On Bored and Keyed Magnaloy Couplings, the keyway is located between the drive lugs on each hub. When the coupling hubs are assembled, each half will have one drive lug located in-line with the keyway of the opposing hub. In each model size, particular bore/key combinations have the potential for interference between the keystock and the drive lug of the opposing hub.
This interference will result if the bore/key size is greater than listed in the table below AND the keystock on this shaft extends into the insert cavity of the hub.
CORRECTIVE ACTION: The interference can be eliminated by shortening the keystock so it does not extend into the insert cavity of the hub. Failure to correct this situation can cause assembly difficulty resulting in coupling failure and damage to the drive or driven equipment.
During the design of mounting systems and coupling installation on these systems, the spacing between shaft ends is an important parameter. Shaft engagement in the coupling bore is important to insure adequate load bearing surfaces for the keystock or spline teeth. A good 'rule of thumb' is one times the shaft diameter for shaft engagement. However, 'additional engagement when available' is the first corollary to this rule.
In our Dimensional Specifications for the Magnaloy Flexible Drive Coupling, the dimensions 'W' and 'X' are given to assist in the proper design of these mounting systems. The dimension 'W' is the minimum shaft separation recommended to prevent contact between the shaft ends. Dimension 'X' is the maximum shaft end separation to insure full engagement in the coupling. This dimension results in both shafts being flush with the inner surface of the coupling and 100% engaged through the shaft length. While this situation is ideal, because of shaft length consideration, it is sometimes not possible to achieve. In these cases, we recommend following the above corollary to the 'one times shaft diameter' rule. The full engagement condition resulting from dimension 'X' is NOT necessary for satisfactory performance of the Magnaloy Coupling and is shown for illustrative purposes only.
On some Magnaloy Coupling Clamp Style coupling hubs there is a setscrew in addition to the clamp bolt. This would be the case, for example, with a bored and keyed coupling hub with the clamp feature. When installing these hubs it is important to tighten the clamp bolt to the required torque value BEFORE tightening the setscrew to it's torque value. Failure to follow this procedure could result in inadequate retention of the coupling on the shaft.
To allow clearance between the bore surface and the clamp bolt on Magnaloy Couplings with the Clamp Option and between the Steel Bushing keyway on Magnaloy Couplings with the Steel Bushing Option, the following maximum bore limitations are noted:
The possibility of fire when machining Magnesium is always a real concern. However, if proper precautions are taken, this risk can be reduced greatly.
Magnesium fire result from combustion of the metal due to heat generation beyond the "Heat of Incipient Fusion". A magnesium fire is very violent and burns with a bright white glow. It has the ability to extract oxygen from liquids and damp powders, so extinguishing by suffocation is necessary. Use of water containing fluids for coolants is not recommended. In fact, coolants are not recommended or necessary in most cases. Where coolants are desired, only mineral oit cutting fluids should be used.
The following list of safety precautions and machining tips for machining magnesium are recommended in conjunction with normal safety practices.
If a fire does result, confine it to a small area and smother it with the extinguisher media. Do not blast it and spread it over the shop. For this reason, we use Dry Ansul Sand in moisture proof containers for pouring directly on any small fire that may occur.
Following are the particulars on tool sharpening, feeds, speeds and depth of cuts recommended for magnesium. These cover the basic machining operations of Drilling, Reaming, Boring and Milling.
Drilling: Shallow-hole drilling (depth is less than 5 times drill diameter) presents few problems and consequently, only a few modifications are necessary for high quality drilled holes. Standard point angels of 118 degrees and chisel edge angles of 120 to 135 degrees which give a relief angle of approximately 12 degrees will give the best cutting action. It is extremely important, regardless of the type of drill used, that the cutting edges be kept SHARP. Deep-Hole drilling can be performed with great speed and precision due to the excellent machining characteristics of magnesium. To extract chips from the hole, it is recommended to use high-helix drills of 40 to 45 degrees. If standard drills of low helix angles are used, it will be necessary to withdraw the drill frequently to clear the chips. The standard drill point angle of 118 degrees is the most satisfactory. Drilling speeds in the range of 75 to 400 surface feet per minute are satisfactory and higher speeds can be used. The feeds used in drilling magnesium should be heavier than those for other metals to secure proper chip formation. Small drills work best with light feeds, as they give slightly coiled or ribbon-like chips which feed out through the drill flutes without jamming. Heavier feeds should be used on large drills to prevent jamming of the chips. Some recommended feed for a few drill diameters are:
Reaming: Reamers for magnesium should have fewer flutes than normal for best results. Under 1 inch diameter - four flutes and over 1 inch diameter - six flutes are best. Reaming feeds used for brass and steel work satisfactorily on magnesium. A definite cut (approx 1/32 inch on the diameter) should be taken to prevent compression of the metal and resulting in undersized holes and poor surface finish. Cutting speeds commonly used in commercial practice vary from 100 to 400 feet per minute. High cutting speeds and medium feeds give the best finish and most accurate holes. The following table gives some recommended ream characteristics for use with magnesium.
Boring and Turning: Lathe set-ups, with due consideration of the more careful chucking pressures for magnesium and a slight difference in tool design, are similar to those used for brass or steel. It is important in all types of lathe tools that the relief angles be sufficiently larger to eliminate rubbing of the tool flanks. Rake angles may vary considerable, but best results are obtained on high-speed steel tools with side and back rake angles of 0 to 15 degrees. Carbide tipped tools should have slightly smaller rake angels to provide more support for the cutting edge. A wide range of cutting speeds, feeds and depths of cut are possible in turning and boring magnesium. Depth of cut as high as .50 inch and feeds from .003 to .002 inch per revolution can be used. The depth of cut, of course, depends upon the amount of stock to be removed, but for all practical purposed any depth of cut can be taken, providing the work is of sufficient size and is properly secured. Heavy feeds provide a very quick means of removing metal, but do not give the best surface finish. However, extremely fine feeds should be avoided as the tend to heat the work more than heavier cuts. Cutting speeds for magnesium up to 5000 feet per minute are appropriate for turning or boring. The following table provides recommended depths of cut, feeds and cutting speeds for turning and boring. The general rule is to turn and bore magnesium as fast as the machine tool, fixtures and work will allow.
Milling: Milling operations provide an opportunity to take full advantage of the excellent machining characteristics of magnesium. Heavy feeds and extremely high milling speeds can be used to remove metal rapidly with excellent surface finish. The following table illustrates some typical machining parameters with magnesium.
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