# R8 Arbor Questions



## RonRock (Jun 11, 2020)

I need an arbor for a Bridgeport No2 boring head. Seems easy enough to just order one wait a week and Bob's your uncle! No such luck. The Bport boring head is a 1 1/4 x 12 thread. Pretty sure that is true, my arbor is stuck in and damaged. But I'm sure that it isn't the more "typical" 1 1/2 x 18 thread that is easy to find.

It has been suggested to me that I buy a 1 1/2 x 18 and turn the threads down and turn in the needed threads. 

Are the arbors hardened? Are R8 arbors generally hardened? Or are they usually soft enough to machine? I actually have a couple other oddball arbors that I need. One for a Tapmatic tapping head that also seems to have an odd thread that Tapmatic don't make an R8 arbor for.

It's always something.

Or maybe I have missed the boat and someone here can point me to an arbor that will fit my No2 boring head. That would be great, but I still have other needs for odd arbors.


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## ErichKeane (Jun 11, 2020)

Why not just scratch-make an R8 arbor?  The lead-in-taper is a touch of a pain to indicate in (use an existing collet/arbor to do so!), but the rest is pretty simple.  Even easier if you have a taper attachment.  I'd suggest 4140 HT.


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## RonRock (Jun 11, 2020)

That is also a consideration. Thank you, ErichKeane.

You answered my next question of what type steel to use if I decide to take that leap.


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## ErichKeane (Jun 11, 2020)

I did a bunch of googling and it seems that most arbors are 'hardened'.  If you really wanted your arbor hardened/ground, you could always just make a thread adapter.  I found on amazon a 3/8-24 and 5/8-16 threaded arbor for ~$25 shipped, you could potentially turn a thread-to-thread adapter for your oddballs.


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## RonRock (Jun 11, 2020)

Would that be accurate enough for an arbor? I considered that, but was concerned that there would be too much "slop" in the threads. May not matter for either a boring head or tapmatic. 

Are you able to make a hardened arbor soft enough to work with then re harden?

With all of that it might be best to just start from scratch and make my own and heat treat before final grind. Sounds easy. Unfortunatly way over my head and ability level. But I might try anyway. Not sure if the old Logan is up to it.


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## Lo-Fi (Jun 11, 2020)

Look for R8 soft end blank:









						0MT SOFT STUB ARBOUR BLANK END 28 X 30MM WITH TANG LATHES MILLING RDGTOOLS 7435353606136 | eBay
					

0 MORSE TAPER BLANK END ARBOUR WITH A TANG. TAPER SHANK IS HARDENED, END IS SOFT TO ALLOW MACHINING. CAN BE USED TO MAKE END MILL HOLDER, DRILL ARBOR, THREADED ARBOR OR MANY OTHER APPLICATIONS, IDEAL FOR BOXFORD AND MANY OTHER MACHINES.



					www.ebay.co.uk
				




A UK link, but you it'll give you the idea. I tend to keep a few in so I can do little jobs like this when I need.


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## ErichKeane (Jun 11, 2020)

RonRock said:


> Would that be accurate enough for an arbor? I considered that, but was concerned that there would be too much "slop" in the threads. May not matter for either a boring head or tapmatic.
> 
> Are you able to make a hardened arbor soft enough to work with then re harden?
> 
> With all of that it might be best to just start from scratch and make my own and heat treat before final grind. Sounds easy. Unfortunatly way over my head and ability level. But I might try anyway. Not sure if the old Logan is up to it.



Presumably your threads would be cut in the same operation, so they should be concentric. Id consider turning the outer-threads ON the arbor though.

That said, Lo-Fi's soft-end-blanks are likely your best bet


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## RonRock (Jun 11, 2020)

New to me. I'll check them out.


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## darkzero (Jun 11, 2020)

The import one I bought was really only case hardened. It was also 1-1/2"-18 that I turned down & rethreaded to 15/16"-16". Was also able to tap the center.


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## mmcmdl (Jun 11, 2020)

I believe I'm holding one in my hand . I can't remember what it was on , but I sure don't need it . I'll take it into work and check it out .


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## RonRock (Jun 14, 2020)

mmcmdl said:


> I believe I'm holding one in my hand . I can't remember what it was on , but I sure don't need it . I'll take it into work and check it out .



What is it?


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## Toolmaker51 (Jul 26, 2020)

Focusing on threads to register concentricity is unproductive. Just counterbore a shallow depth and turn boss size to size, that takes up on a shoulder, not bottom on the bore. Concentric, square, perpendicular and rigid all in one.
Bingo.

PS. Ever see someone theoretically 'assure' position with flat head screws, as if they are dowels? The body and flat head portion are never concentric or consistent in relation to clocking of the eccentricity to threads. And if you refasten with same screws but in other positions it'll not be same as before either.


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## AGCB97 (Jul 26, 2020)

With a boring head, it seems to me that it's purpose is to 'not be concentric' so concentricity of the mount should make no difference. Not so with other types of tools.
Aaron


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