Stub arbor (plus a bonus question)

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Wino1442

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Hi all...I have a couple of "new guy" questions.

I have acquired 2 stub arbors...the 1st is a Shars 1" with a LH thread, the 2nd (which a friend gave to me ) must be Chinese made is a 22mm arbor, but this one has a RH thread..they're both R8 shank. So my question is...why would one be LH and one be RH and/or does it matter?

The bonus question is this: when drilling from a 1/2" hole up to ..say 7/8" how many "steps" would you guys make? Or would you go straight from 1/2 to 7/8 in one shot.

Thanks
 
Many arbors are made left or right hand threads, it largely depends on the direction that the arbor is to be driven, you generally want the nut to tighten in the direction of rotation, so if there is vibration or chatter in the cut, the nut will tend to tighten , not loosen.
 
Wino1442 said:
The bonus question is this: when drilling from a 1/2" hole up to ..say 7/8" how many "steps" would you guys make? Or would you go straight from 1/2 to 7/8 in one shot.
Click to expand...

Depends on how much horsepower you have. In steel I would normally start with a pilot hole the size of the 7/8 bit web, then plow through with the 7/8. In aluminum or other soft materials, I would just drill with the 7/8 and forget about the pilot hole.
 
With my Canedy Otto 21" drill press, I drilled 1-1/4" holes for a boiler tube sheet in one shot, no pilot hole with power feed, followed with a +1/32 machine reamer. It helps to thin the web of the drill when drilling larger holes like that.
Another drilling feat was drilling anchor bolt holes in the base plates for the tower columns for the San Mateo Bridge, one of my tasks as an apprentice, we used a spade drill, I think about 3 1/4" dia. The holes were drilled in one shot, with no pilot hole, as is usual with spade drills, using a 8 ft. arm radial drill with mist coolant.
 
I pilot drill to clear the web and go full diameter after that. For the pilot hole I usally grab drills that are rarely used like 39/67"
 
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