Z axis design suggestion

I'm in the process of getting my Z axis working and had a couple of ideas to make things a bit easier.

The main thing is that everything needs to be pretty close to square/vertical/perpendicular with very little room for deviation and this is a bit of a pain.

I'm not particularly mechanically minded so I may not be able to visualize the consequences of the changes I'm proposing very well but I thought I'd throw a couple of things out there and see what sticks.

The simplest change would be to lengthen the Z axis idler and studding drive rods up through the top corner brackets and hold them in place with an arrangement of a nut and washer on each side as on the bottom brackets. This gets the internal spacing correct and you don't have to worry about adjustments to get the Z axis rods exactly vertical and parallel to the frame.

My corner brackets came from Bits and Bytes and the top ones don't have holes in the correct places although I think the stl files do.

This would require a bit of thinking and changes to instructions as you would have to do everything in a specific and slightly different order but I don't think it would be too hard and it may be that then you could do without the tie brackets and bed constraints.

At that point it may be worthwhile redesigning things further to do without half the vertical rods as there will be 2 rods running parallel to each other for most of their length on each corner where 1 would do (maybe just leave a small additional piece that protrudes through the bottom corner pieces as adjustable legs for each corner). Of course, it may be best to keep both from a strength and stability point of view

The other idea I had is impractical at the moment but may be worth looking into in the future when we can reprap our own motors. Rather than have one Z axis motor and a belt and pulley system connecting each corner, we could have a motor on each corner directly controlling it. This goes against the trend of simplifying things and the only advantage I can see for this is that you can then move each corner independently.

This is good for trying to get everything level in the calibration stage but during normal operation you'd just want to move the platform as a whole up or down. Can anyone think of any other advantages to this? If not, then I doubt it would be worth the added complexity but it was brought up in conversation yesterday and I could see it would have made my immediate problems easier and quicker to deal with.

I am going to make a Z-axis with four tiny steppers wired in parallel. They cost about 1/4 of the price of the Keling motor and it gets rid of the belt, pulleys and stays. I will need four motor brackets and four couplings though, but if I RP then they will only cost pennies.

I think I don't need to support the top of the threaded rods because the bed does that. Without the belt tension there should be far less friction.

I will blog the outcome.

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[www.hydraraptor.blogspot.com]

Reece i would suggest drilling the missing holes in the corner brackets the latest versions had these holes, eD also wrote a good section Z axis setup as it is an area that pays of for precision.

It will also benefit from a tensioner being added so belt tension is not set using the tie brackets which should be used for the vertical alignment.

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Ian
[www.bitsfrombytes.com]

Yeah, Reece, I originally built my Z axis as you described, as I thought that was how it should go. I drilled the extra holes on principle, and you need them anyway to set the bed corner bolts correctly. Follow the directions carefully there - I didn't, and had to re-do that part of the build to get my corner brackets on straight.

But, if you look at the design carefully, locking the tops of the idler rods over constrains the system, and will make the system bind up pretty badly if all four idler rods are not perfectly parallel. The Darwin design has the rods essentially free floating at the top end, with the 180 and 360 bearings on the two corner brackets doing the bed positioning relative to the smooth rod. That's good, as even though I've been very careful, I see that my threaded rods are not completely straight, where as the tougher smooth rods are still very straight, so I should have good accuracy as my Z axis moves. The Darwin design is set up to ignore small lateral variations in your idler rods.

That said, the pulley arrangement is a pain, and really loads up the chassis with belt tension. I also bought a $5 linear stepper; with a longer screw it could make a much simpler (at least mechanically) Z axis drive.

Interestingly, the linear stepper I found is mostly plastic. I think a few extra motors and wiring would be worth some z axis simplification. You could get fancy and do automatic bed leveling with separate drives and some sort of depth feeler on the carriage too. Heck, do a strain gauge on your extruder for your depth gauge, and detect major extruder muck-ups while you're at it! Fun stuff! Getting carried away though.

Wade