Quite an Unusual one

[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.

[Blackrat]

what about heat ? on a hot day the frame is going to expand more than .1mm ?

[jimbo_cnc]

what about heat ? on a hot day the frame is going to expand more than .1mm ?

It may do, but it will stay flat :)

[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.

[EddyCurrent]

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.

You are absolutely correct with that.

[jimbo_cnc]

I'm not sure I agree with your theory for putting the legs in the corners, but we won't worry about that now.

I'm interested in how to make it moveabe and still no twist. Obviously, making it very stiff is a good start. But what you really want is to know the reaction forces with the ground so you can install the machine elsewhere with same contact forces. The reactions don't need to be equal but equal would be sensible.

If you have screw adjusters on each foot, then the torque is an approximate measure of the contact force, so you would carefully go around the machine and even up the torque on each foot adjuster.

You want to do this before your epoxy pour.


Or maybe thick elastomeric pads, where you can measure the deflection as an indicator of reaction force. These might be good for vibration too. What is your plan for fixing to the floor? or does it just sit on the floor ?

Some numbers would be useful. Have you calculated the stiffness of the frame? eg if all the weight is on 2 opposite corners how much dip at the other 2 corners?

[GEOFFREY]

If you made the centre of the bridges slightly higher than the sides would that not encourage the side epoxy to "draw" from the bridges? Obviously there must still be a sufficient depth to enable leveling. G.

[ba99297]

Syliavski I dare to say that your last solution is not sure that will work as you imagine. I have never work on research but I think that a basic principle must be to make small steps every time. With your last solution you move the bridges from the middle to the edges. Who told you that the epoxy will be spreads the same way without the two middle bridges. I think 3000mm is too long distance for 5-7mm epoxy thickness. If I were you I will shim or for fill the gap with epoxy and then sand down as Dean suggest. If I had to recast I will use the same arrangement as your last casting try with the difference that I will make the bridges wider near the side tubes( where the rails will rest on). In other words I will put the reservoirs next to the spots that you mention the problem. As the epoxy has the tension to shrink at a specific spot, make your correction at that spot. See below to see what I mean.