As a matter of economy, the larger sizes of reamers are sometimes made in the form of shell reamers, as shown in Figs. 67 and 68. As several reamers may be used on the same arbor, there is a considerable saving in cost of material.
Size or Hole (in).
Fig. 66. Form of Cut Made by Circular Saw.
Fig. 66. Form of Cut Made by Hand Saw.
Table III gives the size and length of shell reamers from 1 inch to 3 inches in diameter, together with the size of holes, and width and depth of tongue slot.
After drilling a hole 1/15 inch smaller than finish size, the blank should be placed on a mandrel, and a heavy chip taken to remove all the original surface. The drill is annealed, and then placed in a chuck on the lathe and the hole bored .006-inch smaller than finish size. After being put on a mandrel, the ends should be faced to length and the outside diameter turned, leaving .010 to .015 inch on the cutting part for grinding. The balance of the reamer should be turned to size. If it is to be a rose reamer, the edge should be chamfered the proper amount.
The reamer should be held in a chuck on the spiral head spindle in the milling machine, and the tongue slot cut.
Fig. 67. Plain Shell Reamer.
Courtesy of Brown. and Sharpe Manufacturing Company, Providence, Rhode Island.
Fig. 68. Rose Shell Reamer.
Courtesy of Brown and Sharpe Manufacturing Company, Providence, Rhode Island.
In order to get the slot central with the outside of the reamer, a cutter somewhat narrower than the desired slot should be used, which should be set as centrally as possible by measurement, a cut taken, the spiral head turned one-half way round, and another cut taken; the width of the slot should be measured, and the saddle of the machine moved by means of the graduated adjusting screw one-half the amount necessary to make the slot of the right width. The reamer may be placed on a mandrel, between centers on the milling machine, and the flutes cut.
The reamer should be heated for hardening in some receptacle, in order that the fire may not come in direct contact with it. When it reaches a low uniform red heat, it may be placed on a wire hook, plunged into the bath and worked up and down rapidly until all trace of red has disappeared, and should be left in the bath until cold. When cold, it may be heated to prevent cracking from internal strains. If it is to be a rose reamer, it may be left dead hard; if it is to be a fluted reamer, the temper should be drawn to a straw color. The hole should be ground to fit the shank on which it is to be used, or to fit a plug gage, if there is one for the purpose. The reamer may then be placed on a mandrel and ground according to the general directions given for grinding reamers.
The holes in shell reamers are sometimes made tapering - the end of the arbor being made of a corresponding taper - to avoid the necessity of grinding the holes, as any slight change in the size, resulting from hardening, would be compensated for by the taper hole.
These are made as shown in Fig. 69. The shank B and the end A to receive the reamer, are made in one piece. The collar C having two tongues to engage in the slots in the reamer, is made of tool steel; the hole is made of a size that allows it to slide over A. When in position, a hole is drilled through both collar and arbor and the pin D driven in.
When making the collar, the hole is drilled and reamed; the collar is placed on a mandrel, the ends faced to length, and the collar turned to proper diameter. It is then removed from the mandrel, and the tongues are milled. While this is being done, the collar is held in the chuck on the spindle of the spiral head, and a side milling cutter is used. One side is milled, the spiral-head spindle turned one-half revolution, and the opposite side milled; the thickness is measured, and the saddle moved enough to bring the tongues to the required thickness, when the finish cut is taken on each side. After putting on the arbor and drilling the pinhole, the collar is removed and spring-tempered. It may now be placed on the arbor, and the pin driven in place.
Fig. 69. Typical Arbor for Shell Reamers.
When the shell reamer is made with a taper hole, the arbor is made with the end A of a corresponding taper. Otherwise the construction would be the same as for shell reamers having straight holes.