New build.Stell frame cnc 1500X1000.Ball screw and gearing calculations

[ba99297]

I have made some calculations with motor speed at 3000 rpm ( max according Yaskawa ). Tell me if i am wrong

motor speed 3000


case 1-with 2010 ballscrew and 2:1 gear ratio

motor gear ratio 1
ballscrew gear ratio 2
ballscrew length 1400
ballscrew diameter 20
ballscrew pitch 10
ballscrew rpm 1500
ballscrew rpm threshold 1234
rapids mm 15000


case 2-with 2015 ballscrew and 3:1 gear ratio

motor gear ratio 1
ballscrew gear ratio 3
ballscrew length 1400
ballscrew diameter 20
ballscrew pitch 15
ballscrew rpm 1000
ballscrew rpm threshold 1234
rapids mm 15000

Both solutions i think they have the same torque and the same rapids. The differense is that case 2 reduce the ballscrew bellow 1234 threshold.


If i use one motor and two ballscrews i have to tension the timing belt
The follwing us a 2d plan i made in order to tension the belt


The magenta cyrcles are the ballscrew pulleys
The yellow cyrcle is the motor pulley
The green cyrcles are pulleys with no tooth
The motor and the green pulley above the motor will be movable in order to tesnion the belt.
The red colore represent the timing belt

And finally my questions

1. Do you think the above plan is a good solution for my case?
2. can you tell me what pulley width should i buy?
3. Do you now any suppluyer with good prices an quality for such pulleys and belts?
4. Does the timing belts have rpm threshold?
5. If i tension the belt that way ( above plan ) would that reduse its life
6. Cast iron or aluminium is better material for pulleys
7. which case ( case 1 or case 2 that i discribe at the begining ) is better?


Thank you for your time

Vagelis

[JAZZCNC]

Option 2 would be best in this case but you may find locating 15mm pitch screws difficult and expensive.?

#1: Really You don't need the upper tensioners just make the Motor adjustable to tension belts. But yes it would work.!
#2: 15mm belt width will work fine.
#3 Sorry no I buy local.
#4 Yes but much higher than 1500rpm . . Think about Timing belts in Car engines.!!
#5 Can't see why it should provided the tension and alignment is correct, most common cause of belt failure and premature wear is incorrect tension or alignment.
#6 Aluminium will reduce inertia on ballscrew but wear quicker than Steel but again if correctly tensioned and aligned then not an issue. I've had aluminium pulley on my machine for over 5yrs and it's still fine.
#7 See above but Like I said before 2:1 with 10mm pitch will be fine I tell you this through lots of experience not theory.!!

[ba99297]

Jazzcnc thanks for everything
Sorry for insisting to ask but i am trying not to make mistakes ( at least to make as little as possible).


First question
This gear 2:1 and 2010 ballscrew should be applied at all 3 axis ( X,y,Z)
I think Z axis has not issue because of its small length, X also has rpm threshold 2400+rpm

Second question
In order to reduce inertria at Y ( considering that i will use 2 ballscrews ) is it logical to go with 1610 ballscrews instead of 2010 ?

Third question
You told me
"I can tell you from experience that you will easily run 1.5mtr length 20mm screws @ 1500rpm with out any problems provided they are aligned and use correct end bearings."

Are the "made in china BF and BK" that chai sells, the correct end bearings or i should go to something else?

Forth question
A well aligned and tensioned pulley ( really how we mesure tension?) does it have backlash?

Vagelis

[JAZZCNC]

Jazzcnc thanks for everything
Sorry for insisting to ask but i am trying not to make mistakes ( at least to make as little as possible).

No problem and you are doing the correct thing asking questions. Just be careful not to get too hung up on specs and calculations they are helpful guides only not hard fast rules.!

Question #1 X & Y use 10mm pitch but for the Z axis you may want to use 5mm pitch for higher resolution/torque.

#2 If you where using steppers then I'd say yes possibly, but because you have Servos geared which give torque across the full rpm range and also geared 2:1 so doubling torque then No you will be better with 20mm to help reduce chance of screw Whip.

#3 The BK/BF are one type of correct end bearings but depending on your design you may prefer the FK/FF type both work the same just suit different mounting locations.

#4 Well you can buy belt tension meters but they are expensive I believe. After that then it's mostly experience and judgement I'm afraid.
So long has the belts isn't guitar string tight or washing line loose then with common sense you will tell if it feels right or wrong.

Regards Backlash then with the 15mm HTD belts I use then I see very little to none, certainly not enough to show in 99.9% of the work I do.
If you look at this Aztec Calendar you'll see the level of detail that can be done with timing belts and if any backlash was present this level of detail wouldn't be possible.!! . . . .(The timing belts were 4yrs old when this was done.! . . .and the screws are 1550mm long.)
VIDEO0021.3gp - YouTube

[ba99297]

So jazzcnc you sujest

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

15mm HTD timing belts
Is that correct?
All three axis will be moved with 3 Yaskawa sigma II 400 watt ac servo motors

[Jonathan]

No point using a 20mm diameter screw on Z as it's so short that the critical speed of a 1605 screw is plenty. Use 1605 for Z and you'll get better acceleration.

For the other axes I agree with the choice of 20mm screws if you want to get the highest speed from your servo motors. However if you want the best acceleration then using 16mm screws would be better, but this will of course lower the top speed.

[JAZZCNC]

Agree with Jonathan regards the Z axis screw 1605 is correct choice.

Regards the 1610 on X & Y then I don't agree it's the correct choice at this length. Yes it will allow slightly better acceleration than 20mm but with using servos you'll have plenty enough anyway. 20mm screws will handle whip better and give a good balance of both allowing higher speeds if needed, with 16mm higher speeds will be limited due to potential whip.!!

Both would work but given servos not steppers then really think 20mm are the best choice at this length.