Here are two similar but quite different designs of Z axis assembly.
Same travel, same components, but different...

Will they different perform or is that just two ways to make same thing ?

I can't help to think that left concept is more rigid and possibly easier to machine from one piece, with less room for error, or is it ?

upper position ...
http://img124.imageshack.us/img124/3397/z1ob8.jpg

and lower one ...
http://img164.imageshack.us/img164/104/z2ww5.jpg

Dear turpija,

Thank you for your post. It is a good puzzle.

My guess is that the left one might be best, but I could be wrong.

It looks to me that when the z axis is in the down position, the left option looks less prone to flexing.

Best wishes,

Martin

Very interesting idea... I like the left one more!!!

The left one is almost like the upside-down fork design on Super Bikes. And they use it for a reason... (It's stiffer than the normal designs).

The stepper on the left might need to be stronger to take the extra weight that was added.

the design on the left side. looks stiffer and more stable compared to the one on the right.
but the one on the left will require a larger stepper motor or extra gears to produce more torque, then the other one, since it will carry the extra load of the 2 shafts the stepper motor and its mounts, the treaded rod and its assembly. while the one on the right side doesn't.

"edit" sorry point already made. lol

Check out my post http://www.cnczone.com/forums/showthread.php?t=46326 . I Just got done building somthing similar to the one on the left. I originaly had one like the one on the right using 1/2" Aluminum and I had some flex, but only when moving it with my hand. I didn't notice any flex while cutting, but then again I've only been cutting for a few days and take small slow cuts. But I wanted something more rigid and the new design is solid, very solid. I would suggest you use supported rails as I did that way the main plate is super rigid.

I see you all saying motor should be much stronger for left version, but the real difference in weight are only actually rails and lead screw and off course itself ... left one have few plates to carry and a little longer big one, and right one has one bigger plate and one block which is pretty much the same ... so will it require much stronger motor ?

I get 1.3Nm steppers from ebay, do you think left design could be overkill ? I though to directly connect motor to leadscrew, no gears.

2 Cartierusm : nice machine btw. i don't think i would use supported rails on Z because they are quite short max. 10", and they should be 3/4" .. and machine is suppose to work on lightweight ;) materials, engraving ...

Dear turpija,

One of the weaknesses of the one on the left is that the thin vertical that connects to the router plate has twice the unsupported height compared to the one on the right. In the right version, half this vertical plate is really well supported by the bearing block.


Just a thought,

Best wishes

Martin

Dear turpija,

One of the weaknesses of the one on the left is that the thin vertical that connects to the router plate has twice the unsupported height compared to the one on the right. In the right version, half this vertical plate is really well supported by the bearing block.


Just a thought,

Best wishes

Martin

This is correct but the left has both ends supported. The plate combined with the shafts make a little beam. On the right the unsupported length is only half the plate but the router is attached to the bottom of this half.

The lightest and stiffest way to do it would be to put side plates on the right; triangular shaped to span the full width of the router mounting flange and tapering to a point at the top. These would only need to be 5mm thick.

This is correct but the left has both ends supported. The plate combined with the shafts make a little beam. On the right the unsupported length is only half the plate but the router is attached to the bottom of this half.

The lightest and stiffest way to do it would be to put side plates on the right; triangular shaped to span the full width of the router mounting flange and tapering to a point at the top. These would only need to be 5mm thick.

Dear Geof,

I may have misunderstood.

In the "left" design, my guess is that , given that the vertical shafts contribute to a vertical beam function (as you suggested), the addition of vertical , triangular side flanges might work better on the left design. The lack of vertical length on the "right" design means that the side flanges might be less effective at preventing the spindle from flexing along the X axis direction. I'm ignoring weight issues BTW...

Sorry, it's getting a bit complicated to explain in words, and I have no means of doing it in pictures.

Incidentally, Joe's MDF gizmo takes a "belt and braces" approach that pretty much "boxes-up" everything. Pretty sensible.

Best wishes,

Martin