precise plasma templates

[kibodwin]

I am looking to cut some 6mm aluminum for a 3d printer I want to build (mendel i3). The dimensions are quite precise. Does anyone know how to find the percentage needed to add to the template so the final result is the desired dimensions?
I am thinking of just adding the distance from the tip to the edge of the plasma torch to the template. Is this precise enough or is there another way to get the desired results?
Thanks for any advice.
K.

 

[Welderpaul]

Get them water jet or laser cut. Much more accurate than plasma. Our laser cutters claim a tolerance of +/- 0.4mm

 

[waddycall]

Clamp a straight edge to some scrap, cut along it with the plasma for an inch or two and measure the distance from the cut edge to the straight edge.

 

[BrokenBiker]

if it has to be that precise I would choose a more precise process than plasma

 

[kibodwin]

Hi Paul,
Thanks for the reply. I dont really have access or know of anyone who can water jet cut or even cnc cut the part. I would like to make several so cost might be an issue.
Are there online water jet cutting solutions? If you have any I am interested. I will definitively look into it but I was wondering how others get precise plasma cuts or dont they bother as it is never a clean enough cut?
Thanks again,
K.

 

[BrokenBiker]

when I have used plasma (not a great deal of times) I have always allowed myself space for grinding/filing back to correct dimension if it has to be precise

 

[kibodwin]

Hi guys,
thanks for the replies, I think waddycall's idea is what I will definitively try, there I was messing around with calipers!!
I hope not to have to grind off too much for cleaning as it is a bit of a complicated cut. Sanding and deburing should be fine though.
I will give it a go and if I am not happy with the results of the plasma cut then I will get the parts water jet or cnc cut.
Thanks for the pointers,
K.

 

[Wendelspanswick]

You will struggle to get an accurate cut, if the template has external corners the profile will end up with radiused corners.
As an example if you have a square template with four 90 degree corners the finished profile will end up with four straight sides and four radiused corners.
It's what happens when you follow a square corner with a round template follower (the plasma tip).
It happens with bearing guided router cutters as well.
The bigger diameter the bearing or plasma tip the larger the radius.
To give you some idea use a washer with a felt tip pen in the centre hole to trace round a cardboard template and see the difference between the template and the profile!

 

[kibodwin]

hi wendel,
thank you very much for the info, the rounded corners are not an issues, it is more the final size. I will calculate the extra size I need to add to the template to get the correct original size. As per you suggestion I will make a cardboard template and test for size before making a nice metal template.
thanks for the pointer, it is appreciated
=)

 

[chevy2]

If you need quite a few of a certain type of bracket making as you said then thats where laser/waterjet becomes the more favourable option,
for example you may get quoted £20 for the first item and then only £2 for each additional bracket,
for maybe one or two a diy job will be ok but on batches the no brainer is to farm it out.

 

[gerrymoore]

I have to disagree slightly. When I program my plasma CNC it allows me to cut inside, on, or outside the line of cut...it also allows me to adjust this amount. I've never really measured too precisely but it's certainly within less than a milimetre......possibly 0.5mm. I have produced quite a few 'sets' of parts for building CNC's and they have all been extremely accurate....they have to be or the CNC machine wouldn't be!!

 

[rikrobson]

I suspect Plasma cnc will be accurate as the torch is being guided. But it is hard to get consistent movement by hand even when following a template. Expect some fettling.