Joining dashed line segments in large DXF drawings

Typical RC plane plans come in PDF multi-page format… with full-size, untiled plans often being 20" x 30" (508mm x 762mm) or larger. Different cut lines are usually color-coded and some are dashed lines… red (for scoring cuts), as in photo

Given the large drawing dimensions, each segment/gap of a dashed line may be ~10mm ( about 6.5mm segment + 3.17mm gap in this drawing)… but the segments need to be joined together to form one line and I’ve found no easy way to do that in LB.

A workaround is to import PDF into Inkscape, select all, and uniformly shrink (typically by one-half) the drawing dimensions so that the gaps in dashed lines is less than 2mm (max auto-join tolerance setting in LB). Saving as DXF in Inkscape, import into LB, and auto-join then works to join the red line segments into a single, unbroken, line. The drawing then needs to be enlarged to full-size again.

Popular Grbl-based CNC needle-cutters for foam sheet often use servo-driven Z-lift for cutter head… similar to pen-lift plotters. M3/M5 are the commands most used… and GRBL-M3 does a great job creating good gcode for cutters. But unjoined dashed line segments result in many unnecessary cutter up/down motions… whereas joining them allows for smooth line cuts.

I’ve searched unsuccessfully for a couple of days for ways to join these lines segments. Is it possible to do this in LB today? If not, can it be added? DXF auto-join works as long as the gaps in dashed lines is within auto-join tolerance… should the tolerance range be increased to allow full-size drawings to be properly handled? LB is fantastic… would be even better with this additional feature.

Thanks in advance.

It’s feasible, yes - I plan to make a version of the auto-join tool that allows for arbitrary join distance, and is interactive (or as interactive as it can be). Having said that, the file you show contains about 16 such lines. You could quickly just draw over them with a new color, then delete the original layer contents, no?

There’s a very large. and growing, community of folks now using needle-cutters on their CNCs… I have a very long-running, and eclectic, thread on the FT forum dealing with this, and related, topics. FliteTest’s free PDF plane plans are extremely popular with this group and I’m trying to help new CNC and needle cutter users/builders process the plans and produce gcode for their own machines. Most of us have been using Inkscape in some way for years… gcodetools, JTech’s laser plugin, and a sender of some sort. SketchUp/SketchUCAM is also used by some. Getting together a workflow is a major barrier to new users and switching back and forth between new and unfamiliar programs is painful for most.

A 73-year old, retired, engineer, I enjoy building CNC machines – mostly Marlin- and Grbl-based MPCNCs and variants. A new machine on the scene is Edward Chew’s foamboard cutter and it uses the servo-driven Z-lift I mentioned… and his community is growing fast. I’m trying to help streamline a workflow that is very daunting to the influx of new CNC and needle cutter users. Lightburn can do it all and would be my first recommendation… IF this dashed line conversion issue can be dealt with.

Sure, 17 lines (multiplied by several pages per plane and a whole fleet of planes to be built) can be manually massaged, but WHY… when LB’s auto-join works beautifully IF the tolerance on join distance can be specified large enough for these larger drawings; i.e. shrinking them to half-size proved that. Inkscape, with its layering and wealth of node editing tools can also do all the necessary processing for these plans, with a plugin to generate the gcode… but it has a pretty steep learning curve for new users. It is, and has been for several years, my other recommendation.

But using it almost daily for the past month, LB is IMO far easier to use (even my daughter likes it… and she’s one of those new users), has a great reputation and following, runs beautifully on Linux (my preference) and most other platforms (would love to see it on Pi also…), and does EVERYTHING we need it to do… except this one thing. Otherwise, it’s near perfect for this application. BTW we also hang lasers/pens/drag-knives/etc on these machines… so LB could be the “one-stop” shop for all our center-line engraving needs… :wink:

Thanks for your interest and consideration.

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As I said, it’s a planned change - it’s just a matter of when, not if - it’ll happen. The “close shapes” feature has been set up to work this way already. Auto-join with a tolerance is coming. too.


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