Reaming Bronze

[jtrout13]

Hi, I am having problems with my reamed holes, I thought maybe advice would help?

I am attempting to ream out a hole in a bronze bushing for a 3/16in shaft to run free inside it. (shaft is 0.1875in, hole is being reamed 0.1885). I have used these clearances successfully in the past on several applications for shafts.

First, when reaming this bronze, I am using regular cutting oil and running the lathe at 1200RPM. This came from the speed/feed chart in the shop. I find that when I put the reamer in, the cutting oil immediately burns off, leaving a black coating on the end of the reamer which smokes for about 30 seconds before being cool enough to touch. Even after I reamed the holes through (eventually ended up doing it dry), they are now still too small to fit my shaft through.

I will most likely end up putting them on the mill and running the reamer up/down ten or so times through the holes to loosen them a bit. However, I just wondered if there is some special technique I need to be using when reaming on the lathe or when working bronze ??

 

[f350ca]

1200 rpm seems awfully fast for reaming. You can ream that fast but heat build up as you saw is going to kill your reamer.
A trick I use to over ream a hole might help you. Place a piece of shim stock, the thickness you want to enlarge the hole over one of the flutes. In this case .001 inch? As you run the reamer in the shim stock will force the reamer over that much and make the one flute do all the cutting. Works really well for me.
Greg

 

[Jasonb]

Sound way too fast to me at that size I would be going at 100rpm or less.

What size did you drill? you only want to be removing 2-3 thou with teh reamer.

Jason

 

[Foozer]

Seems to fast, when I was, I grabbed a slow motor (300rpm) to ream with. Those times when I needed the hole just a tad, say 0.001 larger than an available reamer, laying a toothpick in one of the flutes prior to reaming would do the trick.

Spinning them to fast just burned the tips dull which meant going to a first OS 0.202, small oops. Second OS 0.218, bigger OOPS up to an including a red faced full over 0.247. Slow and easy...

Robert

 

[gbritnell]

Several things. Brass and especially bronze require an extremely sharp cutting tool so if yours is worn at all it won't cut. Second, you never need to use a cutting fluid for brass or bronze. Even though it's a cutting type fluid it makes it that much harder for the flutes on the reamer to cut the metal. Lastly, if you are only taking .003-.004 with the reamer it will tend so skate over the surface. Allow a little bit more material for the final reaming. And yes your rpm is too fast. I would say somewhere around 500 should be good.
gbritnell

 

[dvbydt]

A few pointers - it depends on what spec bronze, did it drill OK, if so, it should ream. Machine reamers only cut on the front chamfered end, they are barrel ground on the O.D. If you wish to make a machine reamer cut oversize, run a sharp tungsten tool along the flutes so as to raise a slight burr on the OD of each flute. This is only a temporary measure, but might get you out of trouble. Hand reamers, usually with a square driving end, have a long taper on the flutes at the front. These cut on the flutes and are pretty useless on a lathe. If you have a cutter grinder it is worth sharpening the front of a machine reamer but not a hand reamer they never seem to cut how you want them.

Hope this helps,

Ian

 

[jtrout13]

To ream at 0.1885, I drilled at 0.1710, which is 1/64in undersize (the closest drill I have).. So you guys recommend reaming at much slower speeds than drilling? I drilled at 800 RPM and thought I needed to go faster to ream it, for some reason. I've been having inconsistent results with all my reaming, so I'd like to get this straightened out.

 

[MachineTom]

Did you mic that 3/16 shaft, Is it really .1875. Most round stock will be +/-.001 at that size, If Ground and polished -.0005 +.0000 if sold as shafting often with keyway -.001 undersize.

 

[Ken I]

You ream at much slower speeds than drilling typically 1/3 - 1/4 normal sfm - also relatively higher feed rates (since you have 6, 8 etc. flutes cutting an once).

You should have no trouble reaming bronzes - even aluminium bronze as long as your reamer is sharp and you don't feed too slowly (work hardening / rubbing problems).

If you get smoke whilst reaming (other than the odd wisp) - you're doing something wrong.

1200 rpm way too fast - 300-400 recomended.

Ken

 

[Ned Ludd]

Hi Ken,
If you are taking out 1/128in you will have to be very careful that the flutes are not getting stuffed full of swarf. As you can imagine the slightest excess will cause the reamer to rub and not cut which will just generate heat and soften your reamer, which is most likely made of carbon steel. A hand reamer can be used in a lathe or mill but try to remember that they are normally turned at "hand speed" not machine speed. Oh and clear the flutes every few turns.
Ned

 

[Ken I]

Ned, Good point about choking the flutes - I'm typically working in metric with 0.1 step drills - nearer to half of 1/128" so I've never really found this to be a problem but of course I still take care.

If the reamer starts to squeeeeeek its time to back it out and not go more than 2/3 of that on subsequent depths. etc. etc.

Regards,
Ken