Technical Ream Hints
Reaming Speeds – Speeds for machine reaming may vary considerably depending in part on the material to be reamed, type of machine, and required finish and accuracy. In general most machine reaming is done at about 2/3 the speed used for drilling the same material.
Reaming Feeds – Feeds for reaming are usually much higher than those used for drilling, often running 200% to 300% of drill feeds. Too low a feed may result in excessive reamer wear. At all times it is necessary that the feed be high enough to permit the reamer to cut rather than to rub or burnish.
Stock to be Removed – For the same reason, insufficient stock for reaming may result in a burnishing rather than a cutting action. It is difficult to generalize on this phase as it is tied in closely with the type of material, feed, finish required, depth of hole, and chip capacity of the reamer. For machine reaming, .010” on a ¼” hole, .015” on a ½” hole, up to .025” on a 1 ½” hole, seems a good s starting point. For hand reaming, stoke allowances are much smaller, partly because of the difficulty in forcing the reamer through greater stock. A common allowance is .001” to .003”.
Alignment – In the ideal reaming job, the spindle, reamer, bushing, and hole to be machined are all in perfect alignment. Any variation from this tends to increase reamer wear and detracts from the accuracy of the hole. Tapered, oversize, or bell-mouthed holes should call for a check of alignment. Sometimes errors from misalignment can be reduced though the use of floating or adjustable holders. Quite often if the user will grind a slight back taper on the reamer which will also be of help in overcoming the effects of misalignment.
Chatter – The presence of chatter while reaming has a very bad effect on reamer life and on the finish in the hole. Chatter may be the result of one of several causes, some of which are listed:
Too much clearance on reamer
Lack of rigidity in jig or machine
Insecure holding of work
Excessive overhang of reamer or spindle
Excessive looseness in floating holder
Too light a feed
Correcting the cause can materially increase both reamer life and the quality of the reamed holes.
Coolant – In reaming, the emphasis is usually on finish and a coolant is normally chosen for this purpose rather than for cooling.
Reamer Regrinding – In obtaining maximum economy from reamers the same principles apply as in the case of most other cutting tools. One of these principles is not to allow a tool to become too dull. It is best to regrind the chamfer on a reamer long before it exhibits excessive wear or refuses to cut. This sharpening is usually restricted to the entering taper or chamfer. It can be done on almost any tool and cutter grinder. Care must be taken so that each flute is ground exactly even or the tool is apt to cut oversize.
Sharpening the chamfer on a reamer by hand is not recommended as it is practically impossible to keep the cutting edges even.