Thursday, April 8, 2021

Unlock CRA PDF Forms

Unlock Canada Revenue Agency PDF Forms

It appears that there is a relatively new PDF feature to prevent casual copying and saving of a file and that some programs save PDF files with these foolish features active by default.  Many forms from the Canada Revenue Agency are locked in this way, which makes it difficult to do one's taxes, since one can fill the form, but cannot save it. 

One can only print the form.  It should be possible to print to a file or export it to a new PDF file, but it is far better to reset the annoying anti-taxpayer flags, since the 'printed' form cannot be edited easily any more and I always manage to make a mistake or three that need to be corrected after review.

If there is a Linux (virtual) machine handy, install qpdf and use it to reset the silly flags:

  • $ su -
  • password
  • # dnf update
  • # dnf install qpdf
  • # exit
  • $ qpdf --decrypt lockedfile.pdf unlockedfile.pdf

One doesn't need a password to unlock these flags, so the fix is instant.

La voila!


Friday, April 2, 2021

Bucket Vacuum Cleaner

Bucket Vacuum Cleaner for Shop and Yard Work

I need to clean out 50 years of cobwebs and dirt from two garages and a shed.  The cobwebs are like a Hollywood horror movie, so one should enter the shed armed with a broom and a shotgun.  A little 1000 Watt home vacuum cleaner would be instantly full, so I disassembled an old one and mounted the parts on top of a big bucket from the Hornbach hardware store, to give the little sucker a fighting chance. All the surplus Covid filter masks also came in handy in the shed while cleaning.

The trick is to use two buckets, one inside another, plus a little glue for extra strength, otherwise the bucket can collapse when the pipe clogs up.

The most difficult part of this project, is to disassemble the old cleaner.  Evil one-time snaps and hidden little screws, may require using a wrecking bar and hack saw to pry the thing apart.  

A home vac is a very simple device with essentially just one part - the motor-compressor unit.  

The one I took apart also had a triac speed control, so that went into a little box. I turned the speed down just a tad, to reduce the screaming a bit.  I've been wondering whether one could just stick a diode in series with an overpowered universal motor to slow it down to a more acceptable noise level, but that may damp it too much.

The motor is simply held down with three pieces of rigid strapping (a holy metal strip, normally used to tie roof rafters together), on top of the original rubber gasket. Mount a round cartridge air filter (from a large truck engine or another kind of shop vac) under the motor on the inside of the lid.  I again used some rigid strapping, washers and screws.  To clean the filter when the vac doesn't want to suck any more, simply toss it high up into the air in the back garden a few times, when the neighbours are not around.

The suction pipe was semi-permanently glued into a hole in the lid with hot glue.  If your old vacuum cleaner still has a functional pipe attachment mechanism, you may be able to re-use that - mine was worn out - the reason the vac was discarded.

Four little dowel sticks locates the lid on the bucket.  You could slit open some rubber tubing for a better seal around the bucket edge, but in my prototype, the smooth MDF board simply presses against the top of the edge of the bucket and it works well enough.  If the motor can dent the bucket when the pipe is blocked with your hand, then it is sufficiently sealed.  If it collapses the bucket, then you need to drill a little 3 to 5 mm hole somewhere!  

A bottom MDF board with four castor wheels, rounds out the project.

A vacuum cleaner really works with air flow, not vacuum.  When high speed air from the hose enters the large diameter bucket, it acts like an expansion chamber and the air flow slows down dramatically, causing any dirt to fall to the bottom.  You can keep vacuuming up debris till the bucket is about half full.

There are lots of vortex voodoo videos on Yootoob about making your own shop vacuum cleaner in the most complicated way imaginable.  This however, is for those who like to keep it simple: Just mount everything on the lid of a bucket and be done with it.  For the ultimate lazy, almost never need emptying shop vac, you could mount the compressor on the lid of a 120 litre wheelie garbage bin, but I wanted it a little smaller!

I still want to put a case around the motor, to dampen the noise and maybe use it as a leaf blower, but then I need a removable pipe. I also need to fashion a better hold down than the two bungee cords, but this prototype setup works a treat already.

La voila!


Tuesday, March 23, 2021

Knights Of The Round Table

I did my good deed for the week and rescued an old round/oval table.

These tables all suffer from the same design flaw, since the factories copy each other and they don't care about it lasting much beyond the show room door.

 A table with a central leg will only last if it is made from steel. A wooden table that is light enough that normal human beings can still lift it, will eventually split, due to the enormous leverage from the table edge onto the central leg.

The central leg is made from four planks glued together and then turned on a lathe - which also weakens it.  The four feet, are invisibly bolted through into the hollow.

When a knight in heavy armour leans on the table, the central leg tends to split at the bottom or top.

I wedged the spars open and poured in some white glue and let it run down, while spreading it with a little swizzle stick and wiping up with a damp cloth.  Then I clamped it and drilled four holes for dowel rods (the little white points above the clamp jaws in the picture) - while trying to miss the hidden bolts.

To put an 8 mm dowel into hard wood, requires an 8.1 mm hole if you want to be able to tap it in without splintering the dowel in the process, but where to find such a drill bit?  Not all drill bits are made equal.  I have multiple 8 mm bits and one of them, is ever so slightly bigger than the others, so it performs dowel duty.  With MDF, it is not a problem - you can mash an 8 mm dowel into a 5 mm hole if you have to...

There is not much point in putting too many dowels, since next time a heavyset knight leans on the table, it will break somewhere else!

In a couple days, I'll grind the dowel heads down with a Dremel cutting wheel.


Many/most woodworkers use far too much metal in their projects: Hinges, locks, catches, slides, corner brackets, screws and nails...  

These widgets are very expensive and in most cases not necessary.  One can make everything just with wood and glue, even hinges and locks.  You can start by eliminating screws and nails by using wooden pins.  The cost of your projects will reduce dramatically when you avoid using steel and brass fittings and the resulting projects will look rather nicer/olde fashioned/rustic.

A simple assembly trick is to glue and screw a thing together, then remove the screws one at a time, enlarge the hole and tap in a dowel with glue and a rubber mallet.  With an electric screwdriver and drill, this is super quick.

I found that the best way to make dowel pins is to buy ready made ones!  Alternatively, cut 9 mm oak strips with a jigsaw from a scrap block (about 3 inches long works for me), round them a bit with a knife, then hammer them through an 8 mm hole in a steel plate.  I use an old rafter joint bracket which has multiple holes already, clamped in a vice.  A humble washer mounted on a backing block will also work.

There are many videos on Yootoob showing how people make dowels using a drill and various kinds of cutting widgets.  In my experience, this only works with very thick dowels, at least 10 mm diameter.  Thin stock tends to shatter.  Simply turning a dowel in the serrated jaws of a vice works very well, since one can adjust the vice until the dowel is the right size.

Hammering a square peg through a round hole even works when there is a little knot in the peg.  You just get a bent dowel, as the one in the bottom right of the picture, while with a drill lathe turning method, it will shatter at the knot.  

You don't have to sand a dowel smooth - you are going to hammer it into a hole with glue - the roughness will help to fasten it.  I cut and hammer a double handful of pegs and then I can put a project together without nails, screws or weird brackets.


One way to prevent repeated breakage of a round table, is to loosen the table top (back some screws out a quarter inch), so that it is balanced precariously and if anyone would lean on the table, then it will wobble threateningly and teach them not to, but this particular extendable table design unfortunately doesn't lend itself to such an evil solution.


La voila!


Friday, March 12, 2021

The Office

The Office

Do you still remember what an Office is? Those large multistorey buildings where we all used to fearlessly share our cold and flu viruses like a big happy family?

The Book on a lectern where you sign in/out, with The Witch glaring at you for being ten seconds late, whether your nails are clean and your shirt tucked in.  The front desks that are slightly bigger, with a better quality desk lamp and which may even have a carpet!  The CARDEX cards along the wall, the clattering Telex machine at the back...
 Mid 20th Century Office

It is interesting to note how the desks get gradually more messed up towards the rear of the room.  That is always where the real work gets done.

Have fun!


Sunday, January 17, 2021

UAV Communications And Mission Systems

Tactical Unmanned Air Vehicles present an interesting communications challenge.  Flying an RC toy in your back yard is fun, but controlling a heavy aircraft, hundreds of kilometers away over the desert, is something else entirely.  Abu Dhabi IDEX 2021 walk through:

ADASI 500 kg Unmanned Helicopter ready for IDEX 2021

The below book is still a draft and it is published here as a series of PNG files - one per page.  The below should be viewable in any browser.  If you wish to get a PDF file, send a message to herman at aeronetworks dot ca and then we can agree on which FTP service to use.