Attention, Safety Practices, and Loose Nuts

A woodworker describes how a moment's inattention damaged his machine but luckily, not him. The tale sets off a long thread of similar stories (including one fatality) and lessons learned. November 16, 2011

After 30 years of using shapers, for the first time ever I actually forgot to tighten the spindle nut after loading a cutter head. Fortunately I was running the machine in reverse so the nut stayed on, but what did happen surprised me. When I went to remove the cutter it was frozen in place on the spindle. My first thought was that the cutter had galled itself to the spindle. I rented a large gear puller and was very relieved it came off. I discovered that during the time that the cutter was free-wheeling on the shaft it managed to score the shaft very slightly, but enough to inhibit the removing and putting on of cutter heads. I cleaned/deburred the spindle with Scotch-Brite pads and have become wiser in the process. I just wanted to pass along my mistake in hopes it may be of some help. Don't answer that phone... Tighten the nut!

Forum Responses
(Solid Wood Machining Forum)
From contributor M:
Good point! Glad you were able to salvage the head and spindle. Most times the head welds itself to the shaft and one or both need to be replaced.

From contributor D:
I'm wondering about the remark that you had the machine running in reverse, so the nut did not come off. On nearly every wood cutting machine I have worked with, the proper or conventional rotation would tighten a loose nut, not loosen it. If you were running in reverse, the nut would be more likely to come off.

With a shaper, an anti rotation washer is used when the spindle needs to rotate in the direction of the threads to keep the nut from spinning loose. Normal directions - CCW from above - would dictate conventional threads - right hand - and feeding into the rotation from right to left.

Distractions can be problematic. I have always stopped before hitting the on button to consciously remember tightening the nut. The few times I couldn't remember tightening the nut could have been disastrous with the split head, loose knife tooling we used to use everyday.

From contributor R:

You did not run it in reverse or the nut would have spun off.

From contributor I:
I learned my lesson years ago in trade school when a fellow student failed to tighten a spindle nut. The problem in this situation was these were the old style beveled edge cutters, no safety serrations and a brand new set of carbide tipped raised panel cutters. Immediately after startup, the knives began to slip and everyone hit the floor. The instructor managed to crawl up to the machine and shut it down before they let all the way loose. It had machined a perfect circle in the cast iron top where the knives had been below the surface. The machine shop students made a quite nice repair. That incident has stuck in my mind all these years.

I have had a few instances in our shop over the years, both shaper and moulder, and in most cases it has been improper spacers that have been the culprit.

From contributor R:
The point is well made - particularly when working with loose knives. Regarding correcting a galled spindle, only (carefully) work the damaged area with file and/or abrasive. It is tempting to turn on the spindle and take an abrasive to it as one would sand a turning on a lathe. This will take care of the damage, but can result in an undersized spindle.

From contributor J:
Now you know why all airplane pilots are required (by law) to have and use a pre-flight checklist every single time before they fly.

As has already been pointed out, this simple and common slip-up used to "kill Bill" before the advent of safety knives. (Bill really did die in 1978 from a shaper knife to the abdomen.)

A few suggestions...
Paint the spindle nut red to remind yourself of the blood you may spill if you fail to follow proper start-up procedures.
Hang the wrench next to the on/off switch.
Post a permanent sign (or pre-flight checklist) at the machine station.
Be aware that the shaper along with the rip saw are still the most hazardous machines in the shop.

From contributor N:
OSHA cited us years ago for not having a lockout/tagout procedure in place. Now, whenever maintenance (also setup changes) is done, a guard is on the power plug of the machine and it is padlocked. It was originally thought of as a pain, but it really only takes a few seconds to put it on or take it off. You leave to go get that other cutter with the key in your pocket. That way someone else can't inadvertently come along and use it, even if some "do not use" sign gets knocked off by a cleanup person.

From contributor I:
The unfortunate part about our trade school fiasco was there was a standing policy of setting up the heads and an instructor had to check for balance and that the nut was tight before startup. The instructor was right there but he had also failed to follow procedure. Every shaper had its "shield," for lack of a better term - a thick piece of hardwood with a handle you put in front of the cutterhead as you start it up. Like that was going to help! Ah, the good old days.

From contributor D:
I am curious about the unfortunate Bill that was killed by loose shaper tooling. While I have heard "those things will kill you!" plenty of times, this is the first time I have heard a name attached to shaper induced death. Not to be morbid, but do you know the details?

Upon starting a new job years ago, on my second day I directed one of the employees to set up the shaper with any ogee knives in the split head collars and profile the edge of a board. He went white and begged me to do anything - even clean the restroom - instead of running "that shaper - it's gonna kill someone."

I investigated and found that old files had been hand ground into rudimentary (accent on "rude") knives and some knives were made from mismatched and short bevel edge stock. To compensate, the wrench had a nice 4 foot extension pipe for tightening. The previous foreman had bought ends of bar stock at bargain prices, and just tightened the daylights out of the spindle to make them stay in place. Even so, the machine had a reputation, and consequently it was never used.

From contributor J:
Bill and his son had a small custom furniture shop in the same industrial complex as mine. Bill would often walk over an order of wood turning parts from me. He saw me working on my shaper once and then got to bragging about his own skill. Same story - ground-up file shaper knives and such. I had the same kind of drawers from Grandpa all filled with potential lethal projectiles.

Anyway, Bill bragged that he always wore a piece of plywood suspended around his neck "just in case." It didn't help, though, when a knife passed straight through it and him. Afterwards, I dumped the entire contents of several drawers into the dumpster.

I once had a knife fly out and hit the wall. Actually it struck an electrical conduit line, cutting it in two before going through a drywall partition and on into the neighbor's unit. It also sprung the shaper shaft for good. Here's me way back then doing some very stupid stuff.

Click here for higher quality, full size image

From Gary Katz, forum technical advisor:
Great photo!

Every time I visit Jed Dixon he and his guys have a rule with the shaper - every time they tighten the nut, they have to yell "tight" as they're torquing the wrench, before they can turn on the shaper. Now I know why.

From contributor D:
Thanks for the great photo. It could be January of the "Things not to do in a Woodshop" calendar. I'll take the "shaper knife passes through man and kills him" story out of the legend file and give it the credibility it deserves. Regarding the photo, I hope your left hand is blurred from movement and not previous shaper, er, experience.

From contributor E:
This morning some of the old timers over here are cracking up. Your photo has got them all talking about accidents they've seen over the years. All tales we've heard over and over like those a drunken uncle retells every Thanksgiving. It's good to reinforce those memories though - keeps us on our toes. Newer guys always roll their eyes when these old war stories get told, but I know it does them some good too.

From David Rankin, forum technical advisor:
There have been several reports of serious injury and death from cutting tools being thrown from a machine. The cases I am aware of have dealt with shaper collars and square head moulder tools. In the case of the shaper heads, the bolts were either not tensioned correctly or had been over tensioned, resulting in damaged threads. The shaper steel itself must have the same angle as the collar. Some of the cheap shaper steel has angles that differ on the sides. In this case, cheap has nothing to do with price, but with quality.

The old square head moulder tooling also relied on one or two bolts to hold the knife in place. If the head had some distortion or the bolt was not torqued correctly, the knives could be ejected.

It should also be noted that flying wood is as large a concern as the tools. I ran across this specific report:

"FALL RIVER - Machine shop worker Norberto Borges, who decided last weekend he loved the United States so much he wanted to become a citizen, died Monday after a splinter of wood shot off a table saw at Homeland Builders Inc. where he worked and impaled his heart.

Borges, 58, of 33 William St., was walking with another man, when a footlong piece of wood, which measured three-quarters of an inch by an eighth of an inch, broke and shot from the blade, according to pieced together reports."

From contributor K:
25 years ago I worked in a shop where the 2 employees senior to me wore an apron with a square of plywood adorned with a concentric circle target symbol over their groin while operating the shaper - reminds me of the legendary shop rat who poked a hole in his dust mask so he could smoke a cigarette while sanding.

There is still a drywall patch under a breaker box in my present workplace indicating a thrown corrugated knife that cut through a power cable in the wall, narrowly missing an employee. The former owner, who powered up the shaper without torquing the gibs, was subsequently banished to the office.

From contributor T:
While one of my colleagues was operating a shaper, the knife flew out of the tool and hit him in the stomach. He was wearing a leather belt which stopped it and he sustained no injury. Very lucky man.

From what I have read in this thread, the knife should have gone straight through his belt and him. The tool he was using was 125mm diameter and was running at about 3000rpm. I can only presume the knife must have hit him on its large flat surface so as to reduce the chance of penetration.

If this had happened on our new machine which we usually run at 8000rpm, the damage would have been much greater. It's interesting to note that a knife running at 8000rpm has over 7 times more energy than a knife running at 3000rpm even though the speed is only 2.6 times greater.

From contributor L:
After a few years in this business everyone has a story to tell, but we should listen to each one of them. Let me extend my sincere sympathy to the family of Mr. Borges.

We ran loose knives exclusively for 25 years (and still do occasionally) until we started using small corrugated molder heads and insert heads on shapers. We had several wrecks over the years, usually caused by a loose nut on each end of the spindle wrench. Allow me to make the following suggestions.

As already mentioned, kick-backs are probably more likely to get you than thrown knives since they come from any machine in the shop. Concerning shapers: always be sure the spindle nut is not bottomed out on the threads, always have at least as much knife in the collars as out, never take excessive cuts (hog off the waste first), never go into a cold shop in the morning and start up a shaper that's been set up overnight, use good quality steel and never make knives from 2 different bars of steel, power feed when at all possible, and avoid using loose knives anyway if possible. We've had a policy for many years that has been very helpful. When anyone, I mean anyone, sets up a shaper, he asks someone else to check it. You'd be surprised at what you'll see.

One other note; we use insert knives for cope-stick and a few other things. These have 3 knives secured by a gib and a support plate. A man put a gib in upside down a while back and it came out with a fury, tearing up head, knives and all. After that incident we painted the bottom of the gibs red and the topside green. It works.

Be safe.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor M:
While I have heard many more stories about shapers throwing their knives than any other machine, I feel the need to share my story about a potential near miss.

Some time ago I had stopped during the afternoon to change the knives in my DJ-20 jointer. After doing the usual dance with the height gauge and the gib and jack screws, and double and triple checking everything after, I went back to dimensioning a pile of rough stock. I probably ran that jointer for another 45 minutes before going home for the evening, and everything was coming out okay.

When I came back in the next morning I went back to finish dimensioning that pile of wood, but for some reason the jointer was sniping something awful. After determining that the error wasn't in my technique I decided to check the machine. The gib screws for one of the knives had come loose and that knife was nearly out of the cutter head. Realizing how close I came to a potentially dangerous accident was quite terrifying.

After much research, I have decided that I was never changing loose knives on that jointer again and have ordered a new Byrd Shelical cutter head for that machine. I haven't taken the time to make the change yet, but am thinking as soon as I can would be a good time as any for this project, that set of knives is starting to get a bit dull. I hope that I like the Byrd head there as much as I do in the thickness planer.