# Finding center



## drizzle (Aug 13, 2018)

I have a 1.5" piece of 1" solid bar that I need to drill and tap.  I have a precision tool makers vise that is missing the part that the bolt screws into.  I also need to drill a hole in the side for the dowel pin to go through.  I dont have a lathe.


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## BaronJ (Aug 13, 2018)

Hi Drizzle,



Does this help ?  Its intended to find and mark the centre of a bar.


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## JimDawson (Aug 13, 2018)

Do you have a mill and an edge finder?


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## drizzle (Aug 13, 2018)

i have a mill, no edge finder yet and no DRO yet.  I'm sure I can find it with the old school way and if I am off a C hair it will be ok but want to practice doing it the machinist way and testing to see have precise I can be.


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## JimDawson (Aug 13, 2018)

Well, the ''machinist'' way is to use an edge finder.    But since you don't have one, an endmill shank (or any straight rod) will suffice.  Just touch the sides of the rod to the part in the X & Y directions, and move over 1/2 the diameter of the rod + 1/2 the diameter of the part and you're on center.

The other method is to use a tri-square, scribe two lines about 90° apart, and where they cross in the center is center.


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## drizzle (Aug 13, 2018)

JimDawson said:


> Well, the ''machinist'' way is to use an edge finder.    But since you don't have one, an endmill shank (or any straight rod) will suffice.  Just touch the sides of the rod to the part in the X & Y directions, and move over 1/2 the diameter of the rod + 1/2 the diameter of the part and you're on center.
> 
> The other method is to use a tri-square, scribe two lines about 90° apart, and where they cross in the center is center.



aaaaaaannnnd how do I calculate what half the diameter is and then mark that location?


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## RJSakowski (Aug 13, 2018)

If drilling a cross hole, a V block can be used.  Adjust the block until the drill bit is centered on the bottom of the V. and clamp the block.  Place the shaft in the V and spot with a spotting drill or center drill.  Drill your hole to size. 

A tool like this can be used to find the center of a shaft, 
	

	
	
		
		

		
			





If using Jim's method, remember to account for any backlash.  I would buy the edge finders  They are cheap and accurate and c;lose to essential for setup work on the mill


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## higgite (Aug 13, 2018)

If you're trying to align the spindle on the radial center of the rod to drill the cross hole, follow what others have told you already. If you want align the spindle with the center of the end of the rod to drill a concentric longitudinal hole, you now have the perfect excuse to buy a coaxial indicator. I wouldn't leave home without it.

Tom


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## Bob Korves (Aug 13, 2018)

The cross pin and nut that tightens to the underside of the toolmaker's vise is a pretty easy home shop project.  There are no critical dimensions.  Make that vise fully functional again...

Also, for me, designing and making custom parts to make tooling and machines whole again (or better than new!) is highly satisfying work.


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## P. Waller (Aug 13, 2018)

RJSakowski said:


> If drilling a cross hole, a V block can be used.  Adjust the block until the drill bit is centered on the bottom of the V. and clamp the block.  Place the shaft in the V and spot with a spotting drill or center drill.  Drill your hole to size.
> 
> A tool like this can be used to find the center of a shaft,
> 
> ...


Someone gave me one of these about 20 years ago, I found it about the most worthless tool that I have ever owned, it went straight into the scrap.


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## JimDawson (Aug 13, 2018)

drizzle said:


> aaaaaaannnnd how do I calculate what half the diameter is and then mark that location?



Well, 1/2 the diameter of 1.5 is .75 (Dia/2), you'll have to measure the rod that you are using.  Just use the machine dials to move to center, or use a dial indicator to measure the table movement.


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## drizzle (Aug 13, 2018)

some of you are the absolute WORST at giving advice.  OR maybe I am just stupid?  HOW DOES AN EDGE FINDER FIND CENTER????    I'm guessing that people didnt read my entire first post.   Ok, the edge finder found the edge..... now what?  How does my edge finder tell me what 50% of my diameter is when my machine has no digital read out?  Telepathy? Do I turn the lights out for 10 seconds and then back on and I will magically have a pilot hole in the center?  Here is what I have..... I have a bare bones JET JDM18 mill (no DRO), I have a machinist vise that is missing the nut thing that locks the jaw, I have a Yuasa dividing head.  I have a Brown and Sharpe dial caliper, a starett micrometer which is super small, I havent even looked to see how big that goes.  I might have another micrometer in the tool box.  I have a Mitutoyo dial test indicator and a good assortment of machinist rulers and squares that were my fathers from when he was building models of chemical plants for Monsanto to make chemicals that are killing us all.  Oh, and I have an old school tachometer somewhere but not sure where that is or how to use it..  

I'm about ready to just measure a few spots to find center, drill it and call it a day.


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## drizzle (Aug 13, 2018)

OH!!!! I do have some v blocks similar to these. http://www.micro-machine-shop.com/V-blocks_compared.jpg


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## RJSakowski (Aug 13, 2018)

drizzle said:


> some of you are the absolute WORST at giving advice.  OR maybe I am just stupid?  HOW DOES AN EDGE FINDER FIND CENTER????    I'm guessing that people didnt read my entire first post.   Ok, the edge finder found the edge..... now what?  How does my edge finder tell me what 50% of my diameter is when my machine has no digital read out?  Telepathy? Do I turn the lights out for 10 seconds and then back on and I will magically have a pilot hole in the center?  Here is what I have..... I have a bare bones JET JDM18 mill (no DRO), I have a machinist vise that is missing the nut thing that locks the jaw, I have a Yuasa dividing head.  I have a Brown and Sharpe dial caliper, a starett micrometer which is super small, I havent even looked to see how big that goes.  I might have another micrometer in the tool box.  I have a Mitutoyo dial test indicator and a good assortment of machinist rulers and squares that were my fathers from when he was building models of chemical plants for Monsanto to make chemicals that are killing us all.  Oh, and I have an old school tachometer somewhere but not sure where that is or how to use it..
> 
> I'm about ready to just measure a few spots to find center, drill it and call it a day.


No need to yell. There have been past many posts on this subject. A little efort on your part would have found them.  

In the case of using an edge finder, the edge finder makes a distinct jump when it contacts an edge.   At that point, you are half the diameter  of the edge finder from the edge.  For example, if you get a jump at 1.2" and you're using a 1/2" edge finder the location is either .95" (1.2"-1/2*.5") or 1.45" (1.2"+1/2*.5"). If the edge is the fixed jaw of your vise and you have mounted a 1"shaft in the vise, you probably came to the edge from the shaft side. assuming that the vise is mounted with the fixed jaw parallel to the x axis and the fixed jaw is to the rear, The fixed jaw edge is at .95" and the center of the shaft will be .500" (half the diameter of the shaft) less or .45".  As I said before, you have to consider backlash so move the table to something less than .45" and move up to .45"

The process is much easier with a DRO but not impossible using the dial and counting turns.


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## JimDawson (Aug 13, 2018)

drizzle said:


> some of you are the absolute WORST at giving advice.  OR maybe I am just stupid?  HOW DOES AN EDGE FINDER FIND CENTER????    I'm guessing that people didnt read my entire first post.   Ok, the edge finder found the edge..... now what?  How does my edge finder tell me what 50% of my diameter is when my machine has no digital read out?  Telepathy? Do I turn the lights out for 10 seconds and then back on and I will magically have a pilot hole in the center?  Here is what I have..... I have a bare bones JET JDM18 mill (no DRO), I have a machinist vise that is missing the nut thing that locks the jaw, I have a Yuasa dividing head.  I have a Brown and Sharpe dial caliper, a starett micrometer which is super small, I havent even looked to see how big that goes.  I might have another micrometer in the tool box.  I have a Mitutoyo dial test indicator and a good assortment of machinist rulers and squares that were my fathers from when he was building models of chemical plants for Monsanto to make chemicals that are killing us all.  Oh, and I have an old school tachometer somewhere but not sure where that is or how to use it..
> 
> I'm about ready to just measure a few spots to find center, drill it and call it a day.



The edge finder locates the edge of the work, but YOU have to do the math to figure out where the center is.

I did machine/tool & die work for 15 years before I ever saw a DRO, they didn't exist.  I didn't own one until the mid 90's.  I did have an edge finder, and later bought a coaxial indicator.  But a rod in a drill chuck or collet works just fine for an edge finder.  I still occasionally use that method, I have a 1/4 dia hardened rod with a center point ground on it to act as a center punch.  Works great in a drill chuck for a quick punch mark when in the mill.

The machine dials are calibrated in 0.001'' increments, and are normally 0.250'' per revolution.  You read the dials and count turns.  If you need real precision, you use a dial indicator to measure the table movement.

First I think you need to learn to use your measuring tools, it sounds like you are pretty well equipped from that perspective.


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## drizzle (Aug 13, 2018)

ok that is making more sense.  Yeah, I had thought about setting up some cheapy dial indicators on my table to measure the movement of it till I got a decent DRO.


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## RJSakowski (Aug 13, 2018)

P. Waller said:


> Someone gave me one of these about 20 years ago, I found it about the most worthless tool that I have ever owned, it went straight into the scrap.


It is not a precision tool and certainly not intended to deliver positions with a few thousandths accuracy.  It is a visual tool and depending on the visual acuity of the user should be able to center better than .01".

For someone with just a drill press and no way for making precision moves or measurements, it will work.


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## BaronJ (Aug 14, 2018)

Hi Drizzle,

You mentioned in one of your posts that you wanted to find the center the old school way !
I posted a picture of a center finder that can be made very quickly without a mill or any special tools.  I'm sure that you have a press drill and can use a rule to scribe a straight line.

The device pictured is simply a short piece of flat bar,  the only criteria is that it is at least twice as long as the width or thickness of the material that you want to find the center of.  You will also need a few inches of drill rod.  Again it is not critical.  I made mine using 1/4" diameter rod.

Simply scribe a line roughly in the middle right down the flat bar from one end to the other.  Find the middle of that line, its not critical, anywhere within 1/8", 1/4" even 1/2" will do, then mark it with a center punch.  Use a divider and put one leg into the punch mark you have just made,  open up the dividers and scribe a line about twice the drill rod diameter away from each end.  Now mark the point where those two lines cross with the center punch.

Carefully drill three holes !  The ones at the ends should be a good fit for your drill rod, the one in the middle should be a good sliding fit for your center punch.  Now cut a couple of pieces of drill rod at least as long as the thickness of the material that you want to find the center of and secure one end each end of the bar.  Refer to the picture in my first post and the picture in this post.

Also this picture shows a couple of my other home brew center finders.  But more about those later if you want.


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## BaronJ (Aug 14, 2018)

Hi Drizzle,

Further to my previous post, assuming that you will make a center finder for use on flat or round bar, this is how to use it.

Place the center finder over the material that you want to find the center of with a pin on either side and rotate it so the pins touch at both sides.  At this point you can either use your center punch to scribe a line by sliding the whole thing along or just mark as needed.

I noted in another post you said that you have some "V" blocks.  Another poster explained how to use them to find a center for drilling round material. There is another simple way without using a "V" block.  But it requires that you are able to hold the work piece in a vise square to the drill table.  That method simply uses a rule or other thin flat metal plate balanced on top of the round material.  To do this you trap the rule between the work and the drill point and then move the work piece until the rule is level.  This method works best using the mill where you can get accurate fine movements.

It helps others to help you if you can post pictures of what you are trying to do.


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## drizzle (Aug 14, 2018)

Thanks Baron, I will look into making one.  Looks like a fun project


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## macardoso (Aug 14, 2018)

Don't be afraid of counting the handwheels on your mill, DRO's are great, but by no way a necessity. You can even hold sub .001" tolerances if you are careful.  As I understand your project, you have a round bar of steel, and you want to drill and tap a hole through the side of the bar, roughly in the center of the part. Here would be the way I would approach it in your shoes...

1) clamp the part (vise is ideal but there are plenty of other options)
2) put a 1/4" diameter rod in the spindle using a collet or drill chuck (use the back of an endmill or a dowel pin).
3) spin the spindle to make sure it isn't wobbling all over the place
4) using the handwheel which moves the 1/4" pin along the length of your part (X axis?), gently touch the left face.
5)Don't move the handwheel, lift the quill of the machine to clear the pin from the part.
6) Rotate the collar on the X axis handwheel to show 0.
7) You need to account for the fact that you touched the part with the side of the pin, not the center. To do so, divide the diamter in half (0.25/2 = .0125). You now need to offset your axis this amount. Rotate the handwheel one full revolution and then .025 more (probably 25 small ticks on the handwheel). The centerline of your pin is right above the edge of your part. Rotate the collar to read zero again.
8) use your calipers to measure the length of your part (lets say it reads 1.500"). Divide that in half
9) You need to move 0.75 inches. Your handwheel will move the X axis .100" per revolution (edit: common for smaller milling machines, make sure it applies to your machine, it could be .2 or .25 per rev as stated above). So to move the distance to the center of your part, rotate it 7 times stopping on the 0 mark. Move an additional 0.05 (50 ticks of the collar).
*You have now found the center along the X axis*
10) Now using the Y axis hand wheel touch the 1/4" pin to the inside of your vise jaw (it equates to the edge of the round part).
11) Measure the diameter of your part (lets say 1.000"). Divide it by 2. Subtract the .125" to account for the amount you are already inside the vise. you have .375" left to move
12) Zero your Y axis collar, and move the axis 3 revolutions plus .075 (75 small tick marks) towards the center of your part
*You have now found the center along the Y axis*
13) Lock the X and Y axes, put your center drill in your chuck, and drill the part

This description did not account for backlash in the machine, but it won't matter for this part.  Get the hang of finding center as you will still need to do it with the DRO's.  Setup of the part is at least half the battle if not more.

Feel free to ask any questions you may have.

edit: Corrected my numbers to match the size of part you described.


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## RJSakowski (Aug 14, 2018)

BaronJ said:


> There is another simple way without using a "V" block.  But it requires that you are able to hold the work piece in a vise square to the drill table.  That method simply uses a rule or other thin flat metal plate balanced on top of the round material.  To do this you trap the rule between the work and the drill point and then move the work piece until the rule is level.  This method works best using the mill where you can get accurate fine movements.
> 
> It helps others to help you if you can post pictures of what you are trying to do.



I had thought of this as well. It is essentially the same as a method for find the center height for a lathe tool.

Rather than the drill point , I would suggest using a sharp point.  A drill has a flat web at its tip which would create some uncertainty.  I would use an old drill shank or dowel pin sharpened to a point.

I was uncertain as to the sensitivity so I ran the experiment.  Using the flat of my 1/2" parallel, and my 1-2-3 blocks and a height reference on either side, was able to find the center to within +/- .002" on a 3/4" round.  This was about the limit of my ability to see the level.  Without the height reference, about +/- .01".  In determining the center, I lifted the point, repositioned the round, and lowered the point.

This would be an excellent way to center a round on a drill press where you have no means of controlling or measuring movement.


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## BaronJ (Aug 14, 2018)

Hi RJ,

Thank you for your notes.  I do agree with you regarding using the drill,  I tend to forget that not all drills are ground four facet.  Since making my four facet drill grinder, I've made a point of going through all my drill sets and regrinding them.  The net result is that there isn't a flat worth worrying about on the drill tip.

I would recommend that people have or make a drill rod center for just this use, if hardened makes a handy punch.

For the benefit of those looking at the last picture I posted, there are two edge finders shown.  The one in the middle is my version of the Starret Edge/center finder, 1/2" shank and 4 mm probe.  The one on the right is a simple ball race of 1/2" diameter pushed onto a piece of 1/4" drill rod.  I do have a laser one that I made as well.

If anyone wants details just shout.


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