[digits]

Melamine mold sounds good and I like the "box" idea.

re: tall extrusions
There are multiple 8020 choices (esp on Ebay). The one pictured would be good for longer machine frames 8-16 ft. Anyone here interested in a frame longer than 8ft..?
.

Hi Walter, if you use the deflection calculators, they will tell you that you need tall profiles to reduce sagging in long spans of extrusion supported at either end. If the whole lot is embedded in concrete, the entire length of the span is supported by the concrete, so IMHO you can get away with short profiles.

[digits]

I would hazard a guess.Depending on size or application,we probably want 3to4" of E/G which makes tall extrusions necessary.From posts I am seeing 2 different ideas.One where there is a frame of extrusion ,two where there is two pieces of 80/20 surrounded by polymer.Either case we need a mold.3/4 melomine may be a good cheap material.I we had a frame of extrusion we could simply attatch it to a melomine base and pour.In the other style one would build a box and pour allround.
Now we have to accept we need pouring consistancy so the polymer can flow into the 80/20 side slots.I would just use sand in the mix,pour1/2"and manually push stones or aggregate into the epoxy.
Larry

Yes, sorry, I had imagined the frame would be in a wodden box used for the pour. Infact, if your carpentry skills are up to it, the box wouldn't need to be rectangular - it could just be a few inches wider than the 80/20 frame - e.g. you could have a # shaped 80/20 frame with a larger # (I hope that is a hash symbol in all fonts!) shaped pouring box with a large central hole.

I hadn't really considered a pour with just two pieces of 80/20 for mounting rails etc because it I thought it would require a lot more precision in the construction of the pour box, as the box would also have to precisely position the two 80/20 rails and keep them in the same relative position during the pour and curing. IMHO bolting them together with a bit more 80/20 is simpler if a little more expensive.

I'm still not convinced you need tall profile - even with a 3" deep EC block - you could use 40x40mm (1.5x1.5") frame and then just 'jack it up' on a few short sections of 40x40 at the corners as 'feet'. The beauty of 80/20 is that it is very square, and pretty accurate in diameter, so stacks of profile have parallel top and bottom surfaces, and two stacks cut from different pieces of profile of the same spec will have almost identical heights. The stacks can be bolted together either through the stack, or down the sides.

[lgalla]

Digits
Jacking up the corners may prove more difficult to acheive alignment.If jacking up is to save money,the extrusion is cheaper than the filler.Usually one might start with the base.I would recommend building the whole machine first,confirming the alignment of the linear rails,then finally doing the pour.We don't want to end up with an expencive "patio stone"If using 80/20 for the gantry,the larger voids are a perfect candidate for Epoxy/Granite.I had investaged 80/20 before and determined it's not a good machine material,but with E/G it becomes attractive.
One thing might I ask?From previous posts are you talking about water based concrete or polymer concrete?On this thread concrete is concrete,polymer concrete is polyester resin & aggregates and E/G is epoxy/granite or quartz.The first two are worthless to us as neither will stick to aluinium.
Larry

[walter]

No, not water based concrete.
I always thought "polymer concrete" was something more like"epoxy thing" but easily pourable. But that's not the case So maybe we should concentrate on straight E/G or something close to that...

Especially now, after we found a way to lower the cost.

[lgalla]

There is so many posts and questions and answers to this thread,I will try to give good answers.I can argue untill I am blue in the face,but you are not going to get 10% resin period.I have vacuum mixing and 10% would be diffucult.Mixing epoxy generates tons of air entrapment.A 10% resin content is so stiff the vacuum will do a poor job.Why is air entrapment a huge problem?When the epoxy exotherm hits 150 C what happens?The entrapped air expands leaving huge voids,not a good thing.If one will accept say 20% resin content we can pour the material and have less air problems.At this ratio,true the epoxy will "puddle"on the surface.No problemo just push in rocks
and add sand to suck up the excess resin.This would probally bring us near the 10% level.
On another subject aimed at picking Geofs brain.If the hobyist has a frame made extremely stiff by E/G,may he encounter difficult alignment problems?
I am reffering to a reply you gave me many moons ago.Poor alignment on a flimsy frame will result in the frame bending.A solid frame will not bend or flex resulting in requireing more accurate rail mounting.Geof,this is not a quote hope you can remember the reply you gave me.
Larry

[JerryFlyGuy]

Digits
Jacking up the corners may prove more difficult to acheive alignment.If jacking up is to save money,the extrusion is cheaper than the filler.Usually one might start with the base.I would recommend building the whole machine first,confirming the alignment of the linear rails,then finally doing the pour.We don't want to end up with an expencive "patio stone"If using 80/20 for the gantry,the larger voids are a perfect candidate for Epoxy/Granite.I had investaged 80/20 before and determined it's not a good machine material,but with E/G it becomes attractive.
One thing might I ask?From previous posts are you talking about water based concrete or polymer concrete?On this thread concrete is concrete,polymer concrete is polyester resin & aggregates and E/G is epoxy/granite or quartz.The first two are worthless to us as neither will stick to aluinium.
Larry

I'd have to say this sounds the best so far Larry, I've been doing my share of leveling structures of late and know that its not as easy as it looks. Plunking a pc of steel [or 80/20]into the btm of a mold doesn't dictate accuracy in any way. Infact it makes it harder. How are you going to get the two pc's sqr/parrallel and planer? Pretty tough I'd say. On the other hand, using your melimine form and a pre fab'd 80/20 structure [ even if its lightly connected] is going to give you a fighting chance at getting it planer and parrallel. When using a form of this type, you don't have to worry about draft or getting the 'part' out of the mold as you would take the mold off the part instead. If you were going to make several of these, you would need a two pc mold which can be re-assembled [ not as easy as it sounds]

My two cents.

Jerry [ someday I'll build a mill like this, after I get my current mill build completed ]

[lgalla]

Jer thanks for the input and other help.From our previous talks I have a direction to follow with confidence.
To other members following the ideas,I know little of obtaining square and accuracy of the rails,but have confidence in my epoxy knowledge.Jer,I think we are talking about fastening the squared frame to a base,putting the mold frame on,and pouring the matrix up to the "neck"of the 80/20.Jer as you know my computer skills are limited.If members could post a simple drawing of their ideas it would simplify answers.
As stated before I know the route I am going or how to do it.I am posting to try to make members figure it out for them selves.The epoxy pour and surface plate is not a problem for me.I know my posts are complating progress but it is really not that hard.The hard part is the books or articles on E/G.We home type guys cannott realize their specifications but can compromise and still get good results.It is really simple.Mix A&B put in filler untill "HOLY **** BATMAN HOW WE GONNA POUR THAT."A 10% resin content in a 5 gal. pail is gunna be over 100lbs.this is trowel type material.I got the "big contract"to day so my time is limited,but I will try to post.If you guys want to wait my project is 2 to 3 months away,a 6'X12'X4" steel framed E/G table top for a 10hp router.If it doesn't work what do you do with a 3200lb paperweight?
Larry

[atenman1]

Hi Larry
For your 3200lb paperweight, how much gallon of epoxy you would need, and how much would that be? My curiosity is killing me for the next couple month to wait for you project!!!
Thanks
Calvin

[digits]

Digits
Jacking up the corners may prove more difficult to acheive alignment.If jacking up is to save money,the extrusion is cheaper than the filler.Usually one might start with the base.I would recommend building the whole machine first,confirming the alignment of the linear rails,then finally doing the pour.We don't want to end up with an expencive "patio stone"If using 80/20 for the gantry,the larger voids are a perfect candidate for Epoxy/Granite.I had investaged 80/20 before and determined it's not a good machine material,but with E/G it becomes attractive.
One thing might I ask?From previous posts are you talking about water based concrete or polymer concrete?On this thread concrete is concrete,polymer concrete is polyester resin & aggregates and E/G is epoxy/granite or quartz.The first two are worthless to us as neither will stick to aluinium.
Larry

Yes, the rail alignment does need to be checked before the frame is embedded in EG. I don't see the problem with jacking up the corners however - the frame doesn't need to be level relative to the pour box or EG - it just needs to be true and parallel with respect to itself. As long as the vertical columns are mounted directly onto the 80/20 frame, IMHO it really doesn't matter what jaunty old angle they end up at - the machine will be square but not horizontal/veritcal!

I'm not convinced that 80/20 is useless on its own - The Swede's machine on 5bears.com looks pretty stiff to me!

[Mcgyver]

there's a few posts here that talk about the structure using E/G as being made stiff because of the use of EG. I may have missed something but i think this is an incorrect assumption - where did we get that E/G is going to make it stiff? E/G has a very low modulus of elasticity, 1/6 of steel. While there are various advantages to it, a biggy to a home shop machine was vibration dampening, but don't see how its an efficient route to stiffness - its a poor choice of material for this. if the 80/20 isn't stiff enough, maybe you need to make it out of steel, use a larger section of 80/20, cast an I beam into it etc - these are things that will increase the stiffness of the section. before someone does make a 3200 lb paper weight (because they expected rigidity/stiffness and didn't get it) it would be interesting to do the engineering calcs on how much deflection is reduced by a steel/EG section vs steel or AL/EG vs AL.

[JerryFlyGuy]

Thanks for clarifyign Larry, setting it on a surface plate will work fine, that is if you have one that big. Just be sure to wax that sucker or you'll have to use the opposite side of the surface plate only and it will have a BIG HEAVY stand to hold it

Mcgyver
You right Epoxy doesn't have the stiffness of steel, however If I'm understanding the proportions of the machines that are talked about, a machine cast from steel [of the same size] would be 5-10 ton's. By understanding the proportions of the machine you can understand where it gets it stiffness, doing a steel machine of 1/6 the size could be as strong, but would have no-where's near as much vibration dampening.

Jerry

[Mcgyver]

a machine cast from steel [of the same size] would be 5-10 ton's. By understanding the proportions of the machine you can understand where it gets it stiffness, doing a steel machine of 1/6 the size could be as strong, but would have no-where's near as much vibration dampening.

Jerry

Jerry I don't disagree with anything you are saying and am not advocating a 10 ton machine , my point was some posters seemed to be thinking the EG was going to have a big effect on stiffness and I can't see that. whatever the size, each cross section is going to deflect, and if the engineering goal is to minimize that deflection (make it stiff) EG is poor choice of material. I have long liked the idea of EG filled cavities of stress relieve steel fabrications for machine structures, the attraction being its vibration dampening properties. It looks to me like pursuing an EG structure to provide stiffness is an erroneous direction, or at least something that should be engineered/quantified before the construction.

[JerryFlyGuy]

I read ya 5 x 5 McGyver, I personaly plan to make a steel mill [my next project] and then fill the hollow inside w/ the stuff, A person could also increase the stiffness of a mill cast out of this stuff by adding a steel member in the bottom [ as a base], if it is properly tied to the epoxy [possibly by anchors off the pl] then it would form a beam structure w/ a epoxy as a shear web. I think this would give a significant jump in stiffness.

A guy would have to dig into the math of it all or get an engineer to, or do some experiments to know for sure. Lots of possibilities.

Jerry

[Aramon]

We are using machines with Polymere-Concrete frames for years.
These are the best machines we ever had. Very stable and high accuracy.

Epucret is a frame manufacturer for Mikron/Hermle etc.

http://www.epucret.de/files/EPU_News_NR_26.pdf

Guideways of our Mikrons seems to be fixed with Epoxy grout after alignment.

[digits]

Jerry I don't disagree with anything you are saying and am not advocating a 10 ton machine , my point was some posters seemed to be thinking the EG was going to have a big effect on stiffness and I can't see that. whatever the size, each cross section is going to deflect, and if the engineering goal is to minimize that deflection (make it stiff) EG is poor choice of material. I have long liked the idea of EG filled cavities of stress relieve steel fabrications for machine structures, the attraction being its vibration dampening properties. It looks to me like pursuing an EG structure to provide stiffness is an erroneous direction, or at least something that should be engineered/quantified before the construction.

OK, I'm confused! If I had an 80/20 base frame with adequate stiffness in the extrusion to not deflect significantly under the cutting loads and its own mass, wouldn't the vertical deflection be even less if it were simply sitting on a slab of EG?

From what I understand (and the 80/20 deflection calculators confirm) the actual profiles are plenty stiff, but the joints are a bit of an unknown quantity. If instead of just laying the 80/20 frame on top of a slab of EG, it were instead bolted down to it at regular intervals, wouldn't the profiles be more constrained and the resulting structure be more stiff than the frame just sitting on the EG? If that is a true assumption, why wouldn't burying the frame an inch or so into the EG slab be even stiffer than just bolting it down?

I am not advocating filling 80/20 with EG for vertical or suspended horizontal members, but I am confused as to why it couldn't help make a stiffer base than a small quantity of extrusion alone.

[JerryFlyGuy]

Digits, your entirely correct. If you are using a 80/20 mill already and just want to stiffen it up a 'bit', this is the way to do it. If you want to increase the stiffness ten-fold then thats where the stiffness of E/g would come into question and some engineering would be needed.

Some will say its symatic's but have you ever been asked about the fly on a lathe? If a fly lands on the ways of a 12 x 60 lathe, do the ways deflect?
Sure it does, it's immeasurable but it has to, to bear the weight [ I can't remember which law that is]. What's more important is, does this deflection effect your needed parts tolerance's. I'm sure everyone would say NO! But the point being is, what is acceptable deflect for your situation, may not be for the guy doing diamond grinding. We have to all look at these things in an objective perspective. Each person's situation and use of this type of contruction is going to be different. And acceptable results for some, won't be for others. [ Just ask "NC Cam's" about using cheap roller bearings on a 'precision mill' ]

Jerry [got the drive assemblies on my mill last night. I love progress!]

[Mcgyver]

OK, I'm confused! If I had an 80/20 base frame with adequate stiffness in the extrusion to not deflect significantly under the cutting loads and its own mass, wouldn't the vertical deflection be even less if it were simply sitting on a slab of EG?
.

i don't want to try to give a lesson in engineering cuz I'm not qualified, but Ill try to explain where i was coming from. basically it's is the modulus of elasticity of different materials. EG isn't very stiff compared to steel, it deflects more under a given load. its modulus is 1/6 that of steel.

To make the point, Ill exaggerate....suppose that instead of EG, you used balsa wood...would the balsa make the machine stiffer? actually yes, but not to any practical level because the modulus for balsa is very small - it has no stiffness to speak of in this context.

of course that's a ridiculous example, we can all guess that EG is stiffer than balsa. but how much more? and how much in comparison to say steel or even the 80/20 AL? no one was addressing this, yet comments suggested that all of a sudden by adding EG to the structure, it became stiff. fact is its not very stiff. better than balsa, but a lot less than steel or even AL

OKI am not advocating filling 80/20 with EG for vertical or suspended horizontal members, but I am confused as to why it couldn't help make a stiffer base than a small quantity of extrusion alone.

It would make it stiffer - the section is increase and EG does have some stiffness. But the balsa wood would also make it stiffer (in some infinitesimally small way), it's just that it is a poor choice of material if stiffness (vs say vibration dampening) is the objective (or expectation)! with a low Young's modulus you have to use a lot more it than a material like steel with a high modulus.

The question really should be how much stiffer - what is your objective over how stiff plain 80/20 is. Let say "really stiff" means 4x stiffer than plain 80/20. How are you going to get 4x with a material with a low modulus of elasticity? only one way, use a lot of it. and thats' ok if you are balancing various other attributes of the material to arrive at an overall optimal design...obviously very successful machines have been made with it.....my point is that it will lead to an expensive paper weight if its just assumed the machine will be stiff because its EG.

I'm not an engineer, but with a Young's modulus of 1/6 that of steel, it doesn't look like a very effective material to reduce deflection (stiffness) and I'd want to see or do the calculations before before I built something (big and expensive) with the expectation EG was going to make it stiff. still a great material that I want to use in a machine, just want us to avoid assigning it properties it might not have

it would make a great science fair project, cast up a `1" section and with an indicator measure its deflection with an indicator when loaded between two points compared to Steel, AL, etc

[digits]

Thanks guys - I think I get it now.

A quick Google got me some Young's moduli which I think make some interesting reading:

Aluminium ~ 70 GPa
Steel ~ 200 GPa
Cast Iron ~ 120 GPa
Concrete ~ 20 GPa

So if E/G is about 1/6 that of steel, I guess we're looking at about 35GPa - half of the 80/20 frame's stiffness!

What that also suggests to me is that simply embedding two 80/20 rails to support linear rails in a block of E/G without connecting them with more 80/20 to keep them parallel is potentially far worse than just an 80/20 frame on its own.

What I can't quantify though is how much stiffness an 80/20 structure loses by being jointed rather than welded. Perhaps the overall stiffness is a lot closer to that of E/G?

I also think it is interesting to see how aluminium compares to Cast Iron - if you could afford it, it looks like you could have a cast aluminium machine that was just as stiff as a cast-iron one but contained twice as much metal and yet was still 30% lighter!

[lgalla]

HeY Atenman1
40gals $2200 19cuft sand and aggregates 48ft4"X4"W I beams.
weight more like 4200lbs Yes I have a forklift.
I have stated before I am lousy at computer stuff.
Can someone search Google moldmaking technology secrets to hard milling.
Good stuff here.I want to know what the machine is.Could someone post a link
Larry

[fyffe555]

So if E/G is about 1/6 that of steel, I guess we're looking at about 35GPa - half of the 80/20 frame's stiffness!

Not quite, you're comparing apples and pears here. Can't compare a generic piece of E/G with a 80/20 frame directly. Youngs is a modulus not a measure. Mcgyver gave a good description but the Stiffness of a piece of material is a function of its Youngs modulus AND its cross section area AND how far that cross section is from the centre of effort (or neutral line depending on where you went to school). The measure of cross section area and distance of area from centre is the Moment of Inertia. To calculate the stiffness of a material you need to know the Y modulus and the MOI and know the load it's subjected to.

There're various simple formulas to calculate deflection, deformation or yield of any material and load. If you're dealing with two different materials in composite you can just assume there's no movement between the two and calculate each seperately and use the sum as your deflection.

What that also suggests to me is that simply embedding two 80/20 rails to support linear rails in a block of E/G without connecting them with more 80/20 to keep them parallel is potentially far worse than just an 80/20 frame on its own.

Only if the MOI of the E/G is less than 2x the MOI of the extrusion. In practicality the E/G would be many times that and so stronger. But E/G isn't a particularly strong material but its mass adds a lot of benefit to the picture too..

What I can't quantify though is how much stiffness an 80/20 structure loses by being jointed rather than welded. Perhaps the overall stiffness is a lot closer to that of E/G?

For all intents and purposes they are the same. Applied according to 80/20's rules the bolted/jointed might actually be stronger as it involves more material and at greater leverages so spreading the loads wider than a simple welded joint.

I also think it is interesting to see how aluminium compares to Cast Iron - if you could afford it, it looks like you could have a cast aluminium machine that was just as stiff as a cast-iron one but contained twice as much metal and yet was still 30% lighter!

Yes and no. Overall the AL. structure would be twice the volume, 30% lighter and as strong, which is why it's used in aircraft. Under high loads the elastic modulus and yield strengths come into play and AL will locally elastically deform or yield at much lower loads than CI.

Larry's suggestions ( Hi Larry!) are well thought out.

I'd suggest considering how the bearings are attached and the loads. If you're dealing with lower loads, ie cutting wood, then an 80/20 support for a linear bearing would work ok, but the weak point is now the 80/20 extrustion. If you want higher loads you should consider mounting steel rail supports into the E/G.

Fun subject,,,

Andrew