P3Steel Build Log (#10) – Z-Axis

Following on from the x-axis build – I skimmed over the last part, just “installing with the z-axis rods and threaded M5 screw”. This post helps to expand on this part, installing the x-axis and carriage onto the printer with the installation of the z-axis smooth 8mm rods and the z-axis screw – which for this build is the standard M5 threaded rod. Read on!

P3Steel Z-Axis Top Bearings

One of the key changes in the Toolson Edition (one which I think Toolson doesn’t go into it in more importance in the design) is the inclusion of two bearing mounts located at the top of the z-axis for the M5 threaded rod. These are printed and snapped in go two 625ZZ bearings (one on each). The “5” in the 625ZZ bearing means they have a 5mm diameter shaft hole – perfect for our M5 threaded rod! A search for 625ZZ bearings is here, the ones I got are no longer in stock, from one of my preferred sellers Geek World.

The printed STLs are great, and include a support ring which can be snapped away with some pliers to leave a perfect recess for the bearings. You may also want to drill out the large hole with a 5mm drill bit and the smaller one with a 3mm bit to clean it up.

The reason for these bearing mounts I will go into later on in the post…

Hmm… white balance is a wonderful thing…?! 🙂

Once printed and finished they are installed at the top of the frame, inserting the plastic lip into the large hole which is more inwards towards the printer, and lining up the M3 hole with the bolt which secures this plate to the main frame. You will need to remove this 12mm M3 bolt, insert the bearing mount and then secure it with a slightly longer M3 bolt such as a 14/16mm due to the extra plastic. It should look something like the image below, which also shows the 8mm smooth rod sticking out.

You can at this point also drop in the 8mm smooth rods which are the 330mm (320mm if you are using the 2.01 frame) lengths. They slot through the top hole, down into the LM8UU bearings of the x-axis section and then inserted into the matching 8mm hole in the motor mounting plates, which you can see below. They should be a snug fit, and once fitted you should be able to move the x-axis up and down the z-axis without any issue. You’ve just finished the z-axis… but you’re not going to be able to print past the first layer without being able to control the height! This is where the threaded rod and steppers come in!

Z-axis Motors and Couplers

Two stepper motors are installed on either side of the printer under the motor mount plates. I have sandwiched a piece of vibration foam (the stuff that you put under you rug to stop your gran from breaking a hip!) as a cheap alternative to the cork gaskets you can get. I an not at all convinced it does anything now due to it being compressed so much, so I may well remove it one day and replace it with actual cork gaskets. These can now be easily obtained from Amazon or AliExpress (click to find ’em!)

Anyhow – Install the motors with the wires facing either the back of the printer or pointing inwards to keep it all tidy. Then you will need to install some couplers onto the 5mm shafts (if your steppers have 5mm shafts). Tighten the grub screws to the stepper shaft, but leave the top grubs loose so you can insert the M5 threaded rod later.

I have gone for 5mm/5mm flexible shaft couplers which help to eliminate any wobble you may have from your stepper motor to threaded rod – but they are not designed to take any load which is why we are using the top bearing mounts mentioned previously. These top bearing mounts will take the load of the x-axis, carriage and hotend, while the coupler simply acts as its name suggests – coupling the shaft of the motor to the z-axis threaded rod.

Installing the M5 Threaded Rod

Below is the parts list for this section of the z-axis. Unique to the Mk2 of Toolson’s design. It incorporates an M5 nyloc nut, a knurled M5 knob and an “anti wobble coupling” printed part which has a brass M5 nut inserted into it. These parts are doubled up, one on each side of the printer for both z-axis sections. The M5 brass nut is used as a softer metal than the steel M5 threaded rod so this part will wear away before the rod – allowing you to replace these parts easily rather than buying and cutting a new length of M5 threaded rod. You could also use nylon M5 nuts here, as brass M5 nuts are not that easy to find. You can find some brass ones by clicking this link to AliExpress – M5 Brass Hex Nuts, which takes you to the seller that I used to buy a rather obscene minimum amount of 100 of them! But that seemed to be the only cheapest option at my time of purchasing. 🙁

Back to it – drill out the “AWC” part with a 5mm drill bit before inserting the M5 nut. and then that nut should fit snug into the part. Heat it up a little with a solder iron or flame to melt it in if it’s not that snug? The reason for this “AWC” part and nut arrangement will all become apparent later.

First we need to slip the M5 threaded rod down through the top bearing mount, as seen below: (ignore the large 8mm smooth rod – I had not cut it to length at that point!)

Once slipped though the hole in the 625ZZ bearing mount, slide it all the way down to your x-axis. Next you need to slip it through the hole of the x-axis part (either the stepper part or the best tension part). Below you can see the stepper side, which is the “left” side as you look at the printer from the front. Then insert the threaded rod into the anti wobble coupling “AWC” part which needs to be inserted into the hole in the x-axis part. Then you will need to thread it through the thread of the brass nut which lies hidden from the view below. This “AWC” part will take the load of the x-axis and transfer any z-movement of the M5 threaded rod to the x-axis up and down. And in theory, as only the “sticky-out-part” interfaces with the x-axis part via the hole – this decouples any wobble movement from the threaded rod as it turns – allowing the x-axis to only move up and down…. that’s the theory anyhow!

Below you can see the M5 threaded rod threaded onto the “AWC” part. The weight of the x-axis will sit it flush with the x-axis parts, but I have held the x-axis up slightly to give you a better shot of it in place.

Thread the M5 rod through using your fingers to spin it down towards the coupler and then into the 5mm hole of the flexible coupler. Then Tighten up the top grub screws to fasten to the rod. Allow for about a 5mm gap between the threaded rod and the stepper motor shaft – they don’t want to be touching when you tighten up the grub screws – to do this, thread it all the way down till you can feel it resting on the motor shaft, then just lift the threaded rod up slightly by about 5mm (the x-axis will go with it!) and then tighten the grub screws to hold it all in place. You should then be able to push down slightly on the x-axis and the flexible coupler will “flex” a little.

You can also see the process in the previous YouTube clip, embedded below:

Now the x-axis and carriage should be fully connected to the z-axis, and should sit flush on the “AWC” nuts. You won’t be able to move the x-axis up and down now, as this will be limited to about 5mm up and down due to the “AWC” hole. To move the x-axis now – you need to turn the M5 threaded rod. For now you can turn the flexible couplers or turn it between your fingers. You should at this point get the x-axis roughly level by eye, by eyeing up x-axis smooth rods and turning either z-axis threaded rod to move each side up or down.

Now… back to the top…

Installing the Z-axis Top Bearing and Knurled Knob

Back at the top of the z-axis you should now have at either side an M5 threaded rod sticking out your 625ZZ bearing mount, and the 8mm smooth rod flush with the top frame bracket. The M5 threaded rod should stick out of the top about 15/20mm. Next we are going to install some M5 nyloc nuts, and the knurled knob to allow us to easily turn it by hand if we need to – no more lines in your fingers!

First screw on an M5 nyloc nut down until you get to the 625ZZ bearing, like the image below. You may well need to hold or clamp the coupling at the bottom to help you with this, as the nylon will grip onto the thread of the rod very well and want to turn it rather than thread on to it. You can try to hold the threaded rod with your fingers… but kiss your skin goodbye!! When you get to the bearing, you then want to turn it about half a turn more, watching the flexible coupling at the bottom stretch slightly. You don’t want to over do this, but just enough where the load is now transferred from the coupling up to the top and is now being taken by the M5 nyloc nut resting on the 625ZZ bearing sleeve.

At this point, screw on the knurled knob to finish up this part. It should screw on tightly to the M5 nyloc which will then allow you to turn the whole threaded rod easily by hand. As you can see by the image below – I got my M5 rod length spot on!

You don’t need to use a knurled knob, this is just for ease of use. I would recommend at least two M5 fasteners of some type which will “lock” the M5 threaded rod and not let it come loose. You could also print your own knobs which could attach to an M5 nut or use a wing nut or similar? I had some issue finding a supplier of knurled knobs without buying a huge quantity cheap enough. I did then however find a seller on AliExpress which had them available as single units rather than 100/500 etc. Click on the link to go to that seller on AliExpress to find them – Single M5 Knurled Knob. There is a higher shipping cost to offset the single unit price – so I bought a dozen or so as they are very handy! Your final assembly should look something like this:

Why We Use Top Bearings and Flexible Couplers on the P3Steel

In a standard Prusa i3 – as the printer works, any backlash, movement, high vibrations etc are transmitted downwards through the stepper motor coupler into the motor via the stepper’s shaft. Josef’s versions solved this with some flexible tube which allows for misalignment wobble to be reduced, but does not compress or stretch in the z-direction. His new Mk2 product actually does away with the coupler altogether and the threaded rod (or lead screw actually) is now part of the stepper motor shaft. You can also use fixed couplers which do not flex, but this will re-introduce any misalignment of the motor and threaded rod as wobble. Then you can also experiment with “spider couplers” which allow for x/y movement but do not compress and so can take load. These last ones are a little more expensive, but worth experimenting with.

So if I’ve explained that well at all – you should now understand that we are using flexible couplers (the ones with the springy lines in them!) to reduce any misalignment we may have to help reduce wobble of the threaded rod. But to reduce any movement caused by the x-axis and carriage which would compress the coupler as it turns back and forth – we are actually “hanging” or suspending the x-axis load from the top, via the top bearing mounts. The motor and z-axis shaft couplers take no vertical load and so the z-axis layers should not be affected by any compression.

The final piece in the jigsaw is the inclusion of Toolson’s own design of the “Anti Wobble Coupling” which by design decouples the x-axis from the z-axis threaded rod in x and y direction. They only way it is affected is in the z direction, and this is all managed simply by gravity resting the x-axis on the “AWC” parts. A picture tells a thousand words, and a video is even more – so check out Toolson’s video below which explains it perfectly, even on a really badly bend threaded rod.

In my eyes, this part is pure genius and solves so much of the issues that a lot of Prusa i3’s have with z-wobble. I have not fully tested this obviously, but the engineering makes sense, and it seems like a much more improved design than traditional x-axis parts which have the M5 nut embedded into the part and as such any movement or wobble x/y caused by the threaded rod is introduced into the x-axis and you are not relying on the stiffness of your z-axis 8mm smooth rods. Be wary of any design that constrains the z-axis rod at both top and bottom but does not incorporate any anti-wobble mechanism at the junction between the x and z – you are asking for trouble! With the “AWC” part and the fact the x-axis is supported from above, I am hoping that all z-wobble and z-banding should be gone.

</anti-wobble rant over!>