Help me pick the right electronics hardware for a filament printer

[Don McLean]

Thank You everyone for your replies so far! I really appreciate the feedback. Sorry for the delay in writing back, I've been doing alot of thinking about this, and I still haven't made my decisions.

I'd like to start by saying that a short part with lots of XY surface area is more likely to de-laminate than a tall part with a small XY cross section. Larger XY cross sections mean that each layer contracts more as it cools, this means larger forces between the layers and leads to de-lamination.

There has to be a way to mitigate this with the use of rafting and support material?

If you look at this video, in particular 2:51, it explains the "wood grain" strength of 3d printing which is why I can't simply adapt an existing printer to give it a really long Z travel, which would be very simple to do from a mechanical standpoint, although if I did this I would replace the Z axis entirely with one that has square rail supported linear bearings and a proper ballscrew to accommodate the extended length.

By other sensors do you mean X/Y/Z max homing switches? RAMPS supports both a min and max endstop for each axis I believe. Even if it doesn't, it's not hard to add.

No, I mean the crash stop sensors. For example, with two motors on the X axis, you'd have a total of 3 switches, two for the homing to ensure that the gantry is square each time you start up (they also act as crash sensors on that end) and one at the other end of travel that acts only as a crash sensor. So that's three for one axis, however the one that is by it's self can be wired together with other "crash only" sensors so it only takes up one spot on the board for all of them. The two homing sensors would each need their own board slot. Do you typically home to both ends of an axis? I've never seen that before.

To use a larger heat bed you'd probably want to use an external mosfet module. Again, I'd try and use 24 volts if I were you (i.e. not ramps), it boosts the performance of the stepper motors and heated bed/hotend. You could get your machine running with two extruders (or even three with an expander) using a RAMPS but you'd be making some pretty big compromises, so I highly don't recommend it.

That's something to consider for sure. Yes, I'd want 24V minimum. Higher voltage means higher torque at speed for stepper motors. Higher current means higher torque at low speed for stepper motors, but doesn't necessarily have any effect on higher speed torque. Depending on how the system is geared, more voltage is the way to get better performance.

I'm thinking of a 12" x 36" bed with about 10" x 30" as the printable area. Alternatively I could still decide on a 12" x 24" bed with a 10" x 22" printable area. What would you recommend as a heater for those sizes?

how about having a fixed bed and moving the z axis.
That way the size of the bed is not a factor, you can have a larger bed with thicker aluminium, and not worry about moving the weight around. The z axis setup will be much lighter. Plus your bed should not go out of calibration anywhere near as quickly.

So while you're not buildinga delta - with a fixed bed you get many of the benefits and none of the drawbacks.

I have thought about this. There are actually lots of drawbacks from having the Z axis attached to the gantry. For a CNC router, the more Z axis travel you have the stiffer and heavier you have to make everything because when it accelerates back and forth, the gantry will flex due to the moment from the weight hanging below it. So for a 4" Z height, yes it could make alot of sense, but for an 11" Z height it doesn't, unless you want to add more rails / bearing blocks and make the gantry assembly 10x heavier than it would otherwise be. Have you seen any 3D printer designs that use this methodology and work really well? If you have, I assume they look more like CNC routers with big gantries and linear components? The Delta design is it's own kind of beast, however if I could get over the wood grain strength issue previously mentioned, a tall delta printer might make alot of sense.

I am currently building a steel CNC machine, haven't finished yet, but have made others in the past, also very large, weighing in the 1000's of lbs range. I was thinking about adding a 3d print head to my CNC that I'm building now but in reality I don't want to run the bohemeth for 48 hours straight doing a print job, it's somthing that shouldn't be left unattended. Also I'd have to redo all the electronics to accomodate the extra motors for 3D printing as my current board couldn't handle that, and forget about trying to enclose it to keep the heat in, plus the debris etc from the CNC part would just make it messy.

And after your suggestions about the type of head on the bnc3d sigma, I am seriously considering this. The only problem is that it takes up way more space. This would require two moving Z axis heads (if I had a fixed table), and I think that would be a nightmare.

I've also been having a much more serious look at the H-Bot and Core XY designs. Have you ever seen a printer with independantly moving heads that uses H-Bot or Core XY? It is totally possible from a mechanical and design standpoint, but I don't know if the software would get confused with that in addition to the H-Bot or Core XY architecture?

Thanks again for your replies guys! I still don't know what I will do here, so continued advice is appreciated.