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Old 09-16-2010, 08:30 PM   #1
hobby
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Default miniature boring bars

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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Old 09-16-2010, 08:36 PM   #2
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Default Re: miniature boring bars

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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Old 09-16-2010, 09:55 PM   #3
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Default Re: miniature boring bars

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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Old 09-16-2010, 10:02 PM   #4
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Default Re: miniature boring bars

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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Old 09-17-2010, 12:08 AM   #5
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Default Re: miniature boring bars

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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Old 09-17-2010, 03:12 AM   #6
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Default Re: miniature boring bars

Quote:
Originally Posted by Bogstandard
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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Old 09-17-2010, 08:01 AM   #7
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Default Re: miniature boring bars

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_...ING_HEADS.html

I hope this helps


Bogs



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Old 09-17-2010, 12:30 PM   #8
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Default Re: miniature boring bars

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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Old 09-17-2010, 02:59 PM   #9
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Default Re: miniature boring bars

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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Old 09-17-2010, 11:45 PM   #10
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Default Re: miniature boring bars

The latest issue of Model Engineers Workshop (16 has an article on this subject which may assist you



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