Throwing large forms in sections?

[shawnhar]

Tried 3 times now and failed 3 times, lol, steep learning curve. 

Any tips or advice for throwing and joining large sections? I am either not leaving them thick enough or not letting them dry enough as they buckle and collapse at or near the joint. I can place the top piece, and go around the joint "pinching" or smoothing, but then when I try to shape it is when it fails.

These last 2 were almost leather hard and I thought that would be dry enough, they were not tacky enough to leave fingerprints, at least around the top 1/3. Do you think the tops are too thin for this task? 

The left section was 8lbs 14oz, 9 1/2" tall and the right section (top) was 8lbs.

[GEP]

Yes, your walls are too thin for a pot that size to support its own weight.

When I throw a multi-part pot, the two parts are not equal size. I try to achieve 2/3 to 3/4 of the pot's height with the bottom piece. The top piece is just the last 1/4 to 1/3 of the height. So maybe 10 lb bottom and 3 lb top. I also throw and shape the top part with more water than I usually use. I don't want to create too much drag and torque, knowing there is a weak spot at the connection point. 

[shawnhar]

Thanks! That makes sense regarding the drag, I wasn't using much water after joining as I was afraid I might water log it so was mainly just trying to rib it. I'm sure that was creating tons of drag! I will try your suggestion of the bulk of the height on the bottom piece, don't know why that never occurred to me, probably because the videos I saw were equal sections except the very top.

[oldlady]

when you get the rest right, be sure to provide a way for the two pieces to fit together.  put a v shaped groove in the bottom half and a ^ shaped lip on the top.    the photo shows both pieces have flat rims.  

[Benzine]

1 hour ago, oldlady said:

when you get the rest right, be sure to provide a way for the two pieces to fit together.  put a v shaped groove in the bottom half and a ^ shaped lip on the top.    the photo shows both pieces have flat rims.  

Interesting.  I've never done that, I just keep both top and bottom flat, and join them that way.

[shawnhar]

Do you do anything to the joint? I've been going around the seam "pinching" sort of, pushing the top down and bottom up as I go around. I like the groove idea though, might make it easier to seat the top piece evenly.

[neilestrick]

When I make large two piece forms, I leave each section much thicker than usual, like 5/8" to 3/4" thick, and I don't do any shaping, just two cylinders. I make sure the top edge of each piece is flat and free of slurry by scraping it down with a metal rib. Then I put them together, and use a rib on the outside, hand on the inside, to make sure they're lined up and stuck together. No scoring needed. In fact, if you score you'll have little air bubbles in the joint that will show. Because each piece is free of slurry, they'll stick together well. Any slurry and they'll just slide around on each other. Then I do 2-3 pulls. This gets the piece to its final thickness and begins the shaping process, as well as making the joint disappear. I can make pieces much larger and thinner this way vs. doing them in one piece. When I'm doing really big planters, I'll make a base section first, two wall sections, then add a third wall section the next day. Photos attached.

 

[shawnhar]

That is awesome!! - Thank you for such a detailed description and pics!