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Both were listed with, as standard, an all-metric screwcutting gearbox or screwcutting by changewheels and often but not always with the Mbased version fitted with a motor rated at 0. The "T" model is easily recognised by distinctive badges and, on the M model, by a leadscrew and powershaft safety cover arranged to slide on a rail held on brackets bolted to the headstock and tailstock ends on the bed.
Induction hardened as standard, the bed can be ordered either straight or with a detachable gap in both lengths able, in the latter case, to accept a piece of material up to mm 19" in diameter and mm 4. Most models have 12 spindle speeds arranged in geometrical progression in a ratio of 1. The headstock gears, all induction-hardened, run in a simple splash oil bath and are moved by two rather short levers on the front face of the headstock; as a safety measure the levers have to be pushed in before they can be turned and their finish, which is far too smooth, can make them difficult to operate with oily hands.
Early series lathes were fitted with a headstock gear-selector drum in "Delrin" which distorted, preventing movement of the selector forks. The fault was quickly recognised by the makers and a replacement drum part: made available in metal. Screwcutting is provided through a well-supported, ball-thrust-equipped 28 mm 1.
Surprisingly, for a lathe often found in training workshops, the leadscrew is not protected by a cover as on the M, but there are torque-limiting clutches on both the leadscrew and powershaft - though earlier models were protected by a limiter on the powershaft with just a mild-steel shear-pin through the splined shaft of the top changewheel stud to prevent over-load damage to the leadscrew. Both systems are adequate enough to militate the damage that might otherwise be caused by the over-ambitious cuts often set up by apprentices or - if one dare one say it - the over-enthusiastic amateur.
In comparison with earlier Harrison screwcutting gearboxes the "Universal" unit fitted to the M is a considerable improvement and capable of reliably transmitting much great torque. Formed from a one-piece casting it is completely enclosed and holds induction-hardened gears driven by changewheels that have included, over the years, one or more non-metallic intermediates to promote quite running. Controlled by three levers and an 8-position rotary dial the box will generate both English and metric threads: 35 Inch pitches from 2 to 56 t.
By the use of additional changewheels 18 Module pitches from 0. The range of power sliding feeds varies from 0. The box runs in an oil bath a level window is fitted on the front face with the lower gears distributing the oil by splash. The double-wall apron carries a supply of lubricant in its base with a level window let into the headstock-end face that can be distributed to the bed and cross slide by a simple hand-operated plunger pump.
Feeds are engaged by a traditional push-pull plunger and engaged and disengaged a very light-action, flick-up-and-down lever the operation of which is not affected by the how hard the lathe is working.
Fitted with feed screws carrying twin ball-thrust races, that for the cross slide on early models had a nut closed by a wedge in common with many conventional lathes made by the Group to allow the elimination of backlash - though when the assembly is badly worn this arrangement can disguise the imminent failure of the threads. Later machines were modified and the nut made solid--the change also affecting the design of the cross-feed screw, The satin-chrome finish micrometer dials are sensibly large with especially clear graduations with that on the cross slide arranged as a "direct-reading" type to shows the amount taken off the diameter rather than the radius of a workpiece.
Whilst the top slide has a traditional screw-adjusted gib-strip, the full-length cross slide is fitted with a tapered type and the cross and top slides, as well as the saddle, are equipped with locking screws. The mm diameter quill, marked with inch, metric and sometimes both graduations is fitted with a ball thrust bearing, a micrometer graduated collar and accepts a No. As a final touch, tailstocks on later versions of the M carry felt bed wipers to help reduce the inevitable wear to the front section of the sole plate.
Electrical stop, start and reverse of the spindle is by a "third-rod" system controlled by a lever attached to, and moving with, the apron. Both the electrical isolator and coolant pump switch are mounted on the left-hand face of the stand - the latter a unit that is well made and supplied with a chip tray, splash-back and locking tool cupboard as standard. Although safety equipment has varied during a long production run most machines have a useful "power-on" light, a rather small headstock-mounted, mushroom-headed emergency stop button, a long, foot-operated and very powerful spindle-brake and "motor-off" bar and electrical interlocking of the changewheel guard.
The electrical system is built into the left-hand end of the stand and accessible thorough a door equipped with an interlocked isolating switch that can, for additional security, be padlocked in the off position.
Although of an excellent mechanical specification equipment provided as standard with the M has generally been sparse: a single toolpost, drive plate, a 5 to 3 Morse adaptor bush for the headstock spindle often missing on used machines , 2 No. An M weighs about Kg lbs in short-bed form and Kg lbs as a long-bed model.. Harrison M saddle and compound slide rest detail. Centralised lubrication is fitted, activated by the button on the bottom right hand side of the apron.
The lathe shown is fitted with the optional dual English and Metric micrometer dials. As is not uncommon, the photographer has put the toolpost in the one position to be avoided when taking the first cut ….. The cross and top slides are identical to those used on the later Colchester , and series Student and Master lathes Headstock end of an M with the changewheel cover removed and the electrical-control and distribution panel door open.
The 38 mm 1. The speed-control levers had a finish that was far too smooth making them difficult to operate with oily hands. A total of 39 metric, 35 English, 18 Module and 18 Diametrical pitches could be achieved by moving the control levers and either rearranging the standard changewheel set - or employing the extra non-metallic hence quiet-running gears that were supplied with the machine in order for it to achieve its full threading range.
The two large cylinders on the end of the shafts protruding through the side of the apron housed the leadscrew and powershaft overload clutches.
harrison m300 manual