Triple Z Axis
June 01, 2020 04:13AM
Hi All,

I'll put this here rather than in the corexy section, as it could apply to any type of gantry.

I've recently bought one of these, which hasn't arrived yet:

[www.ratrig.com]

I've ordered the optional triple Z axis, but without the steppers, as I'd prefer to run a common belt on a single motor. I've also gone with v-slot rollers, as I'm a bit of a believer in them if they're setup properly, just my personal choice more than a cost thing.

I've got access to water jet cutting at the right price if I email through my own designs in .dxf files, so I'm considering putting an aluminium floor to mount it all on. I'm also thinking of using 8mm pillow block bearings above and below said floor, with a printed block/spacer to house the pulleys (under the floor) on a short length of 8mm bearing shaft, which connects to the lead screw via an 8x8mm coupling above the floor (if that makes sense). This way my pulleys are supported either end by nice oversize bearings, and the printed parts are only spacers. It's all 9mm belts, so I'd have my tensioning via the stepper pointing down through the floor mounted in slotted bolt holes, and a printed housing with some beefy flange bearings as rollers.

[www.banggood.com]

[www.banggood.com]

It comes with all the bits bar the steppers, but I'm a bit concerned about the v-slot post/rollers/bracket in all 4 corners...





I was thinking one in the center at the back and 2 in the corners, right near each Z screw. I fact I was even thinking that attaching the POM trapezoidal nuts and bed mounts straight onto the v-slot roller brackets and getting a 10mm precision cast aluminium bed that was larger and had corresponding mounting points to meet them. Possibly on some kind of ball joint mount/shoulder bolt affair, which might give me some thermal expansion compensation if set up correctly.

So my concern is the four posts...do I leave them like that and go for 3 point leveling and expansion compensation on top of the existing framework, or will it work well enough as it is? It comes with a 4mm thick anodized build plate, which I certainly have my doubts will be flat enough over a 400x400 print area. I'm not keen on a "banana bed" that's leveled by compensation. Much prefer a flat one.

I had a stab at a large scratchbuilt corexy before when I had a business and funds to throw at it. Never came off, and that's all over now. I've paid for this kit, and am prepared to spend about the amount it cost me again on fitting it out, so it's functional necessity only.

All advice and opinions are welcome and appreciated, thank you.
Re: Triple Z Axis
June 04, 2020 01:25AM
Oh well...guess there's no one out there for this one.
Re: Triple Z Axis
June 04, 2020 03:38AM
In most cases it is recommended to use two linear guides and a three point bed. The best explanation about the bed I know is:
[drmrehorst.blogspot.com]
and you can find valuable other construction ideas from him in his other blogs also which I recommend much.

The reason why only two linear guides is: the construction is sufficient for a multiple kg load and more than two guides mean that they must be calibrated very precise, otherwise the linear guides hinder each other (get stuck) and makes it worse. With precise it is meant in the region of few micrometers. Your guides have flexible rollers, so this will avoid stucking, but you don't gain anything, because flexing means loosing precision at the same time.

Edited 2 time(s). Last edit at 06/04/2020 03:44AM by JoergS5.
Re: Triple Z Axis
June 04, 2020 03:49AM
Quote
JoergS5
In most cases it is recommended to use two linear guides and a three point bed. The best explanation about the bed I know is:
[drmrehorst.blogspot.com]
and you can find valuable other construction ideas from him in his other blogs also which I recommend much.

Thanks mate,

Yes, I have looked at Marks work extensively over the years.

When I previously tried to build my own (super expensive) design with linear rails on plate aluminium, I was going to go exactly that way...2 linear rails and 3 precision ballscrews.

On this printer however, I've got v rollers and 8mm lead screws, so I'm a little concerned about wobble. That's why I'm considering the extra vertical rail/rollers.

What I'm wondering is whether the existing configuration in this kit (4 vertical posts with rollers, please see pics above) will even allow 3 point leveling via the leadscrews. It looks like they might work against each other a bit. Mind you, the rollers probably have a bit more "give" which might help with that and some thermal expansion as well.
Re: Triple Z Axis
June 04, 2020 03:54AM
I expect 4 mm for a 400x400 too thin, I would take 8 or more mm thickness. As material so-called MIC6 aluminium (= cast aluminium plate) is a good choice.
Re: Triple Z Axis
June 04, 2020 03:58AM
Quote
JoergS5
I expect 4 mm for a 400x400 too thin, I would take 8 or more mm thickness. As material so-called MIC6 aluminium (= cast aluminium plate) is a good choice.

Yes mate, I've used that on other printers with Keenovo heaters and Printbite surface. Looking at 10-12mm thick for this one, as the flatness tolerance gets better in the thicker sizes.
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