[Pxsi]

I used to be a member of an X2 mill forum, and many people there filled their column with sand and epoxy. From what I remember of the discussion they used fine grain dry sand and pored in epoxy primarily as a binder to keep it in the column and not all over the shop. I think it was the mass they were after to cut vibration. The best part of doing it this way is it is cheap, and lets you extend the machine to its practical limit. If your scratch building a machine that you plan to use commercially it may be a good idea looking into commercial products.

Pxsi

[Pres]

Just fill the column with hot lead. That'll stiffen it up.
I've seen it work on people
- fill 'em with lead and they become stiff.
Its gotta work the same way on a machine.

[Mcgyver]

I've done the concrete thing in the backyard and had to rip it up a couple of weeks later do to a pipe leak and it looked plenty dry to me. But then again this was only 4" thick concrete.
.

Michael,what I've read (can't remember where) is not that it doesn't harden or dry out, but that the curing process (whatever that is) takes a long time and that it will be moving. bridges move all over the place, just stand on one when a big truck is going by or notice the expansion joints. If one were to fill a superstructure and then take the time to scrape/machine/grind everything into alignment, the curring of the concrete could add forces that twists things a few thou or more out - that to me is the big downside of it. I can't quantify that risk beyond saying whether its welds that haven't been stress relieved or curing concrete, in making a precision machine I don't want anything moving about!

[miljnor]

Welded structurs tend to settle for a long while too because most are not stress relieved and the heating/cooling cycle for the sun rising and falling is enough to make the residual stress shift things around abit.

I had a weld table blanchard ground and it settle to a new shape after about 1year. Need to get it reground but I don't have any incentive as I don't do much welding anymore (professionaly anyway)

[lazlo]

You can achieve significant dampening with ordinary concrete, applied correctly. Do a Google search for a document called "Principles of Rapid Machine Design". This was the PhD thesis of an MIT mechanical engineer, and it's all about building high precision machine tools. Many useful techniques and data are covered there.

That's a great paper Bob -- thanks for that cite! I just read the concrete chapters (4 and 5), I'll have to read the rest over the weekend. The author is now at University of Utah, and he put the important part of his dissertation with the concrete dampers on this page:

http://www.mech.utah.edu/~bamberg/re...astDamper.html

I was surprised in the overview of materials damping that lead such as amazing loss factor. Cast iron has twice the vibration damping of steel, and steel has twice the vibration damping of aluminum. No surprises there.

But lead has 8 times the vibration damping of cast iron! So the recommendation to fill the column with lead is probably a good one That also explains the Old-Timer's trick of filling a boring bar with lead shot...

His fancy viscoelastic laminated tubes didn't work so well -- they ended up a third of the vibration damping of the rebar reinforced plain concrete. I wonder how much better they would have been with polymer concrete?

Home Depot and Lowes carries "polymer grout", but polymer means a lot of different things, especially in a consumer-oriented big-box store, so I have no idea how well that would work.

In any event, chapter 5 has a quick and dirty build for a very simple poured concrete pie-segments with rebar reinforcements, and it has amazing vibration damping characteristics. The only catch will be to find the Intraplast-N concrete expansion liquid. I wonder how expensive it is?

Edit: I found Intraplast-N on the web -- it's a grout expander meant for tile. Professional building supply stores carry it:

Intraplast-N

DESCRIPTION: Intraplast-N is a balanced blend of expanding, fluidifying, and water-reducing agents for portland-cement grouts. It produces a slow, controlled expansion prior to the grout hardening. Does not contain chlorides, nitrates, or other chemicals potentially contributing to stress corrosion in steel. Controlled, gaseous expansion occurs before initial set and forces the grout into close contact with the surrounding surfaces.

No. Size
SK INTRA 33 lb. bag, 40/pallet

APPLICATION: Horizontal prestressed tendons. Pre-packed aggregate cavities. Rock fissures and bolting.

DOSAGE: Add 1% by weight of cementious material, (portland cement and if used, fly ash).

http://www.sikaconstruction.com/tds-...aplastN-us.pdf

Here's a store locater for it:

http://buildsite.com/query/detail/product/intraplast_n

[lgalla]

I hear the Hoover Dam is not fully cured yet.We fill hollow tube speaker stands with sand for mass and damping.Works quite well.If you try it on the mill tube if it does not work you take out the sand and try something else.Do not like the concrete idea because it will shrink.Epoxy and sand would be my vote.
Larry

[lazlo]

Do not like the concrete idea because it will shrink.

In that paper that Bob recommended the guy used a concrete additive called "Intraplast-N" which makes the concrete expand when it cures.

I looked more into this, and apparently most of the high-quality grout you can buy at the Big Box stores are non-shrinking Portland Cement mixtures.

[Tristar500]

I'm going with the concrete idea! I'll post more on the exact specs etc later!

Thanks all!

Lawrence

[NC Cams]

Just to add another wrinkle - I recall seeing a techno-documentary where they were using chopped up glass mat (fiberglas mat) as a binding agent to fortify concrete.

Between shrinking, expanding, curing and whatever, you can add more stuff than you can imagine to help fortify concrete.

[svenakela]

... because it will shrink. ...
Larry

Well, THAT is not an option. At least the concrete types I'm using are not shrinking, I even used expanding concrete this summer.

[koslaz]

check this out: http://fotoalbum.web.de/gast/derbaumeister1/CNC-Fraese
It is homemade machine made by a German guy.
Here is the thread on the german cnc site http://5128.rapidforum.com/topic=110...3&search=beton
you have to join the forum though.

[307startup]

I'm surprised no-one mentioned expanding foam...I helped a friend restore a Ferrari 308 that he bought and the tube frame on that car had expanding foam in it (we had to replace a section of the frame as it had been wrecked - thus the low price on an expensive car to restore -he never did recoup his investment, so he kept it and now drives it twice a year!) and we discovered WHY the tubes were filled with foam as it had a very annoying buzzing and vibration in the rear where we had replaced the frame. We ended up drilling a 1/4" hole in the middle of the tube and using mix-your-own urethane foam and a long nozzle we were able to get the tubes filled up and after letting it cure it sure didn't buzz and vibrate anymore. We checked the rear alignment, camber and caster and the foam hadn't distorted the frame as near as we could tell, all specs were on factory...we were using a very nice laser alignment system that another friend owns at his shop, and it's accurate within a half-thou, so I'd say that expanding foam would work very well, and there are additives available such as glass beads that are used for sandwich cores in composite panels (glass beads in the foam, laminated with fiberglass or carbon-fiber and pressed in a 1000 ton press) that are used in all manner of products.

[Mat-C]

I would guess the foam is to prevent water ingress, and in your case to suppress movement of any small particles of rust, debris or whatever.
I can't see it adding much in the way of damping or structural strength.

[307startup]

Actually it dampens vibration quite well. I agree it doesn't add much to structural strength, but if you don't think it quells vibration, take a length of exhaust pipe (scrap or from auto parts store) and fill it with that foam in a can from the local home improvement store. Hold the unfilled piece with your hand and ring it against something solid, then take the filled piece and ring it against something solid...makes quite a different sound and feels differently altogether. Not to argue...its just that the tubes were all filled after the chassis had been welded because the stuff burns and is quite nasty...a good whiff of the fumes will put you in the hospital if not your grave...and yes, I'll admit it would stop most rusting, but a chassis wouldn't be much good if the welds were leaky...not a very strong weld to have someone running at high speeds with lots of high manuevering and braking forces for thousands of miles...just my opinion...

[KSKID]

In that paper that Bob recommended the guy used a concrete additive called "Intraplast-N" which makes the concrete expand when it cures.

I looked more into this, and apparently most of the high-quality grout you can buy at the Big Box stores are non-shrinking Portland Cement mixtures.

We use what is called a high strength non shrink grout all the time for filling underneath column base plates on large commercial construction projects, we use it to fill the voids between the top of the concrete foundations and the bottom of the steel base plates on structural columns, and it does not shrink when curing, heres an insert taken from one of our specs.

A. Non shrink Grout: Pre mixed non shrinking, high strength grout, ASTM
C1107, Type A, B, or C; compressive strength of 5000 psi in 28 days.
1. NS Grout, by Euclid.
2. Construction Grout, by Master Builders.
3. Sonogrout, by Sonneborn.
4. Certi-Vex Grout #1000, by Vexcon.
5. Enduro 50, by Conspec.

[saris]

would this stiffen up the column?





Sorry for the big pic

[philbur]

Would what. Its not clear (at least to me) what you mean.

regards
Phil

would this stiffen up the column?

Sorry for the big pic

[saris]

That big steel monstrosity of mass embedded into the stock x2 column-what I was referring to...

That's what i think it is anyway. The top is also where syil placed the z-axis stepper motor.

It's either embedded and /or bolted to the stock one my guess...

[saris]

this is what a stock X2 column looks like for reference

[philbur]

Aaah now I see. The original picture looks like it's X3 column on an X2. The beefed up column may be stiffer but it still looks awefully flexible at the swivel, which is the point of maximum bending moment.

Regards
Phil

this is what a stock X2 column looks like for reference