How to cut down reflector without scratching surface?

[goldserve]

I'm not sure if this has been discussed in the two years I was here but I can't find it now.

Any good tips to cut down a reflector without scratching the surface?

Would a cut off tool work better?

 

[savumaki]

I was reading this and you may find some good tips there.

http://www.candlepowerforums.com/vb/showthread.php?t=156336

Hope it helps

Karl

 

[cy]

not possible to cut down reflector without some minimal damage to edges.

all you can do is carefully chuck reflector in a lathe. then take tiny cuts. where reflective material meets base material will chip.

mfg process has reflector base machined, then reflective material is vacuum deposited.

 

[Anglepoise]

All I can pass on is my experience with cutting down McGizmo's metal reflectors.

I run the lathe fast and take many, many very small cuts so that these shavings' are the consistency of cob webs . These do almost no damage. Sometimes none. As cy says, if there is damage it will be just at the small hole end.I have tried using a vacuum cleaner and compressed air with no better results.

I then spray with Fantastic and flush under the hot water tap.

I then shake dry and hit immediately with a hair dryer.

Now I have also found that the damage comes from handling, measuring, test fitting etc etc......not the actual machining.

 

[greenLED]

How much do you need to reduce the size by? I've sanded a couple of McR18's with no ill effects on the coating. This might not be practical if you need to do a whole bunch of reflectors, but it works nicely.

 

[jch79]

4sevens shaved down a McR-20 a while back here... There's a few posts talking about how it was done.

john

EDIT: Nevermind - I didn't know you were talking about cutting them down on a lathe. Good luck then!

 

[modamag]

Kevin, I see you're having way too much fun with your lathe.

As for cutting down the reflector you already did couple @ my place don't you remember?

Anyhow here's a recap.

1. Need to get good grip. Use collets if you have them.
If not bore and make a cylindrical sleeve with shoulder to hold the reflector. 3-Jaws holding the sleeve, and reflector is placed inside the sleeve.

2. Sharp Cutters, small feed @ high speed will minimize ribbons which gets sucked into the headstock and damage the reflective coating.

3. Last but not least, vacuum. This provide a small force to "pull" the chips away from the reflector and keeping them clear of the reflective surface.

After all is finish follow David's recommendation of cleaning & drying. I recommend compressed air as the final step.

I was able to turn couple McR-18s down to McR-11 (not the XR version). But it was a PITA when your final length is only like 0.080".

 

[goldserve]

Since I don't have all those tools at the machine shop, I plan to do the following.

I need to take 5.5mm off the front of the reflector so I will

1. Coat the inside of the reflector with a thick oil
2. Use high spindle rates, 700+
3. Use a cutoff tool which is 2.4mm thick so I advance 5.5mm - 2.4mm.
4. Wash the inside of the reflector with some warm soap water and canned air to follow.

That is my modified plan of attack for monday...good?

 

[modamag]

I would rather use facing tool than cutoff for chip manangement.
When you canned air. Keep the can at least 1ft away from the reflector. They are known to "spit".

Try to get the vacuum.

 

[jch79]

I would recommend Falcon Dust-Off brand canned air - it's what I've used since back in the day of film photography :green: - as long as you hold it mostly upright, I've never once had it spit something out at me.

I use the one with the chrome valve head that you just buy replacement cans for, but their new 360 degrees head is supposed to be great.

Here's a link: http://www.dust-off.com/default.aspx?pageid=163&productid=19

The disposable cans are a different story... they're not as powerful, and tend to "spit", as Jonathan said.

john

 

[will]

Be careful with the type of cleaner you use after, some contain lye which can affect aluminum . I have cut down a few with no problems, the very edge may be chipped ever so slightly.

 

[goldserve]

I would rather use facing tool than cutoff for chip manangement.
When you canned air. Keep the can at least 1ft away from the reflector. They are known to "spit".

Try to get the vacuum.

I was thinking, If i need to cut off 5.5mm of the reflector, I can use a cutoff tool to ensure there is only 1 big chunk of metal instead of little hairs. Hrmmm...what to do..i bought two reflectors and slighty ruined the first one...

 

[Anglepoise]

Only attempt a cut off tool if your reflector is held in a collet.

I suspect a 3 jaw will allow the side pressure of the cut off tool, to rip the reflector out.

I have never attempted this job with a cut off tool and wonder what happens as one is 'breaking through'. Thats when you might badly damage the surface.

When in doubt, go the slow way.

 

[gadget_lover]

David makes a good point, but was (IMHO) too subtle. Let me elaborate on what I think he was pointing out.

A parting tool will exert pressure from the side, requiring that you hold the piece very securely. A 3 jaw chuck is prone to crushing delicate things when side pressure is applied. As it crushes it lets go and things get worse quickly.

A facing tool will exert most of it's pressure towards the chuck, making it less likely to crush the reflector. You are only taking off a little (5mm) , so facing will not be too much of a chore.

Thanks David. I'd not thought of it that way.

Daniel.

 

[wquiles]

A facing tool will exert most of it's pressure towards the chuck, making it less likely to crush the reflector. You are only taking off a little (5mm) , so facing will not be too much of a chore.

Thanks David. I'd not thought of it that way.

Daniel.

+1

That is exactly how I do it on my lathe

Will

 

[will]

I cut down two McR 27L reflectors by .220 inch. I used a .040 parting tool and a three jaw chuck with some cutting oil and a fairly slow speed. I had no problems. The inside edge had a bit of a burr, when I removed that with emory paper, every thing looked fine.

This only proves - there are lots of ways to do this.

Why did I cut these down? I had a BHC from H22A, and a New TerraLux that I wanted to use. The standard install of the Terralux only left about 1 turn of the head before it came off. Shortening the reflector gave a few turns and a better feel. I even modified the switch so the TerraLux now acts like the top part of the Mini-Mag switch. I ended up with a nice light.