Thread: Oh crumbs. Here we go!
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.
Now you've gone and done it!!!!. Just remember to enjoy it.
bruceThe more I know, I know, I know the less. (John Owen)
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.
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. :)
Last edited by hoppo; 11-10-2012 at 04:43 PM.
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.
Last edited by hoppo; 11-10-2012 at 04:41 PM.
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.
As far as I can make out the americans have the z connected to the x while we have z connected to y.The more I know, I know, I know the less. (John Owen)
Not for this American.
Normally, the longer axis is the X axis, which typically leaves the gantry as the Y axis, which is where the Z is attached to.
I believe that some people call the gantry the X axis because they stand facing the gantry, so the X axis moves left to right. Having the X axis move left to right is desirable, as that's how you'll see it in your CAD and CAM software. I stand on the side, with the gantry moving left to right.
Well I've managed to restructure my Z Axis. I've had to compromise on the travel to space out the linear bearings a bit more. But hopefully it should now be a bit more rigid. I've also swapped the bearings onto the stationary back plate and moved the rails onto the moving part. I've also been able to shave about 20mm off the width too. It's now approx 160mm wide by 330mm high with 150mm of travel. I don't really want to go less than 150mm of travel. I suppose the I could always add longer rails at a later stage if I ever really need that extra travel, and could also then move the bearings even further apart. Lesson number one learnt, design the bloody thing before you order the parts!
Now to start looking at connecting it to the Y axis. Thanks all for clearing that one up.
Last edited by hoppo; 14-10-2012 at 09:40 AM.