[Zathras]

Love the idea of E/G homebuild but I can only see one method I'm going to get flat surfaces for my THK rails. The self-leveling Epoxy method does not yield a flat surface by any means. At least not the Epoxy I have tried here in Oz.

The way I'm considering casting the rail surfaces is against a Granite surface plate (protected by thin Mylar) using inserts. See pic for general arrangement
I can only think of using some wax/hot glue to temp seal the thread from Epoxy.
This will be rather laborious and maybe risky.

Only other way is to have similar arrangement with long steel rails but I cannot machine 840mm rails. I may need to do a RFQ to see if it's worth doing.

Anyone tried a similar approach, ideas/comments?

[rowbare]

Have you looked through: http://www.cnczone.com/forums/epoxy_...es_thread.html

There is a reference to a German build thread on another forum. I believe they used melamine for the forms though I think they potted in some metal rails for mounting. You could get some ground flat stock and start from that: Bohler-Uddeholm Australia - Ground Flat Stock

Remember that things don't have to be perfect right out of the mold since you can inject some epoxy under the rails at installation time or grind and scrape the surface to spec.

bob

[Zathras]

Bob,

Thanks for the stock link in Oz.
I have seen the post and have considered flat stock but I thought it was too hard to scrape it like iron or bright mild steel for seating rails. Is that not the case?
I also did not expect that malamine was anywhere flat enough for rails, which could be fixed but the only Epoxy I'm aware of that is used for rails is the Moglice product which is expensive (I think).

-Mark

[Kazik_Wichura]

Hi,

I made last days some epoxy granite table for test. I used plywood as a form, and Ericsson's nut as inserts. After removing form mold I have to grind a bit inserts. Now I can drive to it some metal flat and to it some rail.
Next time I will try to made metal flat to be a part of the form. But it will be not easy to get two flats to be parallel when casting is done.

Lucas

[Zathras]

Hi Lucas,

Thanks for the link to your blog. I too was thinking of using some of these type of inserts with the laminated wood mold for the sides.
The problem of getting the two rails flat and parallel is why I need, am trying to use a surface plate.
Two ways to do it is using inserts like you did or make rails with drilled and tapped screws along the length. The problem is I cannot make long rails so have to use inserts.
So I think if I use enough pressure against the surface flate, it will seal the insert threads from the epoxy .... I hope.
The sides of the wood mold against the surface plate will be sealed with sealant like Silastic or some kind of putty.

-Mark

[RomanLini]

Surface grinding is a very common and cheap procedure used for auto cyclinder heads and other big slabs of metal. It might just be easier to leave some metal hanging out and get it ground later. Just bear in mind it will be ground wet, with a water+oil lubricant.

[Zathras]

RomanLini,

True, I have no idea how much grinding costs. I did assume it would be expensive for rails that are 833mm long and mounted on a 70kg(?) 800x900mm block. Not sure if a lot of grinders have that size capacity. I don't know if anyone would do it so maybe I need an RFQ or some ball park figure from someone.
Alternatively I am thinking of just having the mounting rails ground/fly cut out of bright mild steel and casting them face down.


-Mark

[Well_Armed]

Mark, I think your idea of using pre-ground and truly coplanar and flat railing bed inserts placed face down in the mold is the best solution if you are trying to avoid post-production grinding. A tooling jig could also be designed to pre-align the railing beds to be perfectly equidistant (parallel) to each other over their entire distance. Avoiding post-moulding processing such as grinding, or grout-and-place-then-align after molding is a tricky endeavor that I have been trying to think through lately. My latest idea is to use a very flat piece of 1" thick Mic-6 aluminum plate with milled datums for each rail, flip it upside down so it is at bottom of mold, then pour over that. What I'm trying to work around is the possibility for deflection in that Mic-6 plate due to the weight of the casting poured on top. I would not be using a surfacing plate to use as a casting table base so premachining this rail-mounting plate with datums or recesses for the rails will leave pockets in the plate. It will not be perfectly flat on both sides, laying against a perfectly flat surface of an inspection plate. I'm still trying to think of a solution.

[CaptainVee]

@Kazik,
I read the first page on your blog, very nice stuff there.

I noticed that you use silicone spray as a release agent.

I guess it is a very good release agent, which is why SILICONE RELEASE AGENT SHOULD NEVER BE USED.
The mist goes everywhere and prevents stuff from adhering to epoxy or other glues for ever.

Any residue can not be removed, not even by sanding.