Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 26th September 2018, 01:45 AM   #1951
david_reis is offline david_reis  United States
diyAudio Member
 
Join Date: Feb 2009
That arm looks great Carlo. What did you design this to use as the vee part of the bearings where the pen tips sit?

On your 3DToy arm, I believe you designed it for brass set screws that had a vee made by a center drill.

The Bunny looks like it uses something different.
  Reply With Quote
Old 27th September 2018, 10:46 AM   #1952
nocdplz is offline nocdplz
diyAudio Member
 
nocdplz's Avatar
 
Join Date: May 2010
Location: italy
Yes - same pentips bearings as in 3d toy, with just a little mod to avoid the fact that in PLA the threads do not last long: 3mm rivets epoxied to plastic, threaded 2.5mm inside for the v screws
Sorry not to test it. but my old Rabbit works so well...
carlo

ps the Rabbit has just 1 bearing more than a traditional gimballed TA: and -imho- this is crucial to make a working non-servo PLT
  Reply With Quote
Old 27th September 2018, 03:46 PM   #1953
david_reis is offline david_reis  United States
diyAudio Member
 
Join Date: Feb 2009
That's very clever. If I can ever finish assembling my copy of your 3DToy, I'll probably give the 3D Rabbit a shot.
  Reply With Quote
Old 28th September 2018, 07:37 PM   #1954
niffy is offline niffy  England
diyAudio Member
 
Join Date: Nov 2013
Location: Dartmoor
Quote:
Originally Posted by david_reis View Post
That arm looks great Carlo. What did you design this to use as the vee part of the bearings where the pen tips sit?

On your 3DToy arm, I believe you designed it for brass set screws that had a vee made by a center drill.

The Bunny looks like it uses something different.
Just making a depression in the end of a grub screw with a drill bit will not make a very good vee. It will have a flat bottom, straight angled conical sides at a shallow angle and a rough surface. Proper vees do have conical walls but at a steeper angle, normally 45, so the tip is at 90 . The bottom of the vee is also spherical, mine had a radius of about 0.25mm for use with pivots with a tip radius of about half this.
When I made the experimental vees for my linear arm I used M3 stainless steel grub screws. To make a correctly profiled vee I made a punch from the shaft of a 6mm drill bit. I cut the drill and ground the end at 45 to give the correct 90. I polished this to give a smooth surface. With this mounted in my pillar drill, using a fine file, fine wet and dry paper and under high magnification I rounded the tip. I used a 0.5mm drill bit shaft as a reference to make sure I got the correct radius. I again polished this.
I flattened the ends of the grub screws and using a centre drill put a small impression in the centre to align the punch. I tapped an M3 hole in a piece of scrap steel and set the flat end of the grub screw flush with the surface. This is a very important step as I prevents the thread being distorted when being punched. I aligned the punch in the end of the screw and tapped it with a hammer. I now had a near perfectly shaped vee. I polished the vee using a pointed matchstick and polishing compound and my dremel.
The pivots were made in a similar way to making the punch. I used hardened steel sewing pins.
If using fine tip ballpoint pen nibs the radius of the vee will need to be quite large, about double the radius of the nib. Larger radius pivots and vees will yield higher friction, more play and poorer mechanical grounding.

Although the coefficient of friction between brass and steel is lower than between steel and steel utilising steel grub screws for the vees will actually yield lower friction as steel is much harder than brass. With this type of bearing it is the hardness of the materials used that has the greatest influence on the resultant friction. Another possible benefit of using the punch method (cold forging) is that the act of punching should work harden the surface layer of the metal in the vee. I have no idea how significant this will be for bearing performance but it can't hurt. I found that the application of a small amount of petroleum jelly into the vees seemed to make the bearing run a bit more smoothly though I did not measure how much effect this had on overall friction levels (I did measure just about everything else).

The amount of work required to make bearings using this method is much greater than just drilling a pit in the end of the grub screw but it does result in a much higher quality end product.

Niffy
  Reply With Quote
Old 29th September 2018, 07:39 AM   #1955
nocdplz is offline nocdplz
diyAudio Member
 
nocdplz's Avatar
 
Join Date: May 2010
Location: italy
Valuable and interesting advices and experiences, Niffy. I gave some simpler tips on # 1859

--To make the brass cup grains (the trickiest work of this arm) drill and thread an iron block to guide a center drill and make the conical seat, then polished with a small Dremel tip.

More than enough for a 3dToy, for two reasons

1 - a center drill is not a normal drill bit but a precision tool used on lathes - mills to center holes precisely: it does not make a flat surface, but a starting 118 cone, quite smooth if of decent quality/age. A further polishing with a Dremel may help,
2 - with a ball pen tip there are not two surfaces (steel + steel or steel + brass) crawling against each other, but a sphere that rotates in its seat (the pen tip) The vee cup simply holds the sphere in the right position (related to arm's geometry). At the beginning, following the experts, I emptied all the ink with solvent, then I discovered that ink is a much better lubricant, for viscosity and durabilty, of what I used to put in (silicon grease)

that's all folks - let's not complicate our life where it's not needed
carlo
  Reply With Quote
Old 30th September 2018, 11:13 AM   #1956
nocdplz is offline nocdplz
diyAudio Member
 
nocdplz's Avatar
 
Join Date: May 2010
Location: italy
To be clearer.
A ballpen tip is a masterpiece of micromechanics, that no diyer and even a Swiss watchmaker could reproduce (the Chinese themselves who make 95% of the ballpens sold, only in 2017 have managed to make the machines to produce them, instead of buying and assembling them! - Consider that presently they design and build SmartPhones, not bamboo baskets).
In our use (Unipivots & so on) the pen tip must do all the work: the sphere does not rotate on the vee cup. but in its seat, on an ink or grease film). That's why the vee must be 120 degrees or more (not 90!), otherwise is the brass body to rub against the vee cup (and then much better the steel pivot that Niffy talks about)
hope this helps, even if we are off topic
carlo
Attached Images
File Type: jpg pen tip.jpg (96.9 KB, 305 views)

Last edited by nocdplz; 30th September 2018 at 11:15 AM.
  Reply With Quote
Old 4th October 2018, 03:16 AM   #1957
directdriver is offline directdriver  United States
diyAudio Member
 
directdriver's Avatar
 
Join Date: Nov 2005
Default amusing...

YouTube Video: "Tangential tonearm"
  Reply With Quote
Old 4th October 2018, 05:15 AM   #1958
Straight Tracker is offline Straight Tracker  United States
diyAudio Member
 
Join Date: Nov 2010
Location: Prescott, Arizona
Hello directdriver,

I would say "interesting" instead of "amusing".

Ralf
  Reply With Quote
Old 4th October 2018, 02:58 PM   #1959
diyrayk is offline diyrayk  United States
diyAudio Member
 
diyrayk's Avatar
 
Join Date: Aug 2012
Location: Traverse City, MI
Quote:
Originally Posted by directdriver View Post

1. It's not a pivoting arm.


2. Vertical motion of the headshell causes an azimuth shift. There is already an inherent azimuth shift in the surface angle of a record warp and the behavior of this arm compounds that.


I am neither amused nor interested.


Ray K
__________________
If more is better, then too much is just right.
  Reply With Quote
Old 7th October 2018, 09:07 AM   #1960
nocdplz is offline nocdplz
diyAudio Member
 
nocdplz's Avatar
 
Join Date: May 2010
Location: italy
Quote all, Ray, completely: a waving, rolling azimuth is a real nightmare. Adding a second carriage, when just one is more than a problem seems masochistic.
However a cartridge simply sliding on a radial rail represents the perfect geometry: you've only to design a perfect "piston-like" vertical articulation, and to overcome all the issues of the Revox linear tracker. Without a servo, of course.
Nice challenge, nobody till now...
carlo

My compliments for you new arm, Ralf: a superb realization
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Gliding for 90 - mechanical linear tonearms: no airpump, no servo directdriver Analogue Source 33 4th April 2016 12:40 AM
Angling of ports and/or drivers? Dave McReeferson Full Range 11 27th March 2012 08:45 PM
String suspension vs. uni pivot or gimball tonearms nghiep Analogue Source 26 13th August 2011 05:27 AM
Angling drivers left and right in a vertical line-array???? ozziozzi Multi-Way 12 16th January 2009 05:23 AM
Need Amp For 90-0-90 V DC Drafance007 Solid State 15 12th October 2003 09:03 PM


New To Site? Need Help?

All times are GMT. The time now is 04:35 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki