One tool - two uses

**mklotz** · Sep 1, 2015, 10:19 AM

A recent article in American Machinist reminded me of something I made twenty years ago for a friend. The body of the tool is a through-drilled cylinder with one quarter of its body accurately milled away.

Insert the punch, made from hardened drill rod, into the hole, align the edges of the cutaway portion with your scribe lines and voila (not viola - that's a musical instrument), the punch mark is on the intersection of the lines.

But wait, there's more! (He shouts, madly waving his Ginsu steak knife.) Ever had the problem of having to align to the edge of a piece of stock angled in the milling machine vise? Drop the body of the punch over the edge and use the edge finder to locate on its circumference. Since the diameter of the punch is known (or can be easily measured), it's a simple matter to locate the spindle axis directly over the edge.

The one shown is massive enough to not move under the friction of the edge finder but, if you have problems, apply a dab of oil or grease to hold it in place with the capillary action. (I have a miniature version that requires this action to remain in place.)

**kbalch** · Sep 1, 2015, 03:39 PM

Thanks Marv! I've added your Intersection and Mill Alignment Aid to our Measuring and Marking category, as well as to your builder page: mklotz's Homemade Tools. Your receipt:

Intersection and Mill Alignment Aid by mklotz

tags: marking, alignment, mill

**Paul Alciatore** · Aug 6, 2017, 05:55 PM

Marv,

The concept seems simple and it should be useful. But do you have any tips on how to machine it with good accuracy? Yes, I know, touch off on one side and go half the diameter. But just how accurate is that going to get you? Two thousandths may be the limit. I would like to have it down to a few tenths.

**mklotz** · Aug 7, 2017, 09:10 AM

Originally Posted by Paul Alciatore

Marv,

The concept seems simple and it should be useful. But do you have any tips on how to machine it with good accuracy? Yes, I know, touch off on one side and go half the diameter. But just how accurate is that going to get you? Two thousandths may be the limit. I would like to have it down to a few tenths.

Surely you jest, Paul. Two tenths accuracy on something you're going to use to make punch marks? If you want that sort of accuracy use your mill/DRO or a jig borer. How do you intend to make layout lines with tenths accuracy?

**rossbotics** · Aug 7, 2017, 02:18 PM

Paul you will never in your life work within tenths using a center punch, I don't care who told you they could, no such thing,

**Paul Alciatore** · Aug 8, 2017, 12:00 PM

Marv,

NO, I do not ever expect to work to tenths with punch marks. But, as I am sure you are aware, errors do add up. The final error will be the sum of all the errors of every step along the way. There will be other sources of error in the process: lining up the edges with the scribed lines, the concentricity of the punch, the tolerance between the punch and your guide, etc. Many sources of error. And you need to attack each of them. Lets say that my goal was +/- 0.001" overall. That does seem to be a reasonable goal. I may not actually reach it, but it is a reasonable goal. But then each source of error would need to be less than that. Most of them would need to be significantly less than that 0.001". If each of the errors was +/-0.001", then five of them could add up to as much as 0.005". Or if you use the math for the expected error, you will be around 0.003". That would be a large error in my opinion and, with some care, I am sure I can already do better than that.

To reach a reasonable goal in the overall process, an error in the tenths range at each source of error is going to be necessary.

You seem to have many good ideas. I was just wondering if you had any tricks for machining those two flat surfaces on the center line of the device with a really good tolerance. Well, no that should be the center line of the central hole in the device: the OD does not enter into the equation.

I do not think my reasoning is unreasonable or a jest.

Originally Posted by mklotz

Surely you jest, Paul. Two tenths accuracy on something you're going to use to make punch marks? If you want that sort of accuracy use your mill/DRO or a jig borer. How do you intend to make layout lines with tenths accuracy?

**rgsparber** · Aug 8, 2017, 12:55 PM

Marv,

You are an inspiration to me!

http://rick.sparber.org/LACOM.pdf

Thanks,

Rick

**rossbotics** · Aug 9, 2017, 01:23 AM

To make something as critical as you would like it to be would require gage tolerances to be held because of all the accumulated errors, the easiest way to find the corner of that block would be to use the tool like the one Marv made and edge find from both sides of the tool and split the difference, I made a little drawing.

Cheers