Tool offset for cutting foam board.

[Guy S.]

When programming the tool paths, do most people run the tool centerline on all cuts, or do you offset the cutter radius?
I’m looking at some of the Flite Test plans, and things seem to be a all over the place dimension wise. All the score cuts for A and B folds seem to really vary and I’m not sure what the intention of the designer was. Or as a machinist, am I really over thinking this?

 

[rockyboy]

Depends on the tool you're using. With a needle cutter or laser cutter, I always go with the centerline. Dimension tolerances are not that tight and I've not had a problem with over a dozen planes cut and assembled like this. Remember, it's just foam board and hot glue!

If you're routing with a 1/8" or 3/32" bit to cut the foam board, it's going to be trickier. You'll need outside offset on all the edge cuts, but score cuts are going to be a mess unless you can find a router bit around 1/16" or smaller.

 

[Guy S.]

I haven’t cut any planes out yet, but I’ve been running a few tests with a .9mm or .035” cutter with decent results so far. How wide of a cut does the laser used for speed build kits produce?

 

[rockyboy]

Not sure how wide their laser is for the speed build kits, but I've used a 100W CO2 laser down the centerline without any kerf problems. Pretty sure anything in the 1mm or less range will be perfectly fine, and could probably go up to 2mm and still have a kit that builds and flys too, just have a little more sloppy A and B folds.

 

[Guy S.]

The reason I asked in the first place is I wanted to offset all the full depth cuts and all the fold cuts, and centerline the bend cuts. But none of the dimensions on the prints make any sense. Again I tend to over think this stuff. I’m going to centerline everything and see how it builds. Thanks for your help.