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  #1  
Old Thu 09 September 2010, 22:45
chunkychips
Just call me: nick
 
Melbourne
Australia
Has anybody used a leadscrew to drive the Z axis?

Guys

I have searched the forum and did not find any examples of leadscrew usage for the z axis. I know this is not part of the original design but was wondering if it has been considered and dismissed and why.

The reason I ask is that a leadscrew would appear to not need a counterweight or gas spring to keep the z-axis from dropping (even with the power off). All it would need would be some bearings with good axial load ability.

Possible disadvantages:
- slower z-speed

Possible advantages:
- higher resolution
- smaller motor required (although I understand the advantages of having one type of swappable motor around for spares).
- cheaper than rack and pinion ???
- mechanically simpler especially considering no counterbalance required.

If this has already been discussed please point me in the right direction
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  #2  
Old Fri 10 September 2010, 04:46
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
One machine, with a standard AC motor as the spindle. Maybe Puerto Rico? I can't find the thread. But, yes.
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  #3  
Old Fri 10 September 2010, 05:02
obuhus
Just call me: Dmitriy #68
 
Kirov region
Russia
I don't remember whose it is a post, may be this photo will can help.
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  #4  
Old Fri 10 September 2010, 05:05
obuhus
Just call me: Dmitriy #68
 
Kirov region
Russia
And that
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  #5  
Old Fri 10 September 2010, 06:47
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Yes, That is the machine I was thinking about!
Thanks Dmitri.

Nick
You asked if the following is true:

Possible advantages:
- higher resolution - Not really, if you notice, the lead screw (which looks like a 4TPI and the belt drive, which is roughly 1:1 or maybe 1:1.5) would yield a net 4 or 5:1 reduction in speed. The standard build allows for either 3.6 or 7.2 : 1 gearbox solutions or a 3 or 4:1 belt drive solution. Thus, resolution the same (or LESS) when all considered
- smaller motor required (although I understand the advantages of having one type of swappable motor around for spares).
Hp is Hp regardless of reduction...therefore size of motor required remains the same.
- cheaper than rack and pinion ???
Rack and pinion is far cheaper when you consider the cost of the lead screw (top an bottom bearings) and follower nut. Almost double the cost.
- mechanically simpler especially considering no counterbalance required.
Is mechanically simpler, but when you find the daily use of the machine - being able to disengage (or the machine disengaging it for you) the rack allows for a mechanical "release" to the system. The lead screw if jammed or Z-stops......the other parts of the machine are going to break or jump the track.

I am a fan of leadscrews, and use them frequently in machine designs. If you can afford the extra cost, it does have some advantages (NO counterbalance required).

Good luck in your choices.

Last edited by smreish; Fri 10 September 2010 at 06:57..
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  #6  
Old Fri 10 September 2010, 07:29
Art
Just call me: Art #2
 
Lancaster,Texas
United States of America
lead screw

I upgraded to a lead screwand I definately think it is better. My indexer gets a LOT more impact force in the +Z and the rack and pinion would skip teeth.
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  #7  
Old Fri 10 September 2010, 08:31
chunkychips
Just call me: nick
 
Melbourne
Australia
That looks like a complete redesign of the z-axis . I was hoping for something less radical.

Sean
Thanks for the response. Not sure I understood the bit about "Hp is Hp regardless of reduction...therefore size of motor required remains the same." My practical experience (I'm not an engineer) tells me that less torque (at the motor) is required to wind a lead screw than to lift the rack and pinion. Could you please explain this further.

Art
Did your upgrade require a radical redesign of the original z-axis (like the photos above) or did you come up with something simpler? Are you able to share some photos?

The advantages may still be worth the extra cost if I don't have to completely redesign the whole thing.
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  #8  
Old Fri 10 September 2010, 10:25
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Nick,
1 Horsepower is equal to: 550#/FT/SEC.

Please - no one do the math here...it's just an example. Units and such are not identified!

Thus, when calculated in a speed/torque calculation you may find it takes one motor that has an output torque of 550# one second to move 1 ft.....or a 5# output motor 110 seconds to move 1ft.

But both "systems" require the same amount of "work" to do the job.

Thus, the CNC table cutting bit likes a top speed @ 300 inches per minute (nominally 225 inches per minute) do the work.

Using this as your starting datum - the same amount of work is done, just a different rates. But, still the same.

That's where my engineering professor's beat us over the head with A horse, is a horse, is a HORSE. (thank you Professor Jack Miller at UNCSA for this beating 20 years ago

Did this help?
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  #9  
Old Fri 10 September 2010, 10:29
Codered741
Just call me: Cody
 
Lititz (Pennsylvania)
United States of America
lol

He was just asking us the other day if we remembered this.

That and Pascals' law..

Apparently some of us need some more beating....

-Cody
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  #10  
Old Fri 10 September 2010, 17:23
chunkychips
Just call me: nick
 
Melbourne
Australia
Oh I see. So you are taking a constant speed into account. Fair enough. I hadn't thought of that.

"A horse, is a horse..." Of course! Of course! How could I forget Mr Ed's Theorem?
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  #11  
Old Fri 10 September 2010, 18:14
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
Cody.....Good to see Dr. Miller was applying the "pressure" accordingly. Miss all the students at UNCSA - wish I was there again this year.

Keep that Big Blue Plasma machine working Cody (and Jon).

Sean
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