Sturdy and Fast all Steel CNC , my first build

[HoGo]

I just realised the pics I posted were somewhat outdated. In the final version I moved the tabs holding rotating nuts/servos of X axis to the rear and turned them 180 degrees so the pulleys are just at the rear plane of gantry. This was done to make possible to add another pulleys so I can belt the two sides together with one long belt. There are schools of thought (especially on our local CNC forum) that they'd better be tied together so if one side will stall or not work properly the gantry won't damage the rails. I believe that this is not necessary as servos have quite reliable feedback and one stepper just wouldn't have enough torgue to damage rails and the other side will stall within few steps from the first side.

[Boyan Silyavski]

I just realised the pics I posted were somewhat outdated. In the final version I moved the tabs holding rotating nuts/servos of X axis to the rear and turned them 180 degrees so the pulleys are just at the rear plane of gantry. This was done to make possible to add another pulleys so I can belt the two sides together with one long belt. There are schools of thought (especially on our local CNC forum) that they'd better be tied together so if one side will stall or not work properly the gantry won't damage the rails. I believe that this is not necessary as servos have quite reliable feedback and one stepper just wouldn't have enough torgue to damage rails and the other side will stall within few steps from the first side.

I believe the same. Moreover i believe this belt being so long is not a good idea if the expectation is to route aluminum, but that's me. I have a small belt driven machine and on it have the motor steps adjusted for wood and for aluminum differently, to compensate belt stretch. Dont know how that be if using big fat belt 25mm wide. Maybe will not stretch if pre loaded/pre tightened correctly.

Anyways the steppers just stall. Who knows what can happen with servos if stalled, i have no idea. Still not in that league.

[Boyan Silyavski]

At the end i have the profile cut, had to help the guys from the metal shop otherwise it would be next week.

Time to make some sparks and test my recently acquired new toys:
-3 in one plasma cutter, pulse tig , stick 200A
-Mig 250A

I decided to go with the MIG even as it seems that i do better looking welds with the arc welder. Yes, its strange but is so. Would have Tig-ed it but still no Argon bottle. maybe the Mig welds are more difficult to me due to the fact that i use beer gas. The penetration is perfect, before some days welded 10mm pieces without any problem. I was saving quite some time for the 2 machines, the combi cost 470 euro and the MIg 330eur with shipping to Spain. Both from fleabay. Needless to say the Mig was a great deal for the money.

I was a little worried because my welding is 1h practice at home and watching a lot of videos. But it went extremely well. It seems i weld quite well, the only thing is that my head is not shaped for welding helmets, whatever i did it could not fit properly



First did the gantry. Spot welded it, let it cool, then started short welds, then turn, then weld, then let it cool. I used my IR remote thermometer to monitor the temperature of the gantry to not pass 60C. So at the end i welded it quite precisely in fact, without twisting. However i was quite tempted to do a perfectly looking straight weld from one side to the other , but followed the correct procedure.






Then decided to weld the left and right sides and later connect them. The guys at the metal shop told me first to weld the bead square and then the rest. However i decided what i felt was better, for the purpose of easier adjustment . I decided to weld it precisely, like i would not use epoxy. Wanted to check if i am being able to do this.



Please don't laugh at my welds, at least they are really penetrating. The spatter is from the gas i believe.



Ground the welds where the bed profiles go. Now the thing is that i have only 2 large clamps. I tightened slightly all from both sides on my new acquisition, the welding leg supports i acquired exchanging a vacuum pump for them. using a square and a plastic head hammer started playing around until i finished with square bed on one and the same plane.




To make sure the bead is on the same plane i used Bosch alu profile as my Din 874 straight edge is still travelling




That the bed is square and is on one plane dos not mean that the most important part-the rail support profile is on the same plane, even if you welded properly.


I would epoxy it later, but i tried to make it perfect, so i decided to spot weld only from the upper sides, cause as i said i have only 2 large clamps. later would take off the clamps and adjust the squareness and being in one plane of the rails supports. As the bed is spot welded only from the top, Using the clamps end by end i leveled the rails supports. Then soldered.




Then became dark, and i -tired but happy. I know, its not a big deal, but for me-yes, cause i bought 2 welders and started a build without knowing if i can weld or not. So, now i relaxed a bit. The machine frame stays in front of my small workshop, cause now i can not lift it alone. It seems extremely rigid, much more than i expected. When i am finished, will measure the flex from 90kg on the bed /me/ . The gantry seems indestructible. I underestimated the need for hard stops. back to my first design. Monday will go and by some U profile. I thought of stopping it with bolt. No way, it should be something very strong.

[m_c]

The frame looks good.

The welds look fine considering you've not ground the mill scale of before hand. Although MIG welding will burn through the scale, it can lead to weld contamination as standard MIG welding can only burn of a limited amount of contamination.

[Boyan Silyavski]

The frame looks good.

The welds look fine considering you've not ground the mill scale of before hand. Although MIG welding will burn through the scale, it can lead to weld contamination as standard MIG welding can only burn of a limited amount of contamination.

Thanks for the heads up. next time will not only grind 1mm the corners but as you say.

Here are 2 recent pictures. Just soldered the hardstops for the gantry from 100 UPN profile. My friend insisted on soldering 4 short legs, again from UPN100 profile. Strengthwise i would have soldered 6 legs instead of 4, or none at all and lay the machine and thin layer cement the machine on place but i was very curious of the deflection of my design.

Now just measured it so here is the result:

1. Applying 100kg static force/me/ on any one of the bead beams leads to 0.045 mm deflection in the middle
2. Applying the same 100kg to middle of the raised sides supported only at both sides by 9 cm legs from 100UPN profile leads to 0.03mm deflection on that side.

Conclusion: With gantry and bead mounted in real working conditions the overall vertical deflection of the machine will be unmeasurable or less than 0.01mm which is irrelevant especially with 0.8kw spindle. So first impressions are perfect.

Anyways, i will most possibly insert pads in the middle of the machine when placing it on its place, so it will stay rigid and quiet

PS. In fact using the excel file for calculating deflection on gantry and gantry side, i guess the real final value of deflection in all directions of this particular design of the finished machine will be 0.0035mm. Which i believe is great.

[kingcreaky]

it looks really warm there... ive just returned from holiday in turkey, to miserable cold england. :(

top work... keep the photos coming...

[Jonathan]

Conclusion: With gantry and bead mounted in real working conditions the overall vertical deflection of the machine will be unmeasurable or less than 0.01mm which is irrelevant especially with 0.8kw spindle. So first impressions are perfect.

Your test shows that the deflection due to the frame will be very small (<0.01mm), but remember the linear guides and Z-axis especially will all lower the stiffness, so overall your deflection will be greater. Still, your gantry design looks reasonably strong so I expect it will be fine.

[Boyan Silyavski]

Your test shows that the deflection due to the frame will be very small (<0.01mm), but remember the linear guides and Z-axis especially will all lower the stiffness, so overall your deflection will be greater. Still, your gantry design looks reasonably strong so I expect it will be fine.

Thanks. I am aware of that. For me this build is a preliminary build to my real machine. A kind of experiment. Something like how far i could go at every step.

As the machine we all know is a sum of its components.I constantly meditate on "the machine is strong as its weakest part". The Hiwin blocks are with A preload, the deflection calculator tells me the gantry sides deflection cutting aluminum will be lower than 0.01mm, so i guess the weakest part will be the Chinese spindle bearings and the bit. I will be extremely happy if i succeed in making a precise machine, just for the sake of it.