Bronze Bearings

Hi all. I hope you can assist me.

as you can see (hopefully) from the drawing i have a worn bearing at the change wheel end of the headstock. I have purchased some bronze bearing stock and will attempt to make a couple of new bearings for the lathe.

The question I have is what should I ream the bearing out to in order to fit snuggly on the spindle but not bind upi.e what clearance is required. The bushes are split flanged type for a Grayson lathe and I would assume tightening the bearing housing down would take up a small amount of the play

Michael

I'd probably go for 1.120" eg 0.001" larger but bore it rather than ream. Are you able to do it on another lathe so the spindle can be offered up to the bearing as you get close to size?

No unfortunatley i only have the one lathe. After stripping and measuring I had to put it back together.

Why boring as opposed to reaming. I thought it would need a more precise bore hence my thoughts on reaming.

Thanks for the reply

Michael

Definitely bore rather than ream, a reamer that size will cost & also they can do some strange things. boring will be cheaper and more controllable.

Tony

You might be best to turn a piece of steel bar to the exact same size as teh lathe spindlle and then use that to make sure of the final size of the bushing bore. Pay attention to the exact sizing of the OD of the bushing too. It will work better if it is seated well in the hole in the headstock casting rather than contacting only at a couple of points.

You need some clearance for an oil film, the bearings are split for adjustment, and bronze has a tendency to 'close' slightly on reamed holes, so there's little point in reaming rather than boring. Unless you have some large drills you'll need to bore out before attempting to ream. You also need to consider how you're going to measure the bore. Accurate measurement of holes isn't easy if you're chasing tenths. Since you can't use the spindle as a 'gauge' I'd turn a separate gauge first, and use that to size the bore rather than try and measure it directly.

Andrew

The halves should be split before boring and shimmed when clamped together for drilling and boring. You may know this already but I did not think it would hurt to make sure.

Martin

The old way was to make them a few thou undersize and then scrape to fit. I suspect the only way of obtaining a small 3 square scraper may be to make one. I tried to find one for use on Myford bearings but finished up with a huge one that was just about usable on split bearings. It would be no good in these.

There is usually some spindle wear on this sort of set up. A correctly sized bearing for the front accounting for wear probably wont slide along the spindle. As I understand it the clearance should ideally be negligible - even less that a thou.

Just in case you were thinking of using an adjustable hand reamer it would be best to check across all of the blades. They generally aren't all on the same diameter so can do all sorts.

John

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Edited By Ajohnw on 11/08/2016 13:13:17

Thank you all for your replys.

I hadnt thought of turnng a piece of steel bar down to the spindle size for checking the measurements. I shall defininatley do that.

The bronze bearings are split on one side only not completley in half like the ones in a Myford. Would i still need to split first before boring or put the split in afterward.

Michael

I would personally split after boring.

Tony

In that case I would cut after you have done all the turning.

One other tip with the plug gauge is once you have it to size turn a small length of the end say 0.002" smaller that way you will know you are getting close when the reduced length fits into the hole.

There is a possibility the bushing will spring inwards a tad after the split is machined into it.

(Those of a sensitive nature should look away now.) But that can probably be rectified by inserting a screwdriver or the likes carefully into the slot and carefully springing it back out a bit. Or do the oiler bolts etc fit into the slot and spread the bushing apart as is done on old Drummond lathes? There must be something to stop the bushing from spinning in the housing?

Alternatively you could rough machine the bushing. Split it in the one place. Fill the split with solder and then finish machine the inside and outsides diameters. Then melt the solder out afterwards. A lot of mucking about and best avoided if you can.

Edited By Hopper on 11/08/2016 13:41:00

Hi Hopper, there is a small dowel pin that holds the bush in place via a groove in the flange opposite the split.

Michael

I suspect the only way of obtaining a small 3 square scraper may be to make one.

Like this one ?

**LINK**

The cutting edge is approx. 50mm long & approx. 8mm along the edge of the triangle. I have one & it holds an edge well.

Cromwell Tools do a similar sized scraper for about twice as much (plus Vat) - bought one at work this week.

HTH

Nigel B

.

That looks a very reasonable price, Nigel

I paid £4 for a secondhand one, only last week

... Excellent condition, Moore & Wright, so I'm still happy.

MichaelG.

Or if thats too big Tracy's do one that is 1/8" wide and about 20mm long, ideal for scraping any burrs off the inside of bearings after drilling oil holes etc. I use my one quite a lot.

Would I need to scrape the bearings considering I'm going to bore the bearings out to 0.001 oversize. If I do how would I go about doing that with a bearing that has a split cut into one side?

Michael

Michael,

If your boring is successful, you may only need to 'break the edges' with a scraper .

I suggest you run the lathe for a while, then inspect the bearings ... If there are any obvious high spots [or quite likely longitudinal lines] then ease them with a scraper.

There's a useful one-page note here, regarding use of scrapers:

http://neme-s.org/Model_Engineer_Files/2858-How%20to%20use%20Scrapers.pdf

**LINK**

MichaelG.

Thanks MichaelG. When I mentioned to my dad that I would have to replace the bearings in the lathe he mentioned that I would have to scrape them in. I thought that only had to be done with bearings that are in two halves. At the time he gave me a scraper that he made before he retired 20 years ago out of an old file. He was nearly as exited as I was when I purchased the lathe

Michael

Michael,

[Just in case it isn't obvious] The reason you might get longitudinal 'highs' in these split bearings is that when they close up, under adjustment, they can go slightly oval. If you see three similar lines, it's probably not worth messing with them.

MichaelG.

Edited By Michael Gilligan on 11/08/2016 21:21:37