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View Full Version : Bended ballscrews. What i can do?



ba99297
04-06-2014, 08:10 AM
Hi everybody
Yesterday i receive from Chai the above things



2X anti backlash ballscrews RM 2010 C7 end machined -1603mm Overall length
2 ballnuts for 2010 ballscrews





1X anti backlash ballscrews RM 2010 C7 end machined -1153mm Overall length
1X anti backlash ballscrews RM1605 C7 end machined -501mm Overall length
1 ballnut for 1605 ballscrew











3 Set of BK/BF15





1 Set of BK/BF12





1x Ball Nut Mount/Bracket Flange For 1605





3XBall Nut Mount/Bracket Flange For 2010





-------------------------------------------------------------------------------------------------------------------------------------

12515125171251812519
I open the box to see if everything is ok
I attach the bf/bk at the ballscrews, and i realize that the screws seems to be bended
I give them motion with a wireless drill and they are "dancing" like crazy especially one of the 2010 1603mm long ballscrew. It seems to move 4-5mm out of the center axis. Also the other three are whipping(1-2mm).

Here are the videos that i capture
The worst one is at video #1 bended ballscrew 1603mm long - YouTube (http://youtu.be/qu7t29TNRtw)
At the following videos 0-4 the ballscrew is rotating with the help of a cordless drill and the bf/bk fixed on a C shape beam
At the Videos 5-7 i rotate the ballscrew with my hand.

0 bended ballscrew 1101mm long - YouTube (http://youtu.be/EM7oLThK9gs)
1 bended ballscrew 1603mm long - YouTube (http://youtu.be/qu7t29TNRtw)
http://youtu.be/TWbHcTfAPws
3 bended ballscrew 1101mm long - YouTube (http://youtu.be/AZhDI-BVv6I)
4 bended ballscrew 500 mm long - YouTube (http://youtu.be/yDNyyLgZKIQ)
5 bended ballscrew 1101mm long - YouTube (http://youtu.be/6OTeYcGQfl4)
6 bended ballscrew 1603mm long - YouTube (http://youtu.be/mAWP-JvFSps)
7 bended ballscrew 1603mm long - YouTube (http://youtu.be/CUJdG2wxjGo)



My questions are
1. Is this bend so bad that make the ballscrews useless
2. Is there any way to correct the bend
3. What should i expect from Chai?
a.To refund me the money?
b. send other ballscrews with no cost?
c. Something else?
4. If i put that screw to my machine should i have resonanse or bearing ware problems?
5. Did anybody had such problem with Chai? if yes what Chai did ?


Thanks
Vagelis

Wal
04-06-2014, 12:37 PM
Hey Vagelis,

I'm fairly sure that my (considerably shorter) z-screw isn't 100% straight - they could really do with packing 'em in a rigid box as opposed to cardboard/bubble-wrap, but who knows - it could as easily be a factory issue..! I guess it's a bit of a 'get what you pay for' scenario - having said that, it hasn't really caused me a problem. I think your screws look a lot worse than they perhaps are because the bearing blocks don't appear to be fastened down hard and everything's moving around, which is exacerbating the whip.

This is a vid I made when I first got my steppers running:


http://youtu.be/mRMpELNAJNs

It looks REALLY bad, but when everything's bolted down it's actually okay. You could really do with having a look at this with the hardware fixed in place, as opposed to bouncing around on a couple of planks... That'll give you a better idea of how bad (or good) things are.

Chai seems like a decent guy. Always been very helpful on the few occasions I've had to contact him for advice.

Wal.

JAZZCNC
04-06-2014, 12:45 PM
I have told you this in an email but obviously you don't believe me.? . . . . Your cordless drill is exagerating the Wobble greatly and when on the machine and fastened down and aligned correctly it will most likely not be a problem. I have seen worse being used without problems.!!

routercnc
04-06-2014, 01:25 PM
The runout on my cordless drill is huge, so if yours is the same that will make things appear worse.

I recieved a noisy ballscrew which had about 0.5mm run out (measured with it bolted properly to the machine and driven by a stepper motor through a coupling).

I considered returning it but they are packed in carboard boxes so chances are it would be no better if they sent another one.

So I sent it off to a UK company and they straightened it to a claimed <0.05mm run out. Cost £45. After that it ran very smoothly and quietly.

ba99297
04-06-2014, 01:46 PM
Wal thanks for your answer.
Dean of course I believe you
The main reason I upload the videos and the photos is because I want to get a general idea from other members that had the same problem, and get some advices about what to do with Chai.


Ask him to replace the ballscrews
Ask for a refund.
Do nothing because this bend isn’t enough.

Is this bend enough to make such a claim?

Also should I try to straighten the ballscrews?
It is more than possible that if I bolt everything down the problem will be reduced but my main concern is the forces that will be applied to the ballnut and the carriages are enough to ware linear rails and ballscrews.

Generally I want your opinion-advice about what to do with Chai

Routercnc mine ballscrews have a runout 2mm one 1603mm long, and 1mm the other three. You can see that at videos 5,6,7 when i turn the nut with my hand and not with the cordless drill.



Thanks for your time.

Vagelis

Wal
04-06-2014, 02:03 PM
I'm a novice builder, but for what it's worth here's what I'd do:

1. Fit your screws and make an assessment based on the the hardware being fastened down correctly.
2. If it's still bad (and it may prove to be just fine...) then get a quote from someone local to you about getting 'em straightened. The screws probably won't seem like such a bargain by that point, but hey - chalk it up to experience. It'll be less hassle than sending back/waiting on new screws etc.
3. If it's burning you up and you feel strongly that you've got the raw end of the deal* - then write him a calm email explaining your issue.

*Chai is not in the business of selling rubbish - he gets plenty of recommendations and repeat business for a reason, sometimes things don't work out but I'm sure he'll try to help you as best he can.

4. Fit your screws and make an assessment based on the the hardware being fastened down correctly.

Wal.

cambesol
04-06-2014, 04:45 PM
I ordered a set of ball screws and linear bearings from Chai. When they arrived the box was badly damaged at one end. I took photos of the damage before opening. The ends of two rails were bent. I mailed Chai and he said that the cost of shipping was prohibitive for replacement. If I placed another order for whatever I didn't need, he'd happily slip in a replacement. I cleaned the ends up on my mill and ground the linear bearing ends so they are now nice and pretty (previously it looked like they were cut off with a chop saw).

Roll on several months and I build my z-axis. Installed the ball screw etc. and when rotated the re-circulating bearing oscillates up and down. I initially suspected that the screw was bent, but after much fiddling I concluded that the screw was not turned centrally when the shoulder was machined for the fixed bearing mounts. This is because even with the ball re-circulator at the fixed bearing end, it still oscillated by the same amount as when it was in the centre. If the screw was bent I would expect the movement to diminish as the bearing reached the extremes of travel (think plucked guitar string).

As this was discovered six months after delivery, rather than get into a discussion (argument?) with Chai, I priced up a replacement (~£19 delivered). I have fastened the ball screw down with as near as damn it half the error to try and minimise the forces placed on the screw (this makes it have stiff-spots when rotating). It is not brilliant, but I will try it on the machine and then decide to throw more money in Chai's direction. I am a couple of months away from having power on the z-axis so this decision is deferred.

Even with the less-than-brilliant experience as described above, the price is a small fraction of parts sourced in the UK (Moore International etc). I wanted to buy British, but it just doesn't make sense as I would have spent ~£1500 more on the basic drive parts.

Neil.

Danielroyal25
04-06-2014, 08:20 PM
I ordered 4x ballscrews for my 4x4 machine off chai. All are good apart from the y axis one which seems to be bent towards the motor end. This results in the driver stall detect coming into play when the z moves into that area. Was thinking about trying to straighten it myself, but not too sure...
i would e-mail him your concerns, get them bolted in place and run them off the steppers and see how they look then. If you are still concerned e-mail chai to see if he will replace them.

ba99297
05-06-2014, 06:11 PM
I contact with Chai i ask him to see the videos and he told me
-----------------------------------------------------------------------
Dear Vagelis,
Can you adjust it as this linked instruction:

Screw Shaft Straightness (http://www.roton.com/screw_shaft.aspx)

AS you know, the ballscrews have to be checked and adusted Before they are mounting to the machine.

Thank you very much for your consideration and cooperation!

Chai

"

Has anybody followed the above procedure for ballscrew straightening?
I am not sure for the result.

JAZZCNC
05-06-2014, 07:46 PM
Has anybody followed the above procedure for ballscrew straightening?
I am not sure for the result.

Yes it's standard way to straighten any shaft not just ballscrews. . . . BUT . . Trust me on this Vagelis chances are they will be OK when on the machine and setup. If any is bent enough to cause a problem then it's not difficult to straighten them like is shown in the link above and often this can be done in a standard vice with pair of V blocks. It doesn't take much effort to straighten screws just a little patience.!

gavztheouch
05-06-2014, 07:59 PM
Rolled ballscrews, are not made straight and will always need some amount of straightening to make perfectly straight. If you machine is rigid enough it should be able to take some bend in the screw. It is good practice to have all ballscrews staightened before use. For hobby use this is impractical but if you were buying your screws pre machined from a professional company straightening should be included in the price.

Jonathan
05-06-2014, 11:36 PM
Personally I'd have a go at straightening them. Whilst the machine will probably 'work' with bent screws, the life of the system (particularly the ballnut) will clearly be lower. How much lower is hard to say, but why take that chance? It's a similar reason for why you shouldn't exceed the critical speed of the screw - whilst sometimes it can look OK as the nut guides the screw, it's still putting larger than normal radial forces on the nut which the nut isn't designed to tolerate.

I straightened a RM1204 ballscrew a while ago. It wasn't challenging.


often this can be done in a standard vice with pair of V blocks. It doesn't take much effort to straighten screws just a little patience.!

Just remember not to use steel V-blocks as you could damage the threads on the screw.

ba99297
06-06-2014, 07:36 PM
Guys thanks very much for your comments.
You really help me understand that i an go on with my build as this is not a disaster.
Regards this straighten process i have some questions

Yesterday i borrow a dial indicator from a friend
Question 1
If i try to follow the straighten process as described here
Screw Shaft Straightness (http://www.roton.com/screw_shaft.aspx)
and measure the TIR where should the node of the indicator touch ?
I am asking because if i put the node in the lower spot of the thread, as i turn the ball screw and have the indicator stable, the node of the indicator will pass from the lower spot to the higher spot of the thread( as the screw turns). I donít know if i make my self clear.
Is ti logical to put the indicator node on the ballnut that has a cylindrical outer surface so i can capture the TIR.

Question 2
what is a logical distance for the V blocs

Question 3
How much pressure should i apply? I mean if i have a bend like that ) 1mm from the rotation center, i should apply a force to bend the the ballscrew to the opposite dimension so the screw take temporarily this shape (, and after i stop applying the opposite force the screw become straight | . This temporary opposite force is it logical to bend the screw 1mm ( temporarily ) or more? Again i donít know if i make my self clear.

Anyway thanks for your patience.

Vagelis

JAZZCNC
06-06-2014, 07:55 PM
Vagelis.

Q1 You can't use the Node of the indicator directly on the screw you need something flat between the screw and the indicator node.

Q2 For measureing then you want over the full length of the screw. For straightening then it depends on the bend amount and where on screw it's bent. Often just moving blocks slightly in ward of ends and light pressure is enough to straighten.

Q3 Trial and error I'm afraid.? . . . How longs a piece of string.? Often just a little more than the amount of bend will do it but could require more depending on where the bend is on the screw.?

If you go too far then just tweak it back but often you'll creep up on straight. It's honestly not difficult to straighten screws just time patience needed. Don't be afraid you would have to be Very rough to destroy the screw. Just protect the threads while applying bending force and you won't have any problems and you'll be surprised how little it takes to straighten them.( Or bend them.!!)

ba99297
06-06-2014, 08:14 PM
So Dean putting the ballnut on the screw and touch the indicator to the nut i think will work right?

JAZZCNC
06-06-2014, 08:40 PM
So Dean putting the ballnut on the screw and touch the indicator to the nut i think will work right?

NO I wouldn't do that, while in theory it could work I wouldn't do that it may lead to inaccuracy's and make it harder to straighten.

Wal
06-06-2014, 09:37 PM
I am asking because if i put the node in the lower spot of the thread, as i turn the ball screw and have the indicator stable, the node of the indicator will pass from the lower spot to the higher spot of the thread( as the screw turns). I donít know if i make my self clear.
Is ti logical to put the indicator node on the ballnut that has a cylindrical outer surface so i can capture the TIR.

Would you not use a flat tip probe - like the one 2nd from the right in the pic..?

12540

Wal.

JAZZCNC
06-06-2014, 09:56 PM
Would you not use a flat tip probe - like the one 2nd from the right in the pic..?

12540

Wal.

Yep them's what's needed Wal but like finding Hen's Teeth unless your prepared to splashout on expensive dial gauges and then they are expensive for a one off job.!

Edit: I retract that statement I've just found this set at Arc eurotrade (bottom of page).!!. . . http://www.arceurotrade.co.uk/Catalogue/Measurement/Dial-Gauges

longy
06-06-2014, 10:52 PM
Vagelis, look at your video No 4 see how much wobble there is on the of the drill. That will only make the screw vibrate the ball nut, even holding it in your hand it will still act like a vibration unit. Once it's bolted securely to the frame 99.99% of the vibration will go. Like Dean says the chances are it will be ok.

ba99297
07-06-2014, 04:51 PM
Vagelis, look at your video No 4 see how much wobble there is on the of the drill. That will only make the screw vibrate the ball nut, even holding it in your hand it will still act like a vibration unit. Once it's bolted securely to the frame 99.99% of the vibration will go. Like Dean says the chances are it will be ok.

Longy the wobble that you mention isn’t on the drill. That dancing movement of the drill is cause of the ballscrew bending. I can say that because the same drill turn the other 3 ballscrews and the wobble wasn’t so much.. In video #4 is the 500mm 1605 ballscrew that I think that is bended at the edge ( where the drill attach the screw.) and not at the middle.

auhopu
10-04-2017, 02:06 AM
Geia sou, Vageli.

I found this thread after googling for 1605 runout. I happen to have 3 lengths of 750~800mm 1605s that show up to 1.3mm (!) of runout.

I put them on v-blocks and tried to apply force in the middle. I can bend them both by hand or by using a clamp (with a v groove on its plastic end). However, no matter how long I hold this position once I release them they spring back to their original shape.

I am leaving the clamp on one overnight to see if this helps. I am pushing down 0.8m (i.e. 0.15mm further down from the middle 0.65mm position).

I was wondering what did you eventually do with yours.

Cheer,
Elias

auhopu
12-04-2017, 12:54 PM
After finding this topic, I thought to give it a go.

As numerous people with Chinese rolled 1605-C7 ballscrews, I have to somehow deal with bends ...or live with them. In my case, we are talking about 3 items of 720~780mm lengths and 0.54~1.32mm runout (the latter can be seen with naked eye). This is how I am trying to deal with it.

21393

After finding the high spot, I have tried several variations:
- v blocks at ends, quarters, 100mm and 50mm from high spot
- bending down by 0.5*runout, 0.6*runout, 1*runout, 2*runout
- applying force for 1m, 2m, 10m, 1h, 10h

Of course I have not tried all the combinations of the above and I have lost track of what combinations I have actually tried so far. I am trying to deal with the worse runout of 1.32mm and after a couple of days I am down to 1.21mm. I would not call this a progress.

Therefore my question to people that have had (some) success in the past is whether they remember what recipe (v block spacing, amount of bend, time of bend) started showing results.

Jonathan
12-04-2017, 05:11 PM
I think you just need to bend them further, to not spring back. You are probably not applying enough stress to go past the material's elastic limit.

m_c
13-04-2017, 12:52 AM
I think you just need to bend them further, to not spring back. You are probably not applying enough stress to go past the material's elastic limit.

This.
If you don't bend past the elastic limit, then they will just spring back, regardless of how long you leave the clamp on. Position of support blocks, and pressure application point depends on the bend. How much pressure is very much trial and error. Apply pressure, release pressure, check to see how much things spring back, then repeat with more pressure if needed.

magicniner
13-04-2017, 10:13 AM
I put them on v-blocks and tried to apply force in the middle.

For straightening you ideally need to apply a precise displacement then measure to see if you have achieved a permanent change, then keep increasing the displacement applied until you get the required change.
Measuring force is an imprecise way of straightening things, a press with a dial gauge is your friend ;-)

- Nick

komatias
13-04-2017, 02:41 PM
This video has some insight on how it is done:


https://www.youtube.com/watch?v=dzIsR4Mg158