Drilling for .1260" hole

[Kuma601]

In my usual routine I drill .1250" (Those 1/8" drill bits vary from .1247" to .1249") then ream with a .1260" to fit pin stock in my assemblies. On some tasks this becomes tedious so I was debating using a 3.20mm instead. This way I do the hole in one rather than 2 steps. Provided that drill bit is sized accurately.

Thoughts? Advice?

 

[Firebrick43]

drills rarely drill on size. If your fitting dowel pins a reamer is necessary.

 

[larry_g]

It would help if you gave the fit required, the pin size, the materials, if this is a press or slip fit Gotta have all the specs if you expect us to engineer a solution.

lg
no neat sig line

 

[goldtang]

can you use Loctite

 

[RoninB4]

In my usual routine I drill .1250" (Those 1/8" drill bits vary from .1247" to .1249") then ream with a .1260" to fit pin stock in my assemblies. On some tasks this becomes tedious so I was debating using a 3.20mm instead. This way I do the hole in one rather than 2 steps. Provided that drill bit is sized accurately.

Thoughts? Advice?

-It's not about the drill being sized "accurately" it's about how accurately it's been sharpened. Never seen a drill that wasn't sized correctly (within a few .0001's anyway) but how it was sharpened made a huge difference. Just being off center (drill axis) .0005 throws the hole off by .001 so the hole will now be .126 or larger. Most home owners buy cheaply made drills that I wouldn't expect to make a hole on size.

Doing 2 steps is tedious? It can be but what's the priority here fitment or time spent? You haven't stated the fitment required or whether you're using a ground dowel pin or just plain 1/8" round stock. Will a roll pin/spring pin work for your assembly? You also haven't mentioned whether you're using a machine or hand drill for this, it make a difference.

Don't take this personal but if you have any aspirations to become a better machinist/fabricator/manufacturer of a better quality product you're already hitting a stumbling block. Searching for ways to reduce time/cost is a good thing but you may have picked the wrong road to go down. I don't know what your assembly is but 2 step hole making is nothing. Creating a hole that's on size AND location (without WEDM) can be 4 steps. If it's steel that needs to be heat treated then it's 5 steps.

There are several ways to reduce/eliminate time but hoping to get correct size/location in one shot drilling usually isn't one of them. My post is not to be a jerk that criticizes what your methods are, I'm trying to give you the reality of metalworking and hope there's something you'll find useful for what you're doing. Your question shows that you haven't worked in a machine shop where someone helped you with the basics. My critique is not with you but with the people that didn't help you. Ask questions, everybody starts at the beginning not knowing things.

 

[NORTON'S SHOP]

In my usual routine I drill .1250" (Those 1/8" drill bits vary from .1247" to .1249") then ream with a .1260" to fit pin stock in my assemblies. On some tasks this becomes tedious so I was debating using a 3.20mm instead. This way I do the hole in one rather than 2 steps. Provided that drill bit is sized accurately.

Thoughts? Advice?

If you're able to drill a 1/8" hole and ream it to .126 accurately, my hat is off to you. You're a super machinist.

 

[Kuma601]

Thanks @RoninB4 for stating it straight. Agreed that for me to improve rather than saving a step I should be improving the process by not being lazy for achieving as best fit I can. This results in a higher and more consistent result. These are more of an index locator pin in these builds.

These are done on the drill press. At the time this 14" Jet drill press was bought a buddy came over and he tuned it. The arbor and chuck were replaced so at the time he measured it his dial gauge was about .001" roughly give take that .0005". In his opinion he said I got a good one. The bits are a variety of Cleavland, Cle-line and other USA sourced cobalt from Grainger, Travers or MSC. Those bits run slightly undersized which is fine. The pin stock is 416 and heat treated, these vary from .1246"-.1252" when measured. The hole is reamed to match the particular pin the goes into that build.

Granted my "tedious" isn't really when the hole fits right so my laziness in stating it that way. I'll mark the hole with a spotting drill then do the rest of the run followed by the ream.

Rather than a generic size I'll update the reamers for the stock on hand so that it fits well.

 

[Spud McGee]

If you need it accurately sized and placed down to a tenthousandth of an inch and you can do that in 2 steps, consider yourself lucky.

Usually, I spot drill, then drill undersized, maybe drill with another larger bit, and finally ream to size. Bonus points if you add in a step to chamfer.

2 things about drills. They walk around, and they cut oversized. If you are not spot drilling, you may be putting a lot of effort into very precisely sized holes, but they are not precisely where you wanted them to be, because the drill flexed and walked on you.



One thing you may look at are center cutting endmills. They are somewhere in between drilling a hole with a harbor freight drill and making 5 separate operations. They will get you closer to your wanted dimension than the drill alone, which could be close enough.

 

[Etchase]

A 14 jet with 0.0005 runout including the bit is extraordinary. What Chuck did you put in it?

 

[Firebrick43]

If you need it accurately sized and placed down to a tenthousandth of an inch and you can do that in 2 steps, consider yourself lucky.

Usually, I spot drill, then drill undersized, maybe drill with another larger bit, and finally ream to size. Bonus points if you add in a step to chamfer.

2 things about drills. They walk around, and they cut oversized. If you are not spot drilling, you may be putting a lot of effort into very precisely sized holes, but they are not precisely where you wanted them to be, because the drill flexed and walked on you.

One thing you may look at are center cutting endmills. They are somewhere in between drilling a hole with a harbor freight drill and making 5 separate operations. They will get you closer to your wanted dimension than the drill alone, which could be close enough.

End mills, even center cutting ones are frowned upon being used in a drill press due to the lack of ridgidity and end mills shouldn’t be used in a drill chuck.

180 carbide drills with thru coolant in very ridged milling machines is all I used for years at cat. And they still weren’t good enough to eliminate the use of a reamer

 

[MBfreak]

Being "inch" weak, 1 calculate the 0,1260" measurement to the equivalent of 3,2004mm. Ie you are down to fractions of a µm .
Which I believe no drill, mill or the absolute majority of reamers is impossible to produce.
Some kind of elecroforese, as used in making very expensive parts for very expensive watches may succeed,
Then comes the conondrum of actually measure what has been done.
I worked in a instrumentation workshop where we had a Swiss guy with Master Watchmaker degree from Rolex.
"I can do everything to 0,01 mm but below that and with accurcy I have to make ten pieces , measure , and throw away 9. "

Ola

 

[Kuma601]

A 14 jet with 0.0005 runout including the bit is extraordinary. What Chuck did you put in it?

Used an Albrecht arbor with a Jacobs keyless. It doesn't have a .0005" runout. He could not obtain a reading finer than the .001" on his gauge as it slightly moved but not sufficiently enough for him to determine the exact amount finer than the .001" reading. He commented the press will do what I need and anything more precise would require a mill. I have buddies with the same model Jet and theirs seem like a different machine without the tuning.

 

[MushCreek]

In my experience, .001 isn't enough stock for reaming. I usually figure .010 to .015, depending on the hole size. Ideally, a reamer should be in a floating holder, although a rigidly held reamer is usually OK if there's not too much run-out. There are tricks to make a reamer cut slightly bigger or smaller. If I have to hold a really close tolerance, I lap the hole after reaming a bit undersize.

 

[PCustoms]

The pin stock is 416 and heat treated, these vary from .1246"-.1252" when measured. The hole is reamed to match the particular pin the goes into that build.

Why is your pin stock varying so much?

Before you worry about the hole diameter, I would get this under control. Typically pins are much tighter, and go from nominal size UP with a small tolerance to achieve the press fit.

When you press, retaining compound can help if you have variation.

How are you accurately controlling location of your pins? IMHO having a pin pressed into a perfect hole is useless if the hole is 0.05" out of position.

 

[NORTON'S SHOP]

A 14 jet with 0.0005 runout including the bit is extraordinary. What Chuck did you put in it?

Any drill press that has 5/10th's runout is extraordinary.

 

[gfd_703]

Wobble Baby starts playing on the radio when ever I use my jet drill press.

 

[Kuma601]

Why is your pin stock varying so much?

Before you worry about the hole diameter, I would get this under control. Typically pins are much tighter, and go from nominal size UP with a small tolerance to achieve the press fit.

When you press, retaining compound can help if you have variation.

How are you accurately controlling location of your pins? IMHO having a pin pressed into a perfect hole is useless if the hole is 0.05" out of position.

Supplier changes. The original stock was consistent then the replacements resulted in a spread that wound up being scrap. The accuracy of the pins has some tolerance variables to allow fitment. Agreed that being off 0.05" would not be good.

 

[RoninB4]

Supplier changes. The original stock was consistent then the replacements resulted in a spread that wound up being scrap. The accuracy of the pins has some tolerance variables to allow fitment.

-Not good for you. Will SS dowel pins work? Hardened and ground (over/under size too) that are up to 1-1/4" length for around a buck apiece. Dowel pins (ground) will have better/consistent tolerances. If fitment is part of the problem then I think you first need consistent components that will allow you to plan tooling purchases. JMO

If location is off that can be another topic we can all have.

 

[Kuma601]

Thanks @RoninB4! The recent pin stock is 0.1250" +/- 0.001" which has not presented issues in the fitment. Something to be said for obtaining quality spec materials. Makes life easier that it doesn't stack up bad tolerances. Attempting to work around inconsistent sized materials is a PITA. I'm understanding the importance taking proper steps in sizing result in a quality build.

It doesn't go out with the thought, "I wonder if __________."

 

[MushCreek]

I used to make medical parts on a Swiss-type screw machine. My customer sourced the material, .093 SS ground stock. I don't know how they make that stuff, but it was always within .0002 or so over a 12' bar. The way a Swiss machine works, the bar stock has to be very accurate. They would ship me a case of 1000 bars at a time. Being a Tier 3 supplier, the customer providing the material relieved me of having to certify it.

 

[NORTON'S SHOP]

I used to make medical parts on a Swiss-type screw machine. My customer sourced the material, .093 SS ground stock. I don't know how they make that stuff, but it was always within .0002 or so over a 12' bar. The way a Swiss machine works, the bar stock has to be very accurate. They would ship me a case of 1000 bars at a time. Being a Tier 3 supplier, the customer providing the material relieved me of having to certify it.

The bars are centerless ground. Pretty much a requirement when precision parts are made on a Swiss.

 

[motophile]

Mold maker here, ive drilled and reamed a lot of holes. You can change the finished hole size by changing amount of stock left in hole. Bigger chip, bigger hole.

 

[Monza Harry]

Use a "Hi Roc" drill, this drills and leaves a reamed or better finish hole. This one below is 0.128" dia. I remember seeing some available in 0.001" increments but I couldn't find it today. You would need a cutter grinder to make your own, but doing so isn't easy or fast but possible. Harry

item detail

 

[MBfreak]

I have read a machinists handbook. ( Karlebo, the Swedish go to for machinists since 1930. Updated every 5th year)
In order to achieve surface finish below 1µm in any iron based meta, l the only tool that is useful is a diamond ground to 0,02µm.
And a rock solid machine
Used for hi end watches and some gearcutting machines. VERY expensive.

Ola

 

[laser3kw]

a drill will produce a 3 lobe hole. To get a "rounder" hole, you need a ream with four or six flutes. You will always end up with one more lobe than cutter flutes unless the circular feature is ground or EDM.
As other mentioned shoot for a .115" hole and ream to .126"