I have been turning for about 1 year now (not counting my time as a kid with my dad and granddad). I am trying all kinds of things, but really like turning bowls. I came across a Yew tree that had been down for a couple of years so it is pretty much dry. I have successfully turned a couple of bowls from the tree but have had multiple failures due to the tenon splitting off. I will try to describe what I am doing, but I doubt I have the correct terminology so please bear with me. I cut a round off the end of the tree. Then I split it down the middle. Then I mount it on the lathe with the grain running from the back to the front of the lathe. I turn it round (ish) and then turn a tenon on the center of the piece side (not the bark side). Then I put it in my chuck and start hollowing. My first few tries the tenon broke of fairly quickly so I turned a new one and had a smaller bowl. BTW - the blanks are about 14" across. So my idea was to keep the tailstock engaged while I hollow and then remove it when I was almost done. Then just turn off the center "post". That has been working pretty well. But now I am trying to put the tenon on the other side (bark side) so I can make a fluted bowl. Everything went great and it looks awesome until I removed the tailstock so I could remove the center post. I got about 1/2" of the center off and then the tenon split off. I glued it back on last night, but I am afraid it will just break off again in another spot. So how do I turn this bowl without the tenon splitting off? Thank you!!
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Tenon Keeps Breaking Off
- Thread starter Michael Powers
- Start date
A few questions:
First, just for clarification, the tenon that you are using doesnt contain any bark or cambrium (layer between bark and wood) does it? I also assume that you have checked for any cracks or splits in the wood that you are turning.
Second, when you say that you turn it roundish - do you mean that it is still a bit unbalanced? If so, I wouldnt recommend turning with only a tenon for support, as the whipping motion caused by an out of round blank can easily loosen and even break a tenon.
Third, when you seat the tenon in your chuck jaws, make sure that it doesnt bottom out, that is, make sure that the jaws are seated firmly against the bottom of the bowl in addition to gripping the tenon.
You might also try turning using a recess instead of a tenon, though if it is a wood defect that is causing your tenons to fail, this is unlikely to fix the problem.
First, just for clarification, the tenon that you are using doesnt contain any bark or cambrium (layer between bark and wood) does it? I also assume that you have checked for any cracks or splits in the wood that you are turning.
Second, when you say that you turn it roundish - do you mean that it is still a bit unbalanced? If so, I wouldnt recommend turning with only a tenon for support, as the whipping motion caused by an out of round blank can easily loosen and even break a tenon.
Third, when you seat the tenon in your chuck jaws, make sure that it doesnt bottom out, that is, make sure that the jaws are seated firmly against the bottom of the bowl in addition to gripping the tenon.
You might also try turning using a recess instead of a tenon, though if it is a wood defect that is causing your tenons to fail, this is unlikely to fix the problem.
There really isn't any bark left on the tree, but the outside wood is fairly soft. My tenon is mostly in this soft wood - not ideal I know.
When I said "roundish" I mean that is is not quite finished, but it is round and balanced.
The chuck jaws are seated against the bowl, but have not been on all projects - that is a great tip!
I hadn't thought about using a recess instead. I will give that a try. It is too late on the bowl that I have now, but I will try it on the next one.
Thank you!!!
When I said "roundish" I mean that is is not quite finished, but it is round and balanced.
The chuck jaws are seated against the bowl, but have not been on all projects - that is a great tip!
I hadn't thought about using a recess instead. I will give that a try. It is too late on the bowl that I have now, but I will try it on the next one.
Thank you!!!
Michael, just to clarify, you're turning the wood in face-grain orientation, yes? When you say from the back to the front grain orientation, I think perpendicular to the bed ways. In my area of the U.S., we don't have any yew at all, save for perhaps an odd specimen in a park or arboretum. So in other words, I haven't turned any. My advice is purely generalized without respect to wood species. Greg gave great suggestions about keeping the tenon from bottoming out in the chuck, and removing the outer layer of wood. In my understanding, the cambium is the outermost sapwood, where active growth is occurring---a new ring is being formed here. It is weaker than any other layer in the cross section. That said, you don't always have to remove all the sapwood, but in my experience will typically be weaker than the inner heartwood. If a tenon breaks off, typically it's during coring or very heavy handed hollowing cuts. I've cored 100's of bowls, and definitely find the sapwood to be prone to splitting on tenons. I try and remove sapwood unless it is utilized as a feature on a particular bowl. Certain woods, black walnut in my experience, are prone to splitting tenons if I work too hastily. Upon watching an episode of "The Woodwright's Shop", Roy Underhill described one of the favorable properties of working with walnut as to its tendency for easy cleaving--splitting easily along the grain. Yew may be one of these woods?? You may experiment with turning away all the sapwood on some of your blanks and see if you have better results.
Another question. Dose your chuck have tapered or dove tail jaws? If so the tenon should match the profile if the jaws.
Another thing to consider is the size of the tenon. Not just the depth but the diameter. Lets say your chuck fully closed is 2 inches in diameter. The tenon should be only slightly larger than the diameter of the chuck fully closed. The object being to present as much of the surface of the jaws as possible to the tenon. If your jaws close at 2 in. and you have a 3 in. tenon you are trying to hold the bowl with 8 points of the jaws. Less than ideal. And again bottoming out is a major issue.
Bob Edwards
Another thing to consider is the size of the tenon. Not just the depth but the diameter. Lets say your chuck fully closed is 2 inches in diameter. The tenon should be only slightly larger than the diameter of the chuck fully closed. The object being to present as much of the surface of the jaws as possible to the tenon. If your jaws close at 2 in. and you have a 3 in. tenon you are trying to hold the bowl with 8 points of the jaws. Less than ideal. And again bottoming out is a major issue.
Bob Edwards
My mother and I have been learning to turn at the same time, and we've had all kinds of trouble with tenons. She actually gave up for a bit because of it. Here's a couple things I've gleaned from our troubles:
- The tenon breaks because there is more force applied to it than it can withstand, so your options are (a)strengthen the tenon or (b)apply less force. I don't know how to strengthen a tenon, so here's what I can suggest for applying less force.
1- Remember that as your tool moves farther from the center of rotation, the torque on the tenon increases (Torque = Force x DistanceFromAxis). If you know your tenon is likely to break, take the shallowest, gentlest cuts you can when you're working near the rim. Taking 10 passes to reach your depth without breaking the tenon is a pain when you could reach the same depth in 2 passes between centers, but it might get the job done.
2- Make sure your tool is sharp and keep it that way. As the edge dulls, the force applied to the tenon increases, as does the likelyhood the tenon will break.
3- A "slicing cut" will apply less force than a "gouging cut". A "slicing cut" is where you rotate the gouge so that the wings (and the flute) are pointed to the left or right; a "gouging cut" would have the wings/flute pointed up like you use a roughing gouge.
4- When making the slicing cut and the bevel is riding on the piece, make sure not to push the bevel into the piece (I have a bad habit of this - you'll know it's happening because there's excessive heat). The bevel rides the piece to help guide the tool; you're not using it for burnishing.
5- 3- and 4- assume you're using a gouge - the way I do it, at least, a gouge is much easier on the tenon than hollowing with a scraper.
6- Weak tenons seem to dislike the chatter that can come from having the tool too far over the rest, and this makes it harder to keep the cut light, so make sure the rest is as close to the work as possible. Try an 'S' or curved rest, if you can't get a straight rest close enough.
7- If all else fails, cut the tenon off and glue the piece to a hardwood waste block.
Other general observations on tenons:
1- If you have enough wood to make a larger tenon and use a larger set of jaws, the larger tenon will obviously be stronger.
2- If you don't have enough wood to move to a larger set of jaws and/or you don't have a larger set of jaws, making the tenon as large as your jaws will handle might be preferable. The rule of thumb is to maximize the contact area between the jaws and the tenon, but if you know the tenon will be weak, a larger tenon size might be worth the reduced contact area.
3- If you have enough wood for the lip, expanding the jaws into a hollow might prove stronger if you know the tenon will be weak.
4- If you can't do 1-3, glue the piece to a waste block and turn the inside of the bowl first, while there's maximum glue area between the waste block and your bowl. As you move from rim to base on the outside, the glue area will be cut down. As it gets smaller, be gentler.
Hope some of this helps,
MZR
- The tenon breaks because there is more force applied to it than it can withstand, so your options are (a)strengthen the tenon or (b)apply less force. I don't know how to strengthen a tenon, so here's what I can suggest for applying less force.
1- Remember that as your tool moves farther from the center of rotation, the torque on the tenon increases (Torque = Force x DistanceFromAxis). If you know your tenon is likely to break, take the shallowest, gentlest cuts you can when you're working near the rim. Taking 10 passes to reach your depth without breaking the tenon is a pain when you could reach the same depth in 2 passes between centers, but it might get the job done.
2- Make sure your tool is sharp and keep it that way. As the edge dulls, the force applied to the tenon increases, as does the likelyhood the tenon will break.
3- A "slicing cut" will apply less force than a "gouging cut". A "slicing cut" is where you rotate the gouge so that the wings (and the flute) are pointed to the left or right; a "gouging cut" would have the wings/flute pointed up like you use a roughing gouge.
4- When making the slicing cut and the bevel is riding on the piece, make sure not to push the bevel into the piece (I have a bad habit of this - you'll know it's happening because there's excessive heat). The bevel rides the piece to help guide the tool; you're not using it for burnishing.
5- 3- and 4- assume you're using a gouge - the way I do it, at least, a gouge is much easier on the tenon than hollowing with a scraper.
6- Weak tenons seem to dislike the chatter that can come from having the tool too far over the rest, and this makes it harder to keep the cut light, so make sure the rest is as close to the work as possible. Try an 'S' or curved rest, if you can't get a straight rest close enough.
7- If all else fails, cut the tenon off and glue the piece to a hardwood waste block.
Other general observations on tenons:
1- If you have enough wood to make a larger tenon and use a larger set of jaws, the larger tenon will obviously be stronger.
2- If you don't have enough wood to move to a larger set of jaws and/or you don't have a larger set of jaws, making the tenon as large as your jaws will handle might be preferable. The rule of thumb is to maximize the contact area between the jaws and the tenon, but if you know the tenon will be weak, a larger tenon size might be worth the reduced contact area.
3- If you have enough wood for the lip, expanding the jaws into a hollow might prove stronger if you know the tenon will be weak.
4- If you can't do 1-3, glue the piece to a waste block and turn the inside of the bowl first, while there's maximum glue area between the waste block and your bowl. As you move from rim to base on the outside, the glue area will be cut down. As it gets smaller, be gentler.
Hope some of this helps,
MZR
Would you still say this, knowing that his problem is that the tenon is breaking, and not that it's slipping out of the jaws?
I'm a very inexperienced turner, so this is just for clarification, but I wouldn't think the contact area between jaws and tenon would have much effect on the tenon breaking or not...
What am I missing/forgetting?
MZR
Size matters. Depth wise, about 1/4 inch. You can get away with less, but not more than 1/4 inch.
Diameter: Should be about 1/4 the diameter of the bowl, so a 12 inch bowl should have a tenon of at least 3 inches. On a 14 inch bowl, 3 to 4 inches. You can get away with less, but that requires a very gentle touch when turning.
You can over tighten. Snug it up, rotate, and use the other key hole to snug it up again. I go around a couple of times. You do not want it as tight as you can possibly get it. You can snap it off just from tightening it, or put so much pressure on it that the slightest catch will break it.
robo hippy
Diameter: Should be about 1/4 the diameter of the bowl, so a 12 inch bowl should have a tenon of at least 3 inches. On a 14 inch bowl, 3 to 4 inches. You can get away with less, but that requires a very gentle touch when turning.
You can over tighten. Snug it up, rotate, and use the other key hole to snug it up again. I go around a couple of times. You do not want it as tight as you can possibly get it. You can snap it off just from tightening it, or put so much pressure on it that the slightest catch will break it.
robo hippy
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OK, so you're working a tenon on the heartwood, not the sapwood side, as you said in the first post? If so, disregard some of the previous information and misinformation (cambium NOT a player) and look back to the form of the hold. A dovetail hold is a wedge, so the idea is to wedge the piece into the front of the jaws (so a misfit is not eight points) without wedging it to the point of splitting it off. Don't leave too much gap between jaw segments, if you can help it. You have to make it a bit larger so it can be turned back to circular after drying. No need if you use a mortise. Wants what the flat work folks call a shoulder to rest against. Angle of the tenon or mortise should provide just a little bit less space than the metal of the jaws, so it can do a bit of wedging. Bigger tenon is better? Not necessarily, because, as you know, annual rings are natural planes of weakness in the wood, and you can split the tenon off a larger section as easily as a small. Just recall how you can split even difficult woods like elm round and round by dropping the axe between annual rings. Make the tenon base - shoulder - across an annual ring so you get help from two rather than overstress one section of springwood.
What does count is you shouldn't do more than snug the jaws, whatever their form. Then you should attempt to cut the wood as it wishes to be cut to minimize strain even so. You ARE cutting across the rotation rather than into it, right? Snug the tail up and get support until you've got the piece as well-balanced as possible.
If you do have to hold in punky wood - reinforce it by running water-thin CA round and round, to refusal. Let cure and scrape circular once more, and you should be pretty good to go, especially if you support the other side with the tail until you're light and round.
What does count is you shouldn't do more than snug the jaws, whatever their form. Then you should attempt to cut the wood as it wishes to be cut to minimize strain even so. You ARE cutting across the rotation rather than into it, right? Snug the tail up and get support until you've got the piece as well-balanced as possible.
If you do have to hold in punky wood - reinforce it by running water-thin CA round and round, to refusal. Let cure and scrape circular once more, and you should be pretty good to go, especially if you support the other side with the tail until you're light and round.
In my experience, this makes a big difference in the tenon breaking. With the tenon close to the diameter of the jaws--not necessarily just above the minimum diameter, just not at the edge of its capacity--when the jaws have a fairly wide contact area on the wood, the clamping force is distributed very evenly along the inner curve of the jaws. When the jaws are near their capacity, their corners dig in, compressing the fibers at the point of contact with a very uneven distribution of force. I'm not a scientist, but in my educated guess at a good layman's explanation, this uneven clamping pressure would help to pull the fibers apart where the jaws create more tension in the wood than with even clamping pressure. It has been my experience that tenon failures have started near the clamping points, with the wood shearing away from the edge around the jaw marks. Additionally, when in compression mode, the jaw corners can create internal bruising extending far into the tenon, and can't always be removed by turning away just the jaw marks if you want to leave a foot on your bowl. When you then apply finish to what you think is your completed bowl base, you end up with four shaded areas that only show up when you oil your bowl!! I've ended up with some bowls with very small bases that are easily tipped, all because I had to remove marks left by the chuck jaws.
The reverse would be true when using jaws in expansion mode as well--pressure on 4 points would be much higher at the point of contact than evenly distributed radial pressure in a recess.
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Tenon problems
Most of the tips you have been given are helpful considerations that I too would have suggested, but at this point it appears some of them have been ruled out. I believe the cause to be something yet to be mentioned;
Yes, having your tenon near the smallest size will create greater surface contact with the jaws, this is important because you are turning with a "faceplate" grain orientation which means two jaws are compressing side grain, while the other two jaws are compressing the endgrain, causing the splitting effect. So tenon size relative to your jaw size is important but not likely to be the cause. In your case with 14" bowl blanks, the issue is likely to be (at least in part) the tenon diameter relative to the blank bowl diameter. Ideally, you want your tenon size to be 1/3 to 1/4 the diameter of the blank, with larger pieces this is often not possible with a tenon/jaw approach, but this is the ideal. So, the smallest possible tenon in the largest set of jaws might help.
Secondly, (and more likely the primarly cause) is that as a beginner, one of the common bad habbits that develop is that when turning the center portion where the wood fibers travel accross the tool at a slower speed wood removal goes slow and cutting doesn't feel or sound as smooth. Beginners tend to push the tool into the wood harder at this point. As the wood spins the force generated by pushing harder leads to a momentary catch less obvious than with wood spinning at the perimeter, this pressure leverages the object out of center. With the object spinning and the pushing of the tool, these combined forces create the wood splitting effect on the tenon mentioned by MM. When I started turning I did this myself and have seen others do the same, but I have never observed it occurr when a turner was cutting slowly at center without pushing hard. This is why your problem is occurring only when you are working at the center.
Solution; either cut slower with less pressure and sharper tools, and try different tool presentation angles, or start your bowl turning by using a forstner drill bit in a jacobs chuck to core out the center portion until your skill improves. Either way, Good luck!
Most of the tips you have been given are helpful considerations that I too would have suggested, but at this point it appears some of them have been ruled out. I believe the cause to be something yet to be mentioned;
Yes, having your tenon near the smallest size will create greater surface contact with the jaws, this is important because you are turning with a "faceplate" grain orientation which means two jaws are compressing side grain, while the other two jaws are compressing the endgrain, causing the splitting effect. So tenon size relative to your jaw size is important but not likely to be the cause. In your case with 14" bowl blanks, the issue is likely to be (at least in part) the tenon diameter relative to the blank bowl diameter. Ideally, you want your tenon size to be 1/3 to 1/4 the diameter of the blank, with larger pieces this is often not possible with a tenon/jaw approach, but this is the ideal. So, the smallest possible tenon in the largest set of jaws might help.
Secondly, (and more likely the primarly cause) is that as a beginner, one of the common bad habbits that develop is that when turning the center portion where the wood fibers travel accross the tool at a slower speed wood removal goes slow and cutting doesn't feel or sound as smooth. Beginners tend to push the tool into the wood harder at this point. As the wood spins the force generated by pushing harder leads to a momentary catch less obvious than with wood spinning at the perimeter, this pressure leverages the object out of center. With the object spinning and the pushing of the tool, these combined forces create the wood splitting effect on the tenon mentioned by MM. When I started turning I did this myself and have seen others do the same, but I have never observed it occurr when a turner was cutting slowly at center without pushing hard. This is why your problem is occurring only when you are working at the center.
Solution; either cut slower with less pressure and sharper tools, and try different tool presentation angles, or start your bowl turning by using a forstner drill bit in a jacobs chuck to core out the center portion until your skill improves. Either way, Good luck!
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Michael,
A14 inch bowl is way too big to tackle without a lot of practice on 8 and 10 inch bowls.
The bigger the piece the bigger the risk of serious injury.
We all started out not knowing anything about turning.
Tenons sometimes shear because the tenon is parallel to an annual growth ring more likely in wood from a large tree.
The dry wood may have lots of hidden cracks.
The tops of the jaws should have flat to rest against.
If you are getting catches you may not be able to keep any bowl on a tennon.
You mention soft wood. It may not have enough structural integrity for a tennon.
Most likely you need to work on your tool techniques.
I suggest you practIce with smaller 8 - 10 inch bowls of fresh cut green wood.
Contact an AAW chapter. Turners are helpful people. Even just watching someone who knows what they are doing will help.
Some chapters have mentoring programs.
I strongly recommend turning classes.
Be safe
Al
A14 inch bowl is way too big to tackle without a lot of practice on 8 and 10 inch bowls.
The bigger the piece the bigger the risk of serious injury.
We all started out not knowing anything about turning.
Tenons sometimes shear because the tenon is parallel to an annual growth ring more likely in wood from a large tree.
The dry wood may have lots of hidden cracks.
The tops of the jaws should have flat to rest against.
If you are getting catches you may not be able to keep any bowl on a tennon.
You mention soft wood. It may not have enough structural integrity for a tennon.
Most likely you need to work on your tool techniques.
I suggest you practIce with smaller 8 - 10 inch bowls of fresh cut green wood.
Contact an AAW chapter. Turners are helpful people. Even just watching someone who knows what they are doing will help.
Some chapters have mentoring programs.
I strongly recommend turning classes.
Be safe
Al
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I agree with those saying to small a tenon for the size of work. A faceplate will hold better than a chuck. For a piece as large as you are turning I would use a four to six inch faceplate. Four inch would have six to eight holes able to take a 1 inch #14 (1/4) in screw with a hexhead, the kind made for metal. But for that size I think 6 inch. With at least nine holes. You can mount the faceplate on the inner flat to form the outside and foot. Then reverse the faceplate to the foot to do the inside. You can use glue blocks on the foot or just lose some wood where the faceplate is mounted when reverse turning the base for a foot or flat bottom. Most of my faceplates are about 5/16ths thick so 1 inch screws in facegrain work. The thickness of your faceplate will dictate how long a screw to use. A bowl that large in end grain would 1 1/2 inch screws. Side grain at around 17 inches plus get the same. If you ever get smacked with a bowl breaking off youll know its not overkill to be safe. A six inch bowl at a thousand rpm will knock you to the ground. If you are lucky you will just be black and blue a couple weeks.
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Your guess is one of the prime reasons people have trouble with dovetail chucks. It's not about how hard you "grip" and less about the amount of metal in contact with the side of the tenon (wood or metal) than a properly mated shoulder. Once again, it's a wedge. When it's snug, it prevents the piece from pulling away. When it's tightened, it can dig into the wood and split it apart.
So don't tighten, just snug the assembly. That way the force/unit of area is no problem. If you can't pull the nose of the jaws into contact with the bottom of the mortise or the shoulder of the tenon, start over, because tightening is likely to split something.
All great information, thank you!! I glued the tenon back on to my current project last night. I am going to see if that works to finish the bowl with a light touch. If it comes off again, I am going to try to turn a recess and try the chuck that way. I think I have enough wood left in the bottom to pull that off without getting too thin. Thank you again!
Mike
Mike
The comments about the interface between the face of the jaws and the bottom of the bowl are important but difficult to describe. When teaching a new turner to make tenons, I use a spare jaw segment and place it on the tenon and up against the bottom of the bowl. Now by looking at it from the side, one can see how well the tenon fits into the jaws. The jaws get most of their strength from a good contact all of the way around the outer edge of the jaw. In other words, if the bottom of the bowl is convex and slopes away from the jaw leaving a small gap at the outer edge, it will not be strong and may break or twist off. In contrast, if the surface of the bowl coming out from the base of the tenon is flat or slightly concave, the outside edge of the jaw will contact the wood giving it more holding power. Another way to look at it is to think of the bowl that is being levered out of the jaws. Jaws that make good contact at their outer edges will have more leverage than those that only contact at the base of the tenon.
I hope that this adds clarity and not just more confusing. I do a lot of turning and it has been a long time since I broke off a tenon. Maybe I'm just not trying hard enough.
John
I hope that this adds clarity and not just more confusing. I do a lot of turning and it has been a long time since I broke off a tenon. Maybe I'm just not trying hard enough.
John
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If you go to a mortise, remember that your tenon (chuck) should bottom on the interior just as it should have on the exterior. http://i35.photobucket.com/albums/d160/GoodOnesGone/Chuck-marks.jpg Snug, not squash. Overdrive a wedge, and you can't control the split.
Follow up - I glued the tenon back on a few days ago and gave it another go today. Success!! It glued on straight and the bowl turned true. But instead of using a spindle gouge I used a round nose scraper to remove the spur running up the middle of the bowl that the tail stock had been holding. Then I used the scraper to fine tune the sides and bottom.. light touch of course. A couple of the tips that I picked up from this post were to use a lighter touch when tightening my chuck and snug it up from both of the screws, not just one - seems to have made a big difference. The other thing I'm going to try is a recess instead of a tenon - it seems that it would be less likely to split out, if made correctly. I did double check the sides of my tenon when I chucked it up this morning and it was NOT bottoming out and the sides were angled in just about perfect from what I could tell. So it appears that I did that part right. I think the bottom line was I had the chuck way too tight, I was using a very sharp gouge which was cutting way too agressively, and the wood was very soft and dry - all combined to cause my failure. Anyway, I got a lot of great information from you all and I am sure it is going to help me in the future. Thank you!!
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FWIW, http://s108.photobucket.com/albums/n28/MichaelMouse/?action=view¤t=PillarSmall.mp4 Getting what I can with the gouge, following with a parting tool.
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All is well that ends well. Figuring out what went wrong and then being persistent is its own reward.
If I may comment on your above findings, I would like to add my thoughts for whatever they may be worth:
- While tightening the chuck until it has a good solid grip on the wood is plenty sufficient, check it occasionally to make sure that it hasn't become loose. How much tightening a piece of wood can tolerate depends on the type of wood and its condition. Sometimes a piece of wood is not meant to be held in a chuck. Any hidden or visible flaws are reasons to stop. Hidden flaws reveal their presence by a change in the sound that the wood makes as it is being cut. The bottom line is that I would not blamed the chuck for being too tight as much as I would decide that the wood was not meant to be turned in a chuck because it is crappy wood. Here is a link to an excellent article in the American Woodturner by Nick Cook titled, Twenty Ways Not to Turn a Bowl. Nick is one of the best teachers for beginning woodturners.
- I am glad to read that your gouge was very sharp -- many beginners make the mistake of trying to turn with dull tools and as a result, they push the tool harder against the wood to try to compensate for the dull tool. The inevitable result will be either a catch or knocking the turning out of the chuck. As soon as a tool loses its super sharp edge, it is time to stop and resharpen it. Sharp tools are never a problem, but dull tools always are.
- Cutting too aggressively is probably the biggest culprit in causing problems and could be categorized as either brute forcing a dull tool to make dust or going "hog wild" with a sharp tool and taking huge bites. In either case, it is an issue learning good habits.
- Turning dry wood is not a problem other than it is usually much harder than when it was green -- and there is much more dust. Soft wood also is not a huge problem except for punky wood. Turning soft wood requires a gentle touch to prevent grain tear out. Turning punky wood requires an even more gentle touch. Finesse is very important in turning even in very hard woods.
Much of what I would say, has already been said. I noticed the other day that the makers of the Nova chuck suggest that you make the tenon round and compress the chuck tightly. Wow, I have always made dovetailed tenons for both my vicmarc and SN chucks. I think that, depending somewhat on the wood (green, soft, dried, hard, etc) it is ok to really tighten the chuck up. An excellent demonstrator in Columbia even used fulcrum means to tighten her bowl blank.
The problem among beginners is that they often want their tenons to be very wide and too long, neither of which is useful. The longer the tenon, the greater the strain on it. It is very important to have the tips of the jaws (which are flat) to sit on a flat surface. It's also preferable that the flat surface be commensurate with the thickness of the jaw. Keep in mind also, that transferring a blank from either a faceplate or whatever you used to get it round and with a tenon, will still require some additional rounding out. I have noticed that the degree to which this is necessary depends much on the chuck itself.
I generally do this additional rounding, and some of the early hollowing while the blank is still held with the tailstock and a live center. That tends to put less pressure on the tenon.
Having said all of that, when I'm working on a really big piece and I want to core it or make a HF, I sometimes forgo the tenon and use a faceplate.
The problem among beginners is that they often want their tenons to be very wide and too long, neither of which is useful. The longer the tenon, the greater the strain on it. It is very important to have the tips of the jaws (which are flat) to sit on a flat surface. It's also preferable that the flat surface be commensurate with the thickness of the jaw. Keep in mind also, that transferring a blank from either a faceplate or whatever you used to get it round and with a tenon, will still require some additional rounding out. I have noticed that the degree to which this is necessary depends much on the chuck itself.
I generally do this additional rounding, and some of the early hollowing while the blank is still held with the tailstock and a live center. That tends to put less pressure on the tenon.
Having said all of that, when I'm working on a really big piece and I want to core it or make a HF, I sometimes forgo the tenon and use a faceplate.
The torque forces on the tenon do not come from the tenon size, they come from the bowl diameter, and how much tool pressure you are using. Think of it this way, a 12 inch lever with the fulcrum at 1 inch, the one inch side will lift far more (more stress) with less effort than the same lever with the fulcrum at 3 inches with the same amount of effort. I can be far rougher with a 12 inch bowl that has a 4 inch tenon than I can with one that has a 2 inch tenon.
I would never use a lever to tighten up a chuck. Not only do you risk breaking your chuck, you put too much pressure on the wood. The idea of using all key holes on your chuck is an old machine shop trick. It distributes the tightening more evenly. Perhaps that one turner was using the tommy bar type of chuck.
robo hippy
I would never use a lever to tighten up a chuck. Not only do you risk breaking your chuck, you put too much pressure on the wood. The idea of using all key holes on your chuck is an old machine shop trick. It distributes the tightening more evenly. Perhaps that one turner was using the tommy bar type of chuck.
robo hippy
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Since you can't compress the metal, and unless you limit the area of contact severely, the wood, it's plain silly to think of reefing on the chuck. The business of tightening through other holes has to do with taper (collet) holds, not scroll chucks.
Not to mention that the more you drive a wedge, the bigger the opening it makes, until ....
If torque was important, the serrations would be parallel to the axis of rotation.
Not to mention that the more you drive a wedge, the bigger the opening it makes, until ....
If torque was important, the serrations would be parallel to the axis of rotation.
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Based on context, I'll guess that reefing is being used as a derivative of the nautical usage (as in "make steady"a sail, etc.) and not the urban usage (which might have an opposite connotation such as, "loosening up").
If it weren't for friction, I might agree with your statement about using both key positions to tighten a scroll chuck. Because of friction, asymmetrical loads will prevent the chuck jaws from being tightened as tight as when using both key locations -- assuming the same torque applied in every instance. Whether the difference is of great importance or just hand/arm exercise is fodder for Internet forum discussions.
Torque has at least some importance, but bending moment loads are of much greater importance -- think of it as prying a tenon out of the chuck jaws -- and that is a reason that chuck jaws have either serrations or a dovetail wedge circumferentially about the spin axis.