Quite an Unusual one

[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.

[Boyan Silyavski]

Hi there,
Long time no update. Long story short. Bought new epoxy and did it as I thought it would be right. It worked perfectly. As supposed the long rails sucked from the bridge. I went even further and made only 1 bridge. Yeah, the epoxy leveled without problems. I knew it.
This time I used Knauf channel 0.5mm 3m - 3€ from construction material site. Every attempt I am getting better for cheaper.
Also used 8 mm square bar around the epoxy. The channel was 4 mm wide so the bearings not to hit the bar

some photos. Will upload here also but now I am writing from my phone
https://plus.google.com/app/basic/ph...i%26pgpnum%3D1


Ps. Here are the photos:

[mitchejc]

Wow, those epoxy sides came out very nicely. Also a great idea to use those 8mm square bars on the sides of the epoxy.

That base looks VERY solid and straight. I'm wondering how flat those X sides were before the epoxy, did you perhaps check that? The reason I'm asking is that I'm hoping to get away without having to use epoxy because I'm not getting something similar to the West Systems stuff here so I need a plan B.

[Blackrat]

ive just done my gantry epoxy pour , i gotta say it works a bomb !! am pretty impressed how flat and smooth it has come out

i however used a ATH filler in my epoxy , makes the epoxy much harder

if you phone John at AMT composites in Capetown , and ask him about ampreg21 with the super slow hardner ...

[feldah]

Hi there,
Long time no update. Long story short. Bought new epoxy and did it as I thought it would be right. It worked perfectly. As supposed the long rails sucked from the bridge. I went even further and made only 1 bridge. Yeah, the epoxy leveled without problems. I knew it.
This time I used Knauf channel 0.5mm 3m - 3€ from construction material site. Every attempt I am getting better for cheaper.
Also used 8 mm square bar around the epoxy. The channel was 4 mm wide so the bearings not to hit the bar

some photos. Will upload here also but now I am writing from my phone
https://plus.google.com/app/basic/ph...i%26pgpnum%3D1


Ps. Here are the photos:

Sorry to pick up that very old thread. But as I am new can't write messages. Could you explain how you did the dam beside the rails. You welded it on. But how did you make sure it's properly sealed so no Epoxy went under it. For the bridge I understood you took a channel from Knauf.

I was considering to upgrade my CNC with epoxy where I drilled the holes already. To prevent the epoxy to float in the holes. I see two options do it as you did and fill all holes with silicone. Or weld a channel over all holes.
Thanks a lot
Felix.

Sent from my MI 6X using Tapatalk

[Neale]

A good way to seal the leaks around a dam before you pour your epoxy is to make up a very small amount of the epoxy and using a small brush or similar just go round the inside of the dam brushing the epoxy into place. it will run into the holes or bridge the smaller holes but because there is not a large quantity behind it, will not run right through and leak out the bottom. You only need to leave it long enough to stop flowing easily before you pour the main epoxy batch - you do not need to leave it for days to fully harden. I made my dam from gaffer tape, stuck to the sides of the rails so that the edge of the tape was above the rails. Biggest problem was peeling it away from the epoxy when the epoxy had hardened. Next time I shall try pulling it away before the epoxy has fully hardened!

I had to strip my first load of epoxy off the rails and start again, but I had already drilled the rails. I put small pieces of Sellotape over the holes and poured the epoxy over the top. I could see where the holes were and then just drilled through the epoxy after it had set. Worked for me!

[Boyan Silyavski]

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?

i am still not sure. When all is ready and un-leveled, we will see if i am right or wrong. If i had made a table and not all on the floor, the frame would be even stiffer, so that would not be an issue. But As you can see the garage is very small, lets say it will be the machine enclosure :-).

On paper if the table hangs in the air one side and somehow is supported only by one side/cantilever/ the bend will be around 0.03mm or less. In normal conditions with 500 kg gantry in the middle less than 0.03, so for the side twist.
So basically if i have not made any mistake all must be well under 0.05, which seems quite an achievement to me for 3000x1800frame, having in mind it has only 500kg steel in it.



Now my wife went a week before to Bulgaria on a business trip. It is our country of origin so i know where to make it cheaper than here, she managed to order the rest of the laser cut parts, the rotating nut parts, collect them , pack the and bring them to me. Meanwhile emptying on the way back all personal things of hers, cause this weight exactly 32 kg with the suitcase. I could only bow to her for the support.







I wonder how the 2 bearings go against each other? The thick inside ring side should be outside or facing each other? Somebody shed a light please!

I have to find my bloody caliper in the garage, cause the bearings don't enter without force at all. I called today and they said that they made all so that it must be press fit, something like 0.03mm more. I dont have an idea about that, will see how i fix all inside. First will have to bore the 30T pulley. Though actually i am still in a doubt to use the Chinese aluminum pulleys i bought from ali express or order new from belting online. cause some of the chinese pulleys the 20t ones were not straight, though i kept them for the sake of the price. 10x30t pulleys+10x20t pulleys=~86 euro. Having in mind i could not find cheaper than 13-15euro aluminum pulley 30t, one piece.
Unluckily, belting online had only steel ones and even they were getting expensive with the machining.