Enlarging hole in reflector?

[Ian]

I've retrofitted some G4 LED bulbs in to some pond lights, but they're so much larger than the halogen G4s that they replaced. They can't fully fit within the reflector mount, as the diameter of the bulb base is larger than the hole.

I've managed to disassemble the enclosure and remove the reflector mount, so if I can enlarge the hole then the new bulbs will fit just fine. Here's a photo of a similar reflector (not the same, but almost identical):



As I can't get replacements, I've only got one shot at this - so I thought I'd pick your brains before I try enlarging that hole. I'm not sure what the material is, but it's delicate I imagine.

Any thoughts on how you would approach this? I imagine that drilling it out won't end well. My current thoughts were to use a conical metal file and see how that goes.

 

[Harald Kapp]

I'm not sure what the material is, but it's delicate I imagine.

Probably metallizes plastic?

Do you have access to a mill? Removing material from the 'top' of the cone (the smaller end) will automatically enlarge the hole. A fast bit on th emill should work through plastic without breaking it Ideally you add cooling.

 

[GamingAddict]

Try sanding it down on a belt sander ? Of course if you do have access to one.

 

[Ian]

Many thanks for the ideas!

Probably metallizes plastic?

Do you have access to a mill? Removing material from the 'top' of the cone (the smaller end) will automatically enlarge the hole. A fast bit on th emill should work through plastic without breaking it Ideally you add cooling.
View attachment 38085

Yep, it looks like a metalized plastic.

No mill access, unfortunately - just a pillar drill, router table and most hand/power tools.

Try sanding it down on a belt sander ? Of course if you do have access to one.

No belt sander either, but I've been considering buying one for a while, so can get one if needs be (I've got about 5 assorted power tool sanders though ).


I'll do a quick test and see how how easily the material responds to sanding and/or filing.

 

[Arouse1973]

You could try a Dremel with a thin saw blade maybe?
Adam

 

[Arouse1973]

Wrap some tape around the light just below where you want to cut. That will help hold it all together.
Adam

 

[Ian]

Wrap some tape around the light just below where you want to cut. That will help hold it all together.
Adam

Good idea, I hadn't thought about that!

I've taped it up and used a flat file to bring the level down (similar to how Harald suggested), rather than trying to open it up with a round file. Seems to be working so far, although I need to wait until it's light outside to test it in the pond .

Many thanks for all the suggestions .

 

[dave9]

Since you have no belt sander, mark a line showing what to remove and do it manually with a piece of sandpaper taped to something flat like a piece of glass or a counter top checked with a straightedge. Rinse (not wipe) any stray abrasive particles away so you don't scratch the reflective surface.

 

[kellys_eye]

Isn't the reflector designed to have a 'focal point' that you're effectively moving by removing plastic? With a new bulb improperly positioned you won't get the designed beam pattern/width whatever....

 

[dave9]

^ That is true with incandescents (having a spot point of filament light) designed for throw, but to a lesser extent with LED retrofits and flood beam reflectors. The design of the LED bulb often swamps the rest and the more sideways oriented LEDs there are, the more disfigured and floody the beam compared to the original.

In other words if the desired effect is exactly illuminating one thing and only that thing, it could take several attempts with different LED bulbs to (re-)achieve the desired effect, odds being that the closest beam would come from a deeper recessed spot-point from a single higher power LED rather than a Christmas-tree style bulb with rows up and down the bulb assembly.

 

[Ian]

Isn't the reflector designed to have a 'focal point' that you're effectively moving by removing plastic? With a new bulb improperly positioned you won't get the designed beam pattern/width whatever....

The light source is considerably further forward in the reflector too, due to the huge difference in size between the halogen and LED G4 bulbs - so I think the focal point will be quite off. I'm not too worried about the drop in reflector performance, as it's more for stability and aesthetics that I need to add the reflector back in. As long as there is light generated within the pond, that's good enough for this case .

 

[FuZZ1L0G1C]

Enlarging:
I'm thinking of something along the lines of the steel-conduit reamer bit for enlarging the ID.
The actual reamer bit is probably too angled, which would make the mounting unstable.
Another idea would be to get hold of a narrow taper cone, such as on a PVC ground-spike which my solar panel assembly uses (2 cm pipe diameter tapers over about 15 cm).
With suitable sandpaper wrapped around, could be rotated to gradually widen hole.
Focusing:
Maybe a Paxolin PCB threaded and fitted with small machine screws?
Saw a similar 'screw-type' focuser this evening, on a website re constructing a Dobsonian Reflector.

 

[Bluejets]

https://m.ebay.com.au/itm/12x-Ultra...-Bulb-Silver/332173490028?hash=item4d5715376c Are these essentially what you are trying to get to?

 

[Ian]

Thanks for all the advice everyone - the job is done and it works a treat .