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The Art of Scraping Babbitt

Scraping babbitt is something that I never got to see or do. I’d like to hear from the people that have done it and how it’s done. I have bought some tools that I believe to be scraper tools and they look like files with no teeth. Let’s see if we all can learn something new. -- Kevin

I have seen it done by skilled craftsman and this is not a thing for an impatient person to undertake. I have watched it done on the rebuild of a precision surface grinder and there are no shortcuts. The craftsman will use a straight surface such as a granite bar or plate, he will cover the surface with paste bluing and slide the part on the plate, he will then scrape the clean or high spots off the part until he gets the desired number of contact spots per square inch. He may go to the surface plate many times to get the contact area he needs. In round shafts on babbitt he will use the shaft that will run on the surface. For that process the tool looks like a 3 corner file with no teeth. He will have the shaft in and out many times before he gets the desired bearing contact area. This process takes volumes of patience, coffee or whiskey, and determination. Try it on a newly set of cast babbitt main bearings and you will be amazed at how close you feel to your newly restored engine. Many of the large precision engines we see have had their bearings scraped and most steam engines had the main guide box and bearings scraped. It takes much time, but what fun it is. -- Al

About 30 years ago I scraped the mains for an American LaFrance 570 cubic inch "T" head engine. It was fun, except for lifting the crankshaft into the mains about a hundred times. My buddy for the project and I had sore arms and shoulders for about a week! My scraper was made from a half round file and I "ground" it on a belt sander. It was so sharp that I could peel the babbitt off like thin snowflakes. I also could cut the heck out of myself with the scraper. I've still got that scraper and It's wrapped up in an oiled rag so I don't cut myself when groping around in that particular toolbox. -- Elden

I worked at a ship yard for 20 years. One of my jobs there was on the wheel gang, eight of us. Our job was to fit the propeller wheel onto the output shaft. The shaft diameter was usually 34" and the taper about 4 feet long. The propeller wheel was usually about 20 feet in diameter. After using about a 1/2 pint of Prussian blue to cover the taper we would slide the wheel on by using four 75 ton chain falls. Then we would put on the nut (thread size 24" x about 8 t.p.i.) and tighten it. Now you take off the nut then break the taper and remove the wheel with the four 75 ton chain falls. Stick you head in the wheel and grind the high spots with a 4" hand grinder. Clean the shaft, clean the wheel, re-blue and repeat the whole process again. After about 5 tries we would have a fit the Coast Guard and Chief Engineer would approve. All of this would take about 10 hours. I have done this so many times I lost count. Soon I am going to try the bearings on my Monitor - where can I find tiny chain falls? -- Patrick

I am in the process of restoring a 1913 Associated air cooled engine which had a real bad main bearing. After checking on having it poured I decided to pour it myself. I was successful and ended up with a good looking bearing that needed the finishing touches. I had a set of scrapers for doing the bearing scraping given to me so I went at it. It took a little time to get used to what I was doing but shortly I came up with a great fit and as I did it myself I felt good about what I had done. The hardest part of pouring and fitting a babbitt bearing is getting over feeling that you might get it wrong. Forget this as if you did make a mistake it would be nothing to remove it all and go at it again. What a good feeling to be able to do it as they had many years ago. I would do it again in a blink of an eye if the need was to come up again. I hope to have the engine running soon if the weather will just warm up. -- Bob

Scraping bearings differs from scraping ways and other flat surfaces. You can make a good bearing scraper from a triangular file by grinding off all of the teeth and finish honing the tool on an oilstone. The trick is to use your Prussian blue, try the shaft carefully, and don't try to hog off too much metal at once. Take your time and you won't be disappointed. Be sure to add your shim packs each time you try the shaft, so that your final fit will be done with all the shims in place. Scraping ways and other steel surfaces is a different game. The scraper resembles a rectangular file, again without any teeth, and with the tip (opposite end from the handle, or tang) ground to a slight radius, and to a slight angle with the scraper body, in other words the tip is not dead square with the scraper body. Again the surface is blued and tried with a precision flat. The high spots are very carefully removed using a combination twisting and pushing action. A person skilled in this art is known as a "Scraper Hand". As you might expect, good training and lots of experience are needed to master this work. We have all marveled at the ornate "frosting" which is applied to some work, and which actually serves to roughen the surface slightly to hold lubrication. There is a scraping school on the east coast, I believe in the Carolinas, and I know that this gentleman also sells instructional tapes and scraping equipment. This would be a wonderful skill for any machinist to acquire, but I don't think that it is being taught in schools anymore. Info in this is probably available online, I'd search for "hand scraping" or "scraper hand". – Harvey

Most millwrights and millwright helpers in chemical plants learn to scrape. The large multi-rotor compressor and turbines use seals between the wheels in the lower and upper case halves that need to be scraped to exact specifications. As a crane operator I learned this skill between lifting duties. The rotor assembly would be carefully measured. Then the seal assemblies in upper and lower case would be measured. The scraping would start. When the millwrights had the tolerances close they would blue the rotor assembly and set it in the lower half. One or two rotation by hand than it would be removed and checked for the proper clearance. This process continued until all tolerances were to specifications. Sometimes this took up to 36 hours of assembly and disassembly. In 32 years of this work the millwrights in my plant never had a rework. The upper and lower case weight can be 100 tons each. The rotor assembly with the wheels can go up to 50 tons. Rpm on this equipment can be 3800. – Russell

Kevin, I poured new bearings for the transmission shafts on my IHC 10-20 Titan and scraped them. It was a first time attempt but it worked fine if you don’t hurry. I just recently poured and fitted the bearings on an old wood planer. That shaft turns at 5000 rpm more or less and with a wide range of pressures and vibration. They were about 4-5 inches in length. I also found that Permatex makes an aerosol can of blue marking dye which helps a lot. – Doc

For small shafts 1-1/2" or smaller I have used a large black magic marker and coated the shaft with it and it left a nice black spot on the babbitt surface. I have a factory three corner scraper but I have also used my pocket knife honed VERY sharp and use one hand on the point and the other on the handle keeping the blade perpendicular to the bearing surface and carefully scrape off the dark spots. Maybe 2 or 3 thousandths at a time. Clean the shaft, reapply blue/black and repeat until you have the desired contact. One book that I read, said that on these old engines a 50% contact area is acceptable. To pour new bearings it is sometimes easier to use another shaft the same size as the one you want to fit, like a crankshaft. I make a wooden jig to hold the "sample" shaft with the right spacing from the "main cap" or "rod cap" or the "rod". To avoid a LOT of scraping take your time in setting up this "jig". Make sure the "cap" is square and parallel to your shaft. You are better off to set it up so that you will need some shims to start with. As some one said about 1/8" will do.

I have given you enough information to get you so deep into this thing that when you find out when you make your first scraping run you'll say, why did I start this mess. If you don't have the patience to take your wife to the mall and spend four hours with her without grumbling a little, don't try pouring and scraping bearings. It takes PATIENCE! It took me the better part of 8 hours to scrape and fit the three bearings on my 1934 Bell Saw mill. Good luck all who try this. It can be done, but it does take time and patience. -- Don

One final word, when pouring babbitt, make absolutely certain that your form is heated completely dry of moisture. Steam explodes! Safety First! -- Harry


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