Ream or bore?

[Steamchick]

The principles I was taught in the 1960s - if true and still hold today - are:
Boring and honing:
The boring tool transcribes a true circle - which is then passed along the axis of the bore to give a true alignment and cylindrical shape to the bore. The honing process "flattens the peaks" of the machined surface - so the only about 50% of the depth of the machining is retained - thus providing microscopic bearing surfaces and adjacent valleys that retain oil for lubrication. The diamond cut from honing is seen on the surface - and with a small enough "grit" of the stone / abrasive leaves small transitional grooves in the texture of the bore - which permit movement of the lubrication around the surfaces.
A reamer - with multiple cutting edges actually cuts with a natural frequency "wobble"... Like a 3 pointed tool can cut a 4-sided hole - The "multi-faceted" reamed hole is always the number of cutting edges plus 1 number of facets. The shape of the facets is curved, the same a a multi-sided coin is made in order to roll inside slot machines, so the diameter is "true-size" but the centre is actually not a single point but describes the same multiple point connected by curves as the tool has described. However, this only really happens when the reamer is "unsupported" during cutting. When used from the tail-stock of a lathe (other other machine location) the machine resists these forces that want to "wobble" the reamer, so the "highest" cut of the reamer describes a circular hole as it transits a bore. In this case, depending on how secure the reamer is held, how stiff the lathe (or other machine) is within the integrity of the structure, and how accurately the reamer is aligned to the true axis of the bore, will depend on how well reamers make a bore.
But that was the theory I learned in my apprenticeship.
"Tool-makers" know better - as they have it "in their blood" to have very accurately set-up machines, that are relatively "stiff" (compared to the forces involved in machining), and have the best training, experience and practices. But as an amateur - with "imperfect, cheap machines" and methods, I always bore - as reaming has produced the "multi-facets" on one or 2 jobs. (maybe 3 or 4?).
The multi-faceting of reamers has been "Pooh-Poohed" by some I have spoken to in the past, but they are the proper machinists who couldn't give a jot for theory, as they know best. My cheap drilling machine could make a faceted bore quite easily! So "beware the Jabberwock, and cut him no slack", for "slack" allows him to spoil your machining!
K2

 

[goldstar31]

Morning Ken
Thank you for a very expansive expose and with aging sight, I confess to missing a great deal of detail. I hope that others who arte more fortunate - wil, read , learn and inwardly digest the contents.

I was, however, somewhat amused by the term 'the peaks' created in a bore prior to honing. Two points arose and the first one was that I recall 'coring' with coarse abrasive with a Buma bar. Or has dementia finally happened? The second was the words about 'flattening the peaks' wheras the use of a pointed tool in boring seems to create a thread as in screwcutting-- which it is. We gear up a leadscrew to advance and retard progress or try to do it as of old, by hand. It's back to Archimedes or even Gutenberg and his wonderful Bible and cutting wooden gears but friend Maudsley 'did not invent screwcutting'
Then we get to 'parallelism' , a term beloved of nasty geometry teachers for the embarrassment of pimply , snotty nosed street urchins of which I claim membership.
Then comes the 'schoolboy mistakes' of expecting a undersized drilled hole to be corrected by a succession of drills of increasing size. If the drills are thin enough, they will happily follow( blindly) the earlier curve. The famous problem of trying to drill an 1/8th inch diameter bore in African Blackwood almost a whole 13 inches of a D bit fashioned from silver steel rod. I was sort of brought up by a clock and watchmaker who made Northumbrian bagpipes in Ryton of all places! Sounds of derisive snorts as the snots migh remain but my pimples have gone!
Then- I'm nearly finished' is the odd belief that there is a difference between a a twised bit of carbon or tool steel needing to be different to make a drill and make a milling cutter- be it end mill, slot drill or whatever.
They ALL - cut spirals.
Well that;s my opinion

Norman

 

[Richard Hed]

The principles I was taught in the 1960s - if true and still hold today - are:
Boring and honing:
The boring tool transcribes a true circle - which is then passed along the axis of the bore to give a true alignment and cylindrical shape to the bore. The honing process "flattens the peaks" of the machined surface - so the only about 50% of the depth of the machining is retained - thus providing microscopic bearing surfaces and adjacent valleys that retain oil for lubrication. The diamond cut from honing is seen on the surface - and with a small enough "grit" of the stone / abrasive leaves small transitional grooves in the texture of the bore - which permit movement of the lubrication around the surfaces.
A reamer - with multiple cutting edges actually cuts with a natural frequency "wobble"... Like a 3 pointed tool can cut a 4-sided hole - The "multi-faceted" reamed hole is always the number of cutting edges plus 1 number of facets. The shape of the facets is curved, the same a a multi-sided coin is made in order to roll inside slot machines, so the diameter is "true-size" but the centre is actually not a single point but describes the same multiple point connected by curves as the tool has described. However, this only really happens when the reamer is "unsupported" during cutting. When used from the tail-stock of a lathe (other other machine location) the machine resists these forces that want to "wobble" the reamer, so the "highest" cut of the reamer describes a circular hole as it transits a bore. In this case, depending on how secure the reamer is held, how stiff the lathe (or other machine) is within the integrity of the structure, and how accurately the reamer is aligned to the true axis of the bore, will depend on how well reamers make a bore.
But that was the theory I learned in my apprenticeship.
"Tool-makers" know better - as they have it "in their blood" to have very accurately set-up machines, that are relatively "stiff" (compared to the forces involved in machining), and have the best training, experience and practices. But as an amateur - with "imperfect, cheap machines" and methods, I always bore - as reaming has produced the "multi-facets" on one or 2 jobs. (maybe 3 or 4?).
The multi-faceting of reamers has been "Pooh-Poohed" by some I have spoken to in the past, but they are the proper machinists who couldn't give a jot for theory, as they know best. My cheap drilling machine could make a faceted bore quite easily! So "beware the Jabberwock, and cut him no slack", for "slack" allows him to spoil your machining!
K2

The wobble should be minimized with more cutting blades. Also, there are different types of reamers, one type with spiral blades. I thimpfk those spiral type would have minimized this effect.

 

[almega]

I typically only use reamers on smaller holes, which would be difficult to bore and I run my reamers relatively slow to reduce the amount of "wobble" and that seems to give good results with very clean, uniform holes. Anything larger than, say 1/2" and not too deep, I try to bore with numerous spring cuts to "smooth" out the bore and then if further refinement is required either hone or lap the ID. The larger IDs can be deeper, as the boring bars are more stout and less prone to flex.

 

[Steamchick]

The wobble should be minimized with more cutting blades. Also, there are different types of reamers, one type with spiral blades. I thimpfk those spiral type would have minimized this effect.

Hi Richard, the spirals give spiral multi-faceted bores. It is a dynamic effect- usually due to a slack quill as on my drill/mill - but eliminated with close sliding fits on the machine. The wrong speed can cause a resonant chatter that causes it to happen. A curious effect, usually worse on parallel cutters, as the initial taper tends to control the tool when there is a lead.
K2

 

[goldstar31]

Well it is the Ides of March and March Hares are a-bounding.
To my dismay, I have found a fault or faults to suggest that my lat drill and reamer jobs are out by an annoying gnat's c***. So Im arming myself with dial gauge capable of reading a deflection of 'half' of a range of a tenths of a thous.
Oddly there are two new drill chucks which are purported to be high quality. Rohm--- but tonight- one on the Sieg C was jammed, freed with a open ended spanner and a pat or not much more with the palm of my hand. But--- it ain't a Rohm. Now to find what is good, bad or indifferent in my outside little workshop.
One nice thing is that this afternoon's episode of making gear from rusty metal has proved the worth of the Diamond tooling from Eccentric. They came with a had written greetings card. Courtesy is not dead!
Do people accept what comes in the box?

More anon.

Norman