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danielbriggs
18-08-2010, 01:08 AM
Bugger... :confused:

I thought it prudent to take off the stepper motor and slide the ball screw up on my X-axis from my Boxford 160 lathe I'm working on (build thread to follow when I find time) so I could accurately measure the pitch of the screw to calculate the settings for Mach3 motor pulses.

BIG MISTAKE :eek:

It appears that all the balls from the ball screw mounting pillow block have fallen out the bottom. I still have them all in the swarf tray; but that's not the point!!!

I've tried to remove the pillow block, but it seems I'll have to remove the whole X/Z slides to remove it :cry:

Does anyone have ANY ideas as to how to pererably fix or go about replacing the ball screw retainer...? :cry:

Got the biggest sinking feeling and almost shat myself when I realised the bits falling out the base of the slide wasn't old swarf. :surprised:

Ta,
Dan

Robin Hewitt
18-08-2010, 10:32 AM
Hard to visualise, a picture would save a thousand words.

If the nut doesn't have a screw fixing on the side you will need pointy tweezers. Stand the screw vertically so you can fight them in from the end while advancing the nut one ball at a time.

danielbriggs
18-08-2010, 10:43 AM
I can get some pics tonight.
Thanks for that pointer, I'll give it a try.
Looks like it's gonna be a long evening... :cry:

Robin Hewitt
18-08-2010, 11:01 AM
It can be easier to refit the balls if you have the original retainer, the rod cut to just below the nut internal radius. Slightly fiddlier to get it started though. If you make a retainer ensure you bore it so it fits over any reduction on the screw end or they will all drop out again.

i2i
18-08-2010, 11:47 AM
correct me if i'm wrong, you're saying the balls have fallen out of one of the bearings at the pulley end of the ballscrew assembly. If so just replace the bearing, they're quite cheap, and may have needed to be replaced anyway. If it's the ballnut balls that have fallen out then that's a different story.:cry:

danielbriggs
18-08-2010, 01:23 PM
I'd be over the moon (relatively) if it were in fact the pulley end bearings, but no... it's the ball bearings from the ball screw nut (mounted towards the other end of the pulley in the pillow block) :cry:

There didn't appear to be any plates to hold the balls in; I stupidly wound the ballscrew a little too far out of the nut, then the sound of a "pitter-patter" of balls :cry::cry::cry:

Robin Hewitt
18-08-2010, 01:38 PM
There are no 'plates' to hold the balls in, just little diverters that steer them out screw of the and into the recirculation channel.

Ross77
18-08-2010, 02:24 PM
Its not to bad a job, I rebuilt one by trial and error and it works fine, I took off the recirculation tube, held the nut on the centre of the the screw, as best I could, and then feed the balls back down the pick up shaft, I did it from one side and used plenty of oil so I could keep pushing them (and rotating the screw) until they appeared at the other side, (That way there are no gaps). Refit the recirulation tube job done...

I tryed other ways but its easy to jam the whole thing up so take your time :o)

danielbriggs
18-08-2010, 03:50 PM
Cheers guys; will give it a go when I get home tonight.
i2i, you have a Boxford 160 right? Any pointers to getting the X-axis off easily? I tried last night, but to no avail...

Ta,
Dan

i2i
18-08-2010, 05:12 PM
it's going on the bench tomorrow so i'll have a look for you. On the larger machines all you do is take off the motor, unbolt the pulley block, then unbolt the ballscrew block and the whole lot comes out together. Remember to lock off the slide, or it will end up at the bottom of the lathe.

danielbriggs
18-08-2010, 05:25 PM
That's what I did; but after removing the two screws from the black ball screw block, it wasn't budging. Methinks there is another screw or two elsewhere.
I'll chuck a few photos up tonight, should I not have any joy.

Ta,
Dan

i2i
18-08-2010, 05:29 PM
it will be dowelled to the slide, so it may take a bit of jiggling to pull off.

danielbriggs
18-08-2010, 11:21 PM
OK, I'm struggling somewhat... :cry:
I managed to remove the ball screw nut, however I can not for the life of me remove the recirculation tube by sensible means. I've tried several modest methods, but I really don't want to be too heavy handed and damage it further.

Anyone any tips to get the tube off?

I'm starting to feel hopeful it can be fixed now; it's just this damn tube is (hopefully) the last hurdle...

Cheers,
Dan


http://img833.imageshack.us/img833/2462/dsc04320.th.jpg (http://img833.imageshack.us/img833/2462/dsc04320.jpg)

http://img691.imageshack.us/img691/3371/dsc04309h.th.jpg (http://img691.imageshack.us/img691/3371/dsc04309h.jpg)


http://img840.imageshack.us/img840/9602/dsc04310s.th.jpg (http://img840.imageshack.us/img840/9602/dsc04310s.jpg)


http://img188.imageshack.us/img188/9646/dsc04314k.th.jpg (http://img188.imageshack.us/img188/9646/dsc04314k.jpg)

i2i
18-08-2010, 11:38 PM
the tube will be pressed in, but you must be careful not to dent it or the passage of balls will stop. On the larger nuts the tube is clamped in place and is easy to remove. Good luck.

i2i
18-08-2010, 11:40 PM
are any of the balls miss shaped.

i2i
18-08-2010, 11:47 PM
just thought i'd give you an incentive to repair this ballscrew, a new one is 166.92 + vat and delivery.

danielbriggs
18-08-2010, 11:47 PM
Cheers i2i;
No misshaped balls; all perfect.

Just can't get this bloody tube out!!

i2i
18-08-2010, 11:51 PM
be gentle with it.

one important thing, everything must be spotless when reassembling the nut.

danielbriggs
19-08-2010, 12:36 AM
:thumbdown:
:redface:
:confused:
:cry::cry::cry::cry::cry::cry::cry:

The recirculation tube cracked in two with gentle tapping...

Does anyone have a replacement for sale? Or know where to buy a suitable one from?
I *think* the thread was 10TPI...

Boxford spares have a replacement ballscrew and nut. But I'm not going to even mention the price.
Anyone who can help; I'll pay good too. I want the machine back up and running asap!

Cheers,
Dan

routercnc
19-08-2010, 08:28 AM
Hi Dan,

Sorry to hear of your tale of woe. I was about to give some encouragement by telling you about a similar thing which happened to me when the balls dropped out of my Z axis profile bearing when it moved past the end of the rail during assembly (!). I can sympathise with the tap-tap-tap sound followed by crapping yourself. Anyway, they were actual fairly easy to get back in on the linear bearing.

This may not help, but my ballnuts (of different design, but perhaps could be made to work?) were around 55 from MotionControlProducts.

danielbriggs
19-08-2010, 10:04 AM
Thanks for that.
Ideally I'd like to try a drop in replacement; but if I can't find a suitable one then I might be in touch :)

The ball screw is 7.80mm OD, 2.54 pitch.

Cheers,
Dan

i2i
19-08-2010, 10:14 AM
are you sure the pitch is right, they're normally metric. My guess would be 2.5mm.

danielbriggs
19-08-2010, 10:18 AM
I'll double check tonight; I measured ~2.5mm over 1 thread so I measued 5 threads over the fine groove on the OD.
12.80mm over 5 threads.

You don't know of anywhere that would sell drop in replacements would you? (apart from Boxford at this point)

Ta,
Dan

i2i
19-08-2010, 10:33 AM
you can get the larger ballnuts, but not the smaller ones. Saying that boxfords price isn't too bad.

danielbriggs
19-08-2010, 01:01 PM
OK, replacement ball screw and ball nut for the x-axis is 204.95 inc VAT + delivery.
Does anyone have a cheaper drop in solution? Or am I gonna have ta sell my shoes to buy this replacment part?

I couldn't find a suitable sized replacement on MotionControlProducts. :cry:

Ross77
19-08-2010, 02:46 PM
Cant you just remake the recirculation tube? as far as I know it only feeds the balls back to the start, any preload is normally provided by the ball size, I would have thougth a small length of brass or copper pipe that you can get from model shops would be at least worth a go before you shell out all that money :o)

I have a similar looking one at at home but I'm not sure its 2.5mm pitch. I'll have a look when I get home.

i2i
19-08-2010, 03:41 PM
you could replace the whole thing with an aftermarket ballscrew, but you'd end up with a flanged ballnut. Not a real problem but you'd loose a bit of travel.