DLP Projector printer concept

I have been following the DLP Resin printer development with interest, particularly Gary Hodgson et al.

Gary Hodgson Website

One thing I have noticed is that they all seem to mount the projector below and build the part hanging from the build surface. It is also difficult to overcome the stiction of the new layer from the glass. Would it be possible to invert the machine and produce it the other way up in a bath of fluid. See the following image.



The part is shown in red, the projector in yellow. A glass bottomed box attached to the projector is slid across the part say 0.2mm above and then exposed. as shown below.



The projector then slides off (or indeed tilted off) and slides back. The projector/ box rises or the tank lowers for the next layer.

At the end of the process the tank is drained etc. to expose the part.

Ok the projector has to move (or the tank which is heavy), but this seems to me a more simple way to do things than hanging a part upside down. It also has the additional benefit of giving a good sliding squeeze to the fresh layer of photopolymer. The projector is also high and out of the way of any leakage of polymer resin.

Edited 2 time(s). Last edit at 07/03/2012 10:19AM by martinprice2004.

You might be interested by some effort already done on that idea : [www.kickstarter.com]

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

DeuxVis Wrote:
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> You might be interested by some effort already
> done on that idea :
> [www.kickstarter.com]-
> source-3d-dlp-printer


no thats not how that one works, its just it has a top projector.

ah oops sorry didn't get enough into details.

What's the interest of the lateral movement of the projector and box in your design ? Couldn't you just raise it (or lower the tank) on each layer ?

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

@DeuxVis - the main problem is vacuum force created between the part and the vat floor. The secondary problem is the adhesive force of the resin itself. To overcome the latter it's usual to use a "resin-phobic" material - I use a PTFE film for example, others have had success with a transparent silicone. The vacuum force is usually overcome by tilting or sliding the part from the floor. I have been able to produce a couple of test pieces by pulling directly up (because they are quite small parts), but you notice the part "sticking" to the floor and it wouldn't work for larger parts.

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net

@Martin - It's an interesting solution. My concern would be having to move the vat (or projector) around, as you already point out. There's also the fact you would have to be sure your movements are precise when returning for the next layer. Plus the vat draining and refilling part would need some thinking about - it's quite nice on my setup at the moment that the part lifts up and can be removed without having to empty the vat. You'd also still need some material on the glass-bottomed box to stop adhesion of the part.

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net

thanks Gary, got it.

Looks like the kickstarter project I linked does nothing to address that issue - can't be sure as there's no video or pictures of it actually printing.

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

As for the tilt and slide off there are several mechanisms that could simplify this such as the Jansen or Klann meaning that you would only need a linear X axis to acomplish a "peel back" and slide.

How about a twist to release the part. The vat could be circular and the Vat Z axis on a lead screw, raising to the next layer would naturally twist the glass off the part? You could rotate the projected image to take care of the part rotation.

What viscosity is this resin, water, milk, treacle! and how do you handle it, in the dark, or is it stable in daylight until bombarded with UV? Could you just fish the part out without draining the tank?

> What viscosity is this resin, water, milk, treacle! and how do you handle it, in the dark, or is it stable in daylight until bombarded with UV? Could you just fish the part out without draining the tank?

The resin I got from spotamaterials has low viscosity - higher than water though. I can't think of a similar liquid at the moment. It seems quite stable in daylight, but hardens immediately in direct sunlight. I usually shutter my workroom whilst working with it, and keep the resin, tools and such in lightproof boxes most of the time. The B9Creator appears to use tinted plexiglass (or similar) to keep the UV light from the build area.

Fishing out the part wouldn't be too difficult if the vat floor has a suitable resin-phobic covering.

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garyhodgson.com/reprap | reprap.development-tracker.info | thingtracker.net