Bronze Bearings

I have my fathers scraper now - somewhere. It will have been used in anger on bearings. Long time ago though.

It's 3 square, blade a bit over 1" long and I would estimate a bit over 3/16 per side. Having used one that was too big really I suspect that's a sensible size for bearings up to 2" or so.

Having seen some one scraping a surface plate flat to a master not sure that I agree with the comments on use in the pdf. I also saw a man scraping his Bridgeport that I have mentioned before. Same technique in both cases. The blade is held almost vertical and either pushed or pulled horizontally so the net effect is that the end travels in an arc and the angle the blade starts at tends to set how much metal is removed.

I did ask about sharpening 3 square scrapers. Hollow grind and hone the edges. When there is a lot of honed area hollow grind again.

John

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Can't edit that post now but the handle of the scraper remains more or less still and the blade is pushed or pulled some way down it.

John

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I don't have one, but I see the boring of bushed as a job to be held in a collet. With no collet, the 4 jaw chuck is probably the next best, if so don't over tighten or the bore when released will come out slightly square, triangular if you use the 3 jaw, I know, one of my early jobs when I took up this hobby was to make a pair of bronze bushes, I ended up making two pair.

Ian S C

I've always been curious about what I have seen and read about flat scraping .Seen doesn't tie up with what's about on the web. I also used a pretty old huge surface plate during training. The finish on it fits in with the method I described. It didn't fit in with the paring with a chisel like patterns. Other things to like a pretty old Schaublin bed.

I've heard of one other way of "scraping" lathe bearings. It needs a jig with a hole dead on centre with the lathe spindle axis fastened to the bed some how and some sort of boring bar that locates in the hole and the "boring" is done by rotating the bar by hand. As only tiny amounts of material are removed it sounds feasible to me. One odd/interesting aspect is that this fits in with some styles of "ancient" tailstocks where the quill can easily be removed.

Personally if I was the OP I would be having a careful look around at oilite bushes and maybe even sleeving the spindle if it helped use those. That might not work out though. They are press fit and when ever I have used them the hole comes out a bit undersized. Just what's not needed if there are 2 on a shaft some way apart. In my case over a foot.

John

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Edited By Ajohnw on 12/08/2016 11:46:17

If the bearing hole comes out undersized, its because the hole where you press fitted is also undersize.

I was given to understand that the press fitting is intended to "compress" the bearing, but only by the design amount.

Well there is more than one way to skin a cat. Likewise with scraping. Depends too if you are roughing, or getting down to the fine work, or if you are "frosting" for the finished look. It seems to me the British had one way of doing it, the Yanks inevitably had their own way. Swiss engineers I worked with on steam turbines had another way and I believe the Japanese have another again.

It was a 6ft square inspection grade surface plate Hopper. I have seen another as well a bit smaller in an inspection department. Same pattern. The Schaublin bed edges also. They had just about worn off the front edge but still pretty visible on the rear.

The hole size for the oilites was exactly what Boxford machined in. The precision shaft to replace the original spindle was slightly undersized but that didn't help. The fit supposed to be at a level where there is slight friction on the shaft. Much the same as plain bearing lathes as far as I am aware.

John

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Going back to flat scraping, it reminds me of going into the Mandelli machine tools factory in Piacenza, Italy, several times in the 1980s when my sister was their technical translator. At the time they were one of the world leaders in CNC machine tools, and they were forever boasting that their milling machines were accurate to the odd micron. So were the machine beds fine-finished by one of their own machines? No - they were hand scraped. It seems there is no substitute for craftsmanship, although the situation may be different now.

Michael,

My suggestions would be that after rough boring you use the boring tool to create an annual groove in the bearing directly under the oiling point so that some of the oil can easily travel to the bottom of the bearing . Then turn the tool so it is pointing down and create a stopped groove running out along the bottom of the bore either side of the annualar groove so as to distribute the oil . In this way oil will always be available instantly upon start up and so extend the life of all mating surfaces . You should also obviously use the stoutest boring tool you can get in the bore in order to reduce spring and thus avoid bell-mouthing . Repeated final cuts should obviously be taken without any additional cut being applied . The finer finishing cuts should be applied using an angled top slide so as to allow you to better apply small cuts . In addition , you will find it beneficial to change the feed to a different feed , and preferably one which is not a permutation of previous feeds . In this way you will have a better chance of removing more of the peaks from the final surface finish.

Trevor.

I have had good service from small scrapers made from old saw-sharpening three-square files. They are made of good steel and all that is needed is to grind off the teeth, and hone on a fine oilstone. If you want to be clever you can grind a groove along each face between the edges, and this helps to ensure that the honing does not produce a domed surface.

If the grinding causes bluing it is easy to harden the end, and draw it back to a mid straw, before the honing process. And by honing, here, I mean a final smooth finish with a fine stone or wet-&-dry.

Do the same with both ends, and put a cork firmly over the end you are not using.

Regards, Tim