cutting odd angles putting up coving.

[django47]

I put coving up in one room and it was fine because I only had to cut normal corners with the help of a mitre block. The room I'm doing next has got a couple of odd angles, not actual internal or external corners of 90 degrees. A bit like the corners on a 50 pence piece. Is their a trick or some secret nack thats used by tradesmen to cut coving(polystyrene) so that the two pieces make a nice join. Or will I have to buy a proper mitre cutting tool. I made a template from card of the wall/ceiling angle, but can't work out how to use it to cut the correct angle. All the mitre blocks I have looked at only cater for ordinary 90 degree corners (45 each side).
How would a professional solve this problem or would he have the proper tools for the job.
I'm afraid that in my case it's, ' necessity being the mother of invention'.
Please only reply to this if you have a helpful suggestion. Thank you.

 

[big-all]

you need a miter saw with the correct cutting angles

 

[django47]

you need a miter saw with the correct cutting angles

Thanks BA, I thought I might have to get some special tool for the job. You say a miter saw, I'm not sure what that is. It's not one of those big circular saws you use for cutting different angles on timber is it. I only want to cut a couple of pieces of polystyrene. Usually my bread knife makes a perfect cut, almost as good as a hot wire. I am probably thinking of the totally wrong tool aint I?
I'm gonna look on ebay and find out what a mitre saw is. By the way cheers for your helpful answer.
Micky

 

[big-all]

hand mitre saw b/q wicks/homebase about 20 notes
you can lock at the exact angle with a hex screw at the back
http://www.toolstation.com/shop/Hand+Tools/Saws/Precision+Mitre+Saw+550mm/d10/sd70/p76675

 

[django47]

you need a miter saw with the correct cutting angles

Hi BA, just got back from looking at mitre saws and they are the things I thought you was refering to. I only have a couple of little cuts to make in polystyrene. I have seen lots of other tools for jigging up coving ready to saw by hand, without using a great big circular saw. It's a bit like using a sledge hammer to put in a drawing pin. I was hoping to avoid buying more special tools which I will probably never use again.
Worse come to worse, I can make a mitre block using my template to mark out the slots. It would only be a one off made out of 3 pieces of wood. Taylor made for this one job. Just seems such a lot of work to make a couple of cuts.

 

[jerholdsworth]

sorry,i do not where you bought your cove.
usually they also sell a plastic former/guide to create your miters.
BUT strongly reccomend you not to use the poly stuff due to fire and smoke rapid escalation.

edit,if you have a spare piece of your cove and a safe place to ignite it.ie outside garden with a working fire extingiusher available.
try it also with your painted final surface and see results.
to do these tests you need to be sure you will not damage anything.life or property.
personally i would use a plaster based cove,go to selco etc.

 

[Nige F]

from card of the wall/ceiling angle, but can't work out how to use it to cut the correct angle. How would a professional solve this problem or would he have the proper tools for the job.
.
Please only reply to this if you have a helpful suggestion. Thank you.

To get the correct cut angle you need to gauge the existing angle with something like a steel rule or a carpenters slide bevel( I think it`s called that ) then transfer the angle to a flat surface which you will later lay the cove on to cut with a knife - now bisect the angle using a compass with a pencil in one leg - not a good explanation because I struggle with maths etc. But it`s definitely the way it`s done - I`m sure there will be an illustration on the net if you google " bisecting an angle"

 

[django47]

sorry,i do not where you bought your cove.
usually they also sell a plastic former/guide to create your miters.
BUT strongly reccomend you not to use the poly stuff due to fire and smoke rapid escalation.

edit,if you have a spare piece of your cove and a safe place to ignite it.ie outside garden with a working fire extingiusher available.
try it also with your painted final surface and see results.
to do these tests you need to be sure you will not damage anything.life or property.
personally i would use a plaster based cove,go to selco etc.

Hi JW,
you asked where I bought my coving, well I got it at B&Q. I also bought some from Homebase a while back and despite what you say, I am really pleased with the result. I know what happens to polystyrene if you are unfortunate enough to have a fire. It melts and gives off unpleasant fumes. But if my home was to catch fire I think one of the least things I would be worrying about would be fumes from a small amount of coving compared to all the other so called 'Fire Retardant' materials in the home that give off toxic fumes According to your reasoning I would have to throw away my 3 pc suite(foam gives off fumes) most modern doors are expanded polystyrene foam filled and also some double glazing window frames. Yea I was surprised when I saw that too.
So, I don't think i will start having panic attacks over my coving, that looks really nice and the 'pros' far outweigh the 'cons', besides which, how on earth did I get onto all this, all I was asking about was cutting odd angled corners. Also I did ask that only replies that are helpful respond because I have learnt how people who post on this site love to wind up those seeking advice.

 

[django47]

from card of the wall/ceiling angle, but can't work out how to use it to cut the correct angle. How would a professional solve this problem or would he have the proper tools for the job.
.
Please only reply to this if you have a helpful suggestion. Thank you.

To get the correct cut angle you need to gauge the existing angle with something like a steel rule or a carpenters slide bevel( I think it`s called that ) then transfer the angle to a flat surface which you will later lay the cove on to cut with a knife - now bisect the angle using a compass with a pencil in one leg - not a good explanation because I struggle with maths etc. But it`s definitely the way it`s done - I`m sure there will be an illustration on the net if you google " bisecting an angle"

Hi Nige F,
I really appreciate you going to the trouble of explaining how best to cut my 'odd angled coving'. Don't worry about the maths, it wasn't my best subject at school either, in fact I am still quite crap at it. I did make an exact template of the angle. Have you ever worked with coving, it's not like cutting a piece of wood like skirting at the same odd angle. The coving is a sort of 'bow' shape and when you cut it, apart from the angle, you must hold it a certain way otherwise the join will not look at all good. That is why they have mitre blocks specially for the job. The only snag is that they oonly include slots to cut ordinary corners of 90 degrees (2x 45).
I will heed your advice and 'google', bisecting angles, see what I can learn, as long as I don't need a degree in geometry.
Anyway cheers mate, if I find anything really hellpful, I will come back and post to let you know. Bye NF, have a good day.

 

[django47]

from card of the wall/ceiling angle, but can't work out how to use it to cut the correct angle. How would a professional solve this problem or would he have the proper tools for the job.
.
Please only reply to this if you have a helpful suggestion. Thank you.

To get the correct cut angle you need to gauge the existing angle with something like a steel rule or a carpenters slide bevel( I think it`s called that ) then transfer the angle to a flat surface which you will later lay the cove on to cut with a knife - now bisect the angle using a compass with a pencil in one leg - not a good explanation because I struggle with maths etc. But it`s definitely the way it`s done - I`m sure there will be an illustration on the net if you google " bisecting an angle"

I'm back after 'googling' bisecting angles but I'm afraid it's not much help as all it does is tell you how to find half the angle, ie: 90 degrees= 2x 45 degrees. Thats what, 'disecting an angle' actually means.
I know I'm not the brightest star in the galaxy, but I still have a trick or two up my sleeve. I have never been very good at giving up before I have beaten the problem. 'Neceessity is the mother of invention'.

 

[misterhelpful]

You can get the required angle by cutting a template out of card, as you say you have already tried. You should effectively have a trianglular piece of card, which if you fold in half will give you the exact angle of the cut.

The trick now is to turn the coving upside down (ceiling edge at the base and wall edge facing away from you for internal corners, and wall edge towards you for external corners), lay it on the card and follow the angle of the folded template. This method should be relatively accurate, but ,as others have said, a mitre box would be far more precise. When joints need filling, they are far more noticeable with polystyrene coving than plaster, but if I recall correctly, you have your reasons for needing to use the lighter product.

 

[opps]

To work out angles you will need the following: a straight edge such as a spirit level, a bit of string and a calculator (or internet access).

The following uses trigonometry and the fact that all triangles can be made into two right angle triangles. You don’t need to understand the maths, fortunately there are loads of websites that will do the maths for you.

Hold the spirit level so that it touches both walls (it might be easier to get someone to hold it for you). Then take a piece of string and hold one end in the corner, pull the string taught so that it touches the edge of the spirit level. The shortest distance is what you will need to find, make a note of it and call it A (for adjacent). This shortest string distance will be at right angles to the spirit level.

Mark where it meets the spirit level and measure from that mark to the end of the level where it touches the wall. Record this distance as O (for opposite).

You have now created a right angle triangle and have all that you need to calculate your cutting angle using trig..

Head over to

http://easycalculation.com/trigonometry/triangle-angles.php

Tell it you want to calculate the angle in the first drop down list and in the second dropdown list, select hypotenuse (we don’t really want the hypotenuse but select it anyway).

Enter your first measurement (the corner to spirit level string length) in the box that says adjacent.

Enter the second measurement (the distance measured on the spirit level) in the box labelled opposite.

Then hit the calculate button.

The angle that you want will be the one in the greyed out box. , if It is a little too difficult to read then take the angle that is not greyed out and subtract that from 90.

If you make an error inputting the values then hit refresh and try again.
You now have you cutting angle (the green one in my picture)- ie half of the total angle

Hope the above makes sense..
[/img]

 

[jondecs]

Has OP looked here? http://www.british-gypsum.com/pdf/Gyproc_and_Artex_Cove_Range_20pp DL.pdf Page 9 on the PDF


Or trry utube easy mitre.

 

[Nige F]

thanks opps - good link and explanation - I`ll use that myself now