[dfro]

daviddecker and svenakela,

Thanks for the comments. It was a fun casting project and I have learned a lot from Stephen Chastain's books. The cavity inside the steel ring, where the ball spins, was made by cooking up a sand/flour/molasses/water core in the oven. It smelled very good, like cookies on the beach.

With a 4 hp, 18 gallon Craftsman air compressor at probably 80-100 psi, it would go for a couple of minutes and then I would have to turn it off, while the tank refilled. So, to make this work, you would have to have a pretty big air compressor. They don't cost that much, though, and every shop should have one, IMHO. I did just give the Craftsman away, because it was WAY TOO LOUD!! Car without a muffler loud!

Here are some cads of how I might cast them in e/g. It can be scaled to any size you want. I am thinking of trying a 1.250" steel ball. McMaster-Carr sells them for $9.89 for a pack of 10. David, I don't think e/g damping is going to be a significant problem with a big steel ball spinning around rapidly in wide circles.

Here are all the steel parts that I would cut, drill and epoxy together before casting the e/g.



The sides are where the e/g would go.



All ready to be bolted onto a mold to vibrate it. The middle rod is a threaded rod that bolts the bottom plate to the housing. Two bolts go through the bottom plate to bolt it to a mold.



I think this might be my first e/g creation. Casting aluminum is fun, but it is a major production, and dangerous. E/g would be much simpler to do.

Thanks,
Dave

[jhudler]

Anyone looked at Titanium Diboride?

http://www.ceradyne.com/materials/ti...-diboride.aspx

http://www.ceradyne.com/uploads/Tita...et_10-03_1.pdf

[dfro]

Here are my latest sketches of the e/g mill table I plan to make. I think the side walls will greatly increase the stiffness of the table and also improve the stability of the gantry. I changed the reenforcement compared to my previous version and took out one layer of 1" square steel tube in the table. Instead, I am now going to put rebar through the 1" steel tubes, to reenforce it. Solid steel bars will be directly under the leveling epoxy for attaching guide rails and for attaching work pieces to the table.

The guide rail is floating where the leveling epoxy will be poured. I am thinking that I can pour the table and the raised guide rail surfaces at the same time, thus ensuring all three surfaces are aligned at once.





I did not bother to draw some of the nuts, bolts, and brackets that will attach the vertical 1" steel tubes.





Please, share your thoughts.

Thanks,

Dave

[jhudler]

dfro,
I really think you should lose the skeleton and just embed steel members you’re going to use for mounting the rails in the mold. You’re not really gaining anything, and it could in fact wreck all of your hard work when the differing material CTE’s start fighting one another.

You’re also going to lose a considerable amount of vibration damping from the E/G because everything is connected via the sound wave guides in the form of a steel skeleton.

Simply put: You should never have a system that is tightly coupled to a mass of varying density. (standing waves, parasitic oscillations, multimass resonance, ...; AKA nasty stuff!)

Jack

[jhudler]

dfro,
My apology, I should have added this.

I do not wish to dissuade your from your efforts at all!

Your efforts no matter what is designed will expand what we know about E/G and for that I am grateful!

Jack

[jhudler]

Walter,

Do you have a sample of what you cast that can be use for CTE testing?

Something like 1"x2"x12" or 25x50x300mm

Jack

[walter]

I'll make the samples and send them out
on Monday. Will you be able to test damping properties?

[jhudler]

Have to read up on using a laser interferometer to test damping.
It will come down to how fast it can sample, probably easier to hook an acoustic pickup or accelerometer to a sound card.

[dfro]

I do not wish to dissuade your from your efforts at all!

Jack,

No worries. Thanks for the comments. I am hoping to get lots of comments on my design so I can be saved from some costly and time consuming blunders.

My thinking is that I should add the steel tube and rebar to improve the tensile strength of the structure. I think I sould do away with the square tubes and replace them with solid 1" x 1/2" steel bars that have the rebar going through them. But maybe, as you suggest, I should do away with all of the steel reenforcement. The two side walls, will definitely add to the strength of the table. Maybe, that is all the reenforcement that is necessary.

Thanks,
Dave

[jhudler]

dfro,

I don't believe tensile strength is going to be an issue.

If you really want to hold a high precision way bed; purchase some low carbon flat stock, drill/tap mounting holes, hardened and precision ground on one side (rough up the other sides to allow the epoxy to adhere). Your forces are going to be up, down (Z Axis) and some lateral (Y axis) from gantry splay and machining.

You need only make a mold/jig that’s capable of holding the way beds in alignment during the casting process. Once done you can disassemble the mold/jig to reclaim the parts, or keep it in case you need to make another.

This method is exactly how the big boys do it. I wonder if they worry about screwing it up and having all their work incased in rock (I know I do!).

Jack

[yugami]

dfro,

You need only make a mold/jig that’s capable of holding the way beds in alignment during the casting process. Once done you can disassemble the mold/jig to reclaim the parts, or keep it in case you need to make another.

I don't think this is as hard as it sounds on the outset.

Take a long nut (like a threaded rod coupler) and plug up one end. Then have a series of holes in your jig which line up with your mounting holes.

Take the flat side and lay it down and feed machine screws into the mounting holes through the jig. This holds the mounting plate/strip flat to the jig. Use a precision level and loosen/tighten everything into place so that you don't distort your nice precision plate.

The main thing would to be find something to keep the epoxy from running under during vibration. Perhaps something as simple as a light oil on the plate would work as a gasket?

[lgalla]

Dave I agree with Jack.Too much steel.Hollow tubes will resonate.A frame or tubes filled with E/G will not resonate.To be safe,a self supporting steel frame,that is one that can carry the forces or load and damped with E/G is cool.The steel outer frame will also protect the E/G from damage.Also the E/G aggregate mix is more forgiving as the E/G does not support the load only damp.
I chose the I beam as one side is locked by the E/G and the other side is not a hollow and provides a convenient surface for rail mounting.A ballscrew would fit nice in the channel and be semi protected from swarf or dust
Larry

[jhudler]

yugami,
The casting takes place upside down, so you're mounting to what should be a fairly flat surface. Mold release agent can be applied to the top of the way beds along with the mold itself. Dave isn't (IMO) casting any precision surfaces on this, so should suffice.

Even if the way beds turn out to +-.01, all it not lost, there's still shimming.

Jack

[jhudler]

Larry,

I guess we differ on one point, I consider E/G to be load supporting. Dave’s base is I believe pretty much all compression and what tension exists will be well within limits.

Go to www.pat2pdf.org and lookup 5,765,818; Figure 10 (page 11) shows an excellent example of how to maintain rigidity and damping. Good ideas on anchoring attachments. Also take note of the use of PVC tubing (67,65) to provide access holes and the issues with vibration coupling.

Jack

[jhudler]

Larry,
Sorry, I re-read what you wrote; I don't think we differ (philosophically) on this, you were describing an engineering construct.

That's what I get for posting late at night!

Jack

[ckelloug]

Hi all,

It looks like a lot is getting done. I'm in Menlo Park CA until Monday but I've emptied my PM box.

John, I will mail your data package when I get back. Sorry

Regards all,

Cameron

P.S.

I imagine that bouncing a laser off a piece of gold leaf rubbed onto the piece of E/G into a laser diode with the piece suspended by threads and struck with a xylophone mallet would be the ideal way to measure the vibration properties. If done right, one can also extract tensile and shear moduli!

Interesting on titanum diboride but I'd suspect it's much expensive.

[brunog]

I've had everything in plastic cups and did not premix the aggregate. Initial batch was done by volume then carefully weighted. I used that to prepare 120 cups of material, resin and hardener. Aggregates went one by one into the mixer, starting with the largest -which is probably the wrong way around..
20% epoxy is by volume but I tried to lower that number.

And, I'm very interested in seeing your results with vacuum bagging.

Cheers!

Walter,
20% by volume Epoxy is 10% by weight! That' s a very good ratio

Best regards

Bruno

[greybeard]

It's always a pain to admit failure :tired: but it's the only way.

(For new readers, I'm afraid you'll have to refer back to earlier posts of mine for the relevance of this piece of kit to the current thread.)

The particle separator works in principle, but I can see that I could spend the next 12 months getting it right.
As the attached photos may show, the 6ft long beast did give some separation into sizes from 600 microns down to 100 microns, as measured, but there was so much overlap in the size scattering that no useful data might be inferred from what I could see.
It would need a much slower feed mechanism to avoid particles interfering with each other as they fell through the air stream. Also a much better collection method to keep them apart when they reached the base.
Whether it's turbulence in the air stream that's causing it I'm not sure, but I was surprised at the amount of sideways drift from the central input line.
It might also be due to the irregular shape of the sand particles, or just the fact that it is Saturday.
Too many imponderables to make it worth pursuing, I think.
I shall resort to finding a collection of screen materials 3mm to 200 microns, and assume anything that gets through that is part of the 150 -200 micron range. Then make up de Larrard's recipe with known finer particles, zeeospheres etc.

John

[walter]

That actually is a pretty cool idea ↑
With this device anyone can create professional E/G mix simply by using what they can find by the river. Thanks for posting your stuff John, I learn something new every day.

[walter]

I'm doing some assembly work- more pictures to follow later.
_