Why Wouldn't an Intermediate Concrete Fence Post be Symmetrical?

My WAG is so these can be assembled with faces touching in a gentle curve.

That's a good guess.

I'm seconding this guess.

https://en.wikipedia.org/wiki/Draft_(engineering)

Flat face and symmetrical is apparently doable, with the latest mold materials. But the shape that allows easy release has a long history, and the OP image certainly looks like it.

But, those have been removed from the mold's , before they have " set up " .

Thanks.

Now I don't even have to pay their extortionate prices: I can just make my own.

That's the spirit!!

There's a certain satisfaction that comes from that. Almost like the middle digit salute to them.

Normally you would need at least a 2° draft angle and a good mold release to extract from the form. The more the draft angle, to a certain degree anyway, the easier to extract.

It looks like a 6.2 degree angle on the inner feature and 3.6 degree angle on the outside faces of the post.

I didn't do the math. Every form is slightly different. All depends on what concrete mixture (with or without additives) is used. Custom forms I have done were all larger and we used 2° as a minimum.

Making a custom form (out of steel) for the OP, I would go with the math for sure. Plywood form, I don't know as I haven't done one of those for decades.

It's interesting that there is more draft on the shorter feature than the larger feature. I would have thought the inverse. Maybe because the shorter feature is confined to the bottom of the mold?

I think the draft on the sides of the slots is to allow for small angles (deviations from 180^o) between adjacent panels.

Hi Randall,

As others have said the design is for removal from the mold.

Might I add that if you are building your own posts run some deform bar up the center and leave a loop out of the top so you can use some form of lifting device to stand the post and suspend it vertically in the hole. Sure you can manually lift the posts into the holes but that item we call the back may just object.

I have cast 250mm square posts in wooden molds and round posts from 180mm to 250mm PVC pipe with a saw cut down one side clamped together with steel bands and found that oil was an excellent release agent.

Looking at those posts you could make a form with what we call tophat battens and z purlins. A few bolts welded to the outside and some brackets and your on the way to making them. Could even use the plastic pipe and top hat battens with the return edge removed and some self tappers through the flat edge to hold them in place on the inside the pipe. With plastic pipe they can be cast in place, no lifting, no moving and each day a new one can be cast while the recently uncovered one just needs to be wrapped in plastic to control the curing.

Plastic pipe off cuts can be scrounged for a small price from the local recycling yard or refuse tip shop at least from here anyway. I have cast piers for a walkway across a dam and they were up to 2.5m in height.

Happy casting.

Regards Stef

It may have something to do with resistance to frost heaving.

Old concrete street markers were tapered smaller toward the top for this reason.

The slots are the same dimensions on each face. That's all that should matter.

The slots will allow "nail-less" assembly of the fence, I think.

The angle is probably for de-molding, as others have said.

It is simply do do with easy removal from the mould. You loose nothing and gain nothing in the size or shape. What you do gain is who get the finished side and who get the rough side. Normally this is shared cost with a neighbour. If he does not share cost he gets the rough side, you have the nice smooth side.

It is the easiest fence to install, just make sure you pour a good foundation of concrete around each post and the next day slot the panel in. When installing the post install one panel at the bottom to keep the post square. 200m Running meters of wall for 6 persons is 2 days work, complete.

I assume you are using concrete posts and wooden panels, in a small British garden, if so it is one days work to install. Weekend if you are doing this yourself with long day.

If they were symmetrical, they would not be able to get them out of the form.