layout and punches

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: GlennW, Harold_V

Post Reply
User avatar
Tillies in a Bottle
Posts: 12
Joined: Wed Apr 07, 2021 9:19 pm
Contact:

layout and punches

Post by Tillies in a Bottle »

In Moultrecht's book Machine shop Practice he shows what's called a hand prick punch. It's a punch that you would not strike with a hammer but instead would twirljust in your hand. The body of the punch is helix shaped like a drill, and it spins as you pinch the thing lightly and move your hand down.

He says this hand punching is what establishes the beginning of the punch, and we move on to the prick punch and center punch after that.
Does anyone still make these? I haven't found even any pictures of one, let alone one for sale.
I've made my own from a masonry bit, and I was able to get the tip almost as fine as a scriber but not quite. That might be the best you can get out of a green Carbide grinding wheel.
stephenc
Posts: 311
Joined: Sat Jul 05, 2014 6:13 pm
Location: youngstown ohio

Re: layout and punches

Post by stephenc »

Many years ago I had a tiny jewlers drill about the size of a small Sharpi that worked like that . Someone decided they like it more then i did and it disapeared .
User avatar
mklotz
Posts: 428
Joined: Thu Jan 09, 2003 11:35 am
Location: Los Angeles, CA, USA
Contact:

Re: layout and punches

Post by mklotz »

Regards, Marv

Home Shop Freeware
http://www.myvirtualnetwork.com/mklotz
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: layout and punches

Post by pete »

Those Moultrecht books are pretty good, but I think some of the technique's in them were already long out of general practice even when they were first published 40 years ago. And I'm not all that sure what if any additional accuracy benefit's could be gained by starting with something like that hand prick punch idea, a standard prick punch and then finally using a center punch. Doing a proper layout on one off complex parts while using manual machine tools is still very valuable for working out the order of operations and not machining over or on the wrong side of the line on those parts. But other than for hole layout on larger fabrications, hand or drill press work where your not using coordinate techniques, prick and center punch hole locations are methods that are well known to be quite inaccurate anyway unless you just don't have access to a milling machine. And that's the main reason it's now almost never done in commercial shops except on low accuracy work.

It's also 100% related to your layout equipment's built in accuracy, repeatability, your own level of eye sight, knowledge and skills while using the proper technique's. Anyone who cares to check the specifications for even well known brand name height gauges will see it takes some pretty decent money to get below .002" in repeatable accuracy. Then add in all the variables that can and do happen during those hand layouts, prick and center punching and I doubt few here could get multiple holes on a continuous and repeatable basis under a guaranteed .010" for there XY location. And you could probably double that number at least if your using even the best machinist square for those layouts. It's an old school method that due to I suppose tradition by hobbyist's should have died out long ago if you can use the far more accurate coordinate system. I've even watched a few Youtube videos showing prick and center punching hole locations and then using a dro equipped mill to drill the holes. Doing so literally takes much longer and decreases the accuracy by a lot instead of having any positive gains. And yes I am aware that some extremely accurate work was once done by highly skilled workmen using hand layouts and punched hole locations in the past. How many here still do that as there day job and do so enough to replicate that same level of accuracy some of those people could do?
Glenn Brooks
Posts: 2930
Joined: Mon Nov 10, 2014 1:39 pm
Location: Woodinville, Washington

Re: layout and punches

Post by Glenn Brooks »

Very cool thread!

I seem to recall Mr. Pete, aka Tubalcane, doing a video on this process, some time ago. He suggested two alternative methods for manually locating hole centers. One involved the use of a small, jewelers ?? precision drill press to start the center point. The other he used some sort of loupe, or magnifying glass with a prick punch set in the center. Line it up, tap, and move up to center punch.

He also advocated scribing layout lines, then “feeling” the indentation of the layout line with the tip of the punch to center it accurately. I’ve done this latter method fairly often, with good success.

Also have had great success using transfer punches...

Never have found a high accuracy drill press...at least one I could afford to purchase. So I am guessing these all went the way of HS shop class...

Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
User avatar
Tillies in a Bottle
Posts: 12
Joined: Wed Apr 07, 2021 9:19 pm
Contact:

Re: layout and punches

Post by Tillies in a Bottle »

pete wrote: Tue Jun 01, 2021 1:58 pm

It's also 100% related to your layout equipment's built in accuracy, repeatability, your own level of eye sight, knowledge and skills while using the proper technique's.
I totally agree, and really what brought me to the whole topic in the first place is that my old bridgeport C head has someting between .005 to .015 runout. I'm making a Jig for mill arbor support with that brigeport head, and I want the two centers of the overarm and arbor side to be dead on. I'm depending on the accuracy of my layout and punch marks on the jig and then drilling with a small number drill (small like #55) to then exaggurate the mark. So far I've been able to do Mr. Pete's test with measuring between two dowel pins and got it on the money.

As for eyesight, I did the "hand prick punching" by looking at the intersection of two lines by a height gauge under a spindle bore scope- the closest thing to a microscope in the shop. Under the scope I brought in the tip of the hand punch to the center and did the twirling thing with it. I think the advantage of the hand prick punch is that it's mark is very light and even easier to correct than a standard prick punch's mark. It let me bring it back to the scope and tighten up the location .
Attachments
photo from machine shop practice
photo from machine shop practice
down the lens of the redneck shop-microscope
down the lens of the redneck shop-microscope
IMG_20210601_1136128.jpg
User avatar
Tillies in a Bottle
Posts: 12
Joined: Wed Apr 07, 2021 9:19 pm
Contact:

Re: layout and punches

Post by Tillies in a Bottle »

mklotz wrote: Tue Jun 01, 2021 12:36 pm Still available. For example, using "push drill" or "archimedes drill" as search string on Amazon...

neat stuff. kind of like a miniature Yankee drill.
Post Reply