# Accuracy Of Hole Layout , Center Punch, Dividing Head



## visenfile (Feb 13, 2016)

If a careful layout is done for  hole positions and  accurate center punches performed, followed with center drills, can the results be as accurate as using a dividing head? If a template is available can drill bushings match the dividing head accuracy?  Should a center punch point roughly match the drill tip angle? Thanks


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## Wreck™Wreck (Feb 13, 2016)

visenfile said:


> If a careful layout is done for  hole positions and  accurate center punches performed, followed with center drills, can the results be as accurate as using a dividing head? If a template is available can drill bushings match the dividing head accuracy?  Should a center punch point roughly match the drill tip angle? Thanks


Yes, this is what jig bore machines are for. Accuratley bore holes in the jig, insert drill bushings and have at it.


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## brino (Feb 13, 2016)

one thing I found that helped the accuracy of my centre punch marks is a tool like this:
http://www.leevalley.com/en/wood/page.aspx?p=45502&cat=1,180,42311
I was surprised by how well you can see the scratched marks thru the optical post, it magnifies and supplies enough room light to align very well.
It's a very useful tool.

-brino


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## RJSakowski (Feb 13, 2016)

Any hole position located by marking, aligning a center punch is going to be limited by one's visual acuity.  When I had better vision, I liked to think that I could reliably locate holes to +/- .02".  anything better than that and I was fooling myself.  There will be an error in scribing the layout lines, an error in centering the punch on crossed layout lines,  a possible drift of the punch as it is struck, and possible wander of the center drill or drill bit.  In a former business endeavor, I drilled or punched many thousands of holes in 16 ga. aluminum using that method.  

A well laid out fixture with drill guides should get you within a few thousandths but is only as good as the fixture, as Wreck Wreck said.  A dividing head will get you excellent angular accuracy if you are laying out a bolt circle but the can be an error in the circle radius or the location of the circle center.

For accurate layout, I would calculate the x and y coordinates of each hole and use the mill to make precise moves.  Or, if you have a DRO with a bolt circle routine, use that.

If  center punching the old fashioned way, I use a custom center punch with a sharp tip and about a 30º included angle.  This gives me the best possible visual indication of being on the cross scribe marks. After marking the holes with that punch, I follow with a conventional center punch to deepen the punch mark.  If I am using a Roper Whitney hole punch , I would just use the first punch as it is sufficient to locate the hole punch


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## derf (Feb 14, 2016)

That's actually called a "prick punch" It is used to establish the initial dimple accurately, then followed by a "center punch" to guide the drill tip.


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## TOOLMASTER (Feb 14, 2016)

x2




derf said:


> That's actually called a "prick punch" It is used to establish the initial dimple accurately, then followed by a "center punch" to guide the drill tip.


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## stupoty (Feb 14, 2016)

I use a prick punch first, i can get quite good accuracy with a bit of time spent doing the layout.

I had to make a scribe for my height gauge, i think the angle I chose for the tool steel scriber is a bit wrong as i somtimes have some issues with one side being more angles than the other which can push you off a few 0.001 if your not super careful.

Stuart


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## David S (Feb 14, 2016)

If you follow the "building prototypes.." series by Dan Gelbart, he doesn't find the centre of scribed line optically but rather by feel.  He demonstrates scribing two lines at right angles and then sliding the fine punch along one of the scribed lines until it locks into the intersection.  Then tap the punch.

David


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## T Bredehoft (Feb 14, 2016)

David S said:


> He demonstrates scribing two lines at right angles and then sliding the fine punch along one of the scribed lines until it locks into the intersection.



That's how I was taught, back in the 20th century.  It was suggested that with  care, .005 accuracy was possible, but not to count on it. That instruction was followed by suggesting that a Bridgeport with DRO was far more accurate.


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## planeflyer21 (Feb 14, 2016)

T Bredehoft said:


> That's how I was taught, back in the 20th century.  It was suggested that with  care, .005 accuracy was possible, but not to count on it. That instruction was followed by suggesting that a Bridgeport with DRO was far more accurate.



I suppose that sounds better than "Back in the 1900s..."


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## Uglydog (Feb 14, 2016)

brino said:


> one thing I found that helped the accuracy of my centre punch marks is a tool like this:
> http://www.leevalley.com/en/wood/page.aspx?p=45502&cat=1,180,42311



Brino, that's a gorgeous item! I picked up an Opti Center at a flea market for a $1 years ago. Works well. Not nearly as pretty as this one!
And yes many uses. And like RJSakowski, as good as my eyes can see. Occasionally I wish I had an optical comparator. 

Planeflyer21, unquestionably easier to be accurate and precise. ... I've been resisting DRO. I recall Lathe 101 at tech school, I'd been working with lathes in the home shop, we were about 6 weeks into class, when I turned to the guy at the lathe next to mine (he wasn't turning at the time) and observed in sudden complete and honest surprise that the lathe had DRO. He looked at me as if I had three eyes. 

Daryl
MN


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## stupoty (Feb 14, 2016)

Just popped to mind, tublecain on youtube has a couple of videos where he lays out holes using a selection of methods and compares the accuracy.

part 1





part 2





Stuart


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## John Hasler (Feb 14, 2016)

David S said:


> If you follow the "building prototypes.." series by Dan Gelbart, he doesn't find the centre of scribed line optically but rather by feel.  He demonstrates scribing two lines at right angles and then sliding the fine punch along one of the scribed lines until it locks into the intersection.  Then tap the punch.
> 
> David


That's what I do, but I still want to be able to see the intersection well enough to be sure I really am on it with the prick punch.


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## stupoty (Feb 14, 2016)

I use a small 40x magnifier to look at the punch marks after I've punched them to check if their in position and travel them around if their a bit off.  Has worked quite well for things that needed a reasonable level of accuracy.  The optical punches always look quite tempting.

Stuart


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## visenfile (Feb 14, 2016)

Gentleman, thank you for this information.  The prospect of likely .020" accuracy scares a noob like me,  .005" would be great but likely not achievable at first.  I had been toying with the idea of drilling an axle bolt hole pattern  in order to use a set of existing wheels on another vehicle.   I have seen crude looking attempts on you tube where eyeball prick punches are used free hand , wobble bolts for minor hole spacing changes (not applicable), transfer punches are placed in templates, and drill jigs with bushings for $100,  but without my required pattern. I have also watched Keith Fenner you tube several times where he modified an axle. For instruction he started with a dividing head on a lathe, sanity checked with what he called a redneck bolt hole template, and finally partially showed how to layout the 5 holes with Machinery's Handbook derived (?trig) factors.

I am considering practicing on an expendable spare cast iron hub.  The fear (besides not having the wheel  even fit onto the studs) is TIR problems, assuming strength is retained.  Seems like auto lore specifies a max out of round reading of ? .050"? taken off the bare rim bead surface.  Is that the proof of pudding for a primitive attempt? Thanks for your help.

Edit,  BTW stupoty, I think I know what you mean by "traveling them around." Please give detail for benefit of noobs here.


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## stupoty (Feb 14, 2016)

visenfile said:


> Gentleman, thank you for this information.  The prospect of likely .020" accuracy scares a noob like me,  .005" would be great but likely not achievable at first.  I had been toying with the idea of drilling an axle bolt hole pattern  in order to use a set of existing wheels on another vehicle.   I have seen crude looking attempts on you tube where eyeball prick punches are used free hand , wobble bolts for minor hole spacing changes (not applicable), transfer punches are placed in templates, and drill jigs with bushings for $100,  but without my required pattern. I have also watched Keith Fenner you tube several times where he modified an axle. For instruction he started with a dividing head on a lathe, sanity checked with what he called a redneck bolt hole template, and finally partially showed how to layout the 5 holes with Machinery's Handbook derived (?trig) factors.
> 
> I am considering practicing on an expendable spare cast iron hub.  The fear (besides not having the wheel  even fit onto the studs) is TIR problems, assuming strength is retained.  Seems like auto lore specifies a max out of round reading of ? .050"? taken off the bare rim bead surface.  Is that the proof of pudding for a primitive attempt? Thanks for your help.
> 
> Edit,  BTW stupoty, I think I know what you mean by "traveling them around." Please give detail for benefit of noobs here.



I examine the small prick punch hole (easier to see than a big punch hole/dent) and if it's not on the scribe line I angle the punch and tap it in the direction I want then lightly vertical punch it a bit to make it a bit deeper then re examine.  Takes a bit of practice (I'm no way perfect at it) but can be very handy and so long as your going to drill out all the messy looking bits it should be ok.

If you have a bolt pattern on a wheel you may be able to use transfer punches to mark it out but you would still have to align the rim to the mount so maybe that's not so good. 

If you can fit the part on a lathe you could lightly scribe a circle in the part to be drilled first. That would give you a good circle which you could then use with transfer punches to line it up.

Might be worth posting a couple of pics of the parts you want to match up if it's already apart.  

As it sounds like a mission critical component it's good to be light with any scribing so you could buff them out latter to reduce stress risers. (not including the areas that get drilled out)  that's also where a rotory table or DRO "pitch circle diameter" feature might be advantageous to reduce layout scribing 

I just had a quick google about runout on rims and I want to go jack my car up and investigate it now 

Stuart


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## stupoty (Feb 14, 2016)

Side thought, can you get a rim spacer to use as a template maybe ? the holes might not be that accurate though as their probably just clearance holes.  Some one more versed on them might know better though.

Stuart


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## Uglydog (Feb 14, 2016)

Has anyone here ever used *toolmakers buttons* or *discs* to layout holes?
Please note "used" them vs read about them or saw a video?
If so, I've only done the latter, and am curious about your perspective and experience vs other methods. 

Daryl
MN


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## RJSakowski (Feb 14, 2016)

stupoty said:


> I examine the small prick punch hole (easier to see than a big punch hole/dent) and if it's not on the scribe line I angle the punch and tap it in the direction I want then lightly vertical punch it a bit to make it a bit deeper then re examine.  Takes a bit of practice (I'm no way perfect at it) but can be very handy and so long as your going to drill out all the messy looking bits it should be ok.
> Stuart


  I use this practice as well.  If your original punch missed the mark by too great a distance, it also works to punch a second mark in the direction you wish to move the hole, overshooting slightly.  As the second hole is punched, the thin wall next to the first punch mark will deform and slide the punch over slightly.  After punching, confirm the the position is correct and strike a second time to deepen the punch mark.  Follow with the center punch.  As 
Stu said, it takes practice but after a few , you will be comfortable with the process.


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## Dinosaur Engineer (Feb 14, 2016)

If you have a surface plate and height gauge it's possible to layout the holes in a square box instead of a circle. Then with a plate with the required hole size ( reamed preferably ) clamped over the "box" it's possible to adjust the hole plate so that the "box" lines can be made ( and seen) equal around the hole. The hole can then be drilled through the hole plate. The underside of the hole plate should have no chamfers or burrs and the hole should be "clean all the way through. Ideally the hole plate should be hardened and ground on the under surface. If the desired hole is bigger than the hole , the plate may be used as a"spotting" plate and removed for drilling the correct hole size. With this method placing holes in the order of .003" is possible. This method is commonly called " boxing-in holes". Using toolmaker's buttons or discs is a bit more accurate but all of these methods is more accurate than center punching the hole positions. Most pre DRO toolmakers had a selection of hardened "boxing hole plates" and discs.


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## visenfile (Feb 14, 2016)

Great information.  Please keep it coming!

For auto noobs  I should point out that just successful fitting of the new wheel studs through the wheel clearance holes is not so significant.  What matters is that the angled wheel nuts nestle and torque correctly.  You can easily see the seating area of these nuts if you look at the wheel. Any registration problems will by magnified be difficulty seating and torquing and can be dangerous due to work hardening and breaking of the studs.  This is widely known and verboten.  So I guess an attempt at drilling such holes could be evaluated with some blue marker on the wheel counter sunk areas and nuts, not to mention "feel" as the nuts are drawn up, and they must be perfect, no?

I have tried movement of punch marks and it is a good tool even though sometimes the dimple can be distorted and confuse the drill tip of where to enter.
A final question I forgot earlier.  When looking at dimensions of drill bushings I did not see clearance call outs for the drill dia and the bushing ID.  Isn't this one of the main values of the hardened bushing, i.e., keeping the drill from wandering?  Thanks


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## stupoty (Feb 14, 2016)

Uglydog said:


> Has anyone here ever used *toolmakers buttons* or *discs* to layout holes?
> Please note "used" them vs read about them or saw a video?
> If so, I've only done the latter, and am curious about your perspective and experience vs other methods.
> 
> ...



I've been trying to make myself use them recently, I found them really handy, I wanted to make two holes in two parts with very good relative location. I used gauge block stacks under the horizontal and vertical side to set them.  I think with more practice they could be a bit quicker to use as well. 

I've got some that I have made, I actually made them from a part that went wrong  a better surface finish would make them better.













IMG_2338_sml



__ stupoty
__ Feb 14, 2016



						Button Attached to work piece whilst it's being indicated.
					
















IMG_2339_sml



__ stupoty
__ Feb 14, 2016



						Quick spin with it still attached for a visual look.
					




Stuart


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## stupoty (Feb 14, 2016)

Dinosaur Engineer said:


> If you have a surface plate and height gauge it's possible to layout the holes in a square box instead of a circle. Then with a plate with the required hole size ( reamed preferably ) clamped over the "box" it's possible to adjust the hole plate so that the "box" lines can be made ( and seen) equal around the hole. The hole can then be drilled through the hole plate. The underside of the hole plate should have no chamfers or burrs and the hole should be "clean all the way through. Ideally the hole plate should be hardened and ground on the under surface. If the desired hole is bigger than the hole , the plate may be used as a"spotting" plate and removed for drilling the correct hole size. With this method placing holes in the order of .003" is possible. This method is commonly called " boxing-in holes". Using toolmaker's buttons or discs is a bit more accurate but all of these methods is more accurate than center punching the hole positions. Most pre DRO toolmakers had a selection of hardened "boxing hole plates" and discs.



Boxing in the holes, interesting sounding technique I think I will do some googling and reading.

Stuart


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