jhead spindle pulley bearings - preload?

metalmagpie · Jul 30, 2020

I am about to replace the 207 bearings in my stephead's spindle pulley assembly. When it was taken apart, an inner and an outer spacer were found. My outer spacer is 0.1mm taller than the inner (about .004"). When I hold the bearing stack with spacers and compress the inner races together, the inner spacer fits solidly with no play.

I want to reproduce this with new bearings. The new ones won't be identical to the old ones. I can grind the spacers to suit, but I don't understand how to determine what the spacer lengths should be. Looking for some wisdom here.

metalmagpie

Lakeside53 · Jul 30, 2020

You need to measure the differential between the 6207 inner and outer races (of the new bearings) when the outer (or inner) are pressed together. Lead dots or Plastistrip (plastiguage) on the non clamped races is one way. That measure becomes the "nominal" differential between the spacer heights - adjust in 10ths from there. Easy way to determine good enough is Temperature build up after assembly. 10th or two makes a huge difference.

Alternatively put in 7207DUL type bearings (don't need abec 7 for a pulley) with exact equal spacers. Cheap manfs (inc bridgeport which everyone copied) used DB ground radial bearings to save money. Fast forward 40-60 years and we are stuck dealing with this.

jhruska · Aug 2, 2020

The height of the inner and outer races of the replacement bearings should be the same. Duplex bearings (DUL) will have a reduced height of one of the races. That will be the pre-load applied if the spacers are equal height. I never installed Duplex bearings in the step pulley bearing cartridge.
The off the shelf 207's will be fine but I would expect the spacers to be parallel. The bearings may or may not have the high spot runout marked.
If they do just align the two inner marks at the same 'clock' position and do the same for the outer at assembly.

John

Lakeside53 · Aug 2, 2020

"Off the shelf" 6207 (what BP refers to as "207") are not DB or DU ground. With same length spaces the result is quite floppy, and although that for the pulley isn't such a big deal, it really messes with the dog clutch.

Hardinge (BP) wants $400 a set for the replacement ground 6207. They still sell them. You can get ground 7207 from Timken for about $35 each. Not matched set, but better. Timken part 7207WN SU.

metalmagpie · Aug 4, 2020

Lakeside53 said:
You can get ground 7207 from Timken for about $35 each. Timken part 7207WN SU.

Not so sure about that. Yes, there are a few onesies on ebay, but in general the price is north of $100 each.

7207WN SU | Angular Contact Ball Bearings | Ball Bearings | Bearings | BDI Canada

Oilyneil · Aug 4, 2020

I've just replaced the bearings in my J head, I fitted a pair of Nachi 7207 CDU p4 bearings, with the spacers both ground to the same height.
These bearings are a universal fit pair so can be fitted instead of DB or DF sets. It has made a massive difference to the noise of my machine which had been steadily growling more and more.
Wrong country I know, but these are the bearings ,, they come as a matched pair,
7207-CDUP4 Nachi Precision Ball Bearing Pair 35mm x 72mm x 17mm - BearingBoys
I'm not sure if you have seen it, but Robin Renzetti did a you tube video on replacing precision bearings which is well worth a watch.

Lakeside53 · Aug 4, 2020

metalmagpie said:
Not so sure about that. Yes, there are a few onesies on ebay, but in general the price is north of $100 each.

7207WN SU | Angular Contact Ball Bearings | Ball Bearings | Bearings | BDI Canada

I found at least 5... here's one for $38 or so. Several manfs. 'SU are not in pairs. They are sold as individual bearings, but are ground for DB or whatever mounting.

here's a pair for $56 or offer MRC Duplex ball bearing 7207 D-B | eBay

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jhead spindle pulley bearings - preload?

metalmagpie

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metalmagpie

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Oilyneil

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