[vger]

How about rotating the frame 90 degrees...And pouring epoxy into a small jig to create a master rail ??

Great idea. And just rotate it back 180º to do the other side and you have two parallel L's to set your rails against.

Steve

[ger21]

Just found this machine on ebay and saw they used granite blocks for the rail mounts. Just thought it might be of interest.

http://cgi.ebay.com/cnc-system-servo...QQcmdZViewItem

Steve

You could probably get some 3cm thick granite strips from a countertop shop for pretty cheap, and it should be flat enough to mount the rails to for a wood router. Bond the granite strips to your base, or mold them in, drill them and epoxy threaded inserts in.

[ger21]

Great idea. And just rotate it back 180º to do the other side and you have two parallel L's to set your rails against.

Steve

Provided you can rotate it exactly 90°. You're rotational axis would have to be perfectly in line with both faces. You're using gravity to pour flat faces and take alignment problems out of the picture. Rotating it brings them back in.

[BobWarfield]

Uhm.. I've been thinking again.... (chair) (Geof, please put the chair down ).

Leveling the frame with epoxy solves only part of the problem... You still need those pesky 'centerlines' for mounting of linear rails.


How about rotating the frame 90 degrees...And pouring epoxy into a small jig to create a master rail ??



(assuming that frame is totally rigid and you're able to set it at 90 degrees..) What do you guys think?

I see a couple of problems here in addition to what Geof has mentioned.

First, you are showing two pieces, but the piece that is taking the mounting inserts for the rail has them really close to the edge. That's not a happy thing for this material in my understanding--you'd want the fastener inserts away from that edge.

Second, let's assume you contrive a way to pour it as one piece to avoid the first problem. Now the shoulder height (or width when turned 90 degrees) is pretty narrow. I would be concerned that surface tension would warp such a narrow face rather than having it be perfectly straight like a much bigger surface would be.

Seems like you wind up needing to cast the shoulder with a mold that is true, and perhaps doing that in sections rather than at one sitting. Alternatively, you could dispense with the shoulder, and focus on getting the embedded inserts for the rail fasteners exactly true. This can be done by mounting them on threads, adjusting them until true, then locking it all down and pouring in the epoxy granite to set with them in their proper place.

[walter]

Thanks for the input Bob. I'll keep refining the model...
My willingness to go unorthodox ways is always present

[WilliamD]

OK, I have ordered the Epoxy, I got some quart amounts of varying ratios, so we'll see how hard the fast set, and slow set end up. Plus, being able to mix will be another test. I could also use my wife's new KitchenAid for small batches! LOL.

It will take about a week to get here. I'm going to go hunting for some aggregate now, and make some molds. I have some 1/4" plate glass I'm going to support and use as the mold surface. I'll need to check on how flat it really is.

So, I'll check back in another week.

[walter]

Are you going to do it in layers or 'all at once'?

Larry mentioned somewhere that this could be done in layers...

Good luck and keep us posted!

[WilliamD]

I will definetly try layers, as some of the stuff I want to build would be pretty big. I have already started modeling up something that I could build to vibrate the table. Basically a motor with a pulley, turning something that's off center. I will be taking a TON of pictures of everything. A lot for me will depend on the consistency of the material. With a 10:1 mix of Aggregate to epoxy, I can't imagine it "flowing" very well. Definetly not like a "pour," more like a mush I'll pack in the mold. I don't know, we'll see. I will definetly start a new thread, and take any and every suggestion when the project starts.

[lgalla]

William
I don't know or remember why,but plate glass is not a good mold material.
Glass is not as smooth as you may beleive.Ithink it is full of micro pores which will cause bonding of the epoxy.I would assume release agents would work,but I am not sure.I think its coming back to me now.I tried a glass bowl as a mold and it stuck.My resin supplier said "are U stupid epoxy sticks to glass because of the pores.Maybe someone else knows why.If glass was a good mold,everyone would use it.Don't take my word for it try an experement first.
Larry

[Eson]

You must have mold wax or some other kind of release coating. You supplier should have it too.

[WilliamD]

Yes, I was definetly going to coat it with something. I have furniture paste wax, and was going to use that first. I don't know if that will work really well. I will look around for some verified release agents.

[lgalla]

William glad to see someone ready to experement.DO NOT use furniture wax as it cannot take the exotherm heat.Buy mold wax such as Maguires and read the directions.
Larry

[vacpress]

i know a professional italian, old school absurd insane mold maker... not engineering.. model making and sculpture.


one of his big secrets is a huge glass countertop he works on... he said it is 'lab grade'...

[vacpress]

after reading a bit of the thread i noticed a concern about air bubbles durring curring... for silicone and other molds i have used a vacuum chamber. it is less effort than it sounds, and watching all the bubbles magically come out of the liquid material is nice. especially if you have ever made a nice silicone or latex mold just to find an airbubble!

-robert

[the4thseal]

what kind of temperatures are we talking about during the curing process?

[WilliamD]

I found some Maguire's stuff on ebay, but what kind of temps are we talking here? They have wax for high temp, and low temp. It explains the low temp offers better seperation and release, but if I have to have the high temp, I have to have the high temp. Any suggestions?

[Eson]

The temperature is diffrent depending on how massive the layer is. Thicker layer means higher temp. Also the temperature will be diffrent in the core and the mold wall.

[WilliamD]

It might just come down to experimenting, but how thick is a "thick" layer? Are there any kind of equations, or guidlines? Maybe only so many cubic inches at a time?

[lgalla]

William epoxy exotherm can vary between 100 to 200 degrees Generally slow epoxy is low exotherm fast is high exotherm.High volume of fillers decreases the temperature.I would first try 1"thick and if the cure time was very long,try 2"on the next pour.4"all in one pour would need low exotherm epoxy.Since we are hobyists we do not need rapid turn over times and can take our time with slower cures and thinner pours.Air release would be easier in thinner layers.
Larry

[ger21]

For reference, a few weeks ago I mixed up about 1/2" of West System epoxy in a 32oz paint mixing cup. Within 20 minutes it was hard and too hot to hold in my hand. But when brushed on some MDF it took about 8 hours to cure.