Anyone tried using Z axis by turning an embeded nut in cog?
May 27, 2011 02:44AM
Has anyone tried moving the Z axis by embedding a nut within a cog and turning the cog with a belt?
i.e. the threaded rod is fixed and the nut turns to move the axis up or down.
Re: Anyone tried using Z axis by turning an embeded nut in cog?
May 27, 2011 05:00AM
Are you planning on giving this a go? I'm about to embark on building my 2nd printer (Huxley based with customisations to play with various ideas) and might consider knocking something together.

One pro I can see - stability from the static Z rods. One con is that the Z motor would have to be mounted on the X axis I guess which adds to the weight (not sure if this would be a problem)


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Re: Anyone tried using Z axis by turning an embeded nut in cog?
May 27, 2011 06:37AM
Id like to know what speed is achieveable with this technique.
Threaded rod drive is generally considered to be very slow, but a lot of that is to do with the inertia of the rod. If you are just turning the nut, then the inertia of the rod is irrelevant. The question is, how fast can you turn the nut.
Re: Anyone tried using Z axis by turning an embeded nut in cog?
May 27, 2011 11:27AM
The cog approach should work, but like Gary said, it makes the carriage heavier.

As an aside...

I can run my threaded Z at nearly the max speed of my stepper (5 rev/s or so). The inertia of the rod is pretty small, and is a nearly negligible contributor to the steppers load.

The reason Z axis travel is so slow is mostly because the threaded rod has a "gear down" effect. 16 revolutions of the z stepper equate to 1 inch of z travel, where 16 revolutions of the x stepper equate to 16in of x travel.

This is why some manufacturers are switching to multi start lead screws instead of threaded rods. On the lead screws, it only takes 4-8 revolutions to move one inch of z travel.

In my opinion, the real solution is to not care about the z axis speed at all. The only reason we want faster Z is so the extruder has less time to ooze during the z travel. After all, It makes up less than 1% of the build time for most objects.

Instead, if you minimize the filament length from pinch wheel to nozzle, and carefully implement stepper reversing, the z travel ooze all but disappears anyway.
Re: Anyone tried using Z axis by turning an embeded nut in cog?
May 27, 2011 03:47PM
Quote

Id like to know what speed is achieveable with this technique.

With proper acceleration, the usual steppers can make some 1000 rpm, so you can get 1200 mm/min or 20 mm/min with an M8 rod. You need a good bearing suspension for such rpm.


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Re: Anyone tried using Z axis by turning an embeded nut in cog?
May 28, 2011 12:35AM
I cannot see any reason why my idea would not work, but thought I would ask just in case someone had a reason for it not to work, or had tried it and it worked/failed.

The Z axis is already turning by threaded rod. I do not plan to modify the gearing, so that 1 turn of the rod with the current mendel would be the same as 1 turn of the nut with what I am proposing. As Andrew said, the Z axis is slow. I am not worried about this as it is only used to lift the extruder as the part grows in height. The main speed required is in the X & Y axis.

This carries on from my design work done previously, although I got sidetracked with other work. Note as yet I do not have a working model. Here is where I was up to Cluso's Micro-mendel variant

If I mount the threaded Z axis rod rigidly, then I do not require the ball bearings for support, and nor do I require smooth bar for stability (as in the Prusa). This should simplify my design further.

Currently in my design, the Z axis only carries the extruder (I am thinking of Wade's Extruder). It is not mounted on the X or Y axis, so an extra motor should not matter.

Gary: Would be good if you could try it out. BTW, thanks for putting together the writeups on Wade's Extruder and Prusa's Mendel. Both were great to see, and catch up on progress I missed while otherwise occupied.

FWIW I am doing my own electronics using a Parallax Propeller chip (SMT QFP44) and the Allegro A4982/4 driver chips. The A4982/4 are easier to hand solder and provide more area for heat disipation than the A4983/8.
Re: Anyone tried using Z axis by turning an embeded nut in cog?
May 31, 2011 12:27PM
I am currrently using that cog and belt model for the z axis for the TEchzone huxley I have. I have no problems with it right now, just needt o make sure the gear that is on the motor is attached well by either a screw or glued onto the motor axle.

Ive been having more problems with the hot-end than anything else. Techzone sends a difficient hot tip which is known to die very quickly and is known to need extra machining in order to operate to any sort of efficiency.

I think that model will increase the efficiency of the prusa instead of having the two motors on top with couplings.
Re: Anyone tried using Z axis by turning an embeded nut in cog?
May 31, 2011 01:43PM
owism8 Wrote:
-------------------------------------------------------
> Techzone sends a difficient
> hot tip which is known to die very quickly and is
> known to need extra machining in order to operate
> to any sort of efficiency.

Sorry to hijack the thread. Could you give me some references about that ? I just started assembling a techzone huxley so any information that could help me is welcome.
Re: Anyone tried using Z axis by turning an embeded nut in cog?
May 31, 2011 06:40PM
well I have one and it died quick. What i mean by that is the plastic starts oozing out and pushes the brass tip out of the PTFE. Techzone wants you to fix that by putting a wood screw in it and everything should be fine. This requires some clamps and tools which I didnt have and had to purchase. Heres their description of it: [www.reprap.org]

I also went ahead and purchased an Adrian hot tip ( [reprap.org] ) from the following user: CdnReprap , Just PM him and let him know you want one and he will lead you through the address and shipping and payment info. He charged me $45 for the machined parts and the resistor.
Re: Anyone tried using Z axis by turning an embeded nut in cog?
June 01, 2011 01:02AM
Ok thanks. I already got the needed tools to better attach the ptfe, so I'll go that way first.

Thanks and end of thread hijack.
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