New DIY-CNC machine

[Kickn]

Hello all! I'm just new to the forums here and a bit of a noob when it comes to these things so please be patient

I've been planning a new DIY-CNC machine for which I've bought a bunch (it was actually a lot sale on ebay) of various bits and pieces. I wanted to know if (and where it should be posted if not here) this group would be willing to help me work through this project? The machine I want to build must be capable of copper and aluminum.

My first question is that I've been planning on making the frame out of structural aluminum. Is this going to be strong enough for what I want to do?

The other question I have is where to get cheap lead screws from? I have all the rails already - but need the lead screws and some slipnuts - any ideas for here in the UK?

Thanks again all!

[kong]

Of course we're gonna help you Kickn! You can buy motion parts from www.ondrives.com in the UK, I have found their trapezoidal leadscrews to be great, and have made my own nuts from delrin which I bought on ebay. The extrusions you are thinking of using will be plenty strong, especially in something like 80x40 size. What are you wanting to use for a spindle, router or mini-mill head? Both will cut non-ferrous metals easily.

[Kickn]

What a small world eh? I just came accross your thread on Bit-tech

Thanks though for the positive feedback. Maybe you can give me your thoughts on this. My two bing constraints right now are the linear rails I already have and getting the aluminum structural profile in 2m lengths.



The two linear rails shown in the picture are 50" long with 4 super pillow blocks and are 20mm dia. I also have two THK FBW3590R that are 300mm long. These I plan to use as the z axis. I also have two 22" round rails set inside an aluminum block that I plan to use for the Y axis.

so thats linear motion thats x=50"; y=22"; z=12" - big enough I think

My problem is trying to get a solid structure out of as little material as possible. Any thoughts?

[ger21]

You'll probably get quite a bit of sagging from those unsupported rails at 50".

[Kickn]

LOL - I didn't even think of that

I guess those are out the window then - anyone in the UK need some rails?

I was really hoping to use those too.

[kong]

Don't be so hasty to poo-poo the idea. You could go for a fixed gantry, in which case there would be little weight on the long rails, or, have the x as a shorter axis, and use the longer rails as the y. They will still sag, but the amount will be greatly reduced. You could even cut the rails down a bit.

[Kickn]

Where's the gantry normally positioned then? on one end or centred to the board?

[kong]

The gantry would be around the centre mark, then a smaller table (say 30") would travel on the long rails to form the x-axis. You lose cutting distance, but gain a nice solid gantry which could be built very heavily.

[Kickn]

okay - how about something like:




I tied to keep the table support (the cross frame thing in the middle) as long as possible to distribute the strain a bit but I'm not sure if that would really have any effect. I could brace the bottom of that frame as well to keep it from bowing - that should help the rails from bowing shouldn't they?

The only thing I don't like about the fixed gantry is that you loose soo much table space. But if it has to be done then

I was also thinking that if worse came to worse - could I put some plastic shims on the top of the supports and under the table.

I would put the screw in this design in the middle of the table - does that seem right?

Am I on the right track here?

Boy you all are going to be so annoyed with me by the end of this

[kong]

Mate, the only reason I am getting annoyed is because I don't have a lot of spare time to knock up some drawings for you!
You are on the right track here though, screw goes down the middle. Check this site for ali extrusions, they are cheap, and will supply any length you require.
www.mbsitem.co.uk

[Kickn]

I appreciate your feedback and advice mate! Any help is great as I'm a bit of a noob when it comes to this sort of thing.

Thanks for the mbsitem site - I've been so far using farnell for prices and they always seem a bit more expensive

Have you tried milling copper yet with your cnc router?

[kong]

Yup, copper cuts easier than aluminium, well for me anyway. You will need to plan for a coolant system though, even if it is as basic as a can of WD40. It gets messy, so some sort of perimeter guard strips or something are always a good idea.