Just a quick question, what is the ratio (using different rods) to sand a stab or flap to the correct taper?
For example, a 1/2" TE and a 1/4 LE, so what size of rods would I use?

Cheers.

Yup that's what I was wondering but not for a flap, for my stab.

Cheers

Orbs,

Ok, now that we have a better idea of what you are up to....

Using the guides, whether rods or strips, allows you a calibrated way to just blast away with the sanding block. That can be a good thing. Geeterdun! But there are some subtleties that you may want to understand....if I have my brain turned on?

First, the simplest case is if the surface is constant chord, then there is no twist in the resulting sanded surface. Think of the classic strip ailerons. No twist.  I haven't seen many (any?) flaps like that on control line models. If the flap (or elevator) has a tapered planform, and if it has constant thickness as you specified, then you are sanding a twist into the surface. This is ok as long as you do exactly the same to the opposite side. It may help to think of this by looking at the end of the part. The angle you need on the surface at the large-chord end is shallow. The angle you need at the short-chord end is steeper. That means that the surface is not planer. For a nearly constant chord over a long surface like a flap, you may not notice if you don't specifically look for it. And, when you go to lay the flap down to sand the second side, you are pressing down on the part with the sanding block and it deflects and you sand down to the new set of guides. It springs back when you release the pressure and after you are done, you have a symmetric tapered surface. Just the way you wanted it.

As you can imagine, if the taper in planform becomes more exaggerated, perhaps like an elevator, this effect becomes more noticeable. As the surface construction becomes more rigid, the more you will see the rocking tendency when you try to sand the second side. But now you know what it is. If the construction was so rigid that the surface does not deflect and make contact with the workbench under the pressure of the sanding block, then the part will not come out symmetric.

If you forgo the guides and want to do this freehand with a block, then marking centerlines can work well. It takes more finesse, and you also have to remember to sand chordwise--not spanwise with a long block--if you have much of a twist. In other words, if you have a lot of planform taper and a large percentage of thickness change. I use this method all the time. It is especially helpful on surfaces that I sand down to a very thin edge.

Things get more interesting if you also taper the thickness of the surface. For example, you can design the part so that the thickness taper and the planform taper allow the actual surfaces to remain flat. This is very useful when building full-scale airplanes. On models, which can be hand-built and don't require a lot in terms of fixtures it isn't so important.

Hope this helps,

Divot McSlow

Or #*!>< There appears to be a bit of repeat in here . Its Late & doing it in sections . Might tryn edit later. But youll need to read it more than once anyway,
So might be more sense to leave it .
Or " How i walked barefoot  across the Antarctic barefoot in the bush fire season "
SIX Mugs off Coffe should see you through it .  Excuse typeing . This key boadrs not to hot .
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

If making from flat sheet , theres a lot of sanding blocks , the odd one  l o ng .  flat surfaces . And C O A R S E sandpaper toRough Out .
and some days a razor plane , or small wood plane is ratherusefull .

First step,get the blank true on the new cut edge !

Then maybe square off the ends .

Pays to leave the hinge line side ( EDGE ) maybe 1/16 in. + past the ' Finished Size ' .

#*!><

If making from flat sheet , theres a lot of sanding blocks , the odd one  l o ng .  flat surfaces . And C O A R S E sandpaper toRough Out .
and some days a razor plane , or small wood plane is ratherusefull .

First step,get the blank true on the new cut edge !

Then maybe square off the ends .

Pays to leave the hinge line side ( EDGE ) maybe 1/16 in. + past the ' Finished Size ' .

Now for the Highly Technical  Bit .    You want Hex Stick parrallel one , not a fancy curved tube one, or therell be TROUBLE . 

Get your cleared clean flat suface, lay on the BLACK pen . This is very serious . Run the Flap right aroud the stationary pen .
you may need to pickit up & shake it . Or rub the dust of the tip. Occasionally .

Now turn the flap over and repeat .

Pick the flapup . Observe TWO parrallel lines , ' X ' mm / inch Apart . !
Adjust the Eagle Eye , get your clean ruler, so you can read it .
Say the magic dimenson , between the two lines , is 1/8 inch .
Halve it.
Pickup your longish piece of 1/16 in. Scrap . Lay it under thepen. Again Hold Firly. As you were before !
But , while no ones looking , youve changed to a RED pen !
Run the shhet as before, right around . Flip & repeat !.

Theres a highly vivid centerline spliting two dark datum lines , around the whole confabultion. Now . Far Out .

----------------------------------------------------------------------------------------------------------------------------------------------

As we've Not Beveled The Front , Hinge edge Yet , Or even Shaped It, or dressed to the finished line . Till LAST >

THOUGH its a good idea to mark out the Hinge & Horn - Horn Arm locations . NOW . Not Possesing a hinge cutting tool,
I start with the Scalple , and steel rule , or maybe flat with a half depthpacker ( say 1/4 Sq Spruce ) & Scrible the Hinge positions say 1/8 deep ,
both ways ( soendsare knifed square .) Maybe from both sides up if on the bench , flat , with the packer .
And same C Lof horn & ( 1/8 " ) edges , only 1/16 or so deep .

A piece of wire , end cut & filed in  vice way past 45 degrees , makes a good ' router ' fot the horn wire groove . And flap hinge rebates,
Shallow cut & reverse to compact timber . Later dope & repeats to fine tune exact fit. Easiest between knees With steel rule ( and THOSE INK LINES for guides for center & edges .
A six inch LONG 1/8 drill used - for sighting purposes - drilling for flap horn wire legs .
With 1/4 sheet flaps , a few inches along the flap means its got less flap to move ( and less flap to flex ) outboard . Tho needs wire epoxying
tonner edge . sanded & cleaned in solvent .
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

And you still need to do ALL THAT even f your useing FLAT non airfoiled flaps . !

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

USUALLY I then mark it at 50 % chord .
And plane / block sand , and faff about .
With Yellow 60 Wt & later 80 Wt sandpaper .
As it takes it down quick ands less lableto warp things - Like polishing & heating you get with fine paper for major material Removal . !
 
SO , The Rear Half is now symetrically ' V'eed ,Dressed with nce new black paper on a nice straight ( 1 1/2 x 3/4 or whadeva ) stick,
a foot or two long . or bigger . But Eyballed Dead Straight . with No Lumps . And your fingernals Trimmed .
And HIDE those Glass Ball Head Pins !

Or that Pen Line couldvre been 2/3 Forward ! NEXT we put another spanwise line at mid pointof our fresh sanded surface ,
and another at around 1/2 inch or 3/4 back from the LEADING EDGE . And wipe the dust off. And get out the MASKING TAPE.
or that blue 3M stuff .

=========================================================================================

No WhereWere We ?
Mask the Leding Edge Flanks .say 3/8minimum.3/4 for wider flaps . Or youll be udersized at the L E like when you dont use a ticker wire rod at the front .With a 45 degre Bevel. Like the Elevator . SO if your 1/4 ickbakfromtheFRONTof the taper (if it goes right forward . Youlllosse dpth when you bevel it ! ! !
Later .

If you inevitablychew a piecce of the tape. Patch It .Imediately .

Now Block sand your ' front; taper , Sowe've got a Even Dual FlankEach/ Both Sides . For A AIRFOILED Flap .

It Dresses in with minimal bother - with even strokes & pressure . Flipping and conting at Each six or twekve to eliminate warping & bowing .
Dont Lean on it to much , fresh Paper cuts Easy o youll need a few sheets , Say 100 grey & 180 Black .

---------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Last ones I Did , the Halibag ,took from5 till 12 , when I put dinner on !.

I did them Flat Flank ( No Curve ) Flaps & Elevators. and Thought %#@* etc . . . Put 3 mm Sq Bass down the rear edges .
Block Saned ( Coarse ) down till i caught the front edge of the anti ding strip( bass )  with the 100 wt grey ,
With the little 3 x6 x 5/8 dressed block and 3 in skirting ? x 12 in , radiused one side edges , half depth . Other side edges sharp.
On the Sanding Block strip . and Dressed with the 180, 2sheets long cut & glued wrapped three sides of it . Aliphatic . 1/2 Hr in current heats fine.

So thats that Done . The TAIL PLANE ( And parrallel chord elevators ) wereMore Tecnical.

Percentage Lines Eqal Ea Side L & R . Top & Bottom . AFTER going from5/8 Center to 1/2 tips , marked after the aforesaid parrallel pen lines !
With the sraight edge. To get a Taper Line F & R, Equal & even .

To Get My ' 5/8 in. Blank ' a eqal 1/2 at the tips think tapered blank .

Now for the Highly Technical  Bit .    You want Hex Stick parrallel one , not a fancy curved tube one, or therell be TROUBLE . 

Get your cleared clean flat suface, lay on the BLACK pen . This is very serious . Run the Flap right aroud the stationary pen .
you may need to pickit up & shake it . Or rub the dust of the tip. Occasionally .

Now turn the flap over and repeat .

Pick the flapup . Observe TWO parrallel lines , ' X ' mm / inch Apart . !
Adjust the Eagle Eye , get your clean ruler, so you can read it .
Say the magic dimenson , between the two lines , is 1/8 inch .
Halve it.
Pickup your longish piece of 1/16 in. Scrap . Lay it under thepen. Again Hold Firly. As you were before !
But , while no ones looking , youve changed to a RED pen !
Run the shhet as before, right around . Flip & repeat !.

Theres a highly vivid centerline spliting two dark datum lines , around the whole confabultion. Now . Far Out .

----------------------------------------------------------------------------------------------------------------------------------------------

As we've Not Beveled The Front , Hinge edge Yet , Or even Shaped It, or dressed to the finished line . Till LAST >

THOUGH its a good idea to mark out the Hinge & Horn - Horn Arm locations . NOW . Not Possesing a hinge cutting tool,
I start with the Scalple , and steel rule , or maybe flat with a half depthpacker ( say 1/4 Sq Spruce ) & Scrible the Hinge positions say 1/8 deep ,
both ways ( soendsare knifed square .) Maybe from both sides up if on the bench , flat , with the packer .
And same C Lof horn & ( 1/8 " ) edges , only 1/16 or so deep .

A piece of wire , end cut & filed in  vice way past 45 degrees , makes a good ' router ' fot the horn wire groove . And flap hinge rebates,
Shallow cut & reverse to compact timber . Later dope & repeats to fine tune exact fit. Easiest between knees With steel rule ( and THOSE INK LINES for guides for center & edges .
A six inch LONG 1/8 drill used - for sighting purposes - drilling for flap horn wire legs .
With 1/4 sheet flaps , a few inches along the flap means its got less flap to move ( and less flap to flex ) outboard . Tho needs wire epoxying
tonner edge . sanded & cleaned in solvent .
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

And you still need to do ALL THAT even f your useing FLAT non airfoiled flaps . !

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

USUALLY I then mark it at 50 % chord .
And plane / block sand , and faff about .
With Yellow 60 Wt & later 80 Wt sandpaper .
As it takes it down quick ands less lableto warp things - Like polishing & heating you get with fine paper for major material Removal . !
 
SO , The Rear Half is now symetrically ' V'eed ,Dressed with nce new black paper on a nice straight ( 1 1/2 x 3/4 or whadeva ) stick,
a foot or two long . or bigger . But Eyballed Dead Straight . with No Lumps . And your fingernals Trimmed .
And HIDE those Glass Ball Head Pins !

Or that Pen Line couldvre been 2/3 Forward ! NEXT we put another spanwise line at mid pointof our fresh sanded surface ,
and another at around 1/2 inch or 3/4 back from the LEADING EDGE . And wipe the dust off. And get out the MASKING TAPE.
or that blue 3M stuff .

So thats that Done . The TAIL PLANE ( And parrallel chord elevators ) wereMore Tecnical.

Percentage Lines Eqal Ea Side L & R . Top & Bottom . AFTER going from5/8 Center to 1/2 tips , marked after the aforesaid parrallel pen lines !
With the sraight edge. To get a Taper Line F & R, Equal & even .

To Get My ' 5/8 in. Blank ' a eqal 1/2 at the tips think tapered blank .

I had to read Kim's description twice to get what he was  doing, but Matt's description makes my head hurt.

MineToo . and Im just starting toget technical , at the current point . Id wondered why the head aches were  killing me !
This keyboards not even pressure on the keys . Will edit in a few days. When Ive Recovered . 

The " Tapered Thickness Stab ( & Elevators )

likely needs to be digested in chunks , washed down liberally. With the occasional Deep Breath .

The last lot done was a non stop saga , ThoI take the odd break for coffe & a few paragraphs of a unredable book ,
to clear the thoughts for the next step .

Its all Logic ! Best STEP by STEP .Taking it allin atonce overwhelms & puts youoff . So you need the odd ' clear the head ' break .
This had Four Flaps , Joiners , Fairers, and Multi Taper rear . SoI thought id get it down , while still fresh in the grey matter .

BAHH . see footnote .

Wasntlooking to bad at this stage , was starting to cool off .

Id Used a styreene  green grocers offcast box , on the bench , to lift the job 12or 18 inches depending on its sit .
And on end it matched bench hight on the floor . So sat things on it when useng the ' plate glass ' cleaned . For Finaler dressing .

Sanding Blocks along the Span kockof the crests for a few strokes , eyeballing ,keeping matched .
Going Finer and pushing thru acroos half chord, Dressing In Elevators Fairing Though .
( The Odious Dungeon contemplation turned to be oversted. the faied in nicely in a few miutes .0

The 180 ( Fresh ) on a longer block had it honed & finalisedwith minimal concern ,
Turned to a 45 degree cut ( pencilmarked 50 % so 2 mm in ) on the 3/16 deep L E ' flat ' & aft .
Carefully past 12 now & tired . Round Off true & fair in & through ,
Bring trailing edge ( Elevators )dressed fine through acoss tapering the 3 mm Sq hardwood soleft at 2 mmodd or a thick 1/16 fully aft .
A pen along the edge ( back face ) while its still full square , and 100 Wt till the lines disappeared even , eyeballing & attending as you go .
This is where its handy having the Styrene bench near eye level. minimum Bending and rotateing , and me shifting for optimum light.
Sighting along and across .
Seperating intostages.
Checking and a breather .
grabbing the old virneer & locking - drawing along edges to see it maintains a consistant line. Will transverse inor out on a taper- But Still straight .

Lets you avoid propigateing hollows and avoiding lumps  .
the sight , light, and shadow , specially allong , and even shadeing rotateing , seem to keepit  pretty correct .

Where theres golden bits and dark bits in the timberswhere it seems tooptically trickyou , & the Straight Edge along it, with the lamp behind,
eyeing the edge against the wood shows slight discreapancies along / underit  ( THIS KEYBOARDS A BIT NOTEVEN PRESSURE _ LIGHT ! )

================================================================================================

So a final sigh ,coffe , breather tidy , reprepare& clean & dust- discard bluntened paper .
Give the timber a bit of time to resettle  .
FinAL DRESS  OFF WITH 180 , Throw a coat of dope. Coffe & read/ still Warm . Dress in & ANOTHER COAT.

mINMAL ATTNTION TO COOKING * THE BOLED SPUD SLICES THEN STeak brown nicely , with a vigouous apptite .
final Eyeball under the light.
Stinking Hot next day . Chores ! Pinem together & catch last light . 8 pm . for a few pictures .Sorry. almost photoed as I went ,but'd thought memory full.

====================================================

Summary.Soit pays to accurately mark tapers/ cuts/ flanks, at the ends . as you go .
The Elevator C L cut was acurately instated and keept ongoing , as we went. full circumferance of chord.
They need reestablishing before fully faded / eradicated . Tomaintain exactitude .

60 Wt 7 even 40 wt make short work of materal removal.

Cut the paper with a ) ktchen )knfe along a straight edge.
Roll & start creases . But use a hard edge acurately poitiond , to CREASE .

At times you want the paper to end EXACTLY along the seond edge/ fold, so you can workinto a corner .

Left the front ( hinge ) edges 1/16 deep . NOT a dead 90 degree sq cnr . Two 45 deg. flanks on a 1/16 vetical. Later radiused tomatch hinge barrell.

Even need to store carefully . Against a outside ( tin ) wall as ts cooling can induce humidity related twists. so sit em vertical between Coffe Jars .

The Flors needed ' Sorting 'for a few weeks after the new bench . The Compressor'll now fit under it .
Wonder I didnt trip, break a leg ,of snap / smash someting  . Only started to 6 or 7 times . 

Callt a Challenge . Say in4 stages , corrected / trued at each ,keepsthem true & matched .And the stars look good whenyou stepout for a breather,
after the smokes cleared as the nightcoolsoff .

Might edit the obvious typos in a day or so . Addressany complaints tothe management .

FORGOT to Mention the 12 inch B'std FILE , getting a bit old & blunt . But drag the edge along transversing gets a 45 Deg. ' Cross Hatch '
Going Lightly . that sorta ' proves out ' the Level . Or Highlights bumps . The 40 Wt. paper beats a Rasp . 60s less agressive .But quick .