This is an idea I had on the bus on the way home (those in the UK might recognise the First bus logo haha)- one piece extruded stools. I have spent a grand total of about an hour on this, so fire away! I’m treating it as a preliminary concept. It isn’t saving the world through design, it’s just maybe making it a bit more fun.

User = Nightclub or bar goer, or perhaps a meeting attendee. They are aren’t incredibly comfortable, so you will get up and buy more drinks, or at least you won’t fall asleep in them. They could also be used as informal or outdoors home stools.

Maybe even kindergarten?

One piece extruded Polypropylene or similar, maybe even PVC? The second shape is routed out. The little depression on the top can be heated then shaped, perhaps. In these examples, I am using only one routed rounded rectangle shape, but I think it could be cool to have different shapes for different colours, so that people would want to collect all four (or more)

Preliminary name is the silhouette chair. What do you guys think?

Photo 41.jpg

hmmm. that’s an awfully large extrusion.

yeah it is massive isn’t it. 450mm square.

I think it’s doable though, because you can get PVC pipe in that size.

Did you see the rotomolded chairs on the front page today?

yeah i did - i had the idea for the chairs on the bus on the way home, then saw those chairs soon after i got home. They are kind of in the same vein,weirdly enough.

neat idea i guess, but with all the post ops, i think your final price would be more than doing the same thing from a single shot injection or other process. Sure tooling might be expensive, but normally these sorts of things are produced in high quantity that can amortize the costs.

Plus, anything with finishing operations like routing, cutting, etc. normally has much lower surface finish quality than a straight out of the tool molded product (with a few sprues and stuff sanded off).

If you could may be make it only a single extrusion with nothing but a cut (and could cut it to different lengths (ie. chair, bench, etc.) you might have something…


Yeah I think it could be done in injection molding, i seem to have this fascination for extrusion lately…A high quantity would be easy to do, and could make it more flexible as well with regards to the ‘hole’ being in different shapes.

I could make it a single extrusion too, it’s then quite a 2d object, but could still be quite funky.

You obviously have more manufacturing experience than me: Is it prohibitively expensive to do modifcications after extrusion? Things like heating it for a little seat depression or routing it for the hole.

Also someone suggested to me to make them nest…could be cool.

are those dished on the tops?

single piece steel, perhaps, though maybe heavy, spot welded overlapping seam at the bottom, flanged and hemmed around the perimeter for volume and strength.

maybe aluminum, too. that would look pretty hot as polished aluminum, or even powdercoated. it would need some sheetmetal work for rigidity.

thermo-formed sheet plastic?

I’m not that experienced with extrusion per se, but the general principle of any manufacturing method is normally that as much should be done in the tool as possible, avoiding anything that needs to be done after the fact, post op. Biggest thing here is the labor costs. By all means, if someone knows better, please correct me.

Look at it this way- there’s a reason that those cheap-o plastic lawn chairs are injection molded and can be sold for $10. They pop out of the mold and are done! As soon as you get into assembly, finishing, etc. you need (for the most part, people). Even if it took only 15 minutes to heat and rout a part of it, the guy on the line is likely being paid at least $10 and hour, so all of a sudden, you’ve added $2.50 to the cost of the chair, which alone translates to something like $10 at retail.

The key to any manufacturing process is finding what you can do “for free”. If they are extruding something, anything that is linear is free. This gives you the advantage of (for example) having multiple lengths that would be cost prohibitive in injection molding, or parts that slide into each other. You may be all about extrusion now, but you need to find the core competency of the process and work around that, not the other way around.


Yeah I thought about going with metal, that could be a good idea. I kind of liked the bright primary colours, but it might be a bit late-nineties-imac-ish.

I have modelled it in SW using 10mm thick extrusion, but realistically might have to be a bit thinner.

I left all my manufacturing reference books back home, so i’m flying blind a bit here. I might go and check the Lesko book in Uni library if this goes any further.
I think thermo forming could work well too.


it’s all about picking the right process for the job.

to generalize:

low qty, one off- fabrication, machining
low qty - thermoforming
medium qty- rotomolding, extrusion
high qty- injection molding, extrusion

of course there are always exceptions like thermoformed packaging, machined macbooks,etc. ,but i think something like this might be a good guide.


ok, thanks for your advice RK.

Keep the feedback coming - criticism welcomed!

no prob. I’m just a geek about manufacturing processes and economies…

I used to have some sort of chart from school comparing the economies of scale of each from our Mass Production class…I’ll see if I can dig it up, but no promises :wink:


no worries, thanks mate.