Underdrive

Last Updated: 26 Feb 2011

I chose to begin this project at the bottom.  Specifically, the underdrive assembly.  The housing here contains the motor and countershaft, which drives the headstock spindle.  This first photo depicts the as-purchased state of the underdrive.

This really isn't bad - certainly nothing compared to the condition the DoAll drivetrain housing was in!  Most of what's in here is bits of rubber from the vee-belts that link the motor to the large drive wheel.  There's a slight oil film as well, which gets worse as you move toward the top of the housing.  I suspect this is leakage of oil from the headstock down, because there are no oil-lubricated parts in the underdrive assembly.

There are 2 bearings on the countershaft, both of which are smooth and silent.  They are double shielded bearings (not sealed).  It's remarkable that they're still in excellent shape after all these years, but I suppose that has to do with the belt tension being relatively low.

Initially I planned to remove this entire assembly for cleaning.  I changed my mind after getting some good advice that "if it ain't broke, don't fix it".  That means the assembly had to be cleaned in-place (except for the motor and it's mounting plate, which I did remove and clean separately).

To clean this I used a combination of simple green and Brillo pads.  These took care of most of the oily film on the housing walls, and a vacuum sucked up most of the tiny rubber bits.  I did my best to keep contaminants away from the bearings.



This photo is after cleaning, with the motor and its mounting plate removed.  It might not look much better than the dirty photo above, but trust me it's "better enough".

Later...
After running the lathe for a couple hours (total), I became aware of a squeak-squeak-squeak-squeak somewhere in the underdrive assembly.  Near as I could tell, it was coming from one of the two bearings in the countershaft pulley.  You know, the two bearings that I referred to as "smooth and silent" above.  I decided to tackle the problem immediately, even though I was in the middle of my first "real" job in the lathe.

To remove the assembly, begin by removing the motor and its mounting plate as described on the motor page.  Remember to remove the flat belt before proceeding.
 
To extract the counterdrive assembly, you must remove the pivot shaft at the rear of the cabinet.  This shaft is secured on the right side (the side closest to the chuck) by a single socket head set screw.  This photo illustrates the location of the set screw.  It is not possible to see the screw without shrinking down to the size of a house cat or being a contortionist and using several mirrors.  Rest assured it's a socket-head screw (six point), and just feel around until you find it.

You'll need to drive the shaft out to the right.  It's set in babbit!  This may or may not make it difficult to remove.  I was able to drive the shaft out with no particular trouble using a good quality 3/8" diameter punch and a 3-lb hammer.  Several hard its were required to dislodge the shaft initially, then things got easier.

You're pressing this shaft a long distance.  The shaft itself is more than a foot long, and it must be driven completely out of the cabinet.  So you'll need a long punch.  I started with the aforementioned 3/8" x 6" long punch, then moved up to a 1-foot piece of 4340 steel rod (1/2" diameter) that I use as a punch.  I finished up using a 3-foot piece of 4340 1/2" rod to drive the shaft the last few inches.







The assembly must be supported while the shaft is removed, not only to prevent it dropping to the floor when the shaft comes out, but (more importantly), to keep the weight of the countershaft assembly from binding the shaft.  In the first photo here I'm showing my preferred method for dealing with the underdrive assemblies.  This floor jack is convenient, although a smaller model would be even better.  Try to place the jack near the center of gravity for the assembly (take a guess - it's toward the back).

With the countershaft safely supported, disengage the tensioner by removing the return spring and unscrewing the tension adjustment bolt from the countershaft casting, as shown.  The bolt will rotate inside the tensioner, because it attaches using a ball-and-socket joint at the top.  Use pliers on the unthreaded portion as necessary.  This is a somewhat slow process.

In the first photo here we see the extra-long punch required to drive the counterdrive pin out.  It's a three foot long piece of 4340 steel.  I worked my way up from a 10" to a 12" to this 36" model.

When the pin is free, lower the jack.  I pulled the assembly out through the opening on the left side of the cabinet.  It weighs around 30 lb (I think), so it's not too bad to lift.

You're left with the second photo here, which has some parts labeled for nomenclature.






The first task is to remove the vee belt pulley, which is secured using a taper pin as indicated in the first photo.  According to people who work on these machines regularly, this pulley was installed in such a way as to ensure it can never be taken apart again.  Fortunately, your experience may vary.  In my case, the taper pin came free after about 10 solid hits with a 3-lb hammer.

The second photo here illustrates the procedure to pull the pulley from the countershaft.  That's an OTC model 1038 2/3 jaw puller, good to 7 tons.  In the case of this lathe, it took no more than a couple hundred pounds of force to remove that pulley.  It practically fell apart.

With the vee belt pulley removed, the next step is to remove the two bearing retention plates which are secured by 3 bolts (each).  I didn't take a photo of these plates, but it's obvious once you're looking at the assembly.  Also remove the the two shaft nuts in preparation for pulling the rear bearing.

Drive the countershaft in the direction shown in this photo.  The bearings are not tightly pressed into the casting, so it shouldn't take much force to get the shaft into the position shown here.

Once in this position, use a 3-jaw puller to remove the rear bearing.  Unfortunately, I didn't take a photo of this step, but it's just a normal bearing pressing operation.  The bearing comes off the shaft to the right in this photo.

To pull the bearings I used a 3-jaw Posi-Lock model 104, which is far more suited to pulling small bearings than the big OTC model.





With the rear bearing removed, the entire countershaft can be removed from the casting.  However, I found I had to slide the cone pulley to the left in this photo in order to provide sufficient clearance to get the left end of the shaft to clear the bearing hole in the casting.  That's what the first photo here is showing.  Notice I had to use the 2-jaw configuration on the puller in order to get access to the pulley with the casting in the way.  By sliding the pulley all the way to the left (until it contacts the casting), there's enough room to slide the entire thing to the right to clear the left end of the shaft through the bearing hole in the casting.

Remove the two set screws from the pulley cone before pulling on it!

Once you've removed the countershaft from the casting, it's a simple matter of pulling the front bearing (which I also failed to photograph).  At that point, the cone pulley can be pulled off the shaft.  This doesn't take very much force, but just enough to make it more convenient to set a puller on it, as shown in the second photo.

This photo is showing the entire counterdrive assembly in pieces, many of them labeled.  I'll discuss dismantling the flat belt tensioner shortly.




I dismantled this assembly because I had a squeaking bearing.  The original equipment is a New Departure 88026, which fits a 26mm shaft and has an outer diameter of 52mm.  The 52mm part is fairly standard, but the 26mm shaft is uncommon.  I found that EB Atmus (my usual bearing supplier) had Consolidated replacements for around $30 each.  Emerson bearing has cheaper (import) replacements for only $11 each.

The right thing to do is replace these bearings.  Instead, I decided to repack the originals.  I could detect no flaws in these bearings, except that they were devoid of oil - the only thing remaining of the original grease was the binder.

To repack them, the shield on one side had to be removed.  These bearings use a 2-part shield, with a layer of felt between.  The first photo here shows the outer shield removed.  The second photo shows both shields removed and laying atop the bearing.

I always end up destroying the shields when I remove them from bearings.  The problem with going shield-less in this case is the potential for bits of metal from the lathe contaminating the bearings.  But since these bearings may need replacement anyway, I'm willing to accept that risk.

I cleaned the bearings as best I could to remove all the old grease binder, then carefully repacked them with Magnalube Teflon grease.

The experiment failed, however, as I found the squeak-squeak-squeak-squeak returned a few hours after repacking.  Since the assembly had already been out once, it was a piece of cake to remove it again and replace the bearings with new Japanese-origin bearings from Emerson.  I don't regret repacking, since I learned a bit from doing so.

Putting it back together...
The bearing for the vee-pulley end of the countershaft is somewhat tricky to press back on.  There are several ways of handling it, but I used a bench vise to support the bearing with just enough space for the countershaft to slide between the jaws.  The press fit isn't particularly strong, and the bearing is pressed in until it contacts the shoulder of the shaft.

Be sure to protect the threaded end of the shaft.  I put the takeup nuts on and set a piece of steel on top to strike with the hammer.






With the left side bearing pressed on, you'll want to practice putting the shaft into the main casting in order to find a method for yourself that yields good results.

I took some time with steel wool to clean up the casting so that the bearings can slide in and out of their bores with a light hand pressure.  That way there's no need to be pounding the shaft into place.

I was therefore able to position the cone pulley as shown in the first photo here, then insert the shaft (with left end bearing pressed on) from left-to-right.  That's a 2x4 piece of scrap beneath the pulley, which placed it at nearly the correct height.

In the second photo here I'm showing an interim step.  The left side bearing is in place, and the backing plate has been installed.  The right side bearing plate is still loose, and the right side bearing is being driven in from right-to-left.  I used a hammer on a socket sized to contact the inner race of the bearing, since it's being pressed onto the shaft (it slides easily by hand into the casting).

The problem with this part is the need to hold the left end of the shaft securely while the bearing is driven on.  One way of accomplishing this would be to butt the left end of the shaft against a solid wall or heavy object.

My method is shown in the third photo here.  I simply set the assembly angled as shown (it will balance in this position), and tapped the right end bearing on.  It doesn't require very much force.

Although the left side bearing is pressed up against a shoulder in the shaft, there is no such shoulder on the right side bearing.  So the left side bearing must be completely assembled, including the backing plate, so that the right side bearing can be driven into the proper position without the need to measure.  Install the right side bearing plate as well, and press until the bearing contacts the backing plate.  This will ensure the assembly is in the proper position.

The last photo here is a detail view of the right end bearing during the installation.

This is a photo of the completed counterdrive assembly, cleaned and ready to be reinstalled.  These parts were all carefully degreased (despite the look of the photo, they're actually very clean looking in reality).  As usual, I found the grease residue between the shaft and the pulleys that mount to it forced the need for the puller to remove them.  With the residue removed, these parts slid back together with light hand pressure.

The cone pulley is easy to position properly, since there are deep divots in the shaft where the set screws belong.



Tensioner


 It's worth taking a quick look at the flat belt tensioner.  This first photo shows the tensioner dismantled, except that I left the hand lever intact because I couldn't see how it comes apart.  I suspect there's a pin that secures the handle, but attempts to drive out what looks like a pin failed.  In the photo, the swivel bracket rotates about the pin, which is secured by the set screw as shown.

Here I've assembled the two parts from the previous section and the tensioner has been added to the photo.  Notice the oil hole for lubricating the ball-and-socket joint.


I like to paint the insides of my machines gloss white.  This helps brighten things up tremendously, makes it easier to see leaks, and generally improves the visibility of the various parts.  Since it's internal, I don't bother too much with a top-quality finish.  I carefully cleaned the insides with strong degreaser (mostly brake cleaner, in this case), masked a few bits I wanted to keep "original", and sprayed some Rustoleum gloss white (several coats).

I used the floor jack method to install the counterdrive.  With the assembly balanced carefully on the jack pad, I slowly raised it into position.  The trick here is to get the holes in the countershaft hinge aligned with the holes in the cabinet hinges, then drive the hinge pin home.

As usual, the cleaned up hinge pin slid into position with mere hand pressure - no need to pound it into place.  A little bit of teflon grease should keep it nicely lubricated for a long time.

Once the counterdrive assembly is supported on its own, it's a simple matter of putting the tensioner, motor, and belts back in place.