# RPM of a chucking reamer



## pearldiver (Jan 6, 2010)

I have a cobalt 3/16 chucking reamer that I plan to use to ream on a 303 stainless steel thru hole. Could somebody advice me on the correct RPM. I'am afraid if I ran it to fast or to slow I might break the reamer. :-[


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## joeby (Jan 6, 2010)

The cutting speed for 303 SS with a HSS reamer is 45 SFM. That works out to 916 RPM.

 Use cutting oil (I like to use dark thread cutting oil) and feed enough to keep it cutting. I like to put a slight chamfer on the hole before reaming, seems to help getting started without the sharp edge or possible burr being there.

 Another tip is to ream through, stop the spindle, and then retract the reamer. This eliminates any spiral marks in the hole caused by a cutting edge dragging. It doesn't appear to cause any damage to the reamer, just be careful to pull straight out. Reversing a reamer is not good for it.

 An old rule of thumb for reaming was half the speed used for drilling the hole, and twice the feed rate of the drill. I never checked to see if the numbers were valid with this method, I always just used the recommended speeds/feeds from the book.

Kevin


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## websterz (Jan 9, 2010)

joeby  said:
			
		

> The cutting speed for 303 SS with a HSS reamer is 45 SFM. That works out to 916 RPM.
> 
> Use cutting oil (I like to use dark thread cutting oil) and feed enough to keep it cutting. I like to put a slight chamfer on the hole before reaming, seems to help getting started without the sharp edge or possible burr being there.
> 
> ...



The old timers I learned from always told me "A third less speed, a third more feed". ???


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## BobWarfield (Jan 10, 2010)

My G-Wizard Machinist's Calculator, which is calibrated off several manufacturer's recommended speeds and feeds, is definitely in the 1/3 less spindle rpm and 1/3 more feed.

Here is the HSS Reamer, 3/16", 300 series stainless:







and here is the same size HSS Twist Drill: 






If you want to try G-Wizard, it's free during the Beta Test:

http://www.cnccookbook.com/CCGWizard.html

Cheers,

BW


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## joeby (Jan 10, 2010)

Thanks, guys, for checking up on me!

 The numbers I came up with are from the Machinery's Handbook. It classifies 303 as a free machining stainless and SFM at 70 for drilling and 45 for reaming. 316 is 30 for reaming and 50 for drilling, as your post shows, BW.

 30% less speed looks a lot more reasonable than the 50% I mentioned.

 I consider the book figures to be recommended starting points though.

Kevin


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