Friday, February 18, 2011
My Powermatic lathe restoration is almost done, here is what I've learned about this machine.
Here is an exploded view of the stock Robbins & Meyers 3/4 hp 3 phase motor. The bearings are SKF 6203-2RSH/C3's, which were $5.64 each. The belt is a Goodyear 4L230, $5.79. The washers are shown on the wrong ends, the spring washer belongs on the pulley end of the shaft, not the fan.
Here's the variable speed drive. The bearings shown are two 6205-2RSH SKF's, $10.39 apiece. The roll pins in the sheave assembly are short, they can be driven though into the centre where they fall free, and re-driven in from the outside.
This is the plate assembly, this bearing is a FAG 6006.2RSR, $19.07. The machine screw required an impact wrench for removal.
It is mounted into the end of the sheave, note that it does not seat all the way in.
The variable speed pivot arm is attached to the mounting bracket, not shown is the bearing, an 88008 MRC. This is the single most expensive bearing in the machine at $57.19. As it is used to ride around a cam and is not subject to great speed, those on a budget may choose to not replace this bearing. Also, the bolt shown on the end of the pivot arm should not have it's nut in the jam position, it should be on the other side of the arm.
Here is the speed selector assembly. I put a large washer on either end of the spring for smoother action.
When looking at the front if the lathe the cam should form the number "6", a clamp provides pressure against the spring while the screw is tightened.
The head casting is located by two spring pins and secured by four bolts.
These roll pins will also fall out when pushed all the way in, reseat them from the outside. Restrain the snap ring when disassembling, the spring is still under tension when the sheave is fully closed.
Spindle assembly. Note that the indexing wheel is welded to the spacer. This was done by the previous owner, and a wise move. The wheels are known to have wallowed shafts and be prone to damage. They are the weak point in this machine. Drilling, tapping, and bolting these two parts together is another option.
The inboard spindle bearing gets mounted first, it's a Fafnir W206PP, $47.81. I use my bearing seperator to gently pull the bearing onto the shaft.
Next the wide spacer is mounted. This part is inaccessible from this point on.
A piece of all thread is slipped through the spindle, various washers and wood spacers are used to apply pressure where I need it and keep undue stress off the bearings. Be sure to back off the set screw hidden at the bottom of the sheave. This will hold the pulley open, allowing slack in the drive belt. It's a Goodyear 1422V420, $57.19. The outboard spindle bearing is an NTN R16ZZ, $33.43.
Here's the disassembled tailstock. The quill nut is threaded, and is best removed with an appropriate pin spanner. The handle pin is peened into place.
To dissassemble the banjo, first drive out the spring pin retaining the handle and remove it. There is a bronze bushing which must be driven out from the inside before the rod is freed. I used a small pin punch, first I ground the tip flat, then I bent its shaft for clearance. I slowly tapped out the bushing, rotating the shaft to access the perimeter.
I found it easiest to completely assemble and tune the variable speed drive before the lathe was mounted on the base. The belt must be at the top of one sheave when at the bottom of the other, the fit is adjusted by the bolt pushing against the bearing plate and by adjusting the variable speed assembly bracket.
Here's the finished product.
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