[USMCPOP]

Well, I just thought I'd throw a monkey-wrench into the works in terms of cheap fillers and so forth. It could well be that some of these fillers have sufficient strength and are not so specifically graded as to size that they sort of work out overall. Just a thought.

[ckelloug]

usmcpop,

Take a look at the thread index thread on the main page. Lot's of fillers have sufficient strength but it is difficult to form a mixture that has a high percentage of filler without at least reasonable control of the size distribution. We've got research going back 30 years from the scientific literature dredged up from the library.

There's some pretty heavy research that has gone on over the course of a year on this thread: it's not about one or two of us throwing together a machine here, we're working on the general problem of developing the optimal mixture that overcomes some of the problems that E/G has had over the years.

A basic machine can be thrown together with some of the material we've already published here but we're still a ways from dotting the i's and crossing the t's on the provably optimal material. It's a time consuming process. . .

Regards all,

Cameron

[USMCPOP]

Cameron, I wasn't second-guessing, just asking a rather dumb question. I just thought that some inexpensive materials might be accidentally sized according to the needs here. Material science being what it is, you never know, eh? A particular form of Unobtanium alloy will no doubt do the trick, but I haven't yet come up with the mix. Life is grand, no?

[harryn]

One of the reasons that so much time gets spent on the mix aspect, is that epoxy is not cheap. Quality epoxy runs something near $ 50 / gallon, so approx $ 5 - 10 / lb. This starts to add up when you are making a 500 - 1000 lb object.

Cameron is correct that optimization is still ongoing, but if you look at posts from user Walter, he has been quite successful casting some parts that are quite strong and quite good looking. These are probably in the 80 - 85% of near optimum mix that we will ever achieve at home. There is room to go yet, but some of it is hard to mathematically model.

You are right that mixes similar to concrete are not terrible, but might only provide 50 % of the properties that we know how to do now, and would cost perhaps 2X as much.

[Zumba]

Well, I just thought I'd throw a monkey-wrench into the works in terms of cheap fillers and so forth. It could well be that some of these fillers have sufficient strength and are not so specifically graded as to size that they sort of work out overall. Just a thought.

Those fillers may be perfectly suitable in the composite's final state (a cured block), but getting there is the hard part.

Sand by itself is a real PITA to mix with Epoxy. When you get to the very high aggregate densities, it seems nearly impossible. I believe Larry (aka Igalla aka Confucius) was the first to mention 3M zeeospheres, which are ceramic balls used to lower the viscosity of industrial coatings (spraying fiberglass?).

I believe these Zeeospheres make the composite easier to mix and pour. I haven't used any yet, but several other folks have. They also happen to fit in with the aggregate size grading and give the composite a sexy black/grey look, as opposed to beach sand and pumice which would probably look like dried up dog doody. :rainfro:

[lgalla]

Zumba,
Confucius Say:Man with Zeeospheres got balls!
Adam Ant;.....:Zeospheres make Rock Roll!
Zeeospheres are harder than rock.Mohs scale 8 same as hardened steel.I was spraying polyester with ground up marble which is relatively soft,but my pump cylinders only lasted 6 months at $600 a pop.A small% of 850's lowered the spray pressure from 1500psi to 800psi.I was worried the hardness would eat the pump cylinders but I ran the same cylinder for years.Amazing what micro ballbearings can do.
Vibrating the E/G mix can sandpaper away the release agents on the mold.Perhaps the Zees can help.Cameron,what packing ratio can one get using mainly Zeospheres?If you used a maximum of Zeeospheres the strength may be high as they do not have micro cracks as aggregates may have.
Larry SAy:Wish I sales rep for 3M!
Zumba,your photo request received.Can not do it until alone in the shop.Would look suspicious taking close up pics of the machine.
Larry

[jhudler]

Does anyone know any price for moglice? I really want to try to make my own hydrostatic bearings. Besides does anyone know of the minimum amount of space required for moglice to fit, i hope you understand what i mean.

Well... I guess that would depend on how much hydraulic force you can exert and the point at which moglice detonates from dieseling.

Are you creating fixed opposable air bearings?

Jack

[ckelloug]

Larry,

Since zeeospheres are mostly spherical and have a fairly tight size specification, the theoretical answer is somewhere near 68% which is the same for any spherical particle. The small size non-uniformity would in theory raise the density some while the non-ideality of actual mixtures would lower it some. It's impossible to get extraordinarily high densities without multiple sizes.

Most of the concrete mixes, especially fuller's ratio based ones are extraordinarily prone to segregation. I've got a simulator which should give a rough idea of the performance of a given mixture but Jack and I haven't completed version 2 which can actually derive the optimum curve for the materials at hand.

If only there were 27 hours in a day.

Regards all,
Cameron

P.S.

USMCPOP, cheap materials of the right size are good! I think I have actually located a source of very cheap aluminum oxide aggregate which is white, 4 times as strong as quartz and can be purchased graded but I've held off until I have the model working optimally as buying graded material to the wrong curve isn't very appetizing.

[jhudler]

OK here is a photo of a 50 micron patch of 100% - 200 3M Zeeospheres in US-Composite 635 (from the puck).

Makes you want to rethink Gupta and his 31 microns.

Jack

Note: Each pixel is .0666 microns or 66.6 nanometers (hence the prism effect).
The light source is very oblique; like the sun setting on a mountian range.

[jhudler]

Order of magnitude higher and we'd start reading spectral lines.

[ckelloug]

I never did trust gupta and his 31 microns. His paper always smelled like it overlooked something: accurate measurement of surface area among other things. The Gamsky model as used by Gupta also has the disadvantage of not being prescriptive for optimization purposes.

At the rate we're going, we should be able to write a journal article.

[Dan S]

I just finished reading this entire thread.

Would filling steel tubing with epoxy and lead shot produce a rigid machine that doesn’t ring?

I wat thinking something like 2”x6”x1/4” tube would create really stiff uprights etc, and then filling them with epoxy and small lead show would serve to dampen any vibrations.

Opinions?

[greybeard]

I just finished reading this entire thread.

Would filling steel tubing with epoxy and lead shot produce a rigid machine that doesn’t ring?

I wat thinking something like 2”x6”x1/4” tube would create really stiff uprights etc, and then filling them with epoxy and small lead show would serve to dampen any vibrations.

Opinions?

Welcome and well done Dan. If only everyone would follow your example.

I'm not certain, but I would suspect that any mix of sand/gravel/epoxy would give you a better absorber. Though the lead shot has a higher density, and the greater difference in density between the epoxy and the lead is good, you will only get a ~62% maximum packing if you use only one size of shot.

The variable size of the ag mix will both broaden the frequency spectrum absorbed and the much higher packing with the right mix will increase the absorption by virtue of increasing the number of internal reflections/refractions that occur each time the sound waves pass from one medium(the epoxy) into another(the aggregate).
Regards
John

[lgalla]

Please let me know what you find out. I'm interested in using moglice as part of a DIY low friction, low backlash leadscrew. The idea is to take a plain old acme screw, lap it against a brass nut until it is uniform and then make a nut lined in moglice.

The moglice site claims that it is usual to have clearances of .0002 inches on an accurate screw and that this can be polished to .00005. So, if we could lap a screw to be consistent to 50 millionths, we could build one with a backlash of a tenth (twice 50 millionths).

That's not bad for DIY.

Ken

Ken, I would not use a plain old acme screw,Use precision .007/ft.Lapping with a brass nut will not do anything other than widen the gap.
Moglice clearances of.0002 refer to the thickness of the release agent.Pollishing the release agent can acheive .00005.You are in ground ballscrew territory CO orC3 atleast.
Lapping is done with the cast nut and abrasive.Because the nut is an exact replica of the threads where cast and it will be very tight.Lapping lowers the accuracy but must be done to prevent binding.
Is it worth doing?I think so.I will try it myself.Search Google "moglice nuts"lots of info.
Moglice is $50 for 100gm plus shipping.Enough for 2 nuts.Search for Practical Machinist.
Larry

[Dan S]

has anyone tried acrylic water?

http://www.kinkadestudios.com/Mercha...gory_Code=ACRL

I'm not sure of it's mechanical properties (shrinkage etc), but you can get it locally, and its some kind of epoxy.

[jhudler]

Acrylic Water would be in the category of paints, it's an emulsion that dries.
It does not cure with a hardener like epoxy (almost no shrinkage), or catalyze like Polyester (a little to a lot).

[jhudler]

Larry,
Did you find a source online for Moglice?

Jack

[lerman]

Ken, I would not use a plain old acme screw,Use precision .007/ft.Lapping with a brass nut will not do anything other than widen the gap.
Moglice clearances of.0002 refer to the thickness of the release agent.Pollishing the release agent can acheive .00005.You are in ground ballscrew territory CO orC3 atleast.
Lapping is done with the cast nut and abrasive.Because the nut is an exact replica of the threads where cast and it will be very tight.Lapping lowers the accuracy but must be done to prevent binding.
Is it worth doing?I think so.I will try it myself.Search Google "moglice nuts"lots of info.
Moglice is $50 for 100gm plus shipping.Enough for 2 nuts.Search for Practical Machinist.
Larry

What I had in mind was first creating a special nut to use as a lap. Perhaps casting one around the screw using babbit or lead or plaster or plain old epoxy would work. The lap would be six or eight inches long. I would then load it up with abrasive and run the nut back and forth under axial load (in both directions). That would make the pitch (and the size of the valleys) uniform. It should be pretty simple to make a little machine to automatically run it back and forth. Repeat this with smaller abrasive sizes until the finish is suitable.

Then cast the moglice nut in place. One issue is that the lapping really only hits the faces of the threads. The moglice nut could be bored out slightly so that it doesn't touch the minor diameter of the screw. Something similar should be done on the OD of the screw -- perhaps building up release agent on it some how would work.

Ken

[jhudler]

Kenneth,

In order to lap a gear, screw, or telescope mirror, you must first start with something that is already of high surface quality. One of the lapping elements must be softer than the object being lapped.
You cannot take an acne.. err acme screw and lap it to perfection. The method you describe will make them both uniform to themselves, as to what that quality is... is anyones guess.

[lgalla]

Ken,I understand now.A long temporary nut for lapping would probably work to make the acme bar have greater accuracy.Skip the brass nut and use a steel nut which is much cheaper.After casting a Moglice nut It requires a monkey wrench and extreem force to release.Lapping is required.Some guys use Bon Ami and oil.You can acheive 80% efficiency or better nearing ballscrew efficiency.
Jack,You just order from Devitt Machinery. http://www.moglice.com/
I have not had contact with them for years but an e mail resulted in a call the next day eager to help.They offered kits years ago but I don't know if this is the case to-day.
If they call back,Jack,make sure you are sitting down and have the responce[I don't want to purchase the company,only buy a quart]It is very costly,but worth it sometimes.
Larry