CB CNC Part 2 – Finalised Y and Gantry Plates

In the previous videos comment I received some advice about levelling the v wheels. I was planning to recess the spacer for the larger wheels thinking that would reduce parts, but the smart thing to do, as Kyo suggested was to use two precision shims on the smaller wheels. And it means I don’t need as many large washers on the back.

I tested this set up on the y plates I had cut out in the previous video, and seeing that this worked cut the new plates without the recess. So in this version I’ve already changed a few things. These include using less v and mini v wheels on the y plates, centring the anti backlash nut block, adding space under the x axis c beam to install 90 degree brackets, and cutting the large gantry plates out with a lot less holes than the original.

And hopefully at the end, I will have a machine I can share via the opensource platforms. I also resized the countersunk heads to accept the flanged machine screws that I will be using.I’m going to assemble the gantry now, and I will be using the full set of 12 wheels for this part, although I think I could have got away with 8. I’m using the pillar drill vice to push the eccentric spacers into their holes, and to also hold the plate while installing the parts. The machine screws for this part are 70mm long but could be smaller if I was using thinner plates.

The spacing starting from the head of the machine screw is, either one aluminium or eccentric spacer depending on which half of the plate you are fitting, followed by one shim, a larger v wheel, two shims, one aluminium spacer, one shim, a large v wheel, one shim and finally either one aluminium or eccentric spacer. All those parts are being sandwiched between two 12mm birch ply plates.

After assembling everything, I slowly work my way through tightening each one of the eccentric spacers from one side to the other. But I think the birch ply is still too soft to hold the machine screws and wheel all perfectly in their holes, and I could see a tiny gap alongside one set of wheels.

I’ve measured the aluminium and eccentric spacers and they were identical, so I don’t think this was the problem. And the precession shims were pretty precise. To find out why I have this gap, I could dismantle the pieces. I began thinking whether I should use one plate, or space one v wheel per machine screw on opposite sides of the v rail extrusion, but I also don’t want to unscrew and reassemble everything too many times, just in case the plate holes wear down further.

I think it’s more likely that the ply is too soft and doesn’t holding the machine screws parallel, but there is not much I can do about this so I might as well carry on.

The part moves well despite the gap, and there is no noticeable play. This is just a reminder that I will have to re-cut all the plates from a more durable material once the machine is completed.

I’m going to assemble the y plates now, and again using the pillar drill vice to hold the plate. Ok I’m going to put the wheels on the y plate now, and I’m going to make sure that the bearing hole is facing inwards. I am using four mini v wheel and two larger ones for each plate. Four of these are on eccentric spacers, and two are fixed.

The fixed wheels rest against the underside of the rail within the c beam, and are opposing the downward movement of the spindle. That is to say, when the spindle plunges the fixed wheels are less likely to slip or be moved by the forces pushing upwards.

The set up is the same with the larger gantry plates. And again once everything was assembled I gently tighten the eccentric spacers against the extrusion, and checked the distance between the wheels using the vernier caliper.

I think this is going well, especially considering the material I am making this from. There was a gap along one set of v wheels on the larger gantry plates, and while this could cause the Derlin wheels to wear unevenly over time, I am planning to re-cut all the plates once compete which should correct this.

Anyway I’m going to leave this video where it is, while I wait for a few more parts to arrive in the post. In the next video I will make my own anti-backlash nut block using PTFE. Thanks again for watching, sacrificing your thumbs, sharing our comments and if you have joined my patreon since the last, welcome aboard. The link to that and other things will be on screen now.


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