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Z axis design, rails on the spindle, or blocks on the spindle plate?
Hi guys,
I'm making some design decisions about how my Z axis is machanised.
At the moment, I have the below design, but I'm a little confused about what parts to put on what bit.
Is it better to have the Z rails attached to the X carriage, or the Z Blocks, with the rails on the back of the spindle block?
Same question about the motor? fixed ontop of the X axis plate, or moving up and down with the Z axis?
I was figuring, whatever side I put the linear rails on, it probably makes sense to put the motor mounts on that piece also, as it has to be the longest piece?
Any feedback welcome
http://www.cnczone.com/forums/attach...d=336794&stc=1
http://www.cnczone.com/forums/attach...d=336800&stc=1
Re: Z axis design, rails on the spindle, or blocks on the spindle plate?
It's more common to have the rails affixed to the stationary plate and the trucks to the moving plate, but I suppose you could do it either way. The Z axis stepper motor is also attached to the stationary plate; this minimizes wire flexion. The spindle motor goes on the moving plate.
Re: Z axis design, rails on the spindle, or blocks on the spindle plate?
It is somewhat customary to have stationary rails and moving blocks. If nothing else, it reduces the inertia of the moving part. The second picture does look more elegant, but see how much more moving weight you have there? And what's more important, you will lose some Z clearance.
Re: Z axis design, rails on the spindle, or blocks on the spindle plate?
If your Z axis travel is short, put the rails on the stationary plate. If you Z axis travel is long, put the rails on the carriage. You'll see moving-rail carriages on raised rail, portal style machines, for example.
Re: Z axis design, rails on the spindle, or blocks on the spindle plate?
I was wondering about this question for my moving table. It looks like Bridgeport style knee mills have the rails on the underside of the table with the blocks attached to the knee but I can't really see if this assumption is correct.
It seems like it would make sense to fix the bearings instead of the rails in scenarios where the mounting surface (such as the knee on a knee mill) is shorter than the table / rails and desired amount of travel.
It doesn't seem to be as common in CNC routers but I haven't seen any CNC routers where the table is longer than the base it is mounted to.
I have the same question for my Z axis because my X mounting plate is shorter than my Z rails and z mounting plate. I can't tell if it makes any difference to the stiffness of the machine or not.
Re: Z axis design, rails on the spindle, or blocks on the spindle plate?
Quote:
Originally Posted by
Goemon
I was wondering about this question for my moving table. It looks like Bridgeport style knee mills have the rails on the underside of the table with the blocks attached to the knee but I can't really see if this assumption is correct.
Your assumption is correct most machining centers are made this way, it means the cutting area is supported at all times
Re: Z axis design, rails on the spindle, or blocks on the spindle plate?
Quote:
Originally Posted by
mactec54
Your assumption is correct most machining centers are made this way, it means the cutting area is supported at all times
It makes sense if the knee is narrower than the table or if you are trying to maximize the available x-axis travel on a moving table machine. You would need some seriously long (and expensive) rails to do it the other way around on a knee mill.
You would also need a more powerful motor for the Z-axis if you had a 60" wide cast iron knee. They would probably have to switch to a moving spindle design and moving one of those Bridgeport milling heads up and down would be no picnic either.
I decided to run my long axis (X-axis) along a fixed gantry instead of having a moving table for both the X and Y axis for this reason. My X axis rails are only 1000mm (a little under 40") and I need at least 30" of travel. I might have gone the other way if I would have thought about flipping the rails like on a Bridgeport.
My Y axis (the moving table) is much shorter. The rails I bought for it are 27" long but I only actually need 7-8" of travel for now. Still, If I find that it makes sense to switch the X and Y rails or I find a need for a longer Y axis in future, it's good to know that there is a proven way of doing it without needing to buy 60" rails to achieve 30" of travel.
