a Steel Box Section Build with SBR20 & Ballscrews Plus a few questions

[grain_r]

Hey Guys. Thanks for that I would rather know that it isn't correct that's why I though I would post it up just in case I had it wrong. I will have another run at it.

Is the frame about correct for the design ?

My thought are to add one rail at the back and one on the top this way I think i can get less overhang on the Z axis face plate ? although this might be another silly idea. I have even thought about speaking to chai and seeing how much the linear rails would be but because I have the rails already I think i should persist with what I have and then upgrade when I have more knowledge and know what I am using the machine for.

I'm struggling in my own mind how to make the Z a little and because most seem to use linear rails the designs don't fit as easily. if anyone can point me to a design of the Z on round rails it would be much appreciated as a guide

Thanks as always

Rob

[EddyCurrent]

Here's one, just search on Google for "cnc Z axis design" then choose 'images'

http://runawaybrainz.blogspot.co.uk/...thout-cnc.html

[grain_r]

Hey EddyCurrent Thanks very much for that that will certainly help me. didn't think of the Images part of google.

I was trying to incorporate your idea of one rail on the front/Back and one on the top or bottom but it seems to create quite a large gap on the back plate which I'm not sure if it will affect strength. I will get the pencil out I think.

Thanks
Rob

[JAZZCNC]

Is the frame about correct for the design ?

Yes the only thing to watch is the amount of adjustabilty on the bed. If you don't need all that height then raise the horizontal frame supports.
Also doen't hurt to put some 4mm triangle plates on outside to help support the upper legs like in this pic.

My thought are to add one rail at the back and one on the top this way I think i can get less overhang on the Z axis face plate ? although this might be another silly idea.

No not silly at all and machines are often done this way to allow ballscrews on front but like Eddy said before you need to include everything in the design ballscrews mounts the lot to see what clearences you have. Personally I don't like the Ballscrews on front and in firing line so put them at rear out the way or protected behind something with slot for access.

I have even thought about speaking to chai and seeing how much the linear rails would be but because I have the rails already I think i should persist with what I have and then upgrade when I have more knowledge and know what I am using the machine for.

Yes do it because there's far more work to upgrading than you realise so it will never get done and profiled linear rails are worlds apart from those round type rails so make the machine so much more accurate and reliable. With round type rails your constantly chasing the adjustment and they wear out and go sloppy in no time if not looked after. You don't get any of that with profile rails.!!
Chias prices for Linear rails are cheao and the quality is fine and you'll reap the bennifits 2 fold when you come to sell it.

I'm struggling in my own mind how to make the Z a little and because most seem to use linear rails the designs don't fit as easily. if anyone can point me to a design of the Z on round rails it would be much appreciated as a guide

Profiled or round there's really no difference other than clearence between front and rear plates and it's actually easier with round rail as they are deeper so you don't have to machine clearence for the ballscrew.
The design eddy posted is essentially how I make my Z axis which you can see here. I then put aluminium covers over them to protect every thing.

[grain_r]

Hey Jazcnc

Thanks very much for the great reply. I have looked through it and will add the corner bracing and I think I am going to go ahead with the build as original and then see what I actually use it for and then can build a higher accuracy machine with the initial machine later on down the line and I will have learned more about the subject.

I have had another look at the Gantry and I think I am much nearer on this design and I have tried to keep everything out of the way I still need to continue working on it but Just thought I would post it up to see if I'm on the correct lines this time.

I still need to work on the Motor and pulley details and the cable tray too.

I have been looking on aluminium warehouse and the pricing seems pretty good on there for 20mm there seems to be different qualities on there for not much difference in price.

[JAZZCNC]

Wouldn't have the bottom rail that way around personally due to cutting forces and way it doesn't support the front plate. Personally would have top & bottom.
Also I wouldn't make the Y axis wrap around the gantry like that. It doesn't add hardly any strength makes the whole Y axis heavier than needed lowering accelration and increasing inertia plus it makes building harder because unless the Ends are perfectly 90deg they twist and bind the bearings.

Also rather than having the gantry cross beam central to the bearing try offsetting it back a little to allow for Z axis and spindle balancing the centre of Gravity better.

[EddyCurrent]

The bearing blocks look too close together in the vertical direction to me.

[grain_r]

Hey JazzCNC thanks very much indeed for that it sounds like I'm on the right track now, I did think about top and bottom but thought this might split the forces between up and down and back and forwards although doing it this way I guess the loads are on a single rail more for each movement. So will do I will go top and bottom which will be great to get rid of some of the material around the back. I didn't really want it there but it was the only way I could think off to get the rail around the rear to also try and keep it out of harms way too.

I am really sorry when you say move the rails back do you mean so that the spindle is inline with the upright box section of the gantry ? would it maybe worth going for something like 100x50mm box section for the sides and then put the 50x50 towards the rear to the spindle so it is more inline with the uprights of the gantry, I'm sorry if I've misunderstood.
Also on a side note I would like to thanks you very much for helping so many people on this community I have learned so much from you going through many peoples posts and its great to see people just trying to help each other out.

Also EddyCurrent the same goes for you going through peoples posts you are very helpful I just hope that I can get a machine running to be able to get the knowledge to put something back in.
Don't worry I'm not always a soppy sod.
I thought I might have the blocks a little too close but just picked the figure out of the air really for the distance. Is there an optimum or a way of determining the best gap ?. like most I was trying to maximize the cutting depth but because the bed moves I will add some more distance on it and just move the bed on each time I have a thought to making some fiberglass molds with foam for a dash board and though the more depth the better but I guess it will give a worse cut for other things I will have another go at it and go more in depth on the design now I know where I'm going with it all.

thanks chaps.

Rob

[JAZZCNC]

I am really sorry when you say move the rails back do you mean so that the spindle is inline with the upright box section of the gantry ? would it maybe worth going for something like 100x50mm box section for the sides and then put the 50x50 towards the rear to the spindle so it is more inline with the uprights of the gantry, I'm sorry if I've misunderstood.

No was meaning offset back something like this for better centre of gravity and balanced bearing loads while cutting.

Regards bearing distance then I work on Half the travel required.!