Reamer Chatter

What causes it and how do I correct it?

I need to bore a 11/32" hole, +.0015/- 0.000, in 3 aluminum bronze bushings

I tried last night and ended up with a 9 sided hole

seems to me i remember using spiral flute reamers helped some, but all we have is a straight flute...other option is to bore, but bushing is over 3" long, and dont have much in the line of boring bars that small

sugestions appreciated

What rpm are you running the reamer at? The primary cause of chatter, at least for me, is that the speed is on the high side. I start at 1/2 the speed used for a drill of the same size and work down from there.

I havent done a lot of reaming but what I have I
followed the recomendation of a friend who has been
doing this stuff for a long time and he said "turn
SLOW and feed FAST". Seemd to work OK for me.
...lew...

I ream A LOT of . 41, .45 & .5 holes 1.1" - 2.75 deep in 416 SS, 17-4 SS, 4130 Steel, & EDT 150 Steel using a mill. I am trying to get the best finish possible (mirror) and about the same tolerances you are.
I run the straight fluted HSS & Carbide reamer slow (about 1/3rd the drill bit speed) and feed slow. Pull down on the feed lever until you hear the ringing and you hear the just begining of chatter, then slow the feed so you are just below the threshold of the sharp chirping chatter but can still hear a ringing. Use lot's of cutting oil by applying it with a small brush. Using that method will get you a continous chip string. I evacuate the hole when the chip string is about .75 or so long, and blow the reamer off with air, re-oil and start all over again.
Now when I use a lathe to center ream I Use Hartswick's method above of slow speed, fast feed using cutting oil. Keep the reamer as short as needed for the job.
In your case, using a .34375 reamer 3" deep doesn't allow for much ridgidity. If you start getting any harmonics, or the reamer singing, try draping a piece of leather strap over the reamer and clipping it with a clothespin until you have the reamer halfway in and then remove it. It acts as a vibration dampener similar to grabbing it with your hand but without the danger.
ALSO to avoid getting an oversized hole, when you finish reaming your hole in the lathe, stop the lathe and let the part stop turning. Then remove the reamer. Often times removing the reamer while the your part is spinning opens up the hole and drags chips back through affecting the finish quality of your reamed hole.
Hope this helps.

Like Lew and Jack said, slow speed and fast feed. A rule of thumb is 1/2 the RPM of a drill and twice the feed. Also, don't leave too much material to ream out. For 11/32", I would pre-drill with a letter Q.
Boring would also be a good way to guide the reamer straight. Go as deep as your boring bar will reach and then finish with the reamer.
A trick I have used for years is to put a folded piece of paper between the reamer and the workpiece as the reamer is entering the hole. This pulls the reamer into alignment with the hole and dampens vibration before it starts to cut. The nine sided hole you describe is the product of harmonic vibration.

Gordon, you mean that you put the paper over top of the hole and cover it?

That problem of a many sided hole happens to me once in awhile. I call it a "Wankle" after the piston shape. Can anyone explain why. Are spiral
flutes better than straight? Thank You, Old Bill

ugg..im scared to try another with the reamer..i already have to remake one part

and i dont think the material is cheap to try a test piece 3" long

was going around 350rpm..not 100% sure of the SFM of alum/bronze but this has to be close to 1/2 the drill speed

my mistake..its a 19/32nd hole

You could also try dulling the reamer down if need be.

Hone or wire wheel...

Think Snow Eh!
Ox

Way far too fast. Slow it down below 100 rpm.

Leave about fifteen thou for the reamer to take.

Jim

will try 100 rpm...thanks

Slapstick,
Yes, put the paper over the hole and the reamer cuts right through it as it enters the hole. Works great for me. I think that chatter happens because the reamer isn't exactly aligned with the hole and when one tooth hits, the reamer starts dancing around. Once a vibration sets in, it's hard to stop it.

Gordon,
Thanks for sharing the paper trick. I think your analysis of the problem is a good one. I've always found that the ones that don't start smooth are the ones with lobes afterward. Low RPM helps too.