[Zumba]

Very nice work, Jack. No de-airing agent?

Where did you get your Zeospheres? Same place as Walter? How much did you guys pay?

[jhudler]

Walter purchased his at Cary Co. Mine was from Ribelin Supply in Garland, TX.
The 800/850 run about $25-$30 a 50 lbs bag, the 200 from $35-$50 bag.
If they quote you a ridiculous price per bag or pound, then don't hesitate to call them on it. They might send you to another sales department or salesperson, but you will get the lower price. If not move on to the next distributer or call 3M.

Oh, you do! want to pick this up.

Jack

[ckelloug]

Jack,

Your video of lapping the E/G block and wringing it to a gage block is remarkable. Do you have a story on the process behind creating the E/G block? How level did the E/G get on it's own and how much lapping was required to get the surface into that state?

Regards all,
Cameron

[jhudler]

About a little over an hour.
I had originally cast it upon a black granite surface plate, but the release agent was visible in the cured flat. I used a release agent because I didn't want to trust micro-crystalline wax on its own.
So I ended up reverting to using sandpaper for the first few steps.
Something this small is easy to do with sandpaper up to 800 grit.
I then switched to diamond paste on flat glass down to 1 micron.

That was before... I never really mentioned it online because it was such a small thing.

I then used it as a coaster on my desk.

When Walter wanted to see pictures I re-poured a new 1/4 inch top and just used sand paper from 150 - 1500.

Something larger than this would require flat glass on a surface plate, or some serious time on surface grinder, or laser interferometer with the optics to calibrate a surface plate, or an autocollimator. Latter two requiring some serious patience.

Where is it now? Locked to my surface plate... need to get the air hose on it and pop it off! Make an excellent vacuum preloaded air bearing mount for a indicator on a surface plate .

Jack

[Gizmot]

Where is it now? Locked to my surface plate... need to get the air hose on it and pop it off! Make an excellent vacuum preloaded air bearing mount for a indicator on a surface plate .

Jack

funny that you mention that. I have been lurking in the back of this thread for a few months and that is what I'm currently researching.

[Eson]

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.

[lerman]

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.

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

[harryn]

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

Hi Ken, I had no idea you could hand lap a thread to that kind of accuracy. Pretty amazing.

[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.

[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]

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 read about Henry Rowland and his adventures in making lead screws for ruling engines.

[lazlo]

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. Polishing the release agent can acheive .00005.You are in ground ballscrew territory CO orC3 atleast.

Larry, I think you may misunderstand how the Moglice is applied. I'm one of the guys from PracticalMachinist (mentioned earlier) who's cast several Moglice nuts.

First of, there's nothing special about Moglice -- it's just common 2-part epoxy mixed with either molybdenum disulfide or Teflon. The original Moglice formulation (P-500) is 2-part epoxy with molybdenum disulfide and graphite. The newer P-1000 Moglice that many of us on PM are using is 2-part epoxy with Teflon. You can also get each formulation in viscosities ranging from syrup to honey to cake icing to hard putty. I use the P-1000 liquid (honey consistency) to cast Moglice nuts, and the P-1000 "semi" (cake icing consistency) to coat the sliding bearing in the Reeve's drive on my Clausing lathe.

In any event, when you're casting Moglice nuts, the reason for lapping is that there's a trade-off between how much release agent you use, and how stiff the Moglice nut will be.

In other words, assume you have a brand-new precision acme leadscrew, and say it's got a pitch error spec of +/1 thou per foot. So you pick a spot on the leadscrew that you're going to cast a conformal Moglice nut around, and you spray release agent (which is just spray paraffin) to provide a gap, or clearance between the leadscrew and the nut. Each spray of release agent coating is about 1 thou thickness. So if you only spray one coat, you'll end up with 1 thou clearance between the Moglice nut and that spot on the leadscrew where you cast it. If you have an unbelievably accurate leadscrew which doesn't vary more than a thou across the entire length, then you're set. But if the leadscrew is +/1 thou per foot, and you have a 3 foot leadscrew, the Moglice nut will bind at some point on the leadscrew, and you have to grind it off and try again (ask me how I know this ).

Most people rebuilding machine tools find that with a brand new precision leadscrew, and three coats of release agent == 3 thou clearance, you can get a movable, but stiff, Moglice nut. Then you use the Bon Ami as a lapping agent to wear down the Moglice nut to the point were it will slide freely across the length of the leadscrew. Hopefully, the amount you're wearing off with the Bon Ami is less than a thou, or your leadscrew has more than 3 thou pitch error, and you might as well have applied another coat of release agent.

So lapping the Moglice nut is not making anything more accurate, you're just wearing-in the Moglice nut to slide on the leadscrew.

In the old days, when folks like Moore lapped or re-cut precision leadscrews, they would make a map of the pitch error at ever point on the leadscrew. If you measure the valleys of the leadscrew, a variance in height will be twice the pitch error for that individual thread. In the Moore's "Foundations of Mechanical Accuracy" they show a long (life-sized) graph of pitch error they generated for a new leadscrew. Then they take a precision-cut thread lap, and diamond-lap each section of the leadscrew to wear-down the high points. When they're done, and all the high-points are uniform, they've ended up with a leadscrew with a unique, non-standard diameter, so every leadscrew and nut on every machine was unique, and stamped by a special serial number.

Cheers,

Robert

[jhudler]

... Then you use the Bon Ami as a lapping agent to wear down the Moglice nut to the point were it will slide freely across the length of the leadscrew. Hopefully, the amount you're wearing off with the Bon Ami is less than a thou, or your leadscrew has more than 3 thou pitch error, and you might as well have applied another coat of release agent.

Don't you mean you lapped the leadscrew?

Bon Ami or any lapping compound <DEL>will</DEL> could embed itself into the softest material (i.e., Moglice).
<DEL>Unless Bon Ami is softer (I don't know, not softer than Teflon) than both.</DEL> <DEL>In this case both would be lapped to varying degrees. Should the leadscrew bind during lapping, the Moglice nut would most certainly get loaded with grit. In this case the part being lapped would be the leadscrew. </DEL>

The use of lapping compounds has to be carefully thought out. I've seen a few telescopes where the wrong compound was used, only to turn their brass worm gear into a worm lapper; as can be measured by the hour glass shape in the stainless worm and/or hideous squealing sound emanating from same.

Jack

EDIT: Meant or should have said; The scratch hardness, fracture toughness, and size of the abrasive is important. In this case a very fine abrasive that has scratch softer than steel, harder than Moglice, good fracture toughness, and small enough size so if it were to embed in the nut, it would quickly abraded (or fracture) away.
It was a late night.

[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.

[Eson]

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

Well im not sure what i am creating since i cant decide! Im sort of just exploring the possibilities. However my dream is a tri/hexapod with linear actuators and the hydrostatic/air bearing would support the ballscrew since ball bushes will build too much. I have CAD-drawings of my idea but not avalible now.

[jhudler]

Well im not sure what i am creating since i cant decide! Im sort of just exploring the possibilities. However my dream is a tri/hexapod with linear actuators and the hydrostatic/air bearing would support the ballscrew since ball bushes will build too much. I have CAD-drawings of my idea but not avalible now.

Are you trying to build something like a Hexagide?
http://www.indoor.flyer.co.uk/kinematic.pdf (third picture or so)

[Eson]

Are you trying to build something like a Hexagide?
http://www.indoor.flyer.co.uk/kinematic.pdf (third picture or so)

I was thinking of a 'normal' hexapod because of the simple design, however i wonder if the ballscrews are so rigid and was thinking of stabilize them. Might be a good start anyway.
http://hem.bredband.net/b235625/hexapod.jpg

[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.