Incidental optical centre punch

[Canobi]

Seasons Greetings folks *< []: )

I've had an optical centre punch on my "to make" list for ages and was slowly gearing up to make one. I decided to go with 12mm for the punch and got a 12mm reemer and some 12mm x 50mm acrylic rod in preparation:


Not long after, I snagged a bag of hardened and ground dowel pins of varying diameters, some of which also happen to be 12mm x 50mm and figured I could use one to make a punch:


I've had a lot of other financial commitments recently, so have been unable to acquire a piece of brass to make the base with so was saving the project for a later date.

That was until today. I was given a steering column essembly to salvage parts from a few days ago and I decided to strip it down this afternoon.

I was interested in one part in particular as it looked like it could be used as a milling jack. It wasnt until I got it free that I realised that it was actually made up of three pieces and as such, was way too short to make into a jack (bummer) but by shear coincidence the part was perfect as an optical punch base as it's quite heavy and very hard (files just skip across it and I couldn't "soften" the edges with my noga deburr) and the bore is such a good fit for the dowel that when one end is blocked, I get a "pop!" when removing it or the acrylic rod:



With that, I took the acrylic rod and chucked it in an ER32 on my lathe. I then faced, spotted and then sanded the end to get rid of any tool marks. Afterwhich I carefully heat polished it to make it optically clear again and used a permanent fine tipped marker to black the central indent:


I then flipped it round and used my lathe file to make a slight some. I'm given to inderstand that the optimal dome radii is 15° but without a way to accurately achieve that, it took a bit of playing around to shape the end to a usable magnification, in this case it's closer to 24° but it still turned out fit for task:



With the optical part complete, I turned to making the punch, nothing of which was spectacular enough to write home about but it did involve a little hard turning, so I broke out the carbide tooling for this job.

I wasn't entirely sure what the optimal included angle was for a metal punch, so simply set my topslide to copy the business end of one I already had and voila:



I will make a brass base for it one day but at least I have one on hand when I need one


Have a fantastic Christmas one and all and I wish you all the best for the new year.

Canobi *< []: )

[WyoJim]

Nicely Done. Supersized version of a Veritas center punch I purchased years ago.

[Dimitris Polychronis]

Well done, Canobi! I just love tools that are made from salvaged parts or scraps!

Merry Christmas and happy new Year, to you too!
Dimitris

[rossbotics]

Great write up and display Canobi
Think I'll put one of those on my to do list, Happy Holidays to you too and all of yours.

Doug

[thinkbackwards]

Very nice. I'm jealous. excellent description and photos of your technique.

[Canobi]

Thank you for the kind words everyone, a Happy New Year to you all

[Mr.Pete]

O my god This is a cool tool … I need one so badly, my eye sight is going bad … I need 3 hands to use a center punch .

[Canobi]

O my god This is a cool tool … I need one so badly, my eye sight is going bad … I need 3 hands to use a center punch .

I have a few spares, PM me if I can help in any way

[wizard69]

Nice work leveraging found parts. Honestly I wouldn’t bother with a brass base as this one will last forever.

Unless of course you add a light to that base. Old age loves lots of light.

[Canobi]

Nice work leveraging found parts. Honestly I wouldn’t bother with a brass base as this one will last forever.

Unless of course you add a light to that base. Old age loves lots of light.

As a matter of fact, I have indeed been looking into doing just that, though when you posted, much of my idea was still in my head, so figured I should at least make a sketch of the concept so I had something to present with my response.

As it happens, I like to dabble in electronic engineering from time to time and actually enjoy working with surface mount components. I also have PCB design software so I came up with a ring design for the punch base light that will host upto eight surface mounted LEDs, each just 2mm x 1.25mm:


The LEDs are wired in parallel, that way the voltage requirement stays the same regardless of the number of LEDs in the chain, meaning that any number from one to eight can be soldered in place and the circuit will still function. The obvious advantage here being that if one ever gave up the ghost, it doesn't break the chain causing all the others to go out.

The trade-off is that the amount of current, or amps required to run the system increases with every LED added to the chain. Initially, this is what put me off thinking about this idea seriously as LEDs are a hungry lot when they get together for a party and as advanced as we are in so many fields, batteries are literally centuries behind so I was unsure whether I would find a combination suitably compact enough for this idea to become a reality.

However, there is a drive within the industry to take up the slack in portable power by making semiconductors that require less energy in the first place and while I've been out of the loop playing with my machines since putting my home shop together, I was rather pleased to find some surface mount LEDs with a 3v 2mA spec had been developed that still provide a decent amount of lumins

Given that the combined current draw for all eight LEDs would only be 16mA, the system coupd get away with using very small button cells, in this case two SR59. Each one is 1.55v @20mAh and will be placed in series to combine the voltage output to 3.1v which is within the LEDs working voltage range. Even with a meagre 20mAh capacity, the circuit will still produce over an hour of "on" time. Given that they are only used for moments at a time, an hour likely equates to months before the batteries will need changing so it looks like it should be a goer.

Admittedly it took a little thinking to work out the details on how to integrate the electronics but eventually I split the punch base into two halves that screw together, with a plastic housing ring for the button and batteries sandwiched in between so it is secured in place when fully assembled.

The foot of the base hosts the plastic housing ring within the seat in the upper portion and there is a hole for a mounting screw which simply holds it down to capture the pushbutton and prevent the housing from spinning when the neck mates with it as it's aseembled.

The light ring gets screwed in the recess from underneath so the LEDs are facing downward. I may make an acrylic ring cover for the light ring that snaps in place but having just thought of it, I will have to add it to my concept sketch at a later date.

Being it's just a conceptual drawing at the moment, it's not to scale but do have a rudimentary figure of 35mm for the neck of the base as it's the smallest diameter I could fit the electronics into (see attached PDF for higher res image)
Self Illuminating Optical Centre Punch Base Concept.pdf