Jigsawing curves

[IRW]

Hi All,

An upcoming set that I'm building is going to involve jiggying out a number of circles (the first being a disc at 2.6m in diameter, the second being a ring around that at about 40cm wide, with a third, offset ring around that which will be wider at the upstage edge than the downstage edge.

 

Anyway, I was just wondering if any chippy-type people had any tips for how to keep my large curves constant as I'm cutting them out. As each has to fit around the other, obviously accuracy is going to be pretty important.

 

I'm pretty good at the old set building and carpentry work, and usually I'd just whizz them out, and not worry too much if the line of the curve is a little bit wobbly (as in, the audience won't notice), but as the design requires that everything fits pretty much spot on, I was wondering if there are any clever tips? Obviously, having a sharp (and suitable) blade in the jigsaw is top of the list!

 

Give me straight lines, or 'something along the lines of' anyday!

 

Thanks,

 

Ian

 

PS, We're talking 18mm ply.

[dmoorcroft]

If I were drawing out the circles, I'd probably fix some string to the centre, fix a pen to the other end and use this to draw a perfect circle. Could you do the same with a jigsaw?

 

I've never tried it and the method would need risk assessing to ensure using a jigsaw in such a way is safe etc

[mac.calder]

Since it is crucial that they are all "perfect" - cut roughly outside the lines (the closer the better) and then do the rest using elbow grease and sand paper (or an electric sander if you left yourself a really wide margin for error)

[themadhippy]

length of metal the radius of the circle,jig saw firmly atached one end,other end bolted throught the wood?

[callumb]

Use a router with a cutting bit attached to a jigg that's fixed to the centre Of the circle you want to cut out. Perfect circle every time.

[madorangepanda]

Use a piece of string, wire or a timber batten attached to a central pivot.

Make sure that the point it attaches to the jigsaw is near to the centre of the blade.

Let the blade do the work and don't force it forwards, it's slower but gives a neater cut.

 

If you've got one a router may be easier for it, whenever I've had to cut circles or arcs before they've always given better results.

[ramdram]

Buy yourself a cheap router, read up on www. for hints if they are new to you. Nail in centre and a bit of ply or non stretchy cord for radius arm sort of thing...take your time...wear ear defenders...and a mask...and lastly, and most importantly, eye protection.

 

http://www.wwgoa.com/articles/one-great-tip/accurately-routing-large-circles/

[IRW]

If I were drawing out the circles, I'd probably fix some string to the centre, fix a pen to the other end and use this to draw a perfect circle. Could you do the same with a jigsaw?

I did wonder, very briefly;)

 

Since it is crucial that they are all "perfect" - cut roughly outside the lines (the closer the better) and then do the rest using elbow grease and sand paper (or an electric sander if you left yourself a really wide margin for error)

As ever with these things, the build is going to be very tight- if I had more time, this would be the option!

 

length of metal the radius of the circle,jig saw firmly atached one end,other end bolted throught the wood?

Hmm...there might be something in that...

 

Use a router with a cutting bit attached to a jigg that's fixed to the centre Of the circle you want to cut out. Perfect circle every time.

Jiggles, do I understand that you're suggesting the same as madhippy, but with a router? Sounds like a good idea!

 

Thanks for suggestions so far!

 

Use a piece of string, wire or a timber batten attached to a central pivot.

Make sure that the point it attaches to the jigsaw is near to the centre of the blade.

Let the blade do the work and don't force it forwards, it's slower but gives a neater cut.

 

If you've got one a router may be easier for it, whenever I've had to cut circles or arcs before they've always given better results.

Buy yourself a cheap router, read up on www. for hints if they are new to you. Nail in centre and a bit of ply or non stretchy cord for radius arm sort of thing...take your time...wear ear defenders...and a mask...and lastly, and most importantly, eye protection.

 

http://www.wwgoa.com...-large-circles/

 

Thanks chaps, I'm more than capable of using a router (safely)(or indeed most workshop equipment) ;) Just never really had to cut out exceedingly accurate large circles!

 

Edited to add, thanks for the link Ramdram, some useful stuff there!

[kerry davies]

By George he's got it. A Router and the Hippy/Jiggles rod is the way to go. Jigsaws tend to be too flexible for 18mm ply and can "wander". Whenever I have done similar I found it helped to score the ply first with a sharp blade to start the cut and reduce splintering.

 

If you need to sand or file it smooth remember to oppose the curve rather than try to follow it.

Don't know if this makes sense but if the curve is ) then file with a ( motion.

 

Can anyone explain that better, please?

[lightsource]

Ignore the 'piece of string' posts, as there is very little accuracy with a power tool, and has a danger aspect if the string gets wound up in the cutting head. String streches, so you won't get a perfect circle that way.

 

Weather you use a router or a Jigsaw will make little difference in the outcome.

 

TheMadHippy's post is the way I'd do it. Metal guide to a fixed centre point. DeWalt jigsaws have an indentation in the shoe to attach guides, so the tool is always firmly attached to the work surface.

 

Just make sure the initial hole is accurate, for the Jigsaw to do it's work ;)

[Ynot]

Yup.

Pretty much a plus 1 for the fixed radial guide. String will never give the most accurate results because a) it may stretch, even a little, b) if it catches even a little it can put you off the measure, and c) you have no control over the pitch of the jigsaw.

 

I've done this a few times with both jigsaw and router, the latter definitely is the more accurate, though slower with thicker timber, but routing ply might give you problems by biting chunks out of the edge if you're not careful.

 

I've used plastic strip, and strips of 4mm hardboard before now to make the radial. Just make sure it's bolted/screwed/attached however solidly at more than one point on the jigsaw/router, so there's no swivel on the tool.

[IRW]

Ignore the 'piece of string' posts, as there is very little accuracy with a power tool, and has a danger aspect if the string gets wound up in the cutting head. String streches, so you won't get a perfect circle that way.

 

Weather you use a router or a Jigsaw will make little difference in the outcome.

 

TheMadHippy's post is the way I'd do it. Metal guide to a fixed centre point. DeWalt jigsaws have an indentation in the shoe to attach guides, so the tool is always firmly attached to the work surface.

 

Just make sure the initial hole is accurate, for the Jigsaw to do it's work ;)

Yup.

Pretty much a plus 1 for the fixed radial guide. String will never give the most accurate results because a) it may stretch, even a little, b) if it catches even a little it can put you off the measure, and c) you have no control over the pitch of the jigsaw.

 

I've done this a few times with both jigsaw and router, the latter definitely is the more accurate, though slower with thicker timber, but routing ply might give you problems by biting chunks out of the edge if you're not careful.

 

I've used plastic strip, and strips of 4mm hardboard before now to make the radial. Just make sure it's bolted/screwed/attached however solidly at more than one point on the jigsaw/router, so there's no swivel on the tool.

 

Don't worry chaps, I've no intention of using a jiggy on a piece of string- I have assumed all mentions were tongue-in-cheek! ;) Even with a pencil I realised you don't get an exact curve like that a looong time ago, and since then I've drawn my circles with a bit of 2x1 screwed to the central point with a pencil sized hole at correct position at the other end.

 

Unless someone is still to come up with a radical idea, the router is going to be the tool of choice I think. I've just had a close look at the base plate on my router, and there are some handy holes that I'll be able to screw/bolt through to attach it to a suitable radial arm.

[dbuckley]

I use a RotoZip for this kind of thing, with the same pivot / bar approach. It's the same as a router, but smaller, uses a side cut drill about 3mm in diameter. The link is to Amazon, but you can get them a lot cheaper, do a search.

 

Also a useful tool to make outlines like London skylines.

[lightsource]

I think you've got the general perspective, so all the best :D

[Bobbsy]

+1 for the router with a solid guide bolted in the centre of the circle.

 

I've had to do this a couple of times, once making a 6 foot round frame for some rear projection screen that was going to fly in front of a projector and once (the worst) putting a large turntable in the middle of a larger box--that one had to be accurate enough to revolve and narrow enough not to catch the fingers and toes of the actors.

 

I soon gave up on the jigsaw--the small amount of flex in the blade was too much for the accuracy I needed. The router worked a treat--the hardest part being figuring a way to attach it to the rigid pivot--getting that sorted took hours and the actual cutting took moments.