Denford Software & Machines

My Novamill sits in a cold garage, as does the operator when he has to set it going.

This winter I have discovered that if I boot up the machine, on a cold and frosty morning, and use fast traverse straight away then something makes a nasty noise and the Y-axis loses its calibration.

I have taken to moving it to a known point using G01, at a sedate feed rate, and then starting a warm-up programme.

The programme runs for an hour and after this it is fine.

The ballscrews and slides are kept oiled.

Is this normal or a sign of a more serious issue?

It may just be the grease and oil stiffening up or the slides being slightly tight.

I would clean down the slideway and maybe try a thinner oil. The noise would just be the stepper motor stalling so not to worry about.

Ah, so the stepper motor is stalling but the system still counts the steps and thus it loses calibration?

Ta

Exactly, The steps are sent out but if the motor stalls it thinks it has made the move so continues out of position.

If you turn the feed override down to say 50% you should be able to use the machine while it warms up.

has to be a stall, make sure the machine is well oiled.

It may be worth removing the Y axis gib strip & giving it a quick clean & light coating of oil. They tend to have a sticky coating on after a few years. You should be able to see the adjustment screw hiding behind the front bellow on the right hand side. If you leave the stop in at the back it should fit straight back in.

I just have to say I love this site!

I drowned it in oil earlier in the week but I shall investigate the jib strip as Martin suggests. Trouble is that the machine is kept very busy so maintenance is difficult to fit in. I retired in August 2013 and since then I have spent my time making go-faster goodies for radio control cars. Never been happier, so I shall have to make sure that the machine stays healthy!
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BTW The Y-Drive is much noisier than the X-Drive. Is that a symptom of the same thing or just normal?

could be a sign of the ballscrew on it's way out.

What scale and class do you make parts for.?

angel-tech wrote:could be a sign of the ballscrew on it's way out.

Oh dear!
As you know I have been looking at getting a second machine but there are certain things stopping that from happening at the minute.

angel-tech wrote: What scale and class do you make parts for.?

I make parts for 1/10th scale off road buggies at the minute and primarily for one manufacturer but I did make one item for a bloke in USA that was 1/8th scale.

I'm about 90% export. Don't know what the problem is in the UK; they spend a fortune on paint jobs but nowt on car development!

i've made quite a few upgrade parts for the schumacher cougar sv2, and i'm in the middle of a completely new car.

ballscrews can be rebuilt, it's not that expensive.

I thought that I would give an update.

The Y-drive is still limping along and I have now changed the brushes on the spindle motor. It appeared that when I used the spindle at its max speed of 5,000rpm, the drives were picking up extra steps from somewhere.

I found that by limiting the spindle speed to 4,000 rpm the problem went away and I have used it in this fashion for a few months. But the problem came back. The new brushes seem to have cured the problem, although I haven't been brave enough to try it out at 5,000 rpm yet.

Changing the brushes is a pain of a job. The back one is easy enough but the front one is a challenge. When you remove the front cover that travels up and down with the Z-Drive, between the guides, the front brush is facing you. The trouble is that you have to have to fiddle it in and out past the Z ball-screw, which is smack bang in the way! When it comes to refitting the screwed plug that secures the brush assembly in place, I found that a small lump of Blue-Tack on the end of the screwdriver works wonders.

Another way that I have found of stalling the Y-Drive is to leave the machine doing a long job. All the chips build up between the table and the column and if you have shifted enough metal then there comes a point where the table can no longer go all the way back! That one made me scratch my head a bit as it appeared as a sudden error in position of about 2.5mm! I need to figure out some way of stopping the chips from getting down there as I don't want to have to faff about with a vacuum cleaner whilst the thing is in mid-programme.

Brushes, Novamill?

You develop a knack of working round the ball screw after you have changed as many as I have. I think it would take me 30 seconds now to get that one in but much longer the first time even allowing for dropping the cap inside & having to find it.

Martin wrote: ....................... but much longer the first time even allowing for dropping the cap inside & having to find it.

LOL

The little rascal found a new place to hide every time!

Let's talk ball-screws!

I have continued to use the machine, taking care to keep everything well oiled. The jib strips are as tight as they can be without stalling the drives.

But I have a lot of backlash on the x-axis. The machine is converted to Mach3 and I have been experimenting with the backlash compensation feature today. On the x-axis I have set the backlash at 0.12mm and this seems to do the trick, and 0.04mm on the y-axis.

I can limp along like this but I feel that the x-axis ball-screw needs to be replaced or refurbished in some way.

The question is, where can I lay my hands on one and how easy is it to fit? Also, is this going to louse up my home datum switch and lose the datum on all my manufacturing jigs?

This is my latest project and I have noticed that round things are not round any more and drillings are not necessarily in the right place! If another one is ordered I'm not going to be able to start it unless I can cure this problem.

The Ball screws for the NovaMill are still available but Denford do not hold stock.
X Axis RM1/0403A £270
Y Axis RM1/202A £255
Z Axis RM1/302 £390

Will take 6 to 8 weeks to deliver and yes the Datums would have to be reset.

Have you checked the bearings at the end of the screw or are you sure the Ball Nut is the problem? try putting a clock on the end of the screw and see if there is any float from one direction to the other.

i would check the angular contact bearings on the x axis before attempting any work on the ballscrew.

angel-tech wrote:i would check the angular contact bearings on the x axis before attempting any work on the ballscrew.

Hi Tom,

I'm sure that I posted yesterday to thank Steve for his information and to say that at those prices I really did hope that it was the bearings. But it seems to have been lost!

I'm just in the process of trying to measure where the backlash is coming from.

EDIT
I would say that about half of the backlash (0.05mm) is coming from the angular contact bearings and the other half from the jib strip clearance and ballscrew combined.

Hi. You did post a reply but on the wrong thread. No problem.