[made2hack]

Thanks Goemon for all the information. I will shortly cast some moulds and test out your ideas. Although, unfortunately I was planing to pour in the garage, but it is not heated, so I might just build the moulds there and pour inside.

I don't have any bar top resin, I'm using a 2:1 epoxy resin used for industrial flooring, the idea being to mix it with a suitable aggregate for a resistant floor. However, it is workable to 40 minutes and the viscosity is similar to that of other well flowing resins.

I still have to pick up some mould release wax and pva.

Do you know what kind of inserts people use for screws? I'm thinking of trying a few options such as hex nuts, concrete inserts, etc.

[Goemon]

Thanks Goemon for all the information. I will shortly cast some moulds and test out your ideas. Although, unfortunately I was planing to pour in the garage, but it is not heated, so I might just build the moulds there and pour inside.

I don't have any bar top resin, I'm using a 2:1 epoxy resin used for industrial flooring, the idea being to mix it with a suitable aggregate for a resistant floor. However, it is workable to 40 minutes and the viscosity is similar to that of other well flowing resins.

I still have to pick up some mould release wax and pva.

Do you know what kind of inserts people use for screws? I'm thinking of trying a few options such as hex nuts, concrete inserts, etc.

I don't bother with any inserts for screws for this type of thing. If I was making something for multiple uses then I would put more effort into the mold structure but for single use, the screws go straight into the wood using a power drill. The only thought that goes into the screws is to make sure they are shorter than the wood is thick. If they go all the way through the wood then you'd never get them out again.

I'd be careful about substituting a good bartop for any old epoxy. They might seem similar but they aren't. They won't all produce a flat bubble free surface. It is worth investing in a decent bartop for this (there are plenty of poor quality bar tips that should also be avoided).

Also, don't assume that super low viscosity equals greater flatness or less trapped air bubbles. It doesn't usually work like that. Some of the best resins I have (and I have a lot on my shelf) start out relatively thick. What matters is how they cure and release gases.

[made2hack]

[QUOTE=Goemon;2134222]I don't bother with any inserts for screws for this type of thing. If I was making something for multiple uses then I would put more effort into the mold structure but for single use, the screws go straight into the wood using a power drill. The only thought that goes into the screws is to make sure they are shorter than the wood is thick. If they go all the way through the wood then you'd never get them out again.[QUOTE]

Hi Goemon,

I'm not sure how this would work. I've attached an image as to what I want to achieve. A linear rail that is screwed down to the epoxy / granite base. Does the epoxy granite mix not need screw inserts ? Otherwise, how do I screw the rail to the base?

Thanks,

[rocketflier]

Anchor a steel bar in the epoxy that the rail mounts to.

Attachment 383564

Lot more detail photos in this thread:
http://www.cnczone.com/forums/epoxy-...52784-cnc.html

[made2hack]

Anchor a steel bar in the epoxy that the rail mounts to.



Lot more detail photos in this thread:
http://www.cnczone.com/forums/epoxy-...52784-cnc.html

Ok, are those bolts there to anchor the steel bars themselves? And, on the flip side, are the steel bars drilled and threaded? My concern is that an M6 or M8 scren (as per DIN 912) has anywhere from 24mm - 28mm thread length. So, my rail will not be threaded, it will simply have a through hole, the steel bars underneath (or whatever insert I have) has to allow at least 24 - 28mm thread, or if anything, allow the screws to go through.

Or do I have to make my rail also threaded, so that some of the thread is "above ground" and some beneath, so to speak?

[Goemon]

[QUOTE=made2hack;2135894][QUOTE=Goemon;2134222]I don't bother with any inserts for screws for this type of thing. If I was making something for multiple uses then I would put more effort into the mold structure but for single use, the screws go straight into the wood using a power drill. The only thought that goes into the screws is to make sure they are shorter than the wood is thick. If they go all the way through the wood then you'd never get them out again.

Hi Goemon,

I'm not sure how this would work. I've attached an image as to what I want to achieve. A linear rail that is screwed down to the epoxy / granite base. Does the epoxy granite mix not need screw inserts ? Otherwise, how do I screw the rail to the base?

Thanks,

I was talking about the mold, not the gantry itself. For attaching linear rails (or anything else) to the gantry it's as Rocketflier suggested. You need to add steel or aluminum plates (buried under the epoxy granite mix) to allow you to drill and tap mounting holes.

In my case, I have two tool steel bars under the mounting surface which can be drilled and tapped. I chose tool steel because of it's high hardness but I regret that decision. Regular steel would have been fine and far easier to drill. Tool steel adds no stiffness or anything like that.


I am not mounting my rails directly to the gantry surface. I have a precision flat tooling plate that is being mounted to the gantry surface and this plate will hold the rails. This will allow be more opportunity for fine adjustments / squaring if needed. It's also a lot easier to drill a tool plate on my drill press than a gantry I can't lift.


I have a second tooling plate which will be mounted to back of the gantry. I have long bolts that will go through the surface plate, into the embedded tool steel bars buried in the epoxy granite, through the gantry and into the tooling plate at the back to clamp everything in place. I believe this design offers maximum strength and prevents the embedded steel bars from being ripped out of the epoxy granite under a heavy load.


It might sound like over-kill but.... if anything is going to let down an epoxy granite structure, it is the low surface hardness in comparison to iron and steel. I want to prevent the mounting screws from moving after repeated stress.

Forget trying to mount screws directly in epoxy. There are no inserts that solve the low hardness issue.


The only other thing I would say on this topic is that my embedded tool steel bars are 3/8" thick which I now think is too thin. If I was buying them again, I would have looked for at least 1/2" of threading depth.