@misterfish:
As said, Xacto do make a special blade for their balsa stripper (looks a bit like a small flat rectangular chisel) but they're quite hard to find (model shops should stock them but often have to order them in specially). So after I finally ruined the blade that came with the tool (that was years & years ago) I didn't bother any more.
You need a fairly thick-ish blade to match the width of the slot in the base of the tool, but you don't mount the blade into the tool at all, just hold it in position with the handle, as follows:
I normally use either Xacto No. 11, 21, or 25 blades (the Swann Mortion blades which are even better than Xacto are a bit thin for this tool). Just set the blade up in the approrpriate handle (the No. 25 blade uses the big red plastic handle, the other two use any of the Xacto slimmer ali or plastic handles). You must strip the sheet while it's resting on a hardwood cutting board (or a plastic cutting mat) as the amount the blade pokes down below the tool only needs to be a tiny fraction more than the thickness of the sheet you're stripping from and basically that's controlled simply by the point of the blade coming into contact with the wood or plastic beneath the balsa sheet being stripped.
Assuming you're right-handed you "just" support the knife handle at about a 45 degree rearward using the right hand and then using the left hand slide the whole tool and blade/knife combination along the sheet while at the same time making sure that the ali "fence" stays in contact with the edge of the sheet (observe the direction of the grain and make sure you don't strip in a direction which would tend to drive the fence away from the edge of the sheet, so messing up your nice and accurate even width strip). DAMHIKT!
This all sounds a bit crude and remarkably hit & miss but it works surprisingly well after a bit of practice.
There are other, more complicated and "better" balsa strippers on the market, including very expensive ali plate-based tools with built-in micrometer width adjusters but as you may imagine, these are the province of the indoor guys with micro film models.
By the way when you've sorted out the boxes of balsa and plans from your Dad's collection they will almost certainly have a greater value than you imagine (assuming you're not an aeromodeller yourself). The world-renowed magazine "Aeromodeller" has just re-started publishing again after a few years layoff and when you have a list of stuff to sell it would be well worth your while to get a small ad into that mag. I don't think they charge a lot for small ads.
The new publishers are ADH, details:
ADH Publishing Ltd; Doolittle Mill, Doolittle Lane; Totternhoe; Beds, LU6 1QX.
Tel: 01525 222573; Fax: +44 01525 222574; no E-mail listed, sorry.
Hope this helps and is not too much info.
Krgds
AES