8/14/2019 keycutter

1/3

AN INTERNAL

KEYWAY CUTTER

By Dup l ex

THE commercial method of cut-ting internal keyways, by means

of either a slotting machine orsuitable broaching equipment, ishardly likely to be adopted in thesmall workshop for lack of thenecessary tools. The old-time wayof forming these keyways, with coldchisel and file, calls for the skilful

use of hand tools, and is not muchin favour in the present machineage, but we can recall occasions onwhich this was, in the circumstances,the only way of getting the workdone.

In previous articles, we havedescribed cutting internal keywaysin pulleys and collars by adaptingthe lathe to serve as a hand-operatedshaping machine; this method, al-though somewhat laborious, hasthe advantage that two or morekeyways can be accurately spacedby indexing the work from thelathe mandrel.

However, if the workshop isequipped with either a hand or apower shaping-machine, a singlekeyway can be readily cut to ahigh degree of accuracy.

A job of this kind was donerecently in the shaping machinewhen making a two-step belt pulleyfor an electric motor. Here, akeyway, 3/16 in. wide, 1/8 in. deep, and1-7/8 in. in length, was cut in the bore,measuring 5/8 in. in diameter.

Making the Tool

The special tool required for thispurpose is best made in two parts:the shank, and the arm with itsinset cutter-bit. The arm should beof as large a diameter as possible inorder to avoid springing under the

Fig. 1. The finished pulley

pressure of the cut; this part is made

a light press-fit in the shank, and issecured with a nut. The size of theshank will, of course, depend onthe capacity of the machines tool-holder, but robust construction isadvisable to maintain rigidity.

Fig. 3.

Fig. 2.The internal keywayycutting tool

The components of thekeyway cutter

8/14/2019 keycutter

2/3

The inset tool-bit, illustrated inFig. 4, was ground to shape from apiece of 1/4 in. square high-speedsteel, and its length was adjustedso as to cut the keyway to thefinished depth while remaining fullysupported in the arm. As the toolcuts in the forward direction, theback of the cutter-bit must be givensupport against a flat seating, toprevent tipping when under pressure.In the working drawing, the mach-ined seating for the tool is shownas a drilled hole, but this seatingwas finished to size in the followingway. After the arm had beencross-drilled with a letter F drill, a flat was filed at the mouthof the hole on its back surface inorder to form a lead for the tool-bit.This allowed the cutter to be started

June 17, 1954

in the hole and after-wards forced for itsfull length into the armby applying pressure

1in the vice. :: *

In this way, the: :

tool itself, acting as--z -50 .,,

a broach, formed aG,

seating with two smallflat surfaces for sup-porting the back ofthe cutter.

The tool should be Fig. 4.

ground with the ade-quate clearances shown in thedrawing, but top rake is generallybest avoided, as it tends to make thetool dig into the work.

The pressure-screw should beaccurately made, and provided witha flat surface at the tip, so as to

Showing the form of cutter-bit used

give the maximum support to thetool. Some workers prefer to drawthe tool through the work whencutting a keyway and, if this methodis adopted, the cutting pressurewill then be against the tip of thescrew.

Fig. 5. The pulley set up for machining in the shaping machine

670

Fig. 6. Left: the Starrettfractional-inch taper gauge; Right: the Starrettgauge graduated in thousandths of

an inch

Machining the KeywayAfter the outer surface of the

pulley has been painted with mark-ing fluid, such as Talbot Blue,

supplied by Messrs. Buck and Ryan,the keyway is marked-out and avertical centre-line is scribed. Smallwork can usually be gripped in themachine vice; or in cases where ashaping machine is used, an angle-plate with a through passage canbe used for securing the pulley tothe table of the machine. Thescribed centre-line i s set exactlyvertical with a small square restingon the vice jaw, and the tool is thencentred on this line. As the tool willcut on the front cutting edge only,

no side relief is necessary on thereturn stroke, and the clapper-boxis, therefore set vertically.

With a power-driven machine,the stroke and ram position are setto enable the tool to clear the workat either end.

8/14/2019 keycutter

3/3

Although, when machining abatch of parts, it may be an advan-tage to make the cutter-bit theexact width of the finished kevwav.it is perhaps better to work with-arather narrower tool; this willavoid chatter where the machine

lacks rigidity, and will also enablekeyways of various widths to be cutwith a single tool.

A series of cuts is first taken tothe full depth of the keyway, andthe depth can readily be measuredwith a Starrett taper gauge of thekind illustrated on the left ofFig. 6; that is to say, the gauge isinserted in the bore and the diameterof the original bore is subtractedfrom the measurement obtained.Another method is to put a plug inthe bore and then make a direct

measurement with the gauge. Afterthe correct depth has been reached,the reading of the micrometerindex on the tool slide is noted.The width of the keyway can alsobe measured with a gauge of similartype;, that illustrated on the rightof Fig. 6 is a Starrett taper gaugegraduated in thousandths of aninch. To machine the keyway to thefull width, an equal amount ofmetal is removed on either side ofthe centre-line.

For this purpose; the micrometerindex on the table slide is referredto, but any backlash present in thefeed must, of course, be taken intoaccount. If the table slide is locked,the amount of backlash in eitherdirection can easily be determinedon turning the feedscrew. Foraccurate machining, and to preventchatter, it is important to adjustcorrectly the foot fitted tc the over-hanging end of the table; this supportchecks any tendency for the table totilt downwards under the pressureof the cut, but is usually omittedin small, hand-operated machines.

With a little practice, quiteaccurate fitting can be done in theshaping machine and, in the presentinstance, the keyway was cut exactlyat right-angles to the diameter ofthe bore, and the key itself was alight press-fit in the finished seating.

Tool-bits of the Eclipse brand aresupplied heat-treated and ready foruse; those of 3/16in. and 1/4 in. squaresection are obtainable in lengths of2 in. and 2-1/2 in. respectively.

As the tool-bit for the presenttoolholder is only some 5/8 in in

length, the material will have to becut to the finished length after thepoint has been ground. For thispurpose, the tool is either nickedon the grinding wheel, and thenbroken off, or a special cut-offabrasive wheel can be employed.

TEE VALTOCK AUTOMATIC

BLOWLAMP

A NEW type of miniature blow-lamp to work on methylatedspirit has been introduced byValtock Ltd.., 5-6, Sherwood Street,Piccadilly Circus, London, W.l, andis obtainable from most tool dealers.It is of the self-blowing vaporisingtype, and its design enables a highpressure to be obtained at the jetnozzle, resulting in a concentratedhigh-intensity flame. No pumpingis necessary to obtain the pressure,and the vaporiser is of a simple typewhich cannot clog or carbonise.

The blowlamp consists of two

cylindrical containers, both of whichcan be completely sealed, so thatit does not spill when carried in thepocket or tool, kit; these are heldparallel to each other by a springclip which allows of lateral in-dividual adjustment. Both cylinderscontain wicks, one having a plaincap, while the other terminates atthe top with a bent tube, having afine jet at the outlet, which can alsobe capped when not in use. In use,the cap is removed from the firstcvlinder, and this is used to form a

pilot heater for the jet tube, causingvapour to be generated in the secondcylinder under the pressure of itsown expansion. As the vapourescapes from the jet it is ignited by

the pilot flame and burns with asmokeless, almost non-luminous hightemperature flame.

This is an extremely useful ap-pliance for many operations withinthe sphere of the home workshop,including soft-soldering and sweating,light silver-soldering, glass working,etc. It should, however, be re-membered that while the actualtemperature of the flame which itproduces is extremely high, it issmall in volume, so that the actualquantity of heat it produces is lessthan that of a larger flame of lower

intensity. We mention this, not asa criticism of the device, but be-cause inexperienced operators oftenattempt to use small gas or spiritblowpipes for large work whichis definitely outside their capacity,or without taking precautions toconserve and prevent dissipation ofheat. The Valtock blowlamp willsilver-solder small fittings, but cannotbe expected to cope with a boiler.

The appliance is very well madeand finished, the cylinders beingof solid brass tube with screwed-on

caps, no soldered joints being used.It weighs only 5-1/2 oz. and is 5-1/2 in.in overall height; all parts are inter-changeable, and spares can beobtained if and when required.

The Valtock blowlamp in use, silver-soldering a 1/4in. Pipe nipple

471