Accuracy Of Hole Layout , Center Punch, Dividing Head

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
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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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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
 
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
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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.
 
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
 
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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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.
Click to expand...

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
 
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
 
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
 
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
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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.
 
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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