Shake Rattle and Roll

[poolhound]

Before I had actually bought my lathe I picked up a some blanks at an estate sale. One was really large that was rough cut approx 12 round by 11 deep. My lathe is the nova comet II which says it is a 12" lathe so I thought OK lets try this and see what happens. I guess the distance from the center of the drive shaft to the bed is 6" but unless you have an exactly round 12" blank there is no way it will turn.

I hacked bits off the blank at the band saw and mounted a faceplate. I got it to clear the bed by about 1/4 so the blank at this point must have been ~11.5" and the open end must have been bark at some point and was very uneven. I started the lathe on slow and OMG it felt like an earthquake! 1st time I have tried anything with this much mass and to the Novas credit the motor was coping fine it was just the mass of the lathe vs the spinning blank. This coupled with the fact that this lathe is designed with feet and is not bolted to the stand made it even more scary as the lathe began hopping across the stand. I knew that I had to get it roughed round and the shake would stop but I wasnt sure how best to do so safely. In the end I clamped the lathe to the stand which helped somewhat. I turned the lathe on for maybe 30 seconds at a time while I attacked it with a large bowl gouge. Eventually the shaking diminished as the bowl's profile evened out. An interesting learning experience and I now have a few extra todos.

1. Pick up a couple of bags of sand from the borg to add some mass to the stand.
2. Make sure stand is in full contact with floor at all 4 corners
3. Consider options to fix lathe to stand.

Here are a couple of pics of the blank before and after. The roughed exterior is now approx 10.5 x 7 , not sure what the final profile should be, all input appreciated.

[Bill in Buena Park]

Looking good Jon, nice color in that wood, reminds me of redwood. For shape, google "wooden bowl" images, find something pleasing to your eye.

Bolting the lathe to the stand is a must for this size turning. But not sure about adding the sand - I forget which accomplished turner I was reading or saw a video where they said that is hard on the headstock bearings (which is where the stress ends up), better to get blanks as round as possible on bandsaw first. So I do this, also put my lathe on a mobile base, turn only as fast as will not cause wild shaking, and I've adapted my technique to accommodate the little shaking I experience. I also use the tailstock to support at first, even when using a faceplate, to save some stress on the headstock bearings. Then turn up speed as balance allows. I also limit my speed on sizes this big to 1000-1200 rpm when fully rounded/balanced.

[poolhound]

It could be redwood but my guess is mesquite given the abundance of it here. Using the tailstock is a good tip. in this case I could not to that at the start given the odd shape at that end. I think it was mostly the fact that one side was originally the outside of the tree and therefore oddly shaped that made the balance even worse I guess I could have squared off more of this too start on the bandsaw.

The comet II has 3 variable speed settings. I have kept it on the middle one which goes from 530 to 1420 RPM. The lowest range is 250 to 680. Do you think 250 would have been appreciable better in this case?

Looking good Jon, nice color in that wood, reminds me of redwood. For shape, google "wooden bowl" images, find something pleasing to your eye.

Bolting the lathe to the stand is a must for this size turning. But not sure about adding the sand - I forget which accomplished turner I was reading or saw a video where they said that is hard on the headstock bearings (which is where the stress ends up), better to get blanks as round as possible on bandsaw first. So I do this, also put my lathe on a mobile base, turn only as fast as will not cause wild shaking, and I've adapted my technique to accommodate the little shaking I experience. I also use the tailstock to support at first, even when using a faceplate, to save some stress on the headstock bearings. Then turn up speed as balance allows. I also limit my speed on sizes this big to 1000-1200 rpm when fully rounded/balanced.

[Bill in Buena Park]

Jon, as for speed - that will vary with each piece, so you'll have to "play by ear". I'm generally ok at 600 with the pre-shaping at the bandsaw. For the tailstock, given your first picture, you should be able to use a 60-degree cone live center on that. I've found very few odd-shaped pieces that mine wouldn't accommodate. You can always notch in a little (somewhat) flat spot to accommodate where the live center makes contact.