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Steel ball bearing upgrade for CPC925 mounts?


Stu_2011

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Hi

My CPC mount is starting to feel a bit notchy so I suspect that the nylon ball bearings in the mount have become distorted.

It looks like a fairly easy job to replace the bearings but do I replace with more Nylon balls or steel ball bearings? I know lots of people have done the steel bearing upgrade but the engineer in me is cautious - running hard steel bearings against a relatively soft aluminium race is bad practice as the steel bearings can dent the aluminium race if the loads are wrong. I suspect this why Celestron use Nylon bearings in the first place and not steel.

Does anyone have any long term experience of running steel bearings in the CPC mount? I'm particularly interested in this setup on a wedge where the point loads on the individual bearings are much higher.

Thanks

Stuart

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i did this mod with my cpc 9.25, and after around 12 months i striped it down to inspect it. if the bearings were wearig the alloy bearing surface away the grease would of changed colour i.e black, but all was perfect

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Depends what alloy it is. I've just rebuilt an engine cylinder head that has stellite faced valves seating on the plain allow of the head, and the camshaft runs in plain bearings in the head too.

I doubt the mount is quite as tough, but given the relatively puny loading your should be OK.

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i did this mod with my cpc 9.25, and after around 12 months i striped it down to inspect it. if the bearings were wearig the alloy bearing surface away the grease would of changed colour i.e black, but all was perfect

Thanks, good info.. Any sign of wear at all on the aluminium race?

Do you run the mount as standard or on a wedge? I'm not too concerned about the standard operation as the load on the individual bearings will be even and will be very small. It's the wedge operation that I'm concerned about when the uneven loading might causing the denting I'm worried about??

Stuart

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Depends what alloy it is. I've just rebuilt an engine cylinder head that has stellite faced valves seating on the plain allow of the head, and the camshaft runs in plain bearings in the head too.

I doubt the mount is quite as tough, but given the relatively puny loading your should be OK.

I suspect it will be a high silicon casting alloy so something like ADC12 or A380. It won't be heat treated either so it will be very soft I suspect. I could analyse it at work if I really felt the need......

Thanks

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no wedge mate, but baader steel track focuser, badder 2" clicklock diagonal and 2" naglers, and pm lot of weight. and no wear at all. someone else did it on here before me,ill try and find it

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To me, nylon is the root of all evil. People do material science degrees in which they learn of its wonderful self lubricatingness etc etc. I'm not an engineer, I'm a poor old amateur mechanic, and when I see nylon I cringe. Distortion, impossibility of proper attachment, low resistance to pressure. I loathe all things nylon in engineering - but, as I say, I'm an amateur mechanic (quite an old one!) but not an engineer.

Olly

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The wedge will introduce a lot of  extra loading on the bearings but if the originals have survived for a number of years then I would replace like with like the key to any bearing assembly is lubrication and although I might be shot down in flames there is nothing better in my mind than the skywatcher sticky grease.

Alan

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To me, nylon is the root of all evil. People do material science degrees in which they learn of its wonderful self lubricatingness etc etc. I'm not an engineer, I'm a poor old amateur mechanic, and when I see nylon I cringe. Distortion, impossibility of proper attachment, low resistance to pressure. I loathe all things nylon in engineering - but, as I say, I'm an amateur mechanic (quite an old one!) but not an engineer.

Olly

I agree Olly - and I am one of those people with a degree (and PhD) in Materials Science, although I'm firmly a metallurgist. Plastics are some weird non engineering cheap material to me!! When I see astro adapters made on plastic 3D printers I just cringe, they look weak and flexible and not at all suitable for the job.

In my old job I was asked about a material designation on a drawing as the engineer had defined the material as SFP. When questioned about the acronym the first word was "Some" and the last word was "Plastic". The word in the middle can't be published on here..... In general this sums up my views of plastics.

However, I think in this case Celestron used these Nylon ball bearings to ensure that the aluminium race wasn't ever damaged during use. I don't think it was a cost saving measure I think it was genuine design intent hence my original question.

Thanks

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The wedge will introduce a lot of extra loading on the bearings but if the originals have survived for a number of years then I would replace like with like the key to any bearing assembly is lubrication and although I might be shot down in flames there is nothing better in my mind than the skywatcher sticky grease.

Alan

Thanks Alan

I tend to agree, the mount has done well for a quite a few years and is only just starting to go a bit notchy so I'm tempted to replace like for like. I think I can source some HDPE ball bearings and these will be a bit better than the Nylon ones - I think!.

The Skywatcher grease is good, very sticky but does its job well and it stays in place which is important. The use of this grease is design intent and not cost saving in my view.

Stuart

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Thanks Alan

I tend to agree, the mount has done well for a quite a few years and is only just starting to go a bit notchy so I'm tempted to replace like for like. I think I can source some HDPE ball bearings and these will be a bit better than the Nylon ones - I think!.

The Skywatcher grease is good, very sticky but does its job well and it stays in place which is important. The use of this grease is design intent and not cost saving in my view.

Stuart

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I would agree with with both the original mounts use of nylon and skywatchers use of materials its good engineering practice at a fixed cost point, I worked in the aerospace industry and getting a good product was quite easy its much harder when you have to design something for a few pounds.

Alan

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When I did my CPC800 all  those years ago I used a set of  "sacrificial" bearings...  I let it run continuously for a few weeks in the obs powered from a battery strapped to one of the fork arms... I then cleaned everything and used a new set of bearings and re-lubed...

I have been trying to find the original files (and guide graph)  for the attachments that were "lost"   several software upgrades ago but haven't managed it...

The "alleged" engineer in me agrees as well but I bit the bullet and went for it..... we use to substitute the "F" with a "K"   it was "kinder" and less embarrassing to explain using SKP and SKA  there are some very nice and expensive "engineering" plastics out there these days  PEEK is a firm favourite ....

Peter...

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When I did my CPC800 all  those years ago I used a set of  "sacrificial" bearings...  I let it run continuously for a few weeks in the obs powered from a battery strapped to one of the fork arms... I then cleaned everything and used a new set of bearings and re-lubed...

I have been trying to find the original files (and guide graph)  for the attachments that were "lost"   several software upgrades ago but haven't managed it...

The "alleged" engineer in me agrees as well but I bit the bullet and went for it..... we use to substitute the "F" with a "K"   it was "kinder" and less embarrassing to explain using SKP and SKA  there are some very nice and expensive "engineering" plastics out there these days  PEEK is a firm favourite ....

Peter...

hope you ddnt mind me bringing you up peter :smiley:

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I did my cpc800 about 5weeks ago i used a mix of steel ball bearings and nylon rotates a lot nicer than before on my wedge.Before i did the bearings i would always have to rotate the scope back and forth on the wedge to settle the nylon ones in as they would feel notchy.

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Plastics an engineering material? Of course they are! Edited excerpt from something I wrote a few months back:

Advanced Adhesives

We’ve all done it, taken off a little bit too much metal and resorted to using a retainer, or even superglue, where we had planned to have a force fit. But when are we going to stop treating the use of modern adhesives as a ‘cheat’? Two part epoxies date back before the Second World War, and Loctite dates back to 1953. Even superglue is over fifty years old. Engineering grade adhesives are used to hold fighter jets and passenger planes together, yet it is still unusual for hobbyists to use these tried and tested ways of joining materials.

Perhaps it is time for us all to trust these marvellous adhesives and start to learn more about how to design in their use for effective and reliable joints, rather than seeing them as a stop-gap.

Composite Materials

There’s nothing particularly new about composite materials. Paxolin and plywood have been around for donkey's years, and there is a huge range of far more advanced composites out there. Plastics reinforced with glass-fibre, carbon-fibre and Kevlar, for example, have wide applications in industry. In the seventies they were used to make many parts of the space shuttle including the pressure vessels and wing leading edges and in 2010 NASA said they needed to keep up with a paradigm shift from metals to composites occurring in aerospace, automotive, marine, and pipeline applications. But how often do you find them in the home workshop? This is strange, as other hobbyists, notably aeromodellers and ship modellers and even people who make their own fishing rods or bows are happy to use advanced composites.

Surely in the future we will catch up with industry and start taking advantage of the combinations of lightness, flexibility and strength that composites offer.

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When I did my CPC800 all  those years ago I used a set of  "sacrificial" bearings...  I let it run continuously for a few weeks in the obs powered from a battery strapped to one of the fork arms... I then cleaned everything and used a new set of bearings and re-lubed...

LOL! Looking at the old threads I can see your secret is out now!

It's a fair enough  approach - you 'ran it in' :-)

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...... I think I can source some HDPE ball bearings and these will be a bit better than the Nylon ones - I think!.

NO!!   HDPE does not have the same creep properties as Nylon. Under load all plastics creep and you will get flattened HDPE bearings much quicker than with Nylon ones. I don't think that the comparison with a cylinder head is necessarily valid as the cylinder head bearings will be fed with presurised oil keeping the "bearing" surfaces separated while your mounting will be relying on unpressurised grease. I too do not like the possibility that the steel bearings will dent the Aluminium track and as the balls will be easier to replace than the track I would try to stick with the SW Nylon balls

Having spent many years in plastics Research and Development I am continually apalled that plastics are considered as replacements for other materials, to be treated and used the same as the material they are replacing. This attitude has given me a lot of work, determining why the product failed and recommending corrective actions.

Nigel

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LOL! Looking at the old threads I can see your secret is out now!

It's a fair enough  approach - you 'ran it in' :-)

There was a bit more too it than that but you have to keep something back... ;)

My poor old CPC800 was seriously overloaded (but balanced) and running on a wedge all the time ... I haven't stripped it to check....

11848_large.jpeg

Peter...

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NO!! HDPE does not have the same creep properties as Nylon. Under load all plastics creep and you will get flattened HDPE bearings much quicker than with Nylon ones. I don't think that the comparison with a cylinder head is necessarily valid as the cylinder head bearings will be fed with presurised oil keeping the "bearing" surfaces separated while your mounting will be relying on unpressurised grease. I too do not like the possibility that the steel bearings will dent the Aluminium track and as the balls will be easier to replace than the track I would try to stick with the SW Nylon balls

Having spent many years in plastics Research and Development I am continually apalled that plastics are considered as replacements for other materials, to be treated and used the same as the material they are replacing. This attitude has given me a lot of work, determining why the product failed and recommending corrective actions.

Nigel

Thanks Nigel,

The last time I did any real plastics was in my degree and that was a long long time ago. I've been a metallurgist for the last 25 years. I do remember that all plastics undergo visco-elastic deformation but couldn't remember which ones were good / bad etc. I assumed that HDPE would be good as that used to be the material of choice for hip implants etc. Thanks for the clarification.

I think I'm coming to the conclusion that I replace the existing nylon ball bearings with new nylon ones.

Stuart

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