Thread: 5'x3' Ideas and build.
It's been a while since I first posted and I've had plenty of time to think (and re-think) my design...
I thought originally that it would be cool to have something capable of cutting aluminium, but the reality is that to build a machine than will do that 'properly' is a different project altogether... The primary goal for this project is to be able to cut hard/soft woods and be accurate/repeatable in doing so.
Specs so far:
Cutting area maximum 5'x3'.
X Axis driven by 2x 20mm ball-screws with a lead of 5mm driven by a NEMA34 motor connected by cam-belt/pulleys.
Y Axis driven by a 16mm ball-screw with a lead of 5mm driven directly by a NEMA23 motor mounted to gantry side-plate.
Z Axis driven by a 12mm ball-screw with a lead of 2mm driven directly by a NEMA23 motor.
All linear bearings will ride on supported rails.
Main gantry to be constructed from 15mm 6082 aluminium plate.
So, here are my ideas so far:
This clip shows how I propose to build the main gantry:
In order of appearance:
1. The first plate will act as a mount for the linear bearings riding on 20mm supported rails (TBR20 from Zapp) mounted to 80mm aluminium extrusion and will also act as a brace for the...
2. ...vertical cross piece, which also has 20mm supported rails mounted to its front to accommodate the z-carriage. The hole in the arm that drops to either side will accommodate the ball-nuts. There will be a ball-screw on either side of the bed driven by one motor via a belt/pulleys to move the gantry on it's X. The ball-screw for Y motion will run in between the two supported rails and be directly driven by the motor which will be mounted to the...
3. ...side-plate which, when bolted to the other 2 pieces, will hopefully add to the overall rigidity of the structure.
Some questions so far.
I'm using 15mm 6082 aluminium plate for this build. I'm hoping to use M8 35mm hex socket head cap screws to bolt this all together, which means the screws will bite 20mm of the thread I'll tap into the plate edges. Does this depth sound robust enough? Is M8 too big for the edge of 15mm plate?
To allow for a bit of adjustment I'll be making the holes in the face of the plates 10mm in diameter so there will be a bit of slop to play with before torquing everything up once it's all aligned. Does this sound okay?
Where there are slots cut for plate to pass through (the arm which passes through the side-plate, for example) - rather than cut this slot to be exactly 15mm wide, should I make it slightly wider (say 15.25mm) to ensure that the plate passes through okay? .25mm too much?
Obviously there won't be any internal right-angles because the end mill will have a radius. Where there's a square edge that fouls a radius, I'll manually chamfer off the corner to make it fit (see pic below).
Now on to the bed that the gantry sits on:
In order of appearance:
1. C channel which connects the 2 X rails.
2. Spacers to fill the gap between the C channel and the spoil-board.
3. L section which adds rigidity along the Y-axis and connects to the machine frame.
4. 25mm x 25.4mm aluminium spacers. Hole-sawing them at the mo - Pff, long and dirty job...
5. 25mm thick plywood spoil-board.
6. 6mm plate. Ball-screw bearing blocks will mount directly to this.
The T-bolts that secure the aluminium extrusions to the top plate will pass through the top-plate, spoil-board spacers, L section c-channel before being fastened with a nut/grip-washer to the underside of the c-channel.
A general and straight-forward question here. Is this viable?
I have some ideas about how this is all going to connect to the frame, but I'll leave that for now and get a diagram together in the near future... Same goes for the Z-carriage. Meanwhile here are some pics of the adjustable feet I made... First time welding and also had a go a bluing the mild steel plate, didn't come out too bad...
Is there anything here that represents an alarmingly bad design decision? Or could this actually work?
(Bear with me on the wooden legs, all will be explained...)
Last edited by Wal; 22-12-2012 at 12:09 PM. Reason: Pic links fixed.
I'm not 100% certain but I believe the purpose of a spoil board is to get spoiled by chopping into it either accidentally or on purpose. When your spoil board is spoiled past being able to use any more how are you going to change it for a new one without dismantling the whole machine?
Yeah, I hear you on that one - it's not ideal, but I'm going to be clamping a thinner bit of ply between the work and the spoil-board and cut into that rather than the actual table surface.
linearmotionbearings2008 on eBay offers any size you need if you send him a message, along with fast service. I'm not sure if he has TBR bearings still, so you may have to use SBR. TBR are stronger than SBR, but you could probably compensate for that by just using one size bigger, i.e. SBR-25mm.
Using 20mm ballscrews is only beneficial on the X-axis, of a router, if they are 10mm pitch. You can get 10mm pitch, 20mm diameter, ballscrews from China, but not on eBay. If you used RM1610 the critical speed will limit your rapid feedrate to about 6-7m/min, but that's still respectable for this size machine. To get any more is expensive. See this post.
Most people use RM1605 on Z, but if you want to use something smaller (e.g. RM1204) that would work just fine but there isn't really much point unless you're very short for space.
20mm is plenty of thread engagement for M8 in aluminium.
Hi Wal, the single 15mm Y axis (or I think you call it the X axis) plate could do with stiffening as I don't think it will resist twisting very well, especially if the Z axis is at max travel.
Wouldn't an easier solution to your 25mm dia Ali bits you're painfully cutting out if plate have been to buy 25mm round Ali, cut to length, mark the centre and drill?
>Wouldn't an easier solution to your 25mm dia Ali bits you're painfully cutting out if plate have been to buy 25mm round Ali, cut to length, mark the centre and drill?
Maybe, but I don't have a metal saw - at least this way I can be sure that each spacer is an identical height - buying stock cut to length is always a bit hit and miss... The guide bit drills the centre hole too! Bonus.
Yep, it's a pain - but on the next batch I'm going to try drilling a guide hole straight through, cut from one side, flip, re-align and from the other side. It's the swarf not rising cleanly out of the cut after 15mm or so of depth that's making this job a pain - flipping the piece should solve the problem. I can only hope!
I've got a B&Q hand mitre saw which cuts Ali ok and set a stop so the lengths are identical. I'm ok as I'd use the works lathe if i was doing it but cutting my Ali for my cheap router gantry was done in this way.
Cutting from both sides.....ooooooo good luck with that, I can never get cuts to meet in the middle doing that lol
>the single 15mm Y axis (or I think you call it the X axis) plate could do with stiffening as I don't think it will resist twisting very well, especially if the Z axis is at max travel.
Do you not think that the plate that it's bolted to (which sits horizontally behind it) would be enough? When the Z is at max this is the part that's going to be taking the brunt of the forces - hmm... Will have a think.
>Cutting from both sides.....ooooooo good luck with that, I can never get cuts to meet in the middle doing that lol
Hehe. Yep, I know what you're saying. Luckily these spacers will be hidden from view... ;)
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