Giant 20' x 3' x 2' router build

[charlieuk]

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[routercnc]

Charlie,

It's a very unusual machine and I can't quite work out which bit will be which, so the question you've asked about motor sizes is probably proving difficult for anyone to answer.

But be aware that you can move a fair amount of weight with a 3Nm Nema 23 if you give it enough voltage as the ballscrew gives you lots of mechanical advantage. Don't rush out and buy 34's until you posted the final design sketch of the finished moving parts as you'll get a more definitive answer.

Your earlier question about pulley ratio on Z is also tricky since your Z appears to be quite long. Lots of designs are just 1:1 on a 1605 ballscrew for Z. But your travel (if I read the design right!) is quite long so this mught not be your best option. Again, a picture of the overall finished design would get a better answer from the forum on that question.

The wooden template motor bracket looks OK as a concept (assume ~20mm ali in the finished design?). Probably get away without triangulating back to the extrusion. But you'll probably need to recess the underside of the motor mounting area to raise the stepper and leave enough shaft sticking out the top. Also the ballscrew end might also need some pocketing on the top to clear the pulley / grub screw access.

[charlieuk]

I dont have any 3d drawings at the moment i tried to get sketchup to load on my mac but it didnt like it.

If you take a look at thins video it shows something similar to what i am building however i just have the flat table and i have decided to have the two beams coming out on the gantry rather than one so as to stiffen it up and split the two rails apart, then the z axis will go inside the square frame you see on the top in my picture.

the z is quite long i wanted to get as much as posable to be able to work on large block of poly styrene and by large i mean i buy it in 16' x 4' x 2' blocks so should i have aprox 500mm of z travel when done.

the plan is to get all axis bolted up and rolling before getting the motors which hopefully wont be too long, im hoping to get the plates for all the carriages this week. I wasn't to sure how thick the motor mount for the z was going to need to be, i was thinking only 10mm as i didnt think there would be to much load on it using a ball screw but happy to take advice on that and as you say ether recess the some of the areas to get the pulleys on or extend the shaft if that is posable?

many thanks Charlie

[routercnc]

That makes more sense now in terms of the final design. Should have guessed with the O'Neil logo on the wall.

I think 10mm motor plate would also be OK stiffness-wise. What you will need to watch out for is if the bolt heads hit the belt then they will also need to be recessed. M8 cap heads would need 8mm depth of pocket so 10mm plate is then a bit thin.

In terms of recess or pockets for the motor - if you can find the drawings for the motors you might use you can check the length of the shaft. They are not usually that long plus you need access to the grub screw at the base of the pulley so that often means a pocket is required.

The motor plate extends past the extrusion and over the ballscrew - is that bit required? Are you hoping to bolt it to the bearing block as well? If not, you could cut it short and give more space for the pulley on the ballscrew. Just some thoughts . . .

[charlieuk]

cheers many thanks for the reply, yes one of the things i will be cutting is stand up paddle boards but hope to use it for ply would and other things which is why i wanted the table. I see the problem about the bolts, i will have a look in to that one i would have thought i can come up with something there. I have just been trying to keep all the bits i am having to get fabricated as simple as posable as i only have a basic lathe and no milling capabilities so just getting it all laser cut.

i was wondering about using the block to bolt to as well there probably is no need really and possibly not posable as there is all so a plate having to go under it. If i actually could find a large bit of 90deg angle aluminium i could possibly use that for the motor mount and bolt it straight to the side of the z axis rather than the end.

many thanks for the advice! charlie

[charlieuk]

something like this but would have to see what size motor i need and if it would fit.

Aluminium Angle from 2.5" to 100mm many thicknesses and lengths cutting service | eBay


sorry the link didnt properly work they do a 9.5mm thick by 76.2mm deep option

[Jonathan]

cheers many thanks for the reply, yes one of the things i will be cutting is stand up paddle boards but hope to use it for ply would and other things

If you want to cut plywood at all seriously, then I'd be concerned about the strength of your cantilevered gantry design. The cutting force for polystyrene is practically zero, so you can get away with a very weak gantry, but that's not the case for plywood.

Also, for the axis on the gantry (Y-axis?) your bearings are quite close together on the rails compared to the spacing of the rails, so I would be inclined to drive it with one ballscrew on each side, or at the very least make sure the ballscrew is centred between the two rails. The problem with the former is the ballscrew would intersect the Z-axis, so there may not be space for it. If you put a single ballscrew on one side the bearings on the other side will deflect more (i.e. it will rack like a typical CNC router gantry), so the obvious solution is to use two ballscrews. That's quite expensive though so you may want to just try it and see, but keep in mind the possibility of adding another. You could also increase the bearing spacing. It's hard to say for certain as it's difficult to discern which parts of the machine have the lowest stiffness and thus which parts should be improved if you want to cut plywood efficiently.

[JAZZCNC]

Agree with Jonathan about being better to use twin screws for Y axis and to some degree that Z axis will be weak for cutting plywood but with just a simple change it could be made stronger to the point it would manage be ok.
It would cost more due to extra components and ballscrew placement wouldn't be the ideal but would stiffen things up enough. I've quickly thrown together a model to show you what I mean.
Obviously I don't know the spacing etc in side the Y axis frame or how you plan to attach the bearings and what spacing but looking at your pics I think there'd be enough room.? Spindle is just there for affect and the real thing would need extra support.

[charlieuk]

thanks for that jazz i can see what you are saying and we did wonder about the third set of blocks and there is plenty of room to fit it all in and i have made the y frame so i can slide one side in to be what ever size it needs.

i was wondering about using 60x60 or 80x80 for the z axis but the 40x80 in a relatively short length seams crazy strong as it is.

i guess what i will do it try and get the x and y rolling and see how that feels and with the way it is i can pretty much just add to it if does look like its not going to be up to the job. I was planing on using rack and pinion for y could i just run a second motor on the other side rather than a ball screw? or possibly even one motor with a shaft and pinion on ether end like a car axel, although that maybe a little more tricky to build

if needed i could actually make the hole gantry narrower if needed just buy shortening a few bits if it would help.


I should say that i am not after crazy speeds for cutting ply or accuracy for that matter as it will be just for stuff that i would normally make by hand so 1-2mm tolerance would be fine to start with.

many thanks for all the advice i am taking it all on board

[JAZZCNC]

i was wondering about using 60x60 or 80x80 for the z axis but the 40x80 in a relatively short length seams crazy strong as it is.

Yes it may seem strong Now but promise you when there's a spindle on the end with cutting forces acting on it then at full extension at this length which you would be while cutting ply it will twang like a guitar string.!!
The Z axis is THE single most important area on a CNC machine and seen as your going to so much trouble and expense using Profiled linear rails etc why spoil the broth for a pinch of salt.?

Regards R&P then yes it would work ok and seen as your using it on other axis makes sense but you would still need drive it from both sides, thou it would be easy enough to run a shaft across the back of profile. As would it to connect ballscrews with a timing belt, which woud be my first choice.

Tip for you if you use the Bosch Rexroth 45 x90 or it's equivlent then the BK/BF12 bearing block hole centres match the slots and make fastening very easy.
This stuff Profile 45x90S slot 10