Small drill I found at work today.

[gimpyrobb]

Went in the cabinet for some #28 bits and found a #78¡

OMG those are small. Can't imagine why we would even stock them as building 1 has no machining equipment. I know that's too small for a cordless drill to get a grip on.

Just posting as I've never seen one that small, carry on!

[mccutter]

You can get a pin drill holder for those. Used for cleaning carburetor jets, particularly on small motorcycles. The entire pin drill holder can be put in a regular drill motor.

[greywynd]

Somewhere I have an index for 61-80. I think I’ve only used one drill out of it.


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[toprecycler]

About a year ago, a customer came in with some small parts for a freezing tool for freezing water lines so they can do repairs. I think the hole ended up being a number 78. They had bought some new nozzles, but the company shipped ones that the hole was not drilled in them.

They replaced them, but my customer brought the not finished one to me to see if I might be able to put that small hole in.

Challenge accepted. I got boss to order me a set of 70-80 drills with a holder. I made a slip tube for the holder so I could install it in my tailstock chuck, and just hold the holder/ drill with my fingers to drill with. I wanted the light feedback from fingers.

I turned the lathe (20x84 summit) to its highest speed of 1500 RPMs, and with my butt puckering at the high pitch sound from running a big chuck that fast, drilled all the nozzles for him.


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[LKeithR]

Originally Posted by toprecycler

...I made a slip tube for the holder so I could install it in my tailstock chuck, and just hold the holder/ drill with my fingers to drill with. I wanted the light feedback from fingers...

Essentially you made what is known as a " Sensitive Drill"; designed for exactly what you did. Your lathe must be in pretty good shape because with those tiny drills even a hint of misaligment is enough to shatter them.

What gets me about those small drills is how they manage to make the flutes and grind the cutting edges on something that small. The smallest commonly found drill is a #80 which has a diameter of .0135" but Machinery's Handbook actually lists drills down to a #97 which is .0059" in diameter. I've looked at some of those small drills with a microscope and it's amazing how perfectly formed they are...

[gimpyrobb]

Originally Posted by mccutter

You can get a pin drill holder for those. Used for cleaning carburetor jets, particularly on small motorcycles. The entire pin drill holder can be put in a regular drill motor.

I have some of those!
Maybe one or two of these need to head home...

[Whitetrash]

We used those when I was a burner in the fab shop for saving torch tips that got a little buggered up.

[MotorDoctor]

Originally Posted by mccutter

You can get a pin drill holder for those. Used for cleaning carburetor jets, particularly on small motorcycles. The entire pin drill holder can be put in a regular drill motor.

As a motorcycle guy, I have three pin vices set up for cleaning pilot jets. Keihin carburetor jets are sized by actual diameter (a #35 pilot jet is .35mm). I seem to recall they were a #79-78-77. Motorcycle jets are actually undersized, because over time, fuel flowing through the jets enlarges the bore, which can increase emissions. Just drilling the jets to the actual size makes them run much better.
Mikuni jets are different, they are sized by flow rate, a given pressure at a given amount of time. A #150 main jet flows 1.5cc/minute (or so I remember). I don't know what pressure/temperature they used, beyond my pay grade.
A few more years, you will be hard pressed to find somebody that knows how to work on carburetors. Kind of like points, or magnetos.

[mccutter]

Originally Posted by MotorDoctor

A few more years, you will be hard pressed to find somebody that knows how to work on carburetors. Kind of like points, or magnetos.

Somewhere in my archives I have a Keihin jet catalog.

Speaking of carbs, I have to pull them off my XL350 (1-2 progressive). Needles are leaking. Probably time to install the petcock rebuild kit while I'm at it...

[dubby]

When I first got the little cnc mill I ordered some sample tooling parts that came with some itty-bitty drills. Even using the machine I managed to screw them up with a quickness.