PRECISE OPTICAL LAYOUT FOR CENTER PRICKING

[ieezitin]

Hello lads



Marking out center prick marks and getting them dead on center is always a challenge so I had a need to precisely mark out three holes for a master jig plate i needed and thought rather than bash out my pop marks and just go with buttons i would shoot for the size from the surface table and use my trusted optical layout and drill bushing set, old technology but works a treat, i thought i would show this for people who have not seen this done...

My plate blued and marked from the hieght gage and surface table..



A picture of the scope showing the cross-hairs, i positioned it on a 45 deg angle so it shows the black cross-hairs better because sometimes the scribe line will consume it..




shots of the scope laid out over the scribe lines...








once the scope has been zeroed in i take out the scope lens and install a drill bushing and a then slip in a 3/16 center finder punch and very lightly tap it.. this shot shows i removed the drill bushing and put the scope back in and it shows the very small prick mark..


 


here is what it looks like as normal ..

[ieezitin]

I clicked the post too soon... here is the rest..

Here is a shot with the first prick mark, then i used a regular center prick punch to make it deeper, you can get a sense of scale..





Here are the tools i did this with...







I hope this helps people.


All the best Anthony...

[DavidA]

Anthony,

Nice, but are you going to tell us where you get the cross hair optics ?

Dave.

[ieezitin]

Dave

 i have had this setup since 1992 or so, they sell the same gear on ebay or any quality tool shop, i dont remember where i got it,  just google, " optical center scope" and you will find a supplier/vendor... i would suggest dont buy an inferior brand, invest your monies in a quality set-up from a known toolmaker supplier.

Hope this helps..

Anthony ....

[Eugene]

By coincidence I elected to go the optical punch route a month or so ago.

I was advised to try and find a British made version by DanKroy. Unfortunately the company is out of business and the second hand ones are few and far between. So being a patriotic Brummie  with a shamrock in his turban I ordered a British made alternative and a right piece of rubbish it turned out to be.

The heart of these things is the plastic magnifying lens; in my case this was so badly formed that it distorted both the  straight scribed lines and the graticule making it impossible to align accurately. In addition the graticule lines were very thick and coarse, and actually obscured the lines on the workpiece. The single ninety degree punch had heat treatment scale still on it, the whole issue being supplied in a plastic bag. Binned it day oi?

Next up was the Soba version currently advertised at a discount from Axminster ...... absolutely excellent bit of kit; two precision ground crystal clear lenses, one with fine black cross hairs, totherun a dot, one sixty degree and one ninety degree punch, all in a nice wee case. Not sure of the ultimately available accuracy yet, I need a bit of practice, but guessing, it's single figure thous just now.

Unreservedly recommended at around twenty five quid including postage.

Eug

[Joules]

I owed a friend some favours and since I have been working with some perspex rod thought this might be a good Thank You gift.

A simple design for the base, 3D printed of course.



As I have an 8mm reamer that pretty much set the size the bore was going to be.  Next job was machining and polishing the Perspex rod and then setup for marking.



Since the rod at this position is nuts on 8mm, I just had to zero off the top and -4mm for my centre line.  Rotate the Square block collet holder (re-zero as the collets are    )

Put it together and test the optics.



Tight fit, but it will loosen up with use.



My scribe lines are a bit thick, but a quick polish with Brasso of that end would sharpen them up a little.   Next job, find my 8mm silver steel and make the punch.

All the optical surfaces are finished with fine emery paper and oil, cleaned then polished in the lathe with Brasso and paper towel.  5-10 mins work per surface.  If you cock up the marking just polish it out and start again.

[awemawson]

I bought this rather nicely boxed set at a Model Engineering exhibition years ago and it has served me well over the years. You centre it optically, then holding the base still rotate the upper bit to one of the other detentes holding the punch.

[Biggles]

Hi I have been using what looks to be a very similar item from Veritas for woodworking. Veritas Optical Centre Punch. I think it’s gone up a little since I bought mine but Axminster sells them. http://www.axminster.co.uk/veritas-optical-centre-punch-475156

[Joules]

Bit of extra polish sharpened up those lines, add some sharpie and wipe off with paper towel leaving black in the scribe lines.

[ieezitin]

Joules..

Smashing job mate, this would be a worthwhile project for someone to make.

Anthony.

[PekkaNF]

Nice work and always informative to read on these howtos.

How does the accuray on these thingys compares with the scriber on groove and feel method? I'm not blind, but I'm having hard time imaginning this being better, specially if magnification is much less than 5X.

Pekka

[Joules]

Pekka, it's not so much the magnification (1:1 on mine) as the high contrast it gives you.  The Perspex transmits the light down the hole to the work piece.  It's much easier to line up the cross hairs and unlike my auto centre pop doesn't bounce off to one side as I didn't have it vertical when I popped it.   The error on my line centre is 0.125mm off centre, I know this by twisting the perspex over a steel rule and watching the centre point move around the 0.5mm ruler line.   I'm pretty sure I put this error in when I zeroed off the 8mm section and it flexed down under the weight of my height gauge.

Since showing a few people, I have had a few requests for them, especially wood workers as it's GOOD ENOUGH.  With practice I can do better on my centre accuracy, can't find my 8mm sliver steel so will have to pick some up soon.   

[PekkaNF]

Good enough is good enough!

Pekka

[Joules]

I thought I would make a few more this afternoon.

[Ed ke6bnl]

is the plastic just acrylic rod? and what is the outer housing made of.

[Joules]

The outer housing is 3D printed in PLA, but could just as easily be Delrin/Acetal or aluminium/brass, but plastics tend not to mark items.   Yes, 12mm acrylic rod.

[nrml]

I missed this thread completely . Many thanks to all the contributors. I am thinking of making one with a small footprint. I suspect illumination and the need for magnification will be an issue. A small magnetic base with a LED in the wall for illumination should work nicely. Would a tapered plug of acrylic with the big end domed work for the optics? I keep thinking that if it were that simple, someone would have done it already . 

[RussellT]

I've been thinking about making one of these since I saw this page.

http://www.gadgetbuilder.com/OpticalPunch.html

He gives some info about magnification and radii.

Hats off to Joules for his design and construction technique.

Russell