If DIY, the belt can be pressed between idler and inside rim to somewhat lower the effect of slip and creep.
Like this : example
I think some old Philips Belt drive turntable used to have non acting pulley wheel pressing middle portion of the open (Free) belt part to avoid this. Not sure though.
regards
Like this : example
I think some old Philips Belt drive turntable used to have non acting pulley wheel pressing middle portion of the open (Free) belt part to avoid this. Not sure though.
regards
That is called a tensioner.
May or may not be spring loaded.
Very common in cars for timing chains, timing belts and serpentine belt drives in engines, where there is no room for multiple belts.
But as Chris (@anatech) pointed out, these belts are not in need of such a device, in fact it can cause stretching.
And somebody do the speed variation calculations.
May or may not be spring loaded.
Very common in cars for timing chains, timing belts and serpentine belt drives in engines, where there is no room for multiple belts.
But as Chris (@anatech) pointed out, these belts are not in need of such a device, in fact it can cause stretching.
And somebody do the speed variation calculations.
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Do the math, the lower one seems to be a direct entry type of flash program.
https://www.engineersedge.com/mechanics_machines/flywheel_mass_size_design_13981.htm3
https://www.calculatoratoz.com/en/c...lar-speed-and-mean-speed-calculator/Calc-1647
Like we say in India, let him break his head....
https://www.engineersedge.com/mechanics_machines/flywheel_mass_size_design_13981.htm3
https://www.calculatoratoz.com/en/c...lar-speed-and-mean-speed-calculator/Calc-1647
Like we say in India, let him break his head....
I did try an 'industrial' flat belt; 1mm thick x 6mm wide x 1150 mm long. This was completely unsuitable, being far too stiff.
In order for it to work far too much tension would have been needed, with the concomitant excess wear on both the the motor and platter bearings.
In order for it to work far too much tension would have been needed, with the concomitant excess wear on both the the motor and platter bearings.
1150 mm...almost 4 feet!
That is too big for a light duty machine.
Stiff rubber needed for such a long belt.
See here:
https://www.sewingpartsonline.com/blog/sewing-machine-belts-sizing/
Might help
That is too big for a light duty machine.
Stiff rubber needed for such a long belt.
See here:
https://www.sewingpartsonline.com/blog/sewing-machine-belts-sizing/
Might help
Sorry, that should have read 1050mm, I did say that I use a large Papst motor 🙂
Very few belts made for other purposes will be made accurately enough to work satifactorally on a turntable
Very few belts made for other purposes will be made accurately enough to work satifactorally on a turntable
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Found this because I have been dealing with belt transmission in other projects (not audio related) particularly regarding behavior involving shock loads.
Has anybody tried synthetic bowstring material? Typically it is Dyneema/Kevlar with Vectran or GoreTex added at up to 25% composition. It is used because a twisted string of multiple oriented strands will provide very low lifetime stretch (after an initial stretch) with high conformability around tight radii.
ETA: Considering an olympic recurve archer may make a new string every 2-6 months (and the laods involved with such a use) it would most likely live a veeeeeeeery long life on a turntable.
Has anybody tried synthetic bowstring material? Typically it is Dyneema/Kevlar with Vectran or GoreTex added at up to 25% composition. It is used because a twisted string of multiple oriented strands will provide very low lifetime stretch (after an initial stretch) with high conformability around tight radii.
ETA: Considering an olympic recurve archer may make a new string every 2-6 months (and the laods involved with such a use) it would most likely live a veeeeeeeery long life on a turntable.
Very Guys, thanks for the input, very interesting although we (as normal) veered of subject a bit.
TomWH - my Mylar belt has been going about 5 hours/day for over 6 months now and shows no sign of giving up. but I suppose when it want's to let go it will. I purposely have left it in place as i want to try & find it's actual life. Maybe a long process, I contacted Galiber turntables & they indeed do sell a belt. But will only do Courier & that price to NZ is insane.
I would be very interested in finding more about Mikes belt, but cannot find anything is a DIYaudio search. A ny more pionters, was it listed on DIY or another forum.
MKHunt - I don't thing Bow sting would be suitable, have you any idea the poundage required to remove the stretch from from the bowstring. Bows are measured between 40 to 100 pounds!!
Cheers
TomWH - my Mylar belt has been going about 5 hours/day for over 6 months now and shows no sign of giving up. but I suppose when it want's to let go it will. I purposely have left it in place as i want to try & find it's actual life. Maybe a long process, I contacted Galiber turntables & they indeed do sell a belt. But will only do Courier & that price to NZ is insane.
I would be very interested in finding more about Mikes belt, but cannot find anything is a DIYaudio search. A ny more pionters, was it listed on DIY or another forum.
MKHunt - I don't thing Bow sting would be suitable, have you any idea the poundage required to remove the stretch from from the bowstring. Bows are measured between 40 to 100 pounds!!
Cheers
Each strand can support about 75lbs (for example, using 425x material). When fabricating a string for my 40lb recurve (16-20 strands, 8-10 loops), I will pre-stretch to about 300lbs so it will never creep over its usable lifetime. Even a few twisted loops, not pre-stretched, would likely last a few years. If the 'belt' was made with un-twisted strands, then any potential stretch over time could be compensated with a few twists of the loop (since it is round and not flat, there would be no real issue I think?).
The loads on a TT are just so far below its normal load range that neglect (no periodic massaging/VERY light waxing) is more likely to kill it than wear or stretch. The tight radius comformability also seems very promising because the drive motor drive pulley size could be reduced which would also allow the motor to have a greater torque advantage (gearing ratio) when starting a heavier platter or adjusting speed from encoder feedback (if equipped).
Certainly aesthetics could suffer for tables where the belt wraps the outer edge of the platter with an exposed drive spindle. I have a humble and lowly AT-LPW40WN and my hunch says the onboard optical encoder speed system has rather 'gross' (large) adjustment steps which dictate the W+F measurements in combination with platter:motor gearing ratio. But a smaller drive pulley would allow any motor or drive inconsistencies/usable speed adjustments to be less impactful on W+F (I would think).
For example, AT quotes the W+F to be <.15% so 33.33rpm * .0015 = .0499 platter RPM. If we pretend the drive pulley to table pulley ratio is 1:30 that gives a motor speed 'step' ratio of 1.5rpm (at the motor). So assuming that the motor is accurate to within 1.5RPM for each control step of the optical encoder speed feedback, but increase that ratio to 1:40 by using a smaller drive pulley we get a platter speed deviation of +/- .0375RPM (compared to .0499RPM before) which has effectively reduced the electro-mechanical inaccuracy from +/- .015% to +/-.010%. Still 10x higher than a good quartz-locked direct drive TT, but also a significant improvement by about 30%.
My primary thoughts behind it are that:
- Because it takes so much force to stretch the material (which does not exist in a TT), and
- Because at TT loads, the material would have an almost indefinite tensile strength lifetime (excepting natural decay), and
- Because the material is extremely flexible and can bend around tight radii which allows a more advantageous design of the TT drive mechanism, and
- Incredibly low cost 'per belt' when considering belts/quantity of material adjusted for belt projected lifetime
Maybe it would be a decent candidate which is overlooked in most applications except for university studies and research papers.
Potential downsides:
The cons require significant time investment to overcome which is likely part of the reason MFGs don't use such solutions. The belts they sell likely cost pennies or fractions of pennies when ordered in quantity.
Some of these things could be mitigated by bonding the material to the exterior of a more typical soft/stretchy TT belt at the desired (stretched) size. Similar to how a power transmission belt will have kevlar fibers in its mold, but because soft rubber is very poorly suited to power transmission (where coupled components are usually incredibly rigid or high mass and insensitive to slight motor vibration) we do not see commercial offerings of soft+reinforced belts.
Anyway, I have some hundred+ yards of this material as part of another hobby so perhaps when I have some time and after doing a slight regrind of the platter (measured +/- .0075" vertical runout) I will tackle this experiment.
The loads on a TT are just so far below its normal load range that neglect (no periodic massaging/VERY light waxing) is more likely to kill it than wear or stretch. The tight radius comformability also seems very promising because the drive motor drive pulley size could be reduced which would also allow the motor to have a greater torque advantage (gearing ratio) when starting a heavier platter or adjusting speed from encoder feedback (if equipped).
Certainly aesthetics could suffer for tables where the belt wraps the outer edge of the platter with an exposed drive spindle. I have a humble and lowly AT-LPW40WN and my hunch says the onboard optical encoder speed system has rather 'gross' (large) adjustment steps which dictate the W+F measurements in combination with platter:motor gearing ratio. But a smaller drive pulley would allow any motor or drive inconsistencies/usable speed adjustments to be less impactful on W+F (I would think).
For example, AT quotes the W+F to be <.15% so 33.33rpm * .0015 = .0499 platter RPM. If we pretend the drive pulley to table pulley ratio is 1:30 that gives a motor speed 'step' ratio of 1.5rpm (at the motor). So assuming that the motor is accurate to within 1.5RPM for each control step of the optical encoder speed feedback, but increase that ratio to 1:40 by using a smaller drive pulley we get a platter speed deviation of +/- .0375RPM (compared to .0499RPM before) which has effectively reduced the electro-mechanical inaccuracy from +/- .015% to +/-.010%. Still 10x higher than a good quartz-locked direct drive TT, but also a significant improvement by about 30%.
My primary thoughts behind it are that:
- Because it takes so much force to stretch the material (which does not exist in a TT), and
- Because at TT loads, the material would have an almost indefinite tensile strength lifetime (excepting natural decay), and
- Because the material is extremely flexible and can bend around tight radii which allows a more advantageous design of the TT drive mechanism, and
- Incredibly low cost 'per belt' when considering belts/quantity of material adjusted for belt projected lifetime
Maybe it would be a decent candidate which is overlooked in most applications except for university studies and research papers.
Potential downsides:
- Not very forgiving of tension. Poor bearing quality would be exposed very quickly and/or poor tensioning could wear bearings quickly.
- Potential to transfer some vibration.
- Coupling the ends without introducing a radial ridge/anomaly.
The cons require significant time investment to overcome which is likely part of the reason MFGs don't use such solutions. The belts they sell likely cost pennies or fractions of pennies when ordered in quantity.
Some of these things could be mitigated by bonding the material to the exterior of a more typical soft/stretchy TT belt at the desired (stretched) size. Similar to how a power transmission belt will have kevlar fibers in its mold, but because soft rubber is very poorly suited to power transmission (where coupled components are usually incredibly rigid or high mass and insensitive to slight motor vibration) we do not see commercial offerings of soft+reinforced belts.
Anyway, I have some hundred+ yards of this material as part of another hobby so perhaps when I have some time and after doing a slight regrind of the platter (measured +/- .0075" vertical runout) I will tackle this experiment.