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Another close call

Aron Fast

Aron Fast

Joined
Jan 1, 2025
Messages
16
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31
Location
Hesston, kansas
I think near misses are instructive as they can teach us.
Today when coring a 14” oak bowl on my Jet 1640 lathe the 8” tool rest flew apart and hit my jointer.

I was not hurt. I was wearing a face shield and not standing in the line of fire. My tool was near the center of the rest. Speed was about 850 and the tool was sharp.

I think the bolt holding the rest to the post just failed. I reached out to the manufacture and I will update if they respond.

If anything happens now while I lathe I go back over each step to make sure I wouldn’t have done anything different…in this case I wouldn’t have
 

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When you attached the post to the rest, did you torque the bolt or just tighten it as tight as you can get it? Reason for asking is over torquing a bolt can result in failure. Every bolt on airplane is torqued to specs to prevent failure. Here are values for a 3/8" bolt.

 
I agree that that is a failure you wouldn't see coming even with impeccable procedures. But having had a couple of close calls myself recently, I agree that it is crucial to stop everything after a near miss and analyze what went wrong.

I recently admitted in detail having a fairly heavy ash bowl come off a longworth chuck when I was literally done with it, and thus had removed my shield for close inspection of the bottom with the live center and tailstock removed. Long story short, I made a series of careless missteps that resulted in it smashing me directly in the upper lip/nose area after flying off at 1300 rpm:
1. I never should have reversed the beaded rim profile onto a longworth (even though it was well-centered and all the rubber stops were secure). A friction drive or my vacum chuck would have been far more safe.
2. I forgot to change gears from high to low settings on my spindle.
3. When I moved my right hand across to hit the off button and end the turn completely, my finger inadvertently went across the speed knob and cranked it open a good bit.

The last thing I remember seeing before that bowl smashed me in the lip was just a flash of 1350rpm's on the readout, the fatal wobble and it bouncing off the ways into my unguarded face! I was lucky: other than a busted lip that shredded itself against my upper teeth, and some blood, bruising and swelling, I was fine after a few days. This could have easily ended in an ER trip and reconstructive surgery! But I immediately shut everything down, dealt with my wounds, and called my friend and mentor Tim Tucker for a debriefing. More than anything, I wounded my pride in myself as a competent turner, and was actually full of self-loathing rage for a couple of days at my stupidity.

After I got over that, I "got back on the horse," filled the ding in the bowl with colored epoxy, and re-finished it off the lathe, with a hard lesson learned. Lathe on equals face-shield on now, always! It also helped me to watch a few Kirk DeHeer videos and try to really internalize how methodical he is at every step. It's so easy to forget to lock down a banjo when your tool rest is near a spinning chuck, or any of the other stupid mistakes we can make at the lathe.

At least you can say your accident was not due to carelessness, and you weren't injured. The learning never stops either way! I hope you get your tool rest issue sorted out.
 
I took a whack to the face recently, too. I'm bad about wearing my face shield due to our high humidity. I use a jam chuck and turn the tenon down to a nub. The process is to get it close to gone, then turn off the lathe and apply pressure while the lathe slows. The nub comes right off in most cases. This time the center of the tenon must have been in a weak spot. As soon as I got the nub down to where I was ready to turn off the lathe, it broke off. The bowl (which was probably 8" or so) flew off and hit me in the face. I was momentarily stunned and as I was looking around I noticed my vision wasn't right. The bowl had hit me in the left eye and knocked the lens out of my glasses. I never did find it. There wasn't a scratch on me. I checked the RPMs and it was just a hair over 1,000. Normally a bowl won't fly at 1,000 RPMs, but that one did.
 
Kent Reisdorph said:
Normally a bowl won't fly at 1,000 RPMs
Click to expand...

How many bowls have you subjected to a test flight?;)

You are not the only person to say that "A bowl won't fly at X rpms". This makes no sense to me, as the flight potential at a given rotational speed depends largely on workpiece diameter. Even if a smaller diameter piece gets loose and heads for the floor instead of the ceiling it can ricochet off the lathe and hit you in the face.

I use a vacuum chuck when I can, and use the tailstock as well until I get down to the nub. When using a friction drive I undercut the nub, turn off the lathe and either saw it off or turn the piece by hand and cut through with a gouge. I have never had a piece take flight in the 0-10 rpm range. Snapping off the nub always runs the risk of tearout below (above?) the intended foot.

Airhats (PAPRs) supply face protection while minimizing condensation. They are costly, but a lot less than a trip to the ER.
 
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Kevin Jenness said:
How many bowls have you subjected to a test flight?

I use a vacuum chuck when I can, and use the tailstock as well until I get down to the nub. When using a friction drive I undercut the nub, turn off the lathe and either saw it off or turn the piece by hand and cut through with a gouge. I have never had a piece take flight in the 0-10 rpm range. Snapping off the nub always runs the risk of tearout below (above?) the intended foot.

Airhats (PAPRs) supply face protection while minimizing condensation. They are costly, but a lot less than a trip to the ER.
Click to expand...

I think this was the second bowl that took off on me in 2.5 years. I want to buy a PAPR system, but haven't been able to pull the trigger.
 
Aron Fast said:
I think near misses are instructive as they can teach us.
Today when coring a 14” oak bowl on my Jet 1640 lathe the 8” tool rest flew apart and hit my jointer.

I was not hurt. I was wearing a face shield and not standing in the line of fire. My tool was near the center of the rest. Speed was about 850 and the tool was sharp.

I think the bolt holding the rest to the post just failed. I reached out to the manufacture and I will update if they respond.

If anything happens now while I lathe I go back over each step to make sure I wouldn’t have done anything different…in this case I wouldn’t have
Click to expand...
Pardon the pun, but that was a striking failure. I am sure we are all interested in the final analysis.
Looking at your picture it looks like that in addition to the fracture of the threaded shaft there was a fracture of the surrounding cast iron? Illusion? When you remove the remnant post from the banjo could you post a pic of the post and rest side by side? Curious to know the brand of the tool rest?
How far away was the jointer, and was there much damage to it?
 
Well, what kind of tool rest is that? It looks to be one that screws on to a post, and that screw joint is where it failed. Go For a Robust bowl rest, the S curve. Solid metal post welded to the support arm. Far more secure. I had a cast iron tool rest on my 3520A and it broke, mostly due to being made out of cast iron which absorbs shocks well, but can also fracture. PM replaced it for free.

robo hippy
 
Webb: the bolt was hand-tightened

Mark: no damage to the jointer [about 3 feet away], it was BMWood [purchased on amazon], I think the bolt is smaller than 3/8 - looks to be 7mm

Reed: I agree - the design of this tool rest seems to be lacking

I reached out to BMWood and they stated they will replace it for free - I'll let you know if they honor their word.

If turning was my occupation and not just a hobby I would stay away from a tool rest design with a small bolt - although I was near the center of the tool rest this time - I imagine the force near the end could be substantial
 

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Kent Reisdorph said:
I think this was the second bowl that took off on me in 2.5 years. I want to buy a PAPR system, but haven't been able to pull the trigger.
Click to expand...
Kent-Had I not just bought a PEKE PowerCap, I would definitely get the Air MicroClimate aka the space helmet. I have heard great things about it, plus you get to look like an astronaut while turning!
 
If it’s a 1/4” bolt, and stainless with coarse thread (20), the torque value is around 6 foot pounds. Not much. Even less if lubricated. Point is tighten to snug and don’t over tighten which stresses the bolt and sets it up for failure.

If you have access to a torque wrench, I recommend contacting tech support for the recommended torque value when assembling your new one.
 
If it is a 1/4" bolt, I dont believe it is big enough for the application.
I have seen tool rests that are threaded rather than welded to their posts, but the threaded segment appears to be much larger and integral with the post.
 
I don't think I would want a replacement from them considering the failure of the first one. It just wasn't made correctly to withstand the stresses of turning. I do have an old cast iron bowl rest around, from Craft Supplies, and it had a threaded rod for the post. It held up very well to all of my mistakes in my early years. I finally came up with my own bowl rest design which is also an S curve. Robust makes them now. I have a bunch of Robust rests in my shop. There are none better, and the hardened drill rod is the best surface for tools to slide across. I have been making a lot of rolling pins lately, trying to learn some skew skills. I keep thinking about an 18 inch long rest with hardened drill rod. Probably made from wood, but the drill rod epoxied in. Maybe eventually....

robo hippy
 
Aron Fast said:
I reached out to BMWood and they stated they will replace it for free - I'll let you know if they honor their word.

If turning was my occupation and not just a hobby I would stay away from a tool rest design with a small bolt - although I was near the center of the tool rest this time - I imagine the force near the end could be substantial
Click to expand...
The highlighted statement bothered me. Tool failures can happen to anyone as you have proven. I won't offer up any failure theories, but there is plenty of observational evidence in your photo that indicates this tool rest is not a "bargain". I would strongly resist any urge to use that tool rest configuration.
 
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Another, and perhaps best, reason to not use similar 2 pc tool rests. Early in my turning journey I had several threaded 2 pc rests. The post was 1” dia with 1/2” thread. Never had a thread failure thankfully. I did find the rest joint needed to be tightened well to keep from loosening while turning.

I bought them because I could save a few $’s. I found that when I needed to change the tool rest, it was a pita! It took time (and tools) to change out. Buying more tool posts pretty much erased any $ savings. Got rid of them and went with Robust and a couple of @robo hippy rests. Advanced Lathe Tools has nice rests also.
 
Webb Willmott said:
When you attached the post to the rest, did you torque the bolt or just tighten it as tight as you can get it? Reason for asking is over torquing a bolt can result in failure. Every bolt on airplane is torqued to specs to prevent failure. Here are values for a 3/8" bolt.

Click to expand...

Speaking of torques, I keep several torque wrenches. My favorite for low torques is an inexpensive beam wrench: tighten while watching the needle on a scale, calibrated in inch-lbs. This is harder to use in tight places such as under vehicles since it could be hard to see - in those cases a click-type is easier: set the wrench to the torque required and it makes a audible and tactile click. I don't a digital torque wrench worth buying for general use - high precision is rarely needed and I wonder about the calibration accuracy of cheaper wrenches. (Can connect and check one torque wrench against another.)

Also, for non-critical nuts and bolts that I tighten often, after a few times with a torque wrench you develop a feel for the force which is enough. Another thing recommended is to lubricate many types of bolts and nuts before torquing or tightening, often a subject of controversy. There are several factors including environment, materials, application, and type of lubrication. From what I've read, lubrication for most common materials/applications is better than not.

A bit of search give lots of info, for example, this:
www.hextechnology.com

Bolt Lubricant and Torque: A Comprehensive Guide - Hex Technology

Bolt lubricant plays an important role during both the assembly and disassembly of a joint. Learn proper lubrication techniques and how they affect torque
www.hextechnology.com www.hextechnology.com

JKJ
 
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