Cutting a curve into plasticard

C

CoggesRailway

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How do I do it? I am OK with ruler-knife-bend-until-it-snaps but if I want to cut a curve? I don't mean heating and bending a sheet - actuall cutting a curving edge.

Ian
 
One thing I have found cutting a curve freehand ( after its been drawn of course)
is not to hold the blade vertical, as it tends to want to go in a straight line
lean it over a bit on the inside of the curve
 
CoggesRailway said:
Thanks steve possibly but would the plasticard just break as normal?!
Click to expand...

I always on a curve, make sure the ends, 5mm? is cut right through then it tends to snap better
works for me!
Edit;- just thought, are you doing a curve as in a roof curve, or a full circle
 
The method I use is to cut it free hand. This will take practice and you WILL make mistakes. The secret with ANY cut in plasticard is that the first pass of the knife is NOT a cut - it's a scribed marker. If you get the first pass wrong, it's almost impossible for the subsequent cuts not to follow it.

So, to cut a curve I mark it out and then very carefully follow the mark with the blade, BUT NOT EVEN TRYING TO ACTUALLY CUT - it's just a scribe. After maybe two or three (at most) scribes, the blade will always follow the little furrow you've made, so now you can start actually cutting.

I know this sounds a bit iffy, but if you can follow a line when cutting with a jigsaw, with a bit of practice, you can follow a line with a knife.
 
I've not tried it, but what about a pair of dividers? You could even reshape one point to more of a blade shape and then do as Mel says gently, gently till you get a good score, then follow with the knife. The centre point can be protected with a piece of scrap taped in place.
 
I would advocate the circle cutter which I have used many times with success, unless you are a clean living lad like Mel and have a steady hand and good eyesight and then you could give the freehand method a go.
 
Of course the drawback with compass cutters etc. is that they're fine as long as the curve you want to cut has a constant radius, the problem comes when you want to cut a compound curve. Then things can get VERY tricky. A lot of roof profiles, for instance, have several different radii - especially the old Southern Railway designs. :confused:
 
CoggesRailway said:
How do I do it? I am OK with ruler-knife-bend-until-it-snaps but if I want to cut a curve? I don't mean heating and bending a sheet - actuall cutting a curving edge.

Ian
Click to expand...
I have made a very basic disk sander using an old washing machine motor and wooden disk with
sand paper glued on.
I used it to make the frames for my railcar. I cut out the pieces roughly by some other means first.
Hold them together in a 'stack' by double sided tape or screws etc. Then sand them to the desired shape
all as one piece. They must all be the same size/shape this way.

Dean.
 
I use the same method as Mel - ie a few light scribes along the curve, and then heavier cutting strokes - and then a bit of Dean's approach. I tend to cut just outside the intended path and then finely adjust with a piece of sand paper/emery

IMG_5280.JPG


IMG_5281.JPG


If I have a profile I keep checking regularly until it's a close fit

IMG_5284.JPG


Rik

PS Sorry about the hairy knees in the last picture
 
One extra tip for Mels method. If you are ham fisted like me, make the first scribing cut with the back of the blade. It makes a scratch, rather than a scribe, but it won't dig in and wander off
 
Hi Lads
If I have a complex or large curve where dividers or the pin, string and sharp point method will not be appropriate, I use the multiple drillling technique.
Using a very very small drill, I drill holes allong the marked (or even scribed) line at about 2mm distances and then scribe between them and then snap off. This gives a perfect curve which then just needs light sanding to make smooth to get rid of the 'half' holes made by the drill.

Used to use this method, with larger drill size, when 'banging out' holes in hard brick or concrete to install back-boxes for electric sockets. Instead of scribbing the plastic, a bolster and hammer just cut through the weakened drilled brick. Funny how methods translate............
 
I have found that jeweler's snips follow a score/scribe line pretty well, especially on the heavier grade plastic, and then you can finish off with wet and dry
 
yb281 said:
Of course the drawback with compass cutters etc. is that they're fine as long as the curve you want to cut has a constant radius, the problem comes when you want to cut a compound curve. Then things can get VERY tricky. A lot of roof profiles, for instance, have several different radii - especially the old Southern Railway designs. :confused:
Click to expand...
David Jenkinson mentions this problem in one of his books and proclaim a "french curve" template to be the solution:
http://en.wikipedia.org/wiki/French...xiediy.blogspot.com/2010/03/french-curve.html < Link To http://dixiediy.blogspot....0/03/french-curve.html
Find a part of the french curve that fits and use it as a template and cutting guide.
 
ge_rik said:
I use the same method as Mel - ie a few light scribes along the curve, and then heavier cutting strokes - and then a bit of Dean's approach. I tend to cut just outside the intended path and then finely adjust with a piece of sand paper/emery
Click to expand...

I use the same method as Mel too. My early attempts could be a bit hit and miss but with practice you'll get the hang of it.

The curved panels on my boxcab and restaurant car builds were cut freehand: -
6e1c9939729e4e848c28fe07bccca396.jpg

eaec355b743046e686f1a8d0361b191f.jpg
 
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