My Budget CNC Router

Greetings Everyone,
I've been toying with the idea of building my own cnc router for some time now, so here I am taking the plunge. Overall size will be roughly 700mm x 536mm.

I'm on a shoestring budget so I'm going with an MDF design using DIY Linear pipe rails and bearing slides using skate bearings. I know you've all seen this a thousand times already, but maybe you could give me some advice along the way.

The two biggest problems I've had with my build (besides money) are indecisiveness and lack of tools. I have a router, hand drill, and circular saw as my power tools. A basic square, measuring tape and hand saw too.

At first I had a plan, but the more build threads I read, the more I changed things in my own build. Sort of learning from other's mistakes if you will?

Below is the 2D sketchup export of the first part of my build - The torsion box. I know I haven't done the left hand side rails yet. I was just looking at one side to see how it will look.

This will be build using 12mm or 18mm MDF (12mm at the moment as I don't think I'll have enough 18mm for the whole thing - I have yet to see). The steel tube is 26.9mm x 3mm wall cold formed tube from 26 9 x 3mm CF Tube

I'll be adding a single 18mm length of MDF to the side of the torsion box to mount the pipe rails to.

I know I've left the electronics out, but for me its one thing at a time for now. I do have a rough idea of the electronics I will use, namely 439oz-in motors (Nema 23 3.1nm), and PM542 or PM752 drivers from Zapp Automation.

http://i.imgur.com/jmyOj.png

Have you got any more of it designed Neal? Looking at what you have done so far what are your plans for the gantry & the ballscrew that will drive it up & down the table, once you have added a bit more to the design I am sure the more experienced members will be able to give you some pointers.
Will you have a sacrificial board on the table top? 12mm sounds a little on the thin side for the top.

I have planned the gantry to some extent but the sketchup file got deleted somehow. This is basically a Joe's 2006 but on a much smaller scale. I will have the new sketchup render for you tomorrow evening.

As for ballscrews i'll be using 16mm running through the bottom of the gantry, which will also be a torsion box, as will the Y axis.

A little bit of progress. Waiting for my router to arrive so I can trim my boards to size. Should be tomorrow....hopefully. I'm cutting with a hand saw to withing 2mm and then trimming with the router.

Here is the updated sketchup 2D.

http://i.imgur.com/QOPMa.png

http://i.imgur.com/piinQ.png

http://i.imgur.com/nwpPC.png

Due to the cost of ballscrews, and me not needing speed, I think I'll be going with TR10x2D trapezoidal screws from Merchantdice on Ebay. He has a set of three 700mm lengths for about £20.

If your using pipe then I would be inclined to put it top & bottom as was suggested on your other post. Being new myself I don't know for sure but it would seem a much better way of setting it up.
The leadscrews are only 10mm which may not be suitable over the length of the machine plus what are you going to do about bearings for the leadscrews both fixed & free end.

Sorry, double post. Was trying to edit first post.

You mean like this? I thought about that, but how do I make the red mdf part sturdy so that it doesn't flex upward from the weight of the gantry? Any flex at that point would mean the bearings don't make good contact with the rails.

I will be using 10mm bearings for the lead screw, one at each end. The total length is only 700mm, so its not a 8x4' machine that needs a massive leadscrew, surely? No?

http://i.imgur.com/nHkYd.png

Don't use MDF for that part, maybe something like a block of CLS, which ever way you do it you are going to have to be extremely accurate with your sizes.
Leadscrews well from the little I have learned you need a certain amount of speed regardless of how slow you would like to go. So it is possible you will get some sort of whipping with a 10mm leadscrew, don't forget the minor diameter will be less than that, other thing is that I couldn't see any angular contact bearings with a 10mm inside diameter.

Quote:

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Originally Posted by martin54

I couldn't see any angular contact bearings with a 10mm inside diameter.

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1 X 7200 SEALED ANGULAR CONTACT BEARING | eBay

However if the screw is 10mm you need to machine it down to have a smooth cylindrical surface on which to mount the bearing. That means the bearing will need to be smaller, possibly 8mm.
The feedrate you get will be very limited by only having 2mm pitch screws and as Martin has said, if the feedrate is too low the machine can be severely limited. It depends what you want to cut. If it's just most wood and PCBs then you can manage with just about anything, but plastics tend to require quite a high feedrate to ensure the tool cuts and does not rub. You can compensate by using a lower spindle speed and single flute cutter, but there's a limit to how low the spindle can be set before you no longer have enough power to make the cut...