Thread: Runaway bowl

That's a good point. I may do when I go out to H&F.

Hello Fumbler

Couple of simple questions:

• How long have you been turning?
• Were you using a screw chuck in that bigger chuck to hold the timber onto the lathe?
• Did the blank come off or the entire chuck?

If it was the blank and you were using a screw chuck or single screw fitting to hold the blank, the simple answer will be that the thread for the screw chuck was stripped due to the catch. Easily done especially if you are using the wrong tool, which you were.

If the entire chuck came off then there is a real problem because that's impossible unless you stopped the the motor instantly.

If you weren't using a screw to hold the piece onto the chuck and didn't have the tail stock up against the blank how was it being held?

Good idea to put a machined metal or perspex washer/spacer (about 3mm thick) on the drive spindle and the chuck either will seat the chuck better and stop it from coming off in an emergency stop (unless it's very heavy) will also make it easier to break the seal to take chuck off later on.

Been using both on lathes for around 40 years and only ever had one thing wind itself off when lathe was stopped and that was a 6 ft diameter table top 40 mm thick. Nothing was ever going to stop that sucker from coming off. That incident was before I started using the washer/spacer.

Just as an aside the pics you put on look like there are different inserts in each photo. Is that correct or just an optical illusion?

Cheers - Neil

Neil,

with this lathe, about 6mnths, in total about 8yrs, by no means would I call myself a pro, but steady as she goes and I manage to turn out a few nice pieces .

I had the blank tightly on the worm screw in the jaws of the scroll chuck.

The ENTIRE CHUCK WTH BLANK still firmly attached to the worm screw (which is now subsequently bent) came off.

I have never seen it before, and due to the nature of the forces vs threads etc, spindle rotating counter clockwise, thread clockwise, that the momentum of the rotation will keep everything in place, well I this instance, it doesn't seem to be the case.

The blank was only about 120mm diameter and 80mm long, and as the chuck is only rated to 2000rp, and being off centre slighty (I had roughly rounded on band saw) I didn't crank up the revs.

I like everything about this lathe except how it stops, most coast to a stop, cut the power and it slows down, this stops dead, no ifs buts or hey lets take a breather, it stops.

I want to try and replicate it but next time may cause me some damage so i'm taking it easy when turning using the chuck and no tail stock

I have recently asked on here about washers and most said they dont use them, so i may just make one to fit. I have some perspex laying around. But I am also still going to speak to the manufacturer about my experience.

This has been puzzling me - each time I read this thread I leave unsatisfied, because I’ve not been able to come up with a plausible scenario that would explain what happened.

Now knowing that the lathe is braked, and quite heavily by the sound of it, perhaps the catch slowed the lathe down, the lathe tried to recover the speed, drawing start-up levels of current, which caused the breaker to trip, which in turn caused the brake to stop the lathe, allowing the chuck to spin off. The problem is that a catch big enough to stop the lathe would have tightened the chuck up quite nicely even if it was slightly loose.

Does that sound feasible to anyone else or am I bending physics to make it fit?

I suppose it would help knowing how the lathe brakes itself.

Originally Posted by Fumbler

I have recently asked on here about washers and most said they don't use them, so i may just make one to fit. I have some perspex laying around.

Originally Posted by ubeaut

Good idea to put a machined metal or perspex washer/spacer (about 3mm thick) on the drive spindle and the chuck either will seat the chuck better and stop it from coming off in an emergency stop (unless it's very heavy) will also make it easier to break the seal to take chuck off later on.

When turning larger pieces (like 40kg) outboard on an earlier lathe I had problems with the faceplate/chuck unwinding when stopping. I found a very thin rubber washer worked best (for me) in minimising that problem. Rubber won't give you as accurate a seating on the headstock shaft as metal as the variation in the density/compression of the rubber can give rise to a small amount of runout on larger diameter pieces. This could be a problem if your work involves multiple re-chucking or re-fixing to the lathe. But, that was less of a problem for me than than having a 40kg piece take off across the workshop.

I've not found the need for a washer/spacer since moving over to electronic variable speed control lathes, which allow you to dial down the speed before stopping. However, a malfunctioning EVS unit could also create the problem.

Did your lathe stop itself after the catch or was it still spinning? EVS lathes that have a braking function usually ramp down slowly, not stop instantly like you say yours does. I think you have a fault there if that's what it does.

I had a 30# 4 jaw chuck come off my metal lathe.... Does that count ?

Originally Posted by Kbeitz

I had a 30# 4 jaw chuck come off my metal lathe.... Does that count ?

If you found the reason why it came off and it can help me figure out, then yes, it does count.

It was all my fault... I was in a hurry and chucked my 4 jaw chuck inside
my huge 3 jaw chuck and it was not centered. Only two jaws was doing the
holding. Things got exciting for a while. No harm done,.

Well a quick trip to H&F today and I have discovered they were in the process of contacting purchasers of a circuit board issue which needs replacing. After showing them the video of my machine in action, they were concerned due its sudden stop, not step down.

it still doesn't explain how the chuck came in motion, but would still be interested to hear what they think of my lathe and whether it's s lemon or not. The 2 definitely sound different when running, but again, doesn't explain counter-acting threads undoing whilst in motion.

best I nip the chuck up with a spanner tightly in future, and or drill/tap a hole for a grub screw.

Originally Posted by Fumbler

Well a quick trip to H&F today and I have discovered they were in the process of contacting purchasers of a circuit board issue which needs replacing. After showing them the video of my machine in action, they were concerned due its sudden stop, not step down.

it still doesn't explain how the chuck came in motion, but would still be interested to hear what they think of my lathe and whether it's s lemon or not. The 2 definitely sound different when running, but again, doesn't explain counter-acting threads undoing whilst in motion.

best I nip the chuck up with a spanner tightly in future, and or drill/tap a hole for a grub screw.

The best advice and action is not to use the lathe until the issues are fully resolved.

This is pretty much as I expected in my post #7 - strong braking, however with only the chuck and a very small blank involved I still find it very perplexing. There have to be other issues at play as well - not "firming up the chuck on the spindle" etc.

Usually these events are not entirely due to one single issue, more a combination of several "small and un-concerning" issues providing the "perfect storm."

Originally Posted by Mobyturns

The best advice and action is not to use the lathe until the issues are fully resolved.

This is pretty much as I expected in my post #7 - strong braking, however with only the chuck and a very small blank involved I still find it very perplexing. There have to be other issues at play as well - not "firming up the chuck on the spindle" etc.

Usually these events are not entirely due to one single issue, more a combination of several "small and un-concerning" issues providing the "perfect storm."

agreed, and i wont be doing any turning til its been seen to. But again, a perfect storm twice? thanks.

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.

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.

Firstly, welcome to the forum.

In Australia, for whatever reason, we use the M30 x 3.5 spindle thread as a de-facto standard. The rest of the world pretty much uses the slightly larger M33 x 3.5 spindle thread, meaning it makes life difficult to get some turning stuff that screws onto spindle threads here. I wish we did use the M33 x 3.5 in this country, it would make buying some stuff from overseas possible.

Having actually used a lathe with an M33 x 3.5 thread alongside another lathe with M30 x 3.5 thread, I can state it is virtually impossible to get the larger female onto the smaller male.

The English company, Record Power, are, to the best of my knowledge, currently the only manufacturer/supplier of lathes in this country that have M33 x 3.5 on their spindle threads, everyone else has M30 x 3.5.

Mick.