$10 = $40

saving money, time, and coding resources = priceless..

lol, ok, except for the mastercard style explanation, I really don't see why you would want that many motors. The power requirement would be way up there. If you look inside scanner and printers, they use the same timing belt system.

I'm not sure how arnie differs from Darwin, but my opinion is that the 4 screws with a timing belt would work well and keeps it synchronized. Getting it all on there level might be a problem, but I am going to add washers between the platform and it's seating where needed to keep it level.

that's my 2cents at least.
Re: Quick question
May 24, 2008 08:29PM
It's been suggested that much cheaper tin can steppers could be used for the z-axis.

For my mind, linear steppers are probably a much better idea. You can get these with a 150 mm stroke for about $20


They're much cheaper than that if you order directly from China.
Re: Quick question
May 24, 2008 11:42PM
With the linear steppers, you could have one which has the end of its lead screw fixed into the base of the bed, and then simply guide the bed up and down. Simple enough.

Re: Quick question
May 25, 2008 12:54AM
Naah, what you want to do is to screw the steppers to the corners of the bottom of the vertically moveable xy table and fix the ends of the lead screws to the frame. Otherwise you have the lead screw moving around. I learned that one the hard way.
Re: Quick question
May 25, 2008 03:18AM
Forest's idea sounds pretty good. Then just attach the actual motor to the bed. This would also save on the drive screws. So $80 for a decent system, vs$62ish for the current system or the $133 I mentioned for 4 standard steppers.

I might go this way for my next build.
Re: Quick question
May 25, 2008 06:26AM
I have virtually unlimited access to steppers and driver boards suitable for the task (albeit 24v), which may alter my design somewhat from the cheapest.

Although the old adage 'good enough is best' still rings true.

Attaching the stepper to the bed and having static screws makes things a whole lot simpler though thats what I am going to do I think.

Back to BnQ today I reckon for some more bits (although they only had 10mm studding yesterday sad smiley)

Re: Quick question - Z-Axis movement method
May 25, 2008 06:27AM
I retitled the thread to something more useful.

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