Bending the chair legs

A few things became apparent after the test bend.

Firstly that bending around the frame one curve at a time limits the amount of material flow. Next time I need to try bending from the top of the frame down, this will probably require more assistance but should get a better result.

Secondly at only 180 degrees the plastic is still slightly inflexible and it became quite a chore to for the pipe around the frame, using a higher heat should make the plastic more malleable.

Thirdly we allowed for overlap in the material by adding roughly an additional 20mm of pipe to our estimation; this was in fact almost all used up in the material flow at the bends.

The end result had a few minor creases in the plastic at the fold lines, but I think the changes I’m planning to make should remove them in the next attempt.

These factors were all taken on board when during the next two bends that became my chair legs.

I heated the sand up two 230 degrees this time (our ovens max setting) this meant that the pipe was much more malleable, and could be manipulated around the frame with greater ease, and the was less bunching up of the material at the corners which is what caused the creases in the previous test.  Bending the second frame required unscrewing the support braces and curves I had made and moving them out two the second set of dimensions id marked up, but other than that the process was exactly the same.

As a final touch two this process the cess material was cut away and I was left with two useable chair leg frames.

Test bend with Frame

For the first test bend using the frame I heated more sand in the oven to 180 degrees for an hour.
With aid from my father I then proceeded to pour the hot sand into the PVC pipe I was planning to bend then tapped close the open end with duck-tap. We then forced the pipe into the frame and bent it around in a clockwise fashion. at the final bend we twisted the fram allowing the over lap to run under the frame. We had to work quickly as the plastic was cooling quickly.

                                              

Bend Frame Construction

Began the mocking up my bend frame be grabbing a large piece of scrap wood from our shed, the remains of our basketball ring backboard. I marked out the inner dimensions from my construction drawings, in pencil (weirdly enough pink pencil showed up best).  After this I grabbed some pinewood for the frame, and cut down 8 pieces to fit the frame, after this I used a jigsaw to found off the edges, to approximately an 87mm radius.

Afterwards a discussion about the logistics’ of the bend I was trying to active with my father, we came to the realization (he flat out told me) that to do the bend correctly I would require the pipe to be wrap around the bending frame with overhang to allow for the material to warp and stretch but still have enough left over to comfortably form a solid shape.

As a final touch I measure out the width of the plastic pipe (32mm) then screwed in support braces to minimise distortions like I had with my first being trial, namely plastic flattening out under the stress.

Technical Drawings

These two drawings were my method for working out how large a frame I would need to make when bending pipe.

                                               

The first sketch started with a square 400mm by 400mm as my guideline, I then cut out two lengths of papers ruled straight lines down the middle of them then I aligned them to cross parallel to each other over the square. This gave me a rough estimate of the minimum size I needed to make each part. My intention was to make a chair capable of being completely flat packed. I didn’t want the chair legs to interfere with each other when closed.  So I ruled out the lengths I intended my two frames to be; 530mm and 597 mm.
This allowed me to see how my forms would match up, and how the chair would sit when unfolded.

The second sketch I drew up at this point was a 1.1 side sketch of both frames sitting inside each other. I intended to be able to go back and use this as a reference throughout the further development processes. The length measurements are the same as on the other Dimension sketch, other measurements of note are the radius’s on the curves of the frames, all of the are 87 mm.
I used Identical curve radius manly to simplify making the frames Il be bending the pipe forms around.

Bend Frame construction

Began the mocking up my bend frame be grabbing a large piece of scrap wood from our shed, the remains of our basketball ring backboard. I marked out the inner dimensions from my construction drawings, in pencil (weirdly enough pink pencil showed up best).  After this I grabbed some pinewood for the frame, and cut down 8 pieces to fit the frame, after this I used a jigsaw to found off the edges, to approximately an 87mm radius.

Afterwards a discussion about the logistics’ of the bend I was trying to active with my father, we came to the realization (he flat out told me) that to do the bend correctly I would require the pipe to be wrap around the bending frame with overhang to allow for the material to warp and stretch but still have enough left over to comfortably form a solid shape.

I cut the backboard in down about ¾ of its length, then strengthen the last 1.4 with extra pipe wood drilled in place, this would allow me the flex the frame while bending the pipe, allowing the pipe to overlap (with some on the pipe overlapping above the frame, some bellow, insuring that I could cut the pipe down and have it meet in the middle with no gaps.


As a final touch I measure out the width of the plastic pipe (32mm) then screwed in support braces to minimise distortions like I had with my first being trial, namely plastic flattening out under the stress.