Boring Head Question

Everybody has their own way. The loads on a boring tool can be very light, so rigidity is a little less a factor than in heavy machining operations. but...

All my boring heads are R8. I wouldn't have it any other way. When doing hard boring, they seem to chatter a little less. The cost of an R8 arbour is not much more than a straight shank type (in my case between 10 and 20 dollars, at the time I was outfitting) I agree runout is never an issue: the tool is still rotating about the centre regardless.

As for rigidity, when using your boring head for large diameters, say 6" plus, the extra rigidity is helpful - but you can still get the job done with a straight shank, perhaps with a little more chatter.

Anyway, that's my experience - yours is sure to vary! :)
 
While I do use straight shanks on some tools I still prefer a R8 arbor for heavier tools. With an R8 arbor there no risk of the tool falling damaging your table, vise, or workpiece when hitting the drawbar to release the tool.

Sure you should always have one hand holding the tool while you are hitting the draw bar but the risk is there, I do it even with a R8 arbor just out of habit. If you have a tall knee mill it can get akward stretching both arms if you aren't that tall. I have a square column mill so the head raises up & down. If the head is raised pretty high and I have to tippy toe to reach the drawbar it's more of a risk for a tool to slip out of my hand. Luckily it has not happened to me yet but I have came close to it happening before. A step stool might help solve this but I ain't got no time for that. :)

Raising my head to gain access to remove a tool with a long arbor is just as inconvenient as lowering the knee on a knee mill. Actually it's worse in my case cause the handle to move the head is on the side of the column behind the table, not in the front like a knee mill. But I can't recall the last time I had to raise the head to remove a tool. I just move the table off to the side & that usually gives me enough clearance to make a tool change with a R8 arbor. With a table powerfeed & DRO I don't mind it all.

My 2" & 3" boring heads are on R8 arbors & I prefer to keep them that way. My 2" Criterion actually came on a short straight arbor & I switched it out to R8. My 1/2" keyless & 14N chucks are on R8 arbors also. I do have another 14N chuck on a straight arbor but to be honest I never really use that one.

The convenience of a straight arbor for me is not necessarily the easier access for tool change, it's the time saved not having to change the collet when using a 1/2" edge finder or indicator then switching to a tool with a 1/2" arbor. But I pretty much defeated that purpose. That 14N I mentioned & my Tapmatic used to be on 1/2" straight arbors but I switched them to 5/8" straight arbors. Maybe one day I'll make 5/8" adapters for my edge finders.
 
Thanks to all that chimed in, it helped me out. I found a nice used Criterion with a straight shaft that should serve me well.
 
With a straight ahank you can set the BH up in a 3/4" boring bar holder on the QCTP and use it as a ball turner.
 
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