Optical Center Punch Self Holding Punch

**Saltfever** · Sep 19, 2016, 06:44 PM

Thanks for the link. Yes, the suggested Mini LED would make for a much nicer and compact device. Although I am not fond of any button style battery since they tend to be more expensive than your garden variety AAA. Good idea about reducing brightness on the HF light. The HF light is about .995" diameter which I assume is a bit less than the loupe. I'm not sure which light I will use. Also, ambient light, through an empty hole(s) may be enough. I would aim the hole(s) at the cross-hair area. Anyway, a nice project and your great idea I will get to eventually.

**jjr2001** · Sep 20, 2016, 02:13 PM

Another minor mod to the optical center punch. I removed a small rectangle from the bottom of the punch. I thought the acrylic line at the bottom was interfering with the sighting in of the center punch. Just used a 3/8 emd mill and put in a slot down the back side and across the bottom. Left the base nice and solid so it does not tip over.

Cheers, JR

**jjr2001** · Oct 1, 2016, 06:40 PM

I just received my quite small, pocketable or keychain, led flashlight from here:

Useful Stream Light Micro Mini LED Super Bright Flashlights Keychain EDC Tool | eBay

It works very well as is for a bright spot lite to see small details in your work. Have not used it long enough to judge the quality but hey for 1 buck including shipping it is worth a try.

Cheers, JR

**YOUCARS** · Dec 29, 2017, 07:26 AM

Thanks, I will make one of these.

**jjr2001** · Dec 29, 2017, 02:22 PM

Thanks, for checking in. I think you will find it very useful.
Cheers, JR

**garage nut** · Dec 31, 2017, 04:04 AM

I also had no ways of getting a block like that, but I have lots of old number plates I have gathered over the years, so I peeled back the sticky backing with the numbers and glued about 20 off 50 x 50 pieces that I cut from the number plates together and this is the result.
I take it it needs a fairly fast speed in the mill. I have never worked with is stuff.

Optical Center Punch Self Holding Punch-number-plate-block.jpg

**jjr2001** · Dec 31, 2017, 05:31 AM

Now that is a great way to get a block of plastic.
I don't remember the speed I used but it was not real fast.
In my case I step drilled to 5/8" and then bored it to eyepiece diameter.
I would start out slow and increase the speed until it starts to melt!
Then back it off a bit to prevent the plastic from melting.
A few formulas from the net. SFM for plastic about 100
R.P.M. = (3.8197 / Drill Diameter) x S.F.M.
S.F.M. = 0.2618 x Drill Diameter x R.P.M.
I.P.M. = I.P.R. (feed) x R.P.M. (speed)

I found this chart on the net which has drilling speeds for different types of material.
Drill Bit Speed

Cheers, JR

**garage nut** · Dec 31, 2017, 05:57 AM

Chose a brand new 10mm end mill and the mill was still set on 900 rpm. finish was good so stuck to it. According to that chart it was smack on.

Optical Center Punch Self Holding Punch-number-plate-block-machined.jpg

Reading my mind...

my next question was going to be how to get a 20mm diameter hole for the optic. Biggest I have is a 16.

Optical Center Punch Self Holding Punch-punch-block-my-sizes.jpg

Just my sizes seeing I started with 50mm rough. It cleaned up at 47mm.

**jjr2001** · Dec 31, 2017, 07:01 AM

Looks good. Keep us posted.

Cheers

**mklotz** · Dec 31, 2017, 11:44 AM

I don't do much accurate center-punching anymore; coordinate drilling is easier and more accurate. But, when I was starting out, I did enough of it to learn a few things that I'd like to pass along here. These are just observations that others may find useful. PLEASE DO NOT CONSTRUE ANYTHING I WRITE HERE AS CRITICISM OF JR'S DESIGN. With that said (and hopefully taken to heart by all), let me proceed.

Looking at the location of the punch tip from an angle never worked well for me. I decided that a more vertical, magnified view of the location would make things easier to see. To that end, I attached the magnifier close to the punch axis and above the punch tip.

This worked a bit better but was a bit tricky to hold; I knew there must be something better.

I realized that magnification wasn't really necessary in most cases. Almost all the prick punching was done at the intersection of layout lines. If we could locate the punch using the lines themselves rather than trying to hit their intersection, everything would be easier. So, when I ran across this commercial product...

I knew I had found the holy grail of punch locating. :-) The punch is spring-loaded and resides permanently in the base. [Thus avoiding the major complaint associated with the devices that have magnifiers and punches that must be interchanged in a single hole. A major feature of JR's design is eliminating that undesirable design feature.] Scribed in a recess in the base (see next photo) are two lines. When these lines are aligned to the scribe lines, the punch sits directly over their intersection point. A slight tap with a small hammer marks the point well enough to be found by touch with a center punch.

The recess in the base in which the lines are scribed is important. The base will become scratched from contact with metal but the lines in the recess are immune to that scratching so they will remain very visible.

I no longer remember where I bought this device so I took a photo of its box top; that's all the information I have on it.

Later I realized that, while four lines pointing at the intersection are helpful, you really only need two. This observation makes it simple to machine your own version of the device from more durable metal as I did in the photos below...