Quite an Unusual one

**ba99297** · 15-10-2014

Syliavski I am sure you will find the solution. Your mind is sharp so I don’t worry. The only think I want to say is that some times we stack and we become maniac with some specs off the machines that we build. I would be the last one to talk here as I haven’t finished a machine yet. That doesn’t mean that I don’t have an opinion. So I think that the solution to your problem is more than obvious. It is #1 that you suggest. Go on with shimming. As I have read here in the forum many people use only shims. Why it would be such a big problem for you to use shims only in a small area ( near the bridges). Also have in mind that all these people who have already use the epoxy method, may never compare the straightness of the epoxy against a straight edge. The first introduction of that method that I saw here in the forum was Jonathans machine. But this machine ( as your first one ) was smaller. The scale is very important. Even a 3000mm straight edge may have (0,01%=0,3mm loss at accuracy ) I don’t want to introduce my self as the clever who knows everything. Most of the people here in the forum wouldn’t imagine the problem that you come up against. The only positive is that you give us a good lesson unfortunately by spending 200 euros. This is life. This is they way we learn, by making mistakes. No one could blame you. I think go on with shims is the best way to continue. For sure there is a solution about the epoxy method at this scale but if you want to find it you must pay. The most common characteristics that the DIYselfers have I think are stubbornness and persistence. We think that we can solve any technical issue and that make us some time loose time and money. It is useful some time to make a step back, see the things more clear and then go on again. I am no talking as an expert or as an experience constructor, I am talking as a friend ( even if I have never see you, you have helped me and that gives me the right to consider you friend ). Keep going

**mekanik** · 15-10-2014

Just wondering if this might be worth experimenting with.
http://www.ebay.co.uk/itm/SP300-EPOS...item43cfc05850
It's almost like water so could contain a lot of solvent,but might be worth a try, i use it for sealing wood patterns and it takes about a day for any remnants in the mixing container to set solid, how does it compare price wise with the West Epoxy.

**EddyCurrent** · 15-10-2014

@ba99297, very nice post

I think we do know most of the answers it's just we don't have access to the right (hugely expensive and massive) machinery. For example if the frame could be put under a huge surface grinder the job would be done without epoxy and super accurate.
It also makes me wonder what happens when the frame is stood on an uneven floor, okay it's very rigid and the adjustable feet would be set as accurate as possible but would the frame move over time ? and by how much ? 0.1 mm ?

**Tinkerer** · 15-10-2014

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** · 16-10-2014

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** · 16-10-2014

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** · 16-10-2014

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.