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Sheet Metal Brake and 3d Printer.
S. Heslop:
The two go hand in hand.
So i've been planning this for quite a while now but other things kept coming up. I'd like a large 3d printer, about 400x400x500 build volume, but the price they charge for commercial ones is taking the mick and i'm sure I could build one for a fraction of the cost. I've just been very indecisive on how to go about it.
One of the earlier designs I settled on was this.
CoreXY gantry, sheet metal construction. But I was pricing out how to build a box and pan folder before thinking that idea was getting a bit expensive, and I started to dislike the design i'd come up with.
So then I settled on this.
It's a bit of a mess of a design. But I started building it anyways. I couldn't find the nice 50x100 thin walled ESR tubing I had in mind so I went for some 50x100x3mm hot rolled. I think they might've mucked the order up because the walls are more like 4mm. Just the steel for the sides was impossible to lift on my own, so I set out hole sawing bits away. I got two holes put in before deciding it wasn't a great idea. I'm not to keen on the design either. There's some real flaky bits. (This is an older screenshot I just realised. It really started to fall apart when adding the details)
I'm here right now.
Not much to look at, but i'm going for yet another gantry arrangement, copied from a popular commercial machine. Seems it'd be alot easier to build than having to worry about routing miles of belt, and everything fits nicely against the walls of a square box. I've not quite figured out the box part yet though. Seems the routes to take are a welded box section frame with panels bolted/ welded on, big chunky aluminium/ plastic plates that weld or bolt together, or a sheet metal box of some sort.
I've always wanted to do more with sheet metal. If nothing else I think it's cool! So building a big box and pan folder is appealing. Here's the design I was going with previously.
The idea was to rely on cold rolled steel being fairly straight to register the fingers against. There'd be a bolt going through that hole to pull that clamp up.
But I just saw this video. It's a little hard to make out but I think at the start he welds some tiny angles onto a flat to make the T tracks. And I think trying to register on the tops of the fingers is alot more complicated than just registring the bottoms against the table, especially since i'd be making them by hand with most likely a belt sander, so the T track might not need to be that accurate. It'd also be nice to come up with a new design that can make use of all that 100x50xsomething rectangle.
I'm also considering the idea of buying one of the cheaper 3d printers out there to make some parts, and then pillaging it for the steppers. For what was the hot adult nerd toy a couple years ago i'm surprised there's not much of a second hand market for them. Maybe the sales weren't as big as the journalism made them out to be. I've kinda wondered why the Chinese devices look so... prototypal - being assembled from stock parts, laser cut acrylic, and aluminium profiles.
nrml:
I would highly recommend MGN12 linear slides over smooth rods. They are cheap and more than accurate for this application.
https://www.ebay.co.uk/itm/MGN12-250-550mm-Miniature-Linear-Rail-Slide-Carriage-Kossel-3D-Printer-CNC-Laser/382529570288?hash=item59108a05f0:m:mKynaPd9azC-mDeASbymloA
Why not use aluminium extrusions in the size of your choice? You can have them delivered pre-cut from Motedis accurate to less than a mm
S. Heslop:
Huh they seem alot cheaper than last time I looked. I think I was looking at £120 a set back then. I got given 4 bearing blocks and i've got the steel bar as well, so I might stick with round rails for the Z axis. But it opens up options for the X/Y gantry.
Extrusions were the first thing I looked at, but I thought all the brackets you'd need to get everything in the right place would be tricky to make. Alot of the designs using those rely on alot of 3d printed parts. But back then I was also trying to avoid using 3d printed parts...
Joules:
I am trying to bite my lip commenting here, but those long Z bars.... Think about using a 300mm lever on them pivoting about the leadscrew. They are going to move even under light pressure from the nozzle. Supported is the way to go, round or rail.
S. Heslop:
--- Quote from: Joules on September 06, 2018, 04:17:36 AM ---I am trying to bite my lip commenting here, but those long Z bars.... Think about using a 300mm lever on them pivoting about the leadscrew. They are going to move even under light pressure from the nozzle. Supported is the way to go, round or rail.
--- End quote ---
Hah don't worry, I appreciate the comment. With the earlier designs I was going in the opposite direction with 20mm round bars. But like I said I gave up on it because it was going to be absurdly heavy - so i'm kinda going in the opposite direction now. My concern was that putting more weight on the table would make the layers fan out over the whole item (combined with it reaching the mid point of the bars where I believe it'd flex more). I'm also hoping that I could find somewhere to have the stepper motor at the top of the leadscrew so that it's hanging and held in tension, which I think would let you get away with a fairly spindly one.
I've read a few arguments on CNC forums over round vs supported and they never seemed to reach a conclusion. The idea being that the cut-out in the bearings makes them considerably weaker than if you just used unsupported rods and enclosed bearings. But the appealing part of round rods for me is that I don't need to worry about their mounting being straight or shimmed along their length. Just need the ends in the right place.
Looking at commercial machines they all look surprisingly under-built to me.
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