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Reamer cutting oversize???

Billy Boy

Hot Rolled
Joined
Jan 30, 2005
Location
San Francisco, CA
Clearly I've screwed something up, but I just ran 2 test holes with the table locked and my .4990 reamer is definatly cutting .5 + Getting a sliding fit rather than the press fit that I'm looking for on a .5 shaft (actually .4995)

I thought that when reamers lost tolerance they were suppoed to start cutting undersize.

What did I do? I'd like to know so that I don't do it again!

B
 
Very lightly stone the faces of the teeth with a Hard Arkansas file to be sure there are no burrs on the reamer. Try again, if it is still oversize you can try stoning the margins of the teeth.
 
IMO all the above postings are accurate. The other thing that I have found is the cutting fluid. I still use white lead mixed with a good non-detergent oil or the old cool tool when I can find it. I have also heard that lard oil works well for reaming holes the size of the reamer. If I want a hole oversize as you describe I use good old fashion sulferized cutting oil. Best, cdw
 
A few things I've found that can make a reamer go oversize. Too much speed, not enough feed, chucking up too close to the flutes or chopping off the shank. Lack of a lubricant/coolant. On big reamers,
I've run into some oversize problems before on big reamers (7/8 and over) and grinding the flutes off so they are only about 1/2" long worked out pretty well.

As ulav8r suggested stone the flutes, I usually run a piece of carbide down them. This can also work in reverse run a piece of carbide on the inside of the flutes to get it to cut a little bigger.
 
How good was the chuck you were using and were there any burrs on the shank of the reamer?

Normally, I drill the hole 1/64 under the nominal ream size or 31/64ths for a 1/2".

How fast were you spinning the chuck? I usually run the chuck "S L O W" and with lots of cutting oil. I push the reamer thru the hole fast and do not let it run any longer than necessary to clean up the hole. If the hole is too tight, run the reamer a bit faster.-Jerald
 
Step 1, what are your speed and feed?

You should be at 20-35 sfm, and probably .010"-.015" feed per rev. Usually you can get the reamer to cut a little smaller with water-soluble coolant, and a little larger with cutting oil.

Step 2, how bad is your reamer running out? Not at the shank 2" from the cutting edge, but right on the flutes of the reamer? Is it true at the flutes and at the shank?

If not, use a different chuck, collet, or holder that runs true.

Step 3, how much stock are you leaving for finish?

Should be no more than .015", and less if possible.

Check to be sure you're not running into the bottom of the hole if it's a blind hole, that will cause a reamer to try to cut on the side a bit.

If your reamer is checking .4990" across all flutes, then there's no need to stone it. More likely you'll ruin the cutting edge if you don't know what you're doing. You're doing something wrong if it's cutting oversize. The only time you'll need to grind away part of the flutes of the reamer to maintain hole size is if you have runout, and are either unable or too lazy to eliminate it.
 
Ive got to agree with all the above. The only thing that didnt get mention is that some materials just dont ream worth a damn. Any material that is hard to get a good finish on when you turn it (like cold roll,or 4340 in full anneal) is going to do the same crap when reamed. If it tends to tear reaming can be a PITA.
 
Reamers get a built up edge too, usually on a chipped corner so small it's easy to miss. I suggest you go over your reamers edges with a thimbnail and closely examine under magnification were ever it catches. I replace reamers if the edges are nicked and battered from handling. If the damage is light, I often Lay a hard Arkansas wedgie stone in the flute and gently stone a tiny negative rake on the reamer's edge. Stone a tiny bright line representing a 5 degree radial and axial negative rake at the cutting corner.

Don't take too much stock off with a reamer. Locate the hole with a center drill, then drill about 0.010" or less undersized. Then ream. I like to use Tap Magic for reaming really fussy holes. Otherwise most any cutting oil will do. I have reamers I've babied in their factory tubes for 30 years and they still cut to accurate size.
 
When I was an apprentice it was always drill bore ream as the drill may not drill a straight hole allowing the reamer to ream off centre. Leave no more than .005" for reaming 1/2" hole use with plenty of cutting liquid, try this and you will most likely find your reamer cutting to size.
MBB
 
Leave no more than .005" for reaming 1/2" hole
I believe you're a bit shy. Here's a chart from page 31 of the current L&I Reamer catalog:

L&I_Reamer_Allowance.jpg


Quoting from the same catalog page:

"Stock removal on roughing operations should not exceed 2 to 4% of tool diameter in most cases. Stock removal recommendations on finishing operations are .002 to .004."
 
Is your reamer cutting concentricly and coaxially correct? For the best precision you should use a precision piloted reamer and a floating reamer holder like the gunsmiths do. I cut chambers all the time an my .0001 (tenths) indicaters don't reflect any run out on these indicators. The holes are only as true as the reamer and stock set up. You need to dial in on both ends and take two measurements consecutively to get your stock both concentrically and co-axially alligned.
Rustystud
 
.005" works great if you are boring or circle milling first.

I have setup a lot of reamers over the years, indicating them dead true may not help anything, but it sure HURTS nothing. In a general way the more feed the smaller the hole (within reason)....In the job I used them most I had the luxery of usually having 2-3 of about any dia to choose from, undersize and press fit both, I typically picked 2-3 good looking ones, and did everything right programwise (same applies to manual machines) and setupwise, it was not uncommon to find a reamer that cut too big, unusual to find one that cut smaller than it's measured size (but it DID happen now and then)

About 1/4 of the time if a reamer cut overize, one could run it in reverse at say 100 rpm and lightly run a stone over the flutes and make it behave...the rest of the time it was really more time efficient to try the next tool of the 3 hand selects, most of the time you didnt need a third, in fact very rarely. All reamers are NOT created equal either...some are just poop...you'll learn to recognise one over time, and relagate it to use as a pin punch or such hehe

Bill
 
There's a problem with a piloted reamer: If your pilot hole is not straight, the resulting reamed hole will be similarly mis-aligned.

Reamers are self-centering. They do not cut on the edge, only on the face. So once the reamer has cut into the material to its full diameter, it centers in its own hole. I have no problems at all with my L&I reamers.
 
I've had that problem before also when cutting holes to press-fit flanged bushings into. I just put an appropriate sized ball bearing in the hole and bang it with a hammer slightly to deform the lip of the hole.
 
Ok,

The reamer is held in a collet and sqirted liberally with lard oil before and during reaming. I've had to shorten the shank down to about 6", so that may be the issue... except that I was reaming good holes with it like that last week. I am reaming a hole in 1/8" thick O1 steel in the annealed state, and I can't remeber if the RPMs were at 210 or 240.

It does seem as though there are a couple of burs. When I run my finger nail gently down the side of the reamer flutes it gets caught at the very end on a bout 3. I guess I'll grind those out and try again.

I am not currntly in possetion of an Arkansas file or wedgie stone... never even heard of a wedgie stone... googled "wedgie stone" and all that came up was pro westeling and weird porn.

Anyway, I've got a set of nickel/dimond "pocket" stones and an couple of old japanese stones that I could use... though I'm not entirely sure about the geometery that I should use.

I think that I could get the fine pocket stone in under the face of the flute and hit it that way.

B
 
Wedgie stone. Sorry. Personal terminology. A wedgie stone is one that's about 2" x 5" and tapered from about 1/8" along one 5" edge to 3/8" on the other. In cross section it looks like a wedge or the vertical on an exclamation point (!). Hard to beat them for tuning up reamers and drills. I keep a couple of each (hard Arkansas and fine India) on hand and the usable fragments of the ones I busted (they are fragile when dropped on concrete).
 








 
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