# Boring small holes



## Mosey (Oct 24, 2011)

I need to make a flat bottom in several, 1/8" diameter by 1/16" deep holes in brass. A tiny boring-bar would be nice. Drill and reamer will not make the bottom flat enough. Can I make a "D" type bar that will work? Suggestions are welcome.
The holes are for 1/8" shafts for pump gears, so the bottom needn't be absolutely flat, but close. ???


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## Ken I (Oct 24, 2011)

Just grind a drill "flat point" - drill the hole conventionally and then finish with the flat bottomed drill.

I have a selection of these - typically if I badly burn, break or otherwise screw up a drill - I will cut off the end and grind it flat bottomed to add to my collection for just this purpose.

Ken


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## mklotz (Oct 24, 2011)

"Drill" the hole with a 1/8" center-cutting end mill?


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## stevehuckss396 (Oct 24, 2011)

mklotz  said:
			
		

> "Drill" the hole with a 1/8" center-cutting end mill?



I agree.


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## dalem9 (Oct 24, 2011)

If an 1/8 end mill will not work for you.Use a smaller mill then use a very small allen wrench and grind the short end to suit.I've done it and it works .Hope this helps .Dale


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## pete (Oct 24, 2011)

They do make some really,really tiny solid carbide boring bars that are really,really quite expensive. I've seen them listed that would fit in a less than .050 (nope that isn't a typo) hole. Without them being under CNC control and using one of those uber expensive self balancing boreing heads along with screaming high rpms. I'm not all that sure just how well they would work on your comman manual machine tool.

Doesn't sound like that's what's needed anyway. So I'd vote for a D bit, end mill, or reground drill bit. The Live Steam locomotive builders do work like this often when building valves etc. and it's done with user built D bits.

Pete


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## Mosey (Oct 24, 2011)

Done. Over.
The 1/8" end mill did the job, with a smooth, flat bottom.
Thanks, guys.


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## mklotz (Oct 25, 2011)

Mosey  said:
			
		

> Done. Over.
> The 1/8" end mill did the job, with a smooth, flat bottom.
> Thanks, guys.



I'm glad it worked.

Should you want to use this trick in the future, remember that the bottom of the hole is not truly flat. If you look at the end of an endmill, you'll see that the cutting edges are ground with a slight radial angle. In most cases it doesn't matter but if, for some reason, the bottom of the hole needs to be *truly* flat, a D-bit may be required.


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## Mosey (Oct 25, 2011)

Thanks, Marv. Don't want to spoil em with too flat a bottom! They get lazy you know.
Actually, it is just right, with the slightest curvature, giving the end of the shaft a little float in the blind hole. We're talking ten-thousands here.


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## Swede (Nov 9, 2011)

Correct on the "close but not NASA grade" flat bottom that results from a good end mill. I use them all the time as counterbores and many applications where that tiny convexity isn't an issue.

The only time I ever needed a truly flat bottomed hole was the monolithic head block for my deHavilland inline 4-cylinder. The plans called for mounting the head on a plate and doing it in a lathe which would work, but what a setup pain for each, IMO. I'm lazy.

So I bought an ENCO automatic boring/facing head and did it in the mill. What an interesting tool. I know it's not appropriate for tiny holes, but I'd reach for it again for anything larger than about 1/2". It's kind of creepy watching the cutter diameter getting wider with each revolution, approaching a thick wall, and counting on the clutch kickout mechanism to stop the feed... but it definitely works well!


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## Coilmotorworks (Dec 1, 2011)

Make the pump out of three parts, a bottom, a top and a center section (where the gears are). Use Loctite to seal the bottom with the gears removed, clean any over running Loctite. Run bolts all around and down to the bottom plate. A soft sealer carefully applied to the top will allow for future rebuilds of the pump.


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## Rockytime (Dec 13, 2011)

I've been off line for quite some time so I'm behind the time line. However, I am posting a photo of a cheap and easy mini boring bar. It is simply a broken drill bit with the tip ground flat or with just a small rake. It works excellent and one never need be without a small boring bar.



			
				Mosey  said:
			
		

> I need to make a flat bottom in several, 1/8" diameter by 1/16" deep holes in brass. A tiny boring-bar would be nice. Drill and reamer will not make the bottom flat enough. Can I make a "D" type bar that will work? Suggestions are welcome.
> The holes are for 1/8" shafts for pump gears, so the bottom needn't be absolutely flat, but close. ???


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## AussieJimG (Dec 14, 2011)

Just when I was wondering how to bore a small taper for one of those flywheel clamps, this turns up. My lucky day I guess. Thanks
Jim


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