How To Machine Balsa Wood

[Metal Head]

Hi,

I hope I have got the correct section:?. I just searched the above subject matter but only a joke about balsa wood came up:rolleyes:.

Anyway, I have got to turn a 75mm (OD) x 750 long out of a square shaped (100 X 100 X 850mm long) piece. My boss thinks that the best way is to turn it at a very fast speed and use a sharp cutting tool - we are based in a metal work shop. I have never machined this material previously, so I would be grateful for any advice - we don't have a woodwork lathe.

I was thinking of screwing plates on both ends to grip in the chuck and hold with a centre in the tail stock. This would eliminate damaging the wood.

Thanking you in advance
MH

[Skew ChiDAMN!!]

You won't believe the tearout! :rolleyes:

IMHO, from experiences with turning balsa nose-cones for model rockets, you're better off whittling it to a roughly cylindrical shape with a good sharp knife (or even [gasp!] a belt sander) and then mounting it in a lathe at low to medium RPM and using surforms for bulk removal and files then grits for finishing...

If you go ahead with using plates, I'd suggest you make sure they're round with smooth edges, otherwise they're basically miniature circular saws... and when wood-turning your fingers tend to be a lot closer to the spinning bits than when metal turning! :oo:

[joe greiner]

It's difficult enough to get adequate purchase of screws in end grain in harder wood, because they behave more like drills; in balsa just about impossible. In either case, hardwood dowels placed cross grain can give the screws something to engage. I'd leave the headstock end plate square, for mounting in a four-jaw chuck, but round at final diameter at the tailstock, as Skew recommends.

Like Skew says, tearout will be amazing. You'll get more dust and shreds than clean curls. Your tool post and regular cutters will be almost no use at all. I'd suggest carving or hand planing the corners off, repeating until the piece is almost round. All this with the piece rotated by hand. Then, you may be able to make slicing cuts with the plane's blade almost perpendicular to the axis of the lathe to attain the final diameter. Nice thing about a metal lathe is that you have very slow rotation speeds available, but beware of spiral patterns developing in the cuts. As the shape develops, you can increase speed. There's not enough room at the ends to accommodate a hand plane as I suggest; for those locations, I think you could put a flat bar in the tool post, parallel to the lathe axis, to function as a wood-lathe-type tool rest for a skew chisel or detail gouge.

Your final proportions, combined with the low stiffness of the wood, will make it vulnerable to whipping. Use minimal tailstock pressure to reduce bowing. A steady rest would also be advisable; but not the kind usually used on metal (with rigid arms) - better would be something with soft rubber wheels to avoid pressure damage to the balsa. There are many commercial and DIY versions based on skateboard wheels.

I hope this is food for thought. BTW, how many of these will you need? Volume production could alter procedures a bit.

Joe

[China]

I worked machining balsa for a few years producing model aircraft components, to turn up a cylinder we used a lathe and a powered cutter on the toolpost, it was a semi auto set up, we had to get the cutter custom made, I would suggest for a "one off" to rough out with a rasp then move to a file then to abrasive paper etc. a dust mask is essential, you will look like snow man after you finish

[Metal Head]

To China, Sskew & Joe.

I have a big apology to make to all, in that the job is now not going ahead:doh:.

It turns out the undergraduates who wanted the job done had not heeded the words of their supervisor who apparently told them that the task had to be done by using only hand tools. As a result of trying to get the job done outside the scope of work, they have been reprimanded by the Head of the Department late this afternoon and will have their final mark by 30% :2tsup:.

Well I was always taught it doesn't pay to cheat but they are (& rightly so) going to pay a high price for theirs.

Thanks for the advice. I am sure I will not have been the only one who has gained from it.

Cheers
MH