Match Drilling and Tapping Holes

[rgsparber]

When you must drill two or more holes to attach two parts together, the alignment of the first hole is easy. Getting the second hole to align can be difficult if you want close-fitting clearance holes. It only gets worse from there. The problem is solved by using the procedure illustrated in this article.

If you are interested, please see

https://rick.sparber.org/MatchDrillingTappingHoles.pdf


Your comments are welcome. All of us are smarter than any one of us.


Thanks,

Rick

[Paul Alciatore]

Rick, you present some interesting techniques there, but it seems like a lot of trouble to avoid just throwing the parts in a mill-drill and using the handwheel scale (or DRO) to simply locate the two holes the same distance apart. No need to even scribe the locations, although I probably would just as a reality check.

And as for the set screw trick, that would work but it would need to be replaced every time the bolt holding the two parts was loosened. Perhaps that will not ever happen, but there is an easier way to maintain alignment. Just drill a small hole through both of them while they are aligned and then install a spring pin. Two spring pins, one on each side of the bolt would maintain complete alignment. And drilling the two holes is a lot faster and easier than tapping the one. This is an age old technique that probably predates even the advent of the roll pins.

Oh, and the roll pins are a lot better way to align all of the assemblies. With them the holes and bolts holding the two pieces together can be done with more clearance so they would go faster. Pins for alignment and bolts to fasten them together. Each has it's own job.

[rgsparber]

Rick, you present some interesting techniques there, but it seems like a lot of trouble to avoid just throwing the parts in a mill-drill and using the handwheel scale (or DRO) to simply locate the two holes the same distance apart. No need to even scribe the locations, although I probably would just as a reality check.

And as for the set screw trick, that would work but it would need to be replaced every time the bolt holding the two parts was loosened. Perhaps that will not ever happen, but there is an easier way to maintain alignment. Just drill a small hole through both of them while they are aligned and then install a spring pin. Two spring pins, one on each side of the bolt would maintain complete alignment. And drilling the two holes is a lot faster and easier than tapping the one. This is an age old technique that probably predates even the advent of the roll pins.

Oh, and the roll pins are a lot better way to align all of the assemblies. With them the holes and bolts holding the two pieces together can be done with more clearance so they would go faster. Pins for alignment and bolts to fasten them together. Each has it's own job.

Paul,

My goal was to explain how to match drill. It is not a universally known procedure.

Although I do own a mill/drill, many people do not. It would be interesting to learn what the members of homemadetools.net have in their shops.

I admit that match drilling for screws might be overkill because you can always go with a larger clearance hole. But if I was going to install dowel pins, I am positive my skill is not good enough for the alignment needed by independently drilling and reaming the holes.

You may have noticed that I did take the assembly apart to take the picture and then reassembled it. Didn't have any trouble screwing in that setscrew the second time.

I did look through my parts bin for a short roll pin but had none. Going to the hardware store is not an option so I went with what I had - a short set screw. I wasn't going for alignment, I just didn't want the block to turn. There wasn't much material around that screw for flanking 1/8 inch holes. Remember, I had two set screws going horizontal through that block.

Rick

[DIYSwede]

-Thanks for yet another well-written document, Rick!

The neat magnet trick for hands-free horizontal alignment of your work with the vise jaws particularly caught my eyes, so simple and yet operative!
Finally a use for some Microwave Magnetron 3" donut magnets I've had in the shop for a coupla years.
Just gotta check them on the surface plate for flatness first.

"Dang- why haven't I ever thought of THAT!"

Cheers, Johan

[DIYer]

Thanks rgsparber! We've added your Match Drilling and Tapping Method to our Fastening category,
as well as to your builder page: rgsparber's Homemade Tools. Your receipt:

Match Drilling and Tapping Method by rgsparber

tags: tapping, drilling

[Philip Davies]

Thank you again, Rick, for a detailed description of the technique you use to drill and tap matching holes, which incorporated three or four techniques I hadn’t thought of. So often I’ve cursed my ineptness when holes do not align. In my ignorance, I thought it would be simple! I’ve never seen a “spud” before, the magnet is nice, I have a bench block, but didn’t know what it was used for. I like also that you use your brace to debut. I have a bench drill and a compound table, seldom installed. I am not familiar with your #drills nomenclature. Also, I have never thought of using spring pins. Lamentable, eh?

[Saltfever]

** This is offered for Philip.
The imperial system "generally" uses 3 basic sizes. On this chart you will notice fractional, number, and letter sizes. Number drills range in size from .0135" to .228". In addition note the letter drill "E" is also the same size as the fraction drill 1/4". I grew up with the system so it's no big deal and as a machinist I'm bilingual in both metric and imperial.

** Everyone else: Please no "system" bashing or politics. Yes, it's easy to divide by 10 but as a machinist I have never had a perfect integer dimension in either system! When a dimension is toleranced, its either 2, 3, or 4 decimal places regardless of measurement system. I don't care if its u or ".

Edit: . . . substituted letter drills, not fractional.

[mklotz]

... I am not familiar with your #drills nomenclature.

Philip, you need to go here...

https://www.brokenbolt.com/drill-tap-chart.php

and download and print a copy of Starrett's famous chart that collects all the screwy drill nomenclature systems into one page and relates them to the size needed for tapdrills for the more common inferial thread sizes.

This subject arises frequently and presents a ready opportunity for me to preach about nomenclature system design, to wit...




A sensible nomenclature system should satisfy the following criteria...

@ Should provide information about the thing being named. A # 43 or size 'K' drill carries no information about its most important feature, the size hole it will make. This requirement pretty much means that things be labeled by their size in the measurement system in use. A 6 x 1 metric screw tells you OD and pitch directly; a 6-40 inferial* screw makes you work to get the same information. Labeling wire with a number corresponding to how often it's been through the drawing dies may be useful on the wire mill floor but it should never be let loose in the real world where people only care about its diameter.

Not only are sheet metal gauge numbers meaningless, but there are a prolific number of standards to further muddy the waters. Perhaps the USA is finally waking up to the nonsense it's created. In a recent statement, the ASTM has said,

"The use of gauge number is discouraged as being an archaic term of limited usefulness not having general agreement on meaning." (Specification ASTM A480-10a)

@ Should have an intuitive progression. Smaller names should correlate with smaller entries in the progression; larger names with larger entries. A # 80 drill should be larger, not smaller, than a # 1. Similarly with wire and sheet metal.

@ Should be open-ended so that a new item larger or smaller than the original set can be sensibly named. This avoids the idiocy of things like 000-120 screws and AAAA batteries. What do you do if you want to add a drill slightly larger than a 'Z'? Again, labeling by actual size avoids most of these problems.

The makers of coin cell batteries seem to have heard my shouts; see here...

https://digilent.com/blog/quick-coin-battery-guide/