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15th May 2015, 10:32 PM #16.
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Sure, I can appreciate that bearings can run for years on a single load of grease. The size of the motor is not that relevant, it's the soup of water, sap and clay like sawdust that needs to be dealt with and I guess I should have been more specific about this in the first post. The sawdust slurry goes everywhere within a radius of about 2 metres of the cutting area. The blade shooting into the log at around 5000 fpm fires a jet of water and sawdust back directly at the roller fortunately it's at right angles to the bearings. In short it's messy. The sap also contains tannic acid which dissolves quickly in the water and reacts with any exposed steel forming ferric/ferrous tannate and all exposed steel turns black and slowly pit over time, I suspect this is what really seized the sealed bearings and why even the inner ones had a faint gritty feel to them. One good thing about this is despite the large amount of water involved there's relatively little oxide rust on the sawmill
I'm kicking myself for not spotting the ideal grease path is through the shaft/bolt but I'm going to console myself with the excuse that you failed to include it in the sketch!
Sticking with the two bearing idea you have to keep the spacer between the inner races, seeing as you have a lathe you can knock up a lantern ring really easily that will provide the path for lubrication and act as the spacer.
Now that you have stated your priority is to flush grease and contaminants out regularly why not take it one step further and fit an auto greaser? Instead of a grease nipple screwed into the bolt screw on a greaser; low tech would be a Stauffer cap where you just give the cap a turn every so often, or fit a spring loaded Stauffer that you just charge with a grease gun at the start, thus providing a constant trickle of grease. Top of the range would be an SKF lubricator which uses a tiny battery operated gas generator to constantly pressurize the greaser and provide constant lubrication feed. These have an adjustable flow rate and can be switched on and off so you're not greasing stopped machinery if you don't need to.
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15th May 2015, 10:55 PM #17.
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Sorry I used the term "guide" rollers - they are not like a normal upright WW bandsaw guide rollers. The band is under quite a high pressure and makes a hard contact with with the rollers which push downwards on the blade to reduce band flutter and hold it flat in the cut. I guess the pressure on the rollers is not that high. I could try 8.8 but the thought of the blade coming of at speed will require the wearing of brown trousers. I have done it twice at low speed when I was trying to back out of a cut and that was bad enough - luckily no significant damage at all to the blade, a couple of teeth lost their edge but it was not noticeable in the subsequent cutting
I have not fitted the rollers so I have no pics of then but in this pic you can see the wooden blocks that are where the rollers would be located.
This is a somewhat puny log but you can see on the RHS the spray of water that hits the block (roller) on that side.
The photo doesn't really capture the amount of spray involved.
On bigger logs where the log is a lot closer to the LHS block/roller there is a lot of water being flung back onto that block/roller.
After a few cuts the blocks are covered in soggy crud and continue to be doused in water and sap.
.
Just to give you an idea of the size of the blade.
5335mm x 50 mm - the gizmo it's sitting on is the semi auto tooth setter - we also have the sharpener ( https://youtu.be/hyVHW2KhTWs)
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16th May 2015, 07:14 PM #18.
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I had a crack at the grease line through the bolt.
I decided to use an 8.8 bolt because I realised the tension on the band (which is along the band) is nowhere near the tension on the rollers (perpendicular to the band.
Parts
3 is a lantern ring spacer that separates the bearings creating a grease cavity.
A ~7mm wide by 2 mm deep groove has been turned on the inside of the lantern ring to enable grease to come through from the bolt hloe - through the lantern ring and into the cavity between the bearings.
1 is an external spacer that holds the roller away from the mill frame.
2 is another space that also protects the outside bearing from direct spray. The outer most seal of the outside bearing has 8 x 1.5 mm holes drilled in it for exiting of grease.
Here you can see the grease oozing out on the back side
There is a few tenths of a mm gap between the bolt spacer and roller on this side (see read arrow below) and I was hoping some grease would get from the cavity and past the internal bearing and sneak out through the gap so I would not have to drill escape holes in the front face of the roller. However, it appears the way out for the grease on the opposite side of the roller is too easy so I will have to drill some escape holes for the inner most roller.
The biggest problem was getting the grease gun to cooperate and output some grease!!!!
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16th May 2015, 08:52 PM #19GOLD MEMBER
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Nice work Bob, hopefully you'll have the problem licked.
Kryn
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16th May 2015, 09:06 PM #20.
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Thanks Kryn.
I just finished the other roller and that one has two exit holes drilled through the front of the roller so the grease can be flushed through the internal bearing.
I use a 2.5 mm bit and not having a cobalt bit it struggled to get through the roller material which is quite hard.
It's been an interesting learning exercise for me as I haven't dabbled with grease lines before but is shows what can be done with some useful input from fellow members.
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16th May 2015, 09:25 PM #21GOLD MEMBER
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You're right about the useful input, from the members. I am amazed at the amount of knowledge of some of the members here, some of it goes straight over my head, it's that technical, but very handy. I don't think I've seen a thread, that hasn't/can't be answered or replied to.
Kryn
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16th May 2015, 10:43 PM #22SENIOR MEMBER
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Hi Bob,
Nice to see a bit of success.
Phil ( or Bill, I'm easy) lol
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16th May 2015, 10:56 PM #23.
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16th May 2015, 11:34 PM #24SENIOR MEMBER
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Originally Posted by Michael G
Given that they are guide rollers, does the bolt need to be high tensile or will something like an 8.8 do?
Michael
(Psst - it was Phil not Bill)
Posted by BobL
Sorry I used the term "guide" rollers - they are not like a normal upright WW bandsaw guide rollers. The band is under quite a high pressure and makes a hard contact with with the rollers which push downwards on the blade to reduce band flutter and hold it flat in the cut. I guess the pressure on the rollers is not that high. I could try 8.8 but the thought of the blade coming of at speed will require the wearing of brown trousers. I have done it twice at low speed when I was trying to back out of a cut and that was bad enough - luckily no significant damage at all to the blade, a couple of teeth lost their edge but it was not noticeable in the subsequent cutting
Metric Grade 8.8 is high tensile, and from memory is slightly higher in spec than Imperial Grade 5. I can't locate my references here and without resorting to Google, grade 5 has a tensile strength of around 120,000 lb psi, while grade 2 (metric equivalent grade 4.6), would be around 75,000 lb psi. A grade 8 imperial, roughly equivalent to metric 10.9 has a tensile strength of around 150,000lb psi IIRC, and I have the idea, but am far from being certain, that the metric standards are marginally higher than the imperial, but other than for the aerospace industry, in practice they are close enough to being equivalent.
So a metric grade 8.8 is not a soft bolt.
Rob.
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16th May 2015, 11:48 PM #25.
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That's good to know.
The hole down the middle of the bolt is 45 mm long so I got most of the way there with a regular 1/8 HSS bit and just the last 5 mm or so I did with a 1/8" long bit. It seemed to chip out a bit more than mild steel but otherwise it did not seem that hard.
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17th May 2015, 12:09 AM #26SENIOR MEMBER
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That sounds pretty right Bob, ordinary HSS would have no trouble handling it or even grade 8 (M10.9) for that matter. Easier to get a good finish as the chips are less stringy than mild steel, you might sometime have to reduce speed if you are already at full bore for mild steel, but you already knew that.
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17th May 2015, 08:18 AM #27SENIOR MEMBER
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