Stell frame cnc 1500X1000. Adjustable table your opinion please

[ba99297]

It is very possible to go on with epoxy finally as I measure gap (beam against straight edge ) nearly 0,25mm and shimming seams to be very difficult for me.

As i had told here in Greece they import 105 west system epoxy but they don’t import 209 hardener but only 206. So i will make some experiment with other epoxies much more cheaper ( 25 euros / 1,2 kgr). Ebay supplier asks 90pounds for 1.2 kgr 105-209 system.


The problem is that the temperature in my work place is now 16-17 celsious and it is dropping more as Decemper comes. So if i want to apply the epoxy method i will have to make a place with controlled heating system in order to keep the temperature as low as 20-21 celsious.
Second solution will be to go on with shimming and third ( the most expensive ) to ask a friend of mine ( that builds woodcutting machines) to use one of his machines and mill my top beams in order to come in the same plane ( but this will cost).


I want to ask
#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? Is the thread method accurate ( the method that with the use of two threads you create the diagonals of the top rails like X. If the diagonals are in touch at the centre that means that the rails are in the same plane.

#3
When we use the epoxy method we first drill then tap then close the holes and then apply epoxy or we apply epoxy then drill and tap?

#3
What is the right angle to hold a single beveled straight edge? 90 degrees?45? something else?


Thanks for your time
Vagelis

[EddyCurrent]

1. I read the hiwin maual and it says ( for carriages lubrcation ) to use lithium soap base grease. Is tha a MUST or i could use oil ( and what oil ) instead of grease.
2. Do we also lubricate the rails or only the carriages?

1. I think if you use grease then the lithium is a must, but oil can be used, Jonathan used it here for example; http://www.mycncuk.com/threads/6484-...strong-machine
I get the correct grease here; http://www.toolstation.com/shop/Auto...se+400g/p89691
2. Lubricate the carriages only, they will pass lubrication onto the rails.

#3
When we use the epoxy method we first drill then tap then close the holes and then apply epoxy or we apply epoxy then drill and tap?
#4
What is the right angle to hold a single beveled straight edge? 90 degrees?45? something else?

3. I drilled and tapped all the holes after I poured the epoxy, there were no problems by doing this.
4. 90 degrees because you do not want the straight edge to bend in the middle.

[Neale]

I've been working on my machine this evening, and I think that we are a very similar stage of build! I was levelling the frame of my machine (similar size - cutting area about 1500x750) and thinking about epoxy. I have already bought my epoxy (Reactive Resins low-viscosity with slow hardener) but they say that it should not be used below 8C. In my part of the UK at the moment, that's about the night-time temperature and daytime is only about 12C (and probably slightly cooler in my garage).

As well as I can measure it, I have a dip in my rails of about 1.3mm in the centre. Not as accurate as I would like - not sure if it was a bend in the original 100x50 box sections, or welding distortion - but I think that that will be fine with epoxy. However, I could shim it, if I can find some suitable material. Epoxy has the advantage of also bringing both rails into the same plane, of course, which would be much more difficult with shims (tapered shims, anyone?). What I don't know is what kind of tolerance you need to work to with Hiwin rails - what kind of relative twist in the two rails is OK? If both rails are perfectly horizontal in both planes but one is, say, 1mm higher than the other, would this matter? On my machine, that is a twist in the bearing block of about 0.06deg, or 0.001mm across the rail. Doesn't sound like a lot to me, but I have no practical experience of the real-world tolerances on these things.

I'm planning to epoxy first and drill/tap through the epoxy and rail later. My feeling is that this will be easier, and certainly better than trying to remove the epoxy that has leaked into the tapped holes.

[Boyan Silyavski]

#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?

I looked to see if it was tight fit. All theory evaporates when you are trying to check 3m rails, flashlight in your mouth , in a tight garage holding 14kg straight edge. Just dont be in a rush, call somebody to help you, prepare good flashlight and look every 15cm if all is ok. Hold the straight edge with not much pressure, scrape it around and try to feel if all is same or ok. At the end the sound and feel helps more than the eyes at that exercise

#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? Is the thread method accurate ( the method that with the use of two threads you create the diagonals of the top rails like X. If the diagonals are in touch at the center that means that the rails are in the same plane.

At the end it seems they use eye and feel. That doesn't mean really its very precise or of real importance. In reality, measuring between 1800mm separated rails, i can lift one of the rails 1mm and it will still seem to you checking with the edge that all is ok and they are on the same plane. Cause the judge contact area is very small. That is what i discovered the other day. But on the other side if it looks straight and both rails look to be on the same plane checked against straight edge, thats enough good. Cause later when the bed is surfaced say you make a 20cm detail. If your table is wrong say 0.5mm, which is tremendous in my eyes, the 20cm detail will still be made to 0.05 or better. The other point being here that all long and large pieces made on a cnc really don't need such precision/wood, mdf/ or just the temperature difference /expansion overrules the actual machine precision.
However in the future i intend to do gantries, surfacing for small machines and similar stuff in aluminum, that's why i pushed my build for perfection and wasted so much money on epoxies. But that's my explanation of thing, it came to my mind the other day when i was trying to shim my right long rail cause there was some new problem with the epoxy that i have not seen.

[Boyan Silyavski]

I've been working on my machine this evening, and I think that we are a very similar stage of build! I was levelling the frame of my machine (similar size - cutting area about 1500x750) and thinking about epoxy. I have already bought my epoxy (Reactive Resins low-viscosity with slow hardener) but they say that it should not be used below 8C. In my part of the UK at the moment, that's about the night-time temperature and daytime is only about 12C (and probably slightly cooler in my garage).

I have done the first machine at 14-16C, but i believe any lower is not good idea.

What I don't know is what kind of tolerance you need to work to with Hiwin rails - what kind of relative twist in the two rails is OK? If both rails are perfectly horizontal in both planes but one is, say, 1mm higher than the other, would this matter? On my machine, that is a twist in the bearing block of about 0.06deg, or 0.001mm across the rail. Doesn't sound like a lot to me, but I have no practical experience of the real-world tolerances on these things.

For 20 size z1 preload :
-mounting surface parallelism 0.02mm
-block mounting surface 0.01mm

It will withstand more, just loosing life expectancy.

I'm planning to epoxy first and drill/tap through the epoxy and rail later. My feeling is that this will be easier, and certainly better than trying to remove the epoxy that has leaked into the tapped holes.

[vargai]

#2
How does he know when the two rails ( left and right ) are in the same plane?
Vagelis

Hi Vagelis,

As I see you have a longer distance than 1 m to bridge with linear edge
As far as I am concerned when I am get ready to the implementation, one of the 1st thing to buy will be a linear edge and a machine level (and so on).
With machine level you can detect 0,02 mm deviation in 1 m with helping a good linear edge and additionally you can check the single rail twisting, leveling exactly.
I suppose this is the easy way to work in the horizontal plane

[vargai]

bearing block of about 0.06deg, or 0.001mm across the rail.

any CNC producer can be happy with this. I am just wonder how did you measured this 0,001 mm?

[Boyan Silyavski]

Something came to my mind. When doing the epoxy thing, they both should be one temperature with the frame. Means Not pour and then turn the heater on as it would be a disaster. bring a heater to the workshop, turn it on for a couple of hours so the epoxy and the frame will be one temperature. Then leave it for overnight while the epoxy is cured.

[vargai]

regarding to the epoxy itself it seems good thing against vibration too .
Pls advise about the strength and hardness with comparing to ie. AL.
When one bolts onto a rail with M6-is its compression negligible?

[Neale]

any CNC producer can be happy with this. I am just wonder how did you measured this 0,001 mm?

I didn't measure this directly. It's based on a difference in heights of rail of 1mm and a rail spacing of 1m. Looking at the hiwin catalogue, I think they say that the bearing blocks can tolerate a slight rotation around the rail, and a height difference of 0.26mm (20mm rail, 1m spacing). This is a lot more than the figure that Silyavski has given, but I might have misunderstood something.