Poor Finish in Reamed Holes

[Kim]

I've been noticing that many of the holes I ream come out with these concentric marks in them. You can see it in this picture here:


I used a fairly slow speed (190 RPM), and used lots of cutting oil.

I was worried that the chips were causing this, so I cleaned the chips off every 0.1" or so.  I kept the piece rotating during the in & out process, and always adding more cutting oil during the process.

This is a 1/8" reamer.  I started with a 7/64" hole, which is my normal practice (1/64" below the desired size.)

Am I doing something terribly wrong here?

In this case, I'm sure the finish will be good enough to accomplish my goals, but it does seem like I should be able to obtain better.

Thanks for any thoughts or suggestions you may have on my technique.
Kim

[b.lindsey]

Kim, it could be a dull reamer. They seem to dull fast for what they cost Imho. For a 1/8" hole, I think leaving only about .005 to ream is more appropriate.  I would normally drill with a  .120" drill for a hole that size. Just my two cents.

Bill

[Doc]

Bill I agree reamers do tend to dull quickly especially when cutting to much material. The reamer in the photo looks to me to be pretty dull. The smaller the hole the less you leave .015 would be ok for 5/16 and larger but not for smaller dia. 

[Tennessee Whiskey]

Unless it's the camera angle, the edges do look a bit rolled and not crisp. I've also been told to not "peck" a reamer: let the chips channel into the flutes and withdraw the reamer in a smooth and rapid fashion 

Cletus

[gerritv]

Besides checking for sharpness of the reamer, perhaps consider not using cutting oil as it might be holding the chips and running them around causing the circles. Brass is usually machined dry anyway.

Gerrit

[Kim]

Thanks for the great suggestion!

Eric, I have also heard that you shouldn't peck with a reamer, but I was getting so many chips, I was thinking THAT might be causing the issue. Which it might be.

As Bill and Doc said, I should probably be leaving less material before reaming that small of a hole.  I'll try that next time.

Gerrit, I don't usually use anything when cutting Brass, but again, I was worried that was what was causing an issue with my reamer, so I was trying with Oil for the reaming.

And yes, the reamer may be dull too. though I haven't used that reamer THAT much... but maybe I've just been making it work too hard - leaving too much material for it to remove, filling up the flutes and causing other problems.

Lots of good thoughts here, thank you for the input!
Kim

[jadge]

The reamed finish should be way better than shown. 

It's not entirely clear from the picture, but is the reamer a proper machine (or chucking) reamer and not a hand reamer? What is the origin of the reamer?

For a 1/8" reamer I'd allow about 0.008". For brass, bronze and cast iron I ream dry. For other materials I use a flood of soluble oil. Cutting oil just holds the swarf in place rather than doing anything useful.

A rule of thumb for reamers is half the speed and twice the feed of an equivalent size drill. For a 1/8" reamer in brass I'd be running at 800rpm and feeding as fast as I could wind the tailstock handle. And definitely no pecking - in and out in one smooth movement.

Andrew

[Ian S C]

Have you used the reamer on steel? Use reamers, and other cutting tools on brass first, when it starts to get blunt, then use it on steel.
I'm afraid I'm chicken, I use my reamers at hand speed, and with brass don't stop, and keep it cutting, don't let it rub.
Ian S C

[Kim]

Thanks Andrew and Ian, for more interesting points...

Andrew, the reamer was listed as a "chucking reamer", and though I don't remember for sure where I got it, I believe it was likely Victor Tools.  It was run much more slowly than what you describe.  I always thought you were supposed to ream more slowly than you drilled.  I'm learning a lot from your answers!

Ian, again, I don't remember for sure, but it is not out of the question that the reamer has been used on steel too.  I'm sure its been used in aluminum.  Its probably time for another reamer, and I'll have to start keeping track of what's been used on steel or not...

Thanks again for all the helpful input!
Kim

[steamer]

Have you used the reamer on steel? Use reamers, and other cutting tools on brass first, when it starts to get blunt, then use it on steel.
I'm afraid I'm chicken, I use my reamers at hand speed, and with brass don't stop, and keep it cutting, don't let it rub.
Ian S C

What Ian said...and leave less stock for reaming...I usually drill, bore to .005 under, then ream.  The boring operation straightens the hole and makes it round, and the reamer then follows the straight hole.

The other thing to consider, is the position of the tailstock...It needs to be co-axial with the headstock spindle.  Not only front to back, but up and down as well.

Drills are great at removing stock, but rarely make round straight holes.   A drilled hole that has a lot of run out...not uncommon....will pull a reamer and you will not get a straight hole.   Also, plunge in at about half drilling speed with no pecking and when you finish ...STOP the lathe.   Then withdraw the reamer with the spindle stopped. 

Dave

[DTR]

What Ian said...and leave less stock for reaming...I usually drill, bore to .005 under, then ream.  The boring operation straightens the hole and makes it round, and the reamer then follows the straight hole.

Please forgive my ignorance, but why ream AFTER boring? I don't understand what reaming achieves that the boring didn't?

(Apologies to the OP for hijacking the thread)

[fumopuc]

Hi Dave, I would say, a drilled hole is a hole but not with a proper round shape.
If you need a round shape i.e. for rotating a shaft inside, than the result of drlling with following reaming will give a much better result.

[crueby]

Hi Dave, I would say, a drilled hole is a hole but not with a proper round shape.
If you need a round shape i.e. for rotating a shaft inside, than the result of drlling with following reaming will give a much better result.

Dave's original question, I think, was why reaming after using a boring head (mill) or boring bar (lathe). I have the same question - doesn't a boring head/bar give a round, located hole, is reaming after that neccessary?

Chris

[AOG]

Reaming after boreing gives you a very accurate hole. You may not be able to achieve the same level of accuracy by just boring (particularly when using a boreing head in the mill).

Tony

[b.lindsey]

Typically the reamer would give you a smoother finish to the hole. The boring prior to reaming assures it is round and straight. Depending on how much care is taken with the boring operation the bored hole and the reamed hole could be almost identical as far as smoothness though. The definition I always used for reaming when teaching the machine shop class was that it gives you an on size and smooth hole. As others have said though, it won't correct for a wandering hole if the drill doesn't drill straight and thus the need for boring to true the hole up. For most of us though, reaming 3/8" holes or smaller, boring becomes a more tedious thing. The boring bar must be smaller and therefore less rigid. Despite the theory, for holes say 5/16" or smaller, like for shafts to run in for example, I just drill and ream, but do try as much a possible to make sure the drill is sharp and properly ground so it wanders less, and giving it a good start with a center drill or spotting drill. For me this has worked successfully almost all of the time. Just my take on it.

I do disagree with Steamer on one point though. I think the reamer should go in and out both under power, but withdrawing it should be even faster than the reaming cut going in to minimize any rubbing of the flutes.

Bill