What is a Reamer?
Reamers are rotary cutting tools with one or more cutting elements used to enlarge to size and contour a previously formed hole.
Its principal support during the cutting action is obtained from the workpiece.
Maintenance and Salvage
Any inexpensive tool may seem economical initially, but one must ask, “Which is the most inexpensive in overall cost?”
In designing a special reamer the engineer has to consider maintenance costs.
These usually indicate the adoption of inserted-blade types as solid reamers wear quickly and have little salvage value regarding straight hole work.
Taper reamers can be reground many times before its size is lost, but on straight holes the adjustable type provides lower overall cost.
With a solid straight reamer, the only way to salvage it is regrinding to a smaller size or to convert it into some other type of tool.
Floating Fixtures vs. Floating Holders
When a reaming fixture is light in weight, it is practical to use a rigid drive and allow it to “float” on the reaming table.
If the fixture is heavy, it is more advisable to use a floating holder drive to allow for self-alignment.
In screw machines and turret lathes, the reamer will always follow the bored or drilled hole, and if a rigid holder were used, a tapered or “bell-mouth” hole will result.
Therefore, the proper style of floating holder must be specified. It must be “full” floating and allow the tool to adjust itself in directions freely and easily.
This type of tool is used in many ways and is valuable when precision and true alignment are necessary.
It may consist of either a solid or shell style and be as long as 4 ft. or 5 ft. and occasionally even longer.
For long setups, the best practice is to use adjustable shell reamers with straight holes to fit the reaming arbor.
On short setups, solid reamers are used for smaller sizes, but the adjustable type can be used on all jobs where size will permit.
Straight-line reaming calls for special reamers.
As long as the designer aligns to the correct specifications for cutting-edge details, coupled with good common sense regarding the arbor and hole diameters in the bodies of their shell reamers, they will have little to no difficulty.
It is the seemingly easier jobs that designers most often run into difficulty, mostly due to false ideas on economy.
Oil Feed Reamers
All kinds of automatics and nearly all chucking, screw, and single-purpose machines call for generous oil supply.
This is frequently provided by using an “oil feed” reamer, which has an oil hole through the solid metal of the body and shank.
These require suitable oil connections in the machine and such connections must be considered by the designer when drawing the tool.
Except for the need of an extra back taper (about twice the normal amount) and the use of a floating holder, no other special attention is demanded. Either high speed or carbide tipping is satisfactory.
These may be distinguished from lining reamers in that the former are generally used in fixtures by means of hardening and ground bushings.
Whereas the latter may be used directly within the work without fixtures or bushings. Lining reamers do not always have pilots in advance of the first cutting portion.
The diameters of pilots should always be made as large as practical to give rigidity. As the type is special, it may be either solid or shell type, the same economies prevailing as for other types.
Although many designers specify pilots in advance of the cut, it is better to have pilot shanks instead.
Reamers properly designed with pilot shanks are fully as rugged, cheaper to buy, cheaper to use, and much cleaner to operate. If wear strips are included in the design, the whole setup is easier.
Wear strips may be of special bronze or tool steel inserts, carbide, or cast alloys such as Stellite, any of which are replaceable when worn or may be shimmed up for regrinding.
Extension sleeves are sometimes used instead of pilot shanks and serve the same purpose. By utilizing extension sleeves for a pilot shank the designer can accomplish his purpose and still use a standard reamer.
Multiple-diameter reamers are included in this group, which is both broad and varied.
A “step” reamer is valuable when reaming holes that have an interrupted surface due to cross holes, ports, or recesses. In such work, the chips are apt to rest crossways on the edges of the interruptions and case scoring.
By breaking up the operation as a step reamer does, the chips are finer and wash away easily with the cutting fluid reducing spoilage.
Step reamers are made with two or more reaming diameters, each of which cuts its individual portion and assures true alignment.
The details of design are the same as for single reamers, the only extra care necessary being to arrange the relative positions according to work requirements.
In providing reamers for tapered holes, the designer is always faced with a tough problem.
For gradual tapers, ¾ inch per foot or less, production jobs are usually handled by reaming directly from a straight drilled, bored, or punched hole, and it places a severe cutting operation on the reamers.
Steeper tapers are rough-machined prior to reaming, but the chips accumulate rapidly and the end thrust is high. Therefore, any kind of taper requires careful attention to all design details.
Some jobs require inspection with bluing gages to show 75% bearing or better.
Therefore, the reamers must be accurately made – often ground to fit a tapered ring gage – and maintained with equal accuracy.
The tool sharpener must be supplied with gages that are as exact as those used by the inspector.
Taper reamers are almost invariably cleared to the cutting edge. A concentric margin – even only a hairline – is unsatisfactory in a tool of this kind.
Left-hand spiral flutes, varying from 5 to 45 degrees from the axis, are used since straight flutes cause serious chatter. Hand reamers may have comparatively low spiral angles.
Machine reamers require fewer flutes and a steeper spiral than hand reamers.
Duplex Spiral Taper Reamers
Duplex spiral taper reamers are particularly well adapted to precision finishing.
Whenever the extra cost is justified, the designer will find a ready solution to some of his problems through their use.
They have flutes arranged at two or more different angles of spiral and will ream with greater ease and less liability to chatter than any other type of taper reamer.
They are highly efficient on both roughing and finishing operations. If used in holes that have been bored reasonably close to size and taper, they will finish without the need of a roughing reamer.
Taper Pin Reamers
One of the most perplexing jobs is the reaming of long taper pin holes using taper pin reamers due to the small diameter and small taper (1/4 in. per foot).
Straight-fluted reamers are useless except on comparatively short holes – not over 4x the diameter at the small end. Ordinarily, spiral reamers work reasonably well in free-machining materials.
Where the work is tough, “helical” reamers are most satisfactory. For general use, the regular stock items are the best to choose.
For special applications it may be necessary to procure special reamers with pilot shanks and operate through a guide bushing.
Frequently, a series of two or more reamers are needed for a single hole having precision tolerances, even if guided by long bushings. In such instances it is wise to consult the manufacturer for specification details.
Left-Hand Helix vs. Right-Hand Helix
There is a considerable difference in opinion as to the relative merits of right-hand helix angles for straight reamers. If you have never tried the right-hand helix, the best suggestion is to choose your job well and do so.
The old idea that the hand or direction must be opposite that of the cut (i.e. left-hand helix for right-hand cutting) is erroneous. Production reaming with right-hand helix fluting is being done in straight holes with increasing volume and an improvement in quality.
The main problem is ensuring there is not too much stock to be removed from the hole, the alignment between work and tool is correct, there is no lost motion (back lash) in the tool spindle, and that the work is firmly held.
Helical or Spiral Flutes
Unless unavoidable, all straight reamers should have helical flutes and all tapered reamers should have spiral flutes.
The only exception is roughing reamers for extremely coarse or heavy work in straight reaming and steep tapers requiring stepped tools.
The angle of helix need not to be heavy to accomplish its purpose. It may be either left or right hand on straight reamers, but must always be left hand on taper reamers.
Helical fluted reamers are mandatory for use in holes having keyways, splines, oil passages, or surfaces interrupted by a considerable number of cross holes.
Reaming in Aluminum
The usual line of reamers may be used in aluminum, but helical fluting is best for straight holes and spiral for tapered. When properly set up, a right-hand helix is ideal for straight holes, and remarkably smooth holes will result.
Duplex taper reamers give excellent performance on precision work in this material. Extra care is needed to see that sufficient stock is left in the holes, otherwise burnishing will occur.
The designer should keep all of these details in mind when planning for reaming in aluminum.
Correcting Inaccurate Holes
Occasionally, the designer is confronted with the task of supplying a reamer for straightening holes that have run off from the true center line due to irregularities in the subject piece, uneven conditions in the metal, or carelessness in the shop.
When the errors aren't significant, the job can be saved by substituting an end-cutting reamer for one with the conventional chamfer.
An end-cutting function can be given to any reamer by grinding the end off square with the axis, removing the chamfer entirely. In effect, the tool cuts like an end mill.
However, the desired results will not be achieved unless it is well guided and suitably supported – details that the designer must check.