Closing aluminium tube ends

I'm working on a little project (a spotlight) that is basically a bit of aluminium tubing, 50mm ID, 5mm wall thickness. I was wondering the
best way to close the end of the tube that doesn't have the light shining out. I'm hoping to make it water resistant
a) Turn a round plate of 60mm diameter, drill and tap the tube and screw the plate on - problem being the wall thickness isn't that great so I'd be limited to about M3
b) Cut an internal thread in the tube and a threaded plug to fit (probably a 1.5mm ISO thread) - would require some form of sealant/ threadlocker
c) Cut a chamfered plug and bond it to the tube - not sure what adhesive to use
Any other ideas? I'll be using my Myford Super 7 and indexable tools
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Robin wrote:

Five millimeters? Half the thickness of my pinkie finger?
Or 0.5mm?
--
Tim Wescott
Control system and signal processing consulting
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Robin wrote:

Turn a plug .002" over and press it in.
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Ditto.
If you are unsure of the proper interference fit you could turn the plug 0.1mm oversize and then cut a crude thread on it to allow it to squeeze down into the tube more easily. The thread is less hypersensitive than a smooth cylinder to removing small amounts for adjustment, because you effectively trim the groove width rather than the diameter. Since it makes the plug more compliant than the tube the OD is less likely to bulge.
You're Robin in England, right? I am also conversing with a Robin in France about ion thrusters for spacecraft.
jsw
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Loctite. Red or Blue.
Wes
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Turn a plug that is thick enough to drill & tap. Hold with screws through the tube. Bob
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You've about covered your options except for spinning. A little late to plan for that. If you're using any sort of high-temp incandescent, like halogens, it'll cook any sort of adhesive. Heat expansion may loosen pressed components.
Any reason for making one as opposed to buying one? Around here, there's any number of cheap track lights about that size at the big- box home improvement places. Most of those are cast units. Can even get LED bulbs for those now.
Stan
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d. Turn a plug 50 mm with o-ring piston seal groove. Use o-ring for seal . Drill thru tube into plug and use roll pin, screw, epoxy, whatever to keep plug in tube.
Dan
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If I end up turning a plug, is it better to trepan a 50mm circle from a piece of flat bar, or part off a wedge of 50mm round bar? The reason I don't want to buy one is that I have been unable to find something exactly what I want. It's basically a modified X-Lite (http://www.x - eng.co.uk/X-LiteAZ.asp) but with better weatherproofing and a different mount. Although the commercial version is only 35, I'd need at least 4 of them for my application (ideally more) and if they're going to get nicked, I wouldn't want to spend 140. Labour costs aside, I can buy enough tubing to make 10 for 40 (http:// cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=160326428983) and I doubt a small piece of round bar is going to cost a fortune (in fact, I've got some lying around here).
I like the sound of option d - that's why I asked the question! Might use high temperature silicone instead of an O-ring, though unless someone can point me in the direction of an O-ring supplier
Robin (England)
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The silicone caulk would probably work well. If you use it smear some on both parts before pushing the plug in.
I have made larger aluminum disks by cutting a slightly larger blank using a sabre saw , hacksaw, whatever. Then using something kind of like a live center, but with a fairly large flat end. Put on your face plate with some plywood fastened to it and then put some rubber ( old intertube ) next to the faceplate, the aluminum oversize disk, and use the " live center " to apply force to hold the plate against the rubber. The live center was made from a front wheel bearing from a car and some steel bar. The wheel bearing provides the flat surface. Obviously light cuts, but you should not have to take off a lot if you don't make the blank too much oversize. If you make the plugs from flat stock, you could make them with a shoulder so they would seat evenly and use thinner stock.
You might try finding some aluminum at a industrial recycling center.
Dan
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How you going to stop it self destructing, probably fairly fast, given the extreme temperatures its going to achieve.
Andrew VK3BFA.
PS - nice project though - congrats
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How about solder? With the right fluxes and aluminum solder you get a good tight join. Drawn plug of soft aluminum would be suitable, too.
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I've got some aluminium solder stuff, Lumiweld or similar, but can never seem to get the same results the demonstrator shows! Didn't come with flux - you had to melt a pool of solder and then scratch through to break the oxide - I think it then reacted with the aluminium to break the rest of the oxide. Not sure how I'd do it with this application
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wrote:

Try cleaning/saanding the tubing end just before using the stuff.
This will eliminate the oxide issue and enable a better bond.
The demonstrator probably did his demonstration just after giving a spiel during which he was "brightening" his materials.
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Aluminum solder might work, but the thick walls would conduct the heat away so you would need a torch. I don't think I would get good results.
Dan
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wrote:

If you are machining the plugs, on a lath, and if it is a permanent joint they why not try shrinking them into place? You can easily do it in the kitchen, stick the plugs in the freezer and heat the tubes in the oven - about cake baking temperature I think, fish a frozen disk out of the fridge, set in on a board and grab the tube (with a pair of pliers) and just set in place over the plug.
An aluminum tube will expand an amazing amount when heated to, say 350 degrees F.
John B.
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ups.com:

You didn't say what the enviornment is, but I frequently use plastic plugs for steel and aluminum, round and square.
Like these: http://www.mcmaster.com/#tubing-plugs/nv3vm
Ken
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in

The tube is basically a spotlight body, one which I'm hoping will be waterproof. Since the bulbs (MR16) are halogen, they tend to generate a fair amount of heat so I wouldn't be comfortable with a plastic plug. Have always been tempted by the freezing/heating methods - I suppose once joined, the fact the whole assembly is heating up should stop it all falling apart although I'd be tempted to screw in place as well.
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