CB CNC Part 5 – Assembling Z Axis & Spindle Mounting Plates

In the previous video I began assembling the X and Y axis of my new CNC machine, and in this video I will make the Z axis plates and mount a spindle. I’m currently cutting the top and bottom plates, which will hold the bearings and ACME lead screw between a 25cm length of aluminium c beam, and a stepper motor at the top.

You may have noticed I don’t use any over engineered clamping methods… because well the screw has stood the test of time. The helical thread applies a tremendous amount of clamping pressure and they rarely vibrate loose.  Because I also use two wasteboards, a sub wasteboard and a sacrificial one that I can level, when they are also bolted together, this increases the rigidity of the platform.

By not treating the wasteboard like consecrated grown I can clamp through holes and openings of parts, reducing waste and achieving cuts other CNC clamps render impossible – such as the ptfe nut blocks in a previous video.

This piece on screen now contains two parallel channels which will hold the 80mm spindle mounts, which I’m going to cut from 18mm birch ply. I secured my material, centred the bit and began cutting.

The first was cut square, but I decided this occupied too much space and tapered the second. To save myself from cutting the first out again, I mirrored and cut these angles on my mitre saw.

These mounting plates fit nicely into the channels, and when the spindle is slid in place, this should hold everything square.

I’ve already tested whether the lead screw could take the weight of new spindle by balancing it on the z axis of my old machine.

I decided to incorporate extraction into the clamping part of the spindle mount. This will be in the form of a 50mm clear acrylic tube, which I can attach a hanging hose too. Perching next to the CNC machine with an extraction nozzle, playing catch the saw dust will not stand the test of time. That said I’m not sure if my idea is going to work. I’d like to add a pin to the acrylic tube which can let a dust shoe rest upon the working material – however lift when the bit plunges.

I’ll have to save this for another video, but that’s the idea for now.

I am now assembling the spindle mount, beginning by gluing the horizontals mounts to the vertical plate. I clamped, and then gently knocked the pieces into position. Flipped the assembled part over and drove several screwed in the rear.

So I am going to put the wheel now on the back of this plate. They are going to be the same as these on the Y plate. I’m not going to repeat myself, but I will provide a link to how these were installed with the spacing in the information card.

Once the wheels were installed I adjusted the eccentric spacers so the plate would fit onto the c beam. I then placed a blank PTFE nut block onto the rear of the spindle mounting assembly. I then flipped the machine to its side and installed the bottom z axis plate.

I returned the spindle mounting assembly onto the c beam, and with the top z axis plate in place I used a transfer punch, placed through the hole in the bearing to mark the position of the lead screw – on the PTFE.

I drilled and tapped this and assembled everything back onto the z axis – along with the aluminium shims and lead screw locking collars.

Because I’ve yet to install the stepper motor, the weight of the spindle and low resistance of the nut block is forcing the lead screw to turn…

and the spindle to drop.

So I’ve got three trapezoidal screws here. One is the original 8mm screw which was on the upgrade to the x carve. This one is the off-cut from the one I made the tap (in the previous video), and this is a slightly cheaper one I bought on Ebay. And they are all slightly different.

The cheaper one on the right from Ebay has a square thread. The original on the left seems to have a round thread (or a worn out trapezoidal thread). And the middle one seems like, well the middle one with a trapezoidal thread.

All fit on the Delrin nut block which came with the c beam linear actuator, and the trapezoidal and round thread fits on the nutblocks I made with both the trapezoidal and square threaded tap. But the square threaded lead screw doesn’t fit on the one I made with the trapezoidal. In short it’s important to source all your lead screws from the same place – and preferably buy them at the same time.

The reason I’ve taken the spindle off, and taken the lead screw off this one here, is I’m planning to use the smaller openbuilds locking collars on the bottom of the z axis on both the new machine which is too my left, and the older machine which is behind me. And then the larger couplers, which are a bit too large for the z axis, can go on the top where they are less likely to hit on the wheels.

The last thing left is the mounting clamps. I drilled a shallow larger hole using the forstner bit for the head of the machine screw, and a 5.5mm hole all the way through the centre of that.

Ok, I’ve drilled out a countersunk hole, and also piloted it so I could use these machine screws to hold the spindle in place. And what I’m going to do is actually tap the ply. I’m using a 4.2mm bit. To help me find the centre of the hole I have a transfer punch.

Just making sure the thread is nice and clean.

They seemed to screw in well. Just in case the thread doesn’t hold, I could paint the inside thread with wet rot hardener – slightly swelling and toughening the ply. I tried installing the machine screws without this, and they seemed to bite. I really can’t undo this too often.

So that’s the x, y and z axis of the CNC machine assembled, and I’m quite happy with the progress.

It seems sturdy and the birch ply plates are quite striking too.

So in the next video I will install the motors on their raised spacers, and wire those up, as well as the water cooled spindle to a variable frequency drive. I should also start thinking about cable management.

Anyway, thanks again for watching and here are the usual links:


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s