No.O Vertical Head - Seal Heat Generation and a Possible Cure

When I used my little No.O on a regular basis, the double lipped NAK oil seals fitted in the head produced, in my mind, excessive heat. The head would become uncomfortable to touch if run for an extended period even at its lowest normal speed. I never ran the mill at its highest speed of 1140 RPM for fear of causing irreparable damage to the head's Timken bearings.

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I had planned on replacing the seals with something along the line of Bruce "Abratool" 's nylon seals but never got around to it because I bought another mill. That mill has proper labyrinth seals and can be run for hours on end with the vertical head remaining cool. That head's seals -

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Hercus use a simplified version of a labyrinth seal on the roller bearing spindled 9 and 260 and to seal the grinding spindles fitted to the No.3A and No.1 tool and cutter grinders. So I thought I would have a go at making similar non contact seals for the vertical head. I made the upper seal to start with figuring I'd only be half as disappointed if it didn't work. It works but I think it probably can be improved.

The other mill's "proper" labyrinth seal has a bore 0.003" larger than the spindle end it seals. The Hercus 9 has a bore probably 0.012" larger than the spindle. A 5 thou feeler gauge readily slides into the gap.

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Because there was an element of uncertainty regarding the effectiveness of the seal I chose to use easy 1214. I also used a cheap internal grooving tool which worked well. I made the bore 0.004" larger than the spacer the seal seals upon. That bore may need to be enlarged.

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With the new seal installed and the lower lipped sealed end cap removed from the head I ran the mill for ten minutes at 1140 RPM. The initial cold temperature of the head, measured on the upper end cap, was 22C. After 5 minutes it was 34C and at ten minutes, 39C. Previously, with both lipped NAK seals in place, the temperature reached 47C in about four minutes running flat out.

My concern that the bore may not be large enough is that there may be some very slight contact between the ground spacer ( second photo at the top) and the seal because the residual oil was not perfectly clear when I dismantled the end cap. The spacer is not a precise fit on the spindle, rough measuring showed about one thou slop. Further investigation with some lamp black should determine whether there is contact.

If this all works it would be a pretty simple modification for those that own a mill with a hot head. Could be that Bruce and I are the only ones!!

Bob.

Interesting Bob.
Some years back now I fitted a wiper seal to the vertical head on my mill as it was leaking but now it runs hotter than I would like it too. I may have to revisit the head and see if it is worth removing that and putting in a labyrinth seal as you have. I'm working a bit blind here as while the mill manual is extensive and includes parts diagrams and breakdowns, for some reason the head was never documented, so it's all experimental.

Michael

So today I made the lower labyrith seal. Pressed it into the end cap and gave it a test run for ten minutes at 1140 PRM. At the end of the run the upper bearing cap temperature was 34C and the lower cap, 32. I'll probably find a pool of oil on the table tomorrow but the 13's head leaks so the little Hercus will be in good company. Worth the adventure.

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BT

ps. I slipped up to the shed this morning for another temperature test. With a starting temperature of 14 degrees I ran the mill at its lowest normal speed of 500 RPM for ten minutes. The temperature rose to 22C. After 20 minutes of continuous running the temperature reached 25 C. And there wasn't a pond of oil on the table. :2tsup:

Hi Bob, good thinking and nice work as usual.
Tho I am not understanding how the oil does not run out the bottom labyrith seal?
How much oil is in the head, or what is the oil level in relation to the seal?
I thought that it would have a level plug 1/4 or 1/2 way up from the bottom and the oil would
just run straight through the labyrith seal......what am I missing here?

cheers, shed

Quote:

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Originally Posted by shedhappens

Hi Bob, good thinking and nice work as usual.
Tho I am not understanding how the oil does not run out the bottom labyrith seal?
How much oil is in the head, or what is the oil level in relation to the seal?
I thought that it would have a level plug 1/4 or 1/2 way up from the bottom and the oil would
just run straight through the labyrith seal......what am I missing here?

cheers, shed

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Thanks J.

It appears that Hercus opted for a total loss system for the O's head. No plugs, no oil sight glass, nothing.

I was surprised that there was no oil spill so I removed the lower end cap and found oil present above the labyrinth seal but not in the seal's grooves.

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Hercus intended bearing lubrication to occur when oil pumped into the upper end cap nipple made its way through the stopped drill hole and then through a very small gap between the bearing cup and the inner counterbored recess in the end cap.

When I measured the projection of the bearing cup and the depth of the recess, the resulting gap was small, less than 0.001". I increased that gap to about 0.003" and filed a shallow groove in the face of the recess at the oil hole location in an attempt to increase the flow of oil to the bearings. Given the minimal amount of oil present at disassembly this morning, increasing the size of the groove appeared to be the simplest solution.

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My friend Bruce must have had similar concerns about the effectiveness of the original Hercus setup because he notched the bearing cup to create an oil passage.

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Bruce's photo.

I opted for an easier method of creating an oil passage and used a 1/8" ball end mill this afternoon.

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It will be interesting to see where oil from the three pumps of the pom pom oiler has gone in the morning.

Bob.

Thank you Bob, you would think that when you applied oil to the top brg that the oil would wet the seal, if it was
getting hot it is likely that the oil was missing it completely.

When I replaced the seals in the head of my mill I noticed that the drive shaft was getting warm,
I had lubed everything as I assembled it but the seal is well above the oil level and so I tipped the head sideways to submerge the seal in oil and I run it for half an hr or so and appears have come good.
It seemed to me that the seal might have been a bit tight for some unknown to me reason, it runs cooler now so I
have either run it in or burnt it out :rolleyes:

cheers, shed

Shed/J and Others who may find this of some interest.

I thought I would have a look to see where the oil was because there was no apparent leakage this morning. I used soot from a candle flame to blacken the lower end cap to check if the counterbored recess was inhibiting oil flow but the only contact the cap has is with the head casting.

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Then I held the head in my bench vise and pumped oil into the nipple. Oil can be seen running down the spindle to the right of its centreline.

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I imagine most of the oil runs down onto the bevel gear to be flung onto the casting walls where it then drains down onto the lower bearing. The bearing probably benefits from some direct oil spray also.

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So with the issue of leakage not fully resolved I reinstalled the upper NAK lipped seal with a very liberal application of Mobil DTE Heavy /Medium oil and ran the mill at 1140 RPM. After 5 minutes of continuous running the upper end cap temperature was 44C and the spindle, an uncomfortable 57 degrees.

I will stick with my labyrinth seals.

Bob.

I spent a pleasant afternoon reaquainting myself with the little mill, starting work on a pair of adjustable table stops. I removed the lower bearing cap before I commenced and found a fair bit of oil in the counterbore which means oil has passed through the bearings. Still no leaking labyrinth seal.

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The O shares some of its shortcomings with its sophisticated neighbour, the most notable, a lack of Z. 3C collets reduce the frustration. After a few hours starting and stopping and running at 660 RPM the bearing end caps were gently warm.

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Fixed.

BT

Hi Bob, Thanks for the WIP report on the sealing of your mill.
On the mill, how is the drive gear connected to the machine? I've a horizontal machine that has a 3 MT plus a rectangular drive, that I'd like to set up in a similar way, albeit with possibly some more Z room.
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Thanks
Kryn

Here you go Kryn.

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When I made my pretend slotting head I used the spindle nose drive dog slot to provide feed to the head's crank and a 3 Morse blank end spigot to ensure alignment. Could be another way of skinning your cat.

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Bob.