[jestah]

Hi

Jestah... long time lurker first time poster, well in the thread any way. I have recently started to build my own cnc shaper when i stumbled across this thread and im hooked!

well i was hooked until about the 2nd hour of reading posts! While i have given a good attempt to read the thread please excuse me if i ask something already covered.

First up could some one tell me how big the largest home build table using E/g has been? I am guessing that having a vibration table is a big limiting factor to size. Has any one managed to bond smaller blocks together to make a bigger overall size.

I understand the basic process of mixing resin with the granite but has any one attempted to use a technique like resin infusion as it seems to me that this could be a really easy way to get a very good resin ratio.

Resin infusion is a process were a composite part is layed DRY into a mold and then assembled with a resin feed tube that dumps the resin into the mold, you transport it around the mold using a mesh that allows the resin to flow very fast and then to the part where it penetrates any voids. I would think you could do the same, although having an even compaction would be essential to even resin flow, by packing dry aggregate into a mold, settling on a vibe table and then vacuum bagging and infusing.

How accurate are people pouring a table surface as i would like to attempt this some day but can not afford the tooling to mold the size table i would like. I have seen a few smaller table surfaces done with low viscoity epoxy poured onto the centre of a large table but could not find much information about it. Could any one recommend a post to check out.

thanks in advance
Jestah

[ckelloug]

Hi Jestah and welcome.

The first important answer is that none of the DIY-ers have made more than test pieces. No tables produced yet that I am aware of.

The second is that without vibration and careful aggregate selection, it would be difficult to get a stiffness much beyond that of pine. An E/G table with a low fill rate would be more dimensionally stable than wood and likely flatter however. From the academic papers, it looks like the aggregate needs to be carefully selected and vibrated at above 2g to get commercial quality material that which is much stiffer than pine.

The flat part of the table will be as flat as whatever you cast it on. I don't think that our number here have actually done the epoxy surface plate experiment yet but it should be possible to get .0002 per foot which is more than adequate for a router table.

In short, E/G is a nice material but to get rigid structures suitable for metalworking tools, the tools required to make the part are probably more expensive than the part unlike we had hoped.

For routers, it should be possible to use home shop grade low modulus E/G material but nobody has gone through the work to try it yet. Most of the diehards here on the thread like me are trying to perfect a commercial grade material as opposed to just building something.

Regards all,

Cameron

[Brenck]

I was wondering in an alternative to vibration tables we use this concrete vibrators

http://www.laku.com.my/Concrete%20Vi...le%20Frame.jpg

The picture is too big so I posted the link

Have anyone tried?

They are kinda cheap alternative and you can rent one for a couple of days in some places... Does it work?

[jestah]

Count me in! I work for a firm that makes prototype carbon fibre parts and we would like to join the search to make a stable table.

Could some one point me to a website or post with some info about vibe tables as i think i need to understand more about the compacting. In my limited knoloage it seems to me this is the biggest thing holding back the diy build.

What do you guys think about this idea:

build an mdf torsion box to create a flattish casting surface, skin it with a thin released al skin to make it air tight, build in any need features, fill with DRY granite, infuse, demold and fill any exposed thread/mounting holes with wax, build a small side wall and pour a very thin low viscosity slow cure epoxy and then put in our autoclave and spin up the vac pump to degass any air.

I want to do it this way as i have no access to a decent flat table to make a flat casting on. We have a 3x2.5m al plate but it is not very flat -/+ 2-3mm over its length.

also has any one tryed steel ball bearing of the right size so each fit in the gap of the lager one above? it seems this could be a solution that may need less shaking?

Is there any way to search a single thread?

[Mbk]

Hope you like this document guys.

[ckelloug]

Count me in! I work for a firm that makes prototype carbon fibre parts and we would like to join the search to make a stable table.

Great. Several of us have the idea that a mold for a table could be made by casting a slick of low viscosity epoxy with a deairing agent. This will be good to about .0002 in/ft or the curvature of the earth. Precision Epoxy http://www.precisionepoxy.com/ makes epoxy commercially used for making plates on the floor for aligning car suspensions.

To make a cast plate, one will have to get a flat surface perhaps by the self leveling epoxy method and then make a mold and cast a more substantial plate against the flat surface. For a small plate, this will work but for a truly large plate, .0002 in/ft might not be accurate enough.

Could some one point me to a website or post with some info about vibe tables as i think i need to understand more about the compacting. In my limited knoloage it seems to me this is the biggest thing holding back the diy build.

What do you guys think about this idea:

build an mdf torsion box to create a flattish casting surface, skin it with a thin released al skin to make it air tight, build in any need features, fill with DRY granite, infuse, demold and fill any exposed thread/mounting holes with wax, build a small side wall and pour a very thin low viscosity slow cure epoxy and then put in our autoclave and spin up the vac pump to degass any air.

I want to do it this way as i have no access to a decent flat table to make a flat casting on. We have a 3x2.5m al plate but it is not very flat -/+ 2-3mm over its length.

also has any one tryed steel ball bearing of the right size so each fit in the gap of the lager one above? it seems this could be a solution that may need less shaking?

Is there any way to search a single thread?

I don't think anybody here knows if a fully compacted mass of powder can be vacuum infused or not. I've successfully vacuum infused a very loose packed mass of particles with epoxy but that doesn't scale to a tightly packed mass.

In general, Steel shot is more expensive than other fillers and the friction between the randomly oriented balls means that it is just as difficult to compact. It also does not achieve Face Center Cubic structure like the fitting balls into the voids of the larger balls idea would hope.

The models suggest that optimally one needs at least 4 orders of magnitude of size difference between the smallest and largest particles and for 4 orders of magnitude, and 8 carefully selected intermediate sizes between the largest and smallest.

Vibration is the most difficult part for the underequipped and from the research from several places, the part appears to need to be vibrated at at least 2g to compact fully.

The search this thread tool on the right side of the page up by the thread numbers does a passible job. If you are a linux user, I have written a couple of scripts to download the entire thread so I can search it with grep. I've also written some code that allows me to link to posts by post number which I used to make the index thread. If anybody wants to update the index, I'll share my tools with them.

Jestah, Take a look at the links on pg 301 to get a bit more idea of what's going on.

Regards all,

Cameron

P.S. Thanks to MBK for the post on optimizing the EG spindle.

[TRIMI]

YOU CAN BUY TURCITE AT Toll Free: 888-887-2483
Email: [email protected]

THE MACHINE TOOL GROUP

[diverjohn46]

Article in the most recent 'Model Engineers Workshop' magazine.
This involved a project to reduce chatter on a small (X1) mill.
Part of this was to fill the hollow column with epoxy granite to add mass and as a dampening medium.

The outcome was very positive with a very heavily damped column which had not vibration problems and which reduced chatter markedly on this light mill.

Might be of interest, not as a bed or solid mass of a machine tool but to add mass to one.

John

[ckelloug]

John,

Thanks for the reference. I've asked a friend with a subscription to let me borrow the issue when the mail scow finally lumbers across the pond.

I'm still actively working on this but most of what I'm doing right now is work on my lab infrastructure which means very little actual research gets done presently.

Regards all,

Cameron

[jonixllc]

There have been and are many commercial manufacturers of so called "epoxy granite". Hardinge started back in the late 80s. Taylor Hobson at the same time and Philadelphia Resins a little later.
Currently Anocast, Philadelphia Resins, Granitek, etc all provide epoxy granite machine bases
I have designed epoxy granite bases for almost 20 years for ultra-precision machine tools and have never put reinforcement in the bases
Be careful about full cure of the mixture
Typically there is only 8% or so of epoxy to aggregate, so cure time should not be an issue
Be careful of outfits that put more epoxy than 8%

[the4thseal]

Be careful of outfits that put more epoxy than 8%
Reply With Quote

by weight or volume?

[alex_ku]

and why its bad to have more than 8% of epoxy ?

[jonixllc]

By volume.
As for Alex, if you think about it, the physical properties of natural granite (and diabase) are a function of its makeup - quartz, feldspar and mica. If we introduce plastic (epoxy) in any large quantities, we greatly compromise why we are choosing granite - 8% by volume has been shown to yield as close to natural stone as possible
The epoxy acts as a bonding agent and only a bonding agent. The aggregate is sized and shaped so intimate contact is insured between the aggregate particles themselves - the epoxy filling only the voids. This simulates mother nature - almost
Some companies use only quartz, while others use a combination of the three main granite constituants - It has been my experience that there are really three things that you MUST look for in an epoxy granite manufacturer:
1. Mold making expertise (pre-production and production) - some molds start out as wood for pre-production, yielding perhaps 5-10 machine bases - then migrating into aluminum
2. Vibration Table - as the mold is poured and begins curing, it must be vibrated to insure aggregate contact, complete filling of the voids with epoxy and no air pockets - for some large machine base molds, the vibration table must be quite large to accomodate the mass
3. Metrology and fixturing - because epoxy granite yeilds itself to "casting in" features such as threaded inserts, mouting plates, drainage piping, electrical chaseways, etc., the company producing the base must exhibit the ability to place and insure placement of all of these features
Finally, epoxy granite bases do not replace natural granite bases. Natural granite (or diabase) still reign as the most stable platforms for ultra-precision machine tool and metrology bases.

[the4thseal]

thanks for the by volume.

[Oldmanandhistoy]

Hi jonixlic,

Just want to say thanks for your input and welcome to the zone

Regards,

John

[alex_ku]

By volume.
As for Alex, if you think about it, the physical properties of natural granite (and diabase) are a function of its makeup - quartz, feldspar and mica. If we introduce plastic (epoxy) in any large quantities, we greatly compromise why we are choosing granite - 8% by volume has been shown to yield as close to natural stone as possible
The epoxy acts as a bonding agent and only a bonding agent. The aggregate is sized and shaped so intimate contact is insured between the aggregate particles themselves - the epoxy filling only the voids.

I agree with you, but also have my own opinion
All that you say is appliable only if you use right mix of sands. If you have some disbalance (for example low quantity of micro size sand), in case of hobby its possible, than youll get voids, because of small amount of epoxy, and final result will have poor quality.
But if you add more epoxy and use vibration - all corns will fit together with minimum distance between each others and extra epoxy will be on the top of form, where you can remove it. All what i say is based on my own experiments.

PS: sorry foy my poor english.

[alex_ku]

hi all!

I need some help:
meybe some one know links to seller/manufacturer (in EU) of insert nuts applicable for epoxygranite ?
I had one but lost link and cant find it any more

Thanks!

[jonixllc]

hi all!

I need some help:
meybe some one know links to seller/manufacturer (in EU) of insert nuts applicable for epoxygranite ?
I had one but lost link and cant find it any more

Thanks!

Contact: [email protected]
It is located in the midlands, specifically the Leicester area
They used to be the main supplier of epoxy granite bases for Taylor Hobson metrology products as well as Taylor Hobson's line of ultra precision machine tools
Derek Robinson used to be the Managing Director and has good experience in epoxy granite
If they cannot provide you with an EU manufacturer, I can give you a US manufacturer

[jonixllc]

I agree with you, but also have my own opinion
All that you say is appliable only if you use right mix of sands. If you have some disbalance (for example low quantity of micro size sand), in case of hobby its possible, than youll get voids, because of small amount of epoxy, and final result will have poor quality.
But if you add more epoxy and use vibration - all corns will fit together with minimum distance between each others and extra epoxy will be on the top of form, where you can remove it. All what i say is based on my own experiments.

PS: sorry foy my poor english.

Alex-

Your english is OK
You are correct - the correct size of aggregate is of high importance
For most manufacturers, this is what is proprietary in their process
For most ultra precision applications, achieving a base that's as close to natural granite is the goal -strength, mechanical and thermal stability and good damping characteristics
Although epoxy granite has its limitations, manufacturerd properly it also has its advantages

[alex_ku]

Contact: [email protected]

Thanks jonixllc! Waiting for an answer
I prefer an online shop, but we will see.