Ever since I started experimenting with my UP! 3D Printer, I have had issues with part warping. The warping is especially bad when the parts are made with solid fill and take up a lot of room on the build platform. I was getting pretty good results using Kapton tape alone, but when a new and difficult part came around it wasn't cutting it anymore.
I found TechShopJim's great instructable here: https://www.instructables.com/id/100-Warp-Free-Make... about how to make an ABS slurry to help parts stick to the platform. This worked pretty well for me, but I had trouble with applying a thin layer and with storage of the slurry. This instructable details a similar technique that gives me a little better results with less effort, and an additional step to really help warp proof your printer.
Here is what you need to get started:
-Kapton tape (this method might also work with masking tape, but I haven't tried)
-Small squeeze bottle (http://www.mcmaster.com/#1902t14/=pmfznz)
-Scrap ABS part
-Optional: cardboard and tape for draft shield
Step 1: Fill Squeeze Bottle With Acetone
Fill the squeeze bottle with dispensing tip with acetone. This will make it easier to apply only what is needed and prevent making a mess. In a pinch, you could probably get away without using the squeeze bottle and just very carefully pouring, but acetone always seems to pour out a little faster than I want.
Step 2: Squirt a Small Puddle of Acetone on the Build Platform
Use the bottle to squirt a small puddle of acetone on the build platform. About a teaspoon of liquid should be enough. Make sure that the platform hasn't started pre-heating, or the acetone will evaporate right away.
Step 3: Rub Scrap ABS on Platform
Take the scrap ABS part and use it to spread the acetone around the platform. It is a little easier to do this if the part has a flat side.
While you are spreading the acetone, a small amount of the scrap part will be dissolving. This is what we are going for: to dissolve a small amount of the ABS part and deposit that as a thin layer on the build platform. You only need to spread this around in the area where you will be building your part.
Step 4: Preheat the Build Platform
Now that there is a thin layer of ABS on the platform for our part to stick to, we need to preheat the platform before building. Preheating the platform will help insure that the first layer sticks well. I think that a large part of the reason that this helps is that the hot platform prevents the first layer of plastic from shrinking. If the first layer shrinks, then it will stop sticking to the platform and lift up.
Whatever the exact reason, preheating the platform really helps. I usually leave it on for about 10 minutes before I print.
Step 5: Print Part and Remove It From the Platform
Using this method, I find it best to print without a raft. The parts stick well without it and it saves time.
Another option that helps reduce warp is interior part fill. The looser this is, the less risk of warping.
Finally, after the part has printed, it is time to remove from the platform. The parts usually stick so well after the acetone + ABS combo on the platform that this can be a challenge. I have good results with working an exacto knife blade under one corner of the part until it pops off. Another trick that helps is to let the platform fully cool down before part removal (but I usually don't have the patience!)
Step 6: BONUS ROUND: Make an Enclosure for Your Printer
At work, I also have access to a Stratasys FDM machine. The parts produced by this machine almost never warp, and I think a large part of this success comes from the heated build area (I believe a patented feature). Instead of heating just the platform, the Stratasys printer heats the entire enclosure to 100 C. I think this reduces the temperature differential in the part from the material being deposited by the head and the material that has already been laid down by the printer.
I tried to approximate this heated build area by building a cardboard enclosure around my UP! printer. The temperature inside gets quite a bit hotter than the surrounding air, and it seems to help.