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Criterion 3/4 boring head verse 1/2 “ head?

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Swerdk

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#1
I use a PM 935 mill-Looking to purchase a replacement to Chinese boring head - my existing bars are 1/2”. Would it be more advantageous to use a heavier 3/4 head with a 1/2” adapter for bars or just use a 1/2 “ head - I am thinking heavier 3/4 head is more rigid. Second concern with regards to rigidity- would it be better to use a head with a straight R8 shank or would a 3/4 straight shank attached to a collet be equal to rigidity ? These are my present Ebay options


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benmychree

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#2
I would stick with the 1/2" boring head if it suits your needs so far as capacity (diameter) is concerned, bear in mind that a head with larger holes will likely be physically larger than a 1/2"head, diminishing the height available under the head/boring bar down to the table. The only reasons that I would go for the 3/4" head would be that I wanted to use 3/4" diameter tooling and/or I needed the larger diameter boring capacity that the larger head would likely have.
I doubt that you would find much difference regarding the shank issue with a 1/2" sized boring head, perhaps, yes for the 3/4", it may make a difference in ridgidity (lesser) going with a straight shank if you were doing boring with heavier cuts and large diameters and tool overhangs. With the straight shank on the smaller head, tool change would be more convenient due to not having to pull that long R8 shank out of the spindle. The mill that I had at my shop before retirement had a R8 spindle (a Induma 1-S. a Bridgeport type machine, but heavier) and it was a pain when changing tools, frequently having to lower the table to accomplish the task; in my retirement shop I have a Fray vertical mill from the 1940s and a Brown & Sharpe universal with vertical attachment, both have 30 taper spindles; much more convenient to change tools!
I have many (about 7) boring heads that fit the mills, up to 3/4" hole size, and find that I mostly use the 3/8 and 1/2" heads.
 

Swerdk

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#3
I appreciate it. I didn’t take into acct the loss in height With larger bore.


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Dan_S

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#4
You will also loose resolution with the bigger heads is memory serves.

All the heads are 0.001" off the diameter per graduation. However the 2" heads are 0.05" per revolution while the larger heads are 0.1" per revolution.
 

mikey

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#5
The larger issue is the greater centripetal forces the larger bars generate. You are better off with the smaller bars if they will do the job.
 

Swerdk

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#6
OK then I’ll start looking around for the smaller ones thanks for your help guys


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petertha

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#7
My head has 1/2" bores & I have the classic boring tools. But I have also been reducing the shanks of inexpensive import CCMT tooling so I have gradations of lengths, right hand, left hand etc. Nice part is I can swap inserts or change back & forth between aluminum or steel cutters quite readily. They seem to cut very well. Who knows what the mystery metal is but turned down something like 4140.
 

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P. Waller

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#8
You will also loose resolution with the bigger heads is memory serves.

All the heads are 0.001" off the diameter per graduation. However the 2" heads are 0.05" per revolution while the larger heads are 0.1" per revolution.
Not true, you can buy a boring head with .0005" resolution and a built in digital DRO in large sizes.
You will not do so of course.
 
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