Quite an Unusual one

[Tinkerer]

Silvaski, sorry to hear you've hit this snag, particularly after your success on the first machine. In an ideal world Jimbo is right, playing with epoxy is a necessary evil, which is better suited to machining. I'm beginning to wander whether I should weld the top half of my frame with rail beams and investigate whether there are machining services around to do the levelling. Knowing my luck I will have wasted several export batches which could go towards machining cost! I'm sure, the cost and availability of this alternative would likely dissuade me from this. The problem is you need a machine to level it, and the irony is that once finished, the machine you have built may be able to perform the task at hand!

Certainly your post and experience make me Dolby cautious when I get to this stage.

[JAZZCNC]

Not enough bridges IMO. I've only ever done one machine near that size with epoxy and I had 5 bridges with 2 people pouring epoxy.

To late know for you but for others like tinkerman this is why I don't like epoxy for large machines and use the adjustable top rail beam then shim as needed.

[HipoPapi]

Don't go to hard an your self Boyan. I find your dam idea to be a great one. The only drawback is that you lose the connection between the two sides hence they become two separate world's. I will definitely use this dam technic and will try to use something as thin as a raiser blade. Maybe cut open some beer cans and make some stripes of it. I think a thicker dam material could introduce a small unwanted wave. And as you seem to be nuts with precision you won't want that. :)
Sorry for your second fail but thanks for sharing as it is informative. Now I know it requires 21 degrees Celsius and in my case I see a problem there. In fact it even gives me some confidence as the result you have achieved is better than what I aim for in my build do to the nature of application.
Good luck with your next pour tho, if you go for one.

[HipoPapi]

I don't think painting the bottoms would do the job if you try to fix it. But how about leaving the channel sides in place or put some new ones on and after you mount the rails you pour a bit more to fill the gaps. And probably paint them as well just to make sure it gets in there.

[Tinkerer]

Eddy this is what I have been considering. Cost again could be an issue. A naive question, but I presume the starting point for accuracy is clamping the two top rail beams upside down to an accurate level reference point (precision benchtop) and welding top down (upside down)? I'd imagine working the other way will cause significant misalignment. Is this what everyone has done? I understand it will not get to micron accuracy, but it would aid initial accuracy before contemplating need for machining / epoxy?

[JAZZCNC]

I've said it a 1000 times.!!! . . . Build in adjustabilty and between this, shimming and patience you will get the accuracy you require.!!
Most don't even know the accuracy they require and most are aiming far beyond there capabiltys to achive what they think the need.! When the reality is they don't need anywhere near the kind of accuracy they think they do.!! . . . . . For instance whats the point building a machine to 0.01mm accuracy for cutting woods that only need 0.1mm accuracy at best.?

Boyan if all you have is 0.15mm error over 3m length then I'd say your got it about as good as it gets with a single action. Now it's time to either shim or fill the low spot and scrape level. The important bit is that you know the 2 rails are on the same plane any surface discrepencys can be filled or shimmed out.
Look for epoxy putty and fill the low spot then scrape or sand it level checking with your straight edge.

IMO your expecting too much from epoxy over this length.!!

[jimbo_cnc]

Some sensible comments here, bringing us back to reality. Repair the dip, fill, shim, whatever.

What matters is the rail flatness, not the epoxy flatness.

[EddyCurrent]

That's what I did with mine, I used some 5 minute epoxy to correct a small dip and leveled back using a long straight edge. Once the rails are fitted it's going nowhere.
At the time it was referred to as, "a disaster", but that was wrong, it turned out fine.

[GEOFFREY]

I think that Boyan has already removed the epoxy. G.

[Boyan Silyavski]

Hi, i agree about the reality thing and all comments. So i could have shimmed it easily. However it would not be woodworking machine only or mainly... If this was woodworking machine only i would have finished it already.

As i said before, one of the main purposes of this machine will be to surface under the rails smaller machines + surface gantries and Z. I don't have a mill, no money for a mill or place, so have to be clever and have good CNC capable of doing similar jobs in aluminum. So basically this machine will cut mainly aluminum , plastic and when nothing to do - wood. It will have mounted plasma torch and removable water bed 100mm deep, something like 1 square meter, so i could plasma cut some small parts. Yeah, one of the things that i will do in the future is make small machines by order or at least the important parts for them.

Hence the precision desired, required or dreamed of :-)


Will not change the WS epoxy, now that i am deep in it, to say. Will order another B pack. One more try and then will shim if unsuccessful. But i have to know. Can i or not make 5x10 machine using this method. Thats the real question.

In other words i am having fun. Now that i know that i can shim it. Plus i know that if i waste a ton of epoxy and make 5 bridges or additional long parallel bridge in the middle and interconnect all it would work, cause will simulate 4 small machines cast together. But where is the fun or the excellence in doing it like this. I want to find how with minimum effort will make the best result, its difficult to explain.


See below. Thats how i am thinking of to make the next try. bridges both sides only, no middle. Steel, soldered when dry rails mounted then rests carefully cut by hand . 200mm extension, so if anything bad happens it will be there. Rails will suck this time from the bridge, not like before. 140mm reservoirs extension, i cant explain, seems right to me. ~2.5 - 2.8kg mix/ 40mm wide -45mm wide channel/ .

Previous pours showed that rails length seems don't impede flow at this width and depth/ 5-6mm/ so only 2 bridges both ends. In fact i am almost 100% sure that could be done only with one end bridge, all seems so right, but i don't want to experiment right now with this.

What do you think?







PS. about the frame

Yeah i am conscious about the possible misalignment of the machine if it is moved on another premise. But hey, even my small lathe manual says that below should be perfectly flat and horizontal to achieve working accuracy. Its considered when designing the machine to be made so that this is irrelevant. Thats why the triple beams /100x100x4/ both sides-against bend in the middle , that's why the 3 double horizontal beams on bed -against twist. Also that's why the 4 legs are both ends and not say 20 percent inside, cause right now the frame bent what have to bend and combined with the sides and bed strength it will not bend more under 140kg gantry, in other words the gravity stress will work for me. Cause if i have put the legs 20% inside the frame length both sides so the frame would be strongest, when the gantry went one side it would lighten the middle and cause some vibrations.

So the answer is that when moved, legs must be leveled checking long rails against straight edge and even additional supports mildly fixed in the middle so they support, not push up. I told it before on the first build. Speaking about this and that but if you don't have the precision instrument to measure it... IMO a straight edge that could extend perpendicular to both long rails tops is a must for any precision build. I don't see how could be done without this.