This page contains some tips, tricks and advices which may be useful in building an Sonex

 

 

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What happened lately:

I clamped a wooden beam to the workbench using my red C-clamps (the cheap ones from the mail-order hardware store).

I did not even use excessive force when the clamp suddenly broke and the smaller part flew like a shrapnel thru the workshop.

This simple thing could have killed me! (maybe not killed but at least seriously injured). A closer look at the cross section unveiled that this clamp is casted (coarse grain structure) and not forged. A forged (more expensive one) would have bent but not cracked. So look out carefully before you buy tools!

 

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For drilling the flap skin I made two drill guides (thanx David for the idea). One for the top and one for the bottom.

This is the drillguide made from a thin scrap strip of 0.032 material. It's only roughly cut to size. Only the row of guide holes has to be straight. At both ends I bent it over the flap skin's edges and then squeezed for a good fit.

 

The drillguide in use

I fixed it with adhesive tape to the skin (protective plastic still on flap skin), the red marking line shining exactly centered thru the guideholes.

I put two more ribs in each flap. Not to increase the gross weight I lightening-holed the ribs (except inboard rib which holds the actuator plate).

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It's time now to assemble bigger pieces. I'll start with the rear fuselage section (see remark). First task is to check/level the large worktable. Every twist or bend of the table will go into the aircraft structure.

Now what's the most reliable and exact measuring tool? -correct the water level ! This is one of the few tools I would bet my live on. The level is made of a 5 meters of PVC transparent tube. One 'C'-clamp is attached with Scotch transparent tape at each end.

The hose is filled with water. There should be no large air bubbles in the water. One end is clamped at the reference point (here front left edge of table, the other end is clamped to position 1. At the reference point the water level is adjusted exactly drop by drop even with the table-top. Then the water level at position 1 is checked. If the level is 3mm above the tabletop, then this edge of the table is raised by 1.5mm by putting scrap aluminium pieces under this leg. Re-adjust water level at reference-position and re-check. Repeat the procedure for positions 2 to 5.

 

As you can see, the table is perfectly levelled.

Last year I tried to level the table by using my SmartTool and and a straightedge. But because the straightedge was not exactly straight and the SmartTool is only as smart as you calibrate it before I gave up after I sepend a whole sunday. With the walter level the whole procedure took only half an hour and the result was perfect.

remark:

don't try to figure out the views of longerons F26-02/03. They're wrong! I assume this the Sonex builder's test. If you pass then you're entitled for the advanced tasks ;)))

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Precision Measurement

When marking my large sheets I stumbled into some pitfalls, so maybe YOU may avoid these:

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Bending thick material

There was some time ago a discussion in the Sonex eMail list how to bend thick (1/8", 3/16") 6061 plates. One of the results was that using vise and big hammer gives better results than slow bending (vise, hydraulic brake etc.).

I made some other experiences:

In my view key to a good bend is how to support the rear side of the piece to be bent. If this support (e.g. some hardwood pieces) are too far apart, then the metal will not follow the upper forming tool (e.g. round bar), furthermore the sheet will 'fold' producing a rather sharp fold.

this is not good, supporting wooden blocks too far apart. This will produce a 'sharp' fold rather a nice radius.

 

this is much better and will produce a nice bend, about the bend radius of the upper round bar.

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Cutting Sheet Metal

My first experiences cutting 0.025" sheets were scratches at one or both sides of the cutline, either using tin-snips or the bandsaw. The bandsaw is the tool of choice because the pieces will not bend or bow. I use one teeth per millimeter (German's are metric) for cutting thin material.

my current procedure:

from old 1999 wall calenders I rip a big sheet, then spray a thin (thin because then it's easy to remove the paper easily when work is finished) layer of '3M Spray Mount' on the metal, then glue the paper on it. The metal can now be cut, drilled, filed without scratches with the paper on the rearside. Remove spray glue with laqueur thinner before assembly.

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Transferring drawings from the plans onto the sheetmetal

Several parts are labelled 'use fullsize drawing for flat pattern'. No dimensions are shown. The question is now: how to transfer the pattern from the plan onto the sheet metal?

At first I photocopied the pieces on the plans and then spray-glued the copy onto the sheet metal. This method has an DISADVANTAGE: most of the photocopiers make not exactly 1:1 copies. In most cases there is an dimensional distortion. So calibrate your photocopier before!

Next I bought transparent paper and transferred the drawings. If carefully applied this is the best, fastest and most reliable method to transfer patterns.

A last note: don't trust the printed patterns on the plans to be exact to the dimensions shown. Paper expands and contracts with change of humidity. I always prefer to use my steel rulers to scribe the pattern directly on the metal.

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What I have learned the hard way :(

don't be shocked by the complexity of the plans (maybe except canopy construction). After finishing the 300th part things became quite clear/simple to understand

 

if you made a bad part, don't try to save it, better throw it into the dustbin (better yet give the piece some blows with a 4 lb hammer then throw in dustbin). The idea behind: would you like to drive a flying machine made of some not-so-goods parts?

 

try to make all parts with maximum precision. This is a good training for making 'critical parts'

 

if you screw up a part, then do it at least at the beginning of fabrication, this will save a lot of time, or in other words increase care with progress of work

 

don't look forward on how many pieces still to make until the flying machine is finished (only very strong characters can stand this), better look behind how many nice pieces you already have stacked in the shelves.

 

try to make at least a small part every day.

 

do not temporary abandon the project, probably you will never resume.

 

don't hurry to make a part, even the smallest item takes at least an hour to make.

 

don't drink and work. Half a bottle of Italien red wine will increase scrap level by at least 50%, or in other words, save the wine to celebrate completion of a part.

 

be careful with the bench grinder, if the disc grabs a small piece it may zoom though the workshop, even through the (closed) window

 

at the very first beginning make an inventory database and enter every completed part and the place where the part is located, otherwise searching for parts will consume a lot of time (this applys only to the make-pieces-now-assemble-later approach)

 

all comments (also contrary) wellcome