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Thread: Lip Seals and Heat Generation
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28th February 2015, 04:20 PM #1.
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Lip Seals and Heat Generation
I probably should have posted this before the thermometer thread.....
Yesterday I wanted to establish once and for all whether the seals in my mill's vertical head were responsible for the heat that plagues the head when it is run for a short time. The non back geared speeds range from 500 - 1140 rpm. When I used the mill and it was often before I acquired my second mill, I would only use the lowest speed and it became hot after a few minutes of continuous running. So the second mill, the 13, which has 2 horsepower and power feed and doesn't run hot became the mill of choice for vertical work. The little Hercus however can turn a 6 inch saw on its labyrinth sealed horizontal arbor and could turn it ad infinitum. The 13 can only manage 5 1/2".
Michael suggested that bearing preload might be a contributor to the heat problem so I thought I would remove the upper end cap housing the seal and the spacer the seal seals against and mount them on the lathe. I removed the garter spring before commencing a few tests. With the spring in place I'm sure the head would have been generated faster.
Running the lathe at 900 rpm for 30 seconds produced heat in the spacer that was bearable to touch, an additional 60 seconds rendered it nearly untouchable. I could hold the spacer for about 6 seconds .
The original seals were Flaseal 13297s. The replacement seals I have are made by NAK. Seal size is 2.5" x 1.875" x 3/8". The sealing lip is, as close as I can measure, 1.848", the outer diameter of the spacer on which it seals is 1.873". When the spacer is installed in the seal there is considerable turning friction. I downloaded a Timken seal catalogue last night, all 709 pages worth, but it does not identify the internal lip dimension on their similarly sized 472041 and 482041 seals. I'm wondering if there is variation among manufacturers??
The Timken seals are cheap enough in the States but shipping isn't.
When I mentioned this problem earlier Phil "Machtool" very kindly posted to me a V Seal made by NAK for appraisal. It looked promising so I purchased a pair of similar seals from SKF. These seals would mount on the spacer and in the case of the bottom seal, the spindle. The thin lip would need to seal against a sleeve because the seal's OD is less than 2 1/2". What I would do is bore a dummy sleeve to gauge the fit of the seal and test run it in the lathe to see if I have a cure.
An easier cure though would be to try another lip seal. Ben and a few others say their vertical heads are cool running. (Bruce isn't one of the few because he has no seals in his!) It would be great to hear what seals are fitted in those that have them.
Bob.
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28th February 2015 04:20 PM # ADSGoogle Adsense Advertisement
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28th February 2015, 07:15 PM #2GOLD MEMBER
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Hi BT,
I thought your tailstock didn't line up with your headstock? wouldn't that invalidate your test some what?
I assume that spacer is hardened and ground?
Stuart
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28th February 2015, 09:23 PM #3.
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Stu,
The spacer does appear hardened and the tailstock woes were greatly reduced when the chuck was replaced and by using Alan's test bar, adjusting the position of the TS horizontally. It's still probably a couple of tenths out of whack and if that affects the seal then I'm more buggered than I thought.
Bob.
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28th February 2015, 10:22 PM #4GOLD MEMBER
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1st March 2015, 12:48 AM #5.
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Assumption! We know what that is Stu. I haven't checked but I imagine that there would be more run out in the sleeve's fit on the spindle than there is in the tailstock. I'm starting to lean in the direction of a labyrinth seal. Less guesswork in regards to the optimum fit of a V seal and no hardening required. The hardening would be a issue anyway. As far as oil leakage goes, well I'm use to a pond under the vertical heads of both mills.
BT
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1st March 2015, 01:04 AM #6GOLD MEMBER
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I'm just wondering if the heat is the result of the diameter of the spacer being oversize.
Surely smaller=less pressure=less heat.........just a question of if it still holds oil when it runs cool enough.
But I would have 0 idea
Stuart
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1st March 2015, 01:21 AM #7.
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I did think of asking other No.O owners to measure their spacers but a standard 6" Mitutoyo vernier caliper's jaws won't fit between the nut and the seal. The nut comes off easily enough but it's probably too much rooting around .
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1st March 2015, 12:00 PM #8GOLD MEMBER
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Hercus Model O Mill Seals
Bob
Have a look at my post of 5th Jan 2013 @ 2.31pm Post no 9.
Photos & description of Seals I machined up from some Nylon.
Press fit with clearance on the shaft.
Been working well ever since
Also made a modification for the lube to reach the bearings, as shown in the photos.
Bruce
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1st March 2015, 01:12 PM #9.
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Found it Bruce. Thank you - https://www.woodworkforums.com/showth...68#post1593868
At the right hand end of the brown bar at the top of each post is a number. If you right click on the number, options are made available. If you click on " copy link location " you can simply paste that link in the text of a new post or message.
Bob.
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