[walter]

Mine's broke. But it's been here since April http://www.cnczone.com/forums/attach...3&d=1176697432
(Epoxy/Zeeospheres G850).

Will you teach me how to lap the surface?

[harryn]

Walter,
If all you are mounting is linear rails, you can make an equivilent from Zeeospheres. 70% Zeeospheres and 30% epoxy is about the right mixture.

Zeeosheres crush at 60ksi, it would appear to be an outstanding grout or putty for this application.
Plus it can handle a grinder. I made a 4 inch round by 1/2 inch thick, and lapped it to +-5 microns.

Interestingly, there are some theories that suggest that crush strength is not what we should be looking for in the aggregate - but perhaps more likely something related to tensile strength. Some refer to various crack resistance parameters.

The fact that we have these enormous crush / compressive strengths, but the parts are still breaking in the aggregate, is consistent with the idea that the aggregate is actually seeing a sheer or tensile strain when it breaks, not compressive force. If those theories are correct, then the metailic fillers should be quite interesting.

[lgalla]

Walter your picture reminded me of E-bay listing #320203796630
The blocks are sr-20 rails 460mm long.One rail and one block is$25.00
The guy only has 250 of them.Remember SR's are for horizontal use.
Larry

[walter]

"rails!" MINE! MINE! MINE!

[the4thseal]

i did not know that those rails were so sensative to orientation, or do you mean just sub optimal? horizontal in what way?

[lgalla]

THK SR series are best for horizontal loads due to the 90 degree ball contact.Used vertically,the load rating is about 50%.The HSR series has 45degree contact angle and the load rating is the same horizontal or vertical.
The Sr's are usable vertically if they are within your desired load.
Larry

[the4thseal]

that makes sense thank you.

[thomasz]

Hello John!

Hi Thomas. Thank you for posting the Excelsheet.
I see there are two possible values for grading curve index, 4 for compact and 5 for Fuller curve.
Could you explain the "compact " curve, that is how it differs from Fuller ?

These are in principle only two different curves and 0.4 is suitably for our work.

Bye Thomas

[thomasz]

Hello again!

Here some pictures with a few tips are to mineral casting and form construction. I think you know most.

[thomasz]

... and again









Bye
Thomas

[walter]

Thanks for all the useful info, Thomas. Really looking forward to your new machine.

Cheers!

[greybeard]

I just know this post might go wrong, but in order to compact small sections in a mold that I'd rather not vibrate, I've been thinking about small vibrators.

I need to get 30mm down a 10mm gap, and I looked at my electric toothbrush as a possible starting point. Admittedly it's got an oscillating rotary action, but I wondered if this might be effective on this scale.
Can someone tell me if the "concrete poker" that is used for large concrete compaction vibrates only back and forth like a hammer drill ?

Any other (postable) suggestions ? I've got quite a number of small motors, but no facility for making small engineered parts, so the mechanism would have to be salvaged, or off-the-shelf parts.

John

[harryn]

ThomasZ - have you by chance attempted to make any T slot tables or similar with these materials ? I was curious if a sufficiently thick T top would work, potentially with some embedded parts.

[jhudler]

Will you teach me how to lap the surface?

Lapping is something a kin to herding cats.

It can be as easy as using 400 to 6000 grit sand paper on a surface plate,
or impregnating diamond grit on lapping plate. Any of which could cost you your sanity . That's why I chose a 4 inch diameter object, small easy to do and do over. I calibrated my 18x24 surface plate to 2 microns, that took me weeks of fiddling with this zone and that to get it there. Not something I want to do again. I'm obviously not a professional at lapping and probably did it ass backwards.

It's a combination of skill and tools. Some of them extraordinarily expensive for a hobbyist (like a laser interferometer or and autocollimator).
You will need at least an A grade surface to lap anything half the size of the plate into the single digit micron range. If you're going into the nanometer range its time to buy optical flats, cerium oxide...
Have you ever make a telescope mirror? From personal experience it seems to be easier to make a spherical surface than a flat one. Which is why I guess its so easy to screw up a flat.

Jack

[jhudler]

I need to get 30mm down a 10mm gap

Ouch! Sure you can't redesign that? Perhaps this is where you use Zeeospheres 800 and mix up a batch that's very thin and warm, then inject it into the bottom of the 10 mm gap with a suitably sized syringe.
Or fill a plastic bag with it and cut a small bit of the corner off to make a piping bag.
Or drizzle it in a very fine stream that would break up the bubbles. BYK-A-525 de-airing agent is a must here.

[walter]

Still no picture...

:-)

[jhudler]

Never got around to lapping it today. Looks like a sick hockey puck.

I did pull out the optical comparator and confirm it was really sick!

[jhudler]

Hey who's going to do the ballistics testing!
I wanna see how a 12x12x4 inch slab stands up to a 30 caliber round.
Then an armor piercing round if it survives the first one.
Might be a whole new market here!

[walter]

I need to get 30mm down a 10mm gap

Ouch!

I wouldn't worry about that. I got 4" down a 0.75" gap. See the spot under the servo drive- the whole thing is only 0.75" thick



20% epoxy plus BYK A525 and some good vibrations.
_

[vishnu]

Thats a good job. Like to see some videos. You guys here have done a good contribution. I think its time to have a wiki so toddlers like me could start learning without much pain. Have you tested your machine how is the results.