Change in F2 Chamber temp to 35 deg C

Have just noticed that my F2 chamber temp set point has changed from 31 deg C to 35 deg C. Any one else noticed?

I know that the new F3 chamber runs at 35 deg C but I had not made any changes.

Not a problem to me, as I had moded chamber with a heater to run at 37 deg C through controlled trials to enable the viscosity of clear resin to reduce and so drip off support structures more readily and not pool at tips of support structure. I print v thin membrane structures (thinnest measured at 110 to 120 microns).

Will run at 35 deg C with no mod running to see if any better,

I only use heater for clear resin. Not such a problem with model resin.

Any one else noticed?

Yes I noticed - the adhesion to the build plate is significantly better with the extra temp

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Is this introduced in the firmware from May 21st or is there a new one(as you discovered it just now)?
Don’t see another one on the site.

The firmware on mine is rc119-25-75 dated 14th May 2019. That was installed just a few days ago. Preform is 3.0.0

Thanks Dxxxx, will look out for adhesion to build plate change, though I have not had any issues. to date. So if adhesion is better I may have a tough job getting jobs off!

The firmware on mine is rc-1.19.12-75 (14 May 2019) Did not intentionally update recently. Preform is 3.0.1

Project still printing so no comparison yet

Which material are you using? Typically, the print will start (early) at 31ºC, but the set point is 35ºC.

Hi Craig,
Presently using CLEAR V4. Last job “seemed” harder to get off, But that is a perception that would have been coloured by Dxxxx saying that build plate adhesion is higher!

Are there any other subtle affects from this temp change? I am having to push our boundaries as we print thin membranes and small v thin walled cavities.

Last print was an experiment (sample of 3)using default Preform alignment and supports, Running again today using 3 different orientations including repeating yesterdays run(3 samples of each).

Not all resin drained out of cavities of first run, so experimenting with orientation and forced drainage prior to washing. Orientation was not optimal.

I don’t see anything about heater settings changes in the release notes. Having said that, I wouldn’t expect much difference in first layer adhesion from start at 31ºC to 35ºC. In both cases, the build platform starts at room temperature—at least for the Form 2.

I treat auto-orient as a useful guide but not a holy grail. It sounds like you’re honing in on the right orientation for your part.

Hi Craig, As a general rule of thumb, the resin will be more reactive (to UV polymerisation) at 31 - 35c than at 20 - 22c (most peoples room temperature) As the temperature increases he resin viscosity will be lower and the cure will be faster per unit of UV energy applied, hence why people are at a disadvantage using “Open” mode - of course “Open” mode disables the heating system.

The greater reactivity results in greater adhesion to the build plate (assuming the power / exposure time does not get increased when the temperature decreases)

Your observations about the build plate not be heated are spot on - first and foremost the resin is heated through conduction through the poly carbonate tank rather than through air convection in the build chamber, In fact its normally a disadvantage with photo polymerised resins to have a heated build plate for the first layer, ideally it needs to be cooler than the resin temperature to get best adhesion of the first layer (the exact opposite of the FDM type printing process).

To give you some examples in the differences of reactivity at different temperatures of a clear resin (Formlabs Clear v4) we did some spot exposure tests to see what depth of resin cured for a given amount of UV exposure energy.

A focused spot beam of 15mm diameter was projected onto a sample of resin in a test fixture (the sample was in a 15mm diameter cylinder whch contained 10ml of uncured resin). To eliminate the effects of oxygen inhibition the sample was exposed with an inert gas shield present (nitrogen). The resin was exposed to a 5 second burst of UV energy at 405nm with a power of 5mw/cm2. The resultant thickness of cure was as shown below:

20c - 97um cured thickness
25c - 112um cured thickness
31c - 146um cured thickness
35c - 165um cured thickness

As you can see the resin is more reactive as the temperature increases.

Similar trials were done with an adhesion test sample at different temperatures, the test rig allows a 10mm diameter of resin x 200um thickness to be exposed with one face of the test rig being attached to a fixture to allow measurement of tensile force applied to separate the exposed test piece from an aluminium surface (that has been sand blasted to a 32um surface finish)

I understand that the design of the test fixture and the actual measured results are commercially sensitive, therefore the actual measurements are not published here, its sufficient to say that the tensile adhesion force (to an aluminium build plate) of a material printed at 20c is approximately 20% less than one printed at 31c, and 26% less than one printed at 35c.

Hi Dxxxx.

Nice bit of investigative work and thanks for sharing what you can. The bit I was interested in was the relative cured thickness of CLEAR V4 under your controlled experiments. Goes a long way to explain why I am having problems with printing complex cavities.

For these small cavities we have superb results using MODEL V2 at 37deg C by warming the chamber using an auxilary air heater… We ran some trials today at the new 35 deg C regime with no auxilary heating (though our local heatwave in London this may skew those results!) and the results looked good under x 10 mag. Will know more when we section and polish trials.

One minor drawback of the MODEL V2 is that it is opaque and it would be useful to print cavities in CLEAR that we know that they are clear of uncured resin.

We have been running trials of CLEAR V4 at the elevated temp of 35 deg C. Our line of thinking was to reduce the resin viscosity and thus its surface tension to enable our small cavities to drain more efficiently. We had not considered the affects of elevated temperature on the relative increase in cure depth due to increased reactivity! This with the light energy being refracted through the clear cured resin causes resin that should not be cured to be cured. We are probably pushing our expectations too high. (Maybe justification for the F3)

Sounds like more controlled experiments required to hit the sweet spot. Hopefully there will not be much batch to batch variation in the resins.

Thanks again for your feedback.