[Zumba]

If box ways were a good idea on a polymer concrete machine, it would've been done already.

And box ways are not cheaper than linear guides. In fact, they're much more expensive when done properly. Some Chinese manufacturers achieve lower costs by using thin "mystery metal" castings that are ground/scraped by cheap labor... false economy.

[dilbert]

If box ways were a good idea on a polymer concrete machine, it would've been done already.

Not necessarily. Box members are much more efficient use of material whether the material is diamond or epoxy concrete. It may not have been done yet because of the expense. If I'm going to make a tool based on epoxy concrete, I want something that I can move without having to rent or buy a forklift! Box ways will accomplish that.

Remember that structural stiffness is 1/EI.

[Zumba]

Not necessarily. Box members are much more efficient use of material whether the material is diamond or epoxy concrete. It may not have been done yet because of the expense. If I'm going to make a tool based on epoxy concrete, I want something that I can move without having to rent or buy a forklift! Box ways will accomplish that.

Remember that structural stiffness is 1/EI.

You've got some terminology mixed up.

http://www.cncmagazine.com/vol6thru8...-LinrGuide.htm

[roach]

i dont know where under an hour pot life comes from we can take longer that that casting sometimes on small castings larger ones 7 hrs can be the norm
the exothemic reation should drop down draticaly with granite in
id happy to leave it for a 1 hr and still cast
ive melted pots with just resin mixes
but i can say i wish i could show you when we turn on our tables how the mixes go from lumps to flat in secs
we gel coat and they can last at least 1/3 hr and they go off fast
i dont know what to say
the mould can take heat away the enviorment can make a diffrence
as for the polyquarts being modern epoxy granite sounds dated now unfortunatly

[roach]

i worry when we have to cast from a blind hole to a blind hole under a box where if you fill from both ends it traps air and you have to fill from one end if it went off in 45 mins it would be scrapped

[ckelloug]

Well,

After a lecture on the dangers of IPDA from the guy in Tech Services at Degussa, he agreed to let me have samples of IPDA and Trimethyl Hexamethylene diamine. I've also got some samples of chromium and cobalt acetyl acetonates requested from Sachem although I haven't got it confirmed that they're in route.

John,

I'm looking forward to seeing the pictures of your spinning exploit. As for the particle sizes, de Larrard suggests that particles between two consecutive sieves in the French series can be considered uniform for the most part. If they're farther apart than that however, the problem you are talking about will get to be larger and larger as the size difference between the sieves increases.

The trick to making a complex graded material is to take those curves which are generally normal distributions and add them up in probabilistic fashion or to handle the different particle size components for each item you add to the mixture so that you get a total count of the particles in each range. De Larrard's optimal formula is based on the theory that you espoused thousands of posts ago about smaller spheres filling the spaces between bigger spheres. The main difference is that de Larrard used a probabilistic model to account for the random placement of spheres.

I look forward to your samples some day.

If you liked the Kinloch book, it's possible that the Ph.D. Thesis of B.W. Staynes will help you. It is cited as B.W. Staynes Ph.D. thesis-- National Council of Academic Awards May 1972. He got his P.H.D at Brighton Polytechnic. Kinloch is quite readable.

Regards all,

Cameron

[greybeard]

I'm losing a lot of time with medical men at the moment, but will press on regardless.
Herewith attached the latest molds. The one on the left is designed to produce a set of six identical samples with each run. They will need to be trimmed in thickness, so I shall remove the inner layer which should contain air+resin. I hope the outer layer will be more uniform, but I suspect you may get a different result depending on which way up it is !

The right hand one is my first parts of the Z truck, the two uprights that will bolt directly to the router body. They will have a top section containing the z nut joining them. More details to be posted over on my build thread.

Mixing and spinning tomorrow morning, so there may be the first action photos by the afternoon of me trying to get the samples out of the mold.
Regards
John

[greybeard]

Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaarrrrrrrrrr rrrrrrrrrrrrrrrrrrrrrrrrrghhh.

Well, having got that off my chest, herewith update.

Trying to catch up some lost time, I went straight to my recipe of a seven part mix of four graded quartz sands, G800, and G200 zeeospheres, plus cab-o-sil, a sub-micron silica fume.
I reasoned that if the guys casting a thick mix were aiming at 10% resin, then I should have a pourable mix with 20%.
Unfortunately, I had overlooked the thixotropic effect of the cab-o-sil.
An epoxy/crunchy peanut butter mix can't be made pourable by adding more epoxy, and even raising the epoxy content to 50% still left a non-pourable paste.

Back to doing some simpler mix tests, and redesigning the test mold so that I can fill from the front, not the end.

[Steven.ji]

Is it possible to bond Turcite-B on moving slide, then use polymer concrete as friction surface as picture?

[jhudler]

Is it possible to bond Turcite-B on moving slide, then use polymer concrete as friction surface as picture?

Yes you can.

[greybeard]

Jack, that was very succinct. No caveats ?

[greybeard]

Right guys (and this is for you, not the gals, who have their own problems)- this is an "off topic, in-your-face public service" post from greybeard, who has just come back from having a few drinks with the neighbours on a pleasant sunny evening, here in UK, so I'm relaxed enough to post this now.
I'm placing it here because here is where it might have the most impact for self evident reasons.

If you've got any "plumbing" problems, go and see the man with the rubber glove.

I've just been diagnosed as having prostate cancer, and am about to have an MRI scan before treatment is discussed.
So if anyone is in that situation, go for it. You only stand to gain another twenty years or so, at the expense of a temporary embarrassment.
If anyone wants to pm me for support, no probs. I was inspired by a friend being open with the same problem, so if I can help I'd be honoured to do so.

I need thirty years - I've got too many projects to make do with less.

:cheers:

[jhudler]

Jack, that was very succinct. No caveats ?

Didn't want to over complicate the answer.

I'd probably cast in a EG/LF (Low Friction) surface as the way surface... but this would remove the need for Turcite-B.

[greybeard]

Managed to pick up a working Kenwood Chef mixer with all attachments for £8 at the local carboot this morning, so some things are going ok.

[greybeard]

Great - we move forward. :wee: I managed to spin a set of six test pieces for Cameron's machine today.

My mix is
40gm Agsco quartz #4
40gm ditto #2
40gm ditto #1/2
40gm ditto #2/0
35 gm G800 zeeospheres
35 gm G200 zeeospheres

plus 63gm(~21%w/w) DX020 epoxy from Atlas Polymers.
(I think this has now been superseded, but as this is for comparison testing, it's ok for my needs)

The mix was just about pourable at 20 deg C, and the molds were spun at 2500rpm for 3 hours.
OK, so I forgot it - (chair)I had to cut the grass, then the hedge, and then it was lunch time - you know how it is.

When I can find my calculator, I'll edit in the G forces on the mold. Should be somewhere about 90 G I think.
Edit Bit of a suprise - it turned out to be ~225 G !
Getting the samples out of the molds was a bit of a pain. (Notice the chisel) They released ok, but I managed to break one of the molds, so I need to rethink the mold design again. I want to do quite a run of different aggregates, so the mold/demold needs to be a lot easier.

The next stage is to give them a post mold heat cycle to make sure they're fully cured, then into the post.

[romihs]

John,

Those samples look incredibly dense (or should I rather say compact).

Very impressive results, I would love to see some close ups of the EQ, and also some close ups of breaks.

Regards

Sandi

[greybeard]

Hi Sandi.
I've had them on the top of the storage heater over night at ~50deg C, and only just had my first proper look at them. I'll try and rig up a close up photo before I send them off to Cameron, but ask him to post the broken surface photo if possible.

EDIT I've attached a close up of the polished end, not too good, but it does show what I suspect may be segregation occuring at the high G that I used.
If anyone would like to do the maths based on the photo, the density of the Agsco is given as 2.65gm/cc and the zeeospheres as 2.2gm/cc.
I've posted the weights, calculated to give equal real volumes for each component, and I wonder if the grey band below the top dark resin band is all the zeeospheres !
End of EDIT

Cameron - in order to produce a decent x-section for your machine, the "top" surface, a meniscus of 1" radius and consisting mainly of the excess resin, about 2mm layer, needs to be removed. There will also be some quartz in it, and it occurs to me that (a) I have only got a hand held disk grinder, so I can't guarantee the uniformity of the thickness, and (b) if I hit the quartz with the grinder will that generate localized heating sufficient to breakdown the epoxy at that point ?
Any suggestions ?
John

[ckelloug]

John,

Your work is amazing.

As for sample uniformity, I can handle the sample preprocessing. I have a diamond wet tile saw for which I still need to build a table that is good for sample processing. It is however how I cut the last epoxy samples. Getting the samples uniform and square is important although their exact size can float a bit as the size used is one from a thousandths caliper before the test rather than the nominal dimension.

I was thinking the tile saw might be underkill until I looked at a buehler geological sample saw and found out it's literally a tile saw blade from Felker in what amounts to a very powerful tile saw with a nice table and enclosure.

I'll take pictures when I test them. I also still have Jack's samples which I ought to take pictures of.

P.S.
I've been following here but not as closely as usual. I'm working on a subpixel image rotation algorithm in my day job which needs to be done yesterday.

[greybeard]

....
P.S.
I've been following here but not as closely as usual. I'm working on a subpixel image rotation algorithm in my day job which needs to be done yesterday.

Er, yes.

We gave up the "wanted yesterday" work when we left the film props work

Thanks for taking on the sample prep as well.
Going for a whole body scan this pm (wonder if I can scrounge a print to post here ) so I hope to get them in the post to you by Thursday.

I'll send these off first, but I'd like to follow up with some graded local sand tests as a comparison, as well as a set without the zeeospheres in.

John

[ckelloug]

For real fun, try putting an E/G sample laced with Barium Sulphate in your pocket when they scan you. It was really fun to fly with those in my carry-on after I met with Jack!

Best of luck on the scanning!

--Cameron