MadModder

The Shop => Tools => Topic started by: Chazz on August 30, 2011, 01:12:43 AM

Title: Epoxy Granite Mix
Post by: Chazz on August 30, 2011, 01:12:43 AM

I'm cuirious about filling my mill base. Other than the usual health precautions, is there any reason why lead, say from pellet gun ammo or small fishing weights shouldn't\couldn't be introduced to the 'mix' for the mass\damping?

Thanks for thoughts,
Chazz

Title: Re: Epoxy Granite Mix
Post by: nearnexus on August 30, 2011, 02:59:11 AM

Whatever you put into cement to form concrete should be inert if possible - ie. not subject to serious oxidation (and associated expansion).

Lead is in there with the oxidisers, so I wouldn't use it.

The damping effect would be insignificant compared to the overall mix.

Rob

Title: Re: Epoxy Granite Mix
Post by: Chazz on August 30, 2011, 10:25:57 AM

Interesting, they use iron re-bar in concrete and water as the mix?  Wouldn't the epoxy encapsulation literally seal the entire matrix from air?

I also didn't realize Lead was 'up there' in terms of oxidizing, I've got 15 year old lead fishing weights that look the same today as when I bought them.

My wondering about using Lead as part of the mix is that Granite is 'only' approx 165Lbs\Cu.Ft. where as lead is approx 710Lbs\Cu.Ft. or approx 4 times the mass for the same volume. Sooo, if, for example, I substitute .25 Cu. Ft. of Granite for Lead I would have an approximate net weight gain of 130Lbs over the Granite .... Not too shabby?

Hmmm, more research.  :scratch:

Thanks,
Chazz
 

Title: Re: Epoxy Granite Mix
Post by: DavidA on August 30, 2011, 03:37:57 PM

The thing about re bar in concrete is that the lime in the cement prevents the iron from oxidising.

But I also wouldn't have expected lead to oxidise to any extent in cement.

Dave

Title: Re: Epoxy Granite Mix
Post by: Chazz on August 30, 2011, 04:34:34 PM

Hi Dave, that's my point, I'm not thinking of using concrete, but rather 2 part epoxy (like the 'West' system used in boat building).

Cheers,
Chazz

Title: Re: Epoxy Granite Mix
Post by: mike os on August 30, 2011, 05:29:59 PM

personally I find it hard to pick a fault with..... in fact ai would go the whole hog & use all lead/mainly lead, cant see any real reason not too. Epoxied in its not going to be in contact with anything I would not think?

Title: Re: Epoxy Granite Mix
Post by: loply on August 30, 2011, 05:52:13 PM

I guess the only problem with this is the lack of rigidity in lead.

Assuming your objective is to add rigidity as well as mass for absorbing vibration?

Title: Re: Epoxy Granite Mix
Post by: nearnexus on August 30, 2011, 06:44:21 PM

I assumed you were using a cement filler, but epoxy should be OK with just about anything.

Lead does oxidise (eg just look at old bullet heads) but the degree varies with the type (hardness ?).

To really beef up the base density you could mix in plenty of scrap steel punchings (discs seem to be the go), as they do for bank vault walls - but not for that purpose :-)

Should be easy to get from a scrap metal merchant.

Rob

Title: Re: Epoxy Granite Mix
Post by: andyf on August 30, 2011, 07:29:16 PM

I think Chazz is just looking for weight, not rigidity, so lead should be fine.

Depleted uranium is even denser, but its half-life of 7 million (or 4.6 billion, depending on the isotope) might make for a long-term project. Gold is also denser than lead, but a bit expensive just now....

Andy

Title: Re: Epoxy Granite Mix
Post by: dickda1 on August 30, 2011, 07:46:57 PM

You should take a look at this long running thread:

http://www.cnczone.com/forums/epoxy_granite/30155-epoxy-granite_machine_bases_polymer_concrete.html

In some cases, concrete or epoxy can be poured into the cavities of machine castings to provide substantial damping as shown here:

http://www.cnccookbook.com/CCMillEpoxyFill.htm

-Dick