Say I had a lampshade of this shape:

And I (the Mrs) wanted to line the inside of the lampshade with some shiny metallic pink/paper/foil etc to make it look reet posh.

How would I cut said piece of paper/foil to fit the conical shape exactly?

So essentially I want to make another cone shape out of a piece of paper. I can measure the top and bottom diameters, height etc.

How do i do it?

Thanking you kindly.

Simple exercise in reverse engineering…

1. Remove the hoops at the top and bottom of the shade.
2. Cut down the shade from top to bottom (or undo the join where it was put together)
3. Flatten the shade material so it lies flat.
4. Place the now flat shade material onto the shiny stuff.
5. Draw round it.
6. Cut round the outline you’ve just drawn.

You will now have a piece of shiny material that will fit perfectly inside your shade.

HTH

Unless the foil is stretchy, you can’t, it’d end up crinkly and overlapping.

Your best bet is to roll the lamp shade around a large piece of paper and use that as a template. 1st class honours in mathematics by the way, specialising in non-linear dynamics. Your problem makes my head hurt. It’ll be a donut shape you’re looking for rather than a simple parallelogram.

Neither craft nor maths bod, but surely you just need to know the circumference at the top, the circumference at the bottom and the height?

Then you want an isosceles trapezium.

Edit: Hmmm.. actually reading the other answers I think that might not work. 😳

Wrap foil round outside, cut to fit, then place in inside would be pretty close.

You would have the small circumference, and the large circumference as parallel curved lines, a bit like a bend in a road….
Imagine the bottom section of this road, basically two parallel lines but curved, the inside having a tighter radius.

As for fixing it,if its a stiff material and a good fit, you should get away with a push fit and maybe some trim top and bottom that you bend over the rim.

Oh yeah, actually, you want to have the shade on a large piece of paper, mark the top and bottom where the original seam is, then slowly roll the shade along marking as you go until you get to the seam again…
Somewhere along the way you should have a pretty good starting point as to the shape required…

Shape is like this (ignore the dimensions)

make a template by rolling it on a piece of paper like wot ^ says.

Be careful with your materials and adhesives as not to burn your house and everything in it to a cinder.

I am still not sure, but you are right on the donut shape, it isnt simply a parralelogram.

I am not sure taking the existing shade off is an option, but rolling it round onto the paper may work, maybe I will make a card template.

The circumference thing may work? could i just draw one cirle the circumference of the top and another (with the same centre) the circ of the bottom, to get a big donut shape? No that wont work thinking about it, or will it? Now my head hurts.

let her work it out.

Whilst she’s doing that you can go out and buy a fire extinguisher 😉

Be careful not to burn your house and everything in it to a cinder.

I was also thinking that, are lampshades made of flame retardent material and sticking paper, even though it will be metallic on the inside is a no no? Maybe foil is a better option, but cant seem to find any pink aluminium/silver foil anywhere?

Also probably need to think about how I am gonna glue it too so there arent big blobs showing through when the light is on, spray adhesive seems to be the sensible option, but is it flammable?

This might not be not a good idea: foil would reflect heat and light back towards the bulb and the fitting it plugs into.

Having said that, it’s part of a cone, if the cone were all there it would have a point at the top. You need to work out how far that point would above the top and bottom edges. Then you need a large pair of compasses to continue with this plan. Which might not be a sensible move.

*Does anyone have a pic of a very small mushroom cloud*

I am not sure taking the existing shade off is an option, but rolling it round onto the paper may work, mayve I will make a card template

You may have to. Most shades will be fixed via a metal carrier of some sort which is often glued into the trim. Trying to fit something on the inside without removing this would be a bit of a nightmare I’d imagine.

This is not a good idea: foil would reflect heat and light back towards the bulb and the fitting it plugs into.

Lots of modern light shades have matallic reflective insides:

Ok.

Measure the distance between top and bottom. Call this x.

Measure the diameter of the top. Divide it by 2 to get the radius. Call this y.

Measure the diameter of the bottom. Divide it by 2 to get the radius. Call this z.

You need to draw two concentric arcs as per kayak’s drawing. The bottom arc will have a radius of

x
--- * z
z-y

And the top radius will be this figure – x.

I think.

Two parallel arcs. The length of the top arc being the top circumference, the length of the bottom arc being the bottom circumference. The distance between the arcs is the length of the shade and must be perpendicular to both arcs. See fig 1.

fig 1.

Lots of modern light shades have matallic reflective insides:

…and are made to conform to safety standards. Check the batteries in your smoke alarms and check that you can get out of your bedroom windows.

Spray the inside with metallic paint. Innit.

Lots of modern light shades have matallic reflective insides:

… they’ve been designed that way, though.

Two parallel arcs. The length of the top arc being the top circumference, the length of the bottom arc being the bottom circumference. The distance between the arcs is the length of the shade and must be perpendicular to both arcs

So what radius/diamter are the arcs then?

So what radius/diamter are the arcs then?

Read up one edit.

I suspect the answer is going to be “quite large” though.

Lots of modern light shades have matallic reflective insides

Buy one of them?

So what radius/diamter are the arcs then?

I’m not telling you because you will die. Seriously, go out and buy one.

Buy one of them?

I’m not telling you because you will die. Seriously, go out and buy one.

Wheres the satisfaction in that? I want to see if i can do it myself 1st.

I am not sure if you guys are still using 100watt light bulbs, but the energy saving ones we are using really dont give out that much heat …….or light for that matter 🙂

Not telling. I’ve lost weight since I bought my suit and don’t want my shirt to come out of my pants whilst giving evidence at the coroner’s court.

You lot are a big bunch of wussies, modern energy saving light bulbs run pretty cool, there’s a great big hole in the top to let excess heat out, and you’re all going on about fire risks???

It’s really just a case of do it and turn it on, watch it, then monitoring temps after 20 mins or so (plenty of time for temps to stabilise). It’ll be fine.

Spray the inside with gloss black (acrylic) as a base. Then use plasticote chrome projekt paint. Make sure you mask it off properly.

I actually think Harry the spiderwas onto something with his answer, the length of each arc being the 2 diameters, but what is re radius of each arc?

Something to do with the angle?

I’ve got it! One word, GILDING….

What you want is some silver leaf, or gold leaf as you wish, a pot of size(glue) and away you go. You’ll be blinging up everything in sight before long…

Have a look at the below..

Clickety click

[video]http://www.youtube.com/watch?v=YPgeoV6ZL8c[/video]

I actually think Harry the spider was onto something with his answer

Cheeky bleeder! 😉

I actually think Harry the spiderwas onto something with his answer, the length of each arc being the 2 diameters, but what is re radius of each arc?

Have you got my posts on a killfile or something?

Yours din’t have pretty pikchers

Cougar, when you say “And the top radius will be this figure – x.”

You mean the top radius is

x
— * z minus x ??
z-y

Where does tis equation come from then, not doubting you just wunderin like?

That’s right.

It comes from my head, I worked it out on a scrap of paper. I was going to draw it but my Paint skills are weak.

I could photograph it, actually. Sec.

I just gestimated some of the figures and using:

bottom diameter = 0.6m
top diameter = 0.4m
height = 0.5m

gives a radius of the bottom to be 3m?

Where the hell do I get a compass to draw a 3m circle?

I told you it’d be big.

Pen, length of string, assistant?

aha Genius.

1 last problem, where do I get metallic paper/foil big enough to draw a 3m radius circle on? 😯

where do I get metallic paper/foil big enough to draw a 3m radius circle on?

You don’t need to draw the whole circle, just an arc the length of the circumference.

Here’s my working:

(x) being the lamp and (w) being the bottom cone radius (not mentioned in my OP). You’re basically scaling up the small triangle to get the big one.

Please, please do a proof of concept / template with newspaper or something before you cut anything expensive. I made this up in about two minutes.

also where to get started?

Say I manage to draw the 2 arcs with radii as calculated from that equation.

The distance between them should be the heigh of the lamp right (x), which is not the diagonal distance from bottom to top but the vertical distance.

The top and bottom lengths are the top and botttom circumferences of the lamp shade, should I just measure that out on a bit of string and lay along the arc length?

I feel the purchase of a new lampshade coming on…………

1 last problem, where do I get metallic paper/foil big enough to draw a 3m radius circle on?

The stuff that they make airships out of perhaps?