How to dimension knife drawings?

C_Claycomb

C_Claycomb

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Dec 11, 2000
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A situation has arisen where I need to do some technical type drawings of a couple of knives to send to someone else. I did the first lot by hand, and posted via snail-mail, but for the updated drawings I really would like to use email. I have access and experience with CAD (AutoCAD and something called SDRC Ideas), however I am unsure how best to dimension the drawings.

Normally, for my own work, dimensioning a drawing is a waste of time, I draw it at the right size then just trace it whenever I need another copy. When emailing a drawing though, it is necessary to have some dimensions at least so that whoever prints it at the other end can check that they got the size right. It also makes for greater accuracy when checking the finished work.

The thing is, knives don’t have a whole lot of straight edges. They are most inconsiderately made of complex curves. The only thing I have worked on like that is turbine blades, which are described using sections and points plotted around the profile. This is a good method to use on a coordinate measuring machine, but lousy for making measurements or tools by hand.

I am really looking for a pointer to how the knife manufacturing industry records/dimensions/details knives in production drawings, but any suggestions are welcome :D

Chris
 
Many companies will transfer your drawing to a cad drawing for a nominal fee, they will do this to scale if you give them a measurment for eg total length or total width as the cad model will be to the scale of your drawing if it is transferred to a company for cutting out etc (sometimes the dimensions are lost in the importing of the file) If you give them the total length again this will scale it to exactly the dimensions again of your drawing.
 
Dimensioning is done exactly the same way as any industrial drawing. Tolerances are important if multiple parts are involved. Materials information is important for production drawings.

In Germany we use DIN Norm which is German Industrial Standards. There are books with directions for making and dimensioning industrial drawings. I'm sure the UK uses a similair system.
 
Dimensioning is done exactly the same way as any industrial drawing.
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The problem is, for complex curves, I have seen more than one way of creating them on industrial drawings. They all had advantages and disadvantages dependign upon how the dimensions were going to be used. The method of tollerancing was totally different, as was the result of deviations from the stated dimensions. Dimensioning one way helps the guy setting up the tool, doing it another way helps the guy checking the work, and doing it yet a third way gives the best accuracy when someone comes to re-draw the drawing at a later date.:eek:

Kevin, when you mark up your drawings, how to you detail the knife's profile? Do you generate it as a series of interlocking curves centred on defined points, or plot points on the profile, or use a mathematical equation? These are all used in industry.:confused:

I could just do the drawing as a .dwg, leave off most dimensions, and just let the manufacturer sort it out, but I would prefer to leave less to their interpretation if possible.
 
Superimpose a grid of a certain size, say 1/4 inch, on your drawing. Then add a note indicating the size of the grid.

Alternatively, add a "ruler" along all four sides of your drawing.

With either method, the person receiving your drawing will know if they have printed the drawing out at 100% and can adjust it if they have not.

Good luck.

Phil
 
Most industrial production today is done with compter drawings. The curves such as those you are talking about are transfered with the drawing file. Common CAD software such as AutoCAD or Solid Works have automatic dimensioning features as well for printouts.

I use the original CAD files and CAM software to manufacture complex curves. There isn't a need to dimension them, the dimensions are contained in the file.

If you feel the need to use trig or complicated plotting systems to define complex curves then I'd suggest speaking with whomever will be expected to read the drawing and find out what they want and agreeing on a standard. There's no reason to include more printed information in a drawing than is needed for the purpose for which it is being made.
 
that may be, but splines dont always transfer correctly, i've had things water cut and they always send me jpg's of the file they received because theyve had that happen before in the past, i've personally never had a problem but it seems others have
 
It's always prudent to be sure of exact compatability between programs and systems. The combinations of software, operating sytem and file formats are virtually limitless. This is why communication between designers and vendors as well as constant cross checking is so important if you want your parts to fit correctly.

Two problems that come up a lot are smooth bezier curves being converted into short, line segments and scale errors. I know of one case where laser or water jet cut blankes came back about 25% too small! .DXF is seems to be pretty broadly interpreted by different systems.

Always use professional - or at least proven - software to creat your CAD drawing and talk to your vendor before sending a file. Then crosscheck to make sure what they ended up with is what it should be.
 
Thanks! :D That has explained things a bit more.

This morning I went and found several draftsmen with direct experience doing curved stuff and they were unanimous in saying I should use tabulated points plotted around the profile since even if the CAD file got a little scrambled the tablulated numbers would not. The also reckonned that this was the best method to compliment modern manufacturing, water or laser cutting.

I will include some kind of scale lines just to be sure.

Thanks again!:)
 
CAD kills the benifit gained from the art of sketching. I scan my sketches, with a grid, in and work over the lines with MS Paint or now Visio that is easy to learn.
 
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