Can I get some help in getting up to speed with DLP printing? What is one looking for in choosing a DLP projector? What’re some good resources others have found in regards to DLP 3D printers? Is it just me or does it not seem like there is a central/reputable source for this kind of info?
Obviously, the projector resolution will directly translate to X/Y print resolution for a given build area (you can move the projector closer to get finer detail, within limits, at the cost of build area). There are probably certain throw angles that are better than others too.
Really, I just want to reply so that I get notifications of future replies.
I’m glad you replied, now maybe more people will pay attention to my post :p.
I figure resolution is one key aspect, but it seems from what I’ve come across the lumens is most important…followed by native resolution and contrast, etc.
But is it safe to go as far as as long as you have a DLP projector, it’ll “work”? For focusing, does one need a secondary lense or does moving the projector and built in focusing do the trick?
And is it as “easy” as it seems? Z stage and a projector below or on top? Glass vat, with some sort of anti-stick coating? Sorry, really interested in building one, but finding so little info on the fine details of things. Kinda frustrating…
Actually, I think contrast isn’t terribly important. If you calibrate it properly, even the lowest-contrast DLP projector should have plenty of contrast to solidify some areas while avoiding solidifying others. What you do want is good light-dark separation (edges don’t bleed), which (as I understand it) is something that DLP is inherently good at.
Lumens is important if you’re using the stock bulb, but I remember hearing talk about replacing that with a more UV-specific light source (this was early-on, before anyone had actually built one, so it may have turned out to be unnecessary). Of course, if you’re using resin that cures with visible light, you definitely want to use the original bulb and get a high-lumen one.
IIRC, the B9Creator does use modifications to the optics, though it may be as simple as removing a lens (in addition to the color wheel). You definitely want the projector on the bottom, and you’ll need some way to break the suction of the cured layer against the bottom of the vat and allow resin to coat the bottom. B9 moves the vat to the side between layers, though I’ve been thinking about using a continuously rotating vat with etched channels break the suction and pull resin in.
BTW, B9 is “open source”, though I don’t know if that encompasses well-laid-out instructions for self-sourcing, modifying and building everything needed, just design files for cutting the enclosure, or something in between.
interested in hearing more.
Hm, bottom up, rather than top down? I would would have thought z platform slowly sinking into a vat and selectively curing a layer of liquid just covering the object, just like with SLS etc.
I can’t imagine lifting a (large, flat) object off a glass tank bottom it’s been cured right onto several hundred times an object is going to be a fun engineering problem to solve.
I’ve overheard conversations that building from the bottom of the tank is a big fat pain in the ass. What happens is that these resins are basically adhesive. Every time you cure a layer at the bottom of a clear tank, you’re basically gluing it to the bottom of the tank. You’ve got to be able to lift that part off the bottom, ensuring that none of your gantry flexes as it pops off of the bottom. The benefit that it does have, is that much less resin is required in the tank.
The other method, is a meshed floor that is allowed to sink into the vat, being exposed from the top. This requires a bunch of resin in the resivoir, but has the benefit that you aren’t putting stress on your Z axis. The depth of the tank is what determines your maximum build area, unlike the bottom up approach which could have a much higher build area and require less cleaning afterwards.
Do they make “clear” teflon? I would think if there were such a thing as clear teflon coated glass, you could get away with the first method easiest.
The problem with top down building is calibrating the focus to the top of a probably variable volume (matters how much resin is in the vat) and you have to fill the entire vat to do a build. That gets expensive.
with bottom up, you only have to have enough resin in the vat to account for your build volume and to make sure the bottom is covered.
Keeping the surface at the right focus height is a huge potential problem with putting the projector on top. You also have to make sure that the surface is flat. I understand that most resins are pretty viscous, and you will have to wait for it to flow over the surface when you lower the object and even out, while the glass-bottom approach always gives you a smooth surface in the same place.
Also, if you sink the print into a full vat, your interior hollow spaces will be filled with liquid resin. If you use lift the print from a shallow vat (so that the already printed parts are in air), you can lift it enough between layers to let the resin drain out and be replaced with air, so that you can have sealed air pockets inside your print if you want.
So will any DLP projector do?
I’m using a Vivatek D535 in my prototype, with the lens assembly shifted forward by 3mm from the DLP array housing to modify it for close focus. This is a reversible mod but it does destroy the projector for infinity focus - essentially you are giving the projector miopia. You need to do this to get the lumen density up and to get the resolutions needed out of the projector.
I have not really touched my prototype for a while, been busy working on the upcoming OpenBeam deltabot kickstarter. 
@Terence_Tam I was hoping to not have to use a $600 projector. I know B9 uses it too, and it would be a good place to start.
Any further input/thoughts on what one is looking for in a DLP projector?
That’s pretty much what stalled me from working on one. It’s easier to swallow the costs of self-sourcing a machine when the individual components are less expensive. Same reason I abandoned the idea of self-sourcing a laser cutter.
I picked mine up off Amazon refurbished - paid about $350 for it. 
@Anderson_Ta I wrote up my experiences with my DLP printer last year here: http://garyhodgson.com/reprap/2012/06/dlp-resin-printer/ I think most of it is still relevant. Btw, my projector was €170 on ebay.
The biggest resource on the topic seems to be this yahoo group: http://tech.groups.yahoo.com/group/diy_3d_printing_and_fabrication/ There’s a lot of info there if you can wade through it. Definitely worth joining to look at the prints people have made.
There is also discussions about the pros and cons of bottom-up vs top-down, the key points have already been mentioned in this thread.
Feel free to fire any questions you have at me.
@ThantiK - there is clean teflon (see links below) which come in a range of thicknesses. I have tried the 0.025mm, but it tends to rip , so I now have some of the 0.127mm waiting for me to rebuild the machine before I can test it.
http://uk.rs-online.com/web/c/?searchTerm=ptfe+film&sra=oss&r=t
http://docs-europe.electrocomponents.com/webdocs/065a/0900766b8065a8bd.pdf
@Gary_Hodgson Wow, good stuff there. Have you stopped working on the DLP stuff?
I’ve bought most of the major components, projector and extrusions. Still not sure what to do about the vat and the print adhesion issues.
Does anyone know how the Form1 deals with this? I know it has a tilt mechanism built in, but do they have special coating on their vat too?
@Anderson_Ta I haven’t stopped, more that it’s on hold whilst other things happen
Haven’t heard anything about how the Form1 works i’m afraid.
@Gary_Hodgson looks like you got away without having a tilt mechanism in your build, is it something you think is necessary?
A tilt mechanism was always on my “do it when I know it generally works” list - and so I do think it is necessary. Relying on the Z axis to pull up the model resulted in parts often being stuck to the vat floor, and then subsequent exposures welds it to the floor making it hard to get off, particularly without ripping the teflon film that I was using.
One of the advantages of a top-down approach is that you see the progress of the print at every layer, rather than having to peer through the resin and gauge whether the part has detached. (and of course this is even harder once you add pigment to control the layer height!)