Boring bars

[Peter Simpson 2Participant @petersimpson2]

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.

[Peter Simpson 2Participant @petersimpson2]

What is the smallest size

[JasonBModerator @jasonb]

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 1Participant @haroldhall1]

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

[adyParticipant @ady]

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 Stevenson 1Participant @johnstevenson1]

Bottom of this page.

 

Solid carbide boring bars

 

John S.

[mariano diazParticipant @marianodiaz48581]

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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