Reaming Precautions

Reamer Feeds and Speeds

Feeds and Speeds for machine reaming may vary considerably depending in part on the material to be reamed, the type of machine, and the required finish and accuracy. In general, most machine reaming is done at about two-thirds the speed used for drilling the same material. 

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. It is necessary at all times 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 allowance 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.

In machine reaming, .010” on a ¼” hole, .015” on a ½” hole, up to .025” on a 1 ½” hole, are good starting points. For hand reaming, stock 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 include:

Excessive Speed

• 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 very difficult to keep the cutting edges even.