Feedback on DIY 3DP

[Spixe]

Hello!

This is both my first post in here and my first 3D printer build. I started from rock bottom and have read quite a few articles about 3D printers up until now. I have access to stainless steel mainly, so this is what I have been thinking of making the printer of. The design I created in SketchUp is not final at all, and dimensions of shafts and so on are not known yet, so they are just examples.
- The print dimensions of the printer will be about 200x200x200mm.
- I'm planning on using that San-something controller board, since I do not own an Arduino.
- I am most likely going to invest in some Nema 17 steppers.

My concerns:
1: Does the design work?
2: Will the printer be too heavy? I will try to make the moving Z-axis as light as possible, since it has to move up and down.
3: I am aiming to make it fairly sturdy, so I can use it for engraving as well (in metal hopefully) and maybe milling in wood.
4: How important are heatbeds?
5: How big stepper motors would I need for my design, considering it might be fairly heavy compared to normal 3DP's.
6: When buying stepper motors, should I aim for high voltages and low current (ex. 12v, 0.4a) or the opposite (ex. 3.4v, 1.7a)
7: Anything else I should be aware of?

Here is a screenshot of the printer sketched in Sketchup. I can upload the 3D model to the warehouse at some point, if it makes things easier:
http://peecee.dk/uploads/122014/Unavngivet1.png

Oh. And I do not know if this is a the correct category at all, so I hope I am not too much inconvenience.

Thank you all in advance!

[curious aardvark]

looks liek you're using 2 stepper motors for the z axis. Or is one for the extruder ?

design looks sound to me. But I'm no build expert :-)

On the question of heated build plates. I suspect you'll get a lot of different opinions.
Personally I now go out of my way to use cold plate filament.
I love printing with pla - which I do on an unheated bed.

I've also printed with flexible filaments, bronzefill, nylon and laywood wood fibre filament - all on a cold bed.

Hot bed printing is more of a hassle. You have to wait for the bed to heat up, every time you change the bed print temp you need to re-calibrate at the new temperature. Which if you don't have reliable auto-calibration, is a pita.
I've pretty much decided to not buy any more abs. And once I've used up the stock I've got it'll be pla and cold bed filaments all the way.
The advances in filament tech and manufacture are such that you can use pla for pretty much anything you'd use abs for.
Weirdly I find that pla gives more than abs - rather than the it supposedly being brittle. Ive had the same part in both pla and abs where the abs cracks under pressure and the pla doesn't.

It would make more sense to enclose the printer in a chamber and use the heater to directly heat the whole chamber - rather than the printbed alone.
Keeping the model at an even temperature will do a lot more to avoid warping than just heating the bed.

[soofle616]

Link isn't working for me??

The nema17's produce a fair bit of torque. Depending on your drive mechanism (again I can't see your design at the moment) I would think they would be fine to make everything move. HOWEVER, bear in mind that with weight comes inertia which can kill your print quality. The reason for bowden extruders is to lighten up the print head as much as possible. This allows for faster movement, greater accel and decel, and quicker printing. The lack of inertia allows for this. Lack of inertia also allows for repeatable positioning though because with greater inertia comes the need for greater torque to overcome it. If the motor doesn't have the torque to decel or accel the way the software is telling it to it's always going to be "behind" so to speak and will be constantly trying to compensate. Weight on the Z axis isn't as big a deal because it's not constantly in motion, just the occasional step to lower the platform between layers. X and Z though should be as lightweight as possible for best results.

Regarding engraving, I'm not too experienced with it but engraving typically does not require a great deal of force since you're usually talking about a high speed tool removing small amounts of material. Milling on the other hand, requires power AND rigidity. Again without seeing your design, an all metal build could certainly have the rigidity needed to hold the tool in position. The steppers may not have the power to make the cuts though. If the steppers aren't strong enough you risk the tool not being pushed into the material hard enough which would result in spinning the tool on the surface, generating heat, and potentially burning the piece if it's allowed to sit for too long. unfortunately the qualities of a machine that make it good for milling, make it not so good for printing and vice versa. Not that a combination machine couldn't be built but you'd likely have to spend more money on beefier components like slides, bearings, drive screws, steppers, etc.

[Spixe]

Thanks for your replies!
curious aardvark - I was planning on using two stepper motors for the z axis, since it is simpler to have it lower and raise on two shafts instead of one.
I don't know anything about the different types of filament, so I will be reading up on that.
When using cold plate filament, do you still have to heat the surroundings like you suggested in an enclosure or something? If not, then I will definitely go with cold plate filaments! Haha

soofle616 - Link has been fixed. I'm not sure what a "bowden extruder" is. Is it just an extruder mounted elsewhere than on the platform itself? I will be raising the Z platform instead of lowering the bed between layers. I will aim to make it as light as possible! Sounds good with the engraving, too! Makes sense that milling requires sturdier and stronger parts, though, so I will stay with printing and engraving. Thanks!

[Feign]

First, it's more important to keep the stuff moving in the x-y plane as light as possible than keeping the z-axis light. Systems that are used to increase the precision of the z-axis also slow the movement and increase the amount of load it can handle. Meanwhile, the x-y axes tend to move very quickly, if the print head is heavy and moving at appreciable speed, then the frame of the printer gets torqued around by the momentum and introduces most of the worst kinds of imprecision. Of course, it's slightly less of a concern moving the print bed in the x-y and the extruder in the z because the bed is by definition at the lowest and most stable part of the printer.

A 'Bowden Extruder' is when the motor actually pushing the filament and the hot end are separated by a length of flexible tube, allowing the motor and gearing to be static mounted and the hot end to be the only moving part. It's used in pretty much every Delta-style printer (which have very little room on the arms for anything at all), and on several Cartesian printers to keep the x-y carriage as light as possible.

[soofle616]

Ok, now that I can see the drawing here's some more suggestions. For the sake of discussion I'm going to call your bed movement Y axis and your carriage movement X axis

1) Reorient the lead screws and linear guides for your Z axis so they sit along the Y axis. This will shrink your overall dimensions significantly without impacting your build volume
2) There's no reason to leave that much of a gap between your build plate and the frame. Make it fill the width of the frame to maximize build volume (or conversely, shrink the frame to minimize footprint)
3) mount your X axis motor such that the output shaft points directly at the lead screw/linear guide for the Z. This will cause it to stick out farther along Y but will shrink your overall X dimension without affecting your build space. The increase along Y is irrelevant because it will still be significantly smaller than the overall Y footprint.