C-Beam CNC Part 1 – Designing and Testing For Lead Screw Machine

Ok so this machine is running about as well as I can get it to run, and erm, I want to celebrate by trying to make a new one. So I’ve been thinking about this a little bit. No in fact I’ve been thinking about this a lot. And I’ve started to work on a design.

A design based upon the OpenBuilds platform. I have used their C Beam and V wheel extrusions in the past to improving the original x-carve. But this time I want to work with their platform to design a machine. I did some research and found three leadscrew CNC machine that I liked and while lead-screw CNC machine are a little slower than belt driven ones, they are a lot more accurate.

The first is from OpenBuilds Korea and is called the Rovo C-Beam. You can see a lot of work has gone into producing the parts which have a wide range of applications.

The other two machines are variations of the original plate design which I think Mark Carew and his team designed. The first being the CB3030 by UltiBots and the R7 CNC by SMW3D.

Link to similar machines:
Open Builds Korea: http://goo.gl/R5IXnl
Ultibot CB3030: http://goo.gl/OvdhYm
R7 CB CNC: http://goo.gl/SArf38

As these are all based on open source designs, I can find original source files and began editing them to produce a machine myself. I think the lead-screw design is good enough to produce plates with birch ply, and for those plates to be good enough to then router new plates out of a harder or more durable material.

So I am going to cut a few pieces on my CNC machine, spray them with some lacquer to try reduce any warping or swelling of the material, and once a few OpenBuilds parts arrived in the post, I will assemble the plates, and check their fit against a pieces C Beam.

I want to solve as many problems in this initial stage, and create iterations of the plate designs which reduce parts and cost. I also want to make a machine that can cut plates accurately and at a reasonable speed.

So some openbuilds components have arrived and I am now putting together the larger Delrin v wheels and checking the accuracy of the 6mm birch ply plate. Having three wheels on either side mean the holes need to be more accurately aligned than what my belt driven CNC machine can produce. Either that or the machine screws have become skewed and are not sitting at 90 degrees against the plate.

So these holes are a little bit tight. What I’m going to do is just put a nut on the opposite end and just tighten it up so that sinks in.

So I’m going to have to resize these holes just because they are a bit tight. And I think in fact what I will do, is design this so that these are going to be flange machined screws instead of these domed socket ones. Just so there’s a bit more purchase to the material I am using as a plate.

I mean I’m gonna double these up eventually using much longer machine screws so there’ll be a lot more support.

Again this is going to be the opposite side as well and… so I’ll be able to have a proximity sensor attached onto here which will sense the plate.

I’m going to add some v wheels onto this section and see how it fits on the C-beam as well.

17mm and 15.8mm

So because I need to recess these eccentric spacers down this larger v wheel is actually about a mm higher than the mini ones. and it’s forcing the plate to come out. a little bit from the C-beam. so that’s going to have to be the first modification to the design that I’m going to do after these tests. I still prefer the idea of making this with 12mm. And I have already cut some out but I am in a little bit of a predicament because I need to make sure I get the right machine screws so they don’t scratch into the inside of the C-beam. What I might end up doing is buying larger machine screws then I need, and cutting them down after they’ve been secured.It’s not ideal but at least that will grantee that the machine screws are being held securely in the Nyloc nuts. And as you can see now these ones are actually a little bit shy of where the nylon actually is.

20.84mm

So I can get 35mm machine screws, and what I’ll have to do is pack out the back with some washers. It’s not ideal but that two extra mm is enough to hit the inside of the C-beam.

Ok I’ve worked out the spacing for the 12mm birch ply, and 12mm birch ply is pretty bang on 12mm. I’m not sure how much variation you get over different stock, anyway. And that feels really good and I still haven’t put the top pieces on because I still have to recess the next plate but I think I’m going to go with the 12mm. It’s just a lot more sturdier and it’s going to produce a much better machine in the long term.

The extra material holding the machine screws square really makes a difference compared to the 6mm ply. I also don’t think I’ll need as many mini v wheels as I was planning in this section. So I will be using four mini wheels plus two larger ones on top of the C beam for either plate.

Just so I can explain a little bit about the design, this is where the nut goes and you have an opening here to access that. I’ve also added a hang down here so a piece of aluminium extrusion can go across the bottom of the waste board. This place will be supported with the C-beam at the top and a piece of extrusion at the bottom so it’s going to square it up really well.

The final thing I want to do in this video is check the spacing for the XL C beam gantry plate which I am planning on doubling up. Some larger machine screws came in the post and I am going to assemble this and check the spacing.

The holes (for the heads) on this plate are wrong (narrow) but these are a little bit longer so I should be able to mock up the spacing at least. What I’m going to do is use the washer just to make sure the head of the machine screw doesn’t accidentally pop into the holes. I’m only going to do the outer ones in this case, and then based on this drawing here. I’ve got the spacing and layout of the wheels , the spacing and the shims which will make the distance I need.

Is there going to be another plate on the other side?

Yeah the layout is like that one there.

That has to be pretty accurate in terms of what goes between the wheels.

Well yeah that’s the thing, I found the spacing instruction somewhere. I think it was on Martin Barfoed channel – he did something where he had a close-up so I kinda did a drawing of that. Essentially it would be the same for the other open builds machines.

Yeah.

So if I sink the heads of the machine screws 5mm into the ply on one side, I don’t have to make any recesses on the opposite piece, and the machine screws will extend out the same size as the nylon locking nuts.

So I am quickly discovering that a lot of the plates that I cut are completely useless but because I have something to play around with I can learn lessons from these tests.

The other thing I need to what holes I want to keep, because there’s not really any point having this many. I also need to place the machine screws through the gantry plate which would hold the z axis, and check if the heads scratch or hit onto anything.

There is a 1 mm gap between the machine screw and C beam, which is perfect, so now I can go back to the computer and amend the plate vector files.

So for the forseable future, I will be focusing on building a new CNC machine on this channel.

If you’d like to follow the process you can subscribe, or if you are already a subscriber please consider sacrificing a thumb and letting me know what you think of the video in the comment section below.

If you’d like to financially support this project and channel you can also find me on Patreon, the link to which is on screen and in the description.

Anyway thanks again for watching and I’ll CNC you in the future.

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