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Thread: Warping, Cracking and Checking...oh my! (Long post Warning too)

  1. #1

    Warping, Cracking and Checking...oh my! (Long post Warning too)

    Love this site/forum - all of you have been so helpful on my journey in turning. Look forward to seeing the "experts" advice, etc. Watched many of your videos on YouTube too - so helpful.

    In the short time that I've had a lathe (Jan 2021) I've turned about one bowl a day everyday - it's just so relaxing to go from a block of wood to a finished product! However, I've encountered a lot of cracking, checking and just recently, some warping. No matter the finish I put on, some things always seem to develop a crack. Here's my story:

    1. Acquired quite a bit of aromatic cedar from a local farmer - tree was cut down about 7 years ago and has been sitting under barn roof since. First few pieces turned very easily, but after finishing and bringing into house, small cracks (hairline) started developing, mainly from knots or center. One piece even cracked about 1/8" inch on the inside rim. I've since learned that I should avoid turning with the pith in the wood if possible.

    2. Have turned several pieces of kiln dried spalted maple without incident and have no cracks showing in any piece. Same with spalted pecan and Osage Orange (love this wood!)

    3. Magnolia was a tough turn - tearout was fierce. Hard to get smooth finish. (again, under the barn find)

    4. Eucalyptus has a nice smell and able to get really thin walls, but cracking and checking very prominent. (another under the barn find)

    5. Recently found a post of Facebook Marketplace where a guy was selling Red and White Oak blanks - 6"x6"x3" kiln dried for $1 each. I bought 20 pieces and was stoked. After a day, I took all blanks to my friends shop who has a large bandsaw and rounded the blanks - finding that a lot of the blanks were actually Poplar. Took the pieces home and was super excited about turning these....in the end, got about 8 good blanks to use out of the 20. Ugh.

    The next day, I noticed all of the poplar were showing massive checking and even some cracks in grain. Turned one piece and had a terrible time smoothing it. Finished with sanding sealer then with some mineral oil and let sit overnight. Came back next morning and my circle bowl was starting to look like an oval. Turned a piece of the red oak next - love the way oak looks - and next day again, starting to ovalize.

    Tonight, the poplar bowl is a full oval and the top rim is wavy. Oak is same way. When I was turning another piece of poplar, I felt like I was getting sprayed with water droplets - so I'm guessing this wood is green - really green. The other two bowls are now full ovals.

    Finally - Question 1: Do I NOT need to round a square blank until I am ready to turn it? Seems that whenever I do round one or many, cracks and checks are more evident, especially in cedar and poplar and some oak as well. The pieces I purchased from a retail outlet have been nothing but awesome.

    Question 2: What is the forums general consensus on how to finish a bowl? Sanding sealer? Lacquer? Poly? Tung Oil? I'm getting tired of buying a different product to test only to find out it's not what I thought. I'd like to make all bowls and such food safe.

    Question 3: I sand 100, 150, 220, 500 then wipe with tack cloth and finish. Between each finish coat, I lightly sand with 1000. Try to do all initial sanding on lathe spinning at 450 (lowest I can go)

    Question 4: Just got a Nova G3 chuck - been cutting tenons and placing in chuck. Someone told me to make a dovetail angle, but cannot find that literature in instruction manual. Have had a few pieces come off chuck in motion when cutting tenon off - what am I doing wrong? Also, when wood is being trued between centers, making a tenon is simple - but with tailstock in the way, how would you make a recess? This stumps me to no end.

    Question 5: Does lathe speed have any relation to finish or look before sanding? In other words, if I can turn speed up to say, 1200, to make final passes, will the wood finish be smoother than if I do final passes at 800?

    I have a Rikon Midi 70-1218VS - bought from Highland Woodworking. Really like it but then again, can't compare to anything as this is all I've used since 8th grade! Also using carbide tools from WEN Products - square and round. Used to use 3" faceplate before the Nova G3.

    Wish I could post some photos (someone said to pay a nominal fee and I could, but can't remember where to do that) In a nutshell, the woods I've turned and my "opinions:"

    1. Cedar - love the way it smells - turns very easily. Some rough patches/tearout. Shows sanding marks and scrapes easily.
    2. Eucalyptus - Another good smell - tight grain, turns a bit harder than cedar. Smooth finish.
    3. Maple (spalted too) - Very easy to turn. Not much tearout. Finishes well too.
    4. Pecan (spalted too) - Dense. Hard to work - tools must be sharp. Beautiful finish withs spalting. Did not show sanding marks.
    5. Magnolia - hard wood. hard to work; a lot of tearout especially from endgrain. Very light wood weight-wise. Made a chalice from it.
    6. Red Oak - hard, dense, turns well, but must rough really slow. Open grain makes hard to finish.
    7. Poplar - of course, mine was green, and threw ribbons of shavings, but tool caught a lot. Easy to gouge pieces out; a lot of tearout. Dull finish.

    Many thanks in advance - know that your upcoming advice, etc. will help me and other newbies too!

    Brian

  2. #2
    Join Date
    Apr 2018
    Location
    Cambridge Vermont
    Posts
    1,403
    Buy yourself a cheap moisture meter. It sounds like most of your problems with warping, checking, and cracking are from wood that's not dry. If so you'll need to either dry it or rough turn it then dry it. Rough turning it will remove material and speed the drying process. There's plenty of advice on how to dry a rough bowl. I like to just put them in a paper bag packed with green shavings to slowly dry. Warping is going to happen no matter what. It's why you leave plenty of extra when you do the rough turning.

    I like to make a mortise on the blank vs a tenon. As for a "dovetail", just look at your jaws. They will have an angle to them that you'll want to match. I usually use a diamond shaped carbide tool but have used a parting tool. I started off making the mortises as deep as the jaws but once I got a feel for it I now only make them about an 1/8" of an inch deep. They hold just fine.

  3. #3
    The answers to your questions would fill several books. Two to start with are 'Ellsworth on Woodturning" and "Understanding Wood" by Hoadley.

    If there is a woodturning club near you, join it. Hands-on guidance from a mentor is invaluable and will become easier as Covid vaccinations progress.

    Join the AAW forum. Read the Tips and Techniques archive. You don't have to be an AAW member.

    Round off your blanks just before turning. If you have to delay or interrupt the process, put the blank in a big plastic bag. Most checks are in the wood before you start turning, and green wood is the least likely to have drying defects. Seal the endgrain of green logs and don't crosscut until you have to. Trim the ends back to check-free material. Thick sections are the hardest to dry without degrade.

    You can turn green or partially dry wood to finish thickness, but it will change shape. This may be a feature or a bug depending. For round bowls, start with completely dry wood (rare) or rough turn, dry and turn again.

    For a truly "food safe" finish use products that have no toxic ingredients. Look at the MSDS. Cured film finishes may not be toxic, but do you want to ingest microplastics? Some people use walnut oil or tung oil with no additives.

    Sanding schedule is ok except jumping from 220 to 500- use 320 in between. 450 rpm is good for hand sanding As you get better and learn how to sharpen and present steel tools you will be able to start sanding at higher grits. I do a lot of sanding and scraping with the lathe off. Sanding with the lathe spinning removes more soft side grain material whereas most tearout is at the transition to endgrain.

    Your tenons need to be cleanly cut and match the shape of the jaws. Make sure the tenon does not bottom out on the base of the jaws. Stand out of the line of fire and always wear a face shield.

    A good rule of thumb for safety is to keep the product of diameter in inches x rpm between 6000 and 9000. At 9000, the rim speed is about 27 mph. Impact force is relative to the square of the rim speed.

    Speed helps with surface quality up to a point. As your technique improves speed may matter less.

    There are a ton of Youtube videos, many suspect. Stuart Batty, Brian Havens, Al Hockenberry, John Lucas and Mike Waldt are some I have found helpful.

    To join Sawmill Creek, click the 'Donate" button at the top of the page.
    Last edited by Kevin Jenness; 02-25-2021 at 9:33 AM.

  4. #4
    Join Date
    Feb 2008
    Location
    E TN, near Knoxville
    Posts
    10,615
    You got some good advice so far. If wood has been around a long time, there may be practically invisible checks and cracks which may be revealed when you turn. When preparing blanks of any kind I like to cut thin slices off the endgrain (and sometimes the sides) of the wood and bend the slice. If it breaks easily the wood is compromised there. I keep removing slices until I get into good wood or give up and decide to process the wood into some smaller blank(s).

    One thing about cedar, if you sand it with too much pressure it can create checks in good wood from the heat. Years ago I quit power sanding and sanding by hand against the rotating wood - that can generate a lot of heat. After the finish cuts with the gouge I use a negative rake scraper to remove most tool marks then take the piece off the lathe. I use hand scrapers and hand sanding sandpaper for most smoothing. (After the hand scraping I can usually start with 320 or finer paper.) I discovered this early on my first "real" bowl from cedar and devised the scraping method then.

    cedar_bowl.jpg

    The oval shape is normal with face turnings (grain going across the face) since wood shrinks more in the transverse (ring) direction than the radial direction. The way to get a round bowl is to turn it twice - the first time leave the walls thick enough, let it dry and warp, then when completely dry turn it again to make it round. The wood may still "move" a bit with a change in humidity but this can be minimized with a good finish.

    If you are getting tearout as you mentioned, make sure the bowl gouge is razor sharp. If you are getting catches, you are doing something wrong with the tool control - with some experience you should never get a catch. If possible, some instruction with a teacher or mentor will fix that quickly.

    I made a special tool to avoid running to the tailstock when cutting a recess. Or better, I like to use a screw chuck in the top first, add the recess while shaping the bottom and outside (the tailstock is completely out of the way), then reverse and cut the inside.

    This is the tool (which you can view if you sign up as a "Contributor" - it's cheap and worth it!)

    Dovetail_A.jpg Dovetail_B.jpg

    JKJ

  5. #5
    Join Date
    Oct 2008
    Location
    Kapolei Hawaii
    Posts
    3,131
    Are carbides the only tools you have? They are essentially scrapers and may be the reason you are having finish issues. If you like to turn bowls, I would suggest you invest in a bowl gouge and sharpening setup(s). If you don't already have one or 3.
    You turn a bowl a day? Usually takes me well over a day to turn a bowl...... That's fast. I'm slow I guess.
    I was going to mention skipping 320 grit, but Kevin already mentioned that grit. I also use 400. Personally I think those 2 grits are most important. Wet the surface after 400, (raise the nap) let dry and resand with 320/400. Then 500.
    The other 2 book volumes of info is "what finish do you use"....

  6. #6
    Well, I could write a book to answer all your questions.... I do have a bunch of bowl turning videos up on You Tube, which will cover some. So, first, I have noticed that dead standing trees, and ones that have sat under cover for years do tend to crack more than fresh green ones. Not sure why. Cracking is a result of relieving stress in the wood. A solid log will never dry, and will crack more on the outside as it dries, then when you open it up, there is still stress, so that can cause more cracking. If the blanks are wet/green, which the ones you got were, they will warp. You can twice turn them, which is rough turn to 10% thickness, 10 inch blank at 1 inch thick, seal, and let dry for 6 or more months, and then turn again. Many videos on that. I prefer one and done and love warped bowls. With my warped bowls, I make sure to round over the rim, one to keep it from slicing you as it spins, and two, the sharp rim is more prone to starting cracks than a rounded one is. I also use stretch film around the rim. The rim is always the starting place for cracks, and the plastic helps protect the rim. Knots will always crack. It is when, not if. The grain in the knot is different than the side grain for the rest of the bowl, which causes stress, which causes cracks.

    To sand them on the lathe, you need 15 or less rpm to be able to keep the sander on the wood, and if you don't power sand, you may have to stop the lathe and hand sand. I go 100, 120, 150, 180, 220, 320, and 400. It may be a bit redundant, but 100 grit scratches are harder to get out with 150 than with 120. If I do need to start with 80 grit, I still keep that progression. Some times 80 grit scratches go deeper than tool marks. No need to go beyond that for daily use bowls. I apply walnut oil/wax from The Doctor's Woodshop. Best walnut oil product out there that I know of. For sanding, slower speeds work best for sanding. If you are hand sanding, and your fingers are getting hot, you are pushing too hard on the abrasives, and/or turning too fast. Slow down and ease up.

    Some woods just cut better than others. Black Cherry, pear, dogwood, and my favorite, Pacific Madrone, cut like butter. Cottonwood is just plain nasty, but not as bad as coconut palm. 180 grit CBN wheels work for 90% of the cutting you will need to do with your gouges, but some times that 600 grit edge really is nice for some difficult woods. The higher the shear angle is, most of the time, the cleaner your cut is. Scraper flat on the tool rest has 0 degrees of shear. A gouge rolled on its side can have 60+ degrees of shear on the nose. Every wood cuts differently.

    Then, of course, as a martial arts instructor of mine said, "10,000 more times!" If you can get a hands on session, that can also do wonders.

    robo hippy

  7. #7
    First time I read your last line Reed I thought you said "martini instructor" which definitely got my attention!

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