Thread: Runaway bowl

Originally Posted by Woodcrafts_UK

May I suggest a possible cause for the chuck being able to come off the lathe. Having tried to find the specs for this lathe, I found it stated as M30 x 3.5. Many lathes use the more common M33 x 3.5 (T38) size. Is it possible you have the wrong insert? The slight difference will give a reasonable hold if you just mount the chuck by hand but a catch could well loosen it.
And as a woodturning instructor, PLEASE never use a spindle roughing gouge on a bowl blank. Most SRGs are forged tools so have a relatively small tang that cannot withstand the extra effort cutting cross grain. You run the risk of snapping the tool, and the very last thing you want is half a steel chisel come flying at you.

I have been to the shop, and can catagoricslly say I have the correct insert. But as for the roughing gouge, I can't say whether I was using it or not, but the shock of it coming off and chasing me feet across the floor concerned me a touch.

i haven't spun any odd shaped blanks up lately and am also nipping the chuck up tight and all seems apples. But will know when I get back from the EVS circuit board being replaced next week.

Thank you

Originally Posted by Woodcrafts_UK

And as a woodturning instructor, PLEASE never use a spindle roughing gouge on a bowl blank. Most SRGs are forged tools so have a relatively small tang that cannot withstand the extra effort cutting cross grain. You run the risk of snapping the tool

I fully agree!

There are a few exceptions. The old P&N SRGs had a hefty milled tang, as does Doug Thomson's special order SRG. Also, Carter & Sons.

However, the other reason is that few turners have the necessary skills to manage the large potential cut of a SRG on a bowl blank (cross grain), especially with a 1-1/4" SRG. Keep in mind that SRGs don't have the flute profile or the typical swept back grind of a bowl gouge, which are optimised for bowl turning. Using a straight across grind would be courting disaster.

If you need a larger gouge for bowl work, start with a 3/4" BG and see how you go. If you get comfortable with that and you think you need even bigger shavings, the next step up from there is a 1" BG, but they are a bit hard to come by (Crown does/did make one).
There might be a very good reason why they are not being made, other than price...

I think we're getting off track, it's not my incompetence or choice of gouge to use on a 100mm diameter block of burl.

there was something that happened that made the blank and chuck spin faster than the lathe and unscrew the chuck.

besides, I have had many a catch with all manner of gouges, whether it be not addressing the timber correctly, incorrect angle etc. I by no means am a professional and don't claim to be. I haven't had a blank spin off at 3k rpm and go through a window, nor have I had a job break up on me and chunks go flying.

ill chalk this one down to the unexplained and move on, tightening the chuck fiercely, and using the tail stock for longer than necessary.

Originally Posted by Fumbler

I think we're getting off track, it's not my incompetence...

Sorry, Fumbler, if you thought I was implying any incompetence on your part. Far from it!

And, apologies for taking the thread further off topic.

As Woodcrafts_UK had raised the roughing gouge matter in his post I felt I must comment on that and not just leaving it hanging there. My comments were in no way directed at you. I tend to make my comments broadly to anyone who is currently reading the forum or to those who might be reading it in the future. It's my small contribution to fellow woodturners, for what they may be worth to someone now or in the future.

Back on topic, like you, I reckon your incident was probably caused by a faulty control and not a user error. It will be interesting to hear if the problem persists once your circuit board has been replaced.

Originally Posted by NeilS

Back on topic, like you, I reckon your incident was probably caused by a faulty control and not a user error. It will be interesting to hear if the problem persists once your circuit board has been replaced.

I agree, but it’s not going to be easy to prove that all is OK.

Originally Posted by NeilS

Sorry, Fumbler, if you thought I was implying any incompetence on your part. Far from it!

And, apologies for taking the thread further off topic.

As Woodcrafts_UK had raised the roughing gouge matter in his post I felt I must comment on that and not just leaving it hanging there. My comments were in no way directed at you. I tend to make my comments broadly to anyone who is currently reading the forum or to those who might be reading it in the future. It's my small contribution to fellow woodturners, for what they may be worth to someone now or in the future.

Back on topic, like you, I reckon your incident was probably caused by a faulty control and not a user error. It will be interesting to hear if the problem persists once your circuit board has been replaced.

All good, no offence taken.

To a certain degree, a lot of people become complacent and cocksure, when things go right for such a long time, then whammo, it all goes pear shaped. Don't get me wrong, I am guilty of complacency at times, take my thumb incident for example. Had the saw for 10yrs, the previous weekend I had spent an hour straight repatatively cutting small lengths one after the other, some at odd angles. Then a quick 2 minute job put me out of action for 2 months.

i also agree bringing the what not to do's to people's attention is a good thing, I have learnt lots from lots of wonderful people on this site, and am very grateful for all the help, advice, pointers and parts that have been sent my way.

yes, I can't wait to get it back. As I have the conductors batons to finish.

i won't however be trying to reproduce what happened to see if it's fixed or will do it again. Chucks flying round the shed is never a good thing.

Richard

Originally Posted by Colin62

I agree, but it’s not going to be easy to prove that all is OK.

True, as I just mentioned in my reply to NeilS, I won't be replicating the situation to see if all is good.

I just happened on the following comment about a Nova lathe which is relevant here

https://sawmillcreek.org/showthread....32#post2299332

I intended this for the Nova 2024 lathe.


I have had this for several months ......not ready for prime time.
Warning......when under slight stress, motor will suddenly lurch and double it's speed. The engineers are working on the problem. When coring a pine blank on slow speed (100rpm), it slowed for a moment, then raced up to 250 rpm, catching the tool and throwing the blank off the chuck. Same thing when using a roughing gouge at 250 rpm........a slight pause at a small catch the motor raced to 450rpm.
Nova was going to trade out motors but they found that the ones they were going to send did the same thing. I have been waiting several months for them to send me the swing away as well.

That tends to make a lot of sense. The fact that the tool caught on the blank, maybe it spun up to a high speed and with the faulty violent braking maybe it tried to almost instantly get back down to the original set speed and this is where the thread released.

Originally Posted by Treecycle

That tends to make a lot of sense. The fact that the tool caught on the blank, maybe it spun up to a high speed and with the faulty violent braking maybe it tried to almost instantly get back down to the original set speed and this is where the thread released.

In my mind it goes like this:

• lathe spinning at (for example) 1000rpm
• tool catches, dropping rpm to close to zero
• control software sees speed is way down and aggressively ramps up speed
• catch removed, and now the lathe is spinning at twice the speed it should
• control software sees the speed is now way too high and applies the brake

If there’s an additional problem with a brake that is too aggressive, the chuck can easily spin off and we have an entirely plausible explanation that doesn’t rely on fairies

Originally Posted by Mobyturns

If a lathe has EVS and is "underpowered" i.e. not enough grunt or the wrong belt setup is used, it is possible to stall the lathe motor with a "soft catch" (a progressive stalling rather than an abrupt stall/stop), reducing the spindle / blank RPM. When the turner reacts and withdraws the tool the EVS recovers and attempts to return to the selected / dialled speed and increases the spindle / blank RPM.

Most EVS setups are programmed to "ramp up" torque within limits to overcome stall conditions. So it is possible that the combined blank / chuck / insert that is loosely fitted to the lathe spindle may momentarily reach a temporary "overspeed" condition i.e. faster than the lathe spindle, and then becomes loose on the lathe spindle as the EVS recovers to the set speed. This can be a significant issue with larger bowl or platter projects that test the limits / power of mini / midi / cheap lathes and is alarmingly easy to do on any lathe running in "reverse".

The same occurs when a turner uses their hand as a brake on the hand wheel to abruptly slow the lathe spindle, the spindle slows however the inertia / momentum of the insert / chuck / blank overcomes the friction of either the spindle / insert or insert / chuck interface and "goes for a walk."

As I mentioned - one possible cause. Its alarming that lathes with these faults are not being discovered through product testing before reaching the market place.