Complete Teardown and Rebuild
How to restore an Atlas 4800 lathe.
Quick Change Gearbox Transmission
First thing to remove.
Loosen the nut that holds the large gear on the quick change gearbox input shaftYou can use a leather glove to prevent the gear from turning while you turn the wrench. Just let it suck in there as you turn the gear. This beats locking the gear train up, and possibly ruining some gear teeth when you apply force.Inspect your puller to make sure that it won’t damage the gear teeth when you put some torque on the tool. Most pullers, if properly sized for the task, will grab the gear with a slight back angle on the puller teeth, keeping the actual tool away from the edge of the gear.You’ll be left with a woodruff key still attached to the shaft, if not, be sure to look for it………..it may have dropped on the floor.Next….loosen the bolt on the compression collar (some people call this whole assembly a “banjo).Next……..find, and remove the bolt at the opposite end of the “banjo”.The whole assembly will slide off the quick change gearbox imput shaft as a unit.
Once the gearbox transmission(banjo) is removed, you can remove the tumbler.It’s removed by simply pulling the knob, and sliding it out of its bore.There should be a brass washer on the shaft, don’t lose it.
First, remove the spindle output gear on the rear of the spindle shaft. Start the gear moving away from the main body by using 2 pry bars directly opposite each other, behind the gear. This will move the gear enough to place a bearing splitter behind it.If the bearing splitter, and puller, try to move as you tighten the puller…….wedge a hammer or something between the puller and a part of the lathe that will prevent spinning.Normally, this would be the time to remove the rear bearing dust seal, but in this case the seal was damaged and had to be removed later. Next, remove the front bearing dust cover.Some models have a different type of seal, one resembling an automotive wheel seal.
Next, remove the rear preload adjusting nut.This nut is locked to the shaft with a hex set screw. There will be two holes resembling each other, be sure to identify the hole with the set screw. I do not recommend using a pipe wrench if your nut is not damaged, or otherwise hard to remove. I have a bad set of threads on the spindle, and had no other alternative. Normally, you would use a pin type spanner wrench.The set screw should have a lead, or brass, pellet beneath it. Look for it, and don’t lose it. This soft pellet allows the set screw to be tightened without damaging the spindle threads.
Loosen the set screw on the lock collar located inside the headstock.Notice the piece of wood between the bull gear, and the front of the headstock. This will prevent the gear from being damaged as you drive the spindle out. The spindle is then driven out using another piece of wood to protect the rear of the shaft.The shaft, and front bearing will now come out of the headstock.Once the shaft has come part way out, it may be necessary to use a BRASS drift to complete the drive-out.Everything on the shaft will want to drop into the headstock as the spindle is removed. Use care to gently lower each assembly as the shaft releases it.A woodruff key can drop out of the gear cluster as the shaft is removed. Make sure to look for it.At this point, I’m ready to tackle the damaged rear bearing dust cover.Somebody had done a real number on it. Whadya gonna do.I was able to turn the seal with a drift. A slow tedious process, but tis what it is. For something like this (a cast iron part) I prefer the largest diameter drift I can get my hands on. It spreads the force over the damaged area without causing too much further damage. Remember, if you shear what remains of the hex head…..you’re in a world of hurt.
Back Gear Assembly
The back gear shaft runs on two steel bushings. They’re at front, and rear, locations inside the headstock casting. They’re locked in with set screws accessible from outside the case. Do not attempt to drive the shaft out without locating, and loosening the proper screws in the proper sequence.
Front set screw, located on the backside of the headstock. This will be the screw you loosen to drive the shaft out, leave the rear set screw alone for now.Rear set screw is also located on the back of the tailstock case. It will stay in place until the shaft is almost driven out. Notice that the front screw has been loosened, and partially removed at this point.The set screws are pretty long, and extend into the case.After the front screw has been loosened, and partially removed, you can start to drive the shaft out of the case. It is driven out from the rear of the case.Remember to leave the rear bushing set tight, and use a brass drift, or punch, to start the shaft forward.Once the shaft is driven far enough to clear the rear bushing, the set screw can be loosened, and the bushing allowed to be pushed into the case where it will help drive the shaft.Now that the rear bushing is out of the bore, you can insert a longer larger brass drift to continue driving the shaft out. Rear bushing, and shaft, are driven together at this point.You may have noticed a plug in the front bore. You do not need to try to remove this plug prior to driving the shaft out. THE SHAFT WILL DRIVE THE PLUG OUT. The shaft has a small gear on its front that will fit through the bore as its being driven, and force the bushing, and plug out.Continue driving the shaft, be mindful that the gear cluster will want to drop to the bottom of the case….be prepared to support or cushion it.
Slide the rear bushing back into the bore so that the gear cluster can be removed.
Headstock Sub Assemblies
Spindle Shaft Bearings and Races
Once the spindle is removed, the front bearing will have to be pressed off.
Mount the shaft in a vise with adequate padding.You need to remove the roller bearing cage. I find that a pneumatic cutoff tool works best. Cut the area of the cage that is nearest to any critical machined surface at an angle, to prevent scoring the shaft.Then you can do the lengthwise cut. NONE OF THE CUTS HAS TO BE ALL THE WAY THROUGH…….JUST ENOUGH TO SUBSTANTIALLY WEAKEN THE CAGE.Using a chisel, or screwdriver, pry the cage apart, and remove.Now that the inner cone is accessible, the shaft can be mounted in a hydraulic press. I’m using a bearing separator for this because the thin knife edge will grab the shoulder of the cone easily.The cone should come off with relative ease. If it doesn’t, as in this case…….you gotta use heat to expand the cone enough to come loose from the shaft. I don’t like doing this for fear of overheating the shaft itself. It’s a last resort. Heat just enough to break the bond, don’t go into the red color on the metal. Add heat in increments….little bit won’t work, add just a bit more, etc.
Spindle Bearing Races
Find something to protect the threads/bore. In this case I had an old bearing cone on hand. Something with a good tight fit to completely eliminate any chance of slag/spatter ruining the bore.Protect the ways with a welding blanket, or whatever you have on hand.Run a bead around the inside of the race. I used 7018 for the good heat it would provide.The raised weld bead will provide a good surface for using a drift to start the race out of the bore. Then I finished up by using a slide hammer to gently pull it the rest of the way out.
to be continued