Upper Wheel and Related

Upper Wheel and Related Assembly

Last Updated: 26 September 2007 - added more detail about the wheel rubbers, near the bottom of the page.

First, an overview of the upper wheelhouse fully assembled in it's "as purchased" state. The upper door has been removed. Visible are the locknut, camber adjustment knob, and the band tension adjustment wheel.

The upper wheel is secured using the two knobs as shown. The outer knob serves as a camber adjuster for the wheel (to permit proper tracking of the band). The inner knob is just a locknut.

With the knobs removed you gain access to the upper wheel spindle and spindle nut. For this I needed an adjustable spanner wrench. The size of that spindle nut is roughly 1.25", so an adjustable spanner for 0.75" - 2" will work fine. McMaster part number 5471A11.

The local shop wanted $60 for that wrench made by Wright. When I told them McMaster had one for $15, they scoffed and told me it would be cheap made-in-China junk. Turns out the McMaster wrench is an Armstrong, made in USA. Go figure.

	When I stripped the paint from the upper wheel I discovered it's cast aluminum. Rather than repainting it and covering up that nice metal, I plan to simply polish it. The center of the wheel is supported on the spindle by 2 bearings. The spindle diameter is 20mm. The bearings have 2 numbers on them: "N.D. 3204" is marked on the center race, and "47504" is marked on the outer shield. I had hoped that a Google search on those numbers would reveal a supplier, but it wasn't that simple. I was not able to find 3204 or 47504 at any of the online bearing distributors. The DoAll part number for these bearings is 5-01508. Remarkably, a Google search on that number came up with WB Bearings, which cross-referenced 5-01508 to 204 and 47504. This clued me into the fact that bearings are specified by the last 3 digits in the number (204, in this case). A number 204 bearing has an inner race ID of 20mm (which is precisely the diameter required to fit the spindle), so I went back to McMaster and was able to get a pair of double-sealed 6204's very affordably.
But the bearing saga didn't end there. I didn't realize when I ordered the 6204's that the original bearings have retaining rings in them. McMaster doesn't carry these, so after some searching I ended up at another bearing supplier I've used in the past, E.B. Atmus, who seem to have virtually every bearing on Earth. All bearing part numbers across manufacturers conform to certain standards. Among those standards is the use of "NR" in the part number. If present, "NR" denotes a bearing with a retaining ring. Atmus listed the following 6204 bearings with "NR" in the part number (actually, there are a lot more than this listed): 6204 2RSNRJEM (made by SKF) - double rubber seal, with retaining ring 6204 2ZNRJEM (made by SKF) - double metal shield with retaining ring 6204 NR (made by Consolidated Bearings) - open bearing with retaining ring 6204-2RSNR (imported) - double rubber seal, with retaining ring Other part number standards include: Z - metal shield (ZZ would indicate a metal shield on each side of the bearing) RS - rubber sealed (2RS would indicate rubber seals on both sides of the bearing) I placed an order for two of the imported 6204-2RSNR bearings and one 6204-2RSNRJEM. I bought the 6204-2RSNRJEM just to inspect the difference in quality between the imported bearings and those made in the US. The imports were about $4 each, the US-made units were about $12 each.
Below are pictured the import bearing on the left and the "US-made" bearing on the right. Turns out the "US-made" bearing is actually made in Argentina (the "import" is Chinese). Other than the printing on the bearings, these are indistinguishable. The SKF bearing ($12) did come in a little plastic package in the little cardboard box shown. The Chinese bearings came loose in a ziplock bag.

Here's a picture of the upper wheel after some light polishing. It's not the mirror finish I'd like to have, but it's close. I accomplished this level of polish by using:
1) a scotchbrite surface conditioning disk on a 4.5" angle grinder,
2) hand-polishing with 120 grit lapping compound,
3) hand polishing with 240 grit lapping compound,
4) buffing with rubbing compound using a random orbit hand buffer, and
5) buffing with Mother's metal polish using a random orbit hand buffer.

The power buffer I used was too large for this job (buffer diameter was 7"), so if I ever invest in a good smaller buffer I should be able to get mirror-like results. It's good enough for now.

With the upper wheel removed, the complete upper wheel assembly is accessible.

I made an effort to remove the cast iron frame, and possibly made a real headache for my future self. The frame is secured by 4 large cap screws (2 at the top and 2 at the bottom) and has 4 steel dowel pins. To remove it, it must be driven off the dowel pins toward the right in the picture.

I went so far as to remove all 4 bolts and successfully pounded the frame out to the right about 3/8", at which point it contacted the steel shell of the saw on the lower right, preventing the frame from being removed (obviously the saw shell was welded in place after the frame was installed at the factory).

Now for the bad part. It turns out the frame had brass shims in it at the top and bottom rearmost bolts. I didn't realize this whilst attempting to remove it until, while vacuuming away some crud, I sucked up the top 2 shims. By the time I was done, I had bent all the shims (there are 4 total - 2 at the top, 2 at the bottom sandwiched in pairs to provide the proper thickness). I did manage to retrieve all 4 and replace them where they belong (at least as far as I could tell from the pattern of grime on them).

The purpose of those shims, however, is to set the "toe" of the upper wheel so the band will track properly. If I've screwed up the toe, the band may not properly track and either provide poor performance during cutting or, worse, continuously work its way off the upper wheel.

Of course, there's no way to tell whether anything bad will come of this little mistake until the restoration is complete and I attempt to operate the machine for the first time. That could be a couple years from now (8/2/06).

My only consolation is that if the worst happens, it's fairly straightforward to remove the upper wheel, loosen the frame bolts, and change the shims.

The spindle assembly is secured with a pin through a bronze bushing which permits camber adjustment of the wheel. The tension adjustment wheel is held in place by a set screw. Remarkably, the handle on the tension adjustment wheel actually has a tiny spring and ball bearing in it for smooth sliding!

Next up for removal is the upper blade guard assembly. This is what the upper guide block mounts to, and it's movable up and down via a handle at the back of the machine. There's a separate handle that squeezes the guide in its mount to hold it securely.

Here's a partial picture of the upper guard looking up from below.

To remove the upper guard assembly there are 2 sub assemblies to be removed: the guard adjustment mechanism and the guard clamping mechanism.

The adjustment assembly consists of a simple steel cylinder with a knob on one end (see picture of knob above) and a sprocket on the other end. The sprocket is attached to the cylinder using 2 set screws, a 5/16-18 nut and a lockwasher.

Unfortunately, I didn't notice there were 2 set screws until it was too late. I removed 1 set screw, then used a 5-ton gear puller to forcibly remove the sprocket with the other set screw in place. It did some serious damage to the threads, but I was able to repair them with a die.

When I got the saw this adjustment wheel didn't work - the sprocket was not sufficiently secured to the handle shaft, so rotating the adjustment handle did nothing. Disassembly shows why: someone at some point probably left the guard locked in place but applied a tremendous amount of torque to the knob anyway. This very effectively stripped out the handle shaft where the set screws contact it, rendering the set screws useless. I was able to clean up the cylinder this sprocket is sitting on and I should be able to return it to normal functionality.

Considering what this little brass sprocket has been through (torqued until it stripped the steel cylinder then pulled with a 5-ton puller with 1 set screw still in place), it's a miracle it's not bent or broken. Good thing; it would really be a pain to make a new one.

Here's the guard tightening lever. This is simply threaded into the holding fixture, which slides on dowel pins.
Here's the upper guard housing removed. That flat copper spring keeps the guard from slamming down under it's own weight when the tightening lever is loose.

Here are some of the relevant parts cleaned up. I was surprised to find the gear for raising the guard is made of brass, and the depth indicator is made of copper. These are very nice metals when they're shined up, so it's a shame someone decided to cover them up with paint. Think about a modern saw - no way these parts would be anything but plastic or maybe steel.

Pictured are the upper guard clamp housing, copper spring, depth indicator, adjustment sprocket, and the upper wheel spindle.

Reassembly
It was exactly 11 months between disassembly and reassembly of these parts.
Reassembly is basically the reverse of disassembly. First the guide and all its parts are installed, followed by the wheel spindle and finally the upper wheel.

Before	After Note the reflection of the brass gear in the now-shiny guide bar. I left these cast iron parts unpainted, because in real life I think they look excellent in their natural state.

Before	After These guide controls were both chromed. the trim rings were given a bright finish, whereas the handles themselves were done with a matte finish. Both of these are now perfectly restored to their original functionality. You unlock the guide with the lower lever, then position it by rotating the upper handle. The action of the guide is very smooth and easy now.

A note about wheel rubbers
Initially, I purchased two new rubber tires for the wheels. Later, I discovered there are a few companies that offer polyurethane tires as an alternative. The principal advantages to the urethane are durability, ease of installation, and lack of adhesive. The downside is the urethane tires are typically more expensive than the rubber tires. For example, Carter Products offers a urethane tire for $34.95 each. However, I found Sulphur Grove Tool on Ebay, which happens to be located just up the road from me in Tipp City, Ohio. For only $32, I was out the door with two nice urethane tires.

The procedure for installing rubber tires (in case you're inclined to get rubber instead of urethane) is somewhat involved, as the tension is very high. There are a few articles online about it (example). It's basically impossible to do by hand, so you'll need to build a holding fixture of some kind to retain the wheel while you wrestle the rubber over it. Plus they need to be glued.

Urethane tires, on the other hand, are pretty easy to install. They require no adhesive, and they're not as tight-fitting as the rubber ones. Most importantly, you can make urethane quite flexible by heating it up a bit before working with it. To install mine, I warmed up a pot of water on the stove to about 130°F-140°F. I soaked the urethane tire (one at a time) for several minutes. After removing it from the water, I quickly stretched it over the wheel. This took a few tries, since the urethane cooled very quickly (especially on contact with the aluminum wheel), and hence got very stiff. But I did the job without the need for any jigs or special tools - just a bit of patience.

Before	After As I already discussed, new bearings were pressed into the wheel. These can be easily repacked, and should never need replacement again. Note the tension adjustment wheel, which is now chromed a matte finish.

Although not technically any part of the upper wheel assembly, here I will briefly discuss the upper guide itself, pictured in its refurbished state at right.

This particular unit features an internal cavity serviced by a 1/8" NPT port. Based on photos I've seen of other upper guides, that port is meant either to accept a compressed air source or lubricant. Here I've inserted a brass elbow. The larger center hole between the guides is connected to that port, so lubricant (or air) can flow to the blade directly.

The bearing is a 626-series with metal shields on both sides (626ZZ). A small cover snaps over the bearing to provide a smooth surface for the blade to ride. I bought a new bearing from VXB Bearings, who had good prices. The relevant part number is 7323.