Crescent 36" Band Saw Restoration

Modified on 2010/07/31 14:38 by krucker — Categorized as: Bandsaws, Restoration Topics

by Keith S. Rucker

Part 2 - Pouring Babbitt Bearings¶

Table of Contents [Hide/Show]

Part 2 - Pouring Babbitt Bearings
   Introduction
   1 - Saturday, October 23, 2004
      1.1 - Clean the parts
      1.2 - Setting up to pour
      1.3 - Melting the Babbitt
      1.4 - Heat the parts
      1.5 - Prepping the Babbitt for the pour
      1.6 - Pouring the bottom bearing
      1.7 - After the pour
      1.8 - Finish work on bottom bearing
   2 - Tuesday, Nov. 11, 2004
   3 - Monday, Nov. 29, 2004
   4 - Friday, Dec. 3, 2004
      4.1 - Setting up for the pour
      4.2 - The pour

Introduction¶

First a little bit of background. Everybody always wants to know where to buy babbitt metal from and the other supplies. For more information on those topics, see our other entries here on pouring Babbitt:

Now that you have read all of the above and have a good background on how to get started, lets go over how to actually do it. The main thing to remember about pouring babbitt is that it is not rocket science. The first time that I ever did it, I did not have the advantage of being able to read all about it here. This write up is actually about my first try and as you will see, I was ultimately successful!

While most people are scared to death of the thought of pouring Babbitt bearings, the process is actually pretty easy and low tech. And the great thing is that if you mess up - no problem, just melt the bad bearing out and start over again!

1 - Saturday, October 23, 2004¶

With little to do on the saw until the castings of the broken parts get back from the foundry, I decided what the heck, the bearings needed to be poured on the bottom shell of the bottom bearing - might as well go ahead and get that part out of the way. So, for those that have never poured Babbitt bearings before, here is how I do it.

1.1 - Clean the parts¶

The first step in pouring bearings is to clean the bearing shells up real good. You will not want *any* loose material or oil and rust in the area you are pouring the bearing in or the bearing might not stick and hold. Here is the bottom bearing sell of the Crescent 36" band saw I am restoring. There are actually two bearings built into this one shell.

The bearing shell before cleaning

To clean the shell, the first thing you will need to do is make sure that all of the old babbitt has been removed from the shell. When I got this machine, somebody had done a pretty poor job of replacing the babbitt bearings with bronze bearing shells sandwiched between the two halves - so in this case, I did not have remove the old metal. There was, however, a few pieces left in the small holes drilled in the shell though (which are used to help anchor the bearing in place.) To remove the old bearing metal, just use a torch and melt it out. After melting out the old Babbitt, next clean things up real good. When I do this, I usually use a water based de-greaser and scrub the area up real good and then wash it off with clean water. Next, I will often use a wire brush on a drill or side-grinder and brush the area real good. The wire brush will do a good job of removing any old rust of loose materials from the casting.

The bearing shell after cleaning

1.2 - Setting up to pour¶

The next step is to get things set up and ready for the pour. Be sure to take some time here and get things just exactly right. In this case, on the bottom of the bearing shell, there were four milled areas that were all milled to the same thickness giving me four good reference points to hold the shell level on. I first placed the arbor (which had also been cleaned by the way) on two machinist vee-blocks that are exactly the same height and did some measuring to see how thick I needed to make four blocks to hold the shell at the right height to give me the proper clearance on the bottom of the bearing. On this piece, the arbor is 1.5" in diameter and the outside diameter of the bearing shell was 2". This meant that I needed 0.25" of babbitt poured all the way around the shell. Doing a little measuring, I cut four wood blocks to the proper height to hold the shell at the right height for the pour. Before placing the arbor in place before pouring, I first made some dams using the babbitrite material. I then put the shaft in place, making sure that I had the proper clearance all the way around the shell and then molded the damming material up tightly to the shell and arbor. Before declaring it ready for a pour, I did one check of all the measurements to make sure things were properly aligned.

The bottom shell and arbor set up and ready for a pour

1.3 - Melting the Babbitt¶

Now it is time to start melting the babbitt. I cranked up my propane camp stove and put the ingot of babbitt in the ladle to melt. It actually goes pretty quick. It only took about 15 min for the metal to be melted and hot enough to pour.

The ingot of babbitt metal melting on the camp stove

1.4 - Heat the parts¶

At the same time that the Babbitt metal is melting on the heat source, you need to be working on pre-heating the shell and arbor for the pour. If the shell and arbor are not hot enough before pouring, as the molten Babbitt is poured into the shell, it can cool too fast, resulting in a pour that will have lots of wrinkles and voids in it. You basically want to heat the parts up hot enough that when you drop a drop of water on it, it just sizzles away and evaporates instantaneously. It does not need to be red hot or anything like that but near the same temperature as the molten Babbitt. For most pours, if you start pre-heating the parts at the same time that you start melting the Babbitt, they will both be ready about the same time.

Using a propane torch to pre-heat the bearing shell and arbor

1.5 - Prepping the Babbitt for the pour¶

Before actually pouring the babbitt, take a wooden stick and skim any impurities off of the top of the babbitt. The wooden stick is also a good indicator as to when the Babbitt is hot enough to pour. When a pine stick chars (but not burst into flames) after sticking into the molten babbitt, it is usually hot enough to pour.

Skimming the babbitt and checking the temperature with a pine stick

1.6 - Pouring the bottom bearing¶

Now you should be ready to make a pour. Before going any further, a word of safety. You should already have figured this out (if you have not, you probably don't need to go any further) but spilling molten metal on you can be quite dangerous. Be sure to do everything possible to prevent any dangerous situations. Only work in open, uncluttered areas, preferably outside. Also, wear protective clothing - long pants and long sleeve shirts. I also always wear long leather welding gloves and wear an apron throughout the process. And don't forget to protect your eyes - at a bare minimum, wear safety glasses but I will usually also wear a face shield.

OK, now that we have covered safety, lets pour some bearings. Carefully lift the ladle from the heat source and pour the metal into the gap between the arbor and shell. You do not want to do this too fast but you also do not want to take too much time. Pouring too fast will often cause too much metal to be poured, causing some to spill. Pouring too slowly will often result in a bad pour as the metal is cooling too fast to make a good liquid pour. I wish that I had a picture of me actually pouring the bearings but I was working alone and had my hands full - no room for the camera!

In the case of this pour, since I had two pours on the casting, I did them as two separate pours, pre-heating one side and making the pour and then pre-heating the other side and making that pour later. Don't try to and do too much at one time or you may not get your parts properly pre-heated and have bad pours.

The two bearings after the pour

1.7 - After the pour¶

After you finish your pour, the best thing to do is just walk away from it and leave it for a couple of hours. The parts need to cool down before you can do anything further. Do not try and pour water on the bearings to cool them off or you may cool things too quickly causing the bearing to shrink and not hold in place. Also, if you move the arbor while the metal is still too hot, you can actually deform the bearing resulting in a loose fit. After this pour, I went to town to do run some errands and eat lunch. I left things alone for about two hours before even trying to do anything. Just let it cool off all by itself real nice and slow!

When I returned, the first thing to do was to remove the arbor. Before I could do this, I first had remove some of the metal that had bridged over the top. To do this, I used an old wood chisel which cut through the soft metal pretty easily. I then carefully lifted the arbor out of the shell. This is the moment of truth. What you want is a pretty smooth surface all the way across. If there are some areas small wrinkles or voids, no worry but if they are major, you will be better off just melting the metal out and starting over again. Don't get upset if your first pour (or even first couple of pours) do not turn out as well as you like. Pouring Babbitt is part an art and until you get some experience, it does not always turn out just right. The first time I poured Babbitt, I think I had to do it three times before I got it right!

The bearings after removing the arbor

Looking at the picture above, the bottom side of the picture turned out about as good as you can expect - nice and smooth. The top side was a little rough in the center of the bearing but it looks worse in the picture than it actually is - just some small voids on the surface. Remember, we will have to scrape the bearings later on as we fit the arbor to the metal so most of these imperfections will be removed. And even then, you only need about 80% contact across the bearing to have a good fit. Some small imperfections are not a problem.

1.8 - Finish work on bottom bearing¶

Once you decide that you have a good pour, you can start doing some finishing work. First, you will want to get the top of the poured bearing even with the shell. Since Babbitt is so soft, I usually do this with a large rasp file. It does not take long. Just file everything down until the bearing is even with the sides.

After you file everything down, clean it up and see what things look like. Here is how my bearing looks to this point:

Looking good!

At this point, we are only half way done with pouring the bearings - now we have to do the top shells. Unfortunately, I am going to have to wait to do that until I can get the bearing tops back from the foundry. If you have been following this restoration, you know that one of the bearing tops was broken when I got the saw and I brazed it back together and sent it to a foundry to have a new part cast. Until I get the cap back, this is all I can do on this pour. Check back here later and we will cover pouring the top and scraping the bearings to get a good fit.

2 - Tuesday, Nov. 11, 2004¶

The new castings from Cattail Foundry (see: Foundry Sources) came in the week of Thanksgiving. Total time from when I sent the repaired castings off to be used as patterns to when the new castings came back to me was about six weeks. Not too bad I guess. Total price for re-casting the four parts was $114 including shipping. Now that is not bad at all! If I had been able to find new old stock parts, I know it would have cost me more than that.

The new castings next to the repaired parts used as patterns as received from Cattail foundry

3 - Monday, Nov. 29, 2004¶

Seeing that the new castings came in the day I was leaving to go out of town for Thanksgiving, I had to wait until I got back home to do any work. With the new castings finally here the next step was to do some light machining to the parts. First, I took the two bearing shells for the top wheel bearing to a local auto parts store that had an in house machine shop. The part of the two castings that would mate together were kind of rough and I wanted a nice fit. In the automotive machine shop, they placed the two bearing shells on a grinder that they use to smooth the bottom of engine heads to fit on a gasket. The machine is basically a big belt sander with a precision flat surface under the belt. It took him about 5 min to flatten the bottom of both parts to where they would fit and he charged me a whopping $7.00 for the labor. Also, while at the auto parts store, I purchased two different thicknesses of gasket paper to use as spacers between the two castings when pouring the bearings.

I next went to a farm shop of a local farmer that I know very well to use his milling machine. The farmer knows that I use to work as a machinist and has always invited me to use his shop whenever I needed to - as long as I help him out every now and then when they need something done in his shop that his workers cannot do (he does not have a trained machinist working there). On the mill, I drilled out all of the bolt holes so they would line up. On the top wheel bearing, the bottom half of the casting is tapped to receive the bolts from the top bearing. Nothing too challenging but using the mill rather than a drill press made it go much easier.

4 - Friday, Dec. 3, 2004¶

I was able to take off work today at lunch time and decided to spend my time pouring the rest of the bearings on the band saw. The bottom bearings of the bottom wheel bearing had already been poured so part of the job was already done.

4.1 - Setting up for the pour¶

I actually began by working on the top bearing assembly. First, I laid everything out just like I did with the bottom wheel bearing assembly and poured it using the same technique.

Top wheel bearing assembly ready to pour

Next, I got the top half of the bearing ready to pour. The first step was to cut out a series of spacers to use between the two bearing halves. You need to use several spacers of different thicknesses so that as your bearings wear down you can re-scrape them and remove a spacer to tighten the bearing back up. I use gasket paper for this purpose simply because it is relatively cheap, easy to cut out to fit the various profiles of bearing caps and the fact that it is designed to withstand heat, like it will go through with the molten babbitt is poured.

After things cooled down a bit, the shaft was placed back into the bearing half, the spacers put in, the top half bolted into place and retaining compound packed around anyplace babbitt could pour out.

Bearing cap of the top wheel bearing assembly ready to pour

4.2 - The pour¶

To pour the top bearing, the shell was heated up with a propane torch and the molten babbitt was simply poured into the two oil holes in the top. Once cool, everything was unbolted and things cleaned up to be ready for scraping. The oil holes were then drilled out (the babbitt hardens in the holes at it cools).

The same process was then done for the two top caps of the bottom bearing assembly except a small metal funnel was used to get the babbitt in the holes.

Top caps of bottom bearing assembly ready to pour

That is pretty much it. After pouring the bearings, the bearings are scraped using small scrapers to help fit the bearings to the shaft. This is a trial and error process that is done over and over again until you get a good fit.