[greybeard]

One of the criteria for fillers in any successful EG type mix is the range of sizes of the filler particles.
In order to get high packing densities, a fairly wide range of 'sizes' is needed, and though I have zero experience of machining cast iron, I'd suspect this might be a problem.

John

[Razvan Vladeanu]

Hi guys,
I've been following this thread for a long time and i would like to ask if someone know's if it would be a good idea to fill my Proxxon MF-70 cnc column and base with EG. I know it's a very small mill but for that price it's very good. The problem is that the column is made from an aluminum extrusion. Also the cast iron base is powder coated inside and i don't know if epoxy sticks to painted surfaces. Should I sandblast the inside first

[svenakela]

The epoxy will not stick to the powder coat. Epoxy bonds mechanically, the coat is too hard and glossy. Sand blasting or sanding with _very_ low grit is preferred.

[probinson]

Hi guys,
I've been following this thread for a long time and i would like to ask if someone know's if it would be a good idea to fill my Proxxon MF-70 cnc column and base with EG. I know it's a very small mill but for that price it's very good. The problem is that the column is made from an aluminum extrusion. Also the cast iron base is powder coated inside and i don't know if epoxy sticks to painted surfaces. Should I sandblast the inside first

Personally, I would recommend filling the column and not doing anything with the base (if it is well made, of course).

Taking the springiness out of the column will yield a noticeable improvement in surface finish of your cuts. If you have used the machine at all you will notice the difference right away.

The cast iron base, however, should already be about as rigid as it is going to get. You will have to use your own judgement on that. If the base is well constructed, with adequate support webbing, then you would expend considerable effort preparing the piece for no noticeable improvement. If, on the other hand, the base is a thin hollow shell then filling it with EG would be well worth the effort.

Powder coating can be many things (including things like acetyl and nylon that epoxy will never stick to). If you don't remove the coating, be sure to test the adhesion. Don't just assume roughing up the surface will be adequate.

Pete

[Razvan Vladeanu]

Thanks for the replies guys. I think the base is as good as it can be because i don't have much room in it maybe for 0.5 Kg of E.G. . The column definitely needs reinforcement because of its light weight ( aprox 1.5 KG anodized Al 7075 extrusion with 4 mm walls and thicker in the corners 10 mm ). I'm thinking of reproducing the composition of natural granite with between 8 to 12 % epoxy. Mainly it will be silicon dioxide (about 70% of the aggregate) and aluminum oxide in different sizes up to 5 mm. Please tell me what you think about this mixture. Also i have been thinking of the benefits of adding carbon nanotubes ( 5-10 mm strand length ) in E.G. for improved tensile strength in milling machine. A few moths ago i came across aluminum ballistic armor made by Kryron.
They make the armor plates by adding carbon nanotubes to melted aluminum. Could something like this work in a E.G. milling machine? To see what i'm talking about, this is a link to the demonstration and fabrication of aluminum armor. Kryron Ballistic Armor Bourque Industries - YouTube

[probinson]

Also i have been thinking of the benefits of adding carbon nanotubes ( 5-10 mm strand length ) in E.G. for improved tensile strength in milling machine.

It's always tempting to push the limits and try to create the greatest material the world has ever seen but try to focus on the task at hand. ( I am as guilty of this as anybody.)

The aluminum column is already stronger than you will ever need so you will reap no benefit from having a high tensile strength filler. Your goal is to mitigate the undesirable effects of aluminum's elastic nature. The compressive stability and vibration dampening characteristics of EG will do that. High tensile strength is great but, for this particular task, it's wasted effort.

If mentioning the nano-tubes was just an aside for general discussion then I apologize for not recognizing that as a separate topic, unrelated to modification of the existing machine.

Pete

[Razvan Vladeanu]

No need to apologize mister Pete. I understand that for my machine i don't have to worry about tensile strength. The carbon nanotubes part was for a machine made entirely of E.G. . Standard E.G. base and the column made from E.G. and Carbon for tensile strength. I know carbon fiber has a very good vibration absorption and high tensile strength. And could you please tell me your opinion on my mixture from the preavious post.

Thank you.

[probinson]

It would be very interesting to see some deflection test results. Carbon nano-tubes are immensely strong but I have no clue how elastic they are. My gut feeling is that, where EG is typically used, any benefits would be negligible. They might keep your machine from breaking if you dropped it off the forklift but wouldn't make any difference under normal conditions.

In a machine base you want massive pieces so that they are as rigid and vibration free as possible and your parts are overkill in terms of material strength. There is no benefit to using a super strong material when the standard materials are already 100 times stronger that required.

Now, if you are going for some lighter weight machine parts (things like spindle and gear housings) it might be a completely different story. It would be very interesting to see if nano-tube infused EG could compete favorably with other materials. It would be fantastic if you could get the stability of cast iron with the portability of aluminum. I certainly wouldn't mind it if my 16" rotary table was 50 Lbs lighter!

To sum it up, my opinion is that nono-tube infused EG is wasted effort in the standard EG application. It would, however, be very interesting to see how it performs for other uses. It might turn out to be a good compromise between cast iron and aluminum.

Pete

[Razvan Vladeanu]

I agree with you. For the big machines it's not worth it, but for mini high speed mills for cutting aluminum it might be a solution. For my next project i think i'm going to build a mini E.G. mill. Until then i'm going to do some test with normal E.G. versus glass fiber and carbon fiber reinforced E.G. , then compare the best one to cast iron. Have to talk to my theachers at the university to see if they will let me use the testing equipment. But for now i must finish tuning up my little mill to get it working at full capacity so i can start making some money for future projects. I will let you know when i begin testing the mixtures. Many thanks.

[the4thseal]

Where can one by nano tubes?

[johnohara]

Where can one by nano tubes?

Science Daily ran an interesting story about them a year ago: New method for continuous production of carbon nanotubes

Nice to know the price may drop to $15.00 per GRAM. Definitely helps the DIY cnc builder cut costs.

And to read the most recent posts, you'd think carbon nanotubes were available at the local hardware store.

I intend to use Graphene and be done with it.

~john

[JohnMcNamara]

Hi All

A little back of the envelope thinking......

Do micro or other materials improve the strength of epoxy composite structures, and if so what is the optimal physical size of the added objects?

Are the following statements true?

it is generally accepted that the weakest link in a chain determines the chains overall strength.

Epoxy composite materials are a mixture. The tensile strength of epoxy is a mere fraction of carbon nanotubes, graphene, gravel, steel or other materials we may add to the mix.

Adhesive bonds in general are strongest in an application if the force is applied in sheer at 90 degrees to bond line.
Bond two thin pieces end to end and it is relatively easy to break them apart.

The bond is significantly stronger if you glue the pieces side by side and try to break the bond applying a force to the ends,

If the above statements are true?

Would the use of longer strand high tensile material increase the tensile strength of the object?

Should the longer strand material be grain oriented as in say Carbon fibre fishing rods, or the incredibly strong "Bakelite" Penolic impregnated fabric sheets sometimes 25mm thick used by the electrical industry be used?

Can we conclude that the engineering design of the bond line between the epoxy and the matrix of included materials may significantly increase the strength. And that increasing the length of bond line length will significantly increase the strength, even if lower tensile materials are used?

Caveat.

Light weight reinforcement reduces the mass of the object created. That will change the vibration damping characteristics of the material. Will that change be an acceptable compromise to the overall design?

Cheers
John

[William7white]

it is generally accepted that the weakest link in a chain determines the chains overall strength.

[psykhon]

What about the idea of using a sheet of glass as the mold base to copy its flatness? Im not sure if I will find the rigth type of epoxy in here (Argentina) that will self level...

Sorry guys if this is already answered, i could not find much.

[svenakela]

What about the idea of using a sheet of glass as the mold base to copy its flatness? Im not sure if I will find the rigth type of epoxy in here (Argentina) that will self level...

Sorry guys if this is already answered, i could not find much.

I am doing that several times a week.

[castinite]

We have used glass as a casting surface to replicate the flatness. The issues are using vibration to consolidate the mix and the fact the you are using sand as a filler. The vibration can crack the glass and the sand in the mix will scratch the casting surface. Once scratched, it cannot be easily fixed. If you use granite as the surface, it can be vibrated and scratches can be fixed. The other issue with glass is the casting will stick to it. Because it is a very flat, nonporous surface, the casting will match the mold perfectly, like putting two gage blocks together.

I hope this helps.

[probinson]

If you are casting a rigid part in a rigid mold, unless it is a very simple shape, the mold usually destroyed to remove the part. One way to get around this is to cast a flexible shell first. You can do this with fiberglass but I love the look of carbon fiber.

Line the mold with epoxy soaked carbon fiber cloth and vacuum bag that first. Once that cures, being a thin flexible shell, you can free it from the mold fairly easily. Now you can do a dry assembly, add threaded inserts, mounting plates, whatever, and test everything while it is still possible to fix any problems. It is also a lot easier to place things like rail mounts on the shell, where you can bolt on the actual rails, than it is to place them inside the mold and trust that you measured everything correctly.

When you are satisfied that everything is correct, you put the shell back in the mold to cast the EG core. The shell contains the epoxy so there is no sticking to the mold and no scratches from vibrating grit.

Pete

[svenakela]

Aren't you reading my answer two posts up? We're using glass surfaces for molding several times a week.
With a decent release wax it will never stick. Scratches? Maybe, but not on my glass sheets.

[probinson]

Aren't you reading my answer two posts up? We're using glass surfaces for molding several times a week.
With a decent release wax it will never stick. Scratches? Maybe, but not on my glass sheets.

I am reading your post but it seems you are not...

The other issue with glass is the casting will stick to it.

That small typo aside, the only relevant reference to your post was the issue of the aggregate scratching the mold.

Making a complex mold out of glass or powdersoating some surfaces isn't really that practical and my post is about not only casting complex parts but also the benefits of having a positive shell to position all your mounting surfaces and inserts before casting the EG.

Sorry that comes across as a snide remark. Insulting you is not my intention. I was just offering a method of making parts that gives a lot of opportunity to test fit and modify before thing become set in stone, so to speak.

Pete

[Talgat]

Aren't you reading my answer two posts up? We're using glass surfaces for molding several times a week.
With a decent release wax it will never stick. Scratches? Maybe, but not on my glass sheets.

Can you share with your technique?