I would think - the harder the wood, the harder it is for the laser to cut through it. The top cut was burnt and wide. The cut didn't go all the way through to the bottom.
I took some passes with a sharp knife to get through it.
I don't mind hard balsa fins, They'll hold up better on a hard landing.
With laser cutting there is no real need to gang sand fins to get them all the same shape.
Hand cut fins should be stacked and gang sanded to get them a consistent shape. With laser cutting, you draw one then copy and paste it two or three more times. It's the same fins profile over and over.
When sanding off the burnt edges at a 90 degree angle you can see the wedge angle of the laser cut.
I've read instructions where you are told you can leave the burnt edges as is. They say glue will still hold on the charred edge.
Not me. I remove it and square up fin edges with 220 grit on a sanding block.
Agreed. I sand off the charred wood as well. The glue might hold, as they say, but why take a chance?
ReplyDeleteHi Lonnie,
DeletePersonally, I don't think the glue would hold as well on a burnt edge. I still see models at club launches with paint over the burnt edges.
I can't figure out why the instructions still tell you to gang sand all the fins - being laser cut, they are all exactly the same size. Unless you are really heavy handed, you should be able to sand them separately without changing the shape.
Well...admittedly, I'm pretty heavy handed myself when it comes to sanding and have over-sanded fins out of shape from each other, even when gang sanding! I try to keep reminding myself it's balsa, not oak.
ReplyDeleteIt's probably safer for the companies to continue recommending gang sanding laser cut items for novices and hamfisted builders like myself, at least for the additional practice :^)
Hi Lonnie,
DeleteMaybe it is safer for the manufacturers to recommend gang sanding. I guess everybody doesn't have a sanding block!
Get this - Balsa is considered a hard wood!
When I was a kid, the sanding block that I had was literally a block of wood onto which I'd wrapped a piece of sandpaper and tacked (with thumbtacks) into place.
DeleteOne would think you shouldn't have a problem -- but in the unlikely case where the laser cutting pattern is based on a trace of die-cut (aka "die-crunch" or "die-crush") or "printwood" master, then you could have variations in the shape.
ReplyDeleteWith regards to being heavy-handed on sanding, there may be differing opinion on what "fine" grit sandpaper might be. If you go to the hardware store and ask for "fine" sandpaper you'll probably end up with 120 grit, or "medium" and end up with 80 grit -- a bit too coarse for use with balsawood.
There's also the advantage to gang-sanding the parts - if you tack-glue the parts together (so they won't slip) it does help to reduce possibility that the parts will flex (and affect the squareness) of the parts as you sand them.
Hi Naoto,
DeleteI doubt the laser patterns are based on the die cut fin blocks. Die cut blocks are razor blades set into a wood block. These are pressed into the balsa sheets. The blades can shift, three fins could end up slightly different. Gang sanding is needed there for consistency.
Laser cut fins are designed on the computer. You draw one, then copy and paste it as many times as needed. The first one should be the same as the 2nd 3rd or 4th.
I agree, different sandpaper grits have different designations depending on the manufacturer. For me I buy three grits, 100 rough, 220 medium and 400 grit fine. I have some finer stuff, all the way up to 1500 grit for some instrument finish polishing.
The reason why I mentioned tracing was that I'd run across situations where someone was having trouble understanding why you can't scan some diagrams and then have the graphics software autotrace the contours to obtain the vectored paths - and they couldn't figure out why the result ended up looking lopsided. Luckily it was simply working with artwork in the computer and not involving any kind of tooling.
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