Greybeard's Epoxy/Aggregate cnc router

[greybeard]

Having spent some considerable time in CorelDraw producing endless designs for a cnc router, the possibilities of this new composite material have finally given me the impetus to start constructing. So I dedicate this thread to all the others too numerous to mention individually, who have contributed to the Epoxy/Granite thread.

This thread will be edited and updated as I go, but I hope the final result might be a useful starting point for any others. I shall try to incorporate as many of the crazy ideas I've had since first discovering the cnc world, and offer them freely to the community for use or adaption, on the understanding that I incur no liability in any way of form for what your results are.

The constraints that I work with are a lack of precision(or even accurate) tools, and a lack of all but modest finances. Counterbalancing this are a few useful bargains acquired from ebay over the last two years, and an undiminished sense of the power of logic and the imagination.

My initial plan is to build a gantry mount for the router, with pressure rollers feeding the work through in the x axis, with the y travel 18"along the 24" gantry, and the vertical z travel to be 2".
The ways will be cast epoxy/aggregate (e/a), possibly with an embedded glass surface.

DIY built air bearings will be used, based on 10micron carbon block water filter material.
As yet untested, the idea is to slice up a cylindrical block filter, embed the shaped slices separately in epoxy so that individual bearings can be lined up against the epoxy ways.
With glass embedded in the surfaces, I have also considered seeing if the bearings will be self lapping as part of the set-up procedure.

Motion will be provided by three stepping motors, with M10 studding for the y axis, a ball screw for the z axis, and the x axis having a geared drive to the rollers. If the roller drive proves to be problematic, it will be replaced by a punched steel tape drive, yet another project on the drawing board.

With each posting, I hope to include a simplified drawing of the next piece to be made, plus a photo of the current stage of progress.

The first step is to equip the router body with castings to form the z truck. I'm using a cheap 1020watt unit on the principle that it's easily replaced when I finally burn it out, or if I want to change the format.
Although my prime interest in e/a is in using spin casting as a method of compacting the molding and thereby maximising the strength of the recipe, the z truck will be cast directly onto the body of the router. As this part will be subjected to mainly compressive forces, this seemed a reasonable thing to do in the circumstances, and I shall modify the recipe to flow more easily in the narrow confines of this particular mold.
Constructed of a simple timber frame supporting waxed impregnated mdf and polished glass, it's designed to give 10" long surfaces for >4" long air bearings.

I've tried to take the KISS approach to each stage of the design, but allowed a modification at each stage to overcome any inaccuracy.

Thus the two individual castings may be adjusted afterwards to line up with each other, but any surface inaccuracy in the e/a will be dealt with by embedding a glass layer on each face, if it proves necessary.

[jhudler]

Your idea of using carbon block water filter for air bearings is very interesting. Been wondering how to make a porous graphite material... all along I was throwing them out every 3 months... filters that is.

Don't know that I would experiment with self lapping, as this implies landing on the bed would cause damage to the pad surface. You'd need cam follower or something for the machine to settle on (not allowing the pads to touch the waybed) when not in-use or sudden loss of air pressure. You definitely want an air reservoir on machine.

Might look at router tables for ideas on mounting the router. I'm worried about effects of heat from the router on the epoxy. It tends to soften (great for the initial cure) however, after numerous cycles above glass transition temperature the polymer bonds start break down, weaken and the epoxy becomes brittle (someone from the EG group correct if I'm wrong on this it's been a while since I read this).
I have a router table with a precision lift on it, I can take some pictures of it for you.

Cheers!
Jack

[greybeard]

Hi Jack.
The possible thermal effects had crossed my mind, though I'd been thinking more of possible expansion causing distortion.
When I contacted the suppliers originally to ask about duty cycle, and they suggested it might only be 1 hour, I decided to install forced air cooling down through the unit.
I reckoned that I would use the same air flow to remove dust from the work area, so this might also be beneficial to keeping the casting temperature in a good zone.
Re the lapping idea. This was a bit of fancy on my part, I must admit, and the truck will almost certainly have safety rollers installed if the initial testing goes ok. But at this early stage I'm prepared to try anything.
John

[epineh]

Good to hear you are (finally) building yourself a router John , I will be interested in how the Epoxy base goes. I am thinking of building a large-ish router next and looking at different construction methods.

Russell.

[walter]

Good stuff, John. Watching with interest.

[greybeard]

Constructing the z truck mold has shown up some of the problems in designing with a 2d drawing program.
A cheap router with a plastic shell inevitably has irregularities in the shape that will not be carried over into measurements for the casting mold.
This shows up as problems in closing gaps between the plane and curved surfaces of various elements of the mold, and while it would be possible to construct complex shapes to fit those gaps, Plaster of Paris does the job a lot quicker.
Candle wax and a soldering iron quickly seals any surfaces that the plaster is to touch, and the same method will be used to seal against the epoxy when casting.
So the item labeled "wood spacer" will be replaced by "Plaster of Paris spacer".
Hopefully photo tomorrow.

[jhudler]

John,

A simple holder would be a V-shaped rest and the router held in place by large pipe clamps (or large adjustable hose clamps). I don't think the shell could handle the torque and vibration.

Jack

Here's my router table.

[greybeard]

Herewith the photo of the z truck mold. The glass panels that will form the top of the casting, omitted from this photo, will be fixed onto the sloping shoulders visible at each end.
They will come about 2/3 of the way up, leaving a pour gap at the top the full length of the casting.
Each side will be cast separately, needless to say.

The new shell becomes an integral part of the casing of the router, hopefully somewhat stronger than the existing shell, and runs from the metal shroud of the lower bearing to the cap, which will be the next casting to make.
This will brace the upper end, and form an anchor for the z-nut.

[harryn]

I am really interested to see how that works out. I have been toying with different ideas on how to mount a router, including inside of square tubing / UHMWPE slides. Since my project is going along about 1/10th speed, you will end up well ahead of me.

[greybeard]

Hi Harry.
As a slight aside to the present project, but what was part of my original train of thought that led to this design, was the idea of resurfacing angle iron by glueing glass strips onto the surface with epoxy. These could be used with uhmwpe or air slides. Probably not with skate wheels, though.
While the impact resistance of glass isn't wonderful, I reckoned that if I managed to smash it in normal use, I would have a serious problem, and nothing to do with the machine.

[andy_ck87028]

Hi this is a fascinating thread. I have no contribution to make at this point but am posting purely for selfish reasons so that I get an auto alert in yahoo as the thread develops.





Andy

[harryn]

Not too far from what you are attempting (I think anyway) is this project from precision epoxy. http://www.precisionepoxy.com/NPS%20plate.htm

In this project, they poured an epoxy surface plate, and it is used as one surface of a large air bearing.

While glass is quite smooth and flat, it is not usually as flat / level as these epoxy surface plates, at least in part because they contain agents to dramatically reduce the surface tension. (essentially surfactants).

I discussed the idea of using the same epoxy to level out a piece of angle with the precisions epoxy guys - seems like this is a fairly common thing to do in real life useage.

The down side, is that the epoxy surface is not very scratch resistant.