previous page: 1.4 The Ultimate Homebrew Bike Light: IV. Construction
page up: Bicycles Misc
next page: 1.6 The Ultimate Homebrew Bike Light: Battery charger

1.5 The Ultimate Homebrew Bike Light: Mounting bracket


This article is from the Misc Bicycles FAQs, by various authors.

1.5 The Ultimate Homebrew Bike Light: Mounting bracket

19. Cut two pieces of the 3/8" threaded tube, 1/2" long with a hacksaw.

Try not to damage the threads too badly. I wrapped masking tape
around the part that I held in the jaws of the vice. File the edge
that you cut so that it is smooth and can take a nut.

20. Decide how far apart you want the lamp modules to be.

Mine are about 3.5" between centerlines. This is a little too close.
In retrospect, I'd recommend about 4.5" .

21. Cut the aluminum bar to an appropriate length, 5" for example.

22. File the rough edges of the bar.

23. Drill a hole at each end, about 1/2" in from the end.

These holes should be slightly larger than 3/8" for clearance.

24. Place the steel angle bracket on the bar so that the right
angle part comes out about in the middle of the bar.

25. Mark the locations of the holes and drill two mounting holes in
the aluminum bar.

This will be the attachment point to the mating bracket that you will
secure to your bike.

At this point you may want to sand and paint the aluminum bar ( I did ).
Let me also suggest an alternate mounting bracket. I bought an old lighting
fixture at a garage sale for 50 cents some time ago. It was the type
that had a swivel mount between the base and the bulb/reflector assembly.
If you take the swivel apart you'll find that one part has a 3/8"
threaded mounting tube on the end, and it is attached to a nice, thick,
ring. This is how I mounted my light. Instead of an angle bracket, I
drill a third 3/8" hole in the center of the bar and mounted this fitting
to it.

I chose to buy regular bulb sockets. You can save yourself $9.00
by soldering the wire directly to the pins of the lamps. You can
solder the wire directly to the bulb as follows:

1- With an X-ACTO knife, scrape the oxide from each pin of the
2- Strip about 1" of insulation from the wire and wrap it in
a tight spiral around the pin.
3- Solder the wire until the solder flows around the wire and

Note: I got some feedback from Tom Ervolina about the above
instructions. He claims that a female spade lug can slip
over the pins. They should be taped for safety.

The solder does not "wet" the pin particularly well. The wrapped
wire forms a sort of socket and you will get some bonding on the pins.
The sockets are nice because they fit tightly and are high temperature
rated, with fiberglass insulation.

26. Connect the housings to the aluminum bar by using the two, 1/2" long
threaded tubes with two washers and two.

27. Check the length of the wire so that enough slack is present to allow
the bulb to be fully removed from the PVC pipe holder.

28. Cut one of the wires for the switch at the point where the wire just
reaches the bottom to the holder with the bulb completely outside of
the holder. This will ensure that you can assemble and disassemble
the lamp.

29. Solder the wire to the on/off switch.

30. Thread the wire through the hole and the switch into its hole and
fasten with the washer and hex nut.

Before sealing the bulbs in place it is a good idea to test the circuit.
If you are using a socket for the bulb, temporarily plug in the bulb.

31. Connect the wires exiting the lamp holder to your battery or to a 12V AC
or DC source. You can also test it for continuity with an ohmmeter, but
seeing a bright light is a much better test. Assuming that all goes well,
it's time to seal the bulbs in place.

32. If you used a socket it is a bit easier to do this next step. If you
can, remove the bulb from the socket and put aside.

33. Lay a bead of RTV silicone sealer/caulk/glue on the inside lip of the

34. Reconnect the bulb and then carefully, put the bulb assembly in place
on the RTV bead.

35. Lay a second bead around the edge of the lamp. It helps to have the
lamp holder in a vice or support of some kind.

36. Wipe the bead with your finger to form a smooth rounded fillet
all around the inside of the lamp.

Try to minimize the amount that the bead overlaps the active surface
of the bulb, since this will diminish the light output. I tried to keep
mine at 1/8".

37.Set the lamps aside to dry. It will set completely overnight.

If you have problems holding the bulb in place try this trick.

1- Cut a small block of 3/4" scrap wood, about 1" square.
2- Place it on the surface of the lamp and put a rubber band
over it to the rear of the lamp holder in order to keep
the lamp in place until the RTV sets.

If you used a socket, as I did, the wires from the socket might be
sheathed with fiberglass, rather than ordinary plastic insulation.
The fiberglass tends to fray, and is not robust enough for outdoor use.
I placed some heat-shrinkable tubing over the fiberglass and slipped it
up into the hole in the lamp holders. I heated the wire with a heat gun,
but you can shrink it with a match or soldering iron if you are careful.
If you've never done it before, practice with some scrap until you are
confident that you won't torch your new bike light.

38. Join the wires from both lamps and thread them through the cap of the
2-pin male plug from Radio Shack.

39. Pair up the wire, one from each lamp, and solder to a terminal of the
plug. Polarity doesn't matter.

40. Attach the cap and then screw down the strain relief screws on the rear
of the ap.

This completes the construction of the lamp assembly. Now let's turn to
the battery. Since the length of the power cord from the battery to the
lamp will depend upon the mounting location, let's ignore that for the
moment. Whatever length of wire you choose, you'll still need to do the

41. Cut a length of 2 conductor wire ( zip cord ) to length.

42. Examine the wire carefully. Even though the entire wire is uniformly
one color ( usually brown, black, or white ) one of the conductors has
a ribbing on the insulator. If you cannot differentiate one of the
conductors from the other, get a length of 2-conductor wire that is

43. Check that the female spade connectors you choose are the right
size for the male spade connectors on the battery.

44. Strip about 1/4" of insulation from each conductor and solder the
female spade connectors to the zip cord.

I recommend that you slip a 3/4" length of heat shrinkable tubing
over the female spade connectors and shrink it to a tight fit. This
will minimize the possibility of a short circuit.

45. Strip the other end of the wire back about 3/8" and slip it through
the shell of the FEMALE 2-pin connector.

46. Solder the ribbed conductor to the NARROWER of the 2 receptacles.

This is important since the connector is polarized. We will always
make the positive voltage attach to the ribbed wire and to the smaller
pin or receptacle of the connector.

In order to make a neat solder joint do as follows:

a- Twist the strands of the exposed copper wire to prevent
b- Slip the conductor through the hole in the solder tab of
the pin or receptacle, from the inside out.
c- Fold the conductor back towards the wire and crimp.
d- Solder the wire to the pin and trim any excess.
e- Repeat for the other wire.

47. If the battery has some charge you will be able to test your
work. Attach the spade terminals to the battery with the ribbed wire
going to the positive terminal. Plug the connectors together turn on
the light. A lit lamp is a good sign.

48. Attach the shell and tighten the strain relief screws.

If you haven't already done so, attach the spade terminals to the
battery. Be sure to attach the ribbed wire to the positive terminal
on the battery.

If you have a mountain bike you can PROBABLY mount the battery as I
have. I'll describe how I did it and then suggest some alternatives. If
you come up with a really clever mounting technique, let me know.

49. Lay a piece of foam rubber into the Nashbar bike bag. Slip in the
battery on to of the foam. The top of the battery should be near the
bag's zipper. Slip some foam on top of the battery.

50. Wrap some foam around the stem section between the head tube and
the handlebars and tape it together with duct tape, packing tape,
electrical tape, etc.

51. Lay the bag on the foam and attach the two velcro loops around the
handlebar and the other loop under the stem. Push the excess wire
into the bag and close the zippers around it.

Mating the lamp to the bike can tax anyone's ingenuity. I was fortunate
that I was mating the lamp assembly to a mountain bike stem. This is
the most straight-forward connection scheme. If you are attaching it
to a road bike stem, the kind that hides the handlebar clamping bolt,
then it will be more difficult. I was able to make a lamp holder for
my road bike using two clamps, shown below. You can buy them in a
bike shop. They come with vinyl around the clamping part to prevent
scratching. You should be able to get 1" diameter ( road ) or 7/8"
diameter ( mtn ) clamps.

/ \
__ ___| | <--- This part goes around the
__ ______ / handlebar, on either side
^ of the stem, facing forward
Bolt goes through here

Anyway, I describe the easy way, first.

52. If the bolt which tightens your handlebar to the stem is accessible
from the front of the bike then follow these instructions.

Usually, the bolt is a metric, recessed allen head bolt , mounted at a
slight upward angle.

53. Remove the bolt and get a longer one with the same thread, either
allen head or hex head. Most hardware stores carry metric bolts
these days.

54. Drill out one of the holes outer holes on both steel angle brackets
so that they can be bolted together using a common 1/4-20 bolt.

55. Drill a clearance hole for the stem bolt on the other arm of one of
the angle brackets.

56. Mount the angle bracket to the stem and tighten down until the handle
bars are tight. The plane of the angle bracket which extends forward
from the bike should be at right angles to the ground.

57. Bolt the lamp assembly angle bracket to the mating bracket on the bike.

Congratulations! You are sort of done.

Now, back to the road bike riders ( or unfortunate MTN bikers ).

58. The cut another piece of the aluminum bar stock about 4" long.

This is the material that you mounted the two lamp assemblies to.

59. Position the two clamps ( described above ) on the handlebars, facing

60. Place the aluminum bar so it spans between the clamps and mark the
location of the holes that tighten the clamps.

61. Drill two holes in the aluminum bar.

62. Now mount the other steel angle bracket to this bar.


Continue to:

previous page: 1.4 The Ultimate Homebrew Bike Light: IV. Construction
page up: Bicycles Misc
next page: 1.6 The Ultimate Homebrew Bike Light: Battery charger