# boring head mounting threads



## DMO (May 8, 2012)

I have a set of Bridgeport® R8 quick-change tooling of which one of the toolholders is threaded 1-1/2"-20 (male). I was hoping this was for mounting a "standard" thread-mount boring head, but the closest current standard seems to be 1-1/2"-18. This tooling set hasn't been made in over twenty years, but that's nothing. Tooling made by the standards back then should still be around, but I'm not finding it. 

So what is the 1-1/2"-20 threads for?
Dave


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## DMO (May 8, 2012)

dalee said:


> Hi,
> 
> There used to be boring heads with that thread. I've made arbors for them. But not in a very long time. Still, you could modify it. There are many boring heads that use 7/8-20 shanks.
> 
> dalee



Thanks dalee,
 I was starting to think that way, but my toolholder has a nearly 11/16" hole through it, which rules out the 7/8" thread possibility. Do you think that a 1-1/2"-20 boring head will be hard to find?
Dave


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## 8ntsane (May 8, 2012)

They maybe harder to find than the 1 1/2 18 type. I just checked both of mine, and they are the 18 tpi


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## jfcayron (May 8, 2012)

DMO said:


> my toolholder has a nearly 11/16" hole through it, which rules out the 7/8" thread possibility. Do you think that a 1-1/2"-20 boring head will be hard to find?



Have you thought about turning a 1-1/2" 20 to 7/8" adapter?


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## DMO (May 8, 2012)

jfcayron said:


> Have you thought about turning a 1-1/2" 20 to 7/8" adapter?



Making an adapter seems like it might be the most practical solution, and once committed to that, I guess I would have my choice of sizes. I think I would rather go 1-1/2"-20 to 1-1/2"-18 for 'robustness', and that it seems common enough, plus I think it fits my Criterion head, which would make a nice addition. I was looking at some of the larger duplicate toolhoders that were large enough to turn down to make the threads AND leave a shoulder-flange, but they each have a giant setscrew thread right in the side of them, plus I'd be sacrificing something awfully rare, and probably too hard to machine.

So I guess threaded adapter it is.

Thanks everyone for your input.
Dave


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## Tony Wells (May 8, 2012)

I think I have an older boring head with a 1 1/2-20 thread. I checked MSC, and they list a single boring head shank, made by Criterion that fits the 1 1/2-20 thread.


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## DMO (May 9, 2012)

42 said:


> I think I have an older boring head with a 1 1/2-20 thread. I checked MSC, and they list a single boring head shank, made by Criterion that fits the 1 1/2-20 thread.



Aha! I missed that because I was looking for R8 arbors. That suggests there may still be some other things out there that are compatible with what I have. 
I'll investigate some more.

Thanks 42!
Dave


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## Tony Wells (May 9, 2012)

You're welcome, Dave. I'm thinking that if you are patient, you can find an R-8 with that thread. Or maybe just persistent. Someone is bound to still have them, even if they aren't popular these days. I'll look a bit as well.


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## DMO (May 12, 2012)

Well, I did some more checking on that Bridgeport No.2 boring head, and I had it all wrong. It didn't make any sense that Bridgeport would make their R8 solid-holder quick-change system with one of the holders not threaded to match their boring head. Just for references, the threads for the Bridgeport® No.2 Boring head are 1-1/4"-20 (not 1-1/2"-20), and the No.1 Boring head is 5/8"-18 threads. This was from a gentleman retired from Bridgeport, but still active in providing parts. He said they made the boring heads. He said the quick-change tooling they made was modeled after the Erickson 30 quick-change, and so far, Kennametal has access to only the R8 spindle adapter part of that system, but no tool holders. 

So the upshot is that the quick-change tool holder I have will thread into my No.2 boring head, and I will have an improved system once I remove its R8 shank. 
I don't know how I ever got on the idea that the threads I was looking at were 1-1/2"-20. They were right there, plain as day, 1-1/4"-20. Sorry for all the fuss, but I did learn a few things in the process.

Dave

PS: I'd love to find out that there are new solid tool holders out there that with little or no modification will fit into that old Bridgeport line of QC tooling. It is a real fast and solid system.


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