# Finding Center



## epj (May 23, 2015)

I manufacture sight pushers for auto pistols. Most of my designs require a series of holes drilled on the centerline of 1-1/2" bar stock. In reality, the same sizes of steel and aluminum are several thousandths different in width. When mating the two, the holes really need to be centered. 
Anyway, I have a Grizzly 1007 equipped with a DRO Pros glass scale 2 axis DRO. A friend who is a professional machinist helped me set it up. We tramed the table and the vise and found it to be durn near perfect. Out less the than .001 for 360*.  
When I use the DRO to find center I use an electronic edge finder mounted in a collet. When I drill a hole, I also use a collet. I'm still ending up 10-15 thousandths off center. 
Any idea what I'm doing wrong?


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## T Bredehoft (May 23, 2015)

Do you start the hole with a center drill?  They are very short and thus stiff, don't wander about before digging in, which a drill will do.


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## epj (May 23, 2015)

I've tried it both ways. I'm using very short stiff drill bits 3/8". Can't imagine they wander that much. If I use the center drill I have to use the chuck that came with the machine. I'm sure the collet is much more accurate. I need a better chuck, but in looking at what's available, even the high dollar domestic stuff shows several thousandths run out. I'm not building space ship parts, but sure would be nice to get within a couple of thou.


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## JimDawson (May 23, 2015)

+1 what Tom said.  In addition to that, have you checked your center finder to make sure it is accurate and repeatable?  Try finding the center from both sides of the part and see if the center is in the same place.  Also, check your DRO against a dial indicator and see if they agree.  You might also try a mechanical edge finder and see if the accuracy improves.

EDIT:  One thing that I do is to zero off of the fixed jaw of the vice, that way I can do multiple parts without having re-zero.


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## Tony Wells (May 23, 2015)

The way to achieve the best average results is to measure the stock you have at random, find the one nearest the mean average of all the variations, put it in the vise if that is what you are using, and ball off both sides. Zero the first side and then ball off the other side. Never mind what the actual reading is, just half it. You will be as close to center of all your stock as you can expect to be, unless you cut it up and segregate it into classes that fit your desired target zone. You still need to uses an edge finder of some sort to hit both sides, not just one. Let the edge finder measure the stock, thus eliminating any error it may have.


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## Billh50 (May 23, 2015)

I always use an indicator in the collet or chuck to find center. But if using an edge finder I always find edge on both sides and then figure center.


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## epj (May 23, 2015)

Yesterday, I suspected the DRO was giving an erroneous reading. The math didn't seem to add up. Today I placed a 1.5" parallel in the vise and ran the edge finder tom both sides. The DRO read 1.3000, just as it should have. The half function divided correctly, .650. I dunno, I can see (and accept) being off .002-.003, but not 10-15 thousandths. The material I'm using is 1-1/2X 3/8 cold finished 1018. The other parts are 1-1/2"X 1/2" extruded aluminum. Most of the time the steel is 1.496. The aluminum can be anywhere from 1.490-1.510. On average the aluminum is closer to 1.500 than the steel is. So long as I can keep my holes on center, everything works pretty well. If it's more than a couple or three thou off, lots of fitting is required to make the parts work. That's why I bought the DRO in the first place, once it became obvious that the hand wheel scales were not that accurate. Actually though, when we first installed the DRO, the Y axis hand wheel was dead on with the DRO.
I'll try again with the center drill. I'll have to use my drill chuck. Chinese origin, quality suspect. Can anyone recommend a good quality chuck that won't require a second mortgage. Any other suggestions are welcome!


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## JR49 (May 23, 2015)

Tony Wells said:


> put it in the vise if that is what you are using, and ball off both sides. Zero the first side and then ball off the other side.



Tony, thanks for all the great advise you have given us in the past, but, I have to chastise you here lol.  Please, for us beginners, what the ----- does "ball off " mean?  thanks, JR49


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## Tony Wells (May 23, 2015)

I wondered who would be the first to ask, JR. 

It's a slangish term for, originally, using the ball from a wiggler type edge finder. There are times when you want to avoid the very edge of a workpiece, and the straight stem of the cylindrical edge finder won't do that. It finds the outermost point only. I think the term "ball off" meant literally to run the work up to the wiggler until the ball runs off, thus indicating that the spindle centerline is half the ball diameter away from the point (not the line) that the ball contacts the work.


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## RJSakowski (May 23, 2015)

To accurately find the center of  a round feature, I use an edge finder.  The edge finder centers itself to the true spindle axis so runout on a chuck or collet is immaterial.  Set the y axis as close to center as you can. Zero the y readout.  Come in on the x axis until the edge finder jumps.  Zero the x axis.  Back off and find the edge again slooowly.  I usually come in at about 1/10,000th/sec.  Repeat until you have a consistent reading.  Rezero the x axis  and move to the other side of the piece at the same y and z coordinates.  come in to the piece with the edge finder as before.  Note the contact point and repeat as above.  Use your DRO half function to locate the x axis center.  Move the edge finder to some minus y position, same z position and x = 0.  Perform the same center finding operation for the y axis.  

While this may be good enough, I always go back and check the x and y centering again.  If your initial estimate of the y axis center was off, you definitely should recheck the centers.  This process gives me a reproducible center location to .0001".  This may seem like a lot of work but once you are used to it, it is very fast.   When I back off, I use my finger nail or a pencil to nudge the edge finder into running true.  That way, I only have to back off about a thousandth.  Coming back in is then a matter of 12 -15 seconds.  On using the edge finder, the surfaces of the edge finder and the edge you are finding should be clean.  Use a low to medium spindle speed and keep the speed constant throughout the process ( I generally use between 350 and 1000 rpm).

I would definitely use a center drill to start the hole.  You can also use a small end mill (less than the  diameter of your hole). It will cut a hole centered on your spindle axis without regard for any runout.  A drill will then follow the pilot hole and due to its flexibility, it will be true to the center.


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## epj (May 23, 2015)

That would work ok. I have a 1/8" end mill with a 3/8"'shank that I have a collet for.


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## chips&more (May 23, 2015)

The above advice is good. Don’t know your budget or quantity run? If you want a hole where it should be, then get an end mill with a drill point end and hold it in a collet and tighten all your gibs. And get a vise with both jaws that are moveable so it self centers…Good Luck, Dave.


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## Bill C. (May 23, 2015)

I never used a electronic edge finder so this may be already taken into account but what is the diameter of the probe?  Secondly if you have a center drill that fits in one of your collects use it.  I realize the smaller center drill bodies may be to small for most collect sets.  

Good luck tracing your problem.  Sometimes the obvious stares us in the face at least mine did.


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## tbell (May 24, 2015)

Use dead stick to find true center. Place jig borer style indicator in collet eye ball center. Set zero by sweeping edge lift indicator swing 180 move indicator down slowly sweep indicator second edge read difference half reading result dead center. Always use center drill ,drill will run off every time. Center drills come in fraction size, get 3/8 CD no need of chuck. Hope this helps Tom


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## Tony Wells (May 24, 2015)

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


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## Paul in OKC (May 24, 2015)

Only electronic edge finder I ever used was off. Haven't used one since. Try a 'regular' one.


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## epj (May 25, 2015)

Thanks, Guys. I have ordered a #4 center drill which has a 5/16 body. Also ordered a couple of  collets in small sizes to accommodate the small drills I use on part of the holes. I already have collets for the larger drills. Won't get a chance to get in the shop before Thursday. I'll see what happens.


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## Ulma Doctor (May 25, 2015)

just a little tip for center drills, don't run them into the work too deep-
you'll break the tip off- easily especially in 304 stainless (don't ask how i know that )

i always peck drill centerdrills and have lots of bacon grease/mineral oil mix slathered on
good luck


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## epj (May 25, 2015)

My machinist buddy taught me the peck drill trick. He says it helps the bit to center better. I don't drill anything harder than 1018.


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## kuchervano (May 27, 2015)

Comrade, why not spot drill and use a vee block?
Regardless of size variation barstock will always sit centered in vee.


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## Bill C. (May 27, 2015)

kuchervano said:


> Comrade, why not spot drill and use a vee block?
> Regardless of size variation barstock will always sit centered in vee.




That would be the best solution if I was doing it.


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## barrydc1 (May 27, 2015)

You should check youtube for methods of doing what you are doing.  Are you drilling the end of the round stock, or the length and trying to find the center?  I use and electronic edge finder all the time to do this and have never been off finding centers even with a bent probe, because you are just dividing two numbers measured in relation to each other.  You really need to see a YouTube video, as it's worth a thousand words per frame!


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## Jericho (May 27, 2015)

I hate to think the elephant in the room just might be a drill bit in general. Unless it is perfectly made and has a split point which is perfectly centered, I have always had a problem with drill bits walking off center especially on round stock( not what you're using noted). It would seem they have a mind of their own and will follow wherever the leading edge takes it. have you ever tried a cobalt drill bit for this work ? I mean the real deal not just a sniff of Cobalt.


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## barrydc1 (May 27, 2015)

I would never try to drill and accurate hole without using a spotting drill or center drill.  Maybe a screw machine cobalt on that 1018, but even then why not just center drill it?


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## RJSakowski (May 27, 2015)

kuchervano said:


> Comrade, why not spot drill and use a vee block?
> Regardless of size variation barstock will always sit centered in vee.


In one direction only!  I believe the OP is drilling the end of the bar.


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## redgrouse (May 27, 2015)

Hi epj, apologies if I am repeating anyone as I have not read every post but I assume you are holding the work in a vice ? If so and assuming you are making a small batch from the same piece of bar then just use a dial gauge [clock] to centralize your spindle over the work, clock each side of the vice jaws, fixed and moving then you are guaranteed to be dead centre. Zero your DRO and your all set. 

Keep in mind every time you load a new piece you need to maintain the same clamp force on the vice, if you REALLY want 100% accuracy you need to re-zero for each piece.

You must use a centre drill and a correctly ground drill, as for a drill chuck Albrecht  are excellent, maybe a little expensive but they will last a lifetime if you take care of them, mine are now 50 years plus and as good as the day I bought them.

Cheers John


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## Fabrickator (May 27, 2015)

Agreed.  Use a edge finder to find the center of a mounted V-Block.  Some V-blocks have a top "hoop" clamp so the material doesn't roll.  Just drop your bar stock in, use a center drill and then finish with your final size.  If I was doing more than 10, I would just build a quick jig with position stop(s).


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## jasnooks (May 27, 2015)

epj said:


> Most of my designs require a series of holes drilled on the centerline of 1-1/2" bar stock







epj said:


> The material I'm using is 1-1/2X 3/8 cold finished 1018. The other parts are 1-1/2"X 1/2" extruded aluminum.



I believe he's drilling multiple holes along the length of rectangular bar stock, based on these 2 statements.


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## epj (May 27, 2015)

Yes, it's rectangular bar stock. 1-1/2X3/8". Each piece gets 5 holes, four of which are on the center line. The fifth is off near one edge.


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## kingmt01 (May 27, 2015)

barrydc1 said:


> I use and electronic edge finder all the time to do this and have never been off finding centers even with a bent probe, because you are just dividing two numbers measured in relation to each other.


Your edge finder must spin then. If it is a stationary edge finder a bent probe wouldn't work.


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## ustawuz (May 27, 2015)

epj said:


> I manufacture sight pushers for auto pistols. Most of my designs require a series of holes drilled on the centerline of 1-1/2" bar stock. In reality, the same sizes of steel and aluminum are several thousandths different in width. When mating the two, the holes really need to be centered.
> Anyway, I have a Grizzly 1007 equipped with a DRO Pros glass scale 2 axis DRO. A friend who is a professional machinist helped me set it up. We tramed the table and the vise and found it to be durn near perfect. Out less the than .001 for 360*.
> When I use the DRO to find center I use an electronic edge finder mounted in a collet. When I drill a hole, I also use a collet. I'm still ending up 10-15 thousandths off center.
> Any idea what I'm doing wrong?


 
I want to talk to you.  I am a gunsmith and most of the sight pushers are not what I call "good or universal".  I have spent well over $1000.00 on pushers and I still don't like what I have.  Please text me at 336-325-6938.  Thanks, Phil (Ustawuz)


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## Frank W. (May 27, 2015)

The 10 -15 thou off sounds like it could be a backlash problem if your wiggler is being used alternately on each side of the piece.  You could try wiggling one side and then instead of going to the other side wiggle to to a straight edge clamped against the other side.  You would be moving the work in the same direction each time and than when you halve the readings take care to also move the work in the same direction.
Cheers
Frank W.


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## kingmt01 (May 27, 2015)

The DRO should be mounted so that it measures the table poison & not the lead screw. Back lash can't affect this unless he has lash in the scales. I have one scale I need to fix that has lash in it so this is posable.

It doesn't sound like he has a wiggle style center finder. I'd like to see a picture of it myself so we have a better understanding.


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## catskinner (May 27, 2015)

Here is a tool I made over 40 years ago to mark the centers of shotgun ribs for putting in beads. It would only work up to 1/2" but you can make one large enough to accommodate whatever stock you need to find the center of. As you can see the pins on the outside are roll pins and the center punch is stepped and held in with another roll pin.


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## JimDawson (May 28, 2015)

catskinner said:


> Here is a tool I made over 40 years ago to mark the centers of shotgun ribs for putting in beads. It would only work up to 1/2" but you can make one large enough to accommodate whatever stock you need to find the center of. As you can see the pins on the outside are roll pins and the center punch is stepped and held in with another roll pin.



That is very cool.  I never thought of doing that, and have never seen one before.


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## catskinner (May 28, 2015)

Stricktly old school, lol. just have to be precise when you measure out for the pin placement.


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## Tony Wells (May 28, 2015)

Woodworkers use a jig like that to locate dowels on edge. Very effective.


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## epj (May 28, 2015)

That's a pretty nifty looking tool for marking the shotgun ribs.


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## catskinner (May 28, 2015)

epj said:


> That's a pretty nifty looking tool for marking the shotgun ribs.



Thanks, if you are making a lot of those sight pushers you might want to make one about 2" between the pins I think it would save you a lot of time.


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## epj (May 28, 2015)

I have a jig that locates the holes for the production pieces that are done on a drill press.  I need to be able to produce a good accurate jig on the mill for when the jigs wear out or I want to change a dimension.


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## KMoffett (May 30, 2015)

On edge finder accuracy: 




Ken


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## epj (May 30, 2015)

Good video. I seem to have solved most of my issues. The center drill probably was the big thing. I made a couple of tools on the mill using collets for the edge finder and the drill bits. Lots of collet changing. Way too much, in fact. But the results were there. 
I also discovered that my new pricey vise had gotten out of square. Almost .100 over six inches! Took a while to get it back lined up and clamped down more securily. The slots in my table are 5/8, and the keys that came with the vise are .687. So the vise has no keys at the moment. 
Anyway, thanks to all for your assistance. I'll be back soon with more problems, no doubt.


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