A New CNC Build

**Geoff Sims** · 20th August 2009, 12:46 AM

HI Rod

Thanks for your response.

I bit the bullet and opened up my ballscrew and nut. After fiddling around for quite a while, I guessed that there was no way other than to simply screw the ballnut off the end of the shaft as there was no way I could get the orange plugs out.

I was very careful and caught all the ball bearings. As it turns out, this was the only way to open it up as the orange plugs can only be inserted into their seats from the inside. The ball nut actually has three ball races inside and an orange 'plug' for each one. Each race is two threads wide.

The thread through the nut is broken by the three plugs which each have a diagonal slot through them which redirects the balls from one thread back to the other, thus recirculating the balls. Importantly, as I found out later, the sections of thread between each race remain empty and unused.

Anyway, back to the story. The inside of the nut and the balls were all very clean, and surprisingly DRY. There appeared to be no lubrication at all. Initially I couldn't work out why the nut had locked up on the screw, but I found out what I think was the cause when I came to put it all back together after about the sixth try.

Each time I tried to reassemble, I got all the balls back in, but each time, when screwing the shaft through the nut, it would go so far and then lock up. What was happening was that one of the balls would pop out of its race into one of the spare threads between the races as I was assembling. As the shaft revolved, this ball would move around the thread until it ran into the back of one of the orange plugs and jam up against it, causing the shaft to lock. I'm assuming that one of the balls somehow escaped from its race and that's what caused the whole thing to jam up in the first place.

Anyway, I got it back together. What I finally realised was that I had to divide the balls into three and feed them into each race one at a time and then screw the shaft in just enough to block them from coming out again. Then onto the next race, and then onto the last. That way, the whole thing went back together fairly easily and the shaft ran right through the race wiithout binding. You just have to go easy and have a system or sequence.

There was one small hiccup though, and that was that I couldn't get the last ball into the centre race. It just didn't want to go, so that race is one ball short. It doesn't seem to matter though. It runs very smoothly, in fact more smoothly than originally. I've kept that ball just in case it develops any more problems and I need to do another similar operation.

Since this ballscrew is mounted under the bed of my machine and is protected from swarf and dust, I used a bit of sewing machine oil in the ballnut for lubrication. The shaft itself doesn't seem to get oily so the seals seem to be doing their job well and swarf and dust shouldn't stick to it.

I've put my machine back together again and it seems to be working fine. I'm just hoping it remains that way.

Cheers
Geoff

**rodm** · 20th August 2009, 01:22 AM

Hi Geoff,
Pleased to hear your news.
Thanks for taking the time to post the assembly sequence on the forum as it will be a handy reference.
I hope it is plane sailing form here for you.

**Geoff Sims** · 22nd September 2009, 06:46 PM

Hi All

Finally got back to my router again and have machined a couple of trial pieces. One was an acrylic desk nameplate with a logo on it, and one was a new front panel for my power supply/control box. I've given the nameplate to the person it was made for, but the photo is of a similar one which I made on Rodm's Morphy as he was generously giving me a tutorial on machining.

However, it hasn't been plain sailing from there.

I set up to do a back panel for my control box and part way through the job, the X axis just stopped moving. At first I thought it was a repeat of my ballscrew jamming exercise from a couple of posts ago, but I found I could turn the X axis ballscrew by hand fairly easily. Too easily in fact.

For some reason, the coupling between the stepper motor and the ballscrew had sheared in two. I don't know why, but I suspect that maybe the ballscrew momentarliy locked up again. If that's the case, I might be up for a replacement ballscrew. Very blurry picture of coupling attached.

Anyway, I've ordered another coupling and will just have to wait for it to arrive before I can carry on. If it happens again, I'll replace the ballscrew.

Anyone have any other theories as to why this may have happened?

Cheers

**seafurymike** · 22nd September 2009, 09:26 PM

Thats a shame about the X locking up Geoff.
I hope you sort the issue out soon as it's quite frustrating to have a machine, lots of work and no method of getting the current issue resolved in a quick manner.

**WillyInBris** · 22nd September 2009, 09:59 PM

Unsure on your problem but I snapped one of them, my acceleration was high on my gantry and the coupling couldnt handle it.

So I slowed my acceleration and its been ok may have to find a better coupling though that can handle the weight and acceleration unless someone else has a better idea

.

I think Honman has some couplings last time I looked may be able to help you out.

**Geoff Sims** · 26th September 2009, 11:40 PM

Hi Mike, Willy

Sure is a pain. I've been all over the X axis and can't find any issues. Acceleration isn't set particularly high so that shouldn't be an issue. I'll slow it down a little anyway and see what happens.

I've ordered a couple of new couplings, from Peter Homann, and another one (a beefier one from the UK. I needed a couple of spare collet nuts for my Kress spindle, and they were cheaper from the UK due to cheaper shipping, so I got a heavy duty coupling at the same time.

If the helical coupling breaks again, I think I'll be safe in assuming that the ballscrew is the issue. I'll just replace it and use the heavy duty coupling as well. If nothing else goes wrong, at least I'll have a spare.

Now, I've just got to wait until they arrive

Cheers

**WillyInBris** · 27th September 2009, 12:40 AM

Good to hear jeff I would loan you a spare if I had one

need to order a couple more who did you get you couplings from and how much.

Thanks Willy

**WillyInBris** · 27th September 2009, 12:43 AM

Originally Posted by Geoff Sims

Hi Mike, Willy

Sure is a pain. I've been all over the X axis and can't find any issues. Acceleration isn't set particularly high so that shouldn't be an issue. I'll slow it down a little anyway and see what happens.

I've ordered a couple of new couplings, from Peter Homann, and another one (a beefier one from the UK. I needed a couple of spare collet nuts for my Kress spindle, and they were cheaper from the UK due to cheaper shipping, so I got a heavy duty coupling at the same time.

If the helical coupling breaks again, I think I'll be safe in assuming that the ballscrew is the issue. I'll just replace it and use the heavy duty coupling as well. If nothing else goes wrong, at least I'll have a spare.

Now, I've just got to wait until they arrive

Cheers

Question I should have asked before when did it break on start of acceleration from an x to y movement or on a straight rapid?

**Geoff Sims** · 27th September 2009, 01:17 AM

Hi Willy

The coupling broke in the middle of a fairly slow x axis movement towards the home position. The Z axis was up out of the job and there was no load at all. The move was at about 1200mm/min which is not terribly fast.

The coupling from the UK is here: http://www.worldofcnc.com/products.asp?recnumber=55

Cheers
Geoff

**rodm** · 27th September 2009, 01:31 AM

Usually a lock up will cause the motor to stop and you get a grinding noise. It is possible that that nut is still causing you trouble so might be wise to just order a new nut - no need to get a complete ballscrew. I have a tube you can borrow to transfer a new nut onto the ballscrew.
What is the allignment like on the coupling. The coupling only allow a few dergrees of mis-allignment so have a look see if you are bending the couling too much.

**Geoff Sims** · 29th September 2009, 11:53 AM

Hi Rod

The alignment on the ballscrew is fine, as far as I can see. If there is any discrepancy, it's not measurable, so it should be OK.

I hadn't considered just ordering a replacement ballnut. Having had the ballnut off my current ballscrew and experienced the difficulty of putting it back together, it wasn't something I contemplated doing again. Had I been able to get all of the balls back in it may have been OK, but that last one just refused to go in. But, if there is an easy way of getting a new one on without losing all the balls, I think I will take your advice and order a new ballnut.

I've got the day off today so I'm hoping my replacement coupling from Peter H arrives so I can put the machine back together

Cheers

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