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Old 13th January 2020, 08:22 AM   #3201
niffy is offline niffy  Europe
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Join Date: Nov 2013
Location: Dartmoor
Hi Carlo,

Larger wheels will tend to result in lower friction for both of the reasons you suggest. The hertzian strain will be lower. The larger diameter will also ride over imperfections and dust motes more easily.
The reduction in friction isn't just due to the reduced torque at the bearing, although this is a factor. When using a non-recirculating ball bearing, lil casey style, larger balls still result in lower friction even though there is no central bearing element.

Niffy
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Old 13th January 2020, 09:05 AM   #3202
carlthess40 is offline carlthess40  United States
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Is anyone selling one of their diy arms that they are not happy with but still works?
Please message me as Id like to give one a try. Not looking to spend a ton of cash but I do know with all the time and items used do add up
Lots of great ideas on here
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Old 14th January 2020, 08:50 AM   #3203
nocdplz is offline nocdplz
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...Larger wheels will tend to result in lower friction for both of the reasons you suggest ...

Yes Niffy, but is the relevance of their effect that counts.
With our carriage weights (<25gr per wheel), the Hertzian strain (and adhesion too) would remain practically undetectable, on steel as on carbide imho; while the torque to win the bearing's friction is directly multiplied by the radius, and this changes the behavior for sure.
So if I had to make a carriage I would make big wheels with small bearings, as small as possible (eg. vee jewel): that is, I would faithfully copy yours.

...When using a non-recirculating ball bearing, lil casey style, larger balls still result in lower friction even though there is no central bearing element. ...

...The larger diameter will also ride over imperfections and dust motes more easily.


You gave the answer: it's not a matter of friction (as said, no relative motion =0, a grindwheel runs effortlessly even on sand paper) but simply of a lower inclination to lift the mobile masses over the obstacle with such small available forces.

carlo

Last edited by nocdplz; 14th January 2020 at 08:53 AM.
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Old 14th January 2020, 11:11 AM   #3204
niffy is offline niffy  Europe
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Quote:
Originally Posted by nocdplz View Post
...Larger wheels will tend to result in lower friction for both of the reasons you suggest ...

Yes Niffy, but is the relevance of their effect that counts.
With our carriage weights (<25gr per wheel), the Hertzian strain (and adhesion too) would remain practically undetectable, on steel as on carbide imho; while the torque to win the bearing's friction is directly multiplied by the radius, and this changes the behavior for sure.
So if I had to make a carriage I would make big wheels with small bearings, as small as possible (eg. vee jewel): that is, I would faithfully copy yours.

...When using a non-recirculating ball bearing, lil casey style, larger balls still result in lower friction even though there is no central bearing element. ...

...The larger diameter will also ride over imperfections and dust motes more easily.


You gave the answer: it's not a matter of friction (as said, no relative motion =0, a grindwheel runs effortlessly even on sand paper) but simply of a lower inclination to lift the mobile masses over the obstacle with such small available forces.

carlo
Hi Carlo,

When I said "Larger wheels will tend to result in lower friction for both of the reasons you suggest." I was using the term friction to describe the total resistance to lateral motion. This includes rolling resistance which, as you correctly pointed out, does not include any relative motion but does resist motion.

When I was using steel wheels on glass rods I thought that the difference in rolling resistance that could be achieved by using harder materials would be negligible and said so publicly on this forum.

Then Joe gave me some tungsten carbide rods to try. Boy did he prove me wrong.

Glass tends to have a very smooth surface, probably a little better than I managed to polish the carbide rods to, so any difference would be entirely due to the difference in hardness (and maybe electrostatic adhesion) and not due to surface finish. Absolutely everything else in the set up was identical. Same wheels, same bearings, same carriage, same mass/load, same test rig and testing method.

The carbide rods resulted in an 18% reduction in the total resistance to lateral motion (fiction). This reduction is not due to a change in the torque required to turn the wheels as the wheels hadn't changed and so nor had their radius. I was surprised by the degree to which the resistance had reduced.

Changing from the steel wheels to the tungsten carbide resulted in a further reduction of 9%. That's a total reduction of 25% compared to steel on glass.

The move to jeweled vees resulted in further significant improvements, reducing total resistance/friction by a further 31%. A total of 48% reduction compared to the original steel on glass with steel pin bearings.

Of the total reduction about half is due to the actual bearing element and half is due to rolling resistance showing that the hardness of the wheels and rails is very important.
Of the remaining friction/resistance I estimate that about 80% is due to rolling resistance. I can't really move to harder materials so the only way to make further reductions would be to make the wheels larger in diameter or make the carriage lighter.

My current jeweled and carbide rail bearing set up has given me a 70% reduction in friction compared to when I was using boca hybrid ballrace bearings on glass rods.

Niffy
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Old 14th January 2020, 02:06 PM   #3205
nocdplz is offline nocdplz
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Niffy, sorry for possible misunderstanding. I do not doubt the importance of refinements that can be added to a clever project, tested and improved for a long time.
I was just trying to understand how was working the stainless steel ring added by Warrjon to his ball bearings, to find the main reason that transformed an arm with friction problems into a fully satisfactory new one.
The increase in diameter seemed to be a more evident cause than the finishing details: bad workmanship can ruin a good project, while refined materials and processes can lead it to excellence (as in your creations), but will never allow a deficient project to work well.

carlo
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Old 14th January 2020, 07:51 PM   #3206
niffy is offline niffy  Europe
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Ah. We might have had our wires crossed, or at least out of phase.
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Old 14th January 2020, 08:04 PM   #3207
warrjon is offline warrjon  Australia
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Hi Carlo,


As the diameter of the wheel increases the rolling resistance goes down by the square root of the diameter. With the larger diameter wheels the cantilever was deflecting much less, even though I only polished the wheels with 1000grit as I did not have 1500 and 2000.

The Stanton 881s cartridge with Pickering D3000 stylus I am using is very high compliance 30un/nM. Installing the brush also made a difference, the arm now traverses backwards on off center records.

This iteration of the tonearm does not really lend its self to using pin bearings as the arm wand is below the rail. I am gathering the components to make a new arm where the rail will be just above record level. My plan is to make a set of pin bearings from tool steel for the pins and brass for the Vees, wheels will be aluminium and I have bought polished carbide rings.
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SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 14th January 2020, 11:45 PM   #3208
warrjon is offline warrjon  Australia
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Hi Niffy,

One thing that has puzzled me is, you measuring a significant drop in rolling resistance between the glass and carbide rods. Were the rods you measured empty?

Rolling resistance (discounting wheel diameter) is due primarily to deformation of either the wheel or rail. An extreme example would be a railway carriage wheel on sand and steel rail.

This would suggest that the glass rods were deforming under the wheels, I would suspect more likely bending. I am wondering if a carbon rod was inserted into the glass and held with epoxy. My reason for this is I have had issues with supply of carbide rods.
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SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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Old 15th January 2020, 01:14 AM   #3209
niffy is offline niffy  Europe
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Hi Warrjon,

Both the borosilicate glass and tungsten carbide rods are solid. The rods were built into identical support structures as I wanted to be certain that any differences that I measured or, more importantly, heard was entirely down to the difference in rod material. The rail structure consists of a 1mm thick, 19mm wide base plate of tool steel. Along the edges of this base plate run two unidirectional carbon fibre battons, 2mm thick. The channel formed between the battons is where the rods are fitted. On top of the battons are 6mm diameter, thick wall, stainless steel tubes. These are filled with silicone rubber for additional damping. The rail has 10mm thick aluminium end caps bolted and glued to the base plate.
The rails are held together with epoxy adhesive. Each layer was individually glued, clamped and cured in an oven. The clamps not being removed until the rail had cooled to room temperature. This was to prevent warps. Heat curing epoxy massively improves its properties.

The rails are mounted with two M6 bolts at each end. Mounting the rail from both ends makes the whole structure much more rigid.

Bearings 1.PNG

The rails are very inert and very rigid and just make a dull dump if struck. Dead. Of course the tungsten carbide rail is much heavier.

I don't think the rails will bend enough to be noticeable simply due to the mass of the carriage. It may seem crazy but the difference in rolling resistance is due to the material of the rail deforming under the wheels more with the glass rail. I performed many tests (I made 6 different rails and used many different bearings and wheels) and the results were all consistent with this being the case.

Niffy

Last edited by niffy; 15th January 2020 at 01:17 AM.
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Old 15th January 2020, 01:43 AM   #3210
warrjon is offline warrjon  Australia
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Hi Niffy,

It suddenly dawned on me, I grabbed the micrometer and measured the borosilicate rods I have and they are not perfectly round or uniform over their length they vary by 0.07mm. Where as the carbide rods I have are within 0.005mm over their length and diameter.

I'll have to buy new carbide rods from a different eBay supplier and hopefully I'll get the ones I ordered this time.

.
__________________
SP10, ...... DIY Linear tonearm, ......Stanton 881s with D3000 stylus, .....BHL phono,.........Pass B1,
MODULUS 86 power amps x4,.............Active line level OX,......... bi-amped OB speakers with Mark Audio Alpair 12P
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