I am scratch building a plane and want to gang drill lighting holes in the wing ribs. What drill bit works well with balsa. The last time I did this the bit tore or jammed up with the balsa.

I had made small holes in some to allow wires to pass through. I used tubes of brass, and sharpened the tip like a round exacto and put it into my drill... worked great.

I'm sure you're looking for bigger than 1/4" diameter, but it's just my example to point out anything WITHOUT teeth and razor sharp will work well.

Maybe a copper tube from the hardware store? and file the INSIDE the the pipe sharp... I've hard no luck with conventional drill bits or hole saw bits into balsa sheet...

just my .02
hope it spurs some ideas for ya

Don't know what size you're dealing with, but here's a couple of choices for you.

First drill a hole in the ribs/fuse/or anything else using a standard drill. Do it carefully so that it don't tear too bad.

Then chuck a sanding drum or rotary file into a drill press. Use THAT to enlarge the holes to the correct size.

always,
tony

What's the shape and size of the lightening holes ?

To drill a hole in balsa without tearing the balsa. Turn the drill backward Most drill presses will not turn backward so you will probably need to use a hand drill that is reversable.

Good Luck
Lee

This is interesting and gotta try it out. How did you discover this ?

For Larger holes, Forestner bits work reasonably well if you lay the balsa flat on a backup board and feed the bit slowly.
For holes up to 1/2 in. the thin walled brass tubing with the inside beveled to the outside making a sharp edge. Use Dremel and small stone to bevel the end. Keep it sharp. These are good for balsa and thin ply. The tubes can be cut to length or leave then full length (12 in is what I usually get them) and chuck them in a drill. The smaller holes in balsa can be cut by hand rotating the tubing. Good luck

How much weight are you aiming to save?

It can't be be more than about 1/10 ounce, surely. I bet the total weight of the whole ribs is way under an ounce.

I would have thought you will be losing too much strength for the weight saving you could achieve, and you could save at least as much from a less stressed component.

I reckon ARFs lighten their ribs for looks, more than weight saving!

My 2c!

-David C.

Two possibilities for you -

Drill the holes before you cut the ribs.

Get the ribs laser cut.

Hi

copper tube as mentioned above works well - I use the metal part of a shotgun shell for large holes - the trick is to separate the plastic tube from the metal part without deforming it - I use a heat gun turned up high.

Tim

Hi

copper tube as mentioned above works well - I use the metal part of a shotgun shell for large holes - the trick is to separate the plastic tube from the metal part without deforming it - I use a heat gun turned up high.

Tim

Hmmm.........If I left the shells IN the shotgun and aimed at a stack of ribs............................Na, probably make a mess...

Careful now Jemo, you don't want to remove TOO much weight. LOL !

To drill a hole in balsa without tearing the balsa. Turn the drill backward Most drill presses will not turn backward so you will probably need to use a hand drill that is reversable.


I have never tried to drill balsa by reversing the bit direction, but I do have a set of reverse drill bits, used for drilling out broken studs.
This will allow me to use my drill press, I will give it a try.

I would go with the sanding drum method.

You should certainly use the sanding drum for final finishing if possible (depending upon the size of the drum and hole).

Drilling a small hole that a small rotary rasp/file can enter might well be the first step of a three step process--use the rasp to enlarge the hole big enuff for the sanding drum as the second step.

always,
tony

Thanks for the replies from all you out there . The size of the holes range from 1/2 " to 1 1/2 " . I am making ribs for a wing with a 24" cord. I gang cut the ribs all 30 at once. Then I drill the holes, after that I take them out of the jig . Remove the balsa between the holes and you have fast and light wing ribs . this process takes about 2 hours. As for the weight savings the ribs weigh about 1/3 less.

I tried the backward drilling technique last night and it worked absolutely perfectly. I tried it on plywood also and again perfect. Thanks for the great tip.

I used my reverse drill bits, to try the backward drilling. It's not bad, but my crown point bits make a perfect hole.

Of course the quality of the initial hole doesn't mean much if you are going to open it up with a sanding drum or whatever.

I like to use 2-flute end mill bits at high speed. Razor sharp edges and can be used for making round flat bottomed pockets and counterbores, and with a 2-axis vise, you can use them to mill slots and such in wood with your drill press