take a ball point pen use solvent to rinse out the ink and then put a drop of 3 in 0ne Oil into it, precision tungsten ball. You could never make a tip this perfect for the task. see link below.
my latest iteration of "Nanook's 219 tonearm"..
my latest iteration of "Nanook's 219 tonearm"..
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Another suggestion for a spike would be a carbide tipped dead center, very solid. I'm not sure if diamond tipped grinding wheel dresser's have much of a point or not. As for the well, is hard/hard or hard/soft preferable? Perhaps a masonry drill bit could be sharpend to a pointy four facet to make a well in hardened steel. Have you got the use of a lathe? It puzzles me how people manage without one.
I'd be tempted to use a cup point grub screw for the well, high ten steel and really cheap so you can replace the once a year, also use them to ajust the vta with a lock nut. I think some counter sink bits go to a point so could be used to drill a well. Another idea would be a nest of three hard ( carbide or ceramic ) balls for the point to rest in.
Good suggestion with the grub screw. I've used button heads before with the socket head drilled deeper so that the point sits better. Also had good results with a downward facing spike which I made from a longer 4mm grub screw into a cup formed into the end of some 6mm s/s rod. What the lifespan of s/s will be remains to be seen but it's fun playing especially when the end result sounds pretty good.
Big thanks to Nanook for his original thread.
Big thanks to Nanook for his original thread.
The setscrew idea will work. I used M3 setscrews as the pivots for LTA carriage. These were grade 12.9 so already hardened.
To make the radius I used an old drill bit and cut off most of the flute. I then radiused the end to use as a forge. The M3 setscrew screws into the bottom of the shaft, put the jig on the vice and hit the end of the drill with a hammer.
This forges the radius in the setscrew hardening it further. I then used a tooth pick in a hand drill and diamond paste to polish the radius.
Photos in order. Drill forge with 0.2 radius, forge jig and drill, forge ready to hit, pic of the polished radius in the setscrew, its so highly polished you can see the reflection of the microscope in it.
Keep in mind if you use the ball point pen as a pivot pin you need to make the setscrew radius 3 times the radius of the ball.
To make the radius I used an old drill bit and cut off most of the flute. I then radiused the end to use as a forge. The M3 setscrew screws into the bottom of the shaft, put the jig on the vice and hit the end of the drill with a hammer.
This forges the radius in the setscrew hardening it further. I then used a tooth pick in a hand drill and diamond paste to polish the radius.
Photos in order. Drill forge with 0.2 radius, forge jig and drill, forge ready to hit, pic of the polished radius in the setscrew, its so highly polished you can see the reflection of the microscope in it.
Keep in mind if you use the ball point pen as a pivot pin you need to make the setscrew radius 3 times the radius of the ball.
Attachments
S/s - silver steel or stainless? There's stainless and stainless, some hard ( I've got some work hardening stainless at work, interesting to machine....but ideal for a uni-pivot ) and some is soft, like really cheap cutlery - possibly some lead in the mix. How long is it going to be? - sometime I'll get around to making a 14" duel uni-pivot.
Thank God ylu included pictures, I was so lost! But now seeing them it makes perfect sense. Actually wonder if I took a threaded thumb screw, used my drill press to start a drill hole, only go in say 3/16", use your hammer technique, then I'd have a thumb screw VTA adjustment!
Jewels can be used but not the stock Vee type, the pin will ride up the side of the V when the arm is cued up.
What is needed is a double cup jewel as used in the Naim ARO.
This info came from True Pont in the UK.
As a simple and cost effective DIY I like the ball point pen with the setscrew. The ball if sized correctly to the cup it will not ride up the Vee.
What is needed is a double cup jewel as used in the Naim ARO.
This info came from True Pont in the UK.
As a simple and cost effective DIY I like the ball point pen with the setscrew. The ball if sized correctly to the cup it will not ride up the Vee.
yes the cup needs to be hard but not as hard as the tip (tungsten in this example) so a hardened steel grub screw would be good or you could use a softer steel one, make it to what shape inside you want then heat it to cherry red and drop immediately it into a glass of vegetable oil to temper it hard. You want the cup to wear over time and not the tungsten tip.
Pattyt,
My apologies for being late to the party. I built my current unipivot back in the 70’s and it has worked so well I’ve found no reason to revise the design. It remains my primary arm to this day. I opted for the “hard/soft” bearing combination and used a high speed steel drill blank (hard) for the spike and brass (soft) for the bearing cup. I ground the drill blank to a point and polished it. The idea came from a Decca International unipivot tonearm that I had. The Decca bearing was a great design and it performed well for me. The Decca arm incorporated a judicious amount of viscous damping, which I found to be very desirable to have, especially in a unipivot.
I don’t have a good photo of my bearing but found this one on the internet that uses the same design concept as mine:
The base is a cylindrical metal cup with the spike press-fit into a hole in the bottom. The upper brass bearing cup is drilled/machined as a cylinder which sits inverted on top of the spike, and the arm assembly is attached to the top of the bearing cup. The base cup is filled with silicone oil so that the bearing cup cylinder sits in an oil bath. Movement of the arm causes the inverted bearing cup to ‘slosh’ around in the oil and that provides viscous damping.
My arm design was published as a construction article in 3/76 issue of The Audio Amateur magazine. I agree with @cracked case that this type of project is difficult to finesse without access to a lathe. I suppose the inverted bearing cup could be done with a grub screw that could double as a VTA adjuster, but changing VTA that way will also shift the center of gravity, and COG is important when designing unipivots. I’m very happy with my “hard/soft” bearing combination but if I had to do it all over again today I would seriously consider @moray james’ recommendation of using Nanook’s 219 ball point pen bearing. There are lots of good construction ideas in Nanook’s 219 thread.
I attached the TAA construction article along with my design sketches in case you might find some useful ideas there.
Ray K
All Parts:
Part A – Yoke:
Part B – Bearing Cup:
Part C - Bearing Base [spike]:
My apologies for being late to the party. I built my current unipivot back in the 70’s and it has worked so well I’ve found no reason to revise the design. It remains my primary arm to this day. I opted for the “hard/soft” bearing combination and used a high speed steel drill blank (hard) for the spike and brass (soft) for the bearing cup. I ground the drill blank to a point and polished it. The idea came from a Decca International unipivot tonearm that I had. The Decca bearing was a great design and it performed well for me. The Decca arm incorporated a judicious amount of viscous damping, which I found to be very desirable to have, especially in a unipivot.
I don’t have a good photo of my bearing but found this one on the internet that uses the same design concept as mine:
The base is a cylindrical metal cup with the spike press-fit into a hole in the bottom. The upper brass bearing cup is drilled/machined as a cylinder which sits inverted on top of the spike, and the arm assembly is attached to the top of the bearing cup. The base cup is filled with silicone oil so that the bearing cup cylinder sits in an oil bath. Movement of the arm causes the inverted bearing cup to ‘slosh’ around in the oil and that provides viscous damping.
My arm design was published as a construction article in 3/76 issue of The Audio Amateur magazine. I agree with @cracked case that this type of project is difficult to finesse without access to a lathe. I suppose the inverted bearing cup could be done with a grub screw that could double as a VTA adjuster, but changing VTA that way will also shift the center of gravity, and COG is important when designing unipivots. I’m very happy with my “hard/soft” bearing combination but if I had to do it all over again today I would seriously consider @moray james’ recommendation of using Nanook’s 219 ball point pen bearing. There are lots of good construction ideas in Nanook’s 219 thread.
I attached the TAA construction article along with my design sketches in case you might find some useful ideas there.
Ray K
All Parts:
Part A – Yoke:
Part B – Bearing Cup:
Part C - Bearing Base [spike]:
Attachments
Holy cow, never would have thought of the oil bath idea! But, also kinda wondering if all of this is a bit, well, out of my realm. Got ma a 1950s varispeed Sears and roebuck drill press for Christmas and was thinking of just getting some aluminum tubing, round stock, and drill, thread, press, bolt a arm together. Getting a metal lathe and cnc machine, well, honestly would be cheaper to keep a eye out for a 309 arm or something....... bit thanks for all the ideas. This project will be a while over the summer into next winter as being a first time new home owner has put me in the poor house, figured $3k in repairs, total so far is $24,000 and come to find out need a new roof and now a pool liner. Shoulda stayed in a apartment : ( also this is for a second TT, so not a necessity, but have time......
Well I suspect that the OP's hesitation isn't that a unipivot is "out of his league" to fabricate but rather trying to build one utilizing a design that requires him to lay out for the cost of a milling machine.
Looking at the various implementations of Nanook's original 219 arm, a lot can be done using a drill press, a hack saw and some hand files.
Looking at the various implementations of Nanook's original 219 arm, a lot can be done using a drill press, a hack saw and some hand files.
Been there, done that. I started building tonearms with a hacksaw and a hand drill when I was 15. I and other posters offered help, advice, and a link to Nanook's 219 thread for more ideas. Temaad offered a reasonably priced kit. What more should we have done to help out?
Ray K