Keeping drilled holes aligned

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John Hasler
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Re: Keeping drilled holes aligned

Post by John Hasler » Tue Jan 14, 2020 11:39 am

Harold writes:
A simple boring bar for small holes can be made easily from what's left of a small diameter drill.

Or even a large one. The first thing I ever bored was an MT3 taper socket done with a modified
1/2" drill bit. Amazingly, the taper actually turned out to be usable.

John Hasler
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Re: Keeping drilled holes aligned

Post by John Hasler » Tue Jan 14, 2020 11:41 am

I center punch when drilling with my old Craftsman drill press, which has no dials anyway. I don't expect precision from it, though.

whateg0
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Re: Keeping drilled holes aligned

Post by whateg0 » Tue Jan 14, 2020 12:34 pm

John, I think there's a difference between center punching when using a hand drill or drill press for TLAR holes or holes that have 1/16" of clearance and holes that "need" to be located accurately. I wouldn't dare try to drill a hole in the "right place" on the side of my trailer with my hand drill without a center punch. In fact, if it's for lights or something similar, I use a transfer punch to get the hole pretty close. OTOH, I wouldn't dream of using a center punch for making a hole for an alignment dowel in a part. Completely different applications.

Dave

John Hasler
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Re: Keeping drilled holes aligned

Post by John Hasler » Tue Jan 14, 2020 12:49 pm

whateg0 wrote:
Tue Jan 14, 2020 12:34 pm
John, I think there's a difference between center punching when using a hand drill or drill press for TLAR holes or holes that have 1/16" of clearance and holes that "need" to be located accurately. I wouldn't dare try to drill a hole in the "right place" on the side of my trailer with my hand drill without a center punch. In fact, if it's for lights or something similar, I use a transfer punch to get the hole pretty close. OTOH, I wouldn't dream of using a center punch for making a hole for an alignment dowel in a part. Completely different applications.

Dave
I thought that was clear. I center punch when using the drill press because I actually get more accurate holes that way than I would using the drill press and not punching. I never center punch when drilling on the mill [1]: it's counterproductive.

[1] Except for prick-punching as part of layout, but the layout is just an anti-stupidity measure.

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Bill Shields
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Re: Keeping drilled holes aligned

Post by Bill Shields » Tue Jan 14, 2020 1:32 pm

AH...i know about them (anti-stupidity measures)....

I have a list of them written down somewhere.

...would be nice if I could remember where I put the list.

MAYBE...it is with my wife's mobile telephone (which she loses 15 x a day...)
Too many things going on to bother listing them.

Mr Ron
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Re: Keeping drilled holes aligned

Post by Mr Ron » Tue Jan 14, 2020 2:02 pm

Thank you all for your responses. I ordered a carbide 3/16" dia spotting drill, 90°, 1/2" flute length by Republic. Here is an example of what I am doing. The parts will be cut apart after all machining is done.
Lower element top knuckle.jpg
Mr.Ron from South Mississippi

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Bill Shields
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Re: Keeping drilled holes aligned

Post by Bill Shields » Tue Jan 14, 2020 2:09 pm

if you are doing this in a mill, you can probably use just a center drill to spot the holes...anything HSS you have laying around your lathe will be just fine (#1 or #2)
Too many things going on to bother listing them.

Harold_V
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Re: Keeping drilled holes aligned

Post by Harold_V » Tue Jan 14, 2020 4:15 pm

John Hasler wrote:
Tue Jan 14, 2020 11:41 am
I center punch when drilling with my old Craftsman drill press, which has no dials anyway. I don't expect precision from it, though.
I don't have an issue with punching for random drilling, where the drill starts where the punch is applied. A good example of that is when drilling with a drill motor. It's difficult to start a drill (at the desired location) without the resulting dimple of a punch.

That said, punching a location when it is to be achieved on a machine with screws or a DRO is wasted effort, and can prove to be a detriment. We've come a long way since the day of the blacksmith. I see little need to step back to that time unless that's one's objective.

It's hard to describe the joy one receives from drilling a series of holes in one part, then a like pattern in another part, and have them fit without problems, especially when the holes are drilled nominal size, so there's little room for error. If one uses their machine tools properly, that's not hard to do. Introduce center punches and the chance of success dwindles tremendously unless oversized holes are provided. My pride doesn't allow me to work that way.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

johnfreese
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Re: Keeping drilled holes aligned

Post by johnfreese » Tue Jan 14, 2020 5:52 pm

I would mount my drill in my ER16 straight shank holder. I would hold the drill as short as possible and still have enough stickout to get through the metal. A split point or 4 facet grind will not tend to walk off location. Using a carbide drill with this kind of setup would be like wearing a belt and suspenders.

pete
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Re:Center Punching & Marking Out

Post by pete » Tue Jan 14, 2020 9:40 pm

I hope Ron doesn't mind some further OT information.
In one of my T.D. Walshaw books (Simple Workshop Devices) he goes into a bit of detail about hand layouts, center punching, coordinate layouts and machining and an accuracy test that was performed at a technical collage in the UK I'm guessing around the 1960's - 1970's since the book was first published in 1983. The students involved in that test already had a few years of professional training and experience and were listed as all being apprentice tool makers. And they were all being supervised by a very skilled instructor. Keep in mind the average equipment available at that time period and no mention of anything as sophisticated as using dro's was brought up. I'd guess what would have been used was at least good British made industrial level equipment, (a drill press with an X,Y slide?) and going by the hand dials. They were asked to set out, drill and ream 6 holes on a pitch circle. But no hole sizes or the PCD size was specified by Walshaw. But 4 would use normal marking out with dividers, scales etc. 4 to use the coordinate marking out method. And the last 4 to use a compound table to mark out, drill and ream. Each one did his own work piece and the results measured "using very sophisticated measuring equipment." Unfortunately what was used to do that measuring wasn't detailed either. Gauge blocks maybe? But I'll directly quote the test numbers from my book.

Normal Marking out- Average Error-.0112"- Maximum Error-.026" -Minimum Error.003"
Coordinate Marking Out- Average Error-.0080"-Maximum Error-.012"- Minimum Error-.006"
Coordinate Drilling and Reaming-Average Error-.0033"-Maximum Error-.0049"* Minimum Error-.0008"
That's a total of 24 holes and measurements for 4 people using each method, so I'd say the averages, maximums & minimums are enough to have some reasonable meaning.

*That one Maximum test number for the Coordinate Drilling and Reaming was mentioned as being a single "rogue" number and not typical of the rest.

Walshaw summarizes those test numbers by saying "By model engineering standards these were skilled practitioners doing similar work all day long, so it may be assumed that the amateur will do worse rather than better." Then goes on to say "Most model engineers have the equipment necessary to reach the standard of the third group and many could do better since the machine used was well past it's prime." Today depending on what you might have available such as one of those cheap optical center punches you might do a bit better, those still depend on just how accurate you can obtain the scribed cross hair location, accuracy of setting your scriber point elevations, or the built in accuracy of even a digital height gauge. And if you check the allowable + - numbers on any of those you've got to spend some pretty decent money to have any confidence with there accuracy. You could cheat those repeatable accuracy issues by pre-setting any height gauge with decent gauge blocks. That's obviously a slow method most wouldn't bother with unless the part absolutely required it.

Fwiw and my opinion only, that center punching is helpful when drilling with a hand drill so the drill point isn't skating around and for loose tolerance locations as Harold has already said. If the parts going in a machine with an X,Y slide you can half way trust? Then as those numbers show that center punching is a real detriment to accuracy. If it had to be fairly accurate but won't fit on any table slide you've got, I'd probably machine a one time use soft drill bushing and jury rig something to find my location point as best I could. I think I've managed to gather up some fairly accurate equipment over the years including those gauge blocks, and will still do a layout on complex parts to keep the mental midget mistakes to a minimum. :-) But if it needs better than maybe .020" for location then using those coordinates and not center punching at all is I think most would agree going to be superior than any other way. Tool maker buttons are ancient technology today and very slow to use, with them, a half decent and well aligned mill, a good dti and mike you could get pretty close to jig boring accuracy if you really needed it. How exact is the exact you want?

Harold_V
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Re: Keeping drilled holes aligned

Post by Harold_V » Wed Jan 15, 2020 2:31 am

In response to the ability to locate holes consistently, with precision, for the most part, hole locations were held to ±.005" on the electronic chassis that used to be made when the Sergeant Missile was in the development stage. All holes were drilled on drop spindle mills (think BP, although all of ours were either Cincinnatti or Gorton). Holding the required tolerances was not an issue, so long as the proper dial settings were used. It stands to reason that scrap was made occasionally by missed dial settings, however.

We were not afforded the luxury of DRO's at that time. They were yet to be introduced to the shop.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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SteveM
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Re: Keeping drilled holes aligned

Post by SteveM » Wed Jan 15, 2020 11:58 am

Here's the videos where Tubalcain tries different methods for locating and drilling holes.

https://www.youtube.com/watch?v=chVFrmPcDsA
https://www.youtube.com/watch?v=qGj90DasSxs

Go to timestamp 28:16 in the second video to see the results

Spoiler alert - the Bridgeport DRO was the most accurate.

Steve

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