Torque problems: lathe, 3-phase, inverter…

This topic has 13 replies, 7 voices, and was last updated 23 November 2017 at 13:04 by Richard Harris 5.

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17 October 2017 at 13:19 #321937
Richard Harris 5
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@richardharris5
My dad is reporting issues of torque with his wood lathe to me, saying it slows right down and even stops at times… apparently it even did this whilst he was only sanding too. And as I bought him the lathe, everything related to it is my job to investigate

It's a 3 phrase motor with a Jaguar Cub CDS inverter. The exact motor spec is in this photo below, and the exact inverter is within this PDF (this is a link which seems to auto-download, just so you know): http://www.rharris-images.com/wp-content/uploads/2017/10/CDS75-220-Manual-Part35942.pdf

I've recently added a control panel to the front which gives him really easy speed control via a dial, rather than fiddling around with the inverter itself (which isn't the most intuitive thing).

But he seems to think that the torque has dropped recently (before I added the control panel), and that he's had much more torque before…

He's currently working on an oak burr bowl, which is green, but still not the easiest material to cut AFAIK.

Any suggestions on what I could try to get the maximum torque from this? What I tried in the past was changing the torque boost setting to "constant" rather than "variable", and it seems to work perfectly, and would just keep cutting without issue. But it doesn't seem to cut as well anymore.

He has a sharpening place in the workshop and sharpens regularly, for what it's worth.

I imagine this is difficult as it's all just based on what I've heard, rather than learned myself from using. But I did just test it an hour ago myself and observed the motors stopping fully when not cutting even that aggressively.

0.5 KW does seem a touch low ? As it's quite a robust machine, Wadkin Bursgreen BZL. But a part of me would prefer it to stop, rather than throw him across the workshop…

Any suggestions very welcome! Sorry for the ramble!
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17 October 2017 at 13:19 #33086
Richard Harris 5
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@richardharris5
17 October 2017 at 13:29 #321941
John Haine
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@johnhaine32865
Is it running rough? Maybe a phase has gone, either a bad connection or an inverter problem. If it was the first it would probably cause the second! Clearly something has changed (unless it's the bearings!).
17 October 2017 at 15:09 #321956
Ian Parkin
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@ianparkin39383
I have a couple of union graduate lathes fitted with a 1 hp ( 750W) motor on the long bed and a 2 hp (1.5kw) on the short bed one both driven by inverters

I can easily stall the 2 hp motor on a large bowl..even when at 50Htz. So maybe a 3/4 hp motor isn’t big enough
17 October 2017 at 15:55 #321966
Brian Sweeting 2
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@briansweeting2
What's it like if you disconnect your improvement control and revert back to the original system of operation?
17 October 2017 at 17:01 #321979
Mike Poole
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@mikepoole82104
If if he is using the inverter to slow the motor then less power will be available, it is nice to just turn the speed down but using the pulleys to slow the speed will maintain the power and increase the torque. If you halve the speed using the inverter you will have half the power if the drive can maintain the torque, if you use the pulleys to halve the speed you will have full power and double the torque ( excluding any other factors). If the inverter that you link to is the one you are using with single phase input check that the motor is connected in delta.

Mike
17 October 2017 at 17:46 #321987
Muzzer
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@muzzer
As far as I could tell, the thing that fills your pants with mud and throws you across the workshop isn't the motor, it's the inertia of the bowl when the tool digs in. Bowl turning must be the most hazardous of the turning operations on a wood lathe.

Perhaps I'm just too much of a girl's blouse but all that buttock clenching didn't sit well with me and I ended up selling the thing after a while. I realise now that I should never have messed with The Brown Stuff, although I sold it for more than I paid, so I slept well afterwards.

I bought some olive wood from a guy near me. It's a joy to turn, being full of oil and has a lovely colour texture, although it was a rather messy business.

Murray
17 October 2017 at 21:42 #322024
Mark Rand
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@markrand96270
Make sure that the drive belt hasn't been left on the highest speed sheabes of the pulleys. Middle or lower speeds will give a far better result.
23 November 2017 at 12:52 #328655
Richard Harris 5
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@richardharris5
Firstly, please accept my apology for the long response time. This coincided with a very busy period at work for me, and a load of other madness happening that I can't even get into! Fortunately my dad has been pre-occupied so hasn't done too much lathe work lately, plus, it does actually work (and IMO, work well), so it's not an urgent issue…

Posted by John Haine on 17/10/2017 13:29:28:

Is it running rough? Maybe a phase has gone, either a bad connection or an inverter problem. If it was the first it would probably cause the second! Clearly something has changed (unless it's the bearings!).

It sounds "normal" to my ear, seems to run true too. What would it sound like if a phase had "gone"? What would that mean/do?
23 November 2017 at 12:55 #328657
Richard Harris 5
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@richardharris5
Posted by Ian Parkin on 17/10/2017 15:09:58:

I have a couple of union graduate lathes fitted with a 1 hp ( 750W) motor on the long bed and a 2 hp (1.5kw) on the short bed one both driven by inverters

I can easily stall the 2 hp motor on a large bowl..even when at 50Htz. So maybe a 3/4 hp motor isn’t big enough

Thanks Ian, that's certainly a useful point of reference. Do you consider this an issue as such? My dad says "I have to get the chisel *really* sharp and cut lightly on the bigger bowls at times". And I just think "Well, do that then!". He does seem to constantly look for new toys to buy rather than just doing whatever he wants to do…
23 November 2017 at 12:57 #328658
Richard Harris 5
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@richardharris5
Posted by Brian Sweeting on 17/10/2017 15:55:12:

What's it like if you disconnect your improvement control and revert back to the original system of operation?

That would be a BIG faff to do tbh, but I don't believe this to be the issue given what the controller does. We do still have it lying around though, should we need to test this.
23 November 2017 at 13:01 #328659
Richard Harris 5
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@richardharris5
Posted by Mike Poole on 17/10/2017 17:01:08:

If if he is using the inverter to slow the motor then less power will be available, it is nice to just turn the speed down but using the pulleys to slow the speed will maintain the power and increase the torque. If you halve the speed using the inverter you will have half the power if the drive can maintain the torque, if you use the pulleys to halve the speed you will have full power and double the torque ( excluding any other factors). If the inverter that you link to is the one you are using with single phase input check that the motor is connected in delta.

Mike

Thanks Mike, useful thoughts. I think he knows this but probably doesn't always do it so I'll certainly recommend reverting to the pulleys for the most power and torque. He's also not properly bolted the lathe down yet as he did a bit of a rushed job of it when he first got it, and is contemplating a new layout for the workshop. But if he did bolt it down, that would also mean he could use it at sightly higher speed (on the largest pulley) and not reduce the power or torque to stop the lathe wobbling.

I'll also check the motor is connected in delta, thanks!
23 November 2017 at 13:02 #328660
Richard Harris 5
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@richardharris5
Posted by Mark Rand on 17/10/2017 21:42:17:

Make sure that the drive belt hasn't been left on the highest speed sheabes of the pulleys. Middle or lower speeds will give a far better result.

Yep, good point. The largest pulley has a 1 inch chip missing out of it (like someone took a bite through the aluminium). I think this stops him from using it at times but maybe I could solder or epoxy a new bit in place to help.
23 November 2017 at 13:04 #328661
Richard Harris 5
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@richardharris5
Posted by Muzzer on 17/10/2017 17:46:42:

As far as I could tell, the thing that fills your pants with mud and throws you across the workshop isn't the motor, it's the inertia of the bowl when the tool digs in. Bowl turning must be the most hazardous of the turning operations on a wood lathe.

Perhaps I'm just too much of a girl's blouse but all that buttock clenching didn't sit well with me and I ended up selling the thing after a while. I realise now that I should never have messed with The Brown Stuff, although I sold it for more than I paid, so I slept well afterwards.

I bought some olive wood from a guy near me. It's a joy to turn, being full of oil and has a lovely colour texture, although it was a rather messy business.

Murray

Hah! That is good to know, thanks Murray! On the outbound side he is limited to about 21 inches which isn't THAT big, and so far, he seems to just use it for roughing things out (on really large green stuff) and then it ends up on the inbound side anyway, so not really that big/heavy. He has spoken about adapting the outbound side for bigger stuff, but I think he's quite far away from that yet.
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