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Boring tools for Boring Head

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Paul Fallert23/01/2010 03:45:51
89 forum posts
3 photos
Has anyone found a workable tool bit and a simple method for setting that tool bit in a boring head?
 
I've tried brazed carbide boring tools which would not cut when set on the centerline of the boring head. By experimenting, I found that the tools would cut when dropped about 15 deg below the centerline, which violates customary advice.
 
Further, I chipped several tools on a workpiece that contained an existing cross-drilled hole which created an interrupted cut situation. This situation called for a HSS toolbit.
 
Any advice would be appreciated.
John Haine23/01/2010 09:45:43
5563 forum posts
322 photos
I usually use the brazed carbide ones from one of the sets that Chronos etc sell - never had a problem, set the angle by eye usually.  If you look at a commercial boring bar with an insert they usually have negative top rake, as you have found.  I also have a smaller (and nicer) Arrand boring head with which I use a tool which has an 8mm shank with a 3/32 HSS rod at an angle at the end (held by grub screw) on which you grind your own cutting edges - this works fine too and is good for small jobs.  You could easily make  an equivalent.
 
John.
Peter Tucker25/01/2010 19:08:45
185 forum posts
Hi Paul,
 
Do your carbide tips have enough side clearance angle?  On a small hole you may need to round the back of the tip quite a bit.
 
Peter.
Paul Fallert25/01/2010 20:10:14
89 forum posts
3 photos
I have now read the George H. Thomas article on boring  contained on this site (ME 3562-1). Fig. 2, item #7 page 618 makes clear the problem that Peter Tucker refers me to.
 
Does anyone know of a step-by-step on how to make and grind a positive rake (not carbide) boring tool for interrupted cuts?
 
Until I purchased the Boring Head, I had been chiefly confined to drilling and reaming.
 
Thank you for your reply,
 
Paul Fallert
David Clark 125/01/2010 20:42:28
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3357 forum posts
112 photos
10 articles
Hi There
Use a slot drill in the boring head.
They work great as single point boring tools.
regards david
John Haine25/01/2010 20:45:41
5563 forum posts
322 photos
I think George Thomas' book has full instructions IIRC.
 
Stub Mandrel25/01/2010 22:34:15
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4318 forum posts
291 photos
1 articles
I have some HSS boring tools that are somewhat like D-bits.
 
Setting them is quite critical, as you need to angle them to get some top rake, whilst ensuring that the round undersurface doesn't rub. When the hole is near to the diameter of the cutter, it's best to arrange it with no top rake at all. You can add more as the hole opens out a bit, if required.
 
the knack is to look very closely at the tool tip when it is stationary and touching the work. Check for point contact at the cutting edge, and no rubbing.
 
It is a bit trial and error, but as you normally start with hole a lot smaller than finished size, you have plenty to practice on
 
The boring bit is  opening the hole up a few thou at a time!
 
 
Paul Fallert26/01/2010 01:25:05
89 forum posts
3 photos
>John Haine said: "I think George Thomas' book has full instructions IIRC."
 
I don't have either Thomas book.
 
Does anyone know if it is Workshop Techniques or the Model Engineers Workshop Manual?
 
Thank you for your reply,
 
Paul
 
 
malcolm Rixon26/01/2010 05:46:43
5 forum posts
I have both thankfully and the Model Engineers Workshop Manual has a chapter devoted to boring tools , their use in the lathe and another chapter on Boring Heads.
Cheers

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