Sizing files for waterjet

[David Mary]

I realize I need to use an image that is nothing but outlines to convert to .dxf, the question is about sizing.

Usually, when I design a knife, I make a file like this, and then simply trace it out on paper, then onto the steel with a sharpie before cutting the blank our with an angle grinder. The ruler in the file is sized so that it is exact when at 100% zoom on my computer screen. If I should use high res, I wonder if this is all I need to do, just blow up the ruler to 400%, then redraw my blank, measuring all my design elements up against that ruler in my pic, and then convert the image to .dxf and tell the waterjet operator "the knife is supposed to be exactly 6 5/8" from butt to tip". Should that produce a blank of the right size and with properly sized holes? Or is there something I'm missing. Any tips, tricks or suggestions would be appreciated.



P.S. I love the Fred Perrin "LaGriffe" (that's French for the claw, did you know?) style knives, but always wanted a more negative blade to handle angle. This design will solve that for me, and I plan to do some in 5/32 AEB-L and 1084 with a flat zero ground blade.

 

[Nick Dunham]

Once you have the design in CAD, draw a line from butt to tip, and check its length. Use the "scale" command to scale everything up or down to make that line 6.625 units long. If you import the ruler into your DWG, you could just use it for scale. In other words, use your CAD system's units as inches.

That way, there's no confusion, and you're not paying the WJ guy to edit your drawing.

That said, can you explain the purpose of blowing it up 400%? How are you making the original designs?

 

[David Mary]

I have made most of my images at a lower resolution, anticipating tracing them to paper. Now that a machine will read the file, I know that a higher resolution will be better for precision, especially with things like jimping (not for this design but others). That was my reasoning. Also, I use paint.net, not CAD, but I guess that you are basically saying the native ruler for whatever program I am using will be sufficient?

 

[P.Brewster]

you are basically saying the native ruler for whatever program I am using will be sufficient?

Yes, the concept with CAD and vector drawing programs is that the units are "baked into" the drawing, and also that precision is independent from drawing scale. The concept of resolution does not have a place in CAD/vector drawing - resolution only becomes an issue when we want to render the CAD/vector drawing to a screen or to paper.

A good way to wrap your mind around this is to draw a simple 1x1 square with the bottom-left corner at 0,0. Export that as a dxf, then find the dxf file and change the extension from .dxf to .txt. Now you have a text file that can be opened in any text editor, and when you read the contents of that text file, you are basically doing the same kind of "processing" that the waterjet software does - the waterjet software never actually "sees" your drawing. What it sees are a list of instructions that define your geometry. In my example, you would see instructions for 4 lines, each with a start and end point expressed as coordinates, if I'm not mistaken.

 

[DCKHT]

I recommend downloading a free 2D CAD software (LIBREcad or, if you’re ok with a small fee, DraftSight) and teaching yourself to layout your designs on that. That way you can ensure that your dimensions will be correct.

I don’t know what machine your company uses, but the latest OMAX (which is really the industry standard) can cut splines and not just simple radi.

I would also say that i’ve never seen a water jet with high enough cut resolution to cut details like jimping.

If the WJ operator has a DXF, all they have to do is create their cutting path and set the scale to 100%, or 1:1. This will also decrease how much shop time you’ll have to pay for, as alluded to by others in this thread.

Hopefully this was helpful and not just redundant!