I'm a complete noob and today discovered the secret to setting stroke widths. But I can't save from SVG to DXF. I save as SVG (looks great,) then try to "save as" DXF and it gives me the warning "The file xxx was saved with a format that may cause data loss." I save with the presets,close and when I reopen I get nothing.

Hi.

Dxf is more of a cad format. I. e. cad softwares open those rendering either filled shapes or lines, polylines etc. (Don't expect pattern fills, gradients, masking/clipping/filters, just the geometry.)
Probably the latter, in your case. There are 256 predefined stroke widths which are assigned to pens, of which are usually rendered with 0 stroke width/as a hairline by default -all in a cad software.

Therefore my guess is you had a line drawing in your svg file with stroke and no fills, which upon reopening turned to be paths/polylines with no stroke attributes set.

Make sure your imported file is not empty by switching to outlines only rendering mode (Ctrl+5 twice on the numpad).
If it is really empty, then check the save as dxf options, what the paths are converted to.
If none of those work as expected, maybe share which inkscape version&os you are using, and the svg in question.

You might also consider using "Save a copy as" (dxf) and keep the SVG file as the working master.

You can still open the dxf in Inkscape, but it might be best to use a CAD program like LibreCAD to validate the dxf file.

I'm heading back to inkscape to "try stuff" as recommended but in short, all I'm doing is trying to create single block letters in inkscape one-at-a-time and then convert them to use the file in a laser cutter to cut them out. The suggested file format for the laser software is dxf. Pretty basic.... I am saving the originals as svg files then trying to resave and or export the original as a dxf file, maintaining the original svg. The svg is still OK after the process but no joy on the dxf. As mentioned will work on it.

Maybe you can share a file?

I agree, an example file would be good to examine.

TIPS:
When saving a copy as dxf, ensure that text objects created with the text tool are converted to paths before saving as dxf.

(Actually, all objects should be converted to paths, since dxf does not recognize many SVG objects.)

There is often a size discrpancy when saving as DXF. When you open the DXF, try zooming out. In my experience, the DXF is always zoomed way, way in, so that I can't see the contents.

So possibly the file is not really empty.

DXF is a 2D CAD format developed in the stone age by AutoDesk Company. Here's what they have to say:

To be clear:
DXF is unitless. All CAD programs have to assign unit value on import.

Inkscape is no different. That is why there is a scale entry in the input dxf dialog.

Using Inkscape 0.92 and this is the file:

Lazur: My original file had a .001 stroke (per instructor) and a Flat Color Fill. I am trying to convert to dxf so I can cut it out on a laser cutter which I assume will require lines only with no fill.(?)

I tried opening SVG file, tried changing to "outlines only rendering mode" with no changes.

tylerdurden: That's what I'm doing, "Save as..." and am opening or trying to in the laser software, Lasercut 5.3

I also tried converting to paths with no success...

brynn: I zoomed out (and in) as far as possible with no success.

tylerdurden: when I try to importI get the "Seek failed" error...

Hi
Select Text - Ctrl-a (This selects everything - this file contains one text object only.)
Convert text to path. Shift-Ctrl-C
Ungroup.Shift-Ctrl-G

Use Dialog to for next thee operations.
Shift-Ctrl-F to bring up the dialog box.
Remove Fill.
Set stroke to red.
Set stroke width to 0.1 (Or whatever your laser cutter software wants)

Adjust page-size to object (or set object size to pagesize) Shift-Ctrl-P

Save as DXF.

Result:
Test01-1_Modified.dxf

SVG File:

Thanks, Ragistian... I've played with it a little bit. When I open the new dxf it's huge and I have to adjust size which I can muddle through. My stroke is supposed to be .001 per instructions but that comes out invisible so I adjust that so I can see it. But I also need to smooth or connect where the elements (?) come together which I don't know how to do yet. But it's getting there. Much improved over what I was getting. Thanks....