NBTV Camera Question

[gary]

How do you account for the burr on the needle exit point Albert?

[Viewmaster]

How do you account for the burr on the needle exit point Albert?

If the pad is hard the burr is not too bad, the burr being transferred to the bottom of the pad. A soft pad will give more burring. One has to experiment with pad materials.

Anyway it's the actual end exit hole shape that counts. Just leave any small burrs alone which are outside the viewing area.

Have just tried it on a CD and the holes look quite nicely round.

Note for Harry....You mentioned a template. On Stephen's web site is a good piccy of a 32 line Nipkow. You can copy this (as he invites you to) and reduce it to fit your CD as a template.

http://www.sptv.demon.co.uk/nbtv/

[gary]

Anyway it's the actual end exit hole shape that counts. Just leave any small burrs alone which are outside the viewing area.

Well that's really only true when used in a monitor and viewed straight on - for a monitor it will reduce the viewing angle (or at least diminish the quality of the picture).

For a camera it is even more important as the ideal aperture is infinitely thin - a burr around the aperture produces a cylinder effect and would give a tunnel effect on the picture (if severe) - that's why pin hole camera apertures are usually sanded off and rebored a few times.

Anyway you say there isn't much of a burr presumably because of the "backing" effect of the pad so it will probably be ok.

[Viewmaster]

Well Gary, if the burr is a problem then one could try piercing hole undersized then reverse pierce it so that required size is in the centre of the CD or remove burrs with fine emery and repierce...........

Experiment, experiment, experiment, Gary.....just as I have been doing these past 6 months. New methods are never handed to us on a plate.

My method works fine on film, I suggest Harry try it on a CD. If it doesn't work for him then nothing lost except the price of a needle.

Re your tunnel effect. A CD is quite thick so there is a tunnel for starters.

As my signature says," If at first you don't succeed, try, try ,try again....
...........then give up!" (well not really!)

[gary]

Oh indeed Albert. I was merely explaining why I asked the question. I have never tried the "piercing" technique but I know others have, and I have always wondered how they got around that problem. It's actually a problem with drilling too - but it is easier to deburr in that case (I would have thought anyway).

[Harry Dalek]

I have seen tiny drill bits at jaycar and of cause bunnings that might be another ebay thing to get in bulk from china .

hmmm - they have some small drill bits but nothing like .25mm as far as I am aware, but I am happy to be wrong...

sure you should be able to get them online...

Hi Gary i think something here is in range...i do have 3 needle sized drill bits handy but might drop by jaycar and have a look.

I know bunnings have tiny hobby ones but sell them a bit each and not cheap...

I always tried the heating of a needle before trying that way it was very easy and no cracking could happen as albert says no loss if it doesn't work or mistake...with dvds cds endless amount to test so no loss.

http://www.jaycar.com.au/productResults ... UBMIT.y=18

[gary]

Well, technically, the aperture size would ideally be 0.22695625392149 mm

so the smallest there (.3mm) would be 32% oversized - but I suppose you'd still get a picture, albeit somewhat blurred...

[Harry Dalek]

Well, technically, the aperture size would ideally be 0.22695625392149 mm

so the smallest there (.3mm) would be 32% oversized - but I suppose you'd still get a picture, albeit somewhat blurred...

Gary if the size is to large could you cut out a tin foil disk or tape over the holes and pin prick smaller holes as i think Andrew did on one of he's Nipkow few years ago.

I think for the first Nipkow i will try the easy way since i have a Dremel tool that makes life pretty easy but i will track some needles down for a test .

With the Dremel i had an idea also of trying a needle in it the friction might be enough to make a hole as well worth a try .

[gary]

The problem there Harry, as I see it, is finding the centre of the oversized hole prior to piercing.

In truth though, the thickness of the CD would probably be more detrimental than the 32% oversized hole anyway - so maybe .3mm would be, well.... "appropriate"...

[gary]

The advantage of a needle (or conical cutter) over a drill would be that it effectively countersinks the aperture thus giving you a thinner aperture - which for a camera is always good.

The disadvantage, as I see it, is controlling your "piercing" depth - something Albert appears to have solved.

[Harry Dalek]

The advantage of a needle (or conical cutter) over a drill would be that it effectively countersinks the aperture thus giving you a thinner aperture - which for a camera is always good.

The disadvantage, as I see it, is controlling your "piercing" depth - something Albert appears to have solved.

Ok gary what i will do is try a few out one dvd nipkow should work
i just tried Alberts idea out and i can make it very easy just by hand the pin prick hole is as small as so know i can do that side of it .

Ok one step closer.

[gary]

the pin prick hole is as small as .

Ok, it's small, but is it accurate? I mean .19mm would be worse than .3mm...

[gary]

Here are a 1.5 turn and single spiral dxf file at CD size in DXF format:

[Viewmaster]

The problem there Harry, as I see it, is finding the centre of the oversized hole prior to piercing.

Yes Gary, so very true as I found out the hard way!
It's better to approach the correct size in small stages, for as you say an oversize is a loss of centre datum.

Maybe one could mark a tiny circle around the correct centre before starting then if an oversize/off centre mistake is made one has the tiny circle as a ref point.

[Viewmaster]

Gary, Harry, to maintain a datum if cut oversized how about a piece of brass rod with needle sized hole drilled through (that's about .5mm dia plus to suit).

Taper the end (and maybe serrate) and place the needle point onto the datum mark on the CD before piercing.
Whilst holding the needle vertically, slide the rod down and twist to mark (CD marking ink on end?)
This gives a fixed datum dia same size as needle for future reference if needed.