# Help centering a boring head on a mill



## Pmedic828 (Oct 29, 2014)

I searched today to see if any posts exists to explain how to center a boring head on the work.  I have a 3 inch boring head R-8 that I recently purchased (import 1/2 diameter bars) and am looking forward to using it.  I understand that there is a spot that you insert a hex wrench to open or close the head so the diameter of the hole can vary.  How to you center this boring head on the work since there is no center point.  I don't know if I am missing some information, but as a semi=newbie, I have never used anything like this.  I am familiar with hole cutters in wood since there is a center spur but a boring bar is new to me.  Please help!  Thanks in advance.


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## easymike29 (Oct 29, 2014)

The center of the boring head is the center of rotation of the quill.

Gene


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## JimDawson (Oct 29, 2014)

The boring head scribes a circle centered on the spindle center.  So what you have to do is center the spindle on the hole first.  You can do this with an edge finder if you already have a hole.  Or, if you are starting with no hole, then drill a hole first, and don't move the table, you will be on center.  Drill the hole as large as possible before boring to bring it to size.

I hope this is clear.

EDIT:  Be careful about screwing the offset too far, you can run the movable part right off of the threads.  Then the head will fly apart in use.  Where possible I normally screw the head in a direction that the threads engage more (righty tighty).


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## Bill Gruby (Oct 29, 2014)

JimDawson said:


> The boring head scribes a circle centered on the spindle center.  So what you have to do is center the spindle on the hole first.  You can do this with an edge finder if you already have a hole.  Or, if you are starting with no hole, then drill a hole first, and don't move the table, you will be on center.  Drill the hole as large as possible before boring to bring it to size.
> 
> I hope this is clear.



 Da-Da-Da- Dats it folks. Thanks Jim.

 "Billy G"


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## EmilioG (Feb 28, 2016)

Can you start a large hole for boring with a hole saw?


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## wawoodman (Feb 28, 2016)

Yes, as long as you don't lose your center when you switch to the boring bar.

And as long as you're sure the hole saw doesn't wobble. (All of mine, do!)


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## uncle harry (Feb 28, 2016)

EmilioG said:


> Can you start a large hole for boring with a hole saw?



Yes. You;ll need to take many shallow cuts relieving the chips from the resulting groove & saw teeth. Liberal application of lubricant should be applied & use slow speed.
I like to pre-drill a pilot hole & replace the hole saws drill with a hardened pin like a steel dowel, particularly on thinner material.


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## Uglydog (Feb 28, 2016)

If you have a preexisting hole you will need to fiddle with the XY in order to center it using an indicator such as this random one (http://longislandindicator.com/p4.html).
Then you can indicate off the circumference of the hole.
Or if you know the relation of the center to the edges you can dial in from the edges of the work.

What type of set-up indicators do you have? 
And what do you have to hold them in a collet? 

Daryl
MN


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## T Bredehoft (Feb 28, 2016)

Without an indicator, given a hole in the work:
Install the R8 boring bar in the spindle and make it tight. Lower the head 'till the cutting tool is just above the work. 
Rotate the head, moving the table until the rotated head is pretty well centered on the hole.
Reduce the diameter of the cutter until it will fit inside the hole everywhere.
Lower the head into the hole, rotate (BY HAND) the boring head. Move the tool out until it touches the first point.
Using the table, move the work away from the tool until the tool does not touch any  point on the hole. Move the tool out until it touches again, and move the table away.
Keep doing this until the tool touches all around the hole.
Now you can bore the hole larger and be certain you're pretty near the center of the hole.
DO NOT run the boring head at any kind of speed at all. It should turn slowly until  you become very familiar with the process.
Don't try to take one revolution of the stetting screw, keep it under half a turn. Some boring bar adjust one line at a time on the radius, some on the diameter. Be sure you know which yours moves.


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## bfd (Nov 9, 2016)

alright you should understand how to center  the boring head in the hole but you can also center the toolbit just like in a lathe too high or too low is not good the flats on the boring bar are not always right to center the bar. rotate the bar in the hole to make it on center a little high is ok. bill


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