Casting window cills on-site.

[Onoff]

11 hours ago, epsilonGreedy said:

 

Just a hipped roof without a ridge mathematically speaking. I can do hipped roof maths, so let's do the trigonometry in this thread @onoff

 

How many bricks wide is this pillar?

 

 

The pillar is 2x2 bricks so 450x450mm. I want a 50mm overhang around the edges with the drip bead say 25mm in from the edge. 

 

Overall height 130mm so a 65mm pyramid sat atop a 65mm slab. Just got to calculate & cut, 4 precise, triangles that will butt up and glue to each other to form the pyramid.

 

 

Edited May 13, 2021 by Onoff

[Onoff]

Basically this fag packet sketch drawn on a lurching train!

 

The key really is 4 triangles as aforementioned. The angle where the sloping sections meet the vertical sides of the mould, no problem. Just need to figure where the day A edge meets B edge. Fire up the CAD!

 

 

(Just realised I haven't shown the drip bead mouldings).

[dpmiller]

that's a standard item round these parts

 

http://www.carryduffbuildingsupplies.com/products/details/category/Precast-Products-30/Pillar-Caps-76

 

https://www.samuelkirk.co.uk/pillar-cap-22in-550mm-7794-p.asp

[Onoff]

1 hour ago, dpmiller said:

that's a standard item round these parts

 

http://www.carryduffbuildingsupplies.com/products/details/category/Precast-Products-30/Pillar-Caps-76

 

https://www.samuelkirk.co.uk/pillar-cap-22in-550mm-7794-p.asp

 

Cheap too! Look at the stupid prices here:

 

https://ukcaststoneonline.co.uk/product/flat-pier-cap-550mm-x-550mm/

 

 

[PeterW]

8 minutes ago, Onoff said:

 

Cheap too! Look at the stupid prices here:

 

https://ukcaststoneonline.co.uk/product/flat-pier-cap-550mm-x-550mm/

 

 

one is concrete and one is recon stone - different products. 

[epsilonGreedy]

1 hour ago, PeterW said:

one is concrete and one is recon stone - different products. 

 

 

Would I be correct in thinking that the typical art stone window cill is not finished with recon stone and a coloured cement is used instead?

[epsilonGreedy]

4 hours ago, Onoff said:

Fire up the CAD!

 

 

 

Putting your numbers into the online trig calculator at http://www.carbidedepot.com/formulas-trigright.asp

 

Using SideA = 65 SideB = 275

 

I make the pitch of your pyramid to be 13.3 degrees which is good aesthetically speaking because too steep would look a bit toytown.

 

Of more interest the calculated SideC is 282.6mm which is one side of your right angled moulding triangle. The gutter side of your moulding triagle is 275mm i.e. half the length of one side of your plan view.

 

Going back to the online trig page and calculating a new triangle.

 

Using SideA = 275 SideB = 282.6

 

Which gives us a calculated SideC of 394.3mm (*) which on a hipped roof would be the length of the hip rafter and also the 3rd side of your moulding triangle.

 

Hence 4 triangles measuring 275 x 282.6 x 394.3 should fit together to create your 13.3 degree pitched pyramid.

 

However never trust what you read on the internet so let's test my numbers with a different calculation.

 

The plan view length of one of those hip lengths is derived from an isosceles triangle with two sides measuring 275 which gives a SideC = 388.9mm (**)

 

Viewing the same hip rafter triangle from the side we calculate a new triangle with Using SideA = 65 SideB = 388.9 (**) we get... SideC = 394.3 (*) which matches the original calculated SideC ?

 

The pitch of the hip is 9.5 degrees taken from AngleA in this new triangle. That set off an alarm bell in my head then I realised a hip rafter pitch is always significantly lower than the principal roof pitch.

 

 

 

 

 

 

[Onoff]

 

 

On 14/05/2021 at 12:00, epsilonGreedy said:

 

Putting your numbers into the online trig calculator at http://www.carbidedepot.com/formulas-trigright.asp

 

Using SideA = 65 SideB = 275

 

I make the pitch of your pyramid to be 13.3 degrees which is good aesthetically speaking because too steep would look a bit toytown.

 

Of more interest the calculated SideC is 282.6mm which is one side of your right angled moulding triangle. The gutter side of your moulding triagle is 275mm i.e. half the length of one side of your plan view.

 

Going back to the online trig page and calculating a new triangle.

 

Using SideA = 275 SideB = 282.6

 

Which gives us a calculated SideC of 394.3mm (*) which on a hipped roof would be the length of the hip rafter and also the 3rd side of your moulding triangle.

 

Hence 4 triangles measuring 275 x 282.6 x 394.3 should fit together to create your 13.3 degree pitched pyramid.

 

However never trust what you read on the internet so let's test my numbers with a different calculation.

 

The plan view length of one of those hip lengths is derived from an isosceles triangle with two sides measuring 275 which gives a SideC = 388.9mm (**)

 

Viewing the same hip rafter triangle from the side we calculate a new triangle with Using SideA = 65 SideB = 388.9 (**) we get... SideC = 394.3 (*) which matches the original calculated SideC ?

 

The pitch of the hip is 9.5 degrees taken from AngleA in this new triangle. That set off an alarm bell in my head then I realised a hip rafter pitch is always significantly lower than the principal roof pitch.

 

 

 

 

 

 

 

Ta. CAD concurs at 394.3mm on 2 sides. I get 9.49deg on those sides & 13.3deg on the 550mm side. 

 

Making some supports to go inside the mould:

 

[Onoff]

Looking like the mould idea will work. Some scrap 18mm ply (old site hoarding). The 3D printed bits will screw onto the sides. Tbh I should have done them at 9.5deg but they're at 9.

 

 

These will support the top edge of the triangles that form the pyramid:

 

 

I was aiming for 65mm and it's just over. Might change when all screwed together.

 

 

I'm going to use spray adhesive and line the mould with DPM. 

[Onoff]

What happened to the cheap concrete pokers on eBay & Amazon? Doesn't seem that long ago you could get a no name tool with wand for £39.99 or less brand new. Silly money now.

[markc]

6 hours ago, Onoff said:

What happened to the cheap concrete pokers on eBay & Amazon? Doesn't seem that long ago you could get a no name tool with wand for £39.99 or less brand new. Silly money now.

Most of them were returned for a refund or thrown in the bin shortly after purchase and use.

No need for a poker for this job, just tap the mould with a hammer etc. The top return and drip groove strip will cause air to be trapped at the top, drill a series of holes around the top flange to allow the mix to reach the soffit of the mould.

[Onoff]

The plan has merit...

 

 

 

A little fettling required. It'll be accurate enough for a pier cap!

 

[Onoff]

I glued the mating faces of the pyramid with Gorilla Glue. Not a perfect fit at the apex as in a mm or two out but good enough I think. Going to carefully have to multitool the glue off...
 

 

I'm debating next sticking sections of DPM in. Then, at the joins running a bead of silicone and taking it off with the Fugi Cramer tool to get radiused edges.

It's a bloody long time since SWMBO's let me do anything on the lounge floor that involved putting plastic sheeting down...

 

 

[Onoff]

On 09/05/2021 at 20:06, PeterW said:

Yeh it would and just a square of 10mm copper pipe pushed in, or even just scrape off the excess and when it starts to set you could carve in the drip detail with some sort of tool. 
 

Plastering sand in tonne bags is about £40 around here and available from the Jewson/TP/MKM merchants and also from Wickes I think. 

 

Do you reckon a square of 15mm copper pipe will be OK? .....because that's what I've made! ?

 

Thought I'd check back here and saw you'd said 10mm. 

[markc]

No specific size for a drip groove, just needs to form drips

[markc]

istead of allowing the water to cling to the underside of soffit area and then into the wall