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

Hello All.
I'm certainly learning a lot as I read through the posts so thank you very much to the people that answer the questions but also ask the questions that I don't even know I want to ask.

I have come up with my design in sketch Up after finding I can't yet work out Autocad 3d (Although I guess it will come along as I progress)

I haven't as yet finalised my design but thought I would just see if you guys think that I am on the correct approach for my needs

I was a little silly and bought the rails and screws as a kit but i'm happy with the quality of everything I would have probably gone larger but it has its own problems so i'm going to use what I have.

at the moment the design is to use 50x50 Box section with the option of using 100x100 as the top for the rails and the screw next to each other. but I'm not sure whether I really need this ?

The bed is movable for creating a movable table for other things than sheet material and mould making. but I have capped the ends to that I don't have to use the bed as strength as much. It could be an issues if I put long material in but think I'm OK.

I'm using SBR20 rails for everything and SFU1605 screws all round

The project plan is to be able to cut a range of materials from Perspex , Wood & Aluminium, I also want the ability to end mill which is why the rails go right to the front of the machine giving the option to clamp to the frame but still working on that.

The plan is to use a 2.2kw Water cooling system and haven't really though what electronics to go fo as yet but thought I would see the weight of the machine first.

I think Sand in the box section is likely to dampen down any vibrations

I have made the gantry wider than the rails because I didn't think when I ordered the rails that I would be loosing some for the actual plates (Which is why I would have gone bigger)

The rails are 1100mm x 600mm x 280



I have put a design that I think I'm on the right road with but before I get too far thought I would ask you kind people if I am in the right road or if things should be changed ?

I thought I would put this as a build log because it will turn into one sooner or later anyway.


Thanks for looking


http://www.mycncuk.com/attachment.ph...id=13452&stc=1

Rob Grain

I have though Mounting of the rail mounts on a 10mm Steel plate that is tig welded to the box section (Maybe Bolted for a little movement) ? and this way I can have the actual frame as wide as I like but just the cutting will then still be the same but this way I could put larger material on the frame and move it around if I ever wanted to e.g for cabinet doors at the moment I thing I would struggle to fit it on. and yes it is all because I bought before I thought ( I might use that saying again I like it)

I am still unsure if putting the gantry SBR20 rails would be the strongest design for the top and bottom or both on the front, or maybe have the one rail at the top and then the lower rails on the front.

I am really sorry I haven't used the X,Y,Z because I think I get it wrong when I say it, I thing Y is the movement of the whole gantry and the X is the movement of the across axis e.g. moving of the spindle left and right and I know I get the z Right 1 out of 3

If someone could confirm this or tell me I'm and idiot and have it wrong that would be much appreciated.

http://www.mycncuk.com/attachment.ph...id=13453&stc=1


I have chosen the have a sliding Bolt through for the bed in the middle with a bracket tig'd on the box section and then I can bolt through to give extra strength but then at the ends just go through the actual box section of the base although I'm not sure if this will take away a lot of strength from the base.
also I though I would be best to mount the screw blocks on the outside of the gantry to stop dirt getting into the screw. there will be screws on each side to stop any problems however I am currently leaning to using 2 motors and not a timing belt but you might tell me differently.


http://www.mycncuk.com/attachment.ph...id=13454&stc=1


Any comments would be very much appreciated

thanks for looking through and listening to my ramblings



Rob Grain

Take a look at this diagram, you can see that in your design the spindle would hang out from the gantry well past the bearing blocks.

http://www.cncroutersource.com/do-it...NC-router.html

It's usually regarded as X being the rails mounted on the frame, Y being the rails mounted on the gantry, Z where the spindle mounts.
Two motors on X works fine, just remember you would then need to, rate your power supply accordingly, purchase another stepper driver, add 2 home switches. It's generally regarded as advantagous to connect the motor to the ball screws using timing belts, the pulley sizes can also be selected to increase or decrease speed so that your stepper motor is working in it's optimum range while the cutting speeds are also optimum.
You might need this as you indicate 1605 screws all round, I'm using 1610 on X and Y which seems right using 1:1 ratio of pulley

Rob Welcome to the forum. Please don't buy anymore kit until you have your design finished its the biggest mistake people make. Ask as many questions as you can (a few at a time is better) and expect a bit of leg pulling but you will get all the advise you need on here.
There are generally two ways to drive the x screws either with one motor and a belt going to the other screw or using two motors one for each screw, there are for's and against both system. But they both function ok.
You will need more bracing of the frame that what you have. ..Clive

Thanks guys for that, I have put the spindle so that it will go past the frame so that I can cut on the end of material for letting on the sides of work, Although I suppose I am stopping me from being able to cut sheet as long as I would otherwise be able too. I have thought about moving the rails back a little and then making a clamp so that I could lamp it to the internal 'Y' support beam.

I thought I might be under building on the supports. Because I am going through the centre vertical beam I will have to have a change to get the support in. would it be best to brace from corner to corner or is it as strong if I triangle off the corners

I seem to buy the stuff and then learn and I have after many years started to come out of that routine things always work out but always a more difficult path and more stuff for the spares box.

Hello I have been doing a spot of re-design for the bracing Hopefully I haven't gone the other way with it now. I was trying to use a little less steel to keep the cost down but I would certainly rather have a stronger machine.

http://www.mycncuk.com/attachment.ph...id=13455&stc=1

You don't need cross bracing at the ends, a single diagonal will suffice, run it in the opposite direction at the far end. One in the middle might be beneficial too.

Hey Irving2008 great thanks for that. I have made the change I haven't as yet put the middle support in, which I'm guessing that you mean through the centre of the base ?

http://www.mycncuk.com/attachment.ph...id=13470&stc=1

that will be handy too im so close to being able to use x3 7.5 metre lengths so hopefully if I don't mess up cuts and welds I might get away with it. (So we all know I wont and will need more :witless:)

I'm leaning more to the timing belt option because it give me more options on configuration but I'm not sure How I will do that as yet.

Thanks very much for the advice so far it is really appreciated.

Thanks

Rob

If you put a brace in the centre you lose the ability to have a movable bed. ..Clive

There's loads you could shave off this structure most those bits at the bottom are not needed. Something along the lines of this but narrowed down will work. You'll use less steel and still be plenty strong.
Attachment 13472 Attachment 13471

Hey Jazz
Thanks for the design, so if the parts missing at the bottom it doesn't get any-more twist of the table when in use ? or is the sheeting around it structural and stops this. I love the slider system I have been thinking that it would be not the easiest to lift the bed and get the bolts in, I imagine its just watch your fingers time as you take the last bolt out. your design is very much more evolved most certainly. and I love that there is space still underneath, Would you mind if I use your example I feel bad not making the design myself although I will change it to suit.

I'm sorry to ask so many questions but on the bracing does this have to be specific dimensions e.g. a true triangle for the strength like 45 degrees or just has to look correct. i'm not sure how easy it would be to make it belt driven the only think I can think of is to put the motor on the bottom of the bed and then use a pretty long belt in a 'v' shaping. I see the gantry uses ali extrusion I imagine I would still be better to use the box section for my design.

Thanks very much for the help.

Thanks

Rob

Hello Again everyone
I have been designing again and hopefully getting somewhere now thanks to the guidance from you guys. I'm not sure whether to go above the top rail and build up or if it is better to build downwards towards the table my thinking it that the strength of the side will help a little if it is below ? although I will have to shim with something to get a gap from the main frame. or would the gains (If any) really be worth it and just build on top?

http://www.mycncuk.com/attachment.ph...id=13609&stc=1 http://www.mycncuk.com/attachment.ph...id=13610&stc=1

If you are using round rail on the gantry I can't help thinking it's best to have one on the top surface rather than both on the front.
You need to draw the ball screws and motor mounts in place before thinking it's done.

Sorry to say this but that's a dreadful design. The gantry hanging down like that is acting as a lever and with no support at the ends it will resonate like crazy, this will show in the finish quality.
You need the Gantry supported at the ends connected directly to the sliding carriages.

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

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

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

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

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

Quote:

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Originally Posted by grain_r

Is the frame about correct for the design ?

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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.
Attachment 13614

Quote:

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Originally Posted by grain_r

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.

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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.

Quote:

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Originally Posted by grain_r

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.

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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.

Quote:

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Originally Posted by grain_r

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

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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.
Attachment 13616Attachment 13617

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.

http://www.mycncuk.com/attachment.ph...id=13636&stc=1 http://www.mycncuk.com/attachment.ph...id=13637&stc=1

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.

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

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

Quote:

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Originally Posted by grain_r

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.

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No was meaning offset back something like this for better centre of gravity and balanced bearing loads while cutting.Attachment 13649

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

Oh I see. great thanks I like that. So that I might save a little welding heat is there anything to stop me mounting the screw on the base of the box section although It won't be in the centre or is it best to put some uprights in and then mount to that ?

Thanks
Rob

I have been working on the updates and getting there now because I intend to make it my build log I thought I would keep updating with work in progress for my designs so people can see for the future . I'm getting pretty happy with the design now it seems to feel much better and thanks to you guys I am learning so much with each design change.

I am having a problem with the X axis I want to use one motor as people have suggested in the past because of Binding and using belts but I cant think of an easy way without using quite a few wheels to send it around the frame if I go directly across It would hinder the work pieces if they hang over the edge.

http://www.mycncuk.com/attachment.ph...id=13678&stc=1 http://www.mycncuk.com/attachment.ph...id=13679&stc=1 http://www.mycncuk.com/attachment.ph...id=13680&stc=1

Any comments would be most welcome. I havn't put the cable trays or the front axis as yet thats being done at the moment.

Thanks

Rob

I know it's a bit more expense but why don't you make the Y axis rails longer and have the bearings spaced further apart on the top and botom rails? It would give you a stiffer machine and looks like the space isn't needed for cuting as you're rails are shorter than the Y axis already. Eddycurrent hinted at this in a previous post I think.

For some reason I don't like the look of the box section as brackets for X ball nuts.
You seem to be loosing a fair amount of travel in Y direction by having short rails and ball screw.
Think about how you will access grease nipple on Z ball nut once it's all assembled.
Will you put adjustable feet on the frame legs for uneven floors ?
Can't see how you will adjust belt tension for the stepper motors shown.

Also think about how you will bolt it all together, you'll struggle to get the bottom Z axis bearings on as the bolt holes will be covered at the back so you'll have to take it all apart if you need to gt at them. If you extend the top Z axis palte back you can machine into it the adjusting slots you need and also it tucks the stepper down out the way and lowers the height of the Z axis.

Also don't forget that steel box section comes with rounded corners not nice square ones as you've drawn so you'll possibly need larger section (60 x 60) to be able to bolt the bearings to? I'd also extend the small plate you've got on the back of the Y axis for the floating bearing (small) mounting to provide a bit more stiffness for the Y axis, that way you'll not need any diagonal bracing.

If you're not sure what I mean attach the sketchup file (if that's what you're using?) and I'll show you what I mean.

Hey guys Thanks very much for the replies, Unfortunately I was a silly boy and bought the supported rails kit before I knew anything about the subject from Aliexpress. the plan being I will use what I have for now but then look to either create another or upgrade to rails. I have made it wider also so that I can slide work pieces around a little and work with larger materials and then make a second continued cut although most of the things I do will be sheet material and smaller pieces but I wanted an all-rounder for things like my daughters dolls house I intend to make with the machine and other toys too for her and me !

I didn't even think about the tensioning in all honesty that is a very good point I will make it on a movable faceplate. I couldn't think of a different way for the box for the ballnuts otherwise the other option being the ali route but though this might be better on the strength I might be able to make a silicone hose to the grease maybe although I'm not sure if it would just pop off.

I will have a good think to see if I can make those better

Thanks so much guys.

Hey Neil

Thanks very much for the offer of explaining it on the drawing I did try to attach the file but it doesn't seem to like it it seems like it only lets me do standard graphics formats. Is there another way to get it to you.

Thanks very much.

Rob

Zip the file up, or add .Zip as an extension...

Hello Neil

Thanks for the PM although thought it might be easiest to try what irving2008, Many thanks for that irving2008 much appreciated.

Attachment 13682

I'm sorry if the dawing isn't upto much I'm going through a learning curve on sketch up too this is the first time I've used that I try to keep the layers seperate but I forget to change to the correct layer sometimes.


Many thanks for the help

Thanks

Rob

Hmmm....I've only got version 8 and can't open it.....flipping typical!!

Hey Neil No Worries, I've just saved it as a version 8 & 6 Just in case and that will hopefully work.

Attachment 13683


Thanks

Rob

I was too slow, beaten to it haha

thanks very much for doing it all the same. :encouragement:

Quick tip....when creating a part, say a 50 x 50 leg, once you've created it select it all and right click and create a group. It's much easier to move it, rotate it etc. without messing about with the other parts it's placed next to. Might be teaching Granny to suck eggs but I've just tried moving some bits and it's creating some interesting shapes....

Just a thought.
If you made the Z backplate wider, keeping the Y bearing blocks where they are due to short rails etc. you could then move the Z bearing blocks wider and fit a wider Z front plate.
This might give you the opportunity to mount the spindle in 3 positions, left, right, centre, not ideal but maybe useful ?
Or maybe you could then mount another device beside the spindle such as a laser head, 3D printer head ?

Hey Neil,

I'm sorry about that your certainly not teaching granny, I gone more on the lines well that seemed to make the shape I want at the time. I will certainly group then from now on the makes a lot of sense I tried to do it with layers instead of the grouping and then selecting the layer to move things around. Although I certainly got further on sketch-up than on Autocad 3d up to now that's next weeks job then (Well Maybe)

Thanks Eddy that sounds like it would be worth a look at I also though about a plasma cutter for the future for stainless although thats as far as I've gone with it. I appologize not having used one of these things would I be able to set a home and then use different paths for the further cuts ? I'm certainly not worried about having to swap the spindle around between then that would get the hoped for cutting area when I forgot about the bearing blocks when I felt like a shopping trip before I knew anything at all.

thanks

Rob

Quote:

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Originally Posted by grain_r

I appologize not having used one of these things would I be able to set a home and then use different paths for the further cuts ?

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Rob, I think this is what you mean.
Home switches use the 'machine coordinates' whereas the work piece you are cutting uses 'machine coordinates', so a search for those terms should bring up some further reading.
Like a piece of graph paper the home switches will be at 'machine coordinate' X0,Y0 and if you clamped a piece of wood on the table for example and moved your spindle to the bottom left corner, that could be your X0,Y0 'work coordinate' and that's what you typically set to zero in Mach3 for example so that X0,Y0 in your g-code starts cutting in the right place.
So really you can give the machine an X0,Y0 work ccordinate starting point just about anywhere on the cutting table.
Think of the machine as big piece of graph paper that is in a fixed position (machine coordinates) and the work piece as a smaller piece of graph paper that can be moved about on top of it (work coordinates).
So on a 900 x 600 machine, if you put a workpiece with it's bottom left corner in the middle of the bed, that corner might have 'machine coordinate' X450, Y300 and 'work coordinates' X0,Y0

There's also offsets/fixture coordinates that could be usefully employed; http://www.cnccookbook.com/CCCNCGCod...orkOffsets.htm