# miniature boring bars



## hobby (Sep 16, 2010)

Hi guys,
I haven't tried this yet, but I want to start building smaller projects, which require smaller tooling for my benchtop tools.

From my experiance in reaming and boring a hole with a boring bar, in my lathe, I find that I can get a more acurate cylinder bore with a boring bar.

Not to say that my reamers don't do a good job, but it seems like if the preliminary hole is off a bit, from drilling, that a reamer in the small diameter sizes, don't do a good job in correcting it unless I run it in and out like a boring bar, the finioshed hole diameter is of course larger, but a reamer in the small dia, seems to have some flex to it that will follow a crooked drilled hole.

With all that said, I was thinking of making very miniature sized boring bars, without having to purchase them.

I was thinking about using a 1/8" , 3/16" and a 1/4" dia. reamers, and modify them to work as miniature boring bars.

These 3 sizes would take care of the smallest cylinder bores I would be working with.

The way this would be done, is I would grind back all the flutes except one, and this one flute would be ground back top and bottom, leaving a small bit unground, at the very front, past the tapered front, wich would act as the cutter. 

Would this work?
Any suggestions on why this would not work?

Thankyou.


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## tel (Sep 16, 2010)

Sounds like it would work OK but you would save yourself a power of money and work by making them out of cut-off, good quality, Allen Keys.


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## hobby (Sep 16, 2010)

Thanks Tel,

That sounds like a good idea too.

I'll have to look into that as well, when the time comes to make a miniature boring tool.


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## Blogwitch (Sep 16, 2010)

Old blunt drills are even easier to work with, just grind a flat angle across the front and they are ready to use.

Bogs


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## George_Race (Sep 16, 2010)

Bogs:
Can you explain what you mean by a "flat angle" across the front.
I need some small boring bars and have a lot of old HSS steel drills.
George


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## hobby (Sep 16, 2010)

Bogstandard  said:
			
		

> Old blunt drills are even easier to work with, just grind a flat angle across the front and they are ready to use.
> 
> Bogs



Thanks Bogs

the only thing I would be concerned about is the flexation due to the deep flutes in a drill, versus the flutes cut into a reamer.

however , old thrown out endmills may work too, they may be mor rigid, plus theres a second use for them as well.


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## Blogwitch (Sep 17, 2010)

George,

Not a very good C-o-C, but I hope it explains it.

You only need to grind one flat surface straight across the drill, with the two outer cutting tips horizontal, slightly angled to one side and with the nose of the drill angled slightly upwards. That, when ground, will use the left hand cutting edge as the tip of your boring tool. If you don't understand, I will attempt to take pictures to explain what the angles are about.

Hobby,

I have used these drill types to bore out tiny holes, and because of the rigidity of the flutes, they will flex less than a normal boring bar of the same size. The best way to hold them is to put them into a pin chuck and then hold the pin chuck in your toolpost. They are mounted a couple of degrees off straight in, to present the cutting tip to the bore wall.

For boring above 5mm up to where my normal boring tools take over, I use these 'German' type boring bars, the smallest set. Also by making a small adaptor, I fit them into the boring head of my mill for those small precision bored holes.

http://rdgtools.co.uk/acatalog/TOOL_S_FOR_BORING_HEADS.html

I hope this helps


Bogs


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## George_Race (Sep 17, 2010)

Thanks Bogs, you little drawing made it real clear.
Should make it real easy for those very small bore jobs.
George


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## mu38&Bg# (Sep 17, 2010)

I've made boring tools from drill rod. It doesn't take much relieving to make something that works. The solid shank is pretty stiff, but I've never used it on steel. I also have a purchased indexable carbide boring bar for .210 min ID holes. I prefer to use the purchased tool.


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## gjn (Sep 17, 2010)

The latest issue of Model Engineers Workshop (168) has an article on this subject which may assist you


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## rake60 (Sep 18, 2010)

I needed to bore a small, shallow fit, so I took an old end mill and ground all of the flutes off
but one. Then I ground clearance behind that flute to make it a small boring bar.






It worked great!
But, it wasn't my own idea.
A guy I used to work with came up with that solution to boring a small hole on our CNC turning center.

*Thanks B.Todd!*

Rick


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## jpeter (Sep 19, 2010)

I've had pretty good luck boring using carbide end mills. I have lots that have one edge chipped. I arrange the bit in the lathe tool holder in such a fashion that the remaining sharp edge is doing the cutting/boring. I find carbide end mills in the small sizes pretty stiff. Hard to find any other material in small sizes that stiff. And, the angles seem about right for boring too.
Hey, check out my v8.
[ame]http://www.youtube.com/watch?v=B9zt3SF_Flc[/ame]


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## shred (Sep 19, 2010)

I've been known to use old end mills as well-- set 'em at a bit of an angle to provide clearance and away you go.


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## hobby (Sep 26, 2010)

Thanks guys, for all your helpful responses
I apologize for not replying back earlier, but I forgot about this thread, then tonight I was looking at this area of the forum, and seen the title "miiniature boring bars", and it caught my attention, then when I seen it was started by me, I figured I would open it up to review it again.
And I seen the added helpful replies. 
So that's why the late affirmation.

Jim your V-8 looks and runs like a real champion..
Great job on that build...


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## SignalFailure (Nov 4, 2010)

Bit of a late bump for this thread but....

Why not use a piece of stock silver steel to form your tool? For example take a piece of Stubs 5mm, heat to bright red, flatten one end then use the grinder to make it into a nice cutting shape (harded/hone as required). I've made a few of these for boring smallish holes and they work well - the problem with most standard tools I've tried is that they wont fit in the 'ole.

Just a thought 

Paul


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## MachineTom (Nov 4, 2010)

For small boring jobs those Micro 100 solid carbide are the _its for the job. From .125 and up, on ebay I paid like $4 for the little guys, mostly use .230-.490 sizes, generaly around $10 on the bay. There is a guy selling on the bay where he says the bits were used once to cut plastic, I doubted it was true but I bought 2 lots of 5each for $25. The bits did not appear used, and were perfect except no boxes.


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## ttrikalin (Nov 4, 2010)

You must have experience with huge machines. I have only worked on my two Sherlines, and a 1/8 boring bar is quite normal sized... I ground an other small boring bar today, this time I took photos. 

http://www.homemodelenginemachinist.com/index.php?topic=11298.0 

take care, 
tom in MA


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