Disclaimer

This blog is for entertainment purposes only, and is not meant to teach you how to build anything. The author is not responsible for any accident, injury, or loss that occurs as a result of reading this blog. Read this blog at your own risk.

Sunday, April 28, 2013

"Tooling up" - Mill's new back brace


Strengthening the mill column

It took 2 whole days for the conversion, one of which was spent just "tramming" (realigning to vertical) the column!

This type of mill has the ability to tilt the column ± 45 ˚ to make angled cuts. Generally, however, it is preferable to angle the workpiece in the vise instead of the column, since realigning the vertical column can be a lengthy procedure.

Given that one single bolt connects the mill’s column to its base, and the considerable suspended weight of the head (about 40 lbs or 20 kg), it is possible that vibrations occurring during big cuts, might swing the cutting implement (forward / backward) and reduce accuracy.

Using a precision indicator positioned over very accurate “123 blocks”, I measured these deviations by applying moderate pressure on the head of the mill (forward / backward).

The deviation recorded by the indicator was ± 0.001 inches (0.0254 mm). After completing the project of strengthening the tower of the mill, this deviation is reduced to ± 0.0005 in. (0.0127 mm).

Although it doesn't sound like much, this actually translates into a 50% improvement.

For comparison purposes, the average width of a human hair is 0.004”, and we are talking about a movement that is 8 times smaller than that! So, we are literally "splitting hairs".

Unfortunately, the process of realigning the column has become much more involved, since now each bolt wants to impart its own small torque to the column during tightening.

All in all, I think that the gain in precision obtained by this modification justifies, even if only slightly, the increased complexity of the realignment process. Procedure which fortunately will be much less necessary thanks to the update.

This conversion has the added advantage of making the X2 mill a better CNC platform, should I choose to move in that direction.



Looking at the back side of the mill


Adding the back brace


Bracing completed


"Tramming" setup


Left side view of the modified mill



Saturday, April 27, 2013

Removing hard to grab peel-ply


Glassing the outer fuselage presented a good opportunity to demonstrate how to remove hard to grab peel-ply.

I'm sure there are hundreds of ways for doing it, but this is what works for me.



How to remove stubborn peel-ply





Ch. 7 - Fuselage exterior - Part 7


Glassing the outer fuselage (23.0 hrs)

While I wouldn’t recommend glassing the fuselage by oneself, that’s exactly what I ended up doing for a number of reasons. 

The main difficulty consists in the amount of time required to complete the job. Sure, the manual says that it should take two guys 4 hours to complete the job, but I’m starting to get the sense that the numbers in the manual might be a bit optimistic.

I ended up spreading this job over the course of two days, mostly to make it easier on my back. I completed the right side of the fuselage on day one, and the left side the next day, peel-plying the seam in between.

The level of technical difficulty is not great, but the sheer size of the fuselage was enough to make me wonder if I’d ever get to the end of it.

One item that proved invaluable during my solo glassing extravaganza, turned out to be the mobile fiberglass dispenser, much more so than I would have anticipated. It basically behaved like a human helper by holding the fiberglass for me, without any complaints, and best of all, without drinking all my beer.

The only part that was a little tricky was the seam down the middle, where the overlap would occur. To avoid creating a bump in the middle, CP#28 highlights a different layup schedule from the plans.



Modified layup schedule from CP#28


If you notice, items 1 and 3 specify the UNI to be laid at 45˚. The correct bias is 30˚, and that was a mistake later corrected in CP#29.

So, here’s how the work progressed...


Draping the 1st ply of UNI in the front section  at 30˚


1st ply rear layer


Posing with the 1st ply rear section


1st, 2nd and 3rd (front only) plies completed


Peel-ply added to the side


Peel-ply added to the bottom

The next day started with a backache from standing on a concrete floor for 12 hours straight. Later, I removed the peel-ply, and repeated the same process on the left side. As I mentioned, not the most mind challenging of layups, but it still took me 10 hours to get done.


Day 2: removing peel-ply from centerline


1st ply front section getting laid (lucky for him!)


I begun by wetting the cloth to lock in the bias angle, before cutting the fiberglass


1st ply rear section


More peel ply on the bottom...


... and on the side


Proud parent

There were quite a lot of sharp edges to cut off the next day...


Removing excess glass in the form of sharp edges

... but I was finally rewarded with a completed fuselage that I can finally sit and make airplane noises in.


Ready for "show and tell"


The girl with the "XX" tattoo


Most peel-ply removed already




"Man, that's a wide cockpit!  I like it!"


Plenty of room in the rear to keep the GIB cheery



Monday, April 22, 2013

Ch. 8 - Rollover structure - part 2

Rollover outer recesses (11.0 hrs)

Since the longerons were never designed to support a true rollover assembly, and mindful of the issues I have had in the past with the landing gear brackets, I decided to add 3 plies to both sided of each longeron for strength, staggering them by 1” (2.5 cm), like the wing spar cap, for flexibility.

Unfortunately this meant digging more blue foam out of other places I thought I was done with.

While this sounded like a great idea at the time, in hindsight I should have done as Mike did, by glassing the fuselage first, cutting through the skin to install the outer plates, then patching it up.


Mike's neat roll bar


Because I wanted to avoid cutting the outer skin, I ended up complicating things, and making more work for myself. 

Nevertheless, here’s what I did...


Outlining the area to be cut


This tearing down has got to stop, if I am to make any progress!

Area sanded to remove any old micro, and provide a clean future glass/glass bond.


Glassing the inside of the longeron required more trimming of the front seat. 


More tearing down :-(




The structural strength of this juncture had already been compromised by the two cuts I did last week, when I separated the top of the seat from the longeron. 

The whole top 2” of the seat are basically free floating now, and will probably be cut off later as well to reduce weight.


Staggered reinforcement BID layups

BID applied and peel-plied


To make life easier later on, I decided to contour these recesses at this time, micro all sharp edges, and add 1 ply of BID over the top to hold it all together, until the next day.


Shaping to ease later layups in this area

Microed the hard edges, and slurried where BID will go

One single layer of BID applied to hold everything nice and smooth until outer skin layup

Peel-ply over BID

Same on right side

Peel-ply removed the next day, and hard edge sanded to a nice transition with the longeron top

This recess will house the outer plate and nuts of the removable roll bar


As you will see in the next post, this approach worked out beautifully, and I had no issues dealing with fiberglass not wanting to stick in the corners the next day, while glassing the whole fuselage.

Finally, I’ll share my overcomplicated and non-final sketch of how I planned to deal with this area of construction.


A rough sketch of the proposed layup. I did say it was overcomplicated!



Ch. 8 - Rollover structure - part 1


Making of the steel L braces (4.5 hrs)

One recognizable features of the Long EZ, among many others, is the distinctive rollover-structure/headrest built onto the pilot seat back.


My friend Steve's beautiful Long EZ


Over the years this structure must have proved itself more worthy as a headrest than a roll-over, prompting the publication of this warning...


CP#65 page 7


Some builders with flying aircraft re-engineered this area in order to restore protection in case of an upside down termination of the flight, by incorporating a steel tube roll bar.




Many of those who had not built the headrest yet, omitted the fiberglass structure altogether, and fabricating a pure tubular structure.


Chris' cool bird

Wayne Blacklers' rollbar


Personally, I like the fiberglas structure, and I love the fact that many builders have put it to good use by housing instruments for the passenger’s use. 




This is one lucky GIB (Guy/Girl In Back)


Because I did not want to to take the weight penalty of a steel roll bar, plus the fiberglass structure, I decided to go purely tubular.

My good friend Mike has already given this subject a lot of thought, so I decided to “be like Mike” once again, and borrow as much as possible from his research.


My muse... BizMan!


I could not find a steel L channel of the size and thickness I wanted, but I did find it as a rectangular extrusion (1" x 1.75", 0.065" wall thickness), so I ordered it and cut it to the proper size.

Now, on the subject of cutting...

I need to bring up the very real possibility of setting your workshop on fire, being injured by a exploding grinding wheel used in an unconventional manner, or being cut in half by a flying extrusion, if you were to do as I did.

Do not do what I did!

I replaced my table saw blade with the smallest metal cutting grinder wheel I could find. 


"Spare wheel"


I did this in order to limit the speed at which the cutting edge would engage the metal to be cut, thus reducing the chances of the wheel coming apart. 

Along the same line of thought, I also minimized the amount of blade sticking up above the table to the bare minimum necessary to make the cut. 

I also used all devices available on the saw to maintain a straight cut line, this further reduced the exploding wheel thing, and also reduced the likelihood of "table-saw kick-back". 





Table-saw kick-back in action


Should this happen, and you were to be standing behind the extrusion, you’d be as good as dead. The extrusion would be launched at great velocity toward your chest and stomach area, and go right through you like a hot knife though butter.

No surgeon could stitch you back together after this kind of accident!

Needless to say, I stayed well clear of the kickback area, just in case.


Being a bit anal, I've always vacuumed my table-saw after each use. I do this in order to avoid packing saw dust in places where it could interfere with the proper functioning of the saw. 

This turned out to be a good thing for me as you will see, since the amount of sparks thrown while cutting metal could have easily ignited the dry saw dust. 

How do I know? My wooded table has burn marks from the hot sparks landing on it.


2 foot long 4130 steel extrusion

Trimming it down to 17" (43 cm)

Dangerous longitudinal cut

One more unsafe cut to go, to call it a day.

Voilà, extrusion turned into L channel

Trimming the corners

Top longeron braces done


My friend Mike’s design calls for a top L brace as well as a bottom one, in order to “sandwich” the longeron between steel plates, and make it less likely that the roll bar might be ripped off during a crash. I have not made the bottom channel yet.

The next step was a bit controversial in my mind, since it required cutting a structural bond, but I reasoned that I’d be more than making up for it by using steel cross members.


Cutting through a structural bond (sigh)


One more painful decision was that of reducing the longeron thickness slightly, so that the roll bar could seat flush with it.


Countersunk top longeron


With the slightly wakened structure ready, I was finally ready to try the first parts of the roll bar on for size.


Test fitting the left top brace...

... and the right top one.

All I have to do now is acquire a TIG welder, learn how to use it, get halfway decent with it (or at least passable), then make the rest of the roll bar.

It sounds like another learning opportunity to me!

Stay tuned, this might take a while.