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Boring bars

What is the smallest size

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Peter Simpson 223/07/2011 19:31:47
28 forum posts
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I'm in the process of making a Stuart No 9 engine. Reading Tubal Cains book on the subject, he suggests "boring" the piston to allow it to be threaded 3/16" BSF. Does he mean drilling it, as I cannot believe you can bore such as small diameter hole with a boring bar. I purchased a small boring bar from RDG it's about 4mm minimum hole diameter. I have experimented with it on BMS but the finish is poor due the flex in the tool. I'm loathed to bore the piston prior to threading it. I see no advantage in boring the hole over drilling it tapping diameter. Any advice would be greatly appriciated.
JasonB23/07/2011 20:03:43
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25215 forum posts
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You may just get away with your boring bar as 5/32" is tapping size for 3/16BSF (3.97mm)
 
As said the reason for boring is to get a truer hole, you could also use a D bit or slot drill to finish the tapping hole.
 
Of course its all very well having a true tapped hole provided the thread on teh piston is equally as true, my preference would be to make the piston a few thou oversize and onve it is mounted on teh piston rod set that to run true and skim the piston to finished size.
 
J
Harold Hall 123/07/2011 20:17:26
418 forum posts
4 photos
If you really want to bore a small hole look at photograph 5 at--
 
http://www.homews.co.uk/page140.html
 
They are made even smaller than this and are supplied by MSCJ&L, probably others.
 
Harold
ady23/07/2011 22:26:45
612 forum posts
50 photos
You probably have a whole bunch of carbide tipped D-bit drills lying about and being completely ignored because you never even knew you had them in the first place.
 
They're called masonry drills.
 
Very handy for knocking holes into cast iron as well.
John Stevenson24/07/2011 00:30:27
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5068 forum posts
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Bottom of this page.
 
 
John S.
mariano diaz24/07/2011 07:26:39
7 forum posts
If you have to have a good small concentric hole just center drill it ,then drill it 1mm smaller , and put a 5/32 slot drill with a 005 radius (approx) in the milling chuck and feet it slowly in the hole
regards
mariano
 

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