Osiervt's EG CNC build

[osiervt]

Here I have reached my stopping point for the evening. I hit a road block of sorts. When I went to cut the middle two notches on my stringers I found my table saw was going to be too small to do the work. As you can see the stringer hangs off both sides leaving no room for a fence. Without a fence I could mark it and line up the cuts by eye. My fear with this is the notches cut in this manner would not line up perfectly. I tried to use a scrap piece of wood clamped to the table top that would align with the first notch i made but because of the design of the table top I have been unable to secure a piece well enough to remain accurate. So I figure I will sleep on it and see if I can think of a better way to do this with the equipment I have.

[osiervt]

I solved my fence issue. A couple of clamps some scrap wood and a screw and all my problems are solved. Even note the fine adjustment screw. Call it ingenuity or a cob job, either way it worked.

[osiervt]

After finishing off the stringers I dry fit every thing to get an idea of how every thing will fit and what my final product will look like. After this dry fit I pulled every thing back apart. I need to rout out two more sections at the top to fit the metal plates that I will mount the lateral rails to. I will have to make a new sketchup model to show my revised plans.

[osiervt]

As promised here is my new idea for mounting my rail. I will use my THK rails on my Y axis opting for the CNCRouterParts.com linear bearings for my X axis as I think these will be easier to adjust. This is the reverse of my first plans.
You can see in the picture how I plan to clamp them all together before my EQ pour making the mounting bolts and metal reinforcement bonded to the epoxy mix as one unit. I plan on going to get my metal on Saturday. Any comments or suggestions on this design before I go buy my materials are appreciated.

[RomanLini]

Suggestions?

Drill some long holes through all your plywood, and insert some large (5/8" ?) steel reo (concrete reinforcing bar). That will mechanically couple all the epoxy granite compartments.

[ckelloug]

Hi osiervt,

Your build is looking fabulous.

One question I have is about that 2 inch square tube. I take it that the 1/4 inch plate is being bolted to that tube and the bearing will mount on the narrow top of this plate. If I understand your drawing right, I think this defeats the purpose of your beautiful work making a stable base.

If you will be resting the weight of the gantry and spindle on this tube via the bolted connections, I think you will unnecessarily amplify the vibrations in your structure. That tube will have a much higher resonance that the huge E/G structure and will deform by shear under those loading conditions. As a result, I think this suggests you will have a very stable base with a vibrating gantry that might not have a very stable z position due to varying loadings as the gantry moves. This is why the MIT paper suggests embedding the plate for the mounting directly into the E/G rail. Filling the square tube with E/G might help a fair amount on the shear deflection and vibration. Using a solid piece rather than the tube and keeping the thickness as small as practical would also help.

Without doing a finite element analysis, I can't tell you what the magnitude of the static deflection and the vibrations will be. All that I can say with confidence without the analysis is that this design with the tube isn't the minimum vibration way of doing it. If it were me at this stage, I would replace the tube with a section of 1/4 to 3/4 inch plate if I could live with the smaller spacing between the E/G rail and the bearing mount.

At any rate, I hope this is helpful and congratulations on building such a nice looking machine.

Regards,

Cameron

[osiervt]

Cameron you have a way with your points that make a man feel guilty about doing something the easy way instead of the best way. I thought that is was my wife’s job... Im going to have to sit and think of a way to get my two rail ways perfectly in plane and level without spending a ton. If I can figure that out I will do it the right way. I know if I don’t I will end up kicking myself... I don’t know that the tube and rail would have a huge effect as CarveOne has been using them for a while with seemingly no complaints (at least with that part of his machine. But I have the THK rails and am going to have to admit they are probably the best solution, if not the easiest.

[ckelloug]

I'll try and get some numbers for what the effects of the tube might be now that it's after business hours and I can close the stuff I was working on in Linux and boot windows to run NEI Fusion and do a somewhat proper analysis.

I've spent almost 4 years studying how to make E/G and use it in machines. I certainly wasn't trying to guilt trip you, I was just commenting on design principles I've been exposed to in my research.

Regards,

Cameron

[CarveOne]

Cameron you have a way with your points that make a man feel guilty about doing something the easy way instead of the best way. I thought that is was my wife’s job... Im going to have to sit and think of a way to get my two rail ways perfectly in plane and level without spending a ton. If I can figure that out I will do it the right way. I know if I don’t I will end up kicking myself... I don’t know that the tube and rail would have a huge effect as CarveOne has been using them for a while with seemingly no complaints (at least with that part of his machine. But I have the THK rails and am going to have to admit they are probably the best solution, if not the easiest.

My box tubes are 1/8" thick walls and they have been the least of my problems, however, for this application I would recommend using 3/16" thick or even 1/4" thick tubing for the extra rigidity that would be more in keeping with the concrete base idea. This is going to be a nice machine.

CarveOne

[osiervt]

Dont read in to the guilt the guilt trip comment to bad if any thing it was meant as a complement keeping me on the track for a great machine. If I didn't know you were right about creating the weak link in the machine I wouldn't have gone back to trying figure out how to make the embedded rails for the THK's true across the span. Once I get going I want to finish things up taking short cuts like I was thinking of doing here. And in the end I always regret it.

The tubes I was looking at where 3/16 I think but even if I used 1/4 thick tubing as Carveone suggested it wouldn't be as good as an solid metal bed. I'm still of the thought that the tube and rail version would be more than sufficient for my needs, but I'm going this far with it I might as well go as far as I can practically go.

[Khalid]

Very nice

[CarveOne]

Why not mount the rail on top, horizontally? Mounting the gantry will be much easier that way. Your concrete appears to be about 4" thick. You will need 1" of clearance vertically and horizontally for the carriages. Embed a steel plate in the concrete and shape the concrete like this. _----_

A box tube would also work. To get a truly flat surface on the box tube for the rail you may want to skim the box tube surface flat in a milling machine with a face mill. Having the top surfaces flat will help you keep everything clamped true while your concrete sets up.

CarveOne