MATE Building Instructions - Page 8

 

COOLING FINS (6-1)

  1. Centre the remaining aluminium stock and extend 35mm from the jaws. Face end, centre-drill and drill with ascending drills to Ø10mm x 16.5mm deep. Bore to nominal Ø16.5mm (a close, sliding fit on the upper cylinder) x 16.7mm deep. Finish turn to Ø30mm up to jaws. Support with the tailstock.

  2. Set the 1.6mm parting tool square to the spindle axis, retract the topslide to reduce tool overhang, traverse saddle to bring tool as close as possible to jaws for a test cut. Wind cross slide in to touch tool on Ø30mm and zero dial. Calculate final reading at 19.5mm and note. Set spindle speed and feed rate to suit your lathe, the latter fairly coarse to avoid chatter. Lock saddle, apply coolant and commence to cut a test fin. Disengage feed just before Ø19.5mm reading and finish to size with hand feed. Zero dial. Correct any problem with setting and take another cut, after moving saddle 2.7mm to the right, this time down to the zero reading.

    If you are experiencing problems with chips jamming on such a deep plunge cut, try backing the tool out several times. Any thing less than fine, even finning will marr the final appearance of your "MATE", so work out the best way to do the job and set your lathe accordingly. Three ways are suggested:

    • a) Use a longitudinal saddle stop and appropriate twist drill shanks as spacers, inserting for example a 2.7mm drill between the stop and the saddle, locking the stop, removing the drill and advancing the saddle to the stop, and so on.
    • b) Use the graduated leadscrew dial, or saddle wheel dial to advance the saddle.
    • c) Lock the saddle and advance the topslide only. This is the least preferred option, as tool overhang may result in chatter with smaller lathes.

  3. Having chosen your method, retract the topslide back to minimise tool overhang and zero dial. Advance saddle until the flank of the tool touches the faced end. Zero leadscrew/ saddle dials. Retract tool from the face and advance the blade width plus the first fin width, 1.6 plus 1.6, or 3.2mm. lock all slides and cut the first fin. Advance the tool 2.7mm (1.6 plus 1.1), lock slides and cut second fin, and so on until you h,ave made six cuts.

  4. Chamfer the bottom of the first fin and break .the edge of the bore. Break the fin edges with a triangular file in an appropriate safety handle. Part the cooling fins from the stock at about 23mm from the faced end.

In the event your blade width is not exactly 1.6mm, recalculate the total length required to give you a top fin 4.5mm thick and decide how much to face off top. Centre the fins in the chuck with paper to protect the finish and extend 3mm from jaws. Face end and chamfer the top fin 45� x 1mm wide. Centre-drill and drill to Ø4.3mm. Using the tailstock for alignment, tap the M5 x .8mm thread for the compression screw.

CYLINDER SCREW JIG (6-3)

  1. Centre a piece of scrap steel stock and extend 20mm from the jaws. Finish turn to Ø32mm, face end, finish turn to nominal Ø16.5mm (a close, sliding fit in the crankcase bore) x 10mm long. Part off at about 14mm long, re-chuck on spigot and face-off flange to 3mm thick. Break edges.

DRILLING THE SCREW HOLES AND TAPPING CRANKCASE

  1. Fix the rotary table on vertical mill with chuck axis vertical and centred accurately under the spindle axis. Move machine table exactly 12.6mm (half the PCD 25. 2mm) and lock all slides. Centre cooling fins in chuck (protect) and extend top fin 3mm from jaws. Advance rotary table to 0° setting and lock. Centre-drill each of the four screw holes in turn, starting at 0° and advancing to 90° 180° and 270° Starting at 0° again, drill in turn each hole Ø2.7mm, right through all fins. Use the highest spindle speed, plenty of coolant and back out the drill to clear it, if necessary. Starting again at 0�, countersink each screw hole in turn with a Ø5mm slot drill to a depth of 2mm. Slacken jaws and remove fins. Do not alter machine table setting.

  2. Centre cylinder screw jig (18c) on Ø16.5mm in chuck on rotary table. Use 3mm plywood or similar packing to raise the flange evenly above the face of each jaw.

    Advance rotary table to 0° setting, centre-drill each of the four holes in turn at 90° spacing. Starting at 0° again and taking care not to drill into a chuck jaw, drill each hole in turn Ø2.3mm, the tapping drill size for the 6BA cylinder screws. De-burr the cooling fins and screw jig and wash well.

  3. Clamp the crankcase across the machine vyce on the nose and rear face, both protected with paper. Keep it fairly high in the vyce and set the cylinder axis vertical with an engineer�s square along the top of the jaw and the earlier scribed centre-line on the vertical rear face. Place a steel rule on the top of the crankcase as if to scribe precisely a diagonal from one corner to another. Scribe instead a fine line only 4mm long, from one rear corner towards its opposite. Push the screw jig into the crankcase and rotate it until the scribed mark is centred precisely in one of the Ø2.3mm holes. Place one drop of the cyano adhesive under the jig flange, between the two forward holes, to fix it in position.

  4. Clean and oil the machine table under the spindle so that the vyce floats freely. Set the spindle depth stop at 13mm from the top face of the jig flange and, centring each hole in turn under the spindle, hold the vyce firmly and drill Ø2.3mm down to the stop.

  5. Tap each hole 6BA, right through the jig, starting the threads with a taper tap and following with a plug tap right to the bottom of the hole. Ensure that the tap is perpendicular to the face, use a good tapping lubricant or kerosene, clear the hole of swarf before using the plug tap and, most important of all, take no risks.

    If the torque required to turn the tap increases even slightly, is it swarf? Is it lack of lube? Or has the tap bottomed? Investigate and correct, as a broken tap at this stage is not a pleasant thought! When all holes are safely tapped, take crankcase from vyce and release the jig with a sharp tap on a piece of dowel inserted through backplate cavity. Clean all traces of adhesive from top face taking extra care not to mark the surface in any way.

COMPRESSION SCREW (6-2)

  1. Centre Ø5mm silver steel in chuck and extend 20mm from jaws. Face end and chamfer 45� x .5mm wide. Centre-drill and support with tailstock.

  2. Screw cut M5 x .8mm thread by 11mm long. When thread depth has reached .4mm, check fit in cooling fins. Continue to cut thread maximum .02mm per pass until the threads stiffly match. Finish to a smooth, tightish fit by lapping together with Brasso.

  3. Drill the Ø2.5mm x 11 mm long hole up the centre of the screw. This hole reduces the tendency for the compression screw to unwind when running. Part off at 17mm long, re-chuck on threaded end (protect) and chamfer end 45� x .5mm wide.

  4. Clamp screw in machine vyce with packing underneath for support and drill a Ø3/32" hole through the axis at 3mm from the end.

  5. Centre the Ø3/32" silver steel stock and extend a few mm from jaws. Face end, round with file and paper, polish. Reverse in chuck, shorten to 30mm long and finish other end as before. Centre this tommy bar across the compscrew and Loctite the two parts together.

CYLINDER SCREWS (6-4)

  1. Reduce, if necessary, the overall length to 32mm and turn the heads down to Ø4.8mm. De-burr the slots with a Swiss file.

 

This page is Copyright © David Owen 1989-2006. All rights are reserved world-wide.
Reproduction in any form without the written permission of the copyright owner is prohibited.