- Joined
- Mar 26, 2018
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I am finishing a number of timing pulley bores on the lathe and want to achieve a finger press onto a ground 16mm motor shaft. The pulleys are aluminum and currently have a 12mm bore. Before starting the actual pieces I ran half a dozen test pieces in 6061-T6 bar stock. I attempted to use a very cheap (I mean ~$4 cheap) 16mm reamer but not surprisingly it cut like crap (it also has a significant amount of taper along it's length (~0.001-0.002")). My next attempts were fine feeding an indexable boring bar (TCMT21.51 insert) working my way up from the 12mm to 16mm and cutting the last pass at 10 thou off the diameter. It gave an amazing finish and was on size easily within +/- .001 (.0254mm) or less.
My issue is that 15.98mm is quite a bit tighter than a finger press and 16.02mm is a sliding fit. I did hit a few of my test pieces around 16.004mm which went on very nicely, but I'm struggling to get a reliable process to cut them like that every time. Here's my thoughts which I hope someone can chime in on!
1) My roughing cuts going from 12mm to 16mm are not always the same and might be leaving variable amounts of stock for the two finishing passes. Not surprisingly this would change the cutter deflection and change the finished diameter. Is there some magic way to approach a bore size so you don't have to do anything crazy to hit a nice tolerance?
2) If a part came out undersized and I tried to just kiss the diameter with a few tenths, my cutter would rub rather than cut. Eventually I would bump it enough that it would "bite" and blow the hole way over sized. I think a aluminum specific sharp insert (like a TCGX) would avoid the rubbing? Would a smaller nose radius improve this (like a TCMT21.50)? What about those cheap brazed carbide boring bars?
3) Suck it up and buy a better reamer...
I know there are many tricks of the trade for more precision operations, so I'd love to hear anything you guys can share!
Thanks!
My issue is that 15.98mm is quite a bit tighter than a finger press and 16.02mm is a sliding fit. I did hit a few of my test pieces around 16.004mm which went on very nicely, but I'm struggling to get a reliable process to cut them like that every time. Here's my thoughts which I hope someone can chime in on!
1) My roughing cuts going from 12mm to 16mm are not always the same and might be leaving variable amounts of stock for the two finishing passes. Not surprisingly this would change the cutter deflection and change the finished diameter. Is there some magic way to approach a bore size so you don't have to do anything crazy to hit a nice tolerance?
2) If a part came out undersized and I tried to just kiss the diameter with a few tenths, my cutter would rub rather than cut. Eventually I would bump it enough that it would "bite" and blow the hole way over sized. I think a aluminum specific sharp insert (like a TCGX) would avoid the rubbing? Would a smaller nose radius improve this (like a TCMT21.50)? What about those cheap brazed carbide boring bars?
3) Suck it up and buy a better reamer...
I know there are many tricks of the trade for more precision operations, so I'd love to hear anything you guys can share!
Thanks!