Simple, adjustable, printable bottoms-up build platform

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mhackney
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Simple, adjustable, printable bottoms-up build platform

Postby mhackney » Thu Feb 19, 2015 5:52 pm

Now that I have my stock DropLit working I'm turning my attention to improvements and updates. First up, the stock machine has a 1" diameter build platform:

Image

That kind of limits what one can print! It also is very difficult to adjust for any tilt. Mine, in fact, was about .08mm to high on one side and I have to use paper shims to bring it parallel to my vat surface. So after noodling on the problem(s) I came up with this printed in lovely purple PLA on a Rostock Max delta printer:

Image

It has a 64mm x 48mm x 2mm aluminum plate for the build platform. This is basically the full size for the image through the round window in the DropLit base (you can see under the petri dish). This aluminum plate is mounted to an 8mm thick block to provide a little displacement protection to the mechanism (I'm updating the design with a skirt to further protect it. This printed block can be swapped for any size build plate. It is attached to the actual mechanism that you see. The mechanism is basically 3 universal joints spaced at 120°. They can swivel around their hinge points. These are Traxxis RC car universals. Many delta printers use them for the joints on the delta arms. These universals pass through holes in the upper mounting piece. Each of the 3 arms in the mount has a thumbscrew to securely hold the joint in place. A spring on each joint keeps downward pressure on the platform assembly. The cap screws and washers on the top are to prevent the device from spontaneously exploding. This trident part is then attached to the printer carriage in some way. For my DropLit, it is simply a shorter version of the original aluminum dumbbell but printed in PLA.

In use, you loosen all 3 thumbscrews then jog the platform down to your print surface. Once it makes contact, you jog down in .1mm steps until all 3 springs have just a bit of compression. These insures that the aluminum plate and bed surface are parallel. Tighten up the thumbscrews to lock the universals in place and it is rigid and ready to go.

I've made 2 prints so far, much larger than what I could do with the stock build platform.

Next up is a a flex vat with FEP. I got .001, .002 and .005" FEP film from McMaster to experiment with. I've designed a printable vat with stretcher. The prototype looks like it should work fine, I have a few things I want to change so I'm tweaking it and will print another. Photos to come.

cheers,
Michael

mhackney
Posts: 18
Joined: Sun Feb 15, 2015 9:27 pm
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Re: Simple, adjustable, printable bottoms-up build platform

Postby mhackney » Thu Feb 19, 2015 5:56 pm

One thing I noticed, with the larger aluminum plate in contact with the PMDS and a thin film of resin between them, it takes a lot of force simply to separate these parts. Is this normal? Does that happen with the flex vat? I attempted to print a chess rook with a 25 mm base. The first 1.5mm went down fine but then the part stuck to my PMDS and separated cleanly from the aluminum build plate. Being new at this, I have some questions...

How should I prepare the aluminum? Should it be etched, sanded, scotchbrited? I used fine scrotchbright.

What sort of retract speed should I try? Is it best to go fast and "snap" the part free or go slow and pry it off? I'm printing with MJ G+ resin.

What else do I need to know when printing larger surface area bases?

thanks,
Michael

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PomeroyB
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Re: Simple, adjustable, printable bottoms-up build platform

Postby PomeroyB » Thu Feb 19, 2015 6:34 pm


mhackney
Posts: 18
Joined: Sun Feb 15, 2015 9:27 pm
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Re: Simple, adjustable, printable bottoms-up build platform

Postby mhackney » Thu Feb 19, 2015 6:35 pm

Great, thanks for the info!

Kvetak241
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Re: Simple, adjustable, printable bottoms-up build platform

Postby Kvetak241 » Sun Mar 22, 2015 4:49 am

Your alu block doesnt "stick" to your PDMS, the space between is just flooded in really thin layer of viscose resin and while going up, the growing space needs to be reflood, while resin have still just a little space to flow here.. so, in this case, you are fighting just hydromechanic, and while no surface can bond or flex to make it easier, you will need to use some force. Good news, this hydromechanic forces fade away around 0.5mm, so its an issue for just few first layers, and have no influence on print quality (until they move your build platform or so).

The aluminium must be as rough as possible.. resin just need some edge to stick, for me, sandpaper n. 60 did the job.. i also considered steel wool or sandpaper 180 (and higher) unusable, but i am using PDMD coating, flex vats may need less force so less rougness may be ok in this case.

My problem now is decreasing "nonstick" properties of PDMS during printing. At the start, i could not notice any force but after few cm (.075mm layer) it sticks too much that print is riping of my PDMS coating


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