# Boring Head Conversion



## thestelster (Aug 23, 2022)

I have a large robust boring head which is fantastic.  But because it only has one boring bar port, when I have to do large diameter bores, it is quite unbalanced, so I have to reduce the rotational speed, who wants to do that!! I have another boring head with an integral R8 arbor.  It has 2 ports vertically and 1 port horizontally.  But my milling machine has a  40NMTB taper.  I also have and R8/40NMTB adapter.  And I do not want to be changing draw bars whenever I want to use the smaller boring head. 

What I need to do is put some sort of key or screw which will keep the top piece secured so it doesn't unscrew when removing the whole unit from the mill.  I could Loctite it together, but I'd like to be able to remove the adapter if I have to.


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## Chip Maker (Aug 23, 2022)

What about a roll pin?


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## thestelster (Aug 23, 2022)

Chip Maker said:


> What about a roll pin?


Thanks @Chip Maker
But that wouldn't work.  I'd have to drill through the hardened R8 shaft, and through the threads of the top piece.  Plus I can't remove the adapter without taking the top piece off because the opening is smaller than the top piece. 

I'm thinking more like a key that fits into the slot of the R8 shaft, and fits into a notch on the top piece (which I have to machine) and held in place with that screw on the adapter.


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## Darren (Aug 23, 2022)

drill tap at the parting line between the two for a set screwc which would key them together?


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## Susquatch (Aug 23, 2022)

Darren said:


> drill tap at the parting line between the two for a set screw?



The photo looks to me like somebody has already done that!







@thestelster - I try to make sure all my tooling have arbours so I can use them on other tapers. My mill/drill was MT3 and my Hartford is R8. But I had a lot of tooling that came with my Mill/drill that I wanted to be able to use on my R8 Hartford.

Unfortunately, like yours, some of mine are integral. They will get sold with the mill/drill when its time comes.

I know it's a bit late for that this time, but something to think about for future purchases.

Edit - another option is to sell the R8 and buy a new 40NMTB.


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## Darren (Aug 23, 2022)

@Susquatch , look at the circle i drew on. Thats where i am suggesting. The set screw you pointed to is the anti rotation pin, like in an r8 spindle.


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## Hacker (Aug 23, 2022)

On my machine the drawbar is threaded at the top with a nut. I can adjust the drawbar to fit CAT40 and 40NMTB. No need for adapters.


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## thestelster (Aug 23, 2022)

Darren said:


> @Susquatch , look at the circle i drew on. Thats where i am suggesting. The set screw you pointed to is the anti rotation pin, like in an r8 spindle.


Yeah, there might be just enough room to do that.  Thank you.


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## Susquatch (Aug 23, 2022)

Darren said:


> @Susquatch , look at the circle i drew on. Thats where i am suggesting. The set screw you pointed to is the anti rotation pin, like in an r8 spindle.



Ok, makes sense.  I don't have 40 taper. I just assumed the R8 would end about half way up the 40R, and there it is a set screw!  No biggie.


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