# AC gear motor reversing cycle with trip switches

#### JeffN

Joined Dec 14, 2021
14
I'm building a small panel saw set up using a ball screw powered by an AC 120 volt reversible gear motor. I'd like to run a circuit that has the following.

1. a start button that powers the motor to travel about 32"
2. then tripping a (micro?) switch that stops the travel,
3. and then reverses the motor to return to its starting point and stopping.
4. in a ready state to begin again upon pushing the start button.

I have a basic working knowledge of AC circuits with simple switches. I have no idea what type of switches and or controls, or how to wire the circuit to accomplish what I need.

Any help, suggestions, or redirection would be greater appreciated. If possible a simple drawing of the needed circuit would be extremely helpful.

Thank you,
Jeff

#### LowQCab

Joined Nov 6, 2012
2,615
This is a very simple Project .... but .......
The Mechanical bits are very important to get right,
that is, the type of Limit-Switches, their Mounting and Protection, and Protection of the Wiring.

If You can provide a drawing of Your Jig,
I'll come up with a reliable Limit-Switch arrangement.

You also need to supply any and all info on exactly how your Motor Reverses Direction.
Preferably with Pictures to go along with it.

Keep in mind that what You want to do may be EXTREMELY DANGEROUS,
and create projectiles flying across the room at ~200 MPH.
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#### LowQCab

Joined Nov 6, 2012
2,615
What is the size and thickness of the Panels You are cutting ?
This is starting to sound like a bad idea.
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#### BobTPH

Joined Jun 5, 2013
6,035
You may regret this when your hand gets stuck in the way the saw.

Bob

#### JeffN

Joined Dec 14, 2021
14
This is a very simple Project .... but .......
The Mechanical bits are very important to get right,
that is, the type of Limit-Switches, their Mounting and Protection, and Protection of the Wiring.

If You can provide a drawing of Your Jig,
I'll come up with a reliable Limit-Switch arrangement.

You also need to supply any and all info on exactly how your Motor Reverses Direction.
Preferably with Pictures to go along with it.

Keep in mind that what You want to do may be EXTREMELY DANGEROUS,
and create projectiles flying across the room at ~200 MPH.
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First of all I appreciate your concern for safety, I have the same concerns and I want to be aware of all the implications and necessary protections. Let me give you a bit of context.

I have a panel production shop and one of the products requires the production of 3/8" thick plywood panels cut to various sizes and quantities. The sizes range from 16" x 16" to 24" x 24". The material is first cut to 16" x 96" runs, or 24" x 96" runs. Sometimes 50 pcs. or 100's. Prior to my new project I have been cutting them on a very large sliding table saw. This works, but is quite labor intensive. The new saw would be used for cross cut only.

The project I'm building is comprised of a circular saw mounted and captured on sliding rails and ball bearings. The saw cannot just fly off the rails there are heavy stops at either end of the 32" travel that would prevent this. Also the blade is located in such a way that keeps it away from the operator. It's not fully completed yet, but I'm going to run some tests without it being automated and see what tweaks and adjustments need to be made before adding any automation.

Other than a person purposely trying to put their hand in the way of the blade, which is easier to do on the table saw, what concerns do you have? What "things can fly across the room at 200 mph?" Why is this a "bad idea?" Appropriate guards will be added to insure safety.

I'll try to send some pictures of the set up so far, but again, it's not complete yet. I think this might help address the safety concerns.

With the correct set up, this would keep the operator further away from any danger by not needing to touch the saw motor or components. But again, any cautions etc. are welcome. I'd just like to understand what they are, and address them.

Thank you for your time and consideration.
Jeff

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Joined Jul 18, 2013
26,229
You most likely should not reverse immediately in this set up, so you will need some kind of delay before reverse takes place.
I assume this is a AC motor (Induction)?
A simple controller such as a smart relay could be employed ?
Also don't forget the big RED button, the hardest one to find in an emergency!

#### LowQCab

Joined Nov 6, 2012
2,615
Waiting on some pictures or accurate-drawings .
It would probably be best to have the start of Travel,
both forward and reverse,
be manually initiated with 2 separate Push-Buttons.

It sounds like You are describing a "Hand-Held" Circular-Saw that runs on solidly mounted Rails.
If this is the case, it sounds like you're going in the right direction.
I would use a continuous Steel-Cable, with a Pulley on the far-end,
and a V-Belt-Pulley mounted to the Shaft of a Gear-Motor,
with the Cable wrapped 1.5 turns around the Pulley,
this will facilitate adjusting Travel-Speed by changing Pulley sizes.

Have You selected a Gear-Motor yet ?
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#### GetDeviceInfo

Joined Jun 7, 2009
2,122
With the correct set up, this would keep the operator further away from any danger by not needing to touch the saw motor or components. But again, any cautions etc. are welcome. I'd just like to understand what they are, and address them.
When you feed a part through fixed point tooling, the guarding is typically compact around the tooling. With traverse tooling, the guarding ‘envelope’ expands along with it. That guarding should prevent intrusion, while retaining expulsion. As an employer, you want to ensure not only the safety of the worker, but your exposure to claim. I trust you are aware, and I say this only because I’ve seen the chit that can go down. With that being said;
Many saws I’ve worked with retract the blade for the return stroke. This allows rapid return, and maintains cut quality.
I have often added an ‘arbor running’ interlock to the feed drive. Arbor run contactor engagement is often not enough, with a current ‘window’ covering most conditions.
With an auto cycle circuit, one must be able to ‘home’ the carriage.
The ‘big red button’ should extend the perimeter of the safety envelope. A
Variable speed feeds allow a range of blades and materials.
A lockout procedure needs to be implemented.

An auto cycle circuit is relatively simple, if all goes well. It’s when things don’t go well is when the aforementioned chit happens.
Do you have feed motor/ drive selected, and what is it’s description, and what is your electrical source

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#### JeffN

Joined Dec 14, 2021
14
Here are some pictures of what I'm working on. I can work out the details of guards, movement of the material, etc. The circuit and trip switches, etc. is over my head. I'm going to work with a ball screw that is not hooked up yet, but you can see the chrome shaft to the left of the saw. Once I add the stops and guides for the material the operator will not need to touch the saw or the material. The material will be held in place. The big read "STOP" button sounds like a very good idea.

I have not yet selected the gear motor. I want to run some test cuts and get a sense for the rate of feed. This does not have to be lightening fast, that is not my goal.

My goals are 1. Safety 2. Accuracy, and 3. Efficiency

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Joined Jul 18, 2013
26,229
I would say you are going to need some kind of protective cover over that ball-screw!
Particularly if it is the precision type.
In fact, most of the detection devices etc may need it also, may be better to go proximity sensors?

#### JeffN

Joined Dec 14, 2021
14
I would say you are going to need some kind of protective cover over that ball-screw!
Particularly if it is the precision type.
Yes that's correct, planning on that. It's not even mounted yet.

Joined Jul 18, 2013
26,229
I have a basic working knowledge of AC circuits with simple switches. I have no idea what type of switches and or controls, or how to wire the circuit to accomplish what I need.

Any help, suggestions, or redirection would be greater appreciated. If possible a simple drawing of the needed circuit would be extremely helpful.
It should really conform to NFPA79, (code), there is a copy of the older edition out there in PDF if you want to look it over.
How did you intend wiring it? flexible/cabling type etc?

#### JeffN

Joined Dec 14, 2021
14
Waiting on some pictures or accurate-drawings .
It would probably be best to have the start of Travel,
both forward and reverse,
be manually initiated with 2 separate Push-Buttons.

It sounds like You are describing a "Hand-Held" Circular-Saw that runs on solidly mounted Rails.
If this is the case, it sounds like you're going in the right direction.
I would use a continuous Steel-Cable, with a Pulley on the far-end,
and a V-Belt-Pulley mounted to the Shaft of a Gear-Motor,
with the Cable wrapped 1.5 turns around the Pulley,
this will facilitate adjusting Travel-Speed by changing Pulley sizes.

Have You selected a Gear-Motor yet ?
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I'm pondering your cable idea vs. my use of the ball screw. I agree that adjusting the speed will be much easier. Since this is not a CNC set up, the exact position of the saw is not required. I also like the idea of a v-belt pulley to the motor, will allow for initially a loose adjustment at the belt to allow for slippage in initial testing just to insure things are working correctly on the first runs.

#### LowQCab

Joined Nov 6, 2012
2,615
You don't want any "slippage" of the Cable, it needs to be spring-tensioned, and very-tight,
probably around ~50-lbs of Spring-tension.

Speed of the Cut needs to be adjustable,
but adjusting the Speed of the Motor adds a lot of expense to the project,
and Pulley selection for speed adjustment may get You close enough.

The Saw should be mounted to the Sled by the front-edge of the Shoe, with a strong/wide hinge.

The rear of the Shoe should have a mechanical latch mechanism that
holds the rear of the Saw down against spring pressure.
This Latch should be easy to release by hand.
This Latch should also have a release mechanism that can be set up to release the Latch
when any part of the Saw or Sled bumps into an object.

The Spring must be strong enough to be capable of lifting the Blade clear of the Work reliably,
but be soft enough to allow compression by hand,
and also soft enough to not cause any binding in the Latch/Release mechanism.

The Latch will be mechanically released,
via a metal-rod, or similar,
shortly before the end of the Rail travel.
This will cause the Saw-Motor to stop by opening a Switch mounted to the Shoe of the Saw.
This Switch will be spliced into the Power-Cord of the Saw.
This Switch will prevent the Saw from running unless
the rear of the Saw-Shoe is mechanically latched-down securely.

When the Power is stopped to the Saw-Motor, ( by any means ),
a Current-Sensor monitoring the power going to the Saw-Motor
will electrically switch the Gear-Motor direction,
this will bring the "not running" Saw back to the start-position.
The Saw can not "return-Home" with the Motor running, and,
the Saw can not move "Forward" if the Saw-Motor is NOT running.

When the Saw-Motor is running, the Gear-Motor can only run in the "forward" direction,
when the Saw-Motor stops, the Gear-Motor will only run in the "reverse", or "return" direction.

The Gear-Motor runs at all times after the "Start-Button(s)" are pressed,
until it returns to the "Home" or "Park" position,
where it is turned-OFF by a a Mechanical-Limit-Switch, or an Optical-Limit-Switch.
An Optical-Switch is preferred.

The Saw must be manually latched-down into cutting position,
and the "Twin-Start-Buttons" pushed,
before the Saw-Motor and the Gear-Motor will run, and begin a new "Cutting-Sequence".

The "Twin-Start-Buttons" must be mounted far enough apart to insure that
2-Hands are required to start the "Cutting-Sequence",
and both of the Buttons must be a safe distance from the Saw.

A schematic is not realistic until the type of Gear-Motor, and its Wiring requirements, are known.

Do You need help with selecting a Gear-Motor ?, or do You already have one in mind ?
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#### JeffN

Joined Dec 14, 2021
14
You don't want any "slippage" of the Cable, it needs to be spring-tensioned, and very-tight,
probably around ~50-lbs of Spring-tension.

Speed of the Cut needs to be adjustable,
but adjusting the Speed of the Motor adds a lot of expense to the project,
and Pulley selection for speed adjustment may get You close enough.

The Saw should be mounted to the Sled by the front-edge of the Shoe, with a strong/wide hinge.

The rear of the Shoe should have a mechanical latch mechanism that
holds the rear of the Saw down against spring pressure.
This Latch should be easy to release by hand.
This Latch should also have a release mechanism that can be set up to release the Latch
when any part of the Saw or Sled bumps into an object.

The Spring must be strong enough to be capable of lifting the Blade clear of the Work reliably,
but be soft enough to allow compression by hand,
and also soft enough to not cause any binding in the Latch/Release mechanism.

The Latch will be mechanically released,
via a metal-rod, or similar,
shortly before the end of the Rail travel.
This will cause the Saw-Motor to stop by opening a Switch mounted to the Shoe of the Saw.
This Switch will be spliced into the Power-Cord of the Saw.
This Switch will prevent the Saw from running unless
the rear of the Saw-Shoe is mechanically latched-down securely.

When the Power is stopped to the Saw-Motor, ( by any means ),
a Current-Sensor monitoring the power going to the Saw-Motor
will electrically switch the Gear-Motor direction,
this will bring the "not running" Saw back to the start-position.
The Saw can not "return-Home" with the Motor running, and,
the Saw can not move "Forward" if the Saw-Motor is NOT running.

When the Saw-Motor is running, the Gear-Motor can only run in the "forward" direction,
when the Saw-Motor stops, the Gear-Motor will only run in the "reverse", or "return" direction.

The Gear-Motor runs at all times after the "Start-Button(s)" are pressed,
until it returns to the "Home" or "Park" position,
where it is turned-OFF by a a Mechanical-Limit-Switch, or an Optical-Limit-Switch.
An Optical-Switch is preferred.

The Saw must be manually latched-down into cutting position,
and the "Twin-Start-Buttons" pushed,
before the Saw-Motor and the Gear-Motor will run, and begin a new "Cutting-Sequence".

The "Twin-Start-Buttons" must be mounted far enough apart to insure that
2-Hands are required to start the "Cutting-Sequence",
and both of the Buttons must be a safe distance from the Saw.

A schematic is not realistic until the type of Gear-Motor, and its Wiring requirements, are known.

Do You need help with selecting a Gear-Motor ?, or do You already have one in mind ?
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Though I understand your suggestion of lifting the saw up from the cut material, I don't want to add that to the mix. Here's why.

1. The purpose of this cross cut saw is to facilitate the cutting of same size panels usually 16" x 16" or less from pre-cut runs of the appropriate width stock. For example if I'm making 16 x 16 inch panels, I'm feed 16" wide runs of 96" material into the saw. These runs are stacked, 3-4 sheets high. Keep in mind the sheets are 3/8" thick.

2. Having the saw hinge up from the stock would require it to lift much too high, and expose the blade to the operator, I don't want to do that.

3. Additionally, the saw motor does not have a brake it will continue to spin to a stop once the power is cut off anyway.

4. Because the cycle of repeated passes will be relatively "quick" I don't want to turn off the saw motor upon each pass. The action will mimic a radial arm saw, or a chop saw that is being used repetitively. We mill literally 100's of these size wood tiles therefore both safety and being efficient is needed. Both the saw and the wood material will be captured preventing any possible kick back.

5. The way I'm building the set up, the spinning blade will be encapsulated keeping the operator safe and away from the blade. I also think the constant on and off of the saw motor will limit the duty cycle of the motor. Having said all of that. A safety cutoff switch that de energizes everything in case of something going wrong is a requirement.

I have a gear motor on hand with a speed control I think it will work quite well. Attached are some pictures. If you can help with the circuit that would be greatly appreciated.

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Joined Jul 18, 2013
26,229
That appears to be a small AC induction motor with TRIAC control worm & pinion GB, not the best set up, but for your use, it may be worth a try, as you already have it.
The wiring appears in need of a little clean up, however!

#### LowQCab

Joined Nov 6, 2012
2,615
1)
You need a ~14"-Blade and a 5-Horsepower-Motor.

2)
The idea is that the Blade-Guard will cover the Blade when the Saw lifts at the end of a run.

3)
The proposed "Kill-Switch" is a common Single-Pole-Double-Throw configuration.
When it changes position, the power is cut, and the Motor is Shorted-Out,
causing it to come to a complete stop within roughly 1-Second.

4)
Cycles won't be very quick using a "Screw-Drive", unless it can withstand full Motor-RPM.
"Quick" through 1.5" of material is a recipe for burning-up a Motor.

5)
Starting and Stopping the Motor is nothing compared to pushing it hard through 1.5" of material.

Your Motor may well work, but will be very slow-moving with a "Screw-Drive" arrangement.
For faster Feed-Rates, ( maybe ~4" per second ), You will need at least a 1/2-Horsepower Gear-Motor,
( and a more powerful Saw ).

What You want normally starts out at around ~$20,000.oo, for a reason. Multiple Emergency-Stop-Buttons are routine work for any decent Industrial/Commercial-Electrical Company. Personally, I would prefer a single "Dead-Man" Push-Button, which must be held down for the Saw to run. Cheaper, Safer, and quicker responding, than standard Emergency-Stop-Buttons. . . . #### MaxHeadRoom Joined Jul 18, 2013 26,229 Your set up should stop pretty quickly with that gear box, being a worm & pinion version, they cannot be back-fed, so virtually no over-run. Thread Starter #### JeffN Joined Dec 14, 2021 14 1) You need a ~14"-Blade and a 5-Horsepower-Motor. 2) The idea is that the Blade-Guard will cover the Blade when the Saw lifts at the end of a run. 3) The proposed "Kill-Switch" is a common Single-Pole-Double-Throw configuration. When it changes position, the power is cut, and the Motor is Shorted-Out, causing it to come to a complete stop within roughly 1-Second. 4) Cycles won't be very quick using a "Screw-Drive", unless it can withstand full Motor-RPM. "Quick" through 1.5" of material is a recipe for burning-up a Motor. 5) Starting and Stopping the Motor is nothing compared to pushing it hard through 1.5" of material. Your Motor may well work, but will be very slow-moving with a "Screw-Drive" arrangement. For faster Feed-Rates, ( maybe ~4" per second ), You will need at least a 1/2-Horsepower Gear-Motor, ( and a more powerful Saw ). What You want normally starts out at around ~$20,000.oo, for a reason.

Multiple Emergency-Stop-Buttons are routine work for any
decent Industrial/Commercial-Electrical Company.

Personally, I would prefer a single "Dead-Man" Push-Button,
which must be held down for the Saw to run.
Cheaper, Safer, and quicker responding, than standard Emergency-Stop-Buttons.
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Can you work out a schematic for the set up without lifting the saw? I've run some tests and will run more, but the current saw seems to work fine. I've run a production shop for 30 years, I don't overkill my motors and though this is a prototype, and I will learn even if the idea ends up not working, I want to give it a try.

Perhaps my use of "quick" implied faster than the saw can handle, I'm not going to do that.

#### GetDeviceInfo

Joined Jun 7, 2009
2,122
Have you performed a time study on the activities? Working on similar, but larger scale work centers, I had found that efficiencies aren't gained on the saw cut, because it is what it is due to blade and feed rates. The largest gains come from handling the product into and out of the the saw cut. One place I worked cut 'books' of OSB as web for I joists. Pallets of OSB were raised on a hoist, and a stack of 10 were pushed off by a carriage, squared, then advanced through the saw. Fully programmable to account for a variety of joist widths and maximize yield. Fine tuning and some modifications to the hoist/carriage made substantial gains, while the saw cycle itself was allowed to slow somewhat to extend the life of the 32" blades, which would drift as they dulled.
I would seriously be looking at auto feeding the stock, manually stroke the saw, then auto cycling the feed. Once that was perfected, I'd auto cycle the saw stroke. That approach would then deploy a PLC , micro, or computer for a range of products. Add a printer for part ID and your on the heels of mass producers.
Im meeting with a fellow next week who is setting up his cabinet shop. Should be interesting to see what he has and where he wants to go with it,

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