Here's more about the base - you can use google for translation - but the pictures should be quite self-explanatory... DIY Turntable and Linear Tracking Tonearm (samogradnja gramofona i tangencijalne ru?ice) - diyAudio.rs
The position on a plinth is adjusted by math and a paper with a drawing - so, a template
The position on a plinth is adjusted by math and a paper with a drawing - so, a template
If you ask about the arm with four bearings, it doesn't. Well, it works, but it occasionally stops and it appears that one of the bearings has a problem - more friction inside the bearing than between the bearing and the glass tube.
I have six of them (bearings) so I'll try to find which of them are and which aren't up for the job. I eliminated the cartridge as a source of problems, it's not better with the Ortofon OM10 - so, it's not the cartridge.
If I get to the point where it tracks as good as it did with the linear bearing - at least, I'll buy some of those expensive ZrO2 684 bearings - but not before that. I left all the six bearings to sleep over in a petrol bath in a small glass bottle. Will dry and clean them up and see if I can pick four which have adequate freedom of movement...
Colin, I had to re-read what you wrote in this topic and found what I have been missing from the equation. The small brass tubes. The 684 bearing has a nominal 4mm ID and found two small brass tubes with just a pinch larger OD - polished them first with a fine sandpaper (500) then with a polishing cream. Just to get a few hundreds of a mm less OD and to get just a small amount of slack between the tubes and the bearings. I think that this will give it some chance to work. I'll report back.
One quick note on tonearm tube weights - a 5/3mm Al tube is heavier per length than a 8/7.1mm tube (OD/ID) - although, not much, but with these arms every bit counts. At 150mm length, the thinner wall but larger OD tube weighs 4.32grams and the 5mm tube with 1mm wall weighs 5.09 grams. Of course, both tubes are from aluminum.
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I set up the whole assembly, four 684 bearings, cleaned dry, brass tubes, the total assembly with the OM10 (the small additional weight removed) weighing flimsy 14.89 grams and it fails to move - follow the grooves - I decided to re-think it all and take a few days off - it's really frustrating missing something and not knowing what...
Stein2,
I'm really sorry that you are having so much trouble. Before you decide to throw in the towel or go for outrageously expensive bearings please let me make a few simple suggestions.One of our members, DTUT, and I were having some good success with linear trackers having flat window glass set into a 90deg V track and two ball bearings. As in the Cantus design we both found it necessary to clean the bearings well and run them dry. We were both using inexpensive hybrid-ceramic rc car bearings. Then Colin demonstrated the 4 bearing design using similar bearings from a hobby shop iirc. His design was running with lubricated bearings straight from the store.
DTUT was the first to test this configuration and was using clean, dry bearings like what we were accustomed to use with window glass track. What he found was that the new 4 bearing on glass tube would not run well at all unless the clean bearings had some light lubrication in them. For my first and all further test models I used bearings from the V groove track experiments but lubed them with a fairly light clock oil and blew them out with compressed air so only a film of oil remained in the bearing. This is several months now and the carriage has shown no further trouble. Can I explain this difference? No, and still trying to. So give that a try please.
Lead dress and stiffness can make a world of difference. I've found that 30 gauge or finer enameled copper magnet wire, loosely twisted and some 10 inches long and supported so that the entire traverse of the carriage is accommodated by a smooth curve of the wire does the job well.
From what your pics show, I wonder just how well those bearings will do under the best of conditions. The outter races are much thinner than I'm used to seeing and using. Thinness alone won't do anything good or bad but I have seen bearing race distortion with tightness of mounting that could easily make the carriage stop or skip. So make sure that the bearings are not compromised in any way. And make sure the corners are well smoothed and polished. Those corners in the pics didn't look great.
What I have found is that once you get all these little things sorted out, these arms just keep running without troubles at all.
BTW, I'm assuming that the glass tube you are using is white on the inside and smooth clear flawless glass on the outside.
Lastly, I suggest putting the removeable weight back in the OM10. That weight adds 5 grams and I think it may be too light without the weight.
Good luck and keep us posted please,
BillG
P.S. add 10 or 12 grams right back at the carriage plane, but balance the tracking force at whatever you want to use. 1.5 to 1.75 for the OM10. This may not do anything but worth a try.
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Bill, thank you for your offered help to Stein 
.
I'm realizing how much a difficult thing offering a diy project can be, because you want everyone to have equal success. At the same time it's hard to guarantee success unles the build is followed identically, as I notice everyone wants to take it their own way. If it were easy, we would all have working linear arms, but every little detail counts. I agree with your point about bearing edges, these need be smooth, I was lucky and found a supplier of well finished bearings it seems. Glass is mandatory, regardless of it being perfectly straight or not, it is very damn smooth and for Pyrex very hard to scratch.
Stein, stability wise I would sling the weight below the glass tube, not above, in realit there is not much gained since in order for anything close to perfection the pivot would have to be level with the tip of the stylus. Throw another equation into the mix is that on any warp the upwards portion will always be slower than the downwards portion regardless of pivot unless the pivot is below the stylus point, so as food for thought and another wrench thrown into the equation. At the end of the day, we will never have it all, just buy flat vinyl, or cd's.
Colin
.I'm realizing how much a difficult thing offering a diy project can be, because you want everyone to have equal success. At the same time it's hard to guarantee success unles the build is followed identically, as I notice everyone wants to take it their own way. If it were easy, we would all have working linear arms, but every little detail counts. I agree with your point about bearing edges, these need be smooth, I was lucky and found a supplier of well finished bearings it seems. Glass is mandatory, regardless of it being perfectly straight or not, it is very damn smooth
and for Pyrex very hard to scratch. Stein, stability wise I would sling the weight below the glass tube, not above, in realit there is not much gained since in order for anything close to perfection the pivot would have to be level with the tip of the stylus. Throw another equation into the mix is that on any warp the upwards portion will always be slower than the downwards portion regardless of pivot unless the pivot is below the stylus point, so as food for thought and another wrench thrown into the equation. At the end of the day, we will never have it all, just buy flat vinyl, or cd's
.Colin
BillG,
Thanks for your kind attempt to help, but it doesn't help much if I'm trying to do it and do it now, immediately There are days when it's wiser not to do anything.
I spent a lot of time struggling with various linear motion bearings - most of that time I was waiting for them to arrive from the other end of the planet and tinkering. At the end, I got to the point where the system works but not as it is really supposed to - to keep the cartridge tangent relative to the record. Acting as a floating multi-pivot arm constantly making small radii movements it's actually worse than a properly set up single pivot tonearm, which, if well set up, has two zero tracking error points on the record.
So, I decided to try to build something that will actually do the job as it is supposed to. I'm by no means discouraged. What frustrates me is the fact that whatever I want to do or build, requires exactly the sort of materials I don't have stashed around It was easy with the rest of the system, amps, pre-amps and speakers.
In fact, it was quite easy even with the latest addition, the tonearm testing turntable - Turntable Forum • Simple DIY Turntable with a larger plinth than usual, so I can play with various tonearms, primarily tangential/linear tracking tonearm designs.
I will try to follow your instructions and see if I can do anything useful to get this arm into functioning state... Stay tuned
Thanks for your kind attempt to help, but it doesn't help much if I'm trying to do it and do it now, immediately
There are days when it's wiser not to do anything. I spent a lot of time struggling with various linear motion bearings - most of that time I was waiting for them to arrive from the other end of the planet and tinkering. At the end, I got to the point where the system works but not as it is really supposed to - to keep the cartridge tangent relative to the record. Acting as a floating multi-pivot arm constantly making small radii movements it's actually worse than a properly set up single pivot tonearm, which, if well set up, has two zero tracking error points on the record.
So, I decided to try to build something that will actually do the job as it is supposed to. I'm by no means discouraged. What frustrates me is the fact that whatever I want to do or build, requires exactly the sort of materials I don't have stashed around
It was easy with the rest of the system, amps, pre-amps and speakers. In fact, it was quite easy even with the latest addition, the tonearm testing turntable - Turntable Forum • Simple DIY Turntable with a larger plinth than usual, so I can play with various tonearms, primarily tangential/linear tracking tonearm designs.
I will try to follow your instructions and see if I can do anything useful to get this arm into functioning state... Stay tuned
There is one idea I want to try, not sure how wise it is, it would require two roller bearings in-line, above the tonearm height and under the carriage - in line with the cartridge/tonearm tube, a second set of tiny bearings - sideways, as used with pivoting tonearms - to allow the cartridge and tonearm to move up and down, thus, lowering the pivoting point as close to the needle height as possible... Something like this... (just a quick mock-up)
I have those tiny bearings from some other tonearms, not sure which one is from which arm - had loads of broken tonearms in the past, Thorens, NAD(Garrard), Tesla...
I have those tiny bearings from some other tonearms, not sure which one is from which arm - had loads of broken tonearms in the past, Thorens, NAD(Garrard), Tesla...
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Nice pic stein2
If you do it like you are proposing the whole arm will move back and forth with the drag from the vinyl. You would need another set of bearings and rod in front of the sled...
I'd use a narrow tube, say, a "U" or "V" shaped rail...?
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I'm not sure why you would want to do this. Looking at other linear arms, both air bearing and roller bearing, they do not employ this. Even pivot arms don't allow a forwards/backwards movement (Y axis) of the arm. It would seem that you are just adding weight to the arm.
If you are having tracking issues with your current bearings, what are the bearings packed with? Is it a light oil or a grease filled bearing? Just curious.....
If you are having tracking issues with your current bearings, what are the bearings packed with? Is it a light oil or a grease filled bearing? Just curious.....
Stein
Nice arm you've built there. This looks pretty much like the configuration I would use if building an arm with this type of bearing design. Putting the glass tube below the armtube will reduce warp wow and warp induced variation in tracking force. The shallower bearing yoke should also be beneficial.
Are the 2 vertical rods in the arm base there to allow the arm to be raised for record changing?
You seem to have a very long section of armtube protruding behind the weight. Is this for a lift/lower mechanism. Cutting this as short as possible can only help sound quality.
The problem with the bearings that you and others have experienced might not be entirely due to excessive friction. The problem might be eccentricity. All bearing are eccentric to some degree. Precision bearings have eccentricity measured in microns. Budget and rc are a lot worse. In rc applications the outer race is normally held stationary whilst the inner race revolves. Eccentricity at the outer surface of the outer race in this application doesn't matter. In the tonearm it does.
With an eccentric bearing the axil will be go up and down in a sinusoidal curve with length equal to the circumference of the bearing and amplitude dependent on the severity of the eccentricity. If the bearing has an eccentricity of only 1% the steepest part of the curve will be over 1 degree (equivalent at that point of having the tube tilted). A 1% eccentricity in a 10mm diameter bearing is 0.1mm, very difficult to spot with a naked eye.
I had similar tracking problems and tracked it down to a 1.5% eccentricity in one of my bearings.
I hope my explanation makes sense and hope it is of use.
Niffy
Nice arm you've built there. This looks pretty much like the configuration I would use if building an arm with this type of bearing design. Putting the glass tube below the armtube will reduce warp wow and warp induced variation in tracking force. The shallower bearing yoke should also be beneficial.
Are the 2 vertical rods in the arm base there to allow the arm to be raised for record changing?
You seem to have a very long section of armtube protruding behind the weight. Is this for a lift/lower mechanism. Cutting this as short as possible can only help sound quality.
The problem with the bearings that you and others have experienced might not be entirely due to excessive friction. The problem might be eccentricity. All bearing are eccentric to some degree. Precision bearings have eccentricity measured in microns. Budget and rc are a lot worse. In rc applications the outer race is normally held stationary whilst the inner race revolves. Eccentricity at the outer surface of the outer race in this application doesn't matter. In the tonearm it does.
With an eccentric bearing the axil will be go up and down in a sinusoidal curve with length equal to the circumference of the bearing and amplitude dependent on the severity of the eccentricity. If the bearing has an eccentricity of only 1% the steepest part of the curve will be over 1 degree (equivalent at that point of having the tube tilted). A 1% eccentricity in a 10mm diameter bearing is 0.1mm, very difficult to spot with a naked eye.
I had similar tracking problems and tracked it down to a 1.5% eccentricity in one of my bearings.
I hope my explanation makes sense and hope it is of use.
Niffy