Improving a Master Airscrew Balsa Stripper

[Gary Manuel]

My next little project is going to be a plan build made mainly from lots of 1/4" square and 3/16" square strip.

In order to save a bit of money, I plan on making my own strip balsa from sheets of the appropriate thickness balsa.

To this end, I bought a MASTER AIRSCREW MA4000 BALSA STRIPPER.

It looks like this:

It uses standard Number 11 scalpel blades, which fit in like this - it can be handed the other way to suit the user.

The thickness of the strip is adjusted by rotating the knob, which moves the blade in and out.
The thread of the adjuster is 1/32", which means that one turn changes the thickness by 1/32".
It is pretty easy to accurately get the required strip thickness.

The problem is that there is a small amount of free play in the thread, meaning that once adjusted, it is possible to move the scalpel blade in / out slightly.
I'm not happy with this:
These two photos show the cut thickness with the slider pulled in......

....and then pushed out, without rotating the adjuster knob.
Free play is about 1/64" - not much but will result in uneven strips.

This is what I've done to improve it.
Two small holes drilled to suit the screws being used.

Beam fitted to clamp the slider in place. Screws are tightened from below.

The modification is completely removable if need be, But I can't see the need as the problem is fixed.
It just needs the beam tightening screws to be slackened a bit before adjusting and then tightened after adjustment / before cutting.

[TinPot Pilot]

While I have no first hand experience of this stripper I remember reading that it cuts straighter if you remove the tip of the blade. If you try it you can let us know if it makes any difference.

[Peter Miller]

While it depends on what you are using the 1/4 sq for usually that size is hard balsa and the balsa stripped does not like hard wood. You are much better using precut strip.

Cutting strips of 1/16" sheet is a bit of a problem as the sheet tends to rise up the blade. a bit of scrap 3/16" sheet will hold the 1/16" sheet down.

[Stevo]

Yes that will lock it in place so well done. I would debate its true accuracy cutting over 4 or 5mm thick and in hard balsa as mentioned. Theres no substitute for a thickness sander though (oh ... OK so I made one... !).

You may save money by buying some 6mm stock and cutting it down. That piece of advice was given to me by the same person who forged 10p coins, by filing the corners off 50p coins

I've used the SLEC one that runs in a channel, but gave up on that too, although the Avicraft one is supposed to be rated highly.

Edited By Stevo on 26/08/2014 18:44:14

[Broken Prop]

Tinpot is right. Most of these strippers seem to work better if the end of the scalpel blade is snapped off.

Also helps to avoid those pierced fingertips when groping in the drawer for it.........

[Biggles' Elder Brother - Moderator]

I like your solution Gary.

TBH, being a bit lazy and impatient, I tend to use the classical way to solve the backlash in the screw in this device - ie take it past where you want and then make all adjustments in one direction only. If you overshoot then wind back to passed where you want and approach again from the same direction. That way the thread is always positively engaged on one end of its play. The time I've spent doing that over the years would have probably accounted for doing this modification 20 times over - but hey ho!

BEB

[Danny Fenton]

Mine is completely slop free and I cut hard1/4 balsa spars with it...... I do use a sharp blade, and the pic you show does not have the blade fully down, so the thick part of the blade is not in the clamp. not sure if that would make a difference?

Maybe I am just lucky it cuts straight

Cheers

Danny

[Gary Manuel]

Thanks for the tip about breaking the end of the blade off and lowering it down - I can see how that would help stiffen things up and reduce drifting.

Blade is only shoved in part way for checking it out and doing the modification.

I'll give your tips a try when I start cutting. Just been and picked the sheet balsa up from a friend who bought it at the Nationals for me.

[john stones 1 - Moderator]

4000 1/16 square spars later, yep i'm happy with that

John

P.S my balsa stripper cuts fine, just needs a bit of patience you youngsters are always in a hurry

[Plummet]

I had a similar problem with mine.

The problem (from memory!) is that the length of the threaded shaft is a bit too long. I solved it by adding washers between the rotating knob and the fixed bits to reduce friction, and by threadlocking the knob onto the threaded shaft with as little play as possible.

Plummet

[Nigel Day]

That Avicraft one does look good Stevo. I didn't see how many ratings it had but the width range is good.

You sound as though you've got time on your hands and plenty of patience John. Perhaps you could compare them all side by side and give us a report on your results?

[Ron Harrison]

I tend to use a Curved Blade on mine

[Gary Manuel]

Here's the results.

I snapped the end off the blade as shown and adjusted the depth of cut so it would be just more than half of the thickness of the wood. As I am stripping 1/4" (actually 6.5mm) square, I used the thickness of the wood to set the width of cut rather than measuring it before locking the slider in place with my hardwood beam thingummyjig.

This picture shows the stripper in position before cutting. After cutting, the wood was flipped over and cut from the other side.

Here are the 15 strips of 1/4" x 1/4" x 36" (6.5mm x 6.5mm x 915mm), I made from a single strip of 1/4" x 4" x 36" (6.5mm x 102mm x 915mm). Turning a strip through 90 degrees and comparing to an unturned one confirms that they are very square. Note that it is not possible to get 16 cuts of 1/4" square from 4" sheet due to the metric thickness. If you cut the sheet into 16, the "squares" would be 6.4mm x 6.5mm.

The offcut measures 2.5mm by eye all the way along with no signs of taper or twist.

I checked the measurement with a digital vernier gauge (not easy due to softness of the wood) and it varies between 2.54mm and 2.68mm.

I would call this a result. The quality of the squares in my opinion is better than shop bought ones as they are truly square and the edges are undamaged. I will not be buying strip balsa again.

I think it's worth comparing prices of strip versus sheet balsa to see whether there is a cost saving.

Using SLEC online prices (because they are readily available),

1/4" x 4" X 36 sheet is £2.02

1/4" x 1/4" x 36" strip is £0.32

15 strips of 1/4" x 1/4" x 36" would be £0.32 x 15 = £4.80

Cost saving per sheet is therefore £4.80 - £2.02 = £2.78 - and I have a handy offcut strip.

The stripper will have paid for itself by the 4th sheet

[Danny Fenton]

Result! the only other thing I would add, and i think its important is the strips you have cut are as close to identical as you will find. I will agree that a sheet of wood can vary from one end or even one edge to another, however usually they will be consistant. So if you are after spars the strips you have cut should be of equal weight, stiffness, and strength. This not only applies to spars but longerons etc in fuselages will bend evenly.

Cheers

Danny