Processing green bowl-blanks - revist

[MKepke]

I've been working my way through my green blanks very slowly, still looking for ways to speed up. Comments/critiques welcome.

It took me the better part of 2 hours last night to rough turn the outside (only) of a red oak blank approx. 15"x16"x8" deep.

Most of the roughing had to be done at very slow speeds (<500 rpm) due to the shake induced in the lathe by the out of balance blank. My lathe is on wheels..I may put it on blocking and add a couple hundred #s of sand to damp the wobble.

My primary bowl gouge - a Crown 5/8" deep flute - was having trouble getting a good consistent shaving between the slow RPMs and needing a touch up on the grinder. A fair bit of slamming action too, but seems inevitable given my blank started out as an imperfect octagon.

I resorted to my homemade carbide scrapers on several occasions - they produced as much sawdust as shavings, but at least I didn't get the slamming action.

On the positive side, my homemade 5" faceplate(s) is working just fine but I'm not sure that self-tapping sheet metal screws are the best choice for mounting blanks. They don't seem to 'suck into' the wood consistently and I had a couple #14x1.5" screws start to come out on the last blank I use the tailstock religiously now.

The rough turnings are being stored on the shop floor as folks recommended in the other thread.

After last night's turning I came into the house and looked longingly at much bigger lathes

-Mark

[Arlin Eastman]

Mike

You should not be getting any Slamming at all no matter how off sided it is.

If you go from the sides and just take off 1/8" to 1/4" at a time I never get that. I make sure my tool is about 45* to the rest and with the flute at about 10 o clock or 2 o clock and the bevel pointing where you want to go you will have better results.
I sure wish I lived closer but if we did you would not be posting this.

Try this method on a smaller piece of wood to get the hang of doing it this way and then afterwards no more problems.

I have put a whole half of a log on my lathe and did it the way I described and it works.

Arlin

[robo hippy]

Maybe this clip will help some:

https://www.youtube.com/watch?v=mN2bKMQFuFk

I don't know which lathe you have, but being up on wheels is part of the problem as they provide one more wiggle spot, even if you have locking wheels. All of that wiggle added to the wiggle from the out of balance piece of wood can make for a long turning effort. The main thing for me when starting any bowl blank is to start in the middle or center and work my way out to the edge. The wood is turning slower, and you can see and feel the bumps without the extra slamming that you get if you start on the outside uneven corners. Other than that, how you prep your blank is a huge part in getting started. The more parallel your sides are, the less roughing you have to do. I have a couple of other clips up on prepping bowl blanks.

robo hippy

[Steve K]

MKepke said:

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I've been working my way through my green blanks very slowly, still looking for ways to speed up. Comments/critiques welcome.

It took me the better part of 2 hours last night to rough turn the outside (only) of a red oak blank approx. 15"x16"x8" deep.

Most of the roughing had to be done at very slow speeds (<500 rpm) due to the shake induced in the lathe by the out of balance blank. My lathe is on wheels..I may put it on blocking and add a couple hundred #s of sand to damp the wobble.

My primary bowl gouge - a Crown 5/8" deep flute - was having trouble getting a good consistent shaving between the slow RPMs and needing a touch up on the grinder. A fair bit of slamming action too, but seems inevitable given my blank started out as an imperfect octagon.

I resorted to my homemade carbide scrapers on several occasions - they produced as much sawdust as shavings, but at least I didn't get the slamming action.

On the positive side, my homemade 5" faceplate(s) is working just fine but I'm not sure that self-tapping sheet metal screws are the best choice for mounting blanks. They don't seem to 'suck into' the wood consistently and I had a couple #14x1.5" screws start to come out on the last blank I use the tailstock religiously now.

The rough turnings are being stored on the shop floor as folks recommended in the other thread.

After last night's turning I came into the house and looked longingly at much bigger lathes

-Mark

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A couple of points jump out at me when reading your post.
First, 15" diameter X 8" inch blank is a decent chunk of wood. Not giant but still a pretty good mass to be spinning at or near 500rpm's if it's even a little out of balance. I doubt I would start any higher and my lathe is pretty massive at 960lbs. With proper technique it should've taken you only a few passes to start getting a consistent shaving.
Secondly, do you not have a grinder as you mentioned your tool needing a "touch up" on the grinder? A few seconds to do that would've saved you lots of time, again assuming you're using proper technique.
Robo's video is very good and I also like this one from Lyle Jamieson. The blank he's cutting isn't anywhere near round but it is balanced. Even though he's cutting a lot of air the cuts are pretty much effortless because of his technique.


Lyle on rough turning a bowl blank

[EdW]

Getting the lathe on solid ground, with additional weight, will do a lot to reduce the shake and absorb vibration. In addition, I have found that mounting the blank in a well balanced position before starting to turn makes the roughing process significantly easier. You will be able to spin the blank at a higher rpm, with less shake, rattle, and roll. Balance the blank as if you were balancing a wheel. When you spin the blank by hand, you want it to stop turning at random positions; it should not be returning to the same position each time. If it is, the weight is distributed asymmetrically about the axis. You can balance the blank in the following fashion - when you spin the blank and it comes to rest with the heavy spot down, hold the blank while backing the tail stock off until you can move the head stock side of the blank higher, and then crank the tail stock back in. Spin the blank again to see where it stops. If it is still heavy on the bottom, back the tail stock off and raise the tail stock side of the blank; crank the tail stock back in. Keep doing that, alternating head stock and tail stock sides, until the blank comes to rest in random locations after you spin it. It usually takes just a few adjustments until it's balanced.

[MKepke]

I like Jamison's video but his approach of roughing green wood between centers has never worked for me. Invariably the spur center spins (I have a standard 1", 4 tooth spur bit). Maybe I'm not rechecking/tightening the tailstock often enough during use.

I will experiment some more tho as the 'balance point' method would save wear and tear if I can get it to work.

In response to Steve's question, my comment about the grinder was more an admission I should go back to my Wolverine-equipped grinder more often than I do.

-Mark

[Steve K]

MKepke said:

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I like Jamison's video but his approach of roughing green wood between centers has never worked for me. Invariably the spur center spins (I have a standard 1", 4 tooth spur bit). Maybe I'm not rechecking/tightening the tailstock often enough during use.

I will experiment some more tho as the 'balance point' method would save wear and tear if I can get it to work.

In response to Steve's question, my comment about the grinder was more an admission I should go back to my Wolverine-equipped grinder more often than I do.

-Mark

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Mark
I nearly always start between centers. One thing that has helped me is I use a drive center That I ground two opposing spurs off of. Believe it or not it actually works much better than a four spur drive. One of the hardest lessons to learn is that sharpening saves time instead of taking it.

[Wildwood]

Bought one of these over twenty years ago and probably need to replace the center point. Mine still works so can wait until cannot adjust anymore.

https://www.woodturnerscatalog.com/p/107...ter?term=2 prong drive center

Really excels at roughing out wet wood. Ends of a bowl or spindle blank do not have to be perfectly flat.

[Mike67]

Second the votes for a more stable platform and some weight. That'll allow a little more speed which makes the cutting go easier.

[EdW]

I like Jamison's video but his approach of roughing green wood between centers has never worked for me. Invariably the spur center spins (I have a standard 1", 4 tooth spur bit). Maybe I'm not rechecking/tightening the tailstock often enough during use.

There are two ways to help prevent the spur from spinning.
1. If it is the bark side of the blank that the spur is going into, you have to chisel the bark off where the spur will be placed.
2. Once the blank is balanced between centers, crank the tail stock in. Then put the spindle lock on and rock the blank back and forth; doing so leads to the spurs opening up the wood where they are. Then crank the tail stock in more which will drive the blank further into the spurs where the wood has been opened up. Repeat the procedure a few times and the spurs should be well planted in the blank.