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I'm Sick Of Spring Loaded Center Punches

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extropic

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What are your new brackets for?

As far a automatic (spring loaded) center punches, there is definitely a technique required to use them. One of the most important factors, IMO, is to be working on a very stable platform.
 

LarryP

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Used to be able to center punch crossed scribed lines within 0.005" all day long. Eyes were a bit better way back then.
 

coolidge

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Good point Larry, I had to get a magnifying glass out to line these holes up, that's with my reading glasses. But mostly I think its just the lack of quality in those spring loaded punches. You can run the tip down the scribed line but they always seem to punch the hole off center. I bought like 3 of the things and just gave up.
 

ch2co

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Has anybody used one of those optical center punches?? Always thought I might get one to try out.
My Starrett spring loaded punches seem to work quite well. I first hit the mark with one of the little ones, followed by re-punching with a larger one.
I can't claim to run a high precision shop, but I usually hit the mark within a couple of thou.

Chuck the grumpy old guy
 

RJSakowski

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For precision center punching, I use a two part process. First, I use a punch made from a used chainsaw file with a tip ground the about a 30 deg. angle and a needle point. The sharp angle and fine point make it easier to find the center of the scribe lines.

A light tap with a hammer is sufficient to make a point which you can find with a regular center punch. If the punch misses the desired location, you can walk the punch mark over by angling the punch in the desired direction and restriking. I then use a regular center punch to make a sufficiently large enough mark for drilling.

If making your own punch, make sure that you anneal the struck end to prevent the possibility of shattering the end of the punch. A chainsaw file is good for two punches.

Bob Center Punch .JPG
 

RJSakowski

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Gunrunner you need to order a set of these for the Z axis hand crank. Bill did you just spit coffee on your monitor? :rofl:

View attachment 253356
 

coolidge

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Guys here's the rest of the problem, even if you get it punched dead center of your scribed lines then you need to line it up on the mill which unlike a drill press which is sloppy enough that it will find center on its own a mill is rigid enough to drill off center of the punched hole. Trying to line up to a punch mark that is now .050 wide is problematic. I had been bringing a small drill bit down, observing its deflection in the punched hole and adjusting but even that was not fool proof and kind of a pain.

Once the DRO is on the new mill this whole thing becomes moot of course.
 

John Hasler

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Guys here's the rest of the problem, even if you get it punched dead center of your scribed lines then you need to line it up on the mill which unlike a drill press which is sloppy enough that it will find center on its own a mill is rigid enough to drill off center of the punched hole. Trying to line up to a punch mark that is now .050 wide is problematic. I had been bringing a small drill bit down, observing its deflection in the punched hole and adjusting but even that was not fool proof and kind of a pain.

Once the DRO is on the new mill this whole thing becomes moot of course.
When drilling on the mill I just prick-punch and then center drill.
 

JimDawson

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.....unlike a drill press which is sloppy enough that it will find center on its own a mill is rigid enough to drill off center of the punched hole.

One trick that I use in the mill is to leave the work a little loose in the vice or on the table. That way it emulates a drill press and the center drill will find the center of the punch mark. Just make sure the work can't get away from you.

Another way to accurately locate position on a mill is to use an optical center finder. They have a 45X magnifier and are capable of locating a position to .001".
I added a camera to mine, makes it a lot easier to see with my old eyes and stiff neck.
http://www.hobby-machinist.com/threads/microscope-camera.35888/
.
.
 

mattthemuppet2

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if you're careful you can lightly touch the spinning drill l to the punch mark and see if the ring of cut metal is the same width all around the punch mark. i usually do that after lining the flutes up with the hole. tbh, i think stub drills would get me better accuracy - the amount that even decent standard length drills can walk probably outweighs any effort i make at accurately locating it
 

RJSakowski

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It's the fact that drills walk that allow you to hit the center punch. I used to drill thousands of holes in printed circuit boards using #72 carbide drills. The drill would orbit around the center punch before settling on the center. The home made drill press had enough play in it that it would accommodate the offset and drill the hole without breaking the carbide bit.

As long as the point of the drill is inside the center punch and the work is free to move relative to the drill, you should be OK.
 

gjmontll

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Above, Chuck mentioned the optical center punch. I've used LMS's optical center punch for several years. It works quite well, even for my elderly eyes.

http://littlemachineshop.com/products/product_view.php?ProductID=3186&category=

But it does have some drawbacks:
Getting enough illumination when you are bend over it looking into the lens, you're probably casting a shadow over it. Without direct light, the image can be rather dim.
On small/short/narrow pieces, it can be tough or impossible to achieve an adequately steady footing for the base, which is 1.875" in diameter. And any hole within 0.938" of an inside corner is unreachable.(Perhaps you can make your scribe marks on the other side of the material - not always an option)
If you have a bunch of spots to mark, it is a bit tedious, as in: position the base over the scribe marks, insert the lens, look thru the lens and precisely align it, pull out the lens and set it aside (I hold it in my teeth), insert the punch, pick up the hammer, tap the punch, put down the hammer, pull the punch, swap the lens back into position, and go to next spot ...

Greg
 

george wilson

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I was silly enough to buy one of those laser center finders. Forget it! The dot it projects is way too large for accurate work. I can use it when drilling jewelry models(for subsequent casting),but that's about it. I am not sure of the diameter of the dot it projects. .015"? Whatever it is,it's way too large for precise centering.
 

kd4gij

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First it sounds like you have been using harbor freight class spring loaded center punches. :rolleyes: That said I have been known to use starter taps that have a nice point on the end to locate layout points. :shhh:
 

coolidge

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Well show me a spring loaded center punch that's not China these days but I spent $30 on the last one at our huge local hardware store.
 

Bill C.

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Has anybody used one of those optical center punches?? Always thought I might get one to try out.
My Starrett spring loaded punches seem to work quite well. I first hit the mark with one of the little ones, followed by re-punching with a larger one.
I can't claim to run a high precision shop, but I usually hit the mark within a couple of thou.

Chuck the grumpy old guy
If you are referring to the type that has a optical round piece with cross-hairs and a short transfer punch? No, I wanted one. What I have is a optical piece what looks like small magnifying glass that I used check my punch mark location afterwards. It has crosshair and othe markings. I have had it for about 40 years.
 

george wilson

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My old Starret automatic center punch is fine. But,you do have to hold it vertically to prevent the punch mark from being pushed off center when the spring goes off.

I have had it for many years,but usually just use a regular center punch and a small hammer,rather than look for the thing.
 

Ulma Doctor

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I have a couple spring loaded center punches made by Blue Point (snap on tools) they are the cats' meow.
but when i'm serious or when it counts, i use the old hammer and center punch due to the fact that a spring loaded punch doesn't seem to make a very deep punch in harder materials
 

chips&more

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I have a few of those spring loaded punches. I like them, but need to keep an eye on the screw in points on them. The points tend to loosen up/unscrew as you use the punch. And when the points are loose the punch doesn’t punch as well…Good Luck, Dave.
 

Bray D

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This is a newb question for sure, but perhaps this is the place to ask it.

How are you guys locating on your punch dimple once the piece is on the mill table? I can get pretty close by using a punch then 'eyeballing' with my spotting drills, but there has to be an objective approach to locate over the dimple.

Is that what the conical 'finders' are for? Anyone have a link to a video showing how they work?
 

RJSakowski

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This is a newb question for sure, but perhaps this is the place to ask it.

How are you guys locating on your punch dimple once the piece is on the mill table? I can get pretty close by using a punch then 'eyeballing' with my spotting drills, but there has to be an objective approach to locate over the dimple.

Is that what the conical 'finders' are for? Anyone have a link to a video showing how they work?
The methods described in posts 10, 14, and 17 above will work. For accuracy, the optical center finder will get you within a thousandth or two. Allowing the drill to find the center of a punch mark on a loose workpiece is fairly good. I will sometime put a small sharp point in a collet and visually line a workpiece up in the x and y directions.The sharp point is better at eyeballing the center than a drill. When I have to relocate an existing hole, I often put a matching pin in a collet and run the pin into the hole in the workpiece. It will automatically center the hole in the direction parallel to the vise jaws and the vise can slowly be closed while observing movement of the part, The axis perpendicular to the jaws are adjusted to just bring the part into contact with the fixed jaw.
If clamping directly to the table, the process is simpler. Just lower the pin into the hole and clamp. This will work with the sharp point and the center punch dimple as well.
 
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