Hot Bed stickiness!

Another issue I occasionally come across in a large 3d print is the print suddenly losing grip and being swept off the bed by a quick moving delta head.

There are a number of reasons why prints don't "stick".

The first is simply the head not being level or z-axis wrong height, usually after changing a nozzle or hot end.  Do this before any print.  Also watch out to make sure any bed change is even.  My delta is setup to do a "4 point" test, which means it checks the center, x, y and z axis. But if I've stuck a smaller blue 3m paper sticker (see later) the surface isn't even at the edges, so I allow a couple of mm extra for "give."

Blue paper is generally good for adherence on a bigger item, however, you need to cover the whole surface for a full print. Its expensive, so other options might be attractive.

Get a surface "sticker" for the hot bed.  Mine ended up wrecked after one of my axes slipped due to a loose screw, and the nozzle gouged the surface.  Don't be like Laura: check your rod tops and bases for unlevel ends.  There are several specialist surfaces you can also buy that are inexpensive, especially if you don't have a hot end on your printer and its not something you can modify.

A borosiciliate glass pate is useful.  These give the flat bottom of a print a nice surface, and if heated, sticks nicely.  I find they range from about 10 euro up on aliexpress but watch out for any that are not level.

Finally, experiment with cooler or hotter bed temperatures.  PLA can require anything from 50c to 70c, depending on your printer.  As a last resort, another fix I have is to allow the bottom cm to "stick" and then use small pre cut pieces of masking tape to doubly secure the bottom of the print - this works especially well for tall, narrow prints that can get swept away easily by one quick move a few cm further up.
Unicorn horn designed by the Adafruit Ruiz brothers.  I found this needed the "last resort" masking tape to secure the narrow base stitching roles or the upper layers pressure was simply too high. Otherwise this is an excellent print for a delta.

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