View Full Version : Coupling

04-01-2012, 05:32 PM
Is there any where near me where I can Buy 2 new GOOD quality 8mm x 10mm couplings as I bought cheap ones of ebay and they have snapped

one side twice and now the other side

Just as I was jogging for my second cutting job what a pain in the backside (I think the stepper motors are stalling on my x-axis)

I would like to pick them up tomorrow and not wait for the postman


04-01-2012, 09:22 PM
Thank you chip I was going to arc euro Thursday anyway as I need 1/4" and 1/2" collets for the spindle so I will give them a ring first to see if they have the couplings I need


05-01-2012, 11:41 AM
chip thank you for the help arc euro didn't have what I needed So I ordered from Farnell's and they are on there way

word of warning to any one thinking of ordering the cheap one's from eBay DON'T was your time and Money they are crap


05-01-2012, 11:58 AM
James, do you have the Farnell part number handy?

05-01-2012, 12:16 PM
They really shouldn't be snapping regardless of the price. Lower the feedrate limit on the X-axis by about 20% and see if that helps.

John S
05-01-2012, 01:13 PM
What sort of couplings snapped ? Surely not Oldham couplings ?

05-01-2012, 02:00 PM
Mocha the part number is 7075522 (http://uk.farnell.com/jsp/search/productdetail.jsp?sku=7075522&CMP=i-bf9f-00001000)

and it's the cheap couplings from ebay that are snapping

yes Jonathan I will slow the feed rate down and stop pressing shift key as well on the x-axis


05-01-2012, 08:49 PM
Think it's these:


If they're not well aligned then they will probably break do to metal fatigue.

So you'll have bought 7075546, 7075522 and 7002555...16.28 per coupling.

From bearing station a 15T and a 30T HTD timing pulley plus 64T timing belt costs 15.55, 17.05 including postage.

Web Goblin
06-01-2012, 06:16 AM
I agree, these couplings do not like any misalignment. I have seem these snap many times before and it is normally due to alignment problems, but the also tend to flex a bit when trying to drive a heavier load than they are designed for. If there is any play in say the shaft they are connected to, ie if it can move back and forward slightly the coupling starts to contract and expand depending on the rotation direction and this weakens the coupling.


06-01-2012, 08:27 AM
I think pulleys are on the cards I will change after I've used the machine for a bit longer and worked out where to mount them


John S
06-01-2012, 09:53 AM
An Oldham coupling is the only coupling that can take out misalignment in two planes at the same time.
These split ones always have some wind up in them and the Lovejoy jaw type coupling was never designed for zero backlash operation.