[Juditolleson]

great that you got the answers. You can also learn more knowledge about CNC at https://www.bbqpp.com

[peteeng]

Hi CBF - That depends:
1) If you need to assemble the connection and align it and then set it, you would use liquid epoxy. You align the joint make a plasticine dam (or tape or epoxy putty edges) then fill with liquid epoxy. You need to plan a suitable hole or galley at the top of the connection plus a breather
2) if you can align the connection and its self aligning or can be pulled down then reassembled as self aligning then you can use putty.

Peter

Heres a company that can help... they have a distributer in New Jersey
www.prosetepoxy.com

https://www.prosetepoxy.com/standard...bly-adhesives/ putties

https://www.prosetepoxy.com/standard...usion-epoxies/ thin epoxies. I use infusion epoxies because they flow really well

[peteeng]

Hi CBF et al - This may interest yuz - Peter

https://www.scribd.com/document/2466...nical-Accuracy

[peteeng]

Hi CBF et al - I have spoken to the local Sika tech via email and Sikagrout 212 has a compressive E=22GPa plus. He has no tensile or flexural modulus. He agrees adding a good proportion of blue metal aggregate will increase the modulus. Most of my research says this will get to 40GPa. Add enough to the grout but keep it pourable. I'll look up a ratio. Peter

[ChipsBFlyin]

Pete,

Moore's book is great, I've read it years ago but will read it again, I am sure I will come in handy. Thanks for looking up a ratio. I'll come up with some CAD models to demonstrate how I plan on potentially bolting it together.

I do have one question, how does it differ using epoxy here than using it for using it for leveling linear rails? Wouldn't the epoxy joint be the weakest part of my assembly then, since its still under compression?

[ardenum]

Pete,

Moore's book is great, I've read it years ago but will read it again, I am sure I will come in handy. Thanks for looking up a ratio. I'll come up with some CAD models to demonstrate how I plan on potentially bolting it together.

I do have one question, how does it differ using epoxy here than using it for using it for leveling linear rails? Wouldn't the epoxy joint be the weakest part of my assembly then, since its still under compression?

you wanna do it with moglice or a modern equivalent, you align it with screws and setscrews then inject it in between the mating surfaces.

http://manuals.chudov.com/Moglice-Ep...n-Handbook.pdf

[peteeng]

Hi all- Ard thanks for the moglice book. Covers most stuff needed. CDF - levelling epoxy needs to be about 6mm thick to self level. Under that thickness its viscosity (which is very low to enable it to self level) and surface tension and differential curing will not allow it to self level. Epoxies have a modulus of about 3 to 4GPa this is effectively rubber. When you pull a rail down on this sort of surface it will turn into a wave, low at bolts high in between (undesirable). When you use epoxy to set things together the gap is much smaller ideally very small. Moglice has a modulus of around 9 GPa so is a bit stiffer then most. It will have glass microballoons or metal powder added to achieve this. I use aluminium powder sometimes for various jobs, I also have 2mm steel fibres that work well. The surface areas in machine elements are very large and the preloads in this sort of thing are very small so the epoxy does not squish much . Not like the linear rail case. Look at the Moglice doc and you will get the drift. I have modelled this in other threads to illustrate what happens.

The important thing in a connection is its faying surfaces not the preload. You can do up the bolts as hard as you like but this does not make the joint any stiffer. Epoxy maximises the contact surfaces without excess preload.

You can cast precision surfaces off your surface plate if you wish. Just use lots of wax. And remember if you do cast off your plate that the created surface is under vacuum so it will require considerable force to break the bondline. This is best done in shear or warm the part to soften the wax. I had a mould modified once and It was used for vacuum casting. The insert had frozen to the mould and they had decided to go back to the original design. The insert had been waxed in but under vacuum it had frozen itself in. The toolroom had removed all the screws and spent two days trying to get it out. Since I designed it they said get over here and get it out yourself! So I arrived and I got out my heat gun and patiently warmed it and in about 15 mins it "poped" they were staggered... Maybe a liquid agent like silicon or oils would be better on your granite they don't have the mechanical grip that a wax does. Maybe not use your granite Peter

[peteeng]

Hi CBF - I have looked a few datasheets and my tests. Typical addition rates of aggregate to grout are 50% by weight ie 1kg grout to 1kg of aggregate. I have added up to 180% ALOX by weight and its pourable. But alox is denser then granite. This worked out to 50% by volume addition. I expect 50% by volume granite is doable as well. Granite is about 2600kg/m3 and the grout is 2200kg.m3 so similar density... so volume fractions similar to weight fractions... alox has 3.4-4.0 relative density so is dense. but a small scale test will find the max ratio that is pourable. Mix the grout then add the aggregate if done in mechanical mixer... or add aggregate layer to mould pour in grout around it add more agg pour etc. Peter

[ChipsBFlyin]

ardenum,

Thank you for the Moglice book.


Pete,

Thank you for that explanation and clarifying the difference for the epoxy application. Attached you will find the joint that I plan to use for the castings, I plan on having these joint molds machined on a cnc router, maybe out of foam? This way I can control their size, taper and consistency better vs me trying to make them by hand. I hope this reduces the amount of error in the mating surfaces and the amount of epoxy/moglice needed.

Should I be using rebar inside of these castings?

I don't think I plan on casting anything off my surface plate. I think I plan on using steel inserts into the UHPC, then machine them after.

Please note the models shown in the pictures are only for joint illustration, actual castings may differ. I plan on bolting the castings together and filling any gaps in the joints with epoxy/moglice.

[ardenum]

Should I be using rebar inside of these castings?

No, that would be detrimental. You can make the inserts longer and even bend them into L shapes if you must.

[peteeng]

Morning CBF - 1) I would not use a reinforcing steel cage in the cast. I would consider using steel or fibreglass fibres though. The aim is to make a homogenous mass. Reo will create preferred loadpaths thru the structure (steel 200GPa grout 22GPa) 2) I would not use the tenon. I would just land the base on the ledges. I'd have thru bolts to pull the surfaces together where your tenons are. Having that many faying surfaces and tapers would be very difficult to have it come together correctly. Cast iron machines have simple flat surfaces with a few bolts at connections you need to be the same. Plus the construction logic has to be like a pyramid. Each element has to be able to be craned on vertically and set. Heavy parts are difficult to manage if they have to be translated and lifted/"settled down". I was going to say dropped but that's a bad thing.... Peter even with the ledge the joint has to be brought together this means the feet need to translate under load. Big machine parts are "stacked" each piece is placed, aligned then locked down. Ready for the next piece to be placed so at each step the "below" parts are correct allowing the above parts to be aligned... does that make sense? Peter

[ardenum]

Go through Peter's millie thread, there's a lot to read but we've covered a lot of stuff over the years there. Especially valuable are the papers. There are pictures of how to do inserts too.

https://www.cnczone.com/forums/cnc-d...11248-cnc.html

[peteeng]

Hi CBF - Here's the assembly of a large gantry mill. Plus the casting of its bed. Peter

https://www.youtube.com/watch?v=q7lio5V6PsY

[peteeng]

Hi CBF - Here's a good video of a small Makino with lots of good data. Its gantry is really big and the walls are connected together at the rear top where the gantry dead space is. Also it has a triangular gantry. In my modelling all the triangular gantries do very well... Peter

https://www.makino.com/en-us/resourc...t-introduction

[mactec54]

you wanna do it with moglice or a modern equivalent, you align it with screws and setscrews then inject it in between the mating surfaces.

http://manuals.chudov.com/Moglice-Ep...n-Handbook.pdf

It's still a soft flexible joint done like that, Moglice is only a shore 90 so about as hard as boot leather

[ardenum]

It's still a soft flexible joint done like that, Moglice is only a shore 90 so about as hard as boot leather

is there a better method/product?

[mactec54]

is there a better method/product?

No, epoxy is what it is, it's a soft flexible polymer, some formulations it can be hard and brittle or soft and flexible

A better method is to cast the main parts as one-piece, machine where needed and add the other parts

[ardenum]

No, epoxy is what it is, it's a soft flexible polymer, some formulations it can be hard and brittle or soft and flexible

A better method is to cast the main parts as one-piece, machine where needed and add the other parts

Right so that the only 'connections' in the frame between the parts are rails and carriages then...

[ChipsBFlyin]

Pete,

I do like that Makino machine design. I'll see how I can incorporate some of that into my design.

So after spending some time rethinking this project, I think this may be the only way I will be able to bolt it together without the use of epoxy or any other filler. I think I can lap the column and the base, and hopefully I am be able to get good mating surfaces. Current approximate weight of the castings 2.5 tons, here is my revised base casting:

[peteeng]

Hi CBF - I think the design is settling down to a good spot. How are you going to manage to flip a 2T casting? I presume the base will be cast upside down? Peter