Boring

[Nick Webb 1Participant @nickwebb1]

I'm thinking about making Don Unwin's boring head http://www.model-engineer.co.uk/members/digitaleditions/ but there are a couple of things in the article that puzzle me.

Firstly, why is the cross hole in the cutter block (fig 14) inclined?

Secondly, the "special screw" (fig 19) of 0BA size. What's it for? Where does it go?

 

 

 

Edited By Neil Wyatt on 02/05/2017 21:34:55

[Nick Webb 1Participant @nickwebb1]

[Neil WyattModerator @neilwyatt]

Posted by Nick Webb 1 on 02/05/2017 11:54:14:

I'm thinking about making Don Unwin's boring head http://www.model-engineer.co.uk/members/digitaleditions/ but there are a couple of things in the article that puzzle me.

Firstly, why is the cross hole in the cutter block (fig 14) inclined?

Secondly, the "special screw" (fig 19) of 0BA size. What's it for? Where does it go?

1 So that a cutter can be set close to the block without the block fouling the surface when facing.

2 The text suggests the two screws go either side of the feed ring, I assume they are stops?

Neil

[Nick Webb 1Participant @nickwebb1]

OK, 1 makes sense, thanks.

The text says that there are two 2BA screws, and the opposing holes in the feed ring are, from the looks of it, also 2BA, so I assume that the two larger screws go in these – and that makes sense if you want to have two "clicks" of advance per rev, while withdrawing one of them takes you down to 1 "click" per rev. Which all leaves the 0BA screw looking rather redundant?

[Benny AvelinParticipant @bennyavelin86238]

To me it seems like there is only one 2BA screw and one 0BA (see top of page 13), the 2BA is the permanent one and the 0BA can be taken out or put in depending on the feed-rate wanted.

[Nick Webb 1Participant @nickwebb1]

If you're referring to the photo on p13, the way I see it is that one of the 2BAs is in place in the ring – bottom left of the ring. The 0BA screw is too short to go through the feed ring and project into the groove, and having the thread rub on the cam ring would not be a good idea surely.

It seems to me that the first sentence of the first paragraph that starts in the r.h. column of p13 makes it clear that there should be 2 off 2BA grub screws.

[Benny AvelinParticipant @bennyavelin86238]

Well I was referring to the first sentence of the first paragraph in the r.h. column

I understand that sentence as there is one 2BA and one 0BA, both with the end turned down to 3.5mm. However, you are right in that the screw is too short, or at least the threaded portion should be longer. 3.5 mm of 0BA is not very long. There seems to be no real reason for having the second hole 0BA, I would just make two 2BA screws and work with that.

[Nick Webb 1Participant @nickwebb1]

And, of course, I have been thinking awrong. I had been seeing the drawing of the 0BA screw as having the smaller diameter threaded, and being mislead into assuming that 0BA is smaller than 2BA. One day I'll get my head around the idea that with BA, SWG and number drills, a bigger number is a smaller thing. ​ Having things to different scales in the same drawing doesn't help. But yes, I'll go with the 2 off 2BA – though actually they will be M5 as I'm much more at home with metric (see above).

Thanks for the help.

[Benny AvelinParticipant @bennyavelin86238]

Great!

I cannot say that the article is clear about the point of these screws, in general I found the drawings and article hard to understand, but that is maybe my problem

If you decide to build it, please post pics of your progress.

Ps. I never work with BA threads, for us that are not accustomed the reverse numbering is quite confusing at first glance.

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