[Eson]

Does anyone have any idea about how well graphite powder and epoxy is dampening vibrations? Graphite-epoxy is said to be very hard, they cast rockets in it: http://en.wikipedia.org/wiki/Graphite-Epoxy_Motor

[JerryFlyGuy]

NOT WORTH CRAP.. Both Epoxy and Graphite are rather brittle, the reason it works for rocket motors is because its not graphite powder but graphite cloth or twine. The wrap those suckers like crazy. The tension capability's of the graphite is where it really excels, which doesn't really apply to PC structures..

FWIW
Jerry

[greybeard]

IMHO the graphite in the rocket context is there for its thermal properties.
John

[JerryFlyGuy]

True John, graphite is great for thermal transfer as well as a NEGATIVE coef of thermal expansion [gets smaller w/ heat] however even that wiki site says 'due to the filimant wound casings having excellent strength w/ little weight and is stronger than steel" [ I paraphrazed a bit] basically you have a pressure vessel which can burst easily, having a graphite tank/casing which is wound properly is a fantasic weight savings. I'm curious to know what kind of liner or Epoxy they are using as most epoxy's will fail w/ just a slight elevation of tempurature [realitively speaking] a rocket motor is burning at over 2000F, must be quite the epoxy!

Jerry

[brunog]

John and Jerry are right, graphite has good thermal transfer properties and is a ligthweight product, it is used as an epoxy additive (15% in volume)to add slickness to boat rudder constructions, the same way as Teflon powder bur at a much lower cost $14US/lb for graphite vs $60US/lb for Teflon.

Bruno

[greybeard]

Sorry this is off topic, but one of those trivial bits of info.

I'm curious to know what kind of liner or Epoxy they are using as most epoxies will fail w/ just a slight elevation of temperature [relatively speaking] a rocket motor is burning at over 2000F, must be quite the epoxy!

Jerry

Yet another of my backlog of "curious things I have done in my past", I once made large internal turnings in blocks of wet(soaked) mahogany for a glass company, who made cut glass decanter by hand.
The technique involve spinning a blown bubble of glass(red hot) inside the wooden block which has just been taken out of a bucket of water !
The hot glass turns the water to steam and this produces a vapor cushion to spin the glass in.
However, inevitably the wood starts to burn, but once it has built up a layer of carbon on the surface, the mold hardly burns at all, and lasts a considerable length of time.
I suspect something similar happens in the rocket nozzle. The surface of the epoxy does char, but the carbon formed slows down further burning while the graphite already present helps conduct the heat away from the surface.

John

[WilliamD]

I'm going to try and settle some questions on this thread, and do some tests. I just want to make sure I'm getting the right stuff.

I'm going to buy a 1/2 gal kit of EPOX-1505563. It's mixed 2:1, for a slow curing process. I'm going with Igalla's advice, and getting it from http://www.shopmaninc.com/epoxy.html

If someone could confirm that's the epoxy were discussing, I would really appreciate it.

I'm also going to go to Home depot and get some varrying types of sand and aggregate. Mostly just stuff available locally. If I understand correctly, the sand is mixed with the epoxy at 5 parts sand, 1 part epoxy ratio. Is that correct?

I will report on how the curring goes, temperatures, and obviously some nice pictures of the finished results. I have a wide assortment of wood and other substrates to make molds out of.

Any other comments would be appreciated. I'm drawing up a mill I want to make, mostly a square column mill with linear rails and ballscrews. I can't cast the 1000 pounds of cast iron I would want, but I can mix a bunch of sand and epoxy. I like that you can add it in stages. I will work out the vibrating component also, but if anyone has a decent idea, feel free to share.

Thanks again for all the info, had never thought of something like this before.

[brunog]

William,
The epoxy:aggregate ratios i've seen so far are closer to 10% in weight epoxy (including hardener) so 1 part epoxy, 9 parts aggregate.

Bruno

[walter]

Great idea William, thanks for doing this.. I think I'll do the same with polymer concrete- it's time to test some samples.

[ger21]

I think you want the thin stuff, not the thick. The thick will be much harder to mix the sand and aggregate in, imo.

Go back and read post #125 for info on the ratio. Bruno is right, but it may be nearly impossible to pull it off.

[Eson]

I think using polymer as a matrix will be a good deal for us hobby builders. I belive the cost for polymer is about 1/5 of epoxy. I know polymer will shrink more then epoxy but if you have so much aggregates it wont shrink at all.
Also im going to start my cnc-project soon and want to test polymer concrete. I just need to get my hands on some sandblasting sand.

About that graphite-epoxy i posted earlier, its used for the tanks and not for the nozzels. They use carbon-carbon fibres for that, even the space shuttles heatshields are made of carbon-carbon.

[brunog]

Gerry,
Because granite is twice as dense as epoxy. 1:9 epoxy:granite ratio in weight comes out to a 1:4.5 ratio by volume which is feasable.

Bruno

[lgalla]

Guys
Sorry for the lack of input as "thank god" I am swamped with orders and have little time to read the posts in detail.14hr days/14/7 are taking its toll.:violin:
After a hard day a couple of:cheers: makes one as Geof says"obvilious".
Polymer concrete to me is POLYESTER BASED and the(flame2) thing does not apply.POLYESTERS are extremely flamable and bad for your health.Stick with epoxy.
Graphite is graphite,pensil leads ,subway lubricant etc. Carbon fiber is carbon fiber,some how rocket motors or carbon fiber do not see the heat.Carbon fiber in aircraft use must be contained in fiberglas skins to protect against shrapnel in case of failure of the carbon laminate.This thread is about things not related to carbon fiber which is a totally different animal.
The Home depot builders sand is soaking wet,not suitable for E/G.The filter sand or sandblast sand is dry.
Sorry 2 more:cheers: Hope to post "Why I need a E/G router pictures.
Larry

[atenman1]

Hi Larrylet see those "Why I need a E/G router pictures", or may be couple pictures of your subwoofer?

ok, the pics below are from PROLIGH 1000 cast in polymer granite!!! probably casted by ZANITE. The question are
1. is that steel imbedded plate ?
2. why are the texture so rough, what do they used for moulding material?
what is the incentive, or advantage to cast it with rough texture?

http://cgi.ebay.com/LIGHT-MACHINES-P...QQcmdZViewItem

Thanks
calvin.

[brunog]

Calvin,
I checked the spec of the Prolight 1000 at http://www.intelitek.com/products/pr...=1&pid=2&did=3

it is polymer concrete, with embedded cast iron parts, E/G will take the texture of the molds, that's why the base of the machine is rough. The manufacturer probably wanted to replicate a cast iron finish, which is marketing b/s to me.

Bruno

[JerryFlyGuy]

Or, they finished it off w/ "Hammered finish paint" which gives the exact same look. I'm using it on my machine and even though its a welded construction it comes out looking like it's cast iron, kinda neat..

Jerry

[walter]

Jerry, how about a picture?

[JerryFlyGuy]

Sure, when its done .

Seriously though, I'll be posting a brag thread when I do get it done and there will be pictures then. It looks terrible right now as its painted here and there and needs lots for 'final touchup' to pass muster. I hate posting stuff that is only 1/2 way to the 'final product'.

If your looking to see what Hammered Paint looks like.
http://www.rustoleum.com/product.asp...ct_id=21&SBL=1

Jerry

[walter]

Uhm.. I've been thinking again.... (chair) (Geof, please put the chair down ).

Leveling the frame with epoxy solves only part of the problem... You still need those pesky 'centerlines' for mounting of linear rails.


How about rotating the frame 90 degrees...And pouring epoxy into a small jig to create a master rail ??



(assuming that frame is totally rigid and you're able to set it at 90 degrees..) What do you guys think?

[vger]

Just found this machine on ebay and saw they used granite blocks for the rail mounts. Just thought it might be of interest.

http://cgi.ebay.com/cnc-system-servo...QQcmdZViewItem

Steve