Confused dxf files

[mickbeeza]

Hello, I had a go at using DeltaCad to draw a component for laser cutting and saved file in dxf. format.  The laser people were able to download from a memory stick and cut the parts, worked perfect.  

I asked them to copy the files they had drawn for me for previous work, they use auto cad.  As I understand it, saving files in dxf should allow files to be read by other programs as it did with my file for the laser cutting, but when I open these files in DeltaCad the units of measurement comes up as "unknown measurements" and it would appear that where the width of a part was 22mm it shows on the drawing as 22 inch even though it states "unknown".  I have tried all I know to get the drawing to open to the original sizes but without success.  Only way I found was to adjust the scale once it is open.  

What I am wanting to do, is to change some small details on these drawings and return them for cutting, but with the scale changed I'm not sure what size parts I would end up with as the scale would not be 1:1. 

Please can you tell me, am I correct in my understanding of dxf files being transferable (it works one way, why not the other?) and have I got a setting wrong when I try to open them in DeltaCad?  Thanks.

Regards
Mickbeeza  

[AlwMVMO]

Open the DXF file in notepad and search for:  $MEASUREMENT
The next line will be  70  and the line after that will be  0   for English units or  1 for  Metric units.

Next search for  $INSUNITS
The next line will be  70  and the line after that will be one of the following numbers:
0 = Unitless
1 = Inches
2 = Feet
3 = Miles
4 = Millimeters
5 = Centimeters
6 = Meters
7 = Kilometers
8 = Microinches
9 = Mils
10 = Yards
11 = Angstroms
12 = Nanometers
13 = Microns
14 = Decimeters
15 = Decameters
16 = Hectometers
17 = Gigameters
18 = Astronomical units
19 = Light years
20 = Parsecs

If your file shows:

$INSUNITS
 70
     0            <--  then edit this line to  1  for inches  or   4   for millimeters.

If this doesn't help,  then see if they can export their DXF files to a different version.

[mickbeeza]

Hello AlwMVMO. 
Thanks for your reply.  I have checked the files as you recommended and they are showing as being in millimetres.  I tried changing them around to see what happens but without success. I'll have a word with the laser company and get another copy to try.  Thanks for your advice,  I use a mac so downloaded a text editor called Textwrangler from the Apple store which I found easy to use to check this.
Regards
Mickbeeza

[mickbeeza]

Hello, Got this sorted. 

It would appear that DeltaCad read the files as being in inches so an item that was originally 22mm wide came up as 22 inches wide.  Just a matter of sorting out the scale. 

Open one of the files I received  and in place of "unknown units" enter "inches" and drawing scale of 25.4 with viewing scale at 1.00 this brings it to actual size.  Next, select and group the item then copy it to pasteboard.  Open a new file in millimetres and scale of 1:1 then paste the item then ungroup, and I have a drawing I can work with, in millimetres and exact size.  
Just the job.
Another good thing about this, is that I have learnt a little about text editors and file construction from the reply from AlwMVMO.  Thanks

Mickbeeza.

[Admin 1]

AlwMVMO,

It looks like your helpful response to 'mickbeeza' is a good candidate for a similar, though perhaps a more generic, new "Hints & Tips" thread.