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American Tool Works Pacemaker lathe clucth. Based on 1962-model

How it works: The operation of the clutch and brake are pretty simple: When you pull the main clutch lever towards you the linkage makes the actuation lever rotate and push the bronze pads and with them the friction spool over the clutch fingers. This makes the other side of the fingers press against the clutch-pack and engage drive to the spindle. If everything is adjusted correctly the fingers will go all the way inside the friction spool and cam-over so that the clutch is locked in the drive position. When you push the main clutch lever away from you and disengage drive to the spindle, the actuation lever and bronze pads rotate away from the drive clutch and push friction spool against the brake discs which in turn brake the spindle.

Dis-assembly:

Unscrew beltpulley cover-bolts and remove cover from belt pulley.

Remove bronze nut (clutch adjustment nut). Remember to loosen the set-screws first.

Unscrew drive hub nut. Remember to loosen the set-screws here too.

Use threaded holes in belt pulley and suitable puller to remove belt-pulley from drive hub.

Screw the drive hub nut back onto the friction drive hub so that all threads are enganged.

Unscrew and remove bolts from the bearing retainer.

Use suitable puller against center of shaft (with something inbetween to not damage shaft) and back of drive hub nut to pull out friction drive hub with bearings and outer bearing retainer plate as one complete unit.

Remove clutch linkage from the lever on the clutch housing.

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Find correct nut to screw onto the taper pin in the clutch actuation lever to remove pin. Remove set screw from lever. Remove lever from shaft along with the spacer between the arm and the bearing.

Remove the cover on top of clutch casting (4 bolts).

Loosen the cap head bolt on the clutch actuation arm, which sits around the shaft from 2 steps back.

Remove center setscrew and locking set screw from bearing cover on left side of actuation-shaft. Remove shaft from casting with suitable puller/shop tool.

Pull out the actuation arm and the bronze pads. The pads are very loose and will fall off at once.

Loosen both the setscrews on the friction finger hub. Heat the friction finger hub slightly (if needed) and slide it off the shaft. Take care not to loose the friction finger hub retainer (two-part locating ring).

Check shaft transitions for burrs. Remove burrs as needed.

Slide the friction spool off the shaft.

Remove 6 screws from perimeter of clutch housing/casting.

Wiggle housing out from headstock. It has a locating flange inside the headstock.

Remove 3 cap head bolts at the bottom of clutch housing to loosen brake plate retainer and brake plate collar.

Remove retainer, collar and brake plates. Clean everything and remove old gasket material. Check both drive and brake clutch plates for wear. Original thickness: 1,27mm = 0,05" The number of clutch discs in my lathe: Drive: 25 , Brake: 13. If this is the correct number I don’t know but the drive works good.

Parts-layout: Bottom row, L to R: Brake plate collar , Brake plate retainer , Friction spool , Friction finger hub with set-screws and Friction finger hub retainer, Clutch plates with Friction finger plate and Clutch backing plate , Friction drive hub with nut bearings and spacer, Bearing retainer. Top row, L to R: Brake clutch plates , screws for brake plate retainer , Actuation shaft with lever and hardware , Clutch actuation arm , Clutch casting with actuation arm bearing loosely in place.

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Assembly: Before assembling anything clean the casting insides. Especially the drain to the headstock. Including the drain passage in the headstock. Also make sure the counterbore the clutch casting goes into is free of any debris. Deburr and stone any high spots on the mating faces - Headstock and clutch casting. The threaded holes might need a tap run through them to clean out old gasket cement and dirt.

Insert the input-side bearing for the clutch actuation shaft in the casting. Put it in the freezer overnight to make things easier.

Put gasket cement / sealer on the headstock around the hole the shaft goes through and around the drain hole. A little will do it. I recommend loctite 518, which is much more oil-resistant than the usual silicone-based sealers.

Install clutch casting. Make sure the casting is fully seated in the hole in the headstock before tightening any bolts. Tighten bolts evenly.

Insert the brake plate collar and keep it in place loosely with a couple of screws.

Insert the brake plates every other type and correctly aligned (see clutch plate alignment).

Remove the temporary screws, put the brakeplate retainer over the discs and fasten everything with the 3 screws.

Put the friction spool onto the shaft. It is free to float on the keys.

Put the clutch actuator arm and it's bronze pads into it's correct position.

Put the actuator shaft in from the non-input side, through the actuator arm and into the previously installed bearing. Preferably with the shaft in a very cold state.

Put the left bearing onto the shaft and into it's bore. Put on outer circlip.

Put the spacer onto the input side of the actuator shaft. The shaft probably needs deburring as the set-screw does not have a dimple. Deburr so the spacer goes on easily.

Put the clutch lever onto the shaft. Should slip on when heated after deburring shaft.

Align lever and insert taper-pin properly. Insert and tighten set-screw.

Put the bearing retainer and associated set-screws into it's recess on the non-input side of the shaft.

Apply heavy grease to the friction finger hub retainer (split-washers) and place them on the shaft.

Put the friction finger hub onto the shaft, aligned so the set-screw holes and dimples are on the same side of the keys. Also make sure it slips completely over the friction finger hub retainer so that they are completely inside the counterbore.

Look for the set-screw dimples in the holes and align. Insert set-screws and tighten gradually while rocking the holder slightly to make sure the set-screws find the centre of their dimples. I used loctite on the screws since one had fallen out and the other was loose when I opened it up.

Put the friction finger plate (heavy flat washer) onto the shaft.

Put the clutch plates onto the shaft correctly aligned and every other type (see clutch plate alignment). Put some heavy grease on each plate so they stick together. If you don't the outer plates will fall off the keys and you will either damage the plates or have to start over (or at worst both). Put the clutch backing plate (heavy non-symmetric washer) onto the shaft with the flat side towards the plates.

Before you commence make sure the plates and washers are fully up against the fingers and that the fingers are inside the friction spool (clutch engaged). If the fingers are outside after assembling you might find they are locked there and you will have to pull the friction drive hub out again. Also check that the inner bearing in the drive hub does not stick out. If it does you might end up with the clutch so tight it won't engage. I prefer to have the bearing about 1mm below the edge of it's bore.

Put the headstock in the lowest gear to make it easy to turn the input shaft.

Put the complete friction drive hub onto the shaft (housing, 3 bearings and spacer). I find hitting the end with a plastic mallet works good until the outer bearing meets the casting (it moves easily up to that point). Make sure the clutch discs enter the drive hub correctly and that all the discs are up against the fingers at all times.

Put sealant onto the outer bearing retainer.

Use longer-than usual bolts (2-4 is enough) through the retainer to start pulling the drive hub and bearing into place. Switch to normal bolts when needed. Constantly check the clutch discs and make sure everything spins. When the shaft gets harder to turn or discs are not loose on the shaft something is wrong (usually a disc not entering the drive hub correctly). If that happens back of and make it go in correctly with a small screwdriver.

Tighten all the bolts evenly to seat the bearing and drive hub. If everything spins freely bob's your uncle.

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Clutch plate (or indeed brake plate) alignment: The clutch and brake plates must be installed one specific way or the clutch and brake won't work. The orientation of the plates with the pegs on the outer edge doesn't matter. They are the same no matter how they are installed. The ones that rides on the splines though must be installed the same way every one of them. I prefer to have the splines horizontal and install the plates so that there is a part that sticks out towards you on the top. The important thing is that all of them must be aligned and rotated exactly the same or there won't be enough spring force in the clutch-pack to drive the spindle at the designed horsepower. The pegged plates and the ones on the splines must obviously be installed alternately.

Orientation of clutch plates

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Clutch adjustment: The adjustment of the clutch is done by tightening the bronze nut on the end of the inputshaft. The larger outside nut is for holding the drive pulley onto the shaft / friction drive hub. When you tighten the bronze nut with a suitable pin-spanner you move the inner bearings and the spacer between them closer to the clutch plates (or indeed you make the space between the clutch fingers and the inner bearing in the clutch housing shorter). That means that the bearings and spacer slide inside the friction drive hub, since the drive hub is in practice locked in place axially: The large outer bearing is held in place by the bearing retainer and even though the clutch housing theoretically could slip inward toward the clutch (if the press-fit of the bearing let go) there are no forces working that way. The only axial forces on the housing are the clutch fingers pressing it against the bearing, which is locked in place by the retainer. There is also a clue in the parts book: The bearing spacer is called “Friction adjustment sleeve”. Pictures: Sequence – Assembly.

How to pull the Friction drive hub out from the casting as one unit with bearings and retainer.

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Input-shaft with keys.

Brake clutch plates and collar installed. Complete brake unit with brake plate retainer and screws

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Friction spool installed on input shaft. Free to slide on keys.

Friction finger hub retainer can be seen close to Friction spool. Friction finger hub installed over retainer.

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Clutch plates installed on shaft.

Clutch backing plate installed outside clutch plates.

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Bearing retainer with a suitable amount of Loctite 518 applied. If you found this guide useful feel free to send any amount of $ you would like to: cosworth@gmail.com 06.07.2015