Copyright 2000-2007 by Frank J. Hoose, Jr. Home
Repairing 4x6 Bandsaw Bearings
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Copyright 2000-2007 by Frank J. Hoose, Jr. Home
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There I was, in my shop, with some free time over the holidays, thinking I'll finish up installing the DROs on the Sieg Super X3 mill. All I need is a few mounting brackets and I'll be done. Then, whang!, the bandsaw stops working. Strange noises soon led me to suspect the gearbox, and a process of elimination confirmed it.
The gearbox is filled with nasty-looking heavy, foamy brown oil, that looks a lot like the final residue from boiling down a whale (don't ask me how I know this). So I decided to remove the gearbox from the bandsaw to more easily drain the oil-like-stuff and work on the repairs. It quickly became apparent that this would not be a simple repair job: the bearings and oil seal on the shaft are press-fitted into the gearbox casting, with no obvious way to remove them.
Gearbox from 2000 vintage HF
4x6 bandsaw
Since my bandsaw is over six years old, to "save time" I decided to
bite the bullet and buy a new bandsaw from HF. I was in luck, or so I thought, since they
had one in stock; I got in the truck and headed south. It's about a 90 min. round trip
from my house the nearest HF. I got back home and began assembling it, only to soon
discover that the casting was damaged.
The upper part of the vertical casting, including the cast-in handle and the handwheel for
the blade tightening handscrew, were smashed. Called HF. Had just enough time to get back
down there before they closed, but the only other one they had was the floor display - and
we all know how well-cared-for those are!
Broken casting on new
bandsaw
For a brief moment, I considered just salvaging the gear box from the new bandsaw and mounting it on my old bandsaw, but this thought quickly evaporated when I saw that the gearbox on the new bandsaw is not a separate unit: it is cast right into the frame.
New gearbox integral to frame
So, fate seemed to have forced me to tackle the job of repairing the gearbox on the old bandsaw. Looking for help, I posted a few messages and some pictures on the mini-lathe and bandsaw Yahoo groups. I got some good advice, but had already begun my own plan of attack.
The main problem with this repair is in removing the oil seal, bearings and worm-screw assembly. I concluded that the simplest approach would be to drill a hole in the gearbox housing opposite the end of the worm-screw, through which a driver pin could be inserted to drive out the shaft. Ideally, the driving force would be applied as a steady pressures - as from an arbor press. I have a small arbor press, but it did not have enough clearance for this job, so I was compelled to use a hammer instead.
In order to accurately position the hole, I placed the housing on the surface plate and used a height gage to transfer the height of the shaft from each side of the housing to the place where the hole would be drilled.
Transferring the shaft location
I first attempted to drill the hole by hand-holding the housing on my drill press table. Even though I started with small drill bits, and worked my way up to larger ones, it quickly became apparent that the bits were grabbing the work and would probably tear it from my grip and send the housing flying across the shop (no doubt seeking out the nearest window!) So I decided to move the operation over to the Sieg X3 and clamp it down for safety.
However, the shaft extends from the lower side of the casting. On the drill press, I just positioned the shaft to fit through the hole in the table. Also, the side of the housing opposite where I was drilling the hole was not entirely flat, so just getting set up took about 10 minutes. That done, drilling the hole was simple - and safe! In retrospect, though, it would have been a lot simpler just to clamp it to the drill press table.
Set up for drilling on the
Sieg X3
I drilled a 1/2" diameter hole and used a short piece of 7/16" dia. aluminum rod as a driver. Since the worm screw was engaged with the pinion gear, before driving out the shaft with the worm screw, I had to remove the gear. After removing a C-ring, I found that I could not fit a gear puller into the tight space of the gear box, so I drove the other shaft out to get the gear out.
Next I drove out the wormscrew shaft. A few blows from the hammer and the shaft was removed, along with the bearings and oil seal.
Once removed, I found that there was a plastic spacer positioned between the two sets of bearings. It was torn up pretty badly and looked as if it had been worn down from its original height.
Bearings and spacer
With a little more work, I removed the bearings from the shaft. This turned out to be more difficult than I expected since there was no easy way to support the bearing to drive out the shaft. I considered using a gear puller to remove the bearing, but was afraid that the bearing would be ruined because the gear puller would exert all of its force on the outer edge of the bearing. I milled a "bearing support" - just a small piece of 1/8" aluminum plate with a "U" milled into it for the bearing shaft. This enabled me to support the bearing in my large machine vise.
After removing the bearings, they seemed to be working ok; albeit not quite as smoothly as they should be, but serviceable. Apparently, the plastic from the spacer had been catching on the bearing causing the original noise and rough-running. The part number on the bearings is Koyo 949100-279.
Next job was to make a replacement spacer. A quick scan of the junk bins revealed that a piece of 1 1/2" (1.3" actual dia.) plastic electrical conduit was just the thing I needed. A few minutes with a hacksaw and the lathe and I had a nice-looking replacement spacer.
Replacement &
original spacer
Replacement spacer in
place
I reassembled the gearbox, using some conveniently-sized pieces of aluminum scrap to drive the bearings and shaft back into the gearbox housing. I had to repeat this step more than once, as the spacer I had fabricated was too long. Due to the damage to the original spacer, there was no way to tell what its original length had been, so I just took my best estimate. Unfortunately, I forgot to record the length that I finally used, for the benefit of others who may be faced with this repair.
Re-installing the shaft and
bearings
The last step was to turn a plug from Delrin to close off the access hole that I had drilled into the housing. This was a pretty simple task, and I made the plug just a thou or two over the hole diameter to get a snug press fit. I was prepared to have to glue the plug in place with epoxy, but that proved unnecessary - the press fit was sufficient.
Delrin plug made on the lathe
I had saved the original gearbox oil in a small container and now poured it back into the gearbox and replaced the gearbox cover. A quick test with the motor running assured me that I was back in business.
Obviously, before reassembling the gearbox would have been a great time to replace all of the bearings and the gearbox oil. However, I did not know of any local source where I could quickly obtain either, so I decided to move ahead and save those tasks for another day. Now that I know how to take the gearbox apart and put it back together, this does not seem so intimidating.
Mini-Lathe Mini-Mill Bandsaw Grinder Anodizing Lapping Links Safety Premium Content
Mini-lathe: Accessories Adjustments Capabilities Chucks Dial Indicators Features
Getting Started Glossary
Introduction Materials Modifications My Shop Operation
Reviews Sieg
Factory Tool Grinding
Troubleshooting Tuning Versions