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A few general questions about printer design.

Posted by aamcle 
A few general questions about printer design.
August 30, 2018 03:16PM
I'm new I've not had a printer long so new in fact I'm only just about to start my second roll of filament.

When I become interested in a subject I read and read, check the videos and generally try to learn as much as my limits allow.

Now I've seen a number of printer designs that for some reason don't sit well with me, some are built to withstand an Elephant squatting on the hot end others just look wobbly.

If the printer is a decent size say 1000*500*500 build volume then the print head and gantry may be moving quickly and possibly a good distance above the base.

As the frame must be rigid enough to hold everything still how strongly built should it be? Let's consider the Boch Rexroth extrusions (like V Slot) 20*20 or 20*40 or 40*40mm what s enough, would it need metal corner plates?

Which brings me on to linear rods, my old (new to me) CTC Replicator in common with many RepRaps has rods supported only at the ends, how long can you go with end supported rods before they become a liability and linear rails are needed?

Yet another one, a number of big commercial I've seen videos of have fixed beds, presumably because of the weight involved, and a gantry supporting X/Y movements that moves up the Z axis. At what point does it become worth using a fixed bed moving gantry design?

I don't suppose I'll ever build a big printer I don't know what I'd do with one of I did and I may be a sad old geek but things like that interest me.


Atb. Aamcle
VDX
Re: A few general questions about printer design.
August 30, 2018 03:37PM
... for your first printer better look for designs with smaller building areas like 200x200x200mm - "warping" is an issue with many materials and bigger objects ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]
Re: A few general questions about printer design.
August 30, 2018 03:43PM
I'm not likely to build one, it's just interest.

Oh and I've got another question, V Slot or traditional linear rails? I was also looking at supported rods that are used with bearings that have a cut out.


Atb. Aamcle
Re: A few general questions about printer design.
August 30, 2018 09:08PM
I suggest the links in my sig, below, for starters...

There are a few main differences between end-supported round rails and fully supported linear guides. End supported rails must be used in pairs to constrain motion, and as you have already surmised, they can flex. Fully supported linear guides can flex much less, depending on what they are bolted to, but one of their primary benefits is that they provide fully constrained motion via a flat, rectangular bearing block to which it is very easy to attach things like extruders. In some circumstances, they can be used singly, as in the X axis of a coreXY or i3 type printer, and that helps minimize machine size. A single linear guide has two parallel "rails" that prevent rotation or play in the bearing block.

Most of the parts in hobby grade printers/kits are selected to be just or almost good enough to do their jobs at the lowest possible price, which means cheap kits are nearly impossible to upgrade into decency. You'll spend more upgrading a junky printer than you would have spent if you had just bought a better printer in the first place. Some people buy a cheapo kit on the assumption that they'll be able to use those parts to build better printer. Unfortunately, if those parts could be used to make a better printer, the printer they came from would have been better than it was. If you pay for crap, you get crap.

The exact/minimum size of t-slot to use is an engineering problem usually solved by your wallet. 20mm square t-slot is not for large printers. What size t-slot is best for the machine you want to build? That depends on many factors. Small t-slot rigidity can be improved by bolting rigid side panels to the printer. If you aren't going to do that, you need bigger t-slot.


Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: A few general questions about printer design.
August 31, 2018 04:39AM
Thanks.

Aamcle
Re: A few general questions about printer design.
August 31, 2018 05:39PM
What 3d printer do you currently own? And what shortcoming do you perceive it to have?

A kit printer is a good way to get a hands-on feel for why the designers went the route they did (besides cost of course), and why some motion arrangements and frames are stiffer than others. Theory will get you half way there, but experimentation many times unveils aspects not even considered. Thats part of the beauty in 3d printing, you can print up a part in no time, and thumb it over to find its weaknesses.
Re: A few general questions about printer design.
August 31, 2018 06:03PM
Printers are often designed to meet cost and size requirements, so you buy what you can afford and hope it performs well enough. A particularly motivated designer could do the math to verify the parts will perform acceptably before committing to the design.

If you've built a few printers and studied other peoples work you will have an intuitive idea of how a design will print.

To be honest, fixed beds are more likely to be a space-saving measure. If the bed moves the printer footprint must be at least twice as large as the bed. If the bed is stationary, the minimum footprint is the size of the bed. (Plus the frame in both cases).
Re: A few general questions about printer design.
August 31, 2018 10:06PM
Quote
691175002
To be honest, fixed beds are more likely to be a space-saving measure. If the bed moves the printer footprint must be at least twice as large as the bed. If the bed is stationary, the minimum footprint is the size of the bed. (Plus the frame in both cases).

Printers with beds traveling in the z direction are the same size as fixed bed printers. Also, i think fixed beds are tried so seldom due to having to control 3 axes of the print head vs two. With the print head being able to move in three axes, the z-axis has to be very well constrained or the rapid movement in the XY plane would cause print artifacts. The Voron 2 looks interesting in that it is a fixed bed design. Also has a clever printer gantry Z-leveling.
Re: A few general questions about printer design.
September 01, 2018 02:30AM
The best fixed bed ? The Delta smiling smiley


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: A few general questions about printer design.
September 02, 2018 06:06PM
I have an old CTC Replicator clone, I think I have finally got it to a fully usable state but it's so so awkward to do anything with.

The box gets in the way and for PC type reasons (they are geriatric Vista on one Linux on the other) I'm using Mattercontrol and RepG, Mattercontrol is fine RepG is a time warp.

Just checking the heater rod, temperature sensor and fitting a new nozzle took a stupid about of time mainly because of reduced access and having to use a torch to see!

Then to stop the guide rods jumping about I've had to glue them into their sockets, so far I've spent my time printing new rail supports before I can move on to the rest of the printable upgrades.

If I can get some 2020 at a good price I'd enjoy doing a full rebuild with a modern main board and upgraded extruder.



Atb. Aamcle
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