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Build Your Own SLA/SLS • Parts not sticking to build plate with vat and FTD black
Page 1 of 2

Parts not sticking to build plate with vat and FTD black

Posted: Sat Mar 04, 2017 10:07 am
by jon_bondy
I switched from Vorex and petri dishes to FTD black and a vat. The FTD is not sticking to the build plate as aggressively as the Vorex did, which is a mixed blessing. Easy to get parts off the build plate, but ...

Recently, most of the parts end up stuck to the bottom of the vat. They are mostly well formed, so this did not happen quickly: it happened toward the end of the print cycle (in this case, about 15 minutes, with 100 micron layers). I have sanded the build plate repeatedly, but that has not helped.

Any thoughts?

Thanks!

Jon

Re: Parts not sticking to build plate with vat and FTD black

Posted: Sat Mar 04, 2017 2:41 pm
by HTL
If you are using a FEP based flexvat:

Make sure the FEP film is tensioned so that it is rigid.

The build plate should be adjusted so that at the build plates zero height the build plate is laying flat on the FEP film. Do not try to make a gap between the FEP film and the build plate, the build plate should be lightly touching the FEP film.

the first three or four exposures should be 30 to 60 SECONDS the rest of your exposures should be your normal exposure. The long exposures will not harm the FEP film as long as you do not have a thick layer of resin between the film and the build plate. Starting your build with the build plate touching the FEP film ensures that the "attachment layers are thin, thick layers may not cure deep enough to attach to the build plate or each other, thick layers also heat up too much and can damage the film).

If your model still does not stick to the build plate your resin may be over pigmented, resin pigment controls the thickness a layer exposure can cure (the higher the pigment concentration the thinner the possible layer thickness even with long exposures), exposure controls the hardness of the cure.

HTL

Re: Parts not sticking to build plate with vat and FTD black

Posted: Mon Mar 06, 2017 9:32 am
by jon_bondy
Thanks for the advice.

When I push the build plate all the way down, I can see it clearly through the vat film, from below. I increased the exposure for the 1st 3 layers to 45 seconds. I still find a half-height part stuck to the vat at the end of the print. It seems that the part stays stuck to the build plate for about half of the time, and then the vat grabs the part from the build plate. I sanded the build plate recently (within the last 3-4 print attempts).

Could the film be TOO tight, so that if the surface area of a particular layer is larger than the surface area of the initial 3 layers, the vat film cannot release from the print slowly, across the print? I thought that one benefit of the vat was that the part would release almost like a tilting mechanism, but if the film is very tight, could this be failing?

What should I try next, please?

Jon

Re: Parts not sticking to build plate with vat and FTD black

Posted: Mon Mar 06, 2017 12:43 pm
by goopyplastic
If you are printing the parts I saw earlier, they have a mushroom flare partway through?
Generally you want the base layers to have more surface area than any horizontal section on the model, with some room to spare. I suspect that the parts are giving up the ghost on the build plate when the it starts printing the larger feature and the sticking forces from the film exceed that of the build plate. FEP also gets damaged / roughened over time so will stick more and more, parts that have printed fine might start to fail.

I would try adding a support base in creation workshop and re-printing as a troubleshooting step even if you goal is to not have that support element.For resins that have a harder time sticking, we can use perforated build plates, or sacrificial build plates of acrylic etc.

Re: Parts not sticking to build plate with vat and FTD black

Posted: Mon Mar 06, 2017 2:08 pm
by jon_bondy
I tried auto-support generation in CW, but the support bases merge with the part, and one is actually inside the part.

Can someone please remind me how to edit supports in CW? I know there is a way to select a support, delete it, move the top, and move the bottom, but I cannot figure it out for the life of me. This time I will write it down. I need to delete some and to move the bases on others.

Thanks

Jon

Re: Parts not sticking to build plate with vat and FTD black

Posted: Mon Mar 06, 2017 3:49 pm
by C3DC
Lots of good replies in this thread. This is a pretty common issue when using the flexvat.

Here are a few things that will help maximize build plate adhesion (Some have been mentioned already):

- Sand build plate with rough grit sandpaper

- Increase bottom exposure (Rule of thumb I use for flexvats is at least 10X normal exposure time)

- Use base plate in CW support menu (Far left icon)

- Slow your lift down (I personally use around 45-50 for Z bottom speed and 55-60 for Z lift speed)

- Reduce layer height. If you are printing 100 micron layers the part will pull harder on the flexvat. Try 75 micron and see if that helps

- If NONE of those give you success, the guaranteed fix is perforating your build plate.


As far as supports go this is what I would recommend for you:

1. Import part into CW

2. Move part up at least 3mm above build platform (This gives enough room for the part not to adhere to the base plate you will generate in step 4)

3. Auto-generate supports (Click ones you don't want and hit delete)

4. Hit the base plate button (Far left in support menu). It generates a plate wider than your part and also 1mm thick. I generally don't need the plate to be that thick, so I will click it and move it down .5mm (Its fine if it goes below build platform).

Re: Parts not sticking to build plate with vat and FTD black

Posted: Mon Mar 06, 2017 10:34 pm
by jon_bondy
Thanks for your advice.

I tried raising the part up and adding the supports. The print did not fail in the usual way: it was still stuck to the build plate at the end. The print was, however, crap. Inside the forest of spikes, the actual part was malformed.

Does anyone sell a perforated build plate for the LittleRP? I like the sound (and challenge) of a "guaranteed fix". I'm on a roll with failures here, so bring on that guaranteed fix!

:)

Re: Parts not sticking to build plate with vat and FTD black

Posted: Mon Mar 06, 2017 10:46 pm
by C3DC

Re: Parts not sticking to build plate with vat and FTD black

Posted: Mon Mar 06, 2017 11:12 pm
by jon_bondy
I used auto-generate, and the thing is awash with supports. I guess I'm hosed. The frustrating thing is that this exact part has printed successfully quite a few times. Now, all of a sudden, nothing works. Erratic.

Thanks again

Re: Parts not sticking to build plate with vat and FTD black

Posted: Tue Mar 07, 2017 11:20 am
by HTL
The FEP film on a flexvat really cannot be too tight, more problems are caused by the fep film not being tight enough (film sagging in the middle from the weight of the resin, insufficiently tensioned fep also does not allow the resin to squeeze out from between the build plate and fep film after the build plate drops prior to making an exposure).

One additional adjustment you might want to make is to increase the time between when the build plate drops and when the layer exposure begins, if this time is not long enough the resin will not have time to "squeeze out" from between the build plate and the fep film to the correct layer thickness (you will be exposing thick layers that do not or only weakly attach to the build plate). Since the tensioned FEP film is not a rigid plate if your layer exposure is made immediately after the build plate drops there will not be enough "squeeze out" time for the resin to settle onto a flat layer .

HTL