Tool offset issue

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james.miller
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Hardware/Software: Denford Novamill 61105A 1996

Tool offset issue

Post by james.miller » Thu 19 Oct , 2017 13:19 pm

Hi guys,

I've been offered a 1996 Novamill for a great price from a friend. He says that it runs fine other than a issue with the tool offsets.

He said 'you can cut a profile with one cutter then it does a tool change with the ATC and the next tool will run slightly out to the previous one.'

What would you all say this issue is? A worn ballscrew? Something off with the electronics?

I am trying to gauge how much the issue will cost me to repair and whether I can diagnose the issue before handing over my precious cash.

And help would be amazing. :P

Thanks,
James

james.miller
Posts: 11
Joined: Thu 19 Oct , 2017 13:04 pm
Hardware/Software: Denford Novamill 61105A 1996

Re: Tool offset issue

Post by james.miller » Fri 20 Oct , 2017 8:35 am

,
Last edited by james.miller on Sat 09 Dec , 2017 22:22 pm, edited 1 time in total.

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Re: Tool offset issue

Post by TDIPower » Sat 21 Oct , 2017 13:43 pm

The tool offsets need to be set within the control program. You don't say if it is VR2 or VR5 (or something older like the DOS control). If the offsets have not been set up correctly in there then that will be the issue. I personally would be checking that myself and not trusting the friend to have done it right. Check the tool holder for any play too.

Pete

james.miller
Posts: 11
Joined: Thu 19 Oct , 2017 13:04 pm
Hardware/Software: Denford Novamill 61105A 1996

Re: Tool offset issue

Post by james.miller » Mon 23 Oct , 2017 8:29 am

Thanks Pete,

Ahh yeah I suppose human error is a possibility, my friend is a competent CNC programmer/operator though so I hadn't thought of that. I'm going to set the machine up and ask him to try and replicate the error before I hand over any money. Hopefully that is the case.

I'll check the tool holder for play as well. I suppose it could also be that the tool holder isn't pulling up into the spindle properly because the pull studs not in the tool holder correctly or there's debris in the spindle.

I think it's DOS but I haven't seen the software running yet. The PC has been upgraded and it looks like there's been a USB mod done on the RS232 output from the control box. So it's possible that the control software has been upgraded.

I mainly wanted to make sure there wasn't any common issues with these machines that people new of that could be causing this and too make sure that this wasn't an indicator of a obvious major issue with the machine. But I suppose as you say it could be one of a lot of things.

If it's not obvious what the issue is I'll get some photos and videos when I have a go with it next week and post an update. :wink:

Thanks,
James

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Re: Tool offset issue

Post by TDIPower » Mon 23 Oct , 2017 22:27 pm

It could be possible that it has had the control updated at some point by Denford and the USB is an official update, or it could just be a simple plug in USB to RS232 converter to enable a PC without onboard RS232 to run.

Lets hope it has had the Denford upgrade done and you can run the VR control rather than the DOS. I find the DOS control a bind on my lathe. Does it have the 'tutor' keyboard as that would be required for DOS control.

Pete

james.miller
Posts: 11
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Hardware/Software: Denford Novamill 61105A 1996

Re: Tool offset issue

Post by james.miller » Tue 24 Oct , 2017 8:42 am

It didn't have the tutor keypad with it when I last saw it so hopefully that means it's been upgraded. fingers crossed.

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Steve
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Re: Tool offset issue

Post by Steve » Wed 25 Oct , 2017 13:31 pm

In 96 it would have been DOS software. If you check the serial number label on the cabinet it should say what software was supplied with it.


The issue you mention with subsequent tools running out is this in the X or Y axes or the Z If the Z then I suspect offsets.

If X or Y I would check the machine is well lubricated.

If its repeatedly loosing position it could be related to either a mechanical stall or electrical noise.

You could make some tests while cutting air returning to a clock to prove this. Try at slower feed rates when the machine has higher torque in the axes.

Also try without the spindle running as this could electrical noise which could cause miss positioning.

I would also check the spindle speed with a tacho and make sure its not running over speed as this would create noise.

james.miller
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Re: Tool offset issue

Post by james.miller » Wed 25 Oct , 2017 15:04 pm

Cheers Steve,

That's great help I will check all of these things. :) :D

What exactly do you mean when you say "You could make some tests while cutting air returning to a clock to prove this."?

Thanks,
James

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Re: Tool offset issue

Post by Martin » Wed 25 Oct , 2017 22:22 pm

Running the program without a billet & putting a DTI touching on the end of axis set to zero in its home position. When it finishes the cycle the DTI should read 0 if it's repeating.

james.miller
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Hardware/Software: Denford Novamill 61105A 1996

Re: Tool offset issue

Post by james.miller » Thu 02 Nov , 2017 14:21 pm

Thanks for your help guys,

I went to see the machine again yesterday. It is using the VR 5 control software and the control unit has been upgraded recently. Glad I wont have to mess around with the old school DOS control.

I couldn't seem to get it to repeat the issue that I was told it had. So I'm hoping it was a user error. But i'll update you all once I have the machine and have a chance to properly play around with it.

Could you suggest a good low price quiet compressor that would be good to use for the tool changer? It says it needs 100PSI with a max of 150PSI, so I'm thinking a 8bar compressor would do the trick.
I've been looking at these Bambi silent compressors:
https://www.ebay.co.uk/sch/i.html?_from ... or&_sop=15
However they are rather pricey.
Any recommendations you've got for a quiet compressor for around £100-£200 would be great.

Thanks,
James

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Steve
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Re: Tool offset issue

Post by Steve » Thu 02 Nov , 2017 16:04 pm

8 Bar is fine and we use the Bambi at Denford.

I would set the pressure at 80psi.

james.miller
Posts: 11
Joined: Thu 19 Oct , 2017 13:04 pm
Hardware/Software: Denford Novamill 61105A 1996

Re: Tool offset issue

Post by james.miller » Sat 09 Dec , 2017 18:16 pm

Hey guys,

So I have my machine set up and running in my workshop now.

I have now been able to recreate the issue that the machine has. I cut a circular feature then moved the machine back to home position using the home XYZ button on the VR5 control software. I then measured my hole and it was slightly under size so I ran my program again to see if it would take the 0.1mm out that it was under size by. The X had moved by around 0.5mm making my hole oversize.

It has kept the same position on the control and displays the same figures in the program datum position and home position.

I then moved the machine to the home position in jog mode not by pressing the home button and it doesn't move out that way.

It seems to have skip some steps. Does this sound like a electrical noise issue? How would you suggest I go about fixing this?

Cheers,
James

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Steve
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Re: Tool offset issue

Post by Steve » Sat 09 Dec , 2017 19:06 pm

Sending the machine home with the XYZ button makes it find the Home switches. On the Novamill these are proximity detectors. As it is finding a different location when you send it home I would check the switch is secure and the surface it registers when it Home’s is also clean and secure. Normally the Home position would not vary so there must be an issue with the switch detection.

james.miller
Posts: 11
Joined: Thu 19 Oct , 2017 13:04 pm
Hardware/Software: Denford Novamill 61105A 1996

Re: Tool offset issue

Post by james.miller » Sat 09 Dec , 2017 22:34 pm

Thanks Steve,

That's sounds about right.
There was a little muck on the switch but I'm not sure if that's solved the issue and the switch seems firmly in place and so is the bolt that it switches against. I'll run a few tests tomorrow by putting a clock in the spindle and touching it on a set point on the bed and sending it home and returning to the same point again and see if it repeats, as suggested by Martin previously.

If cleaning it hasn't solved the issue do you think it'll be worth replacing the switch? Any idea what switch it is? It seems like there used to be a sticker on it that I presume had a part number at some point but that's worn off.

Enjoying my machine!! Its running well as long as I don't send it home or use the ATC.

Cheers,
James

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Steve
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Re: Tool offset issue

Post by Steve » Sat 09 Dec , 2017 22:47 pm

Make sure the gap between the switch and the bolt it switches again is as small as possible.

Just keep homing it up with a clock on the axes and this should resolve it.

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