Do you ever have a Blow Out Day

Re: Do you ever have a Blow Out Day

Jesper, Denmark

The crack in the bowl, starting about where your thumb is should have lit up the warning lights. I would have proceeded very carefully - or maybe scrapped it immediately.

Sanding and high speed do not go together.

Re: Do you ever have a Blow Out Day

robo hippy

Like Jesper said, the crack that is visible in picture #2 is a warning to me at least. At 2,000 rpm, even with glue in the crack, well it is suicidal. I always keep sanding speeds very low as well. Some days, things just go that way.

robo hippy

Re: Do you ever have a Blow Out Day

John Lucas

Ditto on the sanding speeds. I move the bowl very slow. The main reason is that the sanding disc bounces over low spots when sanding at higher speeds. I now sand at lower speeds than I ever used to because of this and it's really sped up my sanding time.

I tend to turn at high speeds. I've been turning along time. However when turning bowls bigger than 8" I doubt I ever reach 2000 rpm. I don't know for sure because I don't have a speed readout however my lathe only goes to about 3000 and I rarely have the dial much over half way on bowls.

Re: Do you ever have a Blow Out Day

John Lucas

I also meant to say that you don't get cleaner cuts going to high speed. The cutting edge presentation and sharpness are the two main factors along with how deep the cut is. Many people think speed is a factor because they tend to take a smaller bite per revolution and at higher speed you still think your removing wood fast. I do think to a point that higher speeds let you flow around a curve better because your body moves more smoothly. However this is small and the danger of running high speeds is great. More practice and you can learn to move your body smoothly at slower speeds.

Take smaller cuts and try to rotate the edge so the wood is coming across it at a shear angle. And of course cut downhill with the grain anywhere possible. The tearout you are showing on the bowl tells me your either pushing the tool too fast of the edge isn't sharp or it's scraping instead of cutting.

Re: Do you ever have a Blow Out Day

Ron Bauer

One very smart turner once said "Life is to short to turn bad wood". Not worth getting a piece between the eyes. I power sand between 0 and 48 RPM using the lightest possible touch, frequently lifting the pad to ensure I am not getting heavy handed. Faster, less heat, longer life. Ron.

Re: Do you ever have a Blow Out Day

Dale Bonertz

You said that you turned up the speed to 2000 to get a clean cut and finish to sanding. I take that as you were using a scraper or gouge for the cut so you could then re-sand the hump area in the inside bottom. Is that correct?

In the first picture, in the nub that was left, there appears to be a crack through the nub. Also in the picture of the tenon there appears to be a crack on the right side of the tenon. Combining those checks with the ones on the side I think the piece may have been doomed from the beginning. When you turned the speed up to 2000 the strain on those areas became to much.

Be careful out there and look your wood over good.

I count at least 4 cracks.......

Dick Coers

in that end grain. Accident ready to happen.

quick guesses...

Steven antonucci

First, it appears that your bowl was rough turned between centers. If you look over a recent tgread , you'll see the benefits of mechanical attachment ( aka holding in a chuck) in reducing vibration.

Second, if I was a betting man, you cut the bottom section from the large diameter down to the foot. However, that is the wrong way (aka against the grain). On the top side of the curve, it is the correct direction...hence no tear out.

Lastly, those cracks... Been discussed to death, but more vibration... Yeah.

RISK & Dale Nish's bowl speed formula

Geoff Whaling

RPM x diameter (in inches) = 6,000 to 9,000

Dale Nish recommended this as a basis to determine a safe speed to turn bowls. When you consider the bowl size & rpm some turners work at and then calculate the rim speed of a bowl it becomes quite significant at times.

Dales formula gives guidance on a recommended speed range of 750 to 1125 rpm MAX for a sound 8" bowl blank. Unsound blanks or blanks with "natural features" require careful appraisal and stabilization or modified turning & work holding techniques before proceeding & lower speeds.

If you ask those same turners who recommend relatively high lathe speeds to front up to a major league baseball pitcher or a top line cricket fast bowler without any protective gear their response would most likely be - NO WAY!

Lathes potentially can generate objects with significantly higher speed & mass than a baseball or cricket ball. Potentially the "struck by object" event produces severe head & facial injuries that render the injured turner unconscious & incapable of calling for assistance.

Several wood turners have died in similar circumstances in the past ten years. How many received serious life changing injury? A - unknown. How many have had black eyes or significant facial injury? A - many & every club has several examples in recent years. How many turners have lost a bowl off the lathe? - ALL! & it is exceptional to meet one who hasn't - yet ;-)

Yet many turners are quite prepared to accept that level of risk when turning an unsound bowl blank or sanding one at very high lathe speeds. They regularly expose themselves to hazards that are known to produce quite serious even potentially life threatening injuries. The more they expose themselves to hazards with high risk without implementing suitable hazard reduction controls generally means a much higher probability of a failure and injury.

Their response "I've been doing this for X years & nothing has happened" - yet!

Philip,

The others have identified a number of hazards in your particular bowl turning scenario, which in combination present quite a serious risk to your safety.

As a quick summary of hazards,

1. Unsound blank - punky & cracks with high potential for failure.

2. Technique - tool control is producing significant tear out - high potential for severe catches.

3. Tool sharpening - may require attention?

4. Blank mounting technique - between centers at least initially with a soft blank.

5. Unsound tenon - cracks & dia of tenon.

6. Turning lathe speed - unknown but likely high given next point.

7. Sanding lathe speed - very high - 2 times MAX recommended.

8. Use of protective equipment?

9. Potentially turning alone?

10. Emergency plan? - potentially no safety backup plan.

The first five generate a high probability of dislodging the bowl from the lathe or ripping relatively large objects from it.

Combine that probability with high lathe speeds capable of generating objects with high momentum & the risk increases dramatically and so does the severity of a potential injury.

As mentioned above these typical scenarios have caused serious head injuries & brain trauma and often render the injured turner unconscious an unable to call for help.

Turners may "get away with it" for a long time before such a scenario plays out fully & results in the turner actually receiving a direct hit. I liken the risk to fronting up to a blindfolded pitcher or fast bowler at close range. If you do it often enough one ball is eventually going to hit you in the head!

Hand turning is a safe pursuit IF we follow recommended safe turning practices.

p.s. If you look carefully at the 4? cracks near your thumb in photo 2 you may notice that the tear out pattern changes abruptly across the cracks. This indicates a couple of things to me

1. the bowl is flexing across the crack.

2. maybe a fair bit of force is being used to produce the cut.

3. tool presentation & sharpening requires adjustment.

4. it is unsafe to continue in this condition.

DITTO

Lyle Jamieson

Nice evaluation John. Its much better to prevent the torn out grain, I prefer not to sand that much.

Re: Do you ever have a Blow Out Day

phillip Medghalchi

Gentlemen, I needed to clarify few points in this thread I've created. I first apologize for it not being totally clear to state what I wanted to say. However, here is what happened and I hope this will shed some light on what I was trying to ask and learn from your responses.

I wrote, " So as you can see in the pic. @ on the side of the bowl I had tear outs due to the wood being soft not punky, evereything was solid.

So, I proceeded to re-shape and re-true up the tenon and put it back on and started to sheer scrape the outside and inside. At this time I was getting the shavings flying off , but very hot, so I eased off on the tool/ When I got to sanding even though that no power sanding was used I noticed a little hump in the inside bottom, so I cranked up the rpm to around 2000+ so I get a very clean cut and finish to sanding, but there goes the inevitable, it blow up."

Well, the blank was originally rough turned on April 14, then I put it in a shaving bag in card board box. I was aware that the tear out was due to the wood being very wet at the time of roughing and I decided that when I finally go to finish cut it I may be able to correct that by sheer scraping and sanding in opposite direction to get the fibers to lay down and flatten down.

So, this is the run down of what happened.

1- I had to true up the tenon.

2- Then I had to reshape a a little bit to get he shape I wanted to finish the project in so I did that. At this point before all this take place the piece was about 5/8" thick to begin with. it did not [pose any threat to what I wanted to do. the RPM at this point must have been around 800+ ( not too sure, so don't hold me to it)

3- now I notice that as i I am shaping the shavings are getting hot thrown at back of my left hand so I put on my finger less glove and slowed down the speed a little and took the Elsworth ground bowl gouge attempting to sheer scrape to get a cleaner surface. as i am doing this and stop i noticed that few cracks opened up (form what I can recall. first one opened up from rim towrds the base(foot) (please don't hold me to the sequences of the cracks discribed here I am writing as I can remember)

4- I fixed the cracks by applying med. CA glue and I am proud to say I did it so skillfully that after it was all done and sanded (applying sanding sealer around the crack b4 applying CA) so i did a good job as fixing it that i can not even tell where the heck the crack were. Heat generated cracks.

5- So, I got to the point that in my opinion, I thought the piece is safe enough to proceed to the next operation. So,

6- I start sanding the outside applying soapy water on the piece and then hand holding the back up pad and the sanding disk at about 360 rpm (I do not and this is where the misunderstanding happened) sand more than 365 rpm and most of the time even lower than that down to (270-) rpm and then I reverse sand so I get a slick surface when I am done.

So we get this issue resolved that I never sanded at anything of that high speed even though it's tempting and I have seen many turners on You tube doing the sanding at the same high speed as they turn.

Now I go tot the inside and then find out by touching that there was a hump and I needed to get rid of it and try to get a clean surface so it would help me to start sanding at higher no. grit. This is where the culprit happened.

7- so, I got rid of the hump and it was Ok, until I decided to use a round scraper inside to get a consistent clean line inside so when you(customer, other turners) examine the inside it has a nice feel of consistency to it instead of feeling a broken curved surface. (These are my criteria for clean design (consistent lines).

These are my observations of what happened and I am not defending them, just merely trying to learn from the mistakes. I think that sheer scraping was done at too high of a speed like John mentioned and then also the presentation of the tool to the wood may have been questionable. Most importantly, I still think my sharpening skills are still in question (unfortunately, have been watching many demos of sharpening and even had a friend to show me in person, where he was doing all the sharpening and in few instances I was watching his body in the way and really didn't get to see how he was presenting the tools to the wheel, however, unless I do it myself and have someone judge my progress as if I am doing it right and if the sharpness (very subjective to its definition)is absolutely what is expected of a tool to be I am still lacking that skill.

8- The other reason is that I think the bowl was flexing at that speed and I need to use my steady rest of 20" full circle and/or the bowl steady so there is support for this kind of operations.

Now, all comments welcomed as if you see what was taken form this experience.



I just found more pic.s that may clarify this point to f discussion, I just wanted to thank everyone helping out to point out the mistakes. I say if I have put 150 blanks on to the lathe form the day one until now, some of you guys probably put 3000+ blanks so your inputs are very invaluable for this discussion and hope it helps others too. Very much appreciate everyone taking time to reply.

Re: Do you ever have a Blow Out Day

phillip Medghalchi

jasper that crack was on the surface and happened in April, then it closed back up before my last turning the other day. I also, applied CA to make sure it won't go any further, the bowl was thick enough.( of course, these are my personal judgement as I didn't have any one verifying the decision)

Re: Do you ever have a Blow Out Day

phillip Medghalchi

Reed, I posted a detailed explanation, and that crack in my judgment was not all the way through to worry about it at the time which was put away, then again, I am working all on my own and solely making these decisions) which may not be a sound ones, that's why i love these discussion here on WC, which brings wide arrays of eperiences to the table.

Re: Do you ever have a Blow Out Day

phillip Medghalchi

John, all your points are taken and I appreciate you mentioning them. Please read my long post bellow.

Re: DITTO

phillip Medghalchi

Ron, Lyle , please read my post bellow as to clarify my points I wanted to say. Although, your advise have been taken to heart and followed.

Re: Do you ever have a Blow Out Day

phillip Medghalchi

Dale, the nob you noticed was inside the bowl and not the bottom of the foot, i didnt' remember to see any cracks there then, I wear tri-focal glasses too. On the tenon, I do not remember to see any cracks and if there was any I made sure that it would be sound, I have had that happening to me b4 and learned to return the tenon or glue up a glue block or remedy it for good b4 I proceed to shaping or reshaping. thanks for the mentioning of it.

Re: Do you ever have a Blow Out Day

robo hippy

Well, that does explain a few things. Now, I NEVER trust any piece of wood, or I trust them like I do every one who is driving on the road..... Don't think I need to explain that one. In one picture, there is radial checking/cracking from the pith out, and also ring shake. Radial cracks are pretty easy to see, and since they go along the grain, they can be some what invisible till you put some finish on them, or if you get a really good light on it, or take it into the sun light if you don't have full spectrum bulbs. Ring shake can be from stress or just lots of wind, and can be invisible, or if you are looking for it, one spot on a growth ring is a bit wider and slightly different color, usually darker. Both are huge weaknesses in the wood. Glue does close them up, but is no guarantee of holding them together under any type of stress. A bowl spinning at high speed does elongate, and not just because it is drying, because of grain orientation. It does so in the same directions that it does when it dries. This means the bowl is flexing slightly as it spins, and the higher the rpm, the more it flexes. The CA glue is brittle, and holds fairly well till it gets some stress, particularly in a shear line, or with impact. So, never depend on it to hold a piece together.

I always shear scrape with a scraper, and up on its edge at a 40 to 70 degree angle. I do remember Bill Grumbine's bowl videos, and he is using a swept back gouge to 'shear scrape' the inside of a bowl. Thing is that he is holding the gouge level. This, to me, is a scrape with the cutting edge at 90 degrees to the wood rotation, and no shear angle to it. A scraping cut will add to vibration. For a shear scrape with a gouge, the handle has to be lowered to 45 degrees or so, which can be difficult with a gouge on the inside of a bowl. A scraping cut will add to vibration any where near the rim.

I am only doing one show a year now to sell my bowls. I take a big box of all my cracked ones and sell them for $1 to $5 each. They go very fast. Repairing cracks for utility pieces is a waste of time. If I can't turn the crack all the way out, or the bowl cracks during drying, I toss it. You spend a lot of extra time, and can't sell the bowl for extra money. I do make an exception once in a while for 'art' pieces. Pretty much the same thing with knots.

robo hippy

Re: RISK & Dale Nish's bowl speed formula

phillip Medghalchi

Wally, I appreciate the tip you posted. One thing I failed to observe is that I have read Dale's recommendation, however, forgot to make note of it and put it into practice.

my long thread bellow exaplins in detail what happened. to put your mind at ease these are the things I learned early on and put it to practice and I am sure I can improve on them further.

I do turn in between at the beginning according to Lyle's recommendations, I find it easier to reorient the blank to get a better grain pattern for the final design. I never, and I mean it seriously. I learned this at very early stages in my turning endeavor, since I had a friend who had serious face reconstruction because of it. stand in line of fire. At times it gets little uncomfortable to be on the side of the line of fire and it is tempting ,but I made sure that I am to one side or the other even though I have to design my piece. I stop frequently, and maybe tilt my head to look at my curve on the bowl before I go further with it.

I have had (and still does happen) inspect the spigot and make sure it's sound at least visually and at times the darn thing proves me wrong (then again, I don't think I am any exception) to make sure it will hold up for what iam intending to do.

I do not sand at high speed and never did,( please see my long post for detail, and explanation of the error in tying). The highest rpm I ever sanded was about 750 rpm or so and that was when I had my Grizzly Reeves Driven lathe and I wasn't sure where it felt on the speed. Now I have NOVA XRP and digital read out, so I am constantly watching my speed and it's been about almost two years that I ever gotten up beyond 365 rpm for sanding and mostly on Mesquite, which is a sturdier wood. all others based on the texture and stability maybe around 275 and most of the time the back up pad and the discs are held in my hand, not much on the power sander.

I put most of the tips you mentioned above in practice and I am sure I can still improve on them. If a man tells you he knows all there is to know about a trade then you need to run the other way from him since he maybe dangerous to himself.

I am sure we all fall short of following all the precautions in our trade, I strive to do my best and practice as much I can remember and err on the safe side. I am going to find Dale's formula and laminate it and put up in front of the lathe, so i have a good reminder, It was just a dumb assumption of me reading or someone told me that you get a cleaner surface when you sheer scrape at a higher speed, which I guess I am proven wrong here.

I appreciate the time you tokk to share these tips with us.

Re: Do you ever have a Blow Out Day

Keith Tompkins

Phillip, remember that if a crack closes up as the blank dries, it's still cracked..you just may not notice it. But, the crack has severely weakened the structure of the bowl. Personally, If a piece cracks that I'm working on, I don't repair it. It's going to the burn pile.

Re: Do you ever have a Blow Out Day

John Jordan

I'm with Keith-start with cracked wood, end up with a cracked piece. But I rarely have a crack/check, because I thoroughly examine the wood when cutting. and I NEVER used cracked wood.

Some of those cracks were there before you started turning. 2000 rpm is too high by a lot. Some turn pretty fast, but they have experience to do it, and its still not particularly safe, but they at least know what precautions to take. I rarely if ever turn more than 1000, its just not needed. It's been years since I had a piece come off in any manner.

You need to get some help with sharpening and tool control-no surface should ever be that rough-even on softish wood. Never start turning until you have sharpened the gouge, and never fail to sharpen for the last cut. It between as often as needed, but when you touch the tool to the wood, it should be effortless, with a light touch, no bouncing around or death grips.

John

Re: RISK & Dale Nish's bowl speed formula

Geoff Whaling

Wally?? I resemble that

Always hard to pitch a response but plenty of experts looking at the names on this thread, & plenty of competent advice too. Sounds like you have a good grounding on the bowl turning side of things, maybe a little assistance required with sharpening.

Maybe it was a learning exercise however earlier training and your safety precautions look like they saved your bacon. Looking at the cracks and ring shakes in your latter photos I would have tossed the blank long ago as it was doomed to fail. If you are experiencing flexing of the bowl I would suggest that perhaps you are forcing the cut with a not so sharp tool.

"Life is to short to turn crappy wood." now where have I heard that one

My take is "Your life may get shorter turning crappy wood."

Re: Do you ever have a Blow Out Day

phillip Medghalchi

Keith goo advice. I'll make sure to remember that always.

Re: Do you ever have a Blow Out Day

phillip Medghalchi

Thank you John, will try to follow this rule. I think, the main thing is the sharpening that I am inconstant with. I guess I just have to get over the fear and waste some metal to get good at it and do it frequently as you said. Now, that I look back i can see that I get so involved trying to perfect the shape that I neglect the other aspect of the turning in order to achieve a favorable result. After all turning a process of different steps to get to the final point which is well executed article, and I think I am stuck in one part and get too involved in it and forget the other parts need help.

Re: RISK & Dale Nish's bowl speed formula

phillip Medghalchi

Geoff Whaling, I truly apologize for calling you a different name. In other forum when you want to reply and use the orig. posters name it appears automatically, and here it doesn't so meant no offense. Just was trying to get the message across. BTW, do you remember if that foumla of Dale is on his site or where was it that he posted that formula, i like to reprint it and put it up behind my lathe so i can look at it. Hoping down the road I will always remember by heart.