Cutting balsa and ply

[IQChallenged]

"Let's look at the numbers:"

This is probably the most helpful post I've seen. Gonna print it out and put it on the wall. Thanks

[ger21]

Ballendo was the most helpful person around back when he posted that. Unfortunately, I haven't seen him post in a few years, even on the Yahoo groups where he spent most of his time.

[Rockomo]

Great information Gents!

I was wondering what technique was being used to attach the balsa to the table?

[Arbo]

Good question, it would seem you'd almost need a vac table for balsa.

[Jcadwell]

I've used 3M 410B double sided tape to hold parts down. It is a machinists paper tape that is about .005" thick. Works great, although a bit pricey.

[PropNut]

I am going to revive an old thread here, but....

I did my first Balsa project today. I needed ribs for my 1/3rd scale Sopwith Triplane (I nosed over and destroyed the top wing last weekend in front of a crowd of people...you never seem to do those things when you are alone huh?), so I used Vcarve Pro to create the G-code from my original drawings (used DesignCad 16 to create the DXFs) and Presto! I have perfect ribs and rib tips! Thanks to Bellendo for posting the excellent information about speeds amd feeds. this helped tons! I used a 1/16 bit cutting at 60ipm with my Bosch router set for around 12,000rpm.

The pictures are of the parts loose in the spoil. I put them back to take the picture. There were 1/8" tabs before I removed them. Masking tape along the edged held the work piece to the spoil board and I put the depth just slightly through the piece to ensure a good cut along the 48" length (yes, I need to true my spoilboard).

[MadMax]

It's been ages since I've built a RC plane. Man that was a fun hobby.

It's hard to tell from the pics. Are you using quarter grain balsa?

The original poster Markdib mentioned that he had varying performance cutting soft or harder balsa wood. I didn't see any discussion on balsa selection so I'll toss in my 2c here.

There are two basic cuts of balsa wood which yield significantly different material properties which make selection an important process. Take a look:

http://www.dave-cushman.net/aircraft...selection.html

Basically you can buy balsa sheets that are dominantly cut in tangent (A-cut) to the rings of a log or radially across the rings of a log (C-cut or quarter grain). There are cuts between, but they have more warping issues so I'll skip it. C-cut balsa displays better stiffness across the dominant grain direction so it's an ideal material for parts which are meant to be stiff in all directions (e.g. ribs). A-cut is flexible across the grain which makes for poorer ribs, but is nice and formable for sheeting leading edge wing bends.

Very soft balsa woods (sometimes called contest grade) tend to be A-cut close to the periphery of the log (I think) and makes for very poor ribs, but is excellent for light sheeting which really just has to billow out the covering over rib curves.

Man I miss making planes. Back in '93 CNC cutting wasn't so widespread. It was all X-acto knife and jig saw stack cutting. I used to photocopy my rib profiles and use a hot iron to transfer some of the toner.

Try your hand at selecting particular cuts for various parts, you can make lighter planes with stiffer airframes with good material selection. You can also save weight by using adhesives sparingly. My first planes were pretty heavy, dripping with over epoxied joints and cyano saturated sections.

[Arbo]

I've cut some balsa since the last post. 1/16" 2 flute down cut bits. Don't have the timing all right yet. But for hold down I clamp a 2'x4' piece of MDF down, plane it flat, and use 3M-77 on the balsa, push it down. Sticks fine. And the MDF can be replaned if you tear it up. No issues getting the parts up so far.