[ardenum]

…52 degrees after 20’ish hours…

How long do you plan to keep it under?

Another thing, don't remember if it's been asked, but are you going to use any linear scales eg. from ditron? I'm particularly interested how your going to mount them, if any?

[badhabit]

How long do you plan to keep it under?

Untill friday evening or 70c in 12hours...whichever comes first :-) Will most likely just let it cook until friday anyways, i don't have any time to take it out of the moulds before anyways...

...are you going to use any linear scales eg. from ditron? I'm particularly interested how your going to mount them, if any?

No, i am not going with linear scales. Instead i bought relative good ballscrews... i've chosen 32mm hiwin screws for high stifness, i've chosen "Precision"-series and then double-nut with high preload...

[badhabit]

...65c after 36 hours...

[peteeng]

Hi Thomas - Is that the part surface temp? or the air temp? Peter

[badhabit]

Is that the part surface temp? or the air temp?

It is the air-temperature right above one of the parts. But i think it is pretty close to surface temperature. When it showed just below 50c i had my hand in the oven and i could barely touch the metal-parts, this tells me that it is somewhere around 45c(which usually is the limit for me)...

[stef110]

Looking good! Gone look super good once you will stack the base and column together! And that atc looks huge!

[badhabit]

Looking good! Gone look super good once you will stack the base and column together! And that atc looks huge!

It's going to be awesome :-)

How long did you "cook" your castings? and at what temps?

[stef110]

I managed to reach 57 degrees in the end after 2 days of baking.

[badhabit]

I managed to reach 57 degrees in the end after 2 days of baking.

Nice! With the results you have gotten on your machine i feel very confident. I'll turn it of tomorrow morning, then it have had a solid 24h @70c... Then the forms will (hopefully) come of during the weekend!

[badhabit]

I took the castings out of the mould this weekend after they cooled down. They ended up being in the "oven" at 70c(air temp) for 24 hours before i turned it of.

The form came apart very easy and i would defently recommend this phenolic plywood to anyone else trying to cast something. It releases with absolutely no effort, in some places i didn't even needed tools for prying it of, just unscrew the bolts and remove the wood! I started of with taped edges, but the tape released from the mould in some places, so i removed a lot of the tape and just waxed the endgrain of the plywood where it was exposed. It also worked flawlessly. So in summary: Use phenolic plywood, don't wax anything except for the exposed endgrains if any.
Attachment 468312Attachment 468314Attachment 468316
... i've incorporated strategic placed M16 inserts on most sides, designed for lifting the parts, this was very handy and i would defently recommend this. The bottom part was right at the limit of the crane in the shop which maxes out at 1000kg, it struggled with that one. But the top-part was no problem and my CAD also tells me that it should weigh somewhere around 750kg.

Since i absolutely despise "instragram reality" i want to show some of the stuff that didn't go aswell as i hoped. I learned from these issues and maybe others will account for these things, if they want to build something similar...

First issue: Epoxy granite at 12% epoxy does not vibrate particular well, so it is really hard to get air out. We had a rather large concrete vibrator, we had previously tested it with great success on regular concrete. While it does wonders in regular concrete, it does almost nothing in EG :-/ So we couldn't get (all) the air out. This has given som surface inperfections, mostly pin-holes, but also a few holes a bit larger.
Attachment 468318Attachment 468320Attachment 468322
When these holes are at the surface, then there will also be lot inside the structure. While this is not desireable, i don't consider it a problem for this build since it is way overbuilt to get more mass. If i was to make smaller cross sections where strength and stiffness needed to be maxed out, then other meassures have to be taken....
Here is a piece of some of the left-over from the last batch, so this hasn't been vibrated at all, but there is loads of air:
Attachment 468324
Summary: I'm starting to think that vacum degassing is a must to get perfection. Either by putting the entire in a large vacuum chamber or by degassing every batch of mixed EG right before it's put into the mould. Or both. I skipped this because pulling vacuum on a large container 40-50 times wasn't practical for me. If i should do it again or do it more than once, i'd put more effort into this and try to find a way.

(continues in next post, to many images for one ;-) )

[badhabit]

...continued...

Second issue: The concrete vibrated "scared" the surface of the phenolic plywood. The end of the concrete vibrated touch the sides/buttom of the mould during vibrating, we should have avoid this because the voilent rubbing of granite against the wood made it possible for the epoxy to stick:
Attachment 468328Attachment 468330Attachment 468332
It is only a cosmetic thing, but nonetheless something i'd like to have avoided. I'll just grind it off...
Summary: Carefull with the vibrations! Don't touch the sides of the mould. Or better yet: degas using vacuum and avoid the vibrations all together.

Third issue: I had a few places where i needed horisontal faces. I thought this would be ok and we took great care to make sure that they where filled properly. However, the degassing kinda ruined it anyways. Here is the back of the column where the air-cylinder will sit and a "drip-lip" for coolant:
Attachment 468334Attachment 468336
Summary: Air and excess epoxy will collect on horisontal surfaces during degassing. This both ruins the finish, but also makes the edge very brittle because it has no real filler material, just epoxy

Fourth issue: Don't bother with the tape. It just ends up getting stuck to the casting and not the mould. However, take the time to apply silicone to radius inside corners in your mould. I only did a couple because it was very difficult(the assembly order of things made the corners hard to reach). So make the form and the assembly of the form such that putting on the radius is easy.
Attachment 468338Attachment 468340
Summary: Ship taping, use wax on endgrains. Allow for silicone on internal corners in the mould, both in design and assembly.

All-in-all i'm VERY pleased with how it turned out. This will, despite the minor mishaps above, work very well, can't wait to get it machined and start the assembly :-)

[badhabit]

...continued...
Attachment 468332

Oh yeah, almost forgot one issue:
In the design of the mould, it's a good idea the split flat surfaces into multiple parts. The picture above shows some of the parts that gets "wedge" into the casting. If this part was split into 3 pieces then it would have been much easier to take it out. It isn't because it's sticking to the epoxy, it just rubs against the insert and the casting.

[badhabit]

Another thing i found too: I knew that i had to be carefull when tightening the bolts holding the inserts into the form. Even though they are only "finger tight", they still protrude from the casting. It is not the end of the world, but it can/will cause issues when i need to tighten something down to the surface...
Here is a picture where one of the smaller inserts is seen from the side:
Attachment 468344

[peteeng]

Hi Thomas - well done. I think vacuum degassing will be too difficult with a mix like this. I have been involved in degassing epoxy, silicon resins and teflon oil for over 10 years and even these are very difficult to degas in small quantities. The aggregate makes degas very difficult plus there's the water content to deal with. I advise with the type of epoxy you used and others that vibration is a two edged sword. laminating epoxies have thixotropic additives that make the resin thicker when sheared or vibrated not thinner as happens with concrete. The porosity will not change your machining result. Good casting & reporting Thanks for your efforts...Peter

look up newtonian and non newtonian liquids. The thiotrophs are used so the resin does not flow downhill in laminates.... re inserts - the commercial EG casters put a plastic washer under the insert so it produces a small counterbore at the thread.... is there another machine in you Thomas?

[badhabit]

I think vacuum degassing will be too difficult with a mix like this. I have been involved in degassing epoxy, silicon resins and teflon oil for over 10 years and even these are very difficult to degas in small quantities. The aggregate makes degas very difficult plus there's the water content to deal with. I advise with the type of epoxy you used and others that vibration is a two edged sword. laminating epoxies have thixotropic additives that make the resin thicker when sheared or vibrated not thinner as happens with concrete. The porosity will not change your machining result.

yeah, well, i've also degassed quite a lot of different epoxies, but with great success. Will it be easy? no :-) But can it be done? Maybe... there was quite a lot of bubbling on the surface when the EG "just sat there", so my reasoning is that pulling a vacuum on each batch might help remove some of it.... but then again, other than surface finish, does it have an impact on the performance of the finished machine? doubtfull....

re inserts - the commercial EG casters put a plastic washer under the insert so it produces a small counterbore at the thread....

Ah, yes, that would have been a better solution....noted till next time ;-)

is there another machine in you Thomas?

Defently! But it will most likely be something else....diamond lathe or something like that could be fun.....

[peteeng]

Hi Thomas - There are three types of "gas" in a mixture like this. 1) entrailed air from the mixing process, this is the bubbling you saw. These are quite big bubbles of air that due to bouyancy come to the surface 2) Sub critical size bubbles - these bubbles are created via resin mixing and during manufacturing mixing. These are the usual bubbles that are removed in the degas process. These will not rise to the surface due to having not enough bouyancy and the hydrostatic pressure keeps them subcritical (subcritical means that their size is below the volume that is needed to over come viscosity by bouyancy) . Degassing using vacuum reduces the surface pressure and if the bubble gets to the surface it can release if the surface tension allows it. Using surface tension modifiers helps but not alot as these depend on the air/resin interface to work. Once you have vacuum at the surface this dynamic changes and the release slows down. The subcriitcal bubbles need to be moved to the surface to release. This is achieved using flat plate flow, or stream drop methods or bottom up stirring. In the aggregate there is another evil - water. Under the pressures required for degassing this water turns to steam 1ml of water turns into 10,000ml of steam. So the aggregate has to be heat dried or vacuum dried prior to introduction to the resin. Then there is the saturated gases to deal with.... Its complex and going forward here are some suggestions:

1) I have found that degassing the resin from the entrained air can be achieved by heating it to 40-50degs which lowers the viscosity enough for bouyancy to win. Then let it cool down to the ambient temp. Do not concern yourself with the hardener, its viscosity is very low and it does not contain much entrained air. 2) dry the aggregate, vacuum soak is best 3) mix resin very slowly prefer mixing in vacuum look up vacuum mixing systems to copy. 4) Design moulds so there are no horizontal surfaces, precoat mould with resin so it is already wet when you introduce the mix. Don't vibrate. Do the best you can with what you have, don't worry about degassing... Do a dry fill approach with preheated resin with or without vacuum . This sidesteps many of the entrained air issues and mentioned issues here. In the end have fun and get that machine making swarf Peter

[StrawberryBoi]

An absolute wealth of information, this build! Also thank you for the detailed additional info peter, that is also useful. I worked briefly (for about 18 months) with epoxy encapsulation of motor windings and air is an absolute monster. Air bubbles in a winding encapsulation or varnish act like a catalyst for arcing, rather than an inhibitor as the epoxy is intended to do.

We tried the process, in batches no more than 1qt of pre-mix resin, of degassing the higher viscosity resin at an elevated temperature. This was an excellent solution, particularly since the bubbles introduced during mixing were quickly removed from these small batches by a secondary light vacuum post-mix.


The best solution we developed was to:

1) Vacuum evacuate the hot resin (pre-mix) (let cool before mixing)
2) Vacuum a heated molding tool
3) Very slowly mix in hardener with the mixer always submerged, no cavitation.
4) Brief (<30s) vacuum pull on the post-mix.
5) Inject the epoxy at a controlled rate to avoid cavitation and capturing 'void bubbles' as the hot tool initiates curing.

No, these were not fast cure epoxies, but the curing starts on the heated edges and we could form vacuum bubbles with a thin film that sucked in air when you popped them. Cool, but still sending things to the trash can.

Unfortunately I'm almost 100% that the tool vacuum and injection solution will not be even remotely applicable for such a thick section. You'd be injecting in multi-inch diameter pipes and... yeah. I'm eager to eventually get to my own EG build and I am sure I'll be doing it differently, but I haven't fully arrived at what that will look like. Keep building man!

Oh, word of caution, the hardener quite often likes to boil under too much vacuum, do an experiment in a small chamber first to see if it, or even the resin, will boil under sufficient vacuum. Avoid drawing down to that low. If the epoxy is used for critical applications in molds, they will typically be able to provide a recommended vacuum value for degassing upon request.

[ardenum]

I'd be careful about distributing pornography on this forum. I'm sweating profusely while writing this...

[pippin88]

Looking great.

A bit of porosity doesn't matter for what you are building.

If you were trying to make smallest sections possible then a small reduction in stiffness / modulus might matter.

The tiny reduction in stiffness won't affect your big sections.
Remember that material in the middle does like to contribute to stiffness anyway.

IMO much easier, faster and better to make epoxy granite bases slightly thicker, than spend forever and lots of $$$ trying to avoid any air entrapment.

[badhabit]

A bit of porosity doesn't matter for what you are building.

If you were trying to make smallest sections possible then a small reduction in stiffness / modulus might matter.

The tiny reduction in stiffness won't affect your big sections.
Remember that material in the middle does like to contribute to stiffness anyway.

IMO much easier, faster and better to make epoxy granite bases slightly thicker, than spend forever and lots of $$$ trying to avoid any air entrapment.

I agree. However, i was surprised by the amount of air, so at least it will give others a "heads up" or the possibility for them to investigate possible methods of getting the air out(other then a concrete vibrating rod)...

The only "downside" to the air trapped in my elements are purely cosmetic, but i learned something, so i'd call that a success :-D