Stell frame cnc 1500X1000. Adjustable table your opinion please

[ba99297]

So far i understood that i should go even with all steel or all aluminium gantry, as combination of these materials will be a little tricky.
I will ask one more time and if somebody reading the thread i will be glad to hear his opinion. In what directions i must have the ability to adjust
FOr example if i go for all steel gantry, all parts welded and epoxy leveled for y axis rails, also epoxy leveled for the plates that will be bolted on the carriages what are the spots that should not be welded but bolted in order to have the ability to adjust?

[ba99297]

After over a month of inactivity i come back. Just one question before upload some resent photos.
For 2010 ballscrew should i use BF/Bk 15 or BF/BK 17 ?

Thanks

[JAZZCNC]

For 2010 ballscrew should i use BF/Bk 15 or BF/BK 17 ?

BK15 Vagelis.

[ba99297]

Hello everybody. I came back to show my little progress.
I want to remind everyone that we are talking about a cnc router with

X 1800mm
Y 1000mm
Z:300mm

It will be moved with 4 ( 2 x axis, 1 Y axis, 1 Z axis ) 400 watt yaskawa servo sigma II.
Steel is the basic material for the construction ( except z axis that I didn’t design yet )
As the table has been discussed many times, I have nothing to say. I just upload two photos . Basic beam is 80X80X4 mm.



The gantry will be maid from two 120X60 X ( 3mm or 4mm thick steel ). At the end of the gantry frame, 8mm and 10mm steel plates will be welded in order to reinforce the gantry attachment to the side braces that will be bolted on the carriages.





If it will be needed ( I try to avoid it ) the front face and the side (left-right ) faces will be perfectly milled to be vertical each other.

Here I want your opinion about the way I laser cut the steel plate and the way I try to keep everything square in order to avoid (if possible) machining cost. If you notice the plates has been cut in such a way ( like a puzzle ) that it is difficult to distort when I will weld them ( I am planning to tig weld the parts in order to reduce heat distortion). Do you think this trick ( “ puzzle cut “ ) will work ?



The same way I made the side braces here are some photos.





If you notice the side braces have straight slots in order to fine tune the gantry so I will be parallel to the cutting surface.



At the following photo you can see two holes where I will bolt screws that will help me to adjust gantry height.



Also the straight slots ( on the vertical piece of the side braces ) will allow small ( up-down ) movements. Side braces and gantry frame will be bolted together.



As for the ball screw mounts, they are also adjustable.


I want your comments if you wish , an I remind you my basic questions

1. Is the gantry overbuild?
2. Is 10mm steel ( for gantry side braces, front face, and side reinforcing )too much for such a construction or should I go with 8mm 7mm or 6mm. I am asking because if we follow the 1:3 relation between steel and aluminum, 10mm steel equals to 30mm aluminum )
3. Will the puzzle cut technique work?

As for the weight the gantry without the motor that will move y axis and without the ballscrew and of course Z axis, weights nearly 41 kgr ( with 10mm thick steel for the side braces and 8mm steel for the reinforce angles and 4mm 120X60 rectangular beam). If I reduce steel thickness and remove steel from some no critical spots, it is obvious that 41 will be easily reduced to 35 or less.


Thanks for your time

Vagelis

Ps: I will use 1:2 gearing but at the above plans i use 100mm 60 tooth diameter for the ballscrew pulley ( that will give me 1:3 gearing, having in mind that the motor pulley is nearly 3,6mm 20 tooth) in order not to have dimension issues if in the future i want to go with 1:3 gearing.

[Jonathan]

Forget all the cutouts on the gantry which have been included to reduce its mass. The servos you have a plenty powerful enough to move achieve the required dynamic performance for a gantry several times heavier than what you have designed. If you continue with your plan to use 100mm diameter pulleys then the inertia of just one of those pulleys will be more than the equivalent inertia of all three axes! Decide on the rapid feedrate you want, work out what drive ratio is required, select pulleys, then check that the servo motors are capable of driving it with the required acceleration. It is very simple to calculate, so don't compromise the performance of the system by using very large pulleys when they're almost certainly not required. If you're not sure how to work it out then let me know and I'll show you.

In answer to your direct questions:

1. Depends what you want to do with it, but you seem to be in the right ball park.
2. The consequences of using a lower thickness and having to replace it are far worse than the small increase in cost to use 10mm, so unless you're prepared to calculate it just stick with the thickest you're happy to pay for (presumably 10mm).
3. It looks a bit risky to me - the tolerances on the parts would have to be very good for them to fit together properly.

[ba99297]

Jonathan thanks for your responce.
As for the pulleys i am planning to use the following setup

X axis: 2 X 2010 ballscrews 1500mm long with 2:1 gear
Yaxis: 1 x 2010 ballscrews 1000mm long with 2:1 gear
Z axis: 1 x 2005 ballscrews 350mm long with 2:1 gear

As for the speed calculations i have made this thread

http://www.mycncuk.com/forums/gantry...culations.html

So with 2010 ballscrew and 2:1 gear ratio

i will have

motor gear ratio 1
ballscrew gear ratio 2
ballscrew length 1500
ballscrew diameter 20
ballscrew pitch 10
ballscrew rpm 1500
ballscrew rpm threshold ~1200
rapids mm 15000


Vagelis

[Jonathan]

Looks like your motors are rated for 400W @ 3000rpm, so 1.27Nm. If you calculate for 15T pulleys on the motors and 30T on the ballscrews using the following specifications:

Mass of axis in kg: [x y z]=[25 25 20] (X-axis mass halved as two motors)
Cutting force in N: [x y z]=[50 50 250]
Acceleration in m/s^2: [x y z]=[2 2 2] (changing this makes a big difference)
Ballscrews: [x y z]= RM2010
Ballscrew length in m: [x y z]=[1.5 1 0.35]

Yields the following:

Feedrate in m/min: [x y z]=[15.0 15.0 7.50]
Inertia in g-m^2: [x y z]=[0.12 0.11 0.07]
Torque in Nm: [x y z]=[0.38 0.34 0.29] (X torque 0.80Nm if gantry mass=0)
Inertia ratios: [x y z]=[3.65 3.18 2.00]

If you instead used 20:60T pulleys on all axes:

Feedrate in m/min: [x y z]=[10.0 10.0 5.00]
Inertia in g-m^2: [x y z]=[0.24 0.23 0.22]
Torque in Nm: [x y z]=[1.03 1.00 0.97]
Inertia ratios: [x y z]=[7.24 7.03 6.50]

So as you can see, even though at a glance you may think changing the ratio would put less load on the motors, you'd actually more than double the torque requirement by using such large pulleys and at the same time get a lower feedrate. This is because most of the torque goes into accelerating the pulleys and ballscrews, so just to illustrate the point about the gantry mass, here's what happens if you use 15:30T and increase the mass of the gantry to something silly like 1000kg:

Mass of axis in kg: [x y z]=[500 250 250] (X-axis mass halved as two motors)

Feedrate in m/min: [x y z]=[15.0 15.0 7.50]
Inertia in g-m^2: [x y z]=[0.42 0.22 0.09]
Torque in Nm: [x y z]=[1.23 0.65 0.37]
Inertia ratios: [x y z]=[12.73 6.53 2.86]


etc...

In other words, your motors are a jot bigger than necessary!

[References:
http://www.nskamericas.com/cps/rde/x...ive_Torque.pdf
ttp://www.hiwin.com/pdf/bs/ballscrews.pdf]

[Boyan Silyavski]

Forget all the cutouts on the gantry which have been included to reduce its mass. The servos you have a plenty powerful enough to move achieve the required dynamic performance for a gantry several times heavier than what you have designed. If you continue with your plan to use 100mm diameter pulleys then the inertia of just one of those pulleys will be more than the equivalent inertia of all three axes! Decide on the rapid feedrate you want, work out what drive ratio is required, select pulleys, then check that the servo motors are capable of driving it with the required acceleration. It is very simple to calculate, so don't compromise the performance of the system by using very large pulleys when they're almost certainly not required. If you're not sure how to work it out then let me know and I'll show you.

In answer to your direct questions:

1. Depends what you want to do with it, but you seem to be in the right ball park.
2. The consequences of using a lower thickness and having to replace it are far worse than the small increase in cost to use 10mm, so unless you're prepared to calculate it just stick with the thickest you're happy to pay for (presumably 10mm).
3. It looks a bit risky to me - the tolerances on the parts would have to be very good for them to fit together properly.

I second that. The plates will distort not matter what you do. Use 10mm simple solid plates. Dont be afraid for the weight. When everything aligned and smooth, the gantry will slide with astonishing to you ease.

How you came up with such big pulleys? Another thing to point you is to make sure the pulleys are from Aluminum, cause last time i ordered pulleys from belting online assuming they were aluminum they send me steel pulleys. So ask and make sure before buying.

[EddyCurrent]

Dont be afraid for the weight. When everything aligned and smooth, the gantry will slide with astonishing to you ease.

This is correct, when I first assembled my gantry it was easier to slide it with me sitting on top of it.

How you came up with such big pulleys? Another thing to point you is to make sure the pulleys are from Aluminum, cause last time i ordered pulleys from belting online assuming they were aluminum they send me steel pulleys. So ask and make sure before buying.

Yes they sent me steel pulleys but that's what I wanted.

[EddyCurrent]

What Jonathan says, but if you are laser cutting the parts then other than cost you could still go for the cutouts but it sounds like it would be more for the looks than any practical reason.
I could not see how the belts would be tensioned from the motor to the pulley. I used 10mm steel for brackets and it's surprising how springy it is, I don't think you should used anything thinner.