Hey Boyan, does this look good now? Can I send you my cad file to take a look at just to see if everything looks ok?
Mutzy
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Hey Boyan, does this look good now? Can I send you my cad file to take a look at just to see if everything looks ok?
Mutzy
i have these on my list for the 4000mm ballscrew lengths but would you say i would also need them for 1800mm lengths?
Reefy86, how are you? I am no expert in this forum like Boyan, M_C and Jonathan are. They truly understand the science behind the build. I was told once that once you start geting more than about 1574.8 mm the possible whipping action of the ballscrew may have an effect on the life of the bearings... take this into consideration and maybe the professionals could answer the question more directly. Mutzy
That's what i was thinking so in general then i may need 3 of these ordering which i know these are not cheap but what is lol
If it's only whipping in the ball screws and not rotational mass there have been some very elegant, low cost solutions to that,
- Nick
Hello magicniner, forgive my limited intelect, but what is the difference between "whipping in the ball screws and not rotational mass"? what solutions are you referring to? Thanks for the info. Mutzy
The difference between 1-"whipping in ballscrews" and 2-"Rotational mass is thatQuote:
Originally Posted by mutzy
1. "Whipping" is when the length allows sag and rotation then "Whips it around" like a skipping rope resulting in a lot of off-centre mass and the associated vibration and potential damage.
and
2. "Rotational Mass" refers in this case simply to the mass which requires acceleration and deceleration to control a rotating screw assembly.
One of the simplest solutions I've seen is like a sprung saloon swing door with a slot in it, the slot fits the ballscrew and supports it in 3 directions, when the carriage passes it "pushes the door open" and the door swings back once it passes, a few of these spaced out along the screw on alternate sides will control whipping very effectively.
There are other more complex solutions but they can approach the cost of a rotating mount for a ball nut and as stated address only whipping and not rotational mass,
Regards,
Nick
It's not obvious until you do the arithmetic but the inertia of a rotating screw like this can be high - you can easily get to the point that the inertia of accelerating the ballscrew exceeds the inertia of the gantry. As the length of screw goes up, the critical speed - the speed at which whip in the screw becomes excessive - goes down. So you need a bigger diameter screw, which increases critical speed again. But the rotational inertia of the screw goes up with something like the 4th power of diameter. In other words, you can increase the screw diameter to increase critical speed and hence gantry speed, but the increase in inertia will have a massive effect on acceleration and acceleration in turn has a big effect on cutting performance if you are doing anything other than straight cuts. This is what is behind Nick's comment - whip, critical speed, machine speed and acceleration, screw diameter - these are all linked and the art of the engineer is to find an acceptable compromise between them. Or use a different solution, which is why bigger machines use rotating ballnuts or rack and pinion.Quote:
Originally Posted by magicniner
Thanks Magicniner, maybe you can give some names/part numbers and some places where to get these types of ball screw adapters. I'm going for the rotating ballnut myself.
Thanks Neale, It's awesome to have so many smart people to help us little brains get through the learning process.
Cheers to all.
Mutzy
It took me a while to find this but I knew I'd seen it somewhere
https://www.youtube.com/watch?v=NWB6FAJCPhA
And there's this, a more technical but more expensive system
https://www.youtube.com/watch?v=kkcVWIsXGjk
I'm sure there are other ways to skin this particular cat but these are the only two I've come across so far ;-)
- Nick
Here's a vid of an Igus solution for supporting long screws - https://www.youtube.com/watch?v=Duq163m59TU
And I'm struggling to find a video of the system magicniner mentioned, but I'm sure I've seen one at some point.
I have thought about that, especially on a slower machine like my new foam cutter. But anyway one will have to spin 3m 16xx screw at least. Which is way heavier than spinning a nut.Quote:
Originally Posted by m_c
Boyan, If you could look at this, I would appreciate any feedback. thank you
MutzyAttachment 23595
Check out this configuration:Quote:
Originally Posted by magicniner
https://www.youtube.com/watch?v=kkcVWIsXGjk
Some nice food for thought in this vid:
https://www.youtube.com/watch?v=OLpTJp6_qmg
Hi Iam new here and also my English is poor too. I just need to know where can I find such a code (Firmware Version 1.2 Type1.) I can find it in zip file but not download. so much thanks if some one could help me any help will be appreciated.
my Email is: [email protected]
best regards.
hello im thinking to make a new cnc router for size 5x10 so my question is im going to use rotary ball nut,do i need 25mm or 32mm ballscrew for 10 feet axis and do i need high pitch screw such as 25 or 32 since im thinking rotary ball nut doesnt have critical speed maybe i can use 10mm pitch and just spin it 3000-5000 rpm with 1:1 ratio belt,
and im going to pair it with 750-1kw 3000-5000 rpm servo for it i already.
i already got quote for my supplier
rotary ballscrew 3232 10 feet=350 usd
rotary ballscrew 2525 10 feet=300 usd
my target rapid is around 1500-2000ipm
thanks
Hi,Quote:
Originally Posted by teamloks
I'm just finishing a 10x5 machine with rotating ball nut so it's good timing to ask this question.
The first thing to mention is how much the screws sag under there own weight at 10ft long. With NO tension on the screws, it's massive but even with tension on the screws which you must have, there is still more Sag than you would probably expect.
So when the machine is at Rapid feeds and when axes are near the ends it leaves a long length of screw unsupported, so the screw can still vibrate.
On the machine I've built it uses a 25mm diameter with a 25mm pitch with a 1.5:1 ratio. I'm using 220V closed loop steppers spinning which spin between 1500-2000rpm. The machine is tuned at 30mtr/min(1200in/min) and will reach 40mtr/min((1575in/min) however I wouldn't suggest that speed and here's why.
The ball nut was never designed to spin at those rpm's so while you havent got the critical whip factor to deal with you still do have to consider the nut speed and what it was designed to spin at. Most ball nuts expect to be fixed and are designed for low spinning screws. So with Servo's spinning at 3000rpm or higher then you will have trouble with premature wear. Also, the alignment will be much more critical with higher RPM's.
My advice is to use a higher pitch then apply a ratio to lower the rotation speed of the ball nut while still getting the rapid feeds you would like. You will also get the advantage of increasing torque so you can lower the size of servos.
Now, where it gets tricky is with the Ball screw size. The larger Diameter screw will probably Sag more under its own weight so more tension will be needed. So you will need to design strong brackets that allow for the screw to be adjusted for alignment.
My suggestion is to go with a 32mm pitch and ratio of 2:1 that will give the equivalent of 16mm pitch and 1500rpm at the nut with 3000rpm motor. Giving just short 1000in/min which could be pushed up 1575in/min with 5000rpm giving 2500rpm at the nut which I would suggest is pushing the limit.
Hope this helps. Oh and this machine is vertical but that doesn't make any difference.
Attachment 26808
I've read this recommendation several times but doesn't the increase in pitch cancel out the increase in torque so that the maximum linear force that can be applied to the gantry without stalling the motor remains the same? Or are you more concerned about the moment of inertia of the ballscrew itself?Quote:
Originally Posted by JAZZCNC
Kit
Kind of yes but no, or should say maybe your misunderstanding what's being said or maybe I'm not putting it over clear enough..Quote:
Originally Posted by Kitwn
Yes, 32mm pitch with 2:1 ratio will give the same linear torque as 16mm pitch 1:1 so torque is canceled by pitch difference like you say.
However, when I say Torque is doubled so the smaller motor can be used, what I'm referring to is that if 1:1 the 32mm pitch would require a larger motor to give the same linear force as 16mm pitch. So the ratio doubles the torque and allows the smaller motor to have the same linear force as 16mm pitch.
The trades off's and gains are that 32mm linear movement halves but so does rotation speed of the nut. So the pay off is that you get the same feed and torque as 16mm at 1;1 but with half the rotational speed of the nut or screw. This is the main goal to reduce whip and stress on the ballnut.
Hope that makes more sense.!
HI JAZZ thanks for your insight regarding my question just talk with my ball screw supplier he suggest me to use 4040 for 3.2meter axis and 3232 for 2 meter axis..and i might follow their suggestion regarding that if budget is not constraint..anyway maybe i opt for 3232 all axis 4040 is really expensive
Do they know you are rotating the nut and tensioning the screw.? Makes big difference.Quote:
Originally Posted by teamloks
This is the first 10x5 machine using rotating ball-nut I've built, I've built plenty of 8x4 and the difference between them really surprised me.
The secret is keeping the nut rotation speed down and getting a good tension on the screw with nice straight pull.
Good luck
Aha! The point I had missed is that your 'smaller motor' required to drive a 32mm pitch screw with 2:1 pulleys is NOT smaller than the motor required to directly drive the 16mm pitch screw. In fact it may well be the same motor, which is at the heart of what I was trying to say. Thanks for clearing that up.Quote:
Originally Posted by JAZZCNC
Is there a case for using the direct driven screw with a bigger motor? You are saving the cost and complexity of the 2:1 drive and halving the speed required from the motor, so running it in it's higher torque region anyway?
Kit
do you use BK/Fix unit on both end side?Quote:
Originally Posted by JAZZCNC
Don't need end bearings because not spinning the screw. The ends need to be either externally threaded or internally-threaded so you can tension the screws. I've used both methods on different machines and prefer externally threaded as can get more torque.Quote:
Originally Posted by teamloks
The force required to take Sag out over 10ft is considerable so make sure the brackets holding the ends are substantial and adjustable so can align screw in two planes.
Can do either but using a larger motor usually doesn't cost less because requires larger drive and often more volts so larger PSU.Quote:
Originally Posted by Kitwn
However, on long machines rotating nut wins hands down and requires a belt connection, so the ratio is no extra cost. Rotating the screw on the long machine means much larger ballscrew is required and this really starts to ramp up the costs because everything scales up with it, Bearings, couplers, motors, drives, PSU
Even then a rotating the screw system cannot achieve the feeds a rotating nut can.
Reading this thread with interest (as I may need to go this route on my "big" machine soon), I noticed the concerns over rotation speed of ballnuts. This made me recall some stuff I read in the TBI catalogue some months back about different types of ballnut (differing mostly in the configuration of the return paths) and their relative speed capabilities, worth a read and maybe doing the sums they outline there.
Certainly worth a read but what helps with rotating nut is to get shortest length Nut possible.Quote:
Originally Posted by Voicecoil
It's also critical that the Shaft as a Flange which is machined perfectly concentric to the Nut otherwise concentricity to the screw is misaligned so causes big vibrations.
What's the thinking behind the shortest possible nut please?Quote:
Originally Posted by JAZZCNC
The concentricity is an obvious thing and might rule out some of the cheaper offerings if my experience on the machine I've just completed is anything to go by. Having set everything up and got it working smoothly I thought I'd spin one ballnut through 180deg to get better access to the lube nipple. Major fail, that side of the axis got really stiff, it turned out that the casing/flange of the ballnut was something like 1 or 2 degrees out of alignment with the axis of the screw.
access/interference and balance/inertia mostly, it's no big deal and depends on the design to some degree but shorter is better in my experience.Quote:
Originally Posted by Voicecoil
It's not always the case obvious to everyone that's why I mentioned it. However most ball-nuts, even the cheap ones, have a machined reference surface on the outer body which you can chuck upon and skim flange if needed. Thou I've not had any issues if honest.Quote:
Originally Posted by Voicecoil
Do you have design drawings to share for this?Quote:
Originally Posted by SafeAirOne
This is not an ideal setup for a normal machine, even for a heavy duty one. Its better to use the normal angular contact bearings, which are more than enough for the job by any
means.
Now i know more having run my machine a couple of years daily and having made the kit for a couple of people.
I already sait it there #122 , and couple of posts after that.
Not only there is absolutely no gain but there will be loss, using these bearings.
Now if you are constructing a lathe head, then go with them :pirate:
+1 The advantage of roller bearings is the huge radial load they can take, in this case the axial is more significant I think. However there are one or two sizes of tapered rollers that are easily available at a very attractive price which might swing it ;-)
If you will be milling steel using 3 inch cutters yes, not in a 3m woodworking machine case scenario. But don't listen to me, put that bearings there cause they are cheap.And see what happens.Quote:
Originally Posted by Voicecoil
I agree with Boyan and we Both have experience of using rotating ballnut design, so you might want to listen. That design and those bearings are not good for this application because of things which have been stated. They will work ok, but they won't last ok, the forces are in all the wrong places so between this and the heat generated because these ballnuts are being run in ways they where not designed to run it will impact the life and performance.Quote:
Originally Posted by Boyan Silyavski
But you could say what do we know.? In which case go for it.!
Well, this one was bugging me today, so I did some digging and the good Mr NTN came up with the info.
edit I guess it's friction/heat that's the issue?? OK angular contacts may not have the load capacity of rollers, but usually have lower coefficient of friction (1.2....2) than tapered rollers (1.7....2.5). I did see that there's been some recent advances in roller bearings pushed on by trying to get better efficiency in automotive, but they don't seem to be generally available at a nice price
Attachment 28168
What do you think of that design for a 16mm ballscrew? Maybe the pulley should go on the right between the bearing and locknut so I can use a smaller pulley.
The bearings are double row 3805 2RS 25x37x10 spaced 35mm apart.
It is just a copy of the Fenergy angetriebene Mutter and I will probably buy that one anyways.
I just extended the spacing of the bearings and didn't copy other stuff that well.
https://www.google.com/search?q=fene...h=566&biw=1280
Why do you need a rotating ballnut for a 16xx screw? This should say it all. Did you read anything at all from that thread and the forum?Quote:
Originally Posted by Heavyweather
Several times the last 6 or so years.Quote:
Originally Posted by Boyan Silyavski
Why not? I got a 2m belt on belt drive now and 2m 2005 screws but the 16mm is cheaper and easier to do.
Plenty of machines that use it up to 3m (https://www.cnc-aus-holz.at/index.ph...6525#post16525) and some that sell it, some mostly/only the 16mm.
https://team-haase-shop.de/maschinenelemente.html
https://www.ems-moederl.de/ws45.html
(Uses 2 on Y and one on X)
https://schulze-leistungselektronik....ne-kus-mutter/
https://schulze-leistungselektronik....ne-kus-mutter/
http://cnc.a-ueberbach.de/?s=angetriebene%20mutter
Just because someone else uses it doesn't mean it's good or should be used, not every one who builds a CNC is good at it or as the experience to know better.!! . . .For instance one of those guys built his machine from wood which says it all really.!Quote:
Originally Posted by Heavyweather
Also just because a company as designed and sells a product doesn't automaticly make it a good product. I've experienced many products from suppliers like Haase that seem to look good only to find in practise they have some serious flaws, whether that be instantly obvious at time of fitting or appear over time in use.
With some experience of rotating ballnuts then I see such issues occuring over time with this narrow unbalanced design, but you take your chances and time will tell.
My point in this post is to say don't be fooled by what your seeing and reading, because most of those singing the praises are the designers and often those that have bought them won't admit they have issues or even have the experience to know they have issues or what the issues are over time.! . .Often blaming other areas of the machine when things do start going wonky.!
You probably didn't understand the name of the site where the bamboo machine is shown.
I don't see anything wrong with combining wood with a 3m screw driven nut. The nut is a proven design running in EMS machines for years.
What's wrong with 16mm screws?