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KevinC
04-09-2015, 02:20 PM
I have been running the eBay 6040 for 4 months now and it has finally developed a major problem.

My x-axis is jamming up when it gets near the middle of the axis. It causes the whole gantry to jump as it passes across this area and results in a jagged finish on the work piece which is unusable.
It only happens when travelling in one direction - pulling towards the stepper (as opposed to pushing away).
It seems to happen at slightly different points along the axis each time I try to recreate the problem so hopefully it's fixable.
I would guess that it has got dust inside the bearing. I may have caused this by applying spray grease to the ball screw several weeks ago.
I am tempted to strip it down and clean everything but this will be a big job that is a bit out of my league.
Any advice would be greatly appreciated.

Thanks,
Kevin.

mekanik
04-09-2015, 03:07 PM
Hi Kevin
Sorry to hear about you problem.
Try spraying with WD40 and running the gantry back & forward full travel, clean ballscrew exterior and repeat, with a bit of luck that might clear the grease and associated dirt, don't have a machine myself so not sure if it's supposed to be oiled or greased.
Hopefully someone with more experience will be along with some more info
Regards
Mike

KevinC
04-09-2015, 03:35 PM
Hi mekanik,
Thanks for your advice.

I have just discovered a broken bush on the x-axis.

This is obviously the cause of my problems.

I am very happy that this is a simple fix. The thought of stripping this down is a daunting one!

I can't wait to get my new machine from Dean - JazzCNC! It looks like a fantastic machine!

Thanks again,
Kevin.

KevinC
04-09-2015, 03:48 PM
Here is the broken part. I thought it was called a bush but I'm having no luck finding it on eBay when I search for 'CNC bush' which leads me to believe that it's not a bush! Lol
Any idea what it's proper name is?
http://www.mycncuk.com/attachment.php?attachmentid=16007&stc=1
Buy right or buy twice as they say!

mekanik
04-09-2015, 04:39 PM
Hi Kevin
Glad you found the problem.
What your looking for is a flexible coupling.
http://www.ebay.co.uk/itm/Flexible-Shaft-Coupling-CNC-Stepper-Motor-Coupler-Connector-10-Size-for-Choice-/321830446041?var=&hash=item4aee96e3d9
Dean's Machine will be a cracker.
Regards
Mike

KevinC
04-09-2015, 05:11 PM
Thanks again Mike,

Would these work the same as mine?

I notice they don't have the slit/hinge running along the width like mine.

Let me know if you ever need something cut Mike, I owe you one!

Cheers,
Kevin.

Lee Roberts
04-09-2015, 05:35 PM
They should be fine as a direct replacement, however I see allot of this flexable type brake in this way, so I would advise going with a "lovejoy" or even better an "Oldham" type coupling.

.Me

mekanik
04-09-2015, 05:39 PM
Hi Kevin
That's a very kind offer.
The coupling in the link locates and is locked with a grub screw, yours just has a different clamping arrangement so it will be fine.
Your coupling will have sheared for a reason, what you need to do is check that the gantry isn't binding for a start, but i would suspect it's probably a slight misalignment of the motor and ballscrew shafts causing the coupling to flex on each rotation and eventually metal fatigue results in a break.
While your waiting for your coupling try and align the two shafts as best you can, if possible shim the motor to suite.
Good luck
Mike
PS
or what Lee said

KevinC
04-09-2015, 05:48 PM
Thanks Lee,

I just purchased the flexible type recommended by Mike.

I will have a closer look at the Lovejoy & Oldham couplings now.

I can't wait to see the back of this 6040 toy!

The Dean-Machine will be a most welcome upgrade!

KevinC
04-09-2015, 05:54 PM
Thanks again Mike,

That makes sense.

I will try to get them aligned as best I can but I honestly wouldn't know how to go about this.

I guess I'd need one of those gismos for super fine measurements. I don't have one but I've seen them used in a few youtube videos.

Kevin.

mekanik
04-09-2015, 06:55 PM
It's relatively easy if both shaft sizes are the same,use the straight end of a steel rule lay it against the two shafts(piece of white paper behind) and you will see daylight on one of the shafts if there is misalignment, will be tricky though as you will have limited access below your table. If one shaft is bigger than the other put the straight edge on that one and just try to guestimate the run out.
Good luck
Mike

Lee Roberts
04-09-2015, 07:38 PM
Oldham type are great for this as their design allows for misalignment in the hubs, I would still do as Mike suggests though because something isn't right, the original couplings are rubbish though to be honest (no offence) unless everything is perfect, even then you can't really push them to hard, the forces can be to great really for such thin ali, they are designed for light weight machines really, 3D printers, engraving, machines like that.

For the price they pay for them I don't know why they even bother using this type on a machine.

.Me

routercnc
04-09-2015, 09:31 PM
Hi Kevin,

I used to use a short length of stiff rubber tubing (similar to the reinforced sort used on cars for flexible brake hoses) which was a tight friction fit on both shafts. This worked a treat giving a bit of vibration isolation and alignment, and it never slipped or broke. These were fitted to both X motors and the Y motor. Z is belt driven.

16008

After many, many hours of use I decided it would look more professional fitting a coupling so went for the spiral aluminium type. One of them broke eventually, and the problem with them is that it is not obvious that they have broken as they can still transmit drive to the ballscrew most of the time.

I then fitted a larger diameter one, and this has been running for some time although the other day I was looking at them wondering how long they would last.

KevinC
10-10-2015, 10:55 AM
Hi guys, I got the Flexible Couplings recommended by Mekanik (http://www.ebay.co.uk/itm/Flexible-Shaft-Coupling-CNC-Stepper-Motor-Coupler-Connector-10-Size-for-Choice-/321830446041?var=&hash=item4aee96e3d9&clk_rvr_id=909111481908&afsrc=1&rmvSB=true). They do the job but the outer diameter (18mm) on these is quite a bit thinner than the original (25mm).

Also, within a week, a second of the original FC's sheared of in the same way!

I had a bit of trouble getting these new FC's to fit so I sanded the inside with 600 until it fit nicely. Well it is now making a nasty creaking sound when I run it so I expect it to break fairly soon.

So, In preparation for this I am on the market for some high quality Flexible Couplings, preferably Oldham as these seem to be the type that would take most abuse.

I'd imagine steel to be less likely to break than the Aluminium ones I am currently using.

I have found these (very expensive) Oldham FC's on eBay (http://www.ebay.co.uk/itm/8-mm-Shaft-Flexible-Oldham-Coupling-NBK-MOS-32C-8mm-Aluminum-Polyacetal-/281143902164?hash=item41757b7fd4) but there must be something less pricey in the UK!

Another issue I keep running into is that they seem to come without the Polyacetal Spacer thingy in the middle!

Am I missing something or why would one ever want these without the spacer?! Madness! Lol.

If someone could suggest a place to buy these in the UK I would be very grateful!

Cheers guys Kevin.

mekanik
10-10-2015, 11:43 AM
Hi Kevin
Try this link
http://www.reliance.co.uk/shop/index.php?cPath=27_38_193&page=2
Looks like you will have to give them a ring for price.
This one probably cheaper
https://www.cnc4you.co.uk/XD-Coupling-25mm-x-30mm
Regards
Mike

cropwell
10-10-2015, 11:47 AM
I like the idea of the rubber tubing couplings, though I would clamp it to the shaft with hose clips.
I had a coupler break and I replaced it with a similar one, but I wish I had thought of the rubber tube, it is a bodge, but in keeping with the standard of my MD machine.

Rob

KevinC
10-10-2015, 12:12 PM
Mike to the rescue again!

You are a a legend mate! This is exactly what I'm after!

I like the look of CNC4YOU. I'll have a good wee nosey at this now shortly!

Rob,

I've never heard of this particular bodge. I like it!

Sounds like it could pull one out of a hole in an emergency.

Can you elaborate please? What kind of tubing etc?

Cheers mate!

Kevin.

cropwell
10-10-2015, 03:18 PM
Hi Kevin,

I'm just echoing the posting from routercnc further back in this thread. All I am saying is that I would use hose clips to make sure the little fecker didn't slip. I would probably use a bit of gas hose as that is flexible and braided.

I haven't actually done it, but I would probably do it in preference to fitting the ones like yours that broke, even though I have a couple of them spare in a drawer.

I had a lot of trouble with the clamp type slipping and eventually drilled them out and bonded a slitted tube in as a shim to get the internal diameter right for the stepper shaft.

Cheers,

Rob