Mini Longworth Chuck for a lathe with M33 spindle.

The model is a 200 mm diameter (so it fits on your MK3 and MK4 printer) Longworth type chuck. Included models are base adapter plate, front plate with fitting ring, M5 slider nuts and M5 buffer cores. In compression it can hold bowls up to 150 mm diameter. I have not measured expansion capacity but think of 180 mm inner diameter, leaving a 10 mm ring for support of the bowl. 
The adapter plate has an M33 pickup and a nut for a Euro ASR. I think this is a requirement. Plastics, and is PETG no exception, have a high temperature expansion coefficient and even if the fit on the M33 pickup is tight in normal conditions, the friction may become low in a warm environment. I therefore suggest you consider use an ASR. Grub screws easily damage your drive stock and do not go wel, with plastics anyway. An ASR spreads the load evenly and that's what you need for plastics. 
If there is a need for this model with another thread, like 1"x8, let me know and will see if I can provide. 
The cores of the bumpers and the nuts have a notch that prevents them from rotating. I assume, but I have not tried, you can mount them with the notch on the other side to support mounting on expansion.  

In addition to the printed parts you will need you will need 6 pcs of M5 screws of at least 30 mm length. I used nylon screws like these so there is no heavy steel parts being swung around. I contemplated printing the screws from nylon but they are ready available in the hardware store so why take the hassle.  
You also will need some rubbery material for the buffers. I contemplated printing them from flex material like TPE but that material has a low friction coefficient. I used self adhesive rubber tape, but with moderate success. The rubber of the strips offers great friction resistance but the strips peel loose from the bumpers. I may need to use another adhesive. I am also looking at soft silicone tube now, and a different shape for the buffer core. The buffers are a point of improvement.  When I have new designs are available they will be shared. 

I made this chuck for final finish of the bottom of small bowls, dishes etc. For safety I use at low rpm only and I use a backup live center whenever practicable. I use a center with a blunt nose that spreads the load and will not damage my bowl. I do not put load on that live center. It is there just for back-up in case the bowl gets loose somehow. 

I printed my copy of the base plate, the front plate and the nut from Prusament PETG. Ample perimeters and bottom layers, obviously, for they make the stiffness of the piece. I used 0.4 mm nozzle and 0.2 mm layers. 
The slider nuts and buffer cores I printed from Fiberlogy ASA. For the nuts I used a 0.3 mm nozzle and 0.125 mm layer thickness. Detail was needed because the slider nuts have M5 thread inside.  I found the thread may require a little cleaning up with a hand tap to remove elephant's foot and seam.    

Assembly of the chuck is self-explanatory. The fitting ring goes into the front plate. For me it snapped in snugly. If your print needs glue to hold it be careful not to use too much of it.  

The total cost of my (prototype) copy was about EURO 15 in total. Euro 10 approx. for the filament and EURO 4,80 for the bolts. 

If you make one, use it with care and on your own risk. And of course: enjoy woodturning.