Monday, January 6, 2014

For your viewing pleasure

In case you are interested and have about 8 minutes to kill, here is a video I shot while the Dalek was printing. I have a float on a lever in the resin tray (on the left side) that blocks an opto interrupter. Every 10 layers the printer checks the sensor and if it is unblocked it triggers a relay that turns on a fish tank air pump. Air is pumped into the resin jar and forces resin up the tube to the vat. the hissing sound is a pressure relief valve (a small hole in the cap) on the jar. Without it the resin kept flowing for quite a while after the pump stopped. You can see I eliminated the power tilt and went with a passive design. The tray is hinged on one side and allowed to lift and fall back by itself. The thud is the sound of the tray dropping back down. Interestingly, You see that after the first few layers there is almost no movement of the tray. Once the build platform gets some distance from the floor it doesn't have the suction when it lifts. Exposures with small surface areas release so easily that the tray often doesn't lift at all. Unfortunately that also makes it difficult to tell if there has been a printing failure, such as the part separating from the build platform. I changed the front of the resin tray to clear so I could spot a failure before it made a big permanent blob and ruins the Sylgard.

The first couple layers get a longer exposure (about 9 seconds) to stick it to the build plate. After that the exposure is 5.5 seconds per layer. The Z axis lift is also higher for the first few layers. I found that after about 5 layers I only had to lift about 1/8". That helped cut some time off the total print run.

 I also changed the vat floor. My first floor was a piece of 1/4" Plexiglas with a Sylgard 184 coating. I have since switched to regular double thick glass. Nothing special just plain glass. By using glass I can heat cure the sylgard in a toaster oven in about 40 minutes instead of waiting 24 hours for it to cure at room temp. I made the Sylgard layer a little thicker and so far it has held up well, 5 or 6 prints with no noticeable degradation. Also added is a red plexiglas filter/shutter that blocks the lens before and after printing to eliminate accidental exposure during set up and clean up. you can hear it being moved out of the way just before the projector comes on the first time.


  1. John, Interesting way to peel the cured layer from the bottom of the resin vat. It is so simple, I wonder why people still use a stepper motor to activate the tilt on the resin bath. Is your method dependent on the formulation of resin and pigment? Does it matter if the area of the print is thin-walled versus solid cross section? Are you using any special coating or film to aid in the cured-layer release? I've not seen anyone else design their release system in this manner. Thanks for your comments. Walt

  2. Thanks Walt. I know, It almost seems too simple. If you read back you see that I started with the intention of using a motorized tilt but I ran into some problems with it binding (It probably wasn't the best design). Anyway, I got to thinking, why am I tilting the vat and raising the platform when I can accomplish the same thing with only one axis of movement? It lowers the mechanical complexity of the build and you only need one axis and all the associated electronics. The amount the vat lifts is related to the surface area of the cross section. in the video you can see the first few layers lift much higher than later ones because the build platform starts almost touching the vat. Later layers with smaller cross sections barely lift at all. I'll explain some more in my next post.

  3. What a great idea, I'll have to try adding a passive tilt to my printer! Also, what are you using for the build plate?

    1. For now , I'm using a 1/4" aluminum plate. it's probably overkill. I could have used a thinner one. I scuffed the surface with some sandpaper and it seems to work fairly well. I have to be careful with large bases as the resin shrinkage wants to pull and cause it to detach. I'm thinking of changing the platform to a perforated sheet on standoffs. The platform as it is displaces too much resin when it is close to the bottom of the vat.

  4. Hello John Tyson
    I've been reading your blog as reliable documents to make DLP 3D printer.
    Your work is awesome and I'm appreciate you're sharing such valuable documents.

    I'd like to ask you are you using peristaltic pump to supply UV resin to vat with tube?

    1. Thank you, A peristaltic pump is on my list of future upgrades. For now I have a sealed bottle that I put the resin in. I pump air in with an aquarium air pump. The resin is displaced out the tube to the vat. I had to add a small hole to bleed the pressure from the bottle because the resin would keep flowing after the air pump turned off. It works but I think the peristaltic pump would be better.It could be run in reverse to put the resin back in the bottle.

    2. Thank you for your reply.
      I've never had that idea using air pump. It's easy and can reasonable idea.
      I'm actually designing DLP printer as my first challenge now and will use home made peristaltic pump to supply liquid.
      I've already built FDM printer.
      There are some nice peristaltic pump reference in
      Thank you.