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Can't seem to true up larger bowls

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Forum topic by Burbs posted 03-02-2017 05:13 AM 627 views 0 times favorited 11 replies Add to Favorites Watch
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Burbs

48 posts in 524 days


03-02-2017 05:13 AM

So I took the plunge into the turning vortex at Christmas and have been spending every free moment since either reading about turning, watching videos about turning or actually working on the lathe. I was trying to save for a oneway, powermatic, or nova dvr but got impatient and bought a delta 46-460 with a lot of tools/accessories so I’m fairly well setup.
Been doing a lot of small bowl turning with the wood I had in the woodpile that was fairly dry (under 20% moisture content) and have had pretty good success but it’s been mostly small stuff, 6-7” inch bowls not very deep.
The snow finally melted enough now to get in the woods and I brought back some very green maple, birch and ash from blow downs last summer/fall that is much bigger so I’ve been trying to do some 10-12” green bowls and have 6 bigger bowls rough turned in paper bags with shavings.
So why is it that the outside of these big bowls never seem to “true” up? I know that green bowls dry quickly on the outside but it seems like the only way I can get a smooth surface is to take a deeper cut. Is it the weight? Is it because it’s green? Is it because I’m pushing the limit of the lathe? I’m always turning between centers with either a worm screw or faceplate and I’ve tried varying the speeds.
Sorry so long but anyone have any thoughts or explanations?

-- ---The day I learn nothing of value will be the day I'm laid to rest--- Burbs


11 replies so far

View Dustin's profile

Dustin

409 posts in 580 days


#1 posted 03-02-2017 12:56 PM

Burbs,

I’m a novice bowl turner, so please take this with a grain of salt (though what I’ve gleaned has been from much more experienced turners both on here and youtube).

From what I understand, truing up the outside of a green bowl can be diffifult due to, as you indicated, how quickly it dries once turning begins, but also due to the uneven relief of internal pressure/stressors on the wood. For the few green bowls I’ve done, I found it better to rough the outside, then hollow it out, leaving a greater thickness than desired for the finished piece.

And if you’d rather not wait for it to dry over a few weeks, I’ve seen loads of turners pop it in an inexpensive dedicated microwave. And really, this is the time to be testing out what works, when the wood is green and free!

Again, novice here, so hopefully someone better in the know will chime in.

-- "Ladies, if your husband says he'll get to it, he'll get to it. No need to remind him about it every 6 months."

View Wildwood's profile

Wildwood

2188 posts in 1974 days


#2 posted 03-02-2017 12:59 PM

Could be the design of the bowl or bevel angle of your bowl gouge. I have four bowl gouges with different bevel angles and profiles (fingernail or side grind). Many turners like a double bevel to avoid scratches at bottom of bowl; feel it gives better transition from sides to bottom.

Dale Nish had great article in woodturnig design magazine covering design and bevel angles which is no longer on line so hope these links help. Could be other factors contributing to your problem but these solutions might be useful.

http://www.woodturningvideosplus.com/bevel-angles.html

http://woodcentral.com/newforum/grinds.shtml

-- Bill

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Nubsnstubs

1207 posts in 1570 days


#3 posted 03-02-2017 02:54 PM

More than likely it’s just internal stress in the wood. Drying it completely will eliminate it for awhile. After a few years, the wood will take on a shape of it’s own. I say this because a friend showed me 3 forms he got while in Costa Rica back in the late 70’s and early 80’s. They were oval shaped, including the lidded box, which the lid was shaped the same and fit extremely well even today.

I wouldn’t worry about it. If you want your stuff to be round, turn to 10% wall thickness, and let dry. If you don’t mind the warp turn to final thickness for start to finish. ............... Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

View LeeMills's profile

LeeMills

462 posts in 1141 days


#4 posted 03-02-2017 03:04 PM

So why is it that the outside of these big bowls never seem to “true” up? I know that green bowls dry quickly on the outside but it seems like the only way I can get a smooth surface is to take a deeper cut. Is it the weight? Is it because it’s green? Is it because I’m pushing the limit of the lathe?

I’m not sure exactly what you are turning. Are you re-turning some of the rough outs you placed in bags or are these new rough outs to go into bags to be re-turned later?
By “true” I assume you mean warped, not torn grain.
If you just got them from the woods (even though they fell last fall) the wood will still be pretty wet and move a lot. Drying to turn from rough to finish depends on your conditions. For me a 12” bowl takes at least six months to dry enough to finish turn.
The only problem with the lathe that I can think of is if the surface which the faceplate or the top of the jaws (using the wrormscrew) seats against is not flat or worse convex. This could allow the bowl to wobble as it is turned.
I am assuming also that you turn the outside first and then the inside.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

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Burbs

48 posts in 524 days


#5 posted 03-03-2017 10:51 PM

Thanks for the responses guys. Sounds like I just need to rough turn the best I can and wait for them to dry.

I will give some more details. The wood I’m turning is very wet, so wet in fact that the floor is actually kind of wet behind me. The blow downs I cut were from trees that went over i the wind because it was so wet last summer and the whole root system came up so they were either still alive or not dead long.

I have 3 bowl gouges, all 3/8”. A Sorby with a traditional grind, a Sorby with a fingernail grind and a Benjamins Best that I reground with very swept back wings. Bevels from 45-55 degrees with the Benjamins best in the middle at about 50. I get the best cut with the Benjamins Best if I’m doing a push cut. The two Sorby’s I can get a decent cut but I have to keep the bevel away from the wood or it tends to knock on the wood. A pull cut seems to work better.

I’ve been turning the outside and putting a tenon on the end so I can mount in 100mm jaws and then flip around and do the inside leaving the walls about 10% of the diameter. When hollowing, I work around the center so I can leave the tail stock up as long possible. Then I’ve been putting them in 2 brown paper bags with the shavings and closing up and dating.

Another question. I have a couple blanks of birch and maple that are bandsawn round. I had some beautiful spalted maple in the woodpile, but it was kind of soft. What’s the best way to get some spalting on these unturned blanks? Put them outside in the woodpile and watch them? They’re all 10-12” in diameter and 4-5” thick.

-- ---The day I learn nothing of value will be the day I'm laid to rest--- Burbs

View Nubsnstubs's profile

Nubsnstubs

1207 posts in 1570 days


#6 posted 03-04-2017 01:05 AM

Burbs, leave you shavings on the floor under the lathe, stash the rounds in the shavings, and in about a month, I’ll bet you’ll see some spalting starting to form. If you aren’t like me, then put the rounds in a plastic bag with shavings and leave on the floor out of the way, and wait until you get the amount of spalting you want.

If I’m not asking too much, go to my latest thread I just posted, and look at the second half of the video. It was a green Palo Verde turned from start to finish, and then set aside to remove the tenon at a later date. It warped not too awful bad, but enough to aggravate me some. ................. Jerry (in Tucson)

-- Jerry (in Tucson) www.woodturnerstools.com

View LeeMills's profile

LeeMills

462 posts in 1141 days


#7 posted 03-04-2017 01:11 AM

When rough turned I place it in a paper bag and shut the top tightly (tape or staples). I have never put shavings in because some folks say it may cause mold. I do use anchorseal and seal all end grain well before putting it in the bag.

I can’t help much with spalting. Folks do lots of things, from what I hear just covering it with leaves can start it.
Of course the wood must be wet.
Here is a link to Sara Robinsons facebook (Dr. Spalt). I did order her book to try and learn more.
https://www.facebook.com/groups/spalting/
If you look up “spalting sara robinson” on youtube she has several very good videos.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

View Burbs's profile

Burbs

48 posts in 524 days


#8 posted 03-04-2017 01:40 AM

Cool. Thanks again
I cut a large branch off of the huge maple in the backyard last winter and was using one of the bigger pieces as a door stop all summer. That piece developed some nice spalting even in a semi climate controlled environment although it also had some bad checking because it was whole and not sealed but I was able to turn a smaller natural edge bowl from it.
It it true that you need to use wood cut in the winter time for natural edge work? I read somewhere that you need to use wood cut in the winter or the bark will fall off.

-- ---The day I learn nothing of value will be the day I'm laid to rest--- Burbs

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Burbs

48 posts in 524 days


#9 posted 03-04-2017 02:19 PM

Good video Jerry! I’ll watch for more.

-- ---The day I learn nothing of value will be the day I'm laid to rest--- Burbs

View Lazyman's profile

Lazyman

1509 posts in 1227 days


#10 posted 03-04-2017 03:17 PM

When turning green bowls, I have done 2 things. In both cases you rough turn them thicker than you need for the final dimensions There is a formula for how thick based upon the diameter of the bowl but I usually shoot for about 1/2” thick sides for 8” bowls. Then you have to get them dry.

The easiest method is to sweep up the wet shavings from the rough turning, throw them in a cardboard box or brown paper bag, seal it closed with masking tape and store the rough bowl in the shavings for 3-6 months. Every couple of weeks remove the bowl stir up the shavings to prevent mold from growing and rebury the bowl in the shavings and reseal with tape. I use a cheap moisture meter to see how dry it is.

The faster method is to go buy a microwave oven and a kitchen scale at a garage sale use that to quick dry the rough bowl. I weigh the bowl and microwave on medium power for about 2-3 minutes, take it out and let it cool and reweigh the bowl. Don’t cook it too long or at too high temp because it can burn and you may not see that it burned until you start the final turning. I keep a log of the weight and once it stops losing weight it will usually be dry enough to finish turning but you can let it sit for a few days to finish the drying process. I sometimes use my moisture meter to see what percentage I have and then use that to compute whether I have really gotten down to at least 15% when it stops losing weight. If not, I will let it sit for a few days and try to microwave it again to see if I can force a little more moisture out before I start turning, though sometimes I am just too impatient and just finish it anyway.

With both methods, you will find that it warps and possibly cracks significantly but once you re-turn it round it will be much more stable. One way to reduce the warping and cracking is to make sure that the center of the log (the pith) is removed from the blank before you start to turn

If you want to get spalting quickly, lay blank on soil and bury it with leaves or mulch and keep it moist for a few months at least.

-- Nathan, TX -- Hire the lazy man. He may not do as much work but that's because he will find a better way.

View LeeMills's profile

LeeMills

462 posts in 1141 days


#11 posted 03-04-2017 04:23 PM



It it true that you need to use wood cut in the winter time for natural edge work? I read somewhere that you need to use wood cut in the winter or the bark will fall off.

I think it depends a lot on the type of tree. In general, wood cut in the winter is better because the sap has fallen and it is naturally dryer (less shrinkage). I’ve had pretty good luck with walnut, dogwood, and some others. The worst for me as to loosing bark I wanted to keep was cherry and sweetgum. Most of the time if I want a natural edge I remove the bark prior to final turning.
Most of the time, IMHO, leaving the bark makes it look to delicate for use.

-- We cannot solve our problems with the same thinking we used when we created them. Albert Einstein

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