Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Very Interesting discussion. I just wanted to share what I think is going on more graphically.?
The image shows what I believe to a be a bias force that is locked into the ring gear when the clutch is tightened. This is due to the clutch disc being ever so slightly off center due to slop in the needle bearings and/or space between the brass busing and ring gear bearing, also possibly due to deformation of the clutch disc itself or differential pressure on the thrust bearing . Whatever the source, it produces a force that varies on rotation such that at 180 degrees from the CDW it pushes the into gear into the worm by the greatest amount.
Peter
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
Here are the parts I used for retrofit, including Belleville worm block upgrade.
Qty listed as needed per axis. Belleville washers come int 10 pack, so only 1 needed for both axis.
?????
Qty
2???? 5909K38??? ??? Needle-Roller Thrust Bearing for 1-1/4" Shaft Diameter, 1-15/16" OD
1 ??? 5909K28??? ??? Needle-Roller Thrust Bearing for 3" Shaft Diameter, 3-3/4" OD
? ? ? ?
3? ?? 5905K29??? ??? Needle-Roller Bearing, Open, for 1-1/4" Shaft Diameter
? ?? ?
1??? 94065K32??? Belleville Disc Springs for Ball Bearing Trade No. R4, 0.406" ID, Packs of 10
? ? ?
2?????? SR4-ZZC #7 PS2?? BG (.250X.625X.196)
? ? ?? ?
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Re: Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
That's interesting, David. Would you please post the parts numbers for all the bearings you used and the source? I'll probably buy these to have on hand for my next rebuild.
Your RA shaft wear looks pretty similar to what I saw when I did my mount last year. Looking at your photo detail, it looks like the needle bearings gave the shaft a "polish" job. I would bet the needle bearings have a smoother surface than the shaft does, and over time they start wearing down the shaft's high spots. The shaft should perhaps be more finely machined to start with to avoid this wear pattern or a break in period.
Putting the wavy washer on the Dec shaft I haven't heard about yet. Since you can tilt this shaft to horizontal easily, the stiction is usually pretty low. Hope this has helped your balancing efforts.
Thanks,
John
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Things noticed with my G11G regarding recent topics including shaft wear, bearings, worms and miscellaneous
Okay so I've got my mount to a pretty good point. I have the SLW and tucked motors. Guiding is between 0.30 and 0.65.
After working on my DEC axis and getting it all straightened out I started on my RA axis.
After tear down and analysis, here are the things I've noticed regarding recent lengthy threads.
There is a little bit of wear on the upper and lower section of my shaft.
On the section to the right there is only a small little area I can feel with my fingernail that's a little uneven.
I went ahead and replaced the two stock bearings with three of the caged bearings.
I was informed by the metal fabricator who removed the old bearings for me that the stock bearings have more needles
so it should be smoother, however the new bearings are caged so they should have less play. Three bearings
should be better than two I hope.
Replacing the ring bearing with the sturdier model. Measured and they are exactly the same
height. Old bearing has smaller but more needle bearings and the new bearings
have longer needle bearings but fewer. Seems to even out contact surface area.
And the new bearings look like they hold a lot more grease in place.
Have the wavy washer on both axis because my scope is a pain to balance.
Noticed when I had the DEC apart the sharp edges of the washer were digging into the disk
and creating little plastic particles. I assume these particles get into the grease
and can cause the random excursions I had in the DEC axis. What I did was
clean everything up as good as I can and sand down the sharp edges
of the wavy washer till they're rounded slightly and smooth. Seem to fix the
DEC axis, I'll see what effect it has on the RA.
When I did the Bellevue washer upgrade, to get rid of my 76 second error, I ordered a pair of
worm blocks for that just in case I screw something up moment. Comparing them to the
current worm blocks found on the SLW, I found the current worm blocks on my mount
were machine down on one side 0.01mm and the spring side block's index peg also machined
smaller. I assume they are machined to fit against the block holder better and allow more
movement for the spring-loaded block. Just a heads up if you order some.
Technically this shouldn't really affect guiding. When I took this apart,
having never been touched by me before, these two screws
weren't even finger tight. Just put the Allen wrench in and they turned
without any effort. Just a heads up. Heard too many of those horror stories
about IOptron mounts coming from the factory with loose nuts and bolts
causing whacked guiding.
That's one of the reasons why I bought a Losmandy mount.
So time to double check everything on my mount.
I've absorbed a lot of great information and ideas from this group.
Just wanted to share any information that might be helpful to people.
Overall happy with my mount now, just trying to get that last 1%.
David Malanick
?
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
The point, that I didn¡¯t say very clearly, is just that there doesn¡¯t seem to be any simple decoding of the serial #s that works for all years. ?
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On 5 Aug 2021, at 23:28, Les Niles < les@...> wrote:
Lastly, for Michael Herman: my mount is serial # HGM403030066. ?That¡¯s 9 digits as opposed to the 6 and 7 digit serials you posted, and clearly the first two digits are not always the year of manufacture. ?It¡¯s an older instance, with the steel worm wheel, and a 323 area code. ?
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Les,
I agree with your assessment.? In addition, drawing from material science, you must bend the material beyond the yield point before it takes a permanent set.? Before that you are in the elastic region of the material.? Apply force and then remove it, and it will go back to its original state.? That's how springs work.? ?I would also suspect the opposite RA plate would just have as much of an opportunity to bend or cup, probably more so if the worm wheel is stainless.? All depends on the materials, there grades of Aluminum that are stronger than steel.? Again, I don't think you will get anywhere near the yield point of the materials.
From your comments, you seem to feel that when you tighten the clutch, it will align with the worm wheel face and the clutch or opposite end of the RA housing,? Much like a screw with washers aligning perpendicular in a hole even when the hole is greatly oversized.?
It would have been nice to see a robust bearing between the RA disc and the worm wheel, in the same plane as the clutch surface.? That would transfer the radial load on the RA disc to the brass tube, or to the worm wheel and then the brass tube.? I wonder if that is a good home for another radial bearing?? You can pick up a precision needle roller bearing with a 1.75" outer diameter that would fit (with a little boring out) in the brass tube.
I did an short examination last night of the bearings.? That is a hefty bearing in the center of the worm wheel.? I wonder what are the radial forces that invited that size of a bearing.? On the other hand, a bearing with a 2"? bore is going to be large, unless you go for a thin section bearing at 10x the price.? A cost vs function calculation no doubt.
I looked at my worm last night, and confirmed it's the stainless variety.? I observed a significant periodic friction when rotating the worm.? I wonder if it is out of round.? I will need to measure that.? I also wonder how much more accurate the new brass ones are.
My Losmandy seems to be a little younger than yours, my last digits are 72014.
Bob
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
I¡¯ve been following this interesting discussion, learned some things about the design of the mount. ?This afternoon it motivated me to tear my G11 apart ¡ª I¡¯ve had some new clutch discs for a few weeks and they needed to be installed. ?Turns out it needed a good cleaning and re-lube anyway. Because of this thread, I pulled the whole Dec axis apart, including removing the worm wheel entirely so I could see exactly how it goes together. ?Good thing too, because there was a lot of old grease to clean up.
After looking at it, I don¡¯t believe the worm wheel can be warped by tightening the clutch, for two reasons. ?#1 is that the force is applied to the clutch disc by a flat plate that is pulled from the center. ?If the worm wheel were to be bent at all, it would move away from that flat plate, removing the force. ?If there¡¯s any deflection, the only place where the clutch disc can apply force is at the inner edge, which is precisely where the thrust bearing is located on the other side of the worm wheel. ?Reason #2 is that the worm wheel is too strong to bend. ?The part where the clutch disc rides is almost 1¡± thick. ?A rough, very conservative calculation for an aluminum worm wheel with a 5000 lb force gives a deflection of about 1.5 ten-thousandths of an inch. If a worm wheel gets deformed it must be through some other mechanism.
Another observation is that the worm wheel is mounted on a bearing that slips snuggly over the hollow brass shaft. ?The inner race of the bearing is a tight fit on the brass shaft; I can¡¯t feel any play but I suppose there could be a thousandth or two. ?This bearing is going to fix the worm-to-wheel spacing regardless of any wobble of the axis shaft in the needle bearings. ?Also, once the clutch is tightened (and assuming the shaft is accurately perpendicular to the end plate), the shaft will be parallel to the needle bearings; it can¡¯t be cocked off at an angle as some have suggested. ?If there is some looseness of the shaft in the needle bearings such that the shaft is not exactly concentric with the worm wheel after the clutch is tightened, then as the axis turns, one of two things must happen: either the shaft lifts off of the needle bearings, or there is a little sideways slippage at the clutch. ?In any case, the worm-to-wheel spacing should not vary except by the amount of looseness of that inner race on the brass shaft, which as far as I can tell is small on the scale of worm-to-wheel spacing adjustment. ?(Of course this is based on my mount. ?Others could be sloppier, but that would be due to wear or a manufacturing tolerance issue, not a fundamental design flaw.)
Lastly, for Michael Herman: my mount is serial # HGM403030066. ?That¡¯s 9 digits as opposed to the 6 and 7 digit serials you posted, and clearly the first two digits are not always the year of manufacture. ?It¡¯s an older instance, with the steel worm wheel, and a 323 area code. ?
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Hi Bob
Always time for more education.? I thought the worm gear turns a matching ring gear, but I may have read wring info years ago, or I digested it incorrectly.
Anyways, I have only read of one owner who wrote that the top surface of their ring gear was warped, and he showed pictures of his filing it flat by hand.? No idea at that time how it got warped.? His center was higher than his edges.? Now that the construction is becoming revealed better, with the thrust bearing smaller in OD than the clutch surface above, it seems possible that the radial forces could have cupped the lower worm wheel.? Or maybe it was mis-cut at the factory but very very unlikely.? That report has always been a puzzle to me.??
Stay well, Michael Hi Dave,
It's a bad habit, if it's white, and it's supposed to slip, I just assume it's Teflon.? It's probably High Density Polyethylene (HDPE).
Hi Michael,
My worm wheel is silver, and I think it's old enough to be stainless.? Regarding the cupping, do you think you will cup the aluminum wheel before you deform the HDPE clutch material?? The worm wheel certainly has an oversized radial bearing, but I am not sure why, it's not supporting the telescope load.? I noticed they are now sealed.
I can understand why the clutch might affect the meshing, I like to really, really tighten my clutches.? I like to run with a slight imbalance, but even then I make it so tight to prevent slippage.? Could I have tightened the mount so much that the axes are no longer turning smoothly?? Maybe I put a detent into the thrust bearing washers or even put a flat on the needle bearings?? Maybe that's why I can never get a smooth guide in PHD2?
As I said before, designs get tricky when one device has two or more functions, then it becomes a balancing act and one invariably compromises one function or the other, or both, and then it becomes difficult to fix one problem without adversely affecting the other.
Ring gear; sorry, no AKA.? A ring gear is simply a spur gear without the middle.? Just a ring with teeth internally or externally.? The internal tooth one is used in making planetary gears, whether in a little gearbox for our Nema17s, or in optical vacuum coating chamber for rotating the "planets" (lens holders).? They can be an inch across, or 15-30ft, as in a crane rotating mechanism.
Regards,
Bob
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On Thu, Aug 5, 2021 at 09:29 PM, John Kmetz wrote:
Just noting that many topics and messages in the forum seem to be duplicating and repeating. And my posts are getting cut short after writing. Somethi
Truncation problem should be resolved now. A system update apparently caused this. Regards, ? ? -Paul
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Just noting that many topics and messages in the forum seem to be duplicating and repeating. And my posts are getting cut short after writing. Somethi
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Re: 76sec error on new OPW-11
On Thu, Aug 5, 2021 at 05:14 AM, Michael Ben-Yehuda wrote:
If you want to use stored PEC then you need to maintain the relationship between CWD, worm gear and DEC axis orientation across the clutch.?
Michael, Typically when using PEMPro, we use a hour or less of data to create a PEC curve which is then uploaded to the Gemini unit. Therefore we largely measure the behavior of the worm, and possibly some of the profile found on that section of ring gear. It would be nice to have data over the entire circumference of the ring gear, but that would take 24 hours of data, and some method of rotating through various sections of the ring. But how to maintain using the preferred best mating parts and only those parts is something I'm not sure the average user could do in practice. Since you can't see inside during operations, this may be difficult. But regardless of the random ring position which may be at CWD at a Cold Start, the PEC curve plays back with the same worm oscillations being repeated, and PE should be mostly negated for better guiding. Without PEMPro I can readily see the sawtooth pattern in PHD2 during guiding. I think we would all like to see better guiding performance without using a correction curve if possible
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Re: Sky Watcher EQ6 R PRO stripdown and rebuild
Yes not relevant but I¡¯m sure we like to keep up with other mounts technically.?
the reason I don¡¯t go EQ6 pro many years back was:
Losmandy machine everything (not pot metal castings);
Everything is fully repairable,
Full parts available off the shelf.?
I had too much trouble with support with previous mount. ? There was none.?
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Re: Sky Watcher EQ6 R PRO stripdown and rebuild
None of this is relevant to LOSMANY mounts.??
--
Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Whoops!? ?One more time. The copy paste worked before, not sure w
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
I just went downstairs to play with my RA axis.? The thrust bearings did need a good cleaning, I could feel the difference before and after cleaning.? I think my worm is also stainless, is that possible?? I have my worm spring loaded on to the worm wheel, which seems to help in backlash. I have what I would describe as a periodic friction, as if the worm shaft was not straight.? I will need to take a dial indicator to it and see what is going on.? I'm attaching a picture of the rear most thrust bearing washer.? It has taken a set, probably from me cranking down on the clutch.? I am just flipping it over.? I don't see it on the larger worm wheel thrust bearing, so I am good there.? FYI, that 4.5" thrust bearing is like $50 or so...not including washers.? Yikes!
Bob
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Hi Bob
Always time for more education.? I thought the worm gear turns a matching ring gear, but I may have read wring info years ago, or I digested it incorrectly.
Anyways, I have only read of one owner who wrote that the top surface of their ring gear was warped, and he showed pictures of his filing it flat by hand.? No idea at that time how it got warped.? His center was higher than his edges.? Now that the construction is becoming revealed better, with the thrust bearing smaller in OD than the clutch surface above, it seems possible that the radial forces could have cupped the lower worm wheel.? Or maybe it was mis-cut at the factory but very very unlikely.? That report has always been a puzzle to me.??
Stay well, Michael
Hi Dave,
It's a bad habit, if it's white, and it's supposed to slip, I just assume it's Teflon.? It's probably High Density Polyethylene (HDPE).
Hi Michael,
My worm wheel is silver, and I think it's old enough to be stainless.? Regarding the cupping, do you think you will cup the aluminum wheel before you deform the HDPE clutch material?? The worm wheel certainly has an oversized radial bearing, but I am not sure why, it's not supporting the telescope load.? I noticed they are now sealed.
I can understand why the clutch might affect the meshing, I like to really, really tighten my clutches.? I like to run with a slight imbalance, but even then I make it so tight to prevent slippage.? Could I have tightened the mount so much that the axes are no longer turning smoothly?? Maybe I put a detent into the thrust bearing washers or even put a flat on the needle bearings?? Maybe that's why I can never get a smooth guide in PHD2?
As I said before, designs get tricky when one device has two or more functions, then it becomes a balancing act and one invariably compromises one function or the other, or both, and then it becomes difficult to fix one problem without adversely affecting the other.
Ring gear; sorry, no AKA.? A ring gear is simply a spur gear without the middle.? Just a ring with teeth internally or externally.? The internal tooth one is used in making planetary gears, whether in a little gearbox for our Nema17s, or in optical vacuum coating chamber for rotating the "planets" (lens holders).? They can be an inch across, or 15-30ft, as in a crane rotating mechanism.
Regards,
Bob
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Will it make this time???
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Not sure why the other picture neve went through...
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Hi Dave, It's a bad habit, if it's white, and it's supposed to slip, I just assume it's Teflon.? It's probably High Density Polyethylene (HDPE). Hi Michael, My worm wheel is silver, and I think it's old enough to be stainless.? Regarding the cupping, do you think you will cup the aluminum wheel before you deform the HDPE clutch material?? The worm wheel certainly has an oversized radial bearing, but I am not sure why, it's not supporting the telescope load.? I noticed they are now sealed. I can understand why the clutch might affect the meshing, I like to really, really tighten my clutches.? I like to run with a slight imbalance, but even then I make it so tight to prevent slippage.? Could I have tightened the mount so much that the axes are no longer turning smoothly?? Maybe I put a detent into the thrust bearing washers or even put a flat on the needle bearings?? Maybe that's why I can never get a smooth guide in PHD2? As I said before, designs get tricky when one device has two or more functions, then it becomes a balancing act and one invariably compromises one function or the other, or both, and then it becomes difficult to fix one problem without adversely affecting the other. Ring gear; sorry, no AKA.? A ring gear is simply a spur gear without the middle.? Just a ring with teeth internally or externally.? The internal tooth one is used in making planetary gears, whether in a little gearbox for our Nema17s, or in optical vacuum coating chamber for rotating the "planets" (lens holders).? They can be an inch across, or 15-30ft, as in a crane rotating mechanism. Regards, Bob
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Re: Sky Watcher EQ6 R PRO stripdown and rebuild
The machining of the worms at the end of the clutch cylinder was used on the '80s Vixen SP and is still copied to day on the SW EQ-5 and the ES EXOS-2. The general bad machining?of the cylinder to the shaft it rides on makes for very stiff?action when the clutches are released. This makes balancing the payload impossible. A small industry has developed to "tune" these mounts.?
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Re: Relationship between needle bearing wobble and variable worm mesh and backlash
Here are photos of the two versions of G11 worm wheel aka ring gear.? I forgot to add those to the last message.??
One is black and seems smooth anodized aluminum.?
The other is older and appears to be a form of stainless steel.??
The clutch surface of the steel version is rougher than the smooth black aluminum version.
Best, Michael
On Thu, Aug 5, 2021, 11:53 AM Michael Herman via <mherman346= [email protected]> wrote: Nice analysis, Bob.
The G11 ring gear used to be (sometimes during it's production) steel.? It is not black anodized anywhere on its surface...here is a photo.? Later and current production is black anodized.??
If the worklm she'll ( aka ring gear) were steel, I think your idea of using a wider thrust bearing could work.? But for the aluminum variety of G11 worm wheel (I've been calling it a ring gear,...if that's incorrect I apologize) then high clutching force in the center using the steel 1.25 inch shaft could warp it into a cup shape.??
The clutch disk itself also used to grab all through its area from the 1.25 inch diameter center to the 4.25 inch worm wheel OD diameter.? (Not always: the earliest CG11 used a smaller 3.5 inch diameter RA clutch. )?
Nowadays, due to the cutout for the wavy washer, the central area of the clutch top is not contacting the clutch disk except in 3 small radial areas.? Or not at all if there is no wavy washer in place.??
So then you have the new clutch with the central cutout for the wavy washer forces on top at the outside of the worm wheel, and you have the thrust bearing needles radially from the middle from like 3 inch diameter to like 3.7 inch diameter.? Now considering stresses under a string cluch knob force, I can forsee how it could warp the aluminum ring gear... cupping it downward.?? And maybe that could affect how the worm feels the worm wheel teeth if they were quite close.? That is, I'm still trying to understand the report by a few owners that clutch knob force affects the mesh of their worm to worm wheel...what could cause such an effect on the newest mounts.??
The older version steel worm wheel with no wavy washer indent relieves this warpage concern, but the rest of the construction is still mainly aluminum.? Every solid has elastic properties.??
As Dirty Harry once said in a movie, "Man's gotta know his limitations."
Even worms need to know this.
I think it is best to use a high friction clutch pad and keep the axial forces below extreme levels, yet still grip the clutch firmly.??
Have fun imaging!
All the best, Michael
Alan137,
The tilt of the worm wheel (it's not a ring gear) is another issue.? Certainly the worm wheel needs to be elevated above the plate upon which it resides.? There is a large radial bearing and also a thrust bearing, which covers a small portion of the worm wheel diameter, but the shaft clutch disc puts pressure on the entire face of the worm wheel.? If we assume the worm wheel does not flex, then the current bearing arrangement for the worm wheel should be sufficient.? If the worm wheel does show flexure, then perhaps a larger diameter thrust bearing is in order. If meshing of the worm and worm wheel is the concern, then the bearings should be out by the worm wheel teeth for maximum support, not near the center.? In deference to Scott & Losmandy, we are arm chair quarterbacks, the G11 is still a beautiful machine.
The tilt issue still does not change the fact that a tapered bearing for the RA and Dec shafts would minimize shaft tilt, and installation clearances would not be an issue.? Note that tapered bearings use press fit races, both on the outer and inner.? Your wheel hub on your car is an example; to change them the mechanic has to tap them out or use an arbor press.? I could see a fit where a mild tap on the end of the shaft with a dead blow hammer would coax the race off the shaft.?
Maybe using the shaft as one of the bearing surfaces of the needle bearing was a mistake, or more likely a compromise.? ?If you want no slop, you have to captivate the bearing somewhere, you can't just put it together and hope for the best.? Getting better quality bearings is only a partial solution, the design has to be there as well.
Looking at the design, the Teflon pad is doing double duty, it slips and it grips.? It has to provide a stiction free surface to easily nudge the scope, yet in the next moment, we apply tremendous pressure and expect it to NOT slip.? As was mentioned, this is a large range of preload on those thrust bearings.? Instead the Teflon pad being called upon to grip, use a ring in place of the setting circle ring.? Use a full circumference belt that would grip the worm wheel, and then that belt would be attached to the RA axis disc (the disc holding the Teflon pad).? A throw of a lever would apply full grip, or no grip (like a large diameter hose clamp, but with a lever instead of a lead screw).? This would separate the preloading of the bearings from the Telfon clutch performance. You could even use the degree ring itself, cut it in one place, and attach a lever to reduce the circumference.? Then attach it to the RA or Dec axis disc just above it.? Yet, I still see problems with this approach, tightening the ring might put radial pressure on the worm wheel.? Not finished with my coffee yet.
Bob
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David Malanick
Paul Kanevsky
Chip Louie
Michael Herman