Oh crumbs. Here we go!

[hoppo]

I've been wanting to build a CNC router for some time now, and after joining the mycncuk forums some months ago haven't had much time to get my build going. Well, now the days are drawing in fast and the fact that it has been throwing it down with rain all weekend, I got a bit bored so I contacted Chai (from the recommendations found here) and he put together a good package for me, and I've only gone and blummin' ordered it.

So this is what I have winging it's way via fed ex to me.

3 x supported linear rails SBR20-300/700/1100mm rails with SBR20UU bearing blocks.
3 x ballscrews C7 RM1605-350/750/1150mm with ballnuts and standard end machinings.
3 x sets of BK/BF12 bearing mounts
3 x ballnut housing brackets
3 x flexible couplings 6.35mm*8mm

Now during the wait on delivery I'm going to get into CAD, and try to put what's in my head in to some sort of plan as to what I'm going to do with them when they arrive.

Thanks for all your advice so far, I'm sure Ill be back for more soon.

[motoxy]

Now you've gone and done it!!!!. Just remember to enjoy it.
bruce

[Tenson]

If it is anything like my build, it will be a challenge, but rewarding :)

I think if you a 1100mm axis, you will want to use 2x ballscrews on it, one next to each linear rail. I guess you are thinking of putting one ballscrew in the middle, but this can cause the gantry to wobble side to side since it can resonance and flex like a trapezoid (since you can't brace the gantry in all directions), so it is better to hold it at both ends.

Where in London are you? I'm near Lewisham.

[hoppo]

Cheers Motoxy and Tenson,

Not sure what I'm going to do with it once I've built it but yep I'm sure it'll be a challenge, but hey that's half the fun..

I had thought about two ball screws to move the gantry along the long axis, but sure I read on here somewhere that anything with a gantry over 750mm would require two and I could probably get away with only 1 if my gantry wasn't that wide. Accuracy isn't 100% for me at the moment as it's my first machine, but am willing to consider it, especially as the chinese ball screws are relatively cheap.

Incidentally can anyone clarify the axis's? I've seen so many different ways of representaion of X Y and Z. The Z is obvious, but does the Z connect to the X or Y axis? I assume that from the front of the machine the X axis moves the Z along the gantry from left to right as you look at it, and the Y axis moves the gantry closer or further away from you as you look at it. (Thought this should be a fundamental that I need to get right at the start ;) )

I've finished an initial design of my Z axis which seems to look ok to me, but being new to this thought I'd best load it up and let you guys have a look. Please offer up any improvements that you think I need to do.

Oh and if anyone needs any easy to use design software and uses a mac, I recommend Inventor Fusion which is what I created this in and it's free! Last week I had no experience of CAD packages and I've already managed to create something useful, and it animates! Now if I can figure out how to upload it....

Tenson, I'm in Camberwell, good to know I have a CNC neighbour. :)

[WandrinAndy]

Incidentally can anyone clarify the axis's? I've seen so many different ways of representaion of X Y and Z. The Z is obvious, but does the Z connect to the X or Y axis? I assume that from the front of the machine the X axis moves the Z along the gantry from left to right as you look at it, and the Y axis moves the gantry closer or further away from you as you look at it. (Thought this should be a fundamental that I need to get right at the start ;) )....

Z connects to Y which connects to X.

X = Bed/Base of the machine
Y = Across the Gantry
Z = Vertical Slide

Some folk swap X and Y around, but generally not on this forum.

[hoppo]

Brilliant, that clears up my axis issues. :)

I've managed to figure out how to create a picture from my CAD package, so here it is. Z axis version 1! To be honest I'm not 100% happy with it, mainly due to the width of the plate that the spindle will attach to, I'll have a re-think, but I think I have good base to work from.

[irving2008]

Usual comment. Mount the bearing blocks as far apart as possible on the fixed part and the (longer) rails on the moving bit. Gives more rigidity as the bearing blocks can be further apart for the same amount of travel and relatively small increase in cost.

[hoppo]

Was just about to order some aluminium plate to start building my z axis. Had a bit of a panic. Is 15mm thick enough or would I be better off using 20mm for the sliding part and the back plate?

[Jonathan]

Do you know if that applies to the sides too?

It would certainly help, but even better would be to lower the gantry as much as you can and have the tool operating below the level of the X-rails.

Was just about to order some aluminium plate to start building my z axis. Had a bit of a panic. Is 15mm thick enough or would I be better off using 20mm for the sliding part and the back plate?

15mm is OK, but most use 20mm as you don't gain much by going above 20mm. In the whole scheme of things it's not going to cost too much for the extra 5mm...

In answer to an earlier question - standard 6082 is fine for supported rails. Tooling plate is only really worthwhile for proper linear guides.

[motoxy]

As far as I can make out the americans have the z connected to the x while we have z connected to y.