How useful are reamers?

How useful are reamers?

Joined: March 8th, 2004, 11:48 pm

July 1st, 2018, 8:32 pm #1

I have drilled a lot of holes in my life but have never used a reamer. I see them a lot in machining videos. Have I been doing it wrong my whole life?
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Joined: January 11th, 2016, 8:57 pm

July 1st, 2018, 10:52 pm #2

Drills can leave holes in thin or soft materials that are triangular, rather than circular; that are slightly larger than the diameter of the drill; or that tend to wander off-track in long holes. Tapered reamers create nice circular holes. Parallel reamers create perfectly straight, circular on-size holes.

It becomes a matter of the right tool for the job. If you want a hole to put a bolt thru a piece of steel plate, use a drill. If you want to enlarge a hole in thinner material, and keep the hole fairly circular, use a tapered reamer. If you want a hole to create a circular bearing surface (eg, the wrist-pin / gudgeon-pin holes thru a piston,)  use a parallel reamer (with a guide, if you need a perfect hole,) use it slowly and take tiny cuts. Clean the swarf out frequently.

in engineering, a reamer is to a drill as a scalpel is to a chainsaw in surgery.
Breakfast.com halted. Cereal port not ready.
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Joined: October 24th, 2014, 10:51 pm

July 2nd, 2018, 12:01 am #3

Put concisely: Drills don't leave a precisely-sized hole, nor are they guaranteed to be round. A reamer creates a hole of a specific size and makes it round. If you don't need a round hole of a precise size, you don't need a reamer.
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Joined: June 2nd, 2015, 3:34 am

July 2nd, 2018, 12:30 am #4

Reamers are mostly for tool-and-die or mold-making levels of precision -- I've done plastic and sheetmetal and never reamed a hole.      Now when I was in the toolroom,   many hours were passed arguing about which drill, which reamer and proper reaming.     Never used it outside of those situations though.
It is possible to commit no mistakes and still lose. That is not a weakness. That is life.
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Joined: October 8th, 2014, 2:05 pm

July 2nd, 2018, 1:13 am #5

Lord [Redacted] wrote:
July 2nd, 2018, 12:30 am
Reamers are mostly for tool-and-die or mold-making levels of precision
Also firearm chambers. Guns tend to behave better when the part holding the "Boom" has a consistent size and shape.
If it ain't broke, I'll fix it!
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Joined: January 1st, 1970, 12:00 am

July 2nd, 2018, 1:26 am #6

I use reamers all the time.

As noted above, their main strength is they make round, on-size holes. Typical twist drills are not actually what you'd term "precision" cutters- a typical well-ground or new drill, properly used and spotted, will give you a hole generally plus-or-minus .002" to .005" of the marked size.

And, also as noted, they don't always give you a perfectly round hole. "Triangular" is the common description, but "lobed" would be more accurate. Especially in sheetmetal, you can- commonly- get a hole that has three spots that are larger in OD than the rest- a vague hint of a Wankel rotor shape.

99% of the time, nobody cares. The "high points" are only a few thou larger, and the hole just has to pass a screw shank, the body of a bolt, or in the case of a paintball gun, it just has to let pressurized gas through from one part of the gun to another.

When you need more accuracy, where the hole needs to more precisely fit a pin or a shaft, then you ream it. Reamers are a finishing tool- you drill to around .005 to .010" undersize, depending on diameter and material, then- preferably in the same setup- you run the reamer through to shave off that last little bit that makes it round and to a just-so size.

I use them a lot because I'm always needing to get a fairly precise fit, typically for an O-ring seal, or a bolt passage, or a press fit.

Not everyone needs them or uses them- or may need to make a round, smooth on-size hole, but they use an endmill instead. I just did that the other day on the small wheel for my belt grinder. I drilled the hole undersize, and since the shaft of the wheel was 0.624", I simply re-located the hole after the welding was done, and shaved out about 20 thou, giving me a nice smooth, snug 0.625" hole.

If you don't need the location precision, or precision diameter, or smooth bore, then no, chances are you don't need a reamer.

Doc.
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Joined: June 2nd, 2015, 3:34 am

July 2nd, 2018, 2:05 am #7

hinermad wrote:
Lord [Redacted] wrote:
July 2nd, 2018, 12:30 am
Reamers are mostly for tool-and-die or mold-making levels of precision
Also firearm chambers. Guns tend to behave better when the part holding the "Boom" has a consistent size and shape.

Good point,  I often forget about the gunsmithing trade. 
It is possible to commit no mistakes and still lose. That is not a weakness. That is life.
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Joined: January 11th, 2016, 8:57 pm

July 2nd, 2018, 2:22 am #8

And reamers are about the only practical way of creating Machine Tool Tapers - I tried cutting a Morse Taper in the lathe with a boring bar. It was nearly as successful as a chocolate coffee pot.....

And just to keep it interesting expensive - there are 9 standard Morse Taper sizes - they have angles with figures out to 4 decimal places, and only 2 of them have the same angle, so there's not one single reamer for all MTs, or even to suit a couple of sizes. (Can you accurately set your compound rest to 1.4377 degrees? Your tapers don't grip if the angle isn't exact, and unless the bore is as smooth as glass. Only a reamer works.)
Breakfast.com halted. Cereal port not ready.
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Joined: November 30th, 2014, 1:36 am

July 2nd, 2018, 4:06 am #9

In machining it's good to remember that drills are seldom to size or position (talking thousandths), reamers follow a hole and bring it to size and bored holes are usually on position but problematic to size in the .0001 range (I have some "Tenthset" heads that will do it but are a little finicky).

So, to get a hole on position and to size (in .0001) you generally drill for material removal, bore for position and ream to final size.  

Fortunately most of the time you only really need to punch something close and can just drill the dang hole.
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Joined: October 24th, 2014, 10:51 pm

July 2nd, 2018, 4:34 am #10

Beejay5169 wrote: And reamers are about the only practical way of creating Machine Tool Tapers - I tried cutting a Morse Taper in the lathe with a boring bar. It was nearly as successful as a chocolate coffee pot.....

And just to keep it interesting expensive - there are 9 standard Morse Taper sizes - they have angles with figures out to 4 decimal places, and only 2 of them have the same angle, so there's not one single reamer for all MTs, or even to suit a couple of sizes. (Can you accurately set your compound rest to 1.4377 degrees? Your tapers don't grip if the angle isn't exact, and unless the bore is as smooth as glass. Only a reamer works.)
Or you use the right lathe - the one that has the taper attachment.😋
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