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Author Topic: Using Feeler Gauge Blades for sanding down balsa to required thickness  (Read 1538 times)
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Glidiator
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« on: July 19, 2015, 01:32:57 PM »

Havent been able to get balsa sheets less than 1mm thickness in India. Many indoor free flight models which I have been building need 0.5 mm thickness balsa for propeller or wing frame ribs etc.
While building the Minnie Mouse (50% version of Hangar Rat) I needed 0.5 mm balsa for the prop blades.
I ordered for two 26 blade sets of Stanley Automotive Feeler Gauges 0.04 mm to 1 mm thickness measuring gauges from Amazon .in - INR 350 each.
Taped the two 0.5 mm gauges on either side of the 1mm balsa sheet and with sanding block reduced the thickness to exactly the thickness of the 0.5 mm feeler gauge blades.

I can now get any thickness from 0.04 mm to 1.0 mm accurately using this method.

Also plan to fix a razor blade between the two feeler gauges to get balsa strips of required dimension from 0.04 mm to 1 mm quite accurately.
Has anyone tried this method?
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retired1
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« Reply #1 on: July 19, 2015, 02:13:46 PM »

Have you checked the before and after weights?  Somewhere I read that the sanding process slightly compressed the balsa so if you went from 1.00 mm to 0.050 mm, it would probably weigh a bit more than half.  Like changing it from 6 lb to 8 lb balsa.
Fortunately in the mainland USA I can buy virtually any thickness by paying the special order price and the shipping which is frequently more that the cost of the balsa.
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Dave Andreski
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« Reply #2 on: July 19, 2015, 06:05:50 PM »

Havent been able to get balsa sheets less than 1mm thickness in India. Many indoor free flight models which I have been building need 0.5 mm thickness balsa for propeller or wing frame ribs etc.
While building the Minnie Mouse (50% version of Hangar Rat) I needed 0.5 mm balsa for the prop blades.
I ordered for two 26 blade sets of Stanley Automotive Feeler Gauges 0.04 mm to 1 mm thickness measuring gauges from Amazon .in - INR 350 each.
Taped the two 0.5 mm gauges on either side of the 1mm balsa sheet and with sanding block reduced the thickness to exactly the thickness of the 0.5 mm feeler gauge blades.

I can now get any thickness from 0.04 mm to 1.0 mm accurately using this method.

Also plan to fix a razor blade between the two feeler gauges to get balsa strips of required dimension from 0.04 mm to 1 mm quite accurately.
Has anyone tried this method?

Gladiator,
Have any pictures?
Dave
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leop
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« Reply #3 on: July 19, 2015, 09:51:03 PM »

In the November 2013 INAV article on my F1L, I explained, in the addendum, how I made the prop blades by sanding hobby shop[ 1/32" thick balsa sheet.  I had no density gain from the sanding when weighed after soaking and forming the thinned blade forms.  The soaking expanding any compressed balsa cells although I do not think there was much, if any, compression.

LeoP
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Glidiator
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« Reply #4 on: July 19, 2015, 11:59:51 PM »

Hi all,
Posting Pics

Nothing very technical. Just the two blades taped firmly alongside the balsa piece to be sanded.

Used a light touch and did not press down to sand faster.

Will do another piece and check before and after weights.

Anant
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DavidJP
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« Reply #5 on: August 03, 2015, 11:18:40 AM »

Rather clever I think and perhaps a good solution if you cannot buy wood of the required thicknes.

Of course there was a time when ideas like this were always being shown in magazines because you could not buy so many different things and had to improvise. 

And money was short too. 

So maybe we are pretty lucky today?. So much available.

So, did you weigh any pieces?
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Glidiator
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« Reply #6 on: August 04, 2015, 04:47:46 AM »

Hi David,

Took a 1" x 1/2" piece 1mm thickness

Weight  0.13 gms

After sanding -- .07 gms.

Almost half. Also the accurate thickness of the original piece may not have been exactly 1mm.
But gives a fairly good idea of the process

Just ordered 2 Master Airscrew Balsa strippers from Hobby King. We live in an age of convenience and readymade solutions.
Any idea if this stripper is efficient and accurate.
Also looking for a 5:1 and 15:1 winder. Any suggestions where I can get it at a reasonable price. But international shipping almost doubles the cost.

Have an old hand crank of wife's sewing machine. Bit heavy. Must check winding ratio.

Anant
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DavidJP
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« Reply #7 on: August 04, 2015, 05:04:26 AM »

Hello Anant,

I am no expert but the weight loss seems pretty good and logical?

I use two balsa strippers - one made by an engineer friend for heavier stuff, for example hard 1/8th upwards and another that will strip 1/32nd well if you are carefull.  That came from a shop here called Avicraft.  £10. It is on their website.  I am not sure if the companies put up the shipping charges?  It may be interesting to see how much the post office would charge to send one to India.  It would not need any expensive packing.

As to a winder well it depends on the type you want!  Some people spend hundreds of pounds whilst others (and this includes some of the well known contest winners) make do with a hand drill and a piece of bent wire!  Very cheap! You can fit a counter. 

I have a small plastic one for small models - say 20 inch span or so and a hand drill for the bigger ones. But then I am not a serious contest flyer. My small plastic on was about ten pounds.

I find these are OK for me but it might be better if the more experienced people commented.
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Hepcat
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« Reply #8 on: August 04, 2015, 06:25:28 AM »

Gladiator,
I think your method with the feeler gauges is excellent so I am not trying to top it but perhaps the picture below may be useful on occasion.  I don't know who first had the idea but it has been around for years.

The bit of aluminium 'Tee' angle just happened to be handy at the time and is easy to handle.  Almost any sanding block will do.  A thick type of adhesive tape is wrapped around the angle, spaced apart to suit the width of sheet to be sanded and to the thickness you want to sand.  With this method you do require a micrometer or caliper to check thicknesses.

Have you tried the dodge of fixing some fine sandpaper to your bench, sand side up, where the wood to be sanded is placed.  It makes it much easier to hold without breaking?

John
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Glidiator
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« Reply #9 on: August 04, 2015, 07:41:12 AM »

Hi,

Do have a hand drill. Ratio is 3:1.
Also have an electric winder. Got ut for just Rs.300/- (£3??).
But it cant take too much torque. Motor whine changes as torque increases.

Yes, Hepcat have read about putting fine sand paper to hold wood. Probably on this forum.
Will do that when doing next sanding.

My next project is to make my own props and bearings. Have drunk a lot of beer and have a collection of cans. Have been taking the easy way out using Ikara propellers and trimming it as required. Must try the wetting and baking method also.

Anant.
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USch
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« Reply #10 on: August 04, 2015, 11:13:38 AM »

Hi Anant,

for the winder try Mike Woodhouse (has cheap freight charges) at
http://www.freeflightsupplies.co.uk/
or
http://www.kpaero.com/ProductReport.aspx?Category1=rubber
for the yellow winders 1:5, 1:10 and 1:15 ratio.

I use a similar contraption for sanding to a specific thickness, instead of the steel blades I just glued two 1mm plywood strips to a hardwood base. If I have a different thickness to produce I put some tape on the strips to get thicker sheets, if it has to be thinner I place something under the balsa. Rough sanding with a sanding block 20x8x1,5cm, rounded edges!!! and 220 grain wet and dry sandpaper, finishing with 400 grain.

Urs
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« Reply #11 on: August 04, 2015, 12:14:12 PM »

There are several tricks to improve the Master Airscrew strippers.  The biggest one is to replace the #11  blade with either a thicker heavier duty similar blade (for #3 handle) or to use a rounded tip blade for the #1 handle.  Mine uses a large scalpel blade.  The other trick is to sand out the draft that is in the plastic mold.  This tries to let the wood raise during the cut and removing this draft angle greatly improves this problem.  There used to be a long entry containing this and other ideas on the defunct SFA blog but I think that there has been at least one here on SFA.
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Olbill
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« Reply #12 on: August 04, 2015, 04:51:03 PM »

I don't know if Dennis Tyson is still selling strippers but if not maybe someone has one they'll let go of. I use mine every time I build anything. The thickness scale I put on mine is useless except for making relative size change.

When I first started in indoor I used the sanding block with tape strips to sand sheets to thinner dimensions. It worked fairly well but then TruWeight balsa became available and it wasn't necessary to do that any more.

It's actually pretty difficult to find indoor wood anywhere these days.
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lincoln
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« Reply #13 on: August 04, 2015, 11:30:22 PM »

Since it's difficult to find "indoor wood", sanding to thickness can be very useful. It was sad, but I once had 3 1/2 lb balsa that was usable, and I sanded most of the thickness away to make propeller blades for an EZB. I think it might have been as much as a quarter inch to start with! Something like .011" thick, but no heavier than the usual .007 or .008. Maybe I still have some of that around, if I ever bring myself to make another EZB.

If I want to do a bunch of stripping, sometimes I'll get a small block of wood, glue a spacer on it, leaving space at the bottom for the balsa, and glue a razor blade to that. Could be half of a double edged for really thin stuff, or a single edge for other balsa.

If I'm feeling patient, I will use a Harlan stripper.

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Twinchicky
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« Reply #14 on: August 05, 2015, 12:44:30 AM »

The stripper I use is the Jim Jones version. It works, but shortly after I bought it I found that it was cutting strips .023" thinner than what it was showing on the gauge. It's still usable, I just have to remember that the gauge is wrong and I have to subtract 23 thousandths before I cut.
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