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klemchuk
02-21-2011, 12:05 AM
Can anyone explain why a new .999 reamer going through a 31/32 drilled hole will make a hole that a 1.000 shaft will go through with just hand pressure? Rhe reamer is brand new, it mikes at .999 and that was the very first hole. The set up was in my mill, I drilled the undersized hole and with no change in the setup except to put in the reamer, and got an unacceptable result!

becksmachine
02-21-2011, 12:20 AM
Welcome to the club! ;)

The hole could have been misaligned because the drill wandered, maybe .030" was too much to ream, maybe the hole was that size before the reaming operation, maybe the lubrication was insufficient, etc.

What thickness material was this in? Did the reamer flutes get clogged and shove the reamer off center?

Dave

rockrat
02-21-2011, 12:29 AM
I cant say I know all the voodoo that is present with using reamers for tight tolerance work but, I watched a fellow stone a reamer one way for an undersized hole and he stoned it another way for an oversized hole.

Other issues with tight tolerance reamer work include chuck run-out, feeds and speeds, pre-drill size, rigidity of the setup, coolant and or material.

I will often try a reamer out on a scrap piece of similar material if I am worried about tolerance. Just something that an old Indian taught me.

rock~

Stepside
02-21-2011, 12:09 PM
My preference is to drill the hole close to size and then use a boring bar or boring head to get closer and then ream the last .005 to .010.

Unless a drill is "perfectly sharpened" they don't always drill round holes. The reamer will try to follow the drilled hole. The boring bar should provide a round hole that is straight as well.

I like to ream at a slow speed with lots of oil.

Lew Hartswick
02-21-2011, 12:14 PM
I've always been told: Ream at 1/2 speed and feed at twice speed.
I usually use even bigger ratios. Maybe even 3 or 4 .
...lew...

Toolguy
02-21-2011, 12:47 PM
New reamers often cut a bit oversize due to the sharp corner at the bottom of the flute. Usually they will settle down after running through a few holes and be right on. Good advise above too. Especially on larger holes (over 1/2") I like to bore the hole too, to make sure it is straight and on location. Sometimes I will use a regrind (undersize) endmill to bore with, it's quicker and easier than setting up the boring head.

Rustybolt
02-21-2011, 02:58 PM
My opinion.
31/32 leaves too much in the hole try a 63/64 drill. A lot of times there is a wire edge on the cutting edge of a new reamer. Take a piece of polished rod, drill rod will do, and run it smartly along the cutting edge at 90 deg to the edge. This lays the burr down and the reamer should cut to size.

dian
02-21-2011, 03:02 PM
if you try "coolant" instead of oil, you might get a smaller hole. assuming this is in steel.

krutch
02-21-2011, 04:59 PM
.030 is too much and the drill can cut an out of round hole and wander. All these things will contribute to an out of spec hole. Plus the comments of earlier posts apply. Any out of true rotation of the ream, such as a burr/chip on the shaft/collet, will be shown in the finished hole.
I think that +.015 is a better material condition for most ream work, at least for me.
There was a guy at a former work place that would drill then bore a hole before reaming. He did this on a new BPTrac with 3 axis control. He never had anything come back for rework, but it took longer.

ckelloug
02-21-2011, 07:42 PM
Reamers expand when they cut based on the fact that the hole is applying a torque to the reamer. If it's making a hole that's oversize, logic dictates that you want to drill a larger hole before you start reaming. I've never tested this precisely but it's what I took from the charts at Yankee Reamer.

vpt
02-21-2011, 07:50 PM
I haven't used my reamers much but when I have I always start with one reamer under size just to make sure. Then the final reamer doesn't have to take off so much material and I found leaves a nicer finish.

lane
02-21-2011, 07:59 PM
Your hole was too small. Use a 63/64 drill will be better . No more tan .007 per side for a reamer. And large holes over 1/2 inch are hard to ream and hold size any way. Usually for any thing over 3/4 I bore it if I need to hold size .

Carm
02-22-2011, 08:15 AM
Can anyone explain why a new .999 reamer going through a 31/32 drilled hole will make a hole that a 1.000 shaft will go through with just hand pressure? Rhe reamer is brand new, it mikes at .999 and that was the very first hole. The set up was in my mill, I drilled the undersized hole and with no change in the setup except to put in the reamer, and got an unacceptable result!

L&I recommends a start hole 95% of finish.
You didn't state what an acceptable result was.
Can't have run out, floating holder solves that.
Best results with starting rotation just as reamer engages work.
Half drill RPM (+-), twice feed.
Ream a test hole before using your reamer. Mike the size. I have reamers to make holes within a half thou, some are three under.
If you want something dead nuts, use a boring bar.

airsmith282
02-22-2011, 10:00 AM
its possible to that your bar stock is not the mesurment you might have read it to be so perhaps its the under sized part and the hole is fine or you got a bad reamer , reamers are supposed to be made to goto the percicse size needed, so you could also have a defective reamer that is possible. you try runnning a few more holes and if it settles down then it was to sharp of edges which is possible if it does not settle down then try fitting other bare stock peices and see if perhaps with you thoght was this or that was not, of all else failes then take some 1 and 1/8 or waht ever you got and turn it down to 1 inch as needed or what ever the size maybe, if your using calaipers to measure with then, make sure you have a micrometer that is set up right then remeasure, calipers of any grade or price level are no where near the accuracy of a decent micrometer thats claibrated properly..

ckelloug
02-22-2011, 12:09 PM
One other thing I've learned, the torque effects are also dependent on what the material is you are reaming. Tool steel is a lot harder to get right than aluminum.

Rustybolt
02-22-2011, 02:04 PM
A lot of what you call torque effect is chip loading. The chips can get so packed that it is the chips that are cutting and not the reamer. Flood the reamer with coolant or withdraw it frequently.