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chas
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Re: reaming

Post by chas »

waltsweet wrote: Fri Jan 21, 2022 9:10 am For years, I've been buying reamers from Gammons in Manchester, CT*. The cost has been well-worth the experience it gave me. My preferred design has a right-hand cut and left-hand spiral (RHC, LHS). Cobalt-steel costs a little more (and takes a little longer to deliver) but it lasts much longer; for all the trouble and expense, I want it to last longer than HSS. I request TiN coating to reduce friction. Step-drilling relieves some of the wear on the expensive reamers. I know that the simple, homemade reamers can work, but I got tired of fighting with them. When I'm considering a new bore, I prototype it by making a smooth core and molding resin around it.
I use a LeBlond machine lathe because it can develop the torque and it has a large spindle bore so I can put the workpiece deep inside the headstock. For reaming, I have a rotary union at the far left end; a plug in the spindle has a conical seat at the workpiece for a rudimentary seal. Thru the hole in the plug, compressed air drives the chips out of the reamer flutes. In this arrangement, reamer flutes of perhaps 1/8" deep are desirable to maintain pressure differential. Also, with shallow flutes, the core has a larger diameter to resist torsional flexing. Such twisting can ruin the smoothness of a deep hole. I don't design the reamer around the idea of deep flutes to hold chips; quite the opposite. The spiral can reduce chatter but has no value in removing chips,
Many of my reamers have six flutes, but my latest have 5. With five flutes, the "tooth load" increases, which means that more of the force results in cutting, rather than just overcoming friction. More flutes (more cutting edges) means the tool will stay sharp longer, but the driving force increases. As mentioned, the machinist's principle is this: if you have more tool engaged in the work, you're going to need more torque, more horsepower, and you'll have less control. A metal workpiece doesn't flex much, but wood does, so the extra force compounds the problem. In the past, I specified reamers ground with "chipbreakers" as on some milling cutters. The point is to increase tooth load, but designing is tricky and the resulting surface is not as smooth. For small and simple reamers, I specify "blank back" which means a six-flute pattern where 4 are cutting edges and 2 flutes are not there (the tool has a smooth arc instead). More affordable and quicker delivery.
* Of course, Paul S. is in no position to advise you on acoustic considerations. The standard machine tapers (morse tapers) are of limited use. Paul knows metalworking and can suggest these ideas plus whatever has been successful for others who make woodwinds (bagpipes and clarinets).
Thanks for those ideas, Walt. I might think about getting a new reamer for only that section with fewer flutes. I have felt like the six flutes create a lot of friction without much cutting.

I've had a few conversations with Paul and have found him very helpful.
Charlie
Whorfin Woods
"Our work puts heavy metal where it belongs -- as a music genre and not a pollutant in drinking water." -- Prof Ali Miserez.
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