Carbon fiber

[turmite]

Hi guys and gals, that is if we have any gals.

I have a question and don't know where to put it. Moderators do your duty!

I read somewhere about an incompatibality of using carbon fiber and stainless or aluminum. I can't spell the word but it is kinda like electrolytic??? I think this means that the use of these materials together kinda makes a battery or something like that. Anyone know what I am talking about or where to find the info?
Mike

[aconde]

Well I wouldn't call that an incompatibility.

I use them togheter in my Radio Control Helicopters and the only safety measurement I follow to avoid interferences with my PCM receiver is to make sure mass is continuous and common to all pieces in the chassis.

10+ years flying carbon helis with no problems.

Cheers,
Antonio
PS.- Apologies for my english.

[High Seas]

Turmite -
Righto - You need to be "relatively" cautious where you use carbon fiber. Example - if you put it in close contact with stainless steel, and subject them both to salt water immersion - you'll wind up with a good opportunity to create a battery. The current flow is small, and the potential not enough to run your cd player. BUT you will slowly reduce the stainless steel as a result of "electrolysis" or "galvanic reaction" resulting from the presence of disimilar metals in a saline solution.
The challenge in boat building (racing in particular) is getting the weights down and the strengths up while keeping the "normal" metals in one piece. Electrolysis not only works in direct contact - but also THROUGH seawater - so if you expose an un protected piece of stainless to CF underwater - the same thing happens to the prop - the shaft, etc. Bronze is used underwater as a sacraficial anode to prevent the ss from melting away.
Long winded - but a passion of mine - especially since there are soooo many good places to gain the savings and strength with CF - but gotta do it smart! Hope that helps - I can send some more on the electrolysis if you need - PM is OK.

Cheers - JIm

[turmite]

Thanks guys/

Jim this is kinda what I was wanting but I have no intention of immersing a carbon fiber cnc in salt water! I have several really small servo motors and have had the though lately of making a really small 5 axis almost completely of carbon fiber and ?? I knew I had heard of the electrolysis I just didn't know if it was with stainless or aluminum. Does the same thing happen with alum.? Since I don't plan to keep it in salt water should the aluminum honeycomb work fine or should I go to Nomex?

Mike

edited to add:

ps the only steel I plan other than maybe the rails and such is the 4th and 5th axis head. Like I said it will be small.

[High Seas]

turmite - Mike -
Since you won't be submerging the machine - well maybe some coolant? - you'll lower any risk of galvanic action. BUT you'll want to insulate the honeycomb from the CF to totally elminate any possibility. You'll have the potential for a battery if you ever need one!
If you're laying up a panel, using the honeycomb as core - then a layer or 2 of of polyester glass and resin then the cf should do it - I'd think...A layer over the cf of some "finishing cloth" would seal in the cf too and let the "look" print through.
A mini -5 axis - WAAAY cool - I'm working out a desktop digitizer (3axis) in mini so I'm inspired by your 5 axis - eh!? Access to cf AND Al Honeycomb - aerospace surplus? I'm envious!
Cheers - Jim

[turmite]

Hey moderators, I was serious about moving this if it was not in the right place, but I can't even find this place? Where is it located and how do I get there? Ok I know I'm here but whre is here? No tht doesn't sound right either!

I had to use the link from the DIY and I am serious, I cannot see this forum anywhere?

Jim, I won't be using surplus. I live in Arkansas of the USA and it is kinda like the UK here. You can't find anything you need and have to have everything shipped in. The cost of the honeycomb and carbon fiber will not really be too bad considering I already use the fabric, resins and vacuum baggin system. I have enough pre-preg to do the table, xyz axis frames as well as the 4th and 5th axis yokes. I haven't even started the drawings yet. I will have to scale everything off of the motors then go from there. I am going to try to model everything Rhino or Gmax to use this as a project to better learn how to use one of those programs. If you have any input on the honeycomb aluminum or nomex let me know.
Mike

[Sanghera]

Why use Carbon Fiber? Isn't it a bit expensive?

[turmite]

Carbon fiber is something like 10 times as strong as the same amount of steel and bunches lighter. With the honeycomb substrate the stiffness is unbelievable. This machine is at least planned to be really small and really fast. Table will be no larger than a 16X16 in. and possible smaller than that. Fixed gantry with the articulated head. My purpose for the machine is two fold.

First I want to build it! Second I plan to use it in local schools and craft fairs to demonstrate how cnc can be used for lots of things and that most anyone can if they want to build one. I may even do a duplicate machine in mdf and on the cheepy to show it doesn't have to cost an arm and a leg.

Mike

ps how did you find this thread. I am still having to go to the diy link to get here?

[turmite]

Ok I finally found it.

Mike

[RotorRouter]

turmite,

This may be too late; however, you should not bond carbon to aluminium. In other words, it is a No No to bond an aluminum trim tab into a carbon composite rotor blade.

Dave J.

[turmite]

Hi Dave,

Nope not too late. Life took a couple more turns. I will get back to this, soon I hope.

Mike

ps thanks for the help.