Ditching the Print Bottom Plate... Taking Suggestions

So I've had a functional Prusa Mendel i2 doing well the last couple months. I've been printing exclusively with ABS, which means I've been engaged in an unholy war against warping for most of that time. I've made a serious commitment to bed leveling, and I feel that I've progressed as far as I can as long as the following remains true:

1) The Y-axis has LM8UU bearings zip-tied to printed parts that attach to a print bottom plate, attached with springs to a print top plate, attached to a heated bed under a glass sheet.
2) Both the print top plate and the bottom plate are made of 1/4 inch plywood. This isn't entirely rigid, especially on the side of the print bottom plate that only has one bearing.

My plan is to ditch the print bottom plate and attach the y-bearing holders directly to the top plate. I'm taking any suggestions you might have for this endeavor, but I have these specific questions:

1) If I want to ditch the plywood in favor of acrylic, like so many RepRaps I see on YouTube, what acrylic do I use? All the stuff in my local hardware stores is more pliable than the plywood I'm using. Bonus points if you can provide links to Amazon or McMaster with what I should use.
2) Is there a way to connect directly to the top plate without moving my smooth bars for the y-axis above the threaded rods they're currently below?
3) What about printing myself a y-carriage like this one available on Thingiverse? It looks like people like them.

Thanks in advance for your suggestions.

The problem with ditching the print bottom plate is 'How to level the bed?' It could be done with adjustable height bearing holders I guess (if they existed).
In question 2, I guess you mean using a single bed recipe? Well, that could be done also but you would need bearing holders on stilts or a re-design of the printer.

I use wooden blocks cut from an 18x18 mm pine rod as a spacer. This also prevents heat from the aluminium heat bed from softening my pla bearing holder. I connect the bearing holder to the block using 2countersunk wood screws and the plate to the block using a single screw so that it is self aligning. You should only need to level it once which I do with a paper shim if necessary. Of the 15 printers I built, only a few needed it.

Edited 1 time(s). Last edit at 01/07/2013 05:59AM by Greg Frost.

I'm using 6mm aluminum as a bottom plate, with no top plate. However, I'm also using the Helios heat bed from panucatt. It's twice as thick as the MK2, and so is better able to stand on its own. I have absolutely no problems with this arrangement, and, in fact, this bed reaches ABS temps in half the time that my MK2 did.

Thanks for the answers, guys.

waitaki: The plan for bed leveling would be to have the springs between the single plate and the PCB. Or, use an appropriate number of washers to get the bed level. I'm not sure what you mean by "single bed recipe". Greg Frost's 18mm blocks look like the stilts you mentioned.

Greg: Your aluminum beds are self-manufactured, right? I saw in a different post that you were using disassembled irons to make your own heated bed. Cool. But I fear this solution might not be right for me. I'm not a metalworker, per se, and I'd like to not use a heating element as risky as iron would be. Know thyself, and I'm an uckfup.

jbernardis and Greg: I'm intrigued by the aluminum sheet option for replacing my plywood. Where do you normally acquire yours? (FWIW, I'm in the States.) How easy would it be for a complete beginner to cut a 6mm sheet down to size?

Thanks again,
Brad

I got mine from speedymetals.com. I asked for a quote for 230mm x 230mm x 6mm plate and they quoted me $10. Of course it cost another $10 to ship it.

Hi Karmavore ,
It makes sense to me to get rid of unnecessary materials. I too don't like all this 'bed build up' construction. I fancied the idea of having a single heated aluminium plate (heat board sandwiched on top) and with adjustable height bearing holders. Might give that a go sometime...

I used 3mm aluminium. Local metal shop cut it for me. I bought 15 at the time and they were about$6 each. Again, I think adjustable is a waste of time. Make it rigid, adjust once with shims and it should stay flat and level.

Exactly Greg, that's wot I meant by adjustable - not springs, adjusting nuts or whatever..

I plan on taking the "ditch the springs" message to heart. In fact, I'm quite looking forward to ditching them. The tension the produce pushes up on the top build plate, yes, but it also pushes *down* on the bottom build plate, especially on the side with just one bearing. Bed-leveling chaos ensues.

I'll concede that the springs were a good tool that allowed me to build an intuition of how high off the build surface the nozzle should be. The somewhat-adjustable bed was also good while I troubleshot an issue with a PLA extruder "sagging" during prints (and lowering the nozzle). But now that I've got a good feel for the first layer, and my extruder body is ABS, the springs are nothing but trouble.

I'll get to this is the next week or two, I expect. When I've got some results, I'll come back and report how it went.

Thanks again for the help.

I have also been working on this and have made a printed chassis that doesn't require an alloy sheet here: [www.thingiverse.com]
It takes a standard 8" x 8" heater panel mounted direct to it and is working well printing with PLA. As it was made from PLA I wonder how it would go with ABS however the edges of the heater panels are cooler than the rest of the pad so it might be OK.
I have since gone back to a water jet cut 5mm alloy sheet mounted directly to the bearing holders as it gives a very stable flat base to start from. I am also still using springs but what Greg says above does make sense so I will try shimming the one I am building at the moment.

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Richmond, New Zealand
Thingiverse ~ YouTube

Just to add another variant here, i am still using the old "Squashed Frog" base, with LM8UU bearing mounts, an ally top plate, that can be leveled again uses original Mendal printed springs, a layer of insulation on the top plate then the heated pcb, with another ally plate on top to ensure flatness, i have this flat with in 0.1mm from all 4 corners, and has stayed that way for a while now!

i would say that using springs gives a crash buffer! i can safely say that without mine i could have done alot of damage on multiple occasions..lol

sweaving Wrote:

> i would say that using springs gives a crash
> buffer!


Good point!

I wonder how valuable that is. I get the sense that in a crash, the kapton-on-glass layer I have would be ok, but the steppers would strain in a direction they could not go. Who knows if the torque of the the two z-steppers would be enough to do damage to the any of the pieces that would come under strain. If nothing else, it's something to think about.

The business end of the j-head is rather pointy so I would imagine it would break the glass...
I haven't adjusted my current printer since I built it either.

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Richmond, New Zealand
Thingiverse ~ YouTube

On my machine, I have no second nut and spring on my X ends (hex shape channel for Z screw) so if the Z axis drops too far, the axis rides up and the glass is undamaged.

I've done it! A short slideshow of where I started and where I got to is here.

[plus.google.com]

Long story short: I didn't need to provide any extra effort for bed-leveling, beyond just having a well-built, level Mendel to begin with. Why oh why isn't a single-bed design what is laid out on the Wiki? It could have saved me many an hour.

Speedymetals.com was a great source, except they hilariously sent my package to 1234 Call-In St. Can't make this stuff up. UPS, to their credit, was unfazed by this addressing tomfoolery, and just called me to get the proper routing.

I'm glad to be getting to the point where I can start paying back some of the large informational debt I owe the community. Many thanks to Greg Frost and waitaki for their comments, particularly the observation that those springs are not worth the trouble. Thanks too to Triffid Hunter, whose improved bar clamps are now a functional part of my Mendel. If anyone has any questions or comments and further suggestions about what I've done, I'll still be here tracking the thread.

waitaki Wrote:
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> The problem with ditching the print bottom plate
> is 'How to level the bed?' It could be done with
> adjustable height bearing holders I guess (if they
> existed).

They now exist, if a parameterized OpenScad file counts as "adjustable". [www.thingiverse.com]

If I had needed to adjust these, I would have sanded down the ones that were too tall. But, as it turns out, it wasn't necessary.

Edited 1 time(s). Last edit at 02/06/2013 12:07AM by Karmavore.

That's what we like to hear!!

You must admit that had a lot of layers to start with Karmavore, the heater panel can be directly sprung from the single bed like this


I am building a couple of printers at the moment so I'm thinking I will probably ditch the thumb wheel adjusters in favour of tiny M3 nyloc nuts but still retain a spring. Should be the best of both worlds.

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Richmond, New Zealand
Thingiverse ~ YouTube

Your spring setup seems neat and clean. I like it. I'm not sure exactly what I'm looking at, though. Is that a nut on what is essentially a 3mm threaded rod? That would be a nice setup to keep the bed in the place without having a machine screw head sticking up into your print area. And are you printing directly on the PCB? And thumb wheel adjusters, what are those?

For those that visit this thread working on their first Mendel, my advice would be this:

Build your printer without the bed-leveling difficulty the springs introduce. They provide flexibility, sure, but they come with drawbacks and frustrations you don't want to deal with when first starting out. Give them a whirl as a possible future enhancement, if you like. But don't be afraid to hit "Print" for the first time without them.

All that said, I haven't really given my springless printer a chance to really frustrate me yet. We'll see how it goes. But so far, so good.

Thumbwheels are like these: [www.thingiverse.com]

The photo I used above is using the Panucatt Helios heated bed which is power hungry but nice and thick and dead flat. On top of it I use a sheet of 3mm thick glass and print straight on that. The Helios bed comes with 4 x countersunk M3 machine screws and the heater is 3mm thick so the countersink hides the head. This is great and meand you can put a larger sheet of glass on and theoretically print over 8" square.

All of my other printers have used the Prusa type heated beds that I bought from Makerfarm and done exactly the same ie glass on the heated bed spring straight off the x-carriage.

Edited 1 time(s). Last edit at 02/07/2013 12:28AM by Wired1.

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Richmond, New Zealand
Thingiverse ~ YouTube

You mentioned your battle against warping ABS. I use a Stratasys Fortus and Dimension Elite FDM printer and they both are fully enclosed heated ovens essentially. Would we have better luck printing ABS if we built temp controlled enclosures around our Mendels? I plan to try as soon as my Mendel is reliable with PLA.

ben1272 Wrote:
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> You mentioned your battle against warping ABS.

Indeed I did. That's a topic that could launch 1,000 other posts, and I'll let it. A temperature-controlled enclosure is on my list of future enhancements. If you start this before I do, please keep us posted regarding your experience. (Another thought: Doesn't a Mendel90 have a good 1/3rd of the enclosure already built?)

That said, the effort to level the bed has improved my prints. Yesterday, I got my best motor x-end yet, and I did it without a brim. I'm pleased, but not yet satisfied.

Hi,
You might want to do something like I have done.
I used aluminium 3mm thick for both the top and bottom plates and clipped a sheet of 3mm glass to the top plate to print on. I didn't use springs because I had issues with them in the past, so I made some silicone rubber donuts that still allowed me to level the bed, but were very rigid compared to springs.
I have a build site that shows the whole of the machine, including the beds. You might get some ideas from there?

URL is [www.regpye.com.au]

Hope it helps you some.
Cheers

Regpye: I can endorse what you've done. Your website has some nice pics of a sweet build. I'm setting build plate issues aside for a while, but it's surely no fluke that the spring-free are doing so well. Mine sounds much like yours, except I've got a PCB heated bed. 3mm Aluminum, heated bed, clipped glass, kapton tape.