coaxial centre finder, another method

[petertha]

I wouldn't worry too much about the spot size !  Yes smaller is better, but...  If you recall I mentioned that you could focus the ring down to a small spot and that I had noticed that it had a very small black centre.  As a guesstimate this black dot is 0.2 mm in diameter.

I noted you mentioned that before. My laser pointer doesn't have that center hole, its solid red. But I should try it on metal just to be certain. Do you think that's kind of a laser pointer lens aberration, kind of like the magnifying glass focal length principle? I wont make analogous comments about concentrating the ring of a magnifying glass to the point of spontaneous insect combustion & a misspent youth, lest the animal rights activists are monitoring

[rodw]

I have to say this is pretty cool. I emailed a mate with far more experience with Machining than I telling him it was his next project. Not long later he told me he'd ordered his lasers. I asked him what he ordered and this is what he selected http://www.ebay.com/itm/121212852782

So I ordered the same lasers! I'm kinda hoping he'll run off one for me when he fires up his CNC mill!

[BaronJ]

Hi Guys, Peter,

It could very well be an aberration that is peculiar to the laser I use.  Unfortunately I have nothing to compare it with, and Aldi seem to no longer have the laser pointer for sale.  I suspect that you would have to reduce the voltage to to   http://www.ebay.com/itm/121212852782  otherwise it may be too bright to be effective.  I'll see if I can find another laser pointer for sale somewhere, buy one and have a play with it.

[petertha]

Not long later he told me he'd ordered his lasers. I asked him what he ordered and this is what he selected

Keep us informed. That looks similar to what I was getting itchy Buy fingers on. But I noticed in the description of your example they they say focusable = yes. Do you suppose that means you just the laser diode ('light' source)? Because I also see sometimes the lens holder & lenses sold separately, example below. (There are also apparently crosshair & single line styles you can screw on, but that's of no value for our spinning application)

http://www.ebay.com/itm/6-35mm-aspherical-lens-holder-405-G-2-lens-holder-M9-0-5mm-/121492774187?pt=LH_DefaultDomain_0&hash=item1c49889d2b

http://www.ebay.com/itm/5pcs-5mm-Collimating-lens-Focusing-Lens-Laser-Diodes-/121224004668?pt=LH_DefaultDomain_0&hash=item1c3983843c

[BaronJ]

You can pull these lens out of scrap CD drives.

http://www.ebay.com/itm/5pcs-5mm-Collimating-lens-Focusing-Lens-Laser-Diodes-/121224004668?pt=LH_DefaultDomain_0&hash=item1c3983843c

[sco]

I'm still thinking about making one of these laser pointer centre-finders - to get a really small dot would it work to put a piece of foil tape over the lens with a pin hole in it?

Simon.

[Steamer5]

Hi Simon,
 I have a laser center / edge finder, i brought the polarizer unit latter, this allows you to focus the dot. I see from there web site they now include the polarizer & have up rated the laser module. Having followed this thread I've been thinking that it should be possible to use it to build one of these. Not sure how you could make a polarizer but may be a Google would help   

Cheers Kerrin

[sco]

Thanks Kerrin - Can you post a link to the website,

Cheers,

Simon.

[Steamer5]

Hi Simon,
  here you go...  http://www.lasercenteredgefinder.com/main.html
Just had a look & they sell the polarizer as a separate part, you would just have to make yours to fit, or save the hassel & buy the whole thing! I find it quite useful, both for picking up cross lines & setting lathe tools to height, & setting the vice up on the mill....

Cheers Kerrin

[sco]

Thanks again - expensive but looks very good.  I don't suppose you have the mini version - I can't see anywhere on the site what the overall height of the unit is.

Cheers,

Simon.

[Steamer5]

Hi Simon,
 Sorry no, I have the orginal. Can get some dimension of it if you would like, it would be latter as I'm at work, night shift. Had it for quite a few years now. The guys are usually quite quick at answering question. Yep not the cheapest item but I find it handy. My dad liked it & he brought one & a friend of his having seen his.

Cheers Kerrin

[BaronJ]

Hi Guys,

The easiest and probably the quickest way to get polarized material is sunglasses.  Though another source that is freely available but requires dismantling is dead laptop screens or flat screen monitors.  These have, usually two sheets in them.  Don't break the florescent tubes, because of the mercury content and don't break the glass sandwich because the liquid crystal is quite nasty.  Other than that there are other useful sheet materials there.

[BaronJ]

Hi Guys,  almost forgot.

I just got one of these:  5mw red laser.  Its absolutely useless !
Its far too bright.  The spot is rectangular in shape.  At the distances it needs to be used at a 2.5 X 5 mm spot is far too big.
So this is one to be avoided.

I did try to measure the spot size of mine, and its about 2 mm in diameter, not quite round, it has a small flat on one side.  I think that is why I get a tiny black dot in the centre.

I'm still looking for something like the original one that I got from Aldi.

[Arbalest]

To get a really small dot would it work to put a piece of foil tape over the lens with a pin hole in it?

Simon.

I read on another forum that someone has tried this and yes, it does work apparently!

[rodw]

I have to say this is pretty cool. I emailed a mate with far more experience with Machining than I telling him it was his next project. Not long later he told me he'd ordered his lasers. I asked him what he ordered and this is what he selected http://www.ebay.com/itm/121212852782

So I ordered the same lasers! I'm kinda hoping he'll run off one for me when he fires up his CNC mill!

Well, the two lasers turned up today. I had a bit of a play with running them off 3.3 volts and 5 volts stolen from an Arduino and it seems they have current limiting circuitry built in so you can power these directly from 3 to 5 volts. When I started to play i played arou d with 680R and 330R resistors before deciding to run it via a direct connection to a power source.

I found an old LED torch with 3 x AAA batteries in it. Thats 4.5 volts so somewhere in the middle. I turned up an adapter that replaced the torch lens out of Acetal (Delrin) and removed all the LEDs. I now have an awesome pointer that shoots the length of my yard and beyond. The focus is achieved by turning the threaded knurled end. As said before, it is very bright but adding a resistor will fix that and I dont't think the focus needs changing for the length of the mill Z axis travel.

It will be a while before we build the centreing gadget as I helped my mate out for a project by ordering some bolts against my account for a project he's working on. Went from $70 for 12 bolts to $1.68 each. Hopefully, it will earn a CNC version of this...