Safety Aspects of Reversing a Shaper Motor

Modern shapers can be reversed safely, with appropriate precautions. August 3, 2009

Does anyone know how to reverse a single phase motor?

Forum Responses
(Solid Wood Machining Forum)
From contributor R:
Normally it requires re-configuring leads or jumpers inside the junction box on the motor. The diagram for doing this is usually found on the backside of the cover on the box.

From contributor D:
Is this a capacitor start, brushed (old style induction motor with brushes) or split phase (no brushes and no capacitor)?

From the original questioner:
It is a shaper motor on a Weaver shaper. I will look on the motor plate.

From contributor J:
My question is why? Why are you trying to reverse the motor direction on your shaper? What about the spindle nut coming loose? How are you planning to use a shaper that runs backwards? Maybe you need a two-headed shaper with counter rotating spindles? Be careful here - shapers can bite.

From contributor R:
I can't answer your question but I'm really surprised you Weaver does not have a reversing switch. I have three shapers all of different brands and all three have reversing switches.

From contributor M:
We have several shapers with reversing switches (from the factory - Powermatic and Delta/Rockwell). The shaft on all of these has a groove to facilitate a washer (between your cutter head and the securing nut) with a "pin" that rides in the shaft groove. This is what prevents the nut from coming loose.

From contributor J:
My old shaper was a killer with loose knives and all that. The only thing holding the knives from flying out was the spindle nut. If you ever forgot to tighten it or it worked loose, the knives would fly out (through your backbone and the wall). Running it counterclockwise would surely knock the nut loose.

I knew a man who was killed this way (not on my machine). I got rid of the whole thing after that. This was before serrated knives and locking collars. Anyway, why do you run it backwards? Are you climb-cutting or turning the cutter upside down for some reason? Now that I think of it, that would be pretty handy.

From contributor M:
I fail to understand your reluctance to accept that this is a safe practice for reversing switches on shapers. They are quite common, installed by the factory, coming standard on most shapers (Powermatic, Delta/Rockwell, SCMI, Wadkins, SAC, Bridgewood, Grizzly, etc.). As long as you use the provided "pinned" washer, there should be no problem. Many cutters are designed to run either CW or CCW, depending on which work piece surface (top or bottom) you must register the cutter with relative to the shaper deck.

Under what circumstances did this man get killed? Were all parameters properly met in regards to safety on his shaper (properly tightening the nut, size and shape of the cutter, insert size relative to cutter, mechanical or hand feed, depth of cut, feed speed, etc.)? Do you know for a fact that his death was caused "specifically" by the shaft rotation direction loosening the nut? Was he using the proper washers? I for one would be very interested in knowing the facts, considering I routinely (along with my employees) run cutters in both directions depending on the cutter application, and would not wish to incur an accident. I would imagine these manufacturers would be incurring huge insurance payout losses if these reversing switches were unsafe.

From contributor J:
The man who was killed (as I have described) had a long-time custom furniture business and was a customer and neighbor of mine. I occasionally did wood turning for him. He was shaping curved furniture legs when the knife came loose, flew out and struck him through the abdomen.

Old fashion shaper collars use to have simple, slip in knives with nothing holding them in place except for the spindle nut. The nut always tightened against the rotation of the spindle. If you reverse the rotation, the nut could (and would) loosen and spin off. This was actually a fairly common woodworking accident until the advent of safety collars. No, this tragedy was not caused specifically by running the shaper backwards but by those lousy old collars.

They have been illegal now for many years along with that French spindle shaper with the single knife through a slot. Anyway, if you still fail to understand what I am trying to explain, you may (luckily) be too young to remember some of those nasty old machines and practices. Unfortunately, I bet some of them are still around and being used along with the loose knives. Have you ever thrown a big knife from a shaper while standing directly in front of it? I have - wham, bam, roar!

From contributor M:
Okay - I am simply replying directly to the question of "reversing switches". The query posed was not which collars were safe. Though I have never seen firsthand any "flying" knives, I would imagine that it is something that has occurred in some shops. In our shop we have rules and safety standards that are strictly adhered to. Luckily, we have had no incidents with our shapers, either forward or backwards. I've been in this shop for over 38 years.

I'd love to hear from other shops on this subject. If anyone has had an unfortunate incident or know directly of one involving a shaper being used with a factory installed reversing switch, and as a result a knife or cutter has been loosened, I'd like to hear of it. I'm not speaking of any collars or cutter heads that were improperly installed, but rather an incident where a reverse direction was used which caused a knife to come loose.

Based on contributor J's experiences with flying cutters in his shop, I'd prefer now to use as much caution as possible. Contributor J - what caused your knife to be thrown loose while you were directly in front of the shaper? Are you referring to one of these smooth edge cutters? Reverse direction in play?

From contributor O:
I agree that a reversing is an important feature on any modern shaper. We reverse ours all the time, mainly to get extra miles out of rebate inserts or sometimes running panel raisers on top. Iím just a pup with only 35 years in the business. When I started the slip-in and French-head knives were pretty much on the way out. I think the lock edge knives and the locking washers pretty much made double spindle shapers obsolete. Contributor J has a valid point about safety with these but I also think it would be rare to find many in use.

From contributor J:
Yes, the beveled edges of the knives were smooth and simply slipped in and out of the collars. When I first entered the trade, shaping handrail easements and wreathed rail was typically done free-hand directly against the collar. The knives were repeatedly adjusted out until the profile was cut. Guards and hold-down devises were always minimal or not at all.

This was nasty, dangerous work and only the best shaperman in the shop was entrusted with this kind of job. The knives were often large and ground freehand. Grandpa used a scale to weigh them. If they weren't set just right or if they were out of balance for any reason, the shaper would roar and vibrate (and sometimes eject the knives). During this hand-held shaping process kick-backs or break-outs were also common and sometimes injured the worker. I also know two men personally (in other shops) who were severely hurt doing this same kind of work.

Modern (OSHA) shaper practices have largely eliminated these kind of hi-jinks but I think you'd be surprised how many people still get seriously maimed working with shapers.

Running a shaper backwards was a definite no-no in those days because the nut could come loose. Grandpa actually started on belt-driven machines that only required a twist in the belt to reverse the rotation of any machine in the shop so bad stuff happened.

From contributor N:
I'm only a whippersnapper of 30 years in the shop. I have been blessed though with the training of many experienced old timers. Some folks see the old days as a scary thing, and some of it was. It's easy to remember the legendary tragic accidents and forget the millions of board feet of wood safely run. The old guys were just like us, they didn't want to get hurt either, and the smart ones rarely did.

Artful use of the shaper is to me the defining difference between a cabinet shop, and a custom woodwork shop. It is true, most shops these days have little or no training in this distinct craft, and as such should stick to standard rotation, stock cutters, and no climb cutting. If one wishes to take on the greater challenges, he should know he is assuming greater risk, and can reap greater rewards.

Old two spindle shapers with both rotations were used for high production with matched cutters that allowed parts to be run with a stop cut each way on the part. Something few of us need anymore. The pinned washer contributor M explained eliminates worry about loosening the nut regardless of rotation direction. New things are good.

Smooth bevel edge steel is perfectly safe to use if you just observe the same degree of attention to standard practice and routine one gives to any tooling change. This tooling, a decent grinder, and a trained eye can reproduce any profile required in solid wood without having to stick to a tooling catalogue, or wait and pay for custom tooling to be made.

I find the term "safety steel" funny. It is anything but. First, I have seen thousands of smooth steel cutters do their job with no worse than a broken tip or snapped panel raiser (overloaded, you can break anything if you try hard enough). The only cutters that have ever taken flight clear of the head were simply not tightened due to inattention. I have witnessed however the sudden snap-off of serrated "safety steel" in mid run several times.

The break occurred each time at one of the "safety" notches right at the point of greatest stress load, the collar edge. These ground notches are to me just like chipping the edge of a pane of glass, and with some pressure added, the crack runs across the width of the cutter. It is like intentional weakening of the steel. Possibly worse than this steel is the collar used with it. Using smooth steel and collars, adjustment of cutter extension from the collar is stepless and smooth. The "safety collar" requires one to crank a worm screw that engages the serrated steel edge like a rack. This pressure is only applied to the one edge, and I have seen this cock a tall cutter slightly, but enough to hold the collars slightly open leaving the balance cutter loose after tightening the nut.

Clamping chunks of steel between two disks and spinning it fast is counter intuitive and thus frightening to us. Training and experience brings us the confidence we must have to extract all of the potential this amazing machine can present.

My safety protocol is simple.

1. Set it up.
2. Stand back and look at it, picture the motion of the stock, even dry run it with the cutters rotated out of the way.
3. Is there anything at all that makes me uncomfortable or nervous? Go the next step, and assure that risk is eliminated.
4. Hit the switch and work confidently.

All the injuries I have seen and incurred were the result of two factors, being cocky, and/or in a hurry.

From contributor M:
You show experience and great wisdom. I couldn't have said it better. I would like to add one thing - when setting up the smooth bevel edge knives in a cutter head, it should be imperative that both knives are placed exactly the same distance out from the cutterhead, and both knives should be long enough to have at least 2/3 of the knife retained in the cutterhead (or at least back past the shaft). Either one of these parameters can cause an out of balance situation that would result in vibration. This vibration may very well cause the retaining nut to loosen, and then, as contributor J stated - wham, bam, roar! Not a desirable scenario!

I know at least one shop in my area that routinely uses just one knife, and secures a different shape knife or steel opposing the cutter just to hold the heads parallel. I consider this a very dangerous situation, as different knives would be an "unbalanced" setup, again - resulting in excess vibration. Not recommended! We use a mechanism that entails a 1-1/4" shaft about 6" high, secured to a cast iron base plate that is grooved to hold a sliding, vertical "knife edge" brass locating bar. You place your cutterheads on the shaft, and then slide the vertical brass knife up close to the ends of the cutter knives, and then secure both knives when the each just "touch" the edge of the brass knife edge. This jig ensures the knives are registered both equally within 1/1000ths of an inch. These jigs can still be found, I've seen them on eBay and such. Invaluable from both a safety standpoint as well as maximizing the probability of both knives cutting, rather than just one. This is just one, very important precaution in my book.