Giant 20' x 3' x 2' router build

**charlieuk** · 16-03-2014

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** · 16-03-2014

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** · 16-03-2014

Originally Posted by 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

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** · 16-03-2014

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** · 16-03-2014

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** · 17-03-2014

Originally Posted by charlieuk

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

**gavztheouch** · 17-03-2014

What is the biggest diameter collet you can get in that spindle. For roughing out you probably want some large diameter tools.

**charlieuk** · 17-03-2014

all the aluminium i have used so far is ether 40/80 or 80/80 bosh compatible from kjn, i don't think changing the z will be to hard, i have some spare 40/80 i can use however the motor mount may have to go on the top like you have drawn which isnt so great as i have a hight restriction and need to keep it as low as posable so will have to see what i can come up with.

i dont think its going to be posable to do the y with one ball screw any were near the centre as the z will get in the way which mean needing two which would be a nice build but would cost something like a further £350 compared to about £60 ish that rack and pinion would be so will have to have a little think.

I think the max size bit would be 19mm but most i think are just 1/2" shafts so nothing crazy. foam likes to be cut quite quick other wise you get melting issues so you don't need big bits.

**gavztheouch** · 17-03-2014

Would it be possible to use a timing belt and ballscrew. The ballscrew does the main postioning work and the belt just prevents the gantry from racking?

**charlieuk** · 18-03-2014

i think a belt and ball screw may end up getting more complicated than r&p and i would rather try and keep it as simple as posable although i expect it would work.

Just thinking out loud...

If the z axis was mounted to one side of the y gantry and the same side as the rack and pinion and as close to the rails as posable would racking be such a issue?

At present the y rails are 360mm apart, would reducing that help and if so what sort of distance before racking would not be so much of a worry 100mm? 150mm? 200mm? im am just trying to get a good idea in my head of how much of a factor it will be.

many thanks