Wednesday, June 5, 2013

Wooden Bulldozer Toy

One of my nieces has a bit of a thing for bulldozers so I thought I'd make her a nice wooden one. Once I was designing it I thought I may as well make three, one for my daughter and one for a friend's son. The tracks work very well. They are held together with rubber bands made from slices of bicycle tube.
Sketch Plans - some dimensions got changed during the build to fit the stock I had
Prepared stock from recycled Rimu

To make discs without a lathe I roughed them out on the bandsaw then turned them down on a center against the disc sander.

To get the wheels to run smoothly on some standard size dowel I drilled them out slightly undersize then made a custom reamer out of a piece of steel tube to get the right fit.
Reaming a wheel.
Glueing the side plates onto the core of the wheel. Two at once here.
Notching the track plates was very time consuming even using a simple jig on the band saw.

Assembling the track plates into a rubber band chain to make a track.


Tuesday, June 26, 2012

Simple wooden children's block construction set

Simple wooden children's block construction set

I like making little gifts for my relatives and friends children and now that I have my own daughter I have another person for making things for.
Sliding dovetails have always fascinated me so this was a perfect opportunity to let rip with the router table. Prepare some lengths of timber planed to the same dimensions, whatever you have to hand is probably suitable provided it is not treated. To cut the groove, first rough it out with a straight cutter of suitable width to save work on the dovetail bit. Similarly, for the pin, make a light cut part way before the final cut. Cut the prepared profile to lengths. The most time consuming part of the operation is the sanding of all those edges! If you know of a quick way to do it let me know. If you use a pale coloured wood you could dye the blocks with food colouring. What you build from them is up to your imagination.

Tuesday, January 24, 2012

The Homebuilt Bakfiets Cargo Bike

It finally came to that time in life to have a child so my thoughts briefly turned from adventures like caving and climbing to things like "how to transport the offspring in a two-wheeled pedal-powered fashion?" I dislike trailers for child transport because the child is behind you and out of sight where cars can pounce with no warning. Child carriers perched on the bike seem a bit vulnerable if the bike falls over. The solution? A two-wheeled bakfiets cargo bike as used by thousands of mums and dads in Denmark, Holland and increasingly Seattle.

The commercial models aren't readily available in New Zealand and they are rather pricey, although still cheap compared to a car. If other people can hack one together from chopped up bikes, then why not me?

I'm not much of a welder but luckily I have a friend, Bevan, who has a TIG plant and is a dab hand at welding bike tubes, having built himself a tandem bike amongst other projects. I drew up a quick plan and procured the necessary donor bikes. In the end the rear bike was given to me by the same friend who did the welding. I wanted to put a disc brake on the back so a vertical dropout frame was preferable. The frames I had were all the older style sloping dropout so the donated frame was more suitable.

I decided to go with a 26" wheel mountain bike for the rear because most of the bikes in my stable are mountain bikes and I figured a triple chain ring could come in handy when hauling a big load. For the front I bought a trashed old kid's BMX which came with an extra beefy front wheel which I was glad of.

The front end tacked together and the brake bosses ready to go on.The front fork off the BMX was set up for a caliper brake so I shaped up some cantilever bosses (cut from another old fork) to weld onto it. For the steering arm that the steering strut attaches to I used the bottom of a fork arm with the dropout cut off. I left the conveniently M6 threaded fender mount to bolt the ball joint to.

To shape the tubes accurately for joining, I used one of the many tube notching programs available on the web. I cut the tubes with a hacksaw and then did the shaping with a half-round file. I bought a good file for the job which made it much faster.

The main tube joined to the donor bike.I was planning on getting a piece of rectangular hollow section steel for the main tube but my friend came through again (remind me to buy him some beers!) with a length of 2" mild steel exhaust tubing. The main tube is ovalised at the front and welded to the head tube cut off the BMX. The main tube is pierced by the rear head tube which is formed from the top tube of another cannibalised bike. The back of the main tube is ovalised and welded to the donor frame just in front of the bottom bracket.

The bottom of the rear head tube and the stand.A beefy kick stand was formed by cutting and welding two old steel handlebars into an H shape. The top of the H mounts into two cut down quill stems. The quill stem brackets mount onto a small diameter tube that pierces the main tube. They run on a polythene bush made from irrigation pipe.

The rear steerer tube was fabricated by cutting the steerer tube off a donor fork and extending it with some extra tube of a similar diameter. The steering arm was again made from the reused end of a donor fork.

The steering strut that joins the rear steerer tube to the front fork was cut and welded rather than bent because it was easier to do and it also matches the sharp angle of the front of the box better. Getting the positioning of the steering system correct was quite important to allow sufficient turning angle. I didn't get it quite right so that on full left the steering strut rubs on the back of the front tire. Not a big deal really as the full lock is never reached while actually riding. The steering strut has M6 nuts welded into the ends to mount the M6 threaded ball rod ends. I left the rod ends loose in the steering strut so the strut is free to pivot out of the way of the front tire when it hits.

The disc brake mount and brace.

The only other modification was to weld a disc brake mount to the rear of the main donor frame and a small reinforcing brace next to the mount.

To house the cargo I built a plywood box. The bottom and ends of the box are 9mm ply box-jointed together. The box joints were just cut by eye on the cross cut fence of my table saw, as a high precision fit was not required because the plywood is soft pine. Cutting the angled box joint was tricky but I rigged up a tilting fence which did the job. The 7mm sides of the box are joined to the bottom using aluminium angle connected with M5 countersunk screws into T nuts. The box is mounted to the frame using steel saddle clamps and M6 screws into T nuts.

After about six months of intermittent work on the cargo bike and the delivery of a new daughter to use as cargo, I was finally ready to give the whole lot (not the new daughter though) a couple of coats of gloss black enamel paint from a can. A free ride to anyone who can correctly identify all the parts in this photo.

Update 7/5/12
I weighed the bike and it comes in at a very respectable 25kg with the box. Compare with the commercial models which run high thirties.

I added a removable aluminium bar to support a weather cover. It seems to work (see photo below).

The steering bar has turned out to not be quite stiff enough. It is fine during normal riding but flexes when the wheel is pushed on hard. I'll upgrade it to 12mm or larger at some point.
Update 14/9/12
The stand retaining clip was a bit light weight and I had a couple of complaints about it so I remodelled it using a spring.

Tuesday, October 26, 2010

Caving Headlamp

The Plan
I decided I might need a caving headlamp. It needed to be waterproof - as in able to withstand immersion - and able to withstand a beating, so I thought I'll have to make one myself. Also I didn't want to spend a gazzilion dollars which is what would have happened if I had to buy one off the shelf.

The LEDs
I had a couple of old white 3W Luxeon Star LEDs lying around so I thought in the interests of reducing waste I should use them even though the more recent models available now are more efficient.

Current Regulators
The best way to run high powered LEDs efficiently is with a buck regulator set up for current regulation.Modules to do this used to be exorbitantly expensive despite the regulator IC's on them being fairly cheap. Luckily there are some nicely made Chinese units available at I bought the buck regulator circuits that were configured for 800mA and changed the sense resistor to set the max current to 690mA as required for the 3W Luxeons. I also lifted the feedback pin and inserted a 1kOhm resister to allow me to switch in resistance to Vout thereby dimming the LED by reducing the current.

I decided to upgrade my rechargeable batteries from clapped out NiMH AA cells to some nice 18650 lithiums. I soldered leads to each cell and covered them with heatshrink to protect them. The leads are terminated with miniature locking connectors from South Island Components.
I also bought a fancy do-everything charger from dealextreme. This is a very nice unit which can be programmed to do multiple charge/discharge cycles and record the energy in and out - useful for assessing the condition of suspect cells.

LED Configuration and Dimming
The left LED is set up with a DPDT (on-off-on) switch for medium, off, full. It has a spot beam lens for navigational use and illuminating distant features. The right LED is on all the time that the batteries are plugged in. This is a safety feature to avoid bumping the switch and ending up in total darkness unexpectedly. It is controlled by a SPDT (on-off-on) switch for low, full medium power. The currents for the low, and medium settings are set with some small surface mount 50KOhm trimmer pots between the feedback pin of the regulator and Vout.

Lamp Enclosure
The lamp enclosure is made from a block of aluminium milled out to fit the LEDS and circuitry. The Leds are thermally connected to the back of the case so it acts as a heatsink. The front of the case is 5mm thick polycarbonate (aka Lexan), which should be strong enough to stop a bullet should I happen to encounter one. I used some silicone sealant on the front of the case to seal it when putting it together.

Battery Case
The battery case needs to be water proof and rugged. I found just the thing from Witz. Unfortunately, in New Zealand they only seem to be available at a high price from Highbeam. Still, they do seem to be worth it. I sealed the cable entry points of the case and lamp with plastic cable glands from Jaycar. To house and protect the battery case I made a cover from neoprene scraps. This is fixed to the helmet with a nylon strap and a buckle.

Wednesday, October 6, 2010

Working out parallel resistor combinations

Have you ever tried to figure out which two or three resistors to combine in parallel to get a desired resistance? Usually you have a limited stock of components to choose from too. Here is a simple little application written in C# for .net that calculates the best values to use from a given set.

Download Program

Download Source Code

Sorry about the poor design and sloppy nature of the coding. I whipped it up in rather a hurry. Maybe one day I'll have a spare life and get around to improving it.

Sunday, November 9, 2008

Almost free bicycle pannier bags

Turn those old conference bags into panniers!

Bicycle pannier bags for cycle touring are very expensive. For general commuting cycling something cheaper may be sufficient. A simple way to re-use something that you may find kicking around your office is to convert old conference bags to panniers.

I have made two panniers for my wife. Conference bags are great as they often have a carry handle and a shoulder strap all ready to go. All that is needed is to fit a back stiffener and some hooks to them.

I made some hooks from aluminium strip. They are fixed to a 7mm plywood back using a single m5 bolt with a nylock nut. Position the hooks to ensure that the rider's heel will clear the pannier when they peddle.

You will need some sort of fastening to hold the pannier down when you go over bumps. I fitted a loop to the bottom with a bungy to hook over the bottom of the carrier.

Yay! Almost free panniers.

Sunday, September 2, 2007

Do it yourself Secondary Glazing

"I can't believe it's not glass!" Our dining room with secondary glazing installed on painted wooden frames. Sweet basil and a potted avocado tree in evidence.

What is Secondary Glazing ?

Secondary Glazing is retrofitted plastic double glazing. You get significant benefits in heat and sound insulation from the trapped air between the panes. An additional benefit is much reduced condensation on the windows, which is very beneficial to your old wooden joinery if you happen to have it.

The commercial systems are generally about half the cost of retrofitted glass double glazing. The prices for glass and plastic respectively being in the regions of $400 per square metre and $200 per square metre in New Zealand. Doing it yourself works out under $50 per square metre.

The Plastic
Cast acrylic sheet is relatively cheap at around $35 per square metre dollars for low grade. Don't let the grade worry you too much. One supplier I approached tried to convince me I needed A grade UV resistant plastic at about $100 a square metre! Yeah right. I eventually found Award Plastics and talked to Aaron who assured me that they had done this before and the cheapest grade was more than adequate. It certainly looks fine with little distortion or visible marking. The plastic is installed inside the glass so the worst of the UV is filtered out before it hits the plastic anyway.

The plastic comes in 1.2 x 2.4 metre or 2 x 3 metre sheets. I supplied the company with a cutting plan that I hand optimised to fit the sheet sizes available with the aim of producing as little waste offcuts as possible. To glaze wooden joinery one needs to measure the window to the inside of the frame and then add about 30mm to each dimension. This gives 12mm per side for the magnet and a few mm of tolerance. Award Plastics took the cutting plan and cut the plastic as required for no extra charge.

The Magnet
To attach the plastic to the window frame I used brown vinyl magnetic strip, similar to the magnets used in a refrigerator. This can be bought from I bought the 1.2mm x 12mm strip. There is the option of buying the matching A/B pair but this is more expensive and only comes with self adhesive tape. I found that most of the single side strip that they sell will mate with itself correctly in one orientation but not the other. The A/B pair is designed to correctly mate in either orientation. It pays to check with the staff of your supplier to ensure that the magnet will indeed mate with itself.

Improperly mated magnet - note the offset sideways.

Properly mated magnet

The Glue
Initially I tried using self adhesive magnet on both the window frame and the plastic. This worked for a while but the self adhesive glue stays tacky and slowly creeps with the weight of the plastic. The consequence was that the sheets of plastic started detaching, usually on the frame side. In the end I realised that a curing glue was required and so I switched to using Ados F2 contact adhesive on both the frames and the plastic.

You will usually need to cut recesses into the plastic and magnet to clear your window fittings. I did some of my windows with a coping saw and some with band saw. I finished the recesses off with a belt sander. The amount of energy you spend on this step will depend on how tidy a finish you require.

It is important to prepare the surfaces to be glued carefully. On varnished frames the varnish should be scraped off to reveal bare wood. On painted frames the paint just needs to be cleaned, provided that it is in good condition. When using contact adhesive one only gets one shot at the positioning of the glued pieces so be very careful.

The steps to assemble one window are as follows:
  1. Cut the magnet, two strips to fit each edge of the plastic for a total of eight strips.
  2. Peel the protective film off one side of the plastic.
  3. Apply glue to the edges of the plastic where the magnet will fit.
  4. Apply glue to the the magnet that will be fitted to the plastic.
  5. Once the glue is tacky, carefully fit the magnet to the plastic.
  6. Hold the plastic in position on the window and mark lightly the location with a pencil.
  7. Apply glue to the window frame in a 12mm strip next to your marks.
  8. Apply glue to the the magnet that will be on the frame.
  9. Once the glue is tacky, mate the frame magnets to the magnets already glued to the plastic. Make sure that they are mated properly (see pictures above).
  10. Carefully hold the plastic in position on the window and press it into place.
  11. Press around the edge of the plastic to make sure it is glued down.
  12. Remove the plastic carefully from the window by separating the mated magnets.
  13. Press firmly on the magnet glued to the frame to ensure a good bond.
  14. Peel the remaining protective film off the plastic.
  15. Replace the plastic back on the window.

Just a little update 28 May 2010 - I've recently become aware of systems that use a mating pair of plastic extrusions or a single plastic extrusion with a living hinge. These systems have the advantage of not requiring magnets. If these had been around when I did my secondary glazing I probably would have used them. The UK is far ahead of NZ in this market. Check these out...

A further update. April 2011. Thanks to Sarah in the comments tipping me off to the fact that Award Plastics now offers a range of systems for DIY secondary glazing from Tubeway Ltd in the UK। The pricing is fairly steep for the EasyGlaze which is the system that looks the best to me.

Check out this, A thesis on secondary glazing!