Go Back   Home > Forums > Source & Line > Analogue Source

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 16th March 2004, 12:11 PM   #1
Magura is offline Magura  Denmark
diyAudio Member
 
Magura's Avatar
 
Join Date: Oct 2003
Location: Denmark, Viborg
Post How to make a tapered carbon fibre tone arm

Ive been asked to explain how to work with carbon fibre stocking in order to make a tapered carbon tone arm.

Most of this is general for working with carbon fibre, and can be applied to loads of other projects.

First a little about safety:

Epoxy resin is VERY poisonous till cured, it is only to be worked with in a well ventilated area or even better outdoors.

Carbon fibre is only to be ground by wet sanding or the like, never dry, since the dust is dangerous as well.

Wear rubber gloves when working with either epoxy or carbon fibre......try just once without, and youll know why i say this

First id like to know a little about where you guys stand in matters of working with fibre materials? any previous experience? And in case of a yes...what?

This is just to get an idea of what you need from me.

Magura
__________________
Everything is possible....to do the impossible just takes a little while longer.
www.class-a-labs.com
  Reply With Quote
Old 16th March 2004, 12:33 PM   #2
diyAudio Member
 
Jerry T.'s Avatar
 
Join Date: Oct 2003
Location: 6 floors up! In Holland!
I'm pretty handy when it comes to C.N.C. machining (lathe and milling macines), but i've never worked with carbon fibre.
I'm aware of the risks of working with these kind of materials.
Done some work with Polyester, i believe it works on the same sort of principle?!
__________________
Now, ain't that grand !
  Reply With Quote
Old 16th March 2004, 11:01 PM   #3
Magura is offline Magura  Denmark
diyAudio Member
 
Magura's Avatar
 
Join Date: Oct 2003
Location: Denmark, Viborg
Then youre gonna have an easy time making a mold.

Make a positive model of hardwood, make sure all edges are nicely rounded. Add a cylindrical piece to each end of a reasonable size.

You can make the fillets with stuff like plastic padding or the like.

Coat it with several layers of laquer (sand well between coats). I usually use thinned floor laquer. Then coat it with wax (like candle will do fine)

Make a box of wood thats about 10mm bigger than the positive model on all sides.

Get a pack of modelling wax (any kiddo version), fill the box about half up with wax and push the positive model down the wax till its half way down all the way around. Be sure to not get it deeper down the wax than half, in that case you cant get the finished tonearm out of the mold.

Now fill the rest of the box with potting compound.

Let it cure well. Then rip the bottom off the box, take out the modelling wax and wax the whole thing with candle again(including the potting compound),

Fill the space in the box where the modelling wax was removed from with potting compound as well.

Cut off the ends of the whole thing so you will be able to see the cylindrical pieces that you added to the positive.

Break the box off and seperate the two halves.

You should now have a negative mold.

To be continued.

Magura
__________________
Everything is possible....to do the impossible just takes a little while longer.
www.class-a-labs.com
  Reply With Quote
Old 17th March 2004, 12:18 AM   #4
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
The cool thing about building with fiber is that you can make the mechanical properties highly anisotropic. For a tonearm, I'd use some sort of prepreg and think about alternating directions +/- 20 degrees or so with respect to the long axis. I'd use conducting carbon fibers and ground it at the pivot end. And make the headshell integral, of course. You can do this with a mandrel rather than a mold.

Epoxies can indeed be rather toxic, and two-part systems are a real pain to get properly mixed. That's one reason I favor the use of prepregs, but you have to rig together some sort of vacuum bag and cure the thing in an oven. That could be daunting, but he-man DIYers will do whatever it takes.

Wax is a good release material, but spray-on silicones are even better and can take the heat of cure.

If you sand or machine, wear a GOOD respirator, not one of those cheapo paper masks.
__________________
"The way to deal with superstition is not to be polite to it, but to tackle it with all arms, and so rout it, cripple it, and make it forever infamous and ridiculous."- H. L. Mencken
  Reply With Quote
Old 17th March 2004, 01:18 AM   #5
Magura is offline Magura  Denmark
diyAudio Member
 
Magura's Avatar
 
Join Date: Oct 2003
Location: Denmark, Viborg
Quote:
Originally posted by SY

Wax is a good release material, but spray-on silicones are even better and can take the heat of cure.

If you sand or machine, wear a GOOD respirator, not one of those cheapo paper masks.

Even the GOOD respirators are not good enough for dry sanding of carbon. It must NEVER be sanded dry. When wet sanding its harmless.

Problem with silicone spray is that some types dont work well, and im not quite sure wich. What i usually also find problematic with silicone is to remove it afterwards from the item molded.

Theese days i guess its most common to use fibre stocking thats approx -+20 to 25 degrees for such.

When molded in a negative mold, you put an inner bag (made of a condom inside a condom, the outer one just for protection) and apply pressure, then you can press the excess epoxy out of the mold and achieve something close to 90% fibre, wich for anything like this is more than adequate. You may even want to make it 80% for the sake of damping.

Magura
__________________
Everything is possible....to do the impossible just takes a little while longer.
www.class-a-labs.com
  Reply With Quote
Old 17th March 2004, 01:21 AM   #6
Magura is offline Magura  Denmark
diyAudio Member
 
Magura's Avatar
 
Join Date: Oct 2003
Location: Denmark, Viborg
For the sake of those who didnt see the thread this thread is a split from, this is the tonearm in question.

Magura
Attached Images
File Type: jpg wilsonbarm.jpg (35.5 KB, 797 views)
__________________
Everything is possible....to do the impossible just takes a little while longer.
www.class-a-labs.com
  Reply With Quote
Old 17th March 2004, 01:33 AM   #7
diyAudio Member
 
Join Date: Feb 2004
Location: Racine, Wisconsin
Carbon fiber tubing might be your easiest solution. This is a common item in the hobby stores. It is used for model sailboat masts and model airplane wing spars. As model hobbies are about 100 times more common in Europe, this would be a very simple solution. Typically these are spiral wound, but alas, not tapered. I would look just to be sure.

As for building your own, I would sugest looking at a carbon tape. As for the epoxy, this is simple and IMHO not at all dangerous. If it was even moderately toxic, I would be dead. Generally, you will find a very suitable epoxy kit in any marine (boats n' stuff) store. Typically, they will be sold in kits where you can also buy the metering pump. One shot of resin and one shot of hardener (already setup for half volume!!!) and you are good to go. You will find the hardeners in a variety ranging from "very fast" to "slow". The reaction is exothermic and is based on temperature. At 15C you can have an hour of time. At 25C it may be smoking before it's done mixing. A tonearm job would be one shot job... and you can most likely make 5 arms! As for safety, gloves are nice because it takes a week to wear off your fingers. Otherwise, just don't drink it. If the epoxy starts to get warm, throw it away (where it won't start something else on fire) and make your next batch in a more shallow dish. You can also retard the reaction by placing your mixing dish on ice. DO NOT ADD more hardener as it will make the epoxy SOFT.

My proposed method would be to make a mandrel of steel or aluminum. You want this mandrel "draw polished". In other words, polish the tube longitudinally like you were... ah... never mind. Anyway, you want the little, tiny, microscopic scratches to run from one end to the other end, NOT around the mandrel's diameter. Use black wet/dry paper (400-600-1000-1500-2000) and then abrasive powder (we call it rouge). Wax the mandrel with carnuba wax (high end car wax).

You need a friend to turn the mandrel. Wet the mandrel with mixed epoxy and start winding the tape while applying more epoxy with a little brush. Work the epoxy into the tape. Wind up the mandrel and terminate with a clothspin. Now start the process again in the opposite direction and terminate the other end with a clothes pin. Come back the next day and carefully pound the carbon tube off the mandrel. With any luck, it should stand upto 20 kilos of stylus pressure!

I would not feel obliged to make the exterior look pretty (sanding and leveling and such). But that's up to you. The mode epoxy you use for filling (with the addition of filleting powder) the heavier the tone arm will be. The standard filler is "micro balloons". However, being microscopically round, they tend to sag.

Good luck!
  Reply With Quote
Old 17th March 2004, 01:35 AM   #8
diyAudio Member
 
Join Date: Feb 2004
Location: Racine, Wisconsin
I take back everything I said above as I just saw the tone arm. This must be made in a female mold. Have you considered buying a CD player?
  Reply With Quote
Old 17th March 2004, 02:44 AM   #9
diyAudio Member
 
Join Date: Feb 2001
Location: Vancouver, B.C., Canada
You can buy tapered carbon tube in Europe and the U.S., it comes in various lengths, taper ratios and lay-ups.

http://www.deltronix.net/cgi/acp_display.exe

I use carbon tubes and carbon cloth all the time in R/C glider building and canoe/kayak building. Any work that is going to generate dust has to be done outside and wearing U.N. Nuclear Industry approved respirator filters.

If you get any carbon dust on your clothes leave them outside for washing, the dust is very carcinogenic.

WEST SYSTEMS is an excellent epoxy for use with carbon, and you want to use the slow hardener.

When I make tapered carbon tubes on a mandrel for a R/C glider tail boom I do a 25% epoxy to carbon layup but this might not be optimal for a tonearm.

Polyester is not suitable for using with carbon, it has weak structural properties compared to epoxy and polyester working time (pot life) is to short. The resonant properties of epoxy may be better suited to audio applications as well.

If you can find an appropriate tapered carbon tube at a Vendor then IMO you will be far ahead of the game, learning to control layups and getting a well made part out of a mold is time consuming and can be expensive.

Of course it is also a lot of fun but if you want to get your project going without too much fuss then a factory tube is a good idea.


T.D.
  Reply With Quote
Old 17th March 2004, 05:08 AM   #10
diyAudio Member
 
Join Date: Feb 2001
Location: Vancouver, B.C., Canada
Here is a link to some photos' of carbon booms for sale so you can get an idea of what is available.


http://www.rcgroups.com/forums/showt...hreadid=210375



T.D.
  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
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Kevlar, Aerogel, Carbon Fibre, Paper - Which is the best ? Fanuc Multi-Way 12 4th February 2009 07:06 AM
FS: Black Diamond Racing Carbon Fibre Blocks transducer Swap Meet 0 20th December 2005 08:29 PM
Carbon Fibre Heatsinks..! owen Pass Labs 3 10th November 2005 06:37 PM
Damping carbon fibre tubes Derekva Analogue Source 5 24th December 2003 09:54 PM
Anyone recognise these carbon fibre drivers? Ian J Multi-Way 12 14th May 2003 10:03 PM


New To Site? Need Help?

All times are GMT. The time now is 04:57 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2