[alexccmeister]

I read on this thread someone used MDF as mold and it was really easy for the epoxy once set to be release from the mold. Anyone else used MDF? I think the poster said that the reason why the part was so easy to be released because a thin layer of the MDF actually get peeled off with the epoxy.

Is using MDF detrimental for the epoxy?

[greybeard]

MDF certainly delaminates very easily, even more so if you wet it, so I expect this is true.

But do you really want a brown hairy casting ?

I can just imagine Walter's reaction - (chair)

John

[walter]

Good question Alex.

Mold release is still unknown category- I've tested 3 differend agents and none of them works well or leave a good finish. Not sure about MDF -there is no stiffness in this material.

I have general idea what lagre manufacturers do with their molds, with spraying stuff, gelcoats and all, but no time to test it. I'm really into machine building so I'm leaving it for others.

[greybeard]

Walter - hope I wasn't out of line.
At least mdf is widely available/cheap/flat, and could be braced externaly.
John

[alexccmeister]

Walter - hope I wasn't out of line.
At least mdf is widely available/cheap/flat, and could be braced externaly.
John

That is the reason why I am thinking about using MDF. I was going the route of plywood when I saw lots of very very flat MDF board in the carpenter's workshop.

If all it does is leave hairy casting, I think I can live with that as I can alway sand them down. I was more concern with the MDF absorbing the epoxy before it sets and causing the top layer to have little binder to hold the stone chips.

Walter, thanks. I know you already have tons of input on this topic and not meaning to take anything away from the thread. But I think I know what I need to do now. thanks.

[walter]

Yeah, there is no problem really.. It should be about freedom, not restrictions. Anything can be made to work- Part size, complexity and budget should be your guidance.

And to me, it's not about the mold. It's about vibrating the mold. You really have to shake that thing, the whole E/G idea is build around vibrocompacting. It doesn't seem that important, but wait til you get to 100lb molds and beyond. That's where the real issues are. Everything else is a small potato.

[alexccmeister]

Hi Walter,

Thanks. I will definitely want to vibrate the mold as you said.

One question if you don't mind answering. I am planning to put bolts into the mold before pouring the epoxy in. The bolts are for locking my Z column in place. Doing this way will create a lot more work for me. Is it possible to drill holes in the epoxy after it has set, say after a week, and put an expansion bolt in? Will the epoxy casting crack? How near to the edge should any hole be drilled to prevent the casting breaking off when I insert some bolts in it? Thanks.

[walter]

One question if you don't mind answering. I am planning to put bolts into the mold before pouring the epoxy in. The bolts are for locking my Z column in place. Doing this way will create a lot more work for me. Is it possible to drill holes in the epoxy after it has set, say after a week, and put an expansion bolt in? Will the epoxy casting crack? How near to the edge should any hole be drilled to prevent the casting breaking off when I insert some bolts in it? Thanks.

Yeah, very important questions. I don't have a lot of experience with this but my guess would be don't drill it. Actually, it's not about drilling- you can probably drill it if you want to- it's about not mounting stuff directly to E/G.

I've seen a lot of mineral castings and not one had anything bolted to it. Anything that has to be bolted or mounted is done via massive steel mounting plate embedded in the composite. I'm talking about commercial E/G- which is superior to our homemade stuff.

My advice would be use heavy duty inserts or deeply embedded plates and then drill. Mounting anything to E/G is not a good idea.

I'm still working on your "steel reinforcements" question. Will post a drawing this weekend.

Cheers!

[ckelloug]

From what I've read, adequate mold release is 5 coats of a mold release wax designed for epoxy. Five coats of wax sprayed with a uniform layer Poly Vinyl Alcohol (PVA) is likely optimal. I assume MDF will stick to the epoxy . MDF is good stuff however because it is likely to hold tolerance as it is naturally flat and doesn't want to warp. It is also good as it won't have grain characteristics. It isn't the strongest stuff in the universe but it's probably apt to produce a nicer finish than wood and strong enough for most parts. Using wood for a mold, sanding it from 80 grit all the way to 220 is probably important. I doubt most mold releases will work well on a rough surface. Larry also suggested using cheap counter top laminate from home depot like Formica or Nevamar as the mold surface with the release wax. MDF fuzz won't look sporty

www.uscomposites.com has mold release products and it's where many of us have been buying epoxy. (same site as www.shopmaninc.com) I haven't started my experiments yet so the above is from reading lots of vendor web sites.

I'm not sure if you'd want to put expansion bolts in later though drilled holes. I think this could potentially put stress on the material and make it more likely to break there as it would cause tensile loading which could be significant. I haven't made any parts so I don't know the magnitude of the problem. I think that expansion bolts are probably a bad idea though. If I wanted to put bolts into a part without setting them into the epoxy, I'd use 1/2 or 3/4 bolts in the center of the part going all of the way through, and large washers on both sides. This ensures that the material is only loaded in compression. Rather than drilling for them, I'd insert teflon rods into holes predrilled in the mold and covered in mold release. The epoxy would then flow around the rods and leave bolt holes. If I was casting in the bolts, I'd want to make sure that the head was buried deep in the epoxy so that there would be both mechanical and bonding to ensure it didn't rotate as well as a lot of material for it to push against.

The reason that bolts don't get used is that you don't want to put large tensile loads on this material and bolts can do that if done wrong. You either need to use a large metal plate with threaded holes to distribute the bolt force over a lot of material or run the bolts all of the way through as I described so that the bolt is placing the material in compression. It is import to avoid placing holes or imperfections along the outer edges of the part as this is the part under the greatest load.

Drilling this material probably will be challenging as it will be pretty hard. In concrete, you'd use a hammer drill with a carbide bit. This material will probably chew up bits. Even worse, if you leave a rough edge, it can lead to cracks forming there causing the piece to break under load.

Walter's right that threaded inserts are probably easier than bolts. I wouldn't want to have to drill or sand this stuff.

As for the ubergood finish, somebody might want to ask Larry about what gel coats are and how to do one.

--Cameron

[martinw]

IMVVHO, probably not a good idea. I think you might have much better luck with resin anchors. I'm not sure how you would form the hole to take them though (drill or cast). I have absolutely no feel for how the stuff behaves when drilled, but I would guess that you may have problems if you SDS hammer drill close to an edge.

Best wishes

Martin

[alexccmeister]

Thanks guys. My questions are answered. My original plan is to place long threaded bolt deep with in the epoxy casting and as an added measure to weld the bolt to the reinforcement cage I am building that will sit nicely within the casting. I am leaving about 10mm cover on all side clear of the reinforcement cage. I am also placing 10mm steel plate with bolt fixed to it embedded within the casting. That should hold the casting in place.

I was hoping to drill but seems not a good idea to do that. So that eliminates one way and I can work on the right way. Thanks again.

[lgalla]

Expansion bolts,maybe explosive bolts,I assume theE/G would crack.I read somewhere that embbeded anchors,inserts,bolts etc.are so strong you can strip the threads before the E/G will give up.Did not pay to much attention to the article as the statements are rather general.Cast in place should be plenty strong.
Previously someone used screwed together Melamine,waxed,and had no release problems.Melamine is the cheapest material which will work with the added benefit of being two sided which makes it very stiff.Unsealed wood or MDF are poor choices.
On difficult hard to release molds,aircraft guys have done this,paint the waxed mold with latex.This guarantee's release and the latex is sanded off.Also guarantee's non sporty look.
For sporty,ubergood finishes and gelcoats,this is difficult to say the least.Will have to scratch my head a bit on this one.
Larry

[Geof]

Hi Walter,

Thanks. I will definitely want to vibrate the mold as you said.

One question if you don't mind answering. I am planning to put bolts into the mold before pouring the epoxy in. The bolts are for locking my Z column in place. Doing this way will create a lot more work for me. Is it possible to drill holes in the epoxy after it has set, say after a week, and put an expansion bolt in? Will the epoxy casting crack? How near to the edge should any hole be drilled to prevent the casting breaking off when I insert some bolts in it? Thanks.

I suggest you do not consider trying to drill holes after casting the polymer composite/ There are two reasons for this; first, it will be very difficult to drill, second, an expansion bolt exerts significant tensile forces on the material it is in and the polymer composite is weak in tension.

The problem you are considering is one that, I think, has not been addressed in this thread. The focus of this thread, to me, appears to be optimising the structural properties of the polymer composite, aka epoxy/granite. What has not been adressed adequately, in my opinion, is the interfacing between the structure and the function. By this I mean how do you get the precise mounting locations for linear guides, ballscrews, etc., in/on the polymer composite?

In my view you do not get it by building a precise mold and then coating it with several layers of release agent because it is the release agent that defines the final precision. I defy anyone to lay down a coating of wax, or similar, with a precision of +/- in the fractions of a thousandth of an inch.

I think the only way to get a precise integration of the function and structure is to build a precise jigging/mold sytem which holds all the functional elements in their correct position. These functional elements need to have anchor points that get embedded in the polymer composite but it is not the mold that defines the final precision/accuracy of what is being produced it is the jigging system for the functional components.

And at the Do It Yourself level building this precise jigging system is as difficult, or more difficult, than simply fabricating the final structure and then embedding/filling selected parts of it in/with polymer composite for vibration damping.

[ckelloug]

Geof,

I agree completely that accurately building parts is going to be difficult. I think Walter is relying on using metal parts that are accurate and just building the structure out of E/G. Such a structure can be squared by shimming and grouting the pieces together. I do doubt that any of the pieces made without precision tooling will be to thousandths tolerance but I know that Walter at least is building a woodworking machine where a 64th of an inch is probably good enough. He's also using a wooden mold for his beam.

To get precise flat surfaces, one would probably have to cast a thin layer of self leveling epoxy over a part or something like that. Another possibility, albeit expensive, would be to make the mold out of machined and polished teflon.

My reply to alexmeister was suggesting using the mold as a crude jig for placing some bolt holes. I personally haven't concerned myself with the accuracy problem because nobody has asked. Many here seem to know what they want to build and how they want to build it and seem to look here for advice on making decent E/G.

I'm not sure that the alignment problems for an E/G framed machine are any harder than the alignment problems for a metal framed machine built at home by folks without precision tools. Do you have any suggestions about designing a machine that can be made in a semi-precise fashion and successfully aligned at home? I could be missing something about why E/G is harder to align than metal for the folks without metalworking tools.

Regards all,

Cameron

[greybeard]

I'm assuming that "melinex" film aka cooking foil aka mylar will give a good, if not perfect, release from epoxy without the need for any additional release agents.
For any flat surfaces, I intend to use a spray adhesive on mdf, then lay the film onto that. The adhesion is good enough over an area to hold ot flat to the mold during casting, or in my case during spinning.
My current design for beams has evolved from circular cross sections to truncated triangular ones, with three point suspension for the moving parts.
Each apex has a channel into which my metal ways will be embedded post curing of the main beams. It will be at this stage the alignment of the ways will be adjusted.

John

[ckelloug]

John,

I know I still owe you some data. As for mylar, it sounds like it will work. Dupont Tejin films lists it for such applications although they do mention that there are silicone coated varieties for even better release properties. The only issue I can see is that depending on the glue used, a thin mylar film may transfer the glue pattern to the surface leading to odd texture/flatness.

--Cameron

[greybeard]

Cameron - good point re thin film, but I'm hoping to find foil, slightly thicker to avoid that, and also give some re-usability.
Alternatively, does polycarbonate give a good release ?
My local window glaziers always have cheap off cuts of it

John

[ckelloug]

John,

Looking at http://www.sdplastics.com/polycarb.html they suggest that polycarbonate can be bonded with epoxy. I suspect that Polycarbonate is not the droids you're looking for.

I've been stalled on E/G lab work due to work on my shop but I've been doing some very interesting research on titanate and Zirconate bonding agents as well as cheap nonreinforcement.

For the E/G heads on this thread, take a look at http://www.dupont.com/tyzor/ titanate and zirconate bonding agents.

Also take a look at http://www.nanocor.com/tech_sheets/T11%20-%20I30E.pdf which is a datasheet for a nanoreinforcement clay for amine cured epoxies.

Regards all,

Cameron

[greybeard]

Hi Cameron.
Thanks for the thumbs down on the polycarb. Saves me experimental time

That nanoclay link was a little puzzling as I couldn't work out what Tg represented from the context. They use the term several times but I couldn't crack it.

On the subject of clay and epoxies.
Having carefully washed out any dirt from my original sample of "ballast", my first source of an aggregate, it occurs to me that I was probably washing out all the finest particles of the total mix.
I know that the cement people think that dirt is anathema to a strong mix, so washing out is recommended, but leaving out organic material for the moment, I wonder how you define "dirt", and how does it differ from clay. From my days with pottery clay, I think of it as flat aggregates of silicate particles, and could these particles be a useful part of the total mix that we are seeking ?
Mind you, it could be that the clay particles might retain water unless high temperatures were used for the drying process before mixing with the resin, giving further complications.
Ho hum.

The particle separator continues its development, only the transparent front to add now. Lost a good friend to the big C last week, so progress somewhat slow. The sort of guy that, after you'd seen him, you felt better for it. I shall miss him.

Regards
John

[brunog]

IMVVHO, probably not a good idea. I think you might have much better luck with resin anchors. I'm not sure how you would form the hole to take them though (drill or cast). I have absolutely no feel for how the stuff behaves when drilled, but I would guess that you may have problems if you SDS hammer drill close to an edge.

Best wishes

Martin

I have been working on this issue months ago and the simplest solution I found was an allthread coupling with 2 flat washers and a carriage bolt to hold everything together.

As for passing bolts through, any rigid plastic pipe(PVC,ABS) or even copper pipe, conduit will do the trick with flat washers at the end, then seal the pipe with ...... how about 5 minute epoxy.

To make the moulds I am going to use Baltic plywood, it's more expensive than MDF or melamine, but it's strong,stable and I can get better results out of it.

Best regards,

Bruno