Stell frame cnc 1500X1000. Adjustable table your opinion please

[Boyan Silyavski]

Dean thanks for your good words
As more than a year has passed since my last attemp of rails intalation, today i go on
I had some questions that i wrote 1,5 year ago (30-11-2014 #171).
I repeat them in order to understand what level of accuracy i have to achieve

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#1 ( very important to know what I am trying for )
When you measure the flatness of a beam ( or epoxy surface) against a straight edge, what is the acceptable tolerance-gap ( so we assume the surface is straight) . I use light to understand whether my top beams attach the straight edge. The touching points can be easily seen. But at other points althought i can see that there is no touch ( light passes through) , the 0,02mm Gap Filler cant pass through the gap. So what is the critical gap ? the light passing test ( that is less than 0,02mm ) or the 0,02mm gap filler test?

#2
When someone use the solution with the adjustable top beams ( without epoxy) or the shimming method how does he succeed to have the top rails in the same plane. How does he know when the two rails ( left and right ) are in the same plane?

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Hiwin maual (among others) has this table that says ( if i read right the table) that the height H of a rail has a range +- 0.1 mm for normal accuracy rails



Thanks for your time
Vagelis

#1
For me its very simple. Depends on table size. For under 1m everything more than 0.05 anywhere is unacceptable. For bigger tables 0.1 deviation on height is the limit. So hiwin is right.
Now i want to tell you that it took me a week to mount my 2 long rails . I mounted them and dismounted them 5 times, not counting the 3 pours of epoxy. So at thend depends what you will use the machine for.

My standard is very simple. if i can notice a gap with naked eye, its unacceptable. Be it 1m or 10 meters table.


#2
yeah, thats why i dont like this method. Ask Dean. But it should be possible if you of course have straight edge that can lay on top of both of them at the same time. i doubt though you could achieve same precision as with epoxy

[ba99297]

Boyan thanks for your answer.

#1
For me its very simple. Depends on table size. For under 1m everything more than 0.05 anywhere is unacceptable. For bigger tables 0.1 deviation on height is the limit. So hiwin is right.

I guess when you measure in mm, so when you say 0.05 you mean 0,05mm and when you say 0.1 you mean 0.1mm right?

So even if i can see light pass between the rail and the straight edge but the 0,02mm filler strip can’t pass through the gap you think is OK for a 1800mm long table?
Really after epoxy cure, when you attach the straight edge on the epoxy surface is there any gap between the epoxy and the straight edge? The epoxy surface is perfectly flat against the straight edge? If the answer is YES i have an idea here

http://www.mycncuk.com/threads/9511-...t-work?p=76521

Vagelis

[Boyan Silyavski]

Yes, i meant in mm. But to tell you the truth i found that the hardest thing is to avoid for dust not to get trapped in between when mounting, cause that could f%%ck all previously achieved precision. When i lay the rails i lay the edge first and scrap them against the epoxy so no dust goes trapped there. And there is a lot of particles of it even in a new workshop :-)

My straight edge was perfectly flat against he epoxy when i was happy with the result. But even in my best result, at one end of the bed under one of the rails there was need to shim / if you read the whole thread about my machine you will remember that i was experimenting a lot with the epoxy pour, so i found the way to do it properly/

So yes, to your idea about the DIY epoxy straight edge, but remember the main thing i discovered when pouring 3m rails, i needed to over extend the epoxy both sides 25cm/?? read the thread again but make it so to be on the safe side/ so it shrinks there, after that just cut it to the size of the profile.Similar to what you will do with the meniscus.

[JAZZCNC]

#2 i doubt though you could achieve same precision as with epoxy

So when leveling across the planes, not the Rail length I mean planer level, what precision do you get with Epoxy then Boyan.? . . . . . If you can quote me figures then how are you measuring it.?

[Boyan Silyavski]

So when leveling across the planes, not the Rail length I mean planer level, what precision do you get with Epoxy then Boyan.? . . . . . If you can quote me figures then how are you measuring it.?

I was writing it down and knew you would say something :-)

Very soon i will be able to answer to you question with numbers, when i move my machine against the straight edge.


But what i was saying is: its almost impossible for you to level better the rails than the gravity levels the epoxy, speaking about them being in the same horizontal plane. measurable or not - its a fact. For me at least.

How do i know that? It was very difficult for me to straighten them left right and square them, with a helper, i could only imagine the nightmare of making them horizontal too at the same time. The thing is- i dont lie to my self, i am very sincere person and i know when i can not do truly properly something. So i am not pretending. fact is that i am also very precise and detailed person. With 2 words- if i could not do it 95% of people will not do it at all. Not to speak that how many people at the forum have 2m straight edge.

I know you have long edge, i know you do it that way, but dont compare your expertise to the people learning how to do a thing.I will not encourage any body do it that way, because IMO its the more difficult way. So what i am saying- epoxy is the way for me , not detachable sides.

[JAZZCNC]

I know you have long edge, i know you do it that way, but dont compare your expertise to the people learning how to do a thing.I will not encourage any body do it that way, because IMO its the more difficult way. So what i am saying- epoxy is the way for me , not detachable sides.

Boyan I don't have a problem with Epoxy Method and I use my self because it's quick and accurate enough for any wood router. I do have problem with people quoteing accuracy and tolerences they can't possibly measure or verify. You do this and I feel it's wrong because your guessing and giving people the wrong idea. Your input to Forum is great and appreciated by many, me included and please don't take offence. But personaly it irratates me to see figures quoted, not just by you but also others that can't be verified or should say they don't have the means to verify.

The simple fact is unless you can have the base Surfaced in one go on machine then your accurecy is limited to the tools and care you take. Unless you can measure from Accurate surface plate or CMM machine to measure tolerences then your purely guessing or assuming tolerences.

Over building and Fantasy tolerences are not required for any router designed for mostly for wood. Also if machine this size is to be used for cutting aluminium then again the tolerences needed are still low because it will be mostly limited to and probably used mostly for profile cutting and maybe the odd pocket which most decently strong routers can manage.
It can't and will not have the tolerences needed for anything more challenging like Mould making in aluminium or harder materials without being done properly surfaced. Also at this size it would need to be substantialy stronger to be any good and last any length of time if used in more industrial way.!

Just because you can cut steel with a machine built at DIY level doesn't mean it does it very well or can do it for long.!! . . . . . To think otherwsie is foolish.!


People need to be realistic and stop quoting tolerences and accuracys they can't possible verify.! They also need to calm down and realise over building isn't clever or wise it's mostly just wasted money for the type of work they do with the machine. It also often compromises the machine if they don't match other components to there over built frames whcih they rarely do.!!

[Jonathan]

Plenty of readings regarding the accuracy in my build log.

Of course that says nothing about what might happen in the months after pouring, if the frame isn't stress relieved...

[JAZZCNC]

Plenty of readings regarding the accuracy in my build log.

Of course that says nothing about what might happen in the months after pouring, if the frame isn't stress relieved...

Bit of difference in size Jonathan it's 2x width and 3 x length.!!

[ba99297]

Thanks everybody for your answers
Reading all these useful comments I want to say that I this machine won’t be used to achieve magic tolerances. As Dean said
“…router designed for mostly for wood……… is to be used for cutting aluminum then again the tolerances needed are still low because it will be mostly limited to and probably used mostly for profile cutting”

To be honest I don’t know yet what exactly I am going to use the machine for. I just build a “weapon for hunting” I have never been in the “forest” before with that kind of automated “weapons”. Till now I hunt with catapult (traditional handy tools).
I get involved with many kinds of materials ( wood, steel, alloy) and like to mix them in my construction. That is why the machine is a middle solution (all around machine). That of course means that when you earn in one level you will miss in another level. I think an all purpose machine is impossible to be build as there are parameters opposite each other ( accuracy vs size, stiffness vs light weight and all these vs cost ). The main principal that I try to achieve ( not only in cnc construction but also in my way of life ) is to have the best value for money. So I am trying to achieve the better result with the means and the efforts that I have.
The added value of course at this attempt is your help, even your well disposed disagreements that make me understand things better. In my country we use to say that “sciolism is worst than ignorance”. Many times here in mycncuk I realized that I had sciolism for many aspects that had to do with constructions. Many myths in my mind have been basted especially with Deans help who is something more than an “auto-answer machine” . I could not not mention Jonathans help especially through his Servo sizing software and his inspired constructions, and also I cant forget that the main idea for my machine frame, come out from Syliavskis thread. And all the others that these last months participate to encourage me, correct me, and generally help go one step beyond. I know that I am not too fast in making steps, but I also know that ( for me ) the most important is to make small steps than trivially jumps. This attempt for me is like a trip. I prefer to make the “trip” with a slow train looking “out of the window” , more than ride a fast car and reach the end some days earlier. A Greek poem describes it better. Whoever want to read it (in English ) can find it here
http://www.cavafy.com/poems/content.asp?cat=1&id=74
Thanks for your time