Keyway Cutting

Keys and keyways are a very common feature of machinery and naturally of models too. The common round-ended keyway, for a feather' key, is easily produced on a parallel shaft by holding the shaft in the vice and using a small endmill, or two-flute 'slot-drill'. Fig. 24 shows the setup for this operation.

Various parts of car and motor cycle engines, gearboxes, and other machinery components in the past have had wheels mounted on tapered shafts with the keyways following the slope of the taper. Modelling one of these would involve following the same procedure. One way in which this can be done is shown in Fig. 25. The vice holding the shaft is set on a tilting angleplate so that the top of the

Fig. 24 Milling feather keyway

Feather Key Operation

Fig. 24 Milling feather keyway

Feather Key Shaft
Fig. 25 Milling feather keyway on tapered shaft

tapered part comes parallel with the machine table. The shaft shown in the picture is a simple one and quite short, and could have been just tilted in the vice in a set-up like that of Fig. 24. But a long shaft might well foul the table at its lower end so the elevation which the angleplate gives could in such a case prove essential.

Small endmills are rather frail tools at best and liable to easy breakage. The disc type cutter is more robust and a collection of these acquired either as the need for one crops up, or bought cheaply secondhand, is worth while. Of course the disc cutter cannot always go close to a shoulder on the shaft, and copying a prototype may in some cases rule it out. For the work done in the home workshop there is no need to insist on the relatively expensive side-and-face cutters, (those with teeth on the faces as well as the periphery) because the slitting saw, with teeth only on the periphery, will do quite well. These are made in a very great variety of thicknesses, and are always coming on the surplus market at low prices. One of these is shown in Fig. 26 milling an ordinary sunken keyway, the shaft being held in a vice with enough overhang to avoid the cutter touching the vice.

WOODRUFF KEYS

The Woodruff key is one widely used in industry. This is in effect a slice off a round bar, cut in half and set into the shaft in a recess made by a small diameter slitting saw. This is rather an oversimplified description, but it will serve well enough as an introduction to the Woodruff key for those in home workshops without industrial experience. Seriously, the Woodruff key, which I think was of American origin, has some very real advantages for the mass production industry, and some of these are of just as great importance in the home workshop and the field of light engineering.

Fig. 26 Milling keyway with slitting saw

For a start the key itself can be parted off from a piece of round mild steel or silver steel. So its diameter is settled with accuracy from the bright bar. The thickness needs careful control, but if it comes off a bit too thick it can be rubbed

Fig. 27 Set of four Woodruff key way cutters

Fig. 27 Set of four Woodruff key way cutters down on a flat file. It needs to be cut in two on a line which is nearly a diameter, but the cut edge can readily be filed to bring it to final shape. The keyway is made by a simple cutter like a slitting saw, of the same diameter as the bar from which the key is made, with an integral shank of preferably some standard diameter which can be run true in a collet on the miller. So the shape of the keyway profile - and its width - is settled by the cutter form. The cutting part of the cutter is set in line with

TABLE

WOODRUFF KEYS & KE.YWAYS

A

B

C

D

E

F

G

*

kk

■109

•073

037

•100

•030

fe

140

104

037

104

037

%a

172

123

053

•129

•045

*

•203

155

053

•187

•060

the diametral line of the shaft, then the cutter is fed in by a predetermined amount.

The resulting keyway is deep enough to give the key a good hold, so that it cannot roll over, and yet the shaft is not unduly weakened. Normally the top of the key is just clear of the keyway in the wheel or lever which is being secured, its purpose being to provide either torque or angular location, and some means such as a grub screw may have to be used to prevent endwise movement.

Woodruff cutters are not very cheap, but they can easily be made in the home workshop, from silver steel. The process is really quite simple. A blank can be turned, making a shank to suit some standard collet, then with the shank held in the collet the working part of the cutter can be turned to its diameter, and thickness. The sides should be very slightly undercut by setting a knifetool a little off square. Using a simple un-geared dividing head the teeth can be cut in two operations using an ordinary end mill; there is no need for angular cutters, as the diagram on the opposite page indicates. The number of teeth is not important, but six is a convenient number for small cutters. It is possible to file the teeth if you do not have access to a dividing head, as the spacing is not at all critical, but it's a little more difficult. Fig. 27 shows a batch of cutters made to the sizes in Table II and Fig. 28 shows a keyway being cut. There seems to be no place where sizes of Woodruff keys and cutters are displayed for model engineers. Machinery's Handbook gives sizes which are used in industry, but the sheer range of sizes is itself confusing, and of course the tables are liberally sprinkled with tolerances that modellers could neither follow nor want. I have therefore picked out a few sizes which I think will serve our purpose, and as we don't have to provide interchangeability in our products, if anybody wants to depart a bit

Fig. 28 Milling Woodruff keyway

Fig. 28 Milling Woodruff keyway

from these dimensions he can certainly do so. Up to date of writing I have not seen any specification of Woodruff keys in metric sizes.

The cutters shown in Table II have screwed shanks to suit Clarkson and Osborn chucks, which have collets that close on the cutter shank through end thrust exerted by the cutter against the inside of the chuck. If you are making cutters for use in a Clare chuck or just to use in a 3-jaw, these threads are not needed. It may be noticed that the cutters shown in Fig. 27 are stamped with their size details. It is a good plan to have a set of small stamps, say 1/16 in. characters, so that appropriate identity can be marked on all home made tools, jigs, etc as well as model components. The holes drilled in these cutters were provided for the convenience of the hardener. They were hardened for me by a firm where liquid-salt baths are used for heating and quenching tools. A small hole enables the tool to be hung on a wire in the baths without damage to cutting edges.

A Course In Wood Turning

A Course In Wood Turning

Ever wondered what wood turning is all about? Here are some invaluable information on how to make beautiful items out of wood! That one little strategy from A Course In Wood Turning that I implemented not only worked, but the results were completely astonishing. I had never seen anything like it! Now, keep in mind that I had tried a lot of other products up until this point. You name it, I probably tried it! That’s how desperate I was to improve my skills with wood turning.

Get My Free Ebook


Post a comment