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Doc Nickel
05-24-2008, 06:41 PM
I have an AC Tech VFD on my Sheldon lathe, and while I love the features (easy reversing, speed control, soft start, etc.) I heavily disliked the membrane switches. They had no "feel" and weren't well placed. (I mounted the VFD box knowing, however, that I'd be adding remote buttons, so that wasn't really a fault of the box.)

I've been doing a great deal of lathework recently, and got tired of poking at the stock controls. I first looked around for "real" machine controls- good industrial buttons that were designed for the job.

However, most of them were $30 to $50 each and went up from there. I didn't necessarily need them to be water or oil proof (no flood coolant, lathe's indoors) and they didn't need to be rated for heavy AC current (5V signal, virtually nil amperage.)

So I ordered a handful of big buttons designed for arcade video game cabinets. :D

They ran me about $2.50 each, have a replaceable microswitch supposedly rated for ten million actuations, and they were available in a variety of colors. I got 'em in last Thursday, and spent Sunday installing them.

The housing is a chunk of 1-3/4" x 4" aluminum box tubing, with endplates milled from a bar of 2x1/4".

http://www.docsmachine.com/machineshop/buttons03.jpg

The front face is angled, and both plates are stepped to lock into the box tubing. Two 3" 10-32 screws go from the front and thread into the back to hold everything together.

http://www.docsmachine.com/machineshop/buttons06.jpg

Then it simply bolts to the side of an aluminum tray that some previous owner had mounted to the top of the headstock cover (partly as a place to set tools and parts, and partly to cover a slot in the lid, that had probably been cut for an overhead style belt drive.)

http://www.docsmachine.com/machineshop/buttons08.jpg

A light signal wire runs down the back and connects to the VFD. It works great, the buttons are easy to stab, have a nice solid "clicky" feel and I don't have to reach as far.

Doc.

SGW
05-24-2008, 07:15 PM
Looks good! Where did you order the buttons from?

Doc Nickel
05-24-2008, 07:59 PM
I picked these up from Quarter Arcade (http://www.quarterarcade.com/Browse.aspx?c=All.Parts.GameControls.Buttons), but Happ Controls (http://www.happcontrols.com/pushbuttons/pushbuttons.htm) has a wider selection. (I went with QA simply because their "checkout" system was considerably easier and faster.)

I got four each red and green, two blacks, and one each white and yellow. Less than $50 including shipping. I may well eventually redo the Logan lathe with a 3ph/VFD as well, as I like the speed control and soft start of the Sheldon. If I do, I'll make another box just like this, and mount it in a similar location (the Logan already has a drum switch mounted in the same relative position.)

Doc.

SGW
05-24-2008, 08:30 PM
Thanks Doc. I may look into that. I've got some wimpy Rat Shack pushbuttons on my VFD remote that work, but they sure don't look the part.

J Tiers
05-24-2008, 10:33 PM
May I suggest a fairly simple modification? A guarded setup to make it easy to push "stop" and harder to push 'go".

The usual way is to put the "go" button inside a ring or guard (or recess it), and leave the "stop" button sticking out.

That way, you can simply slap the buttons in an emergency, and automatically have a nearly 100% chance of stopping the machine.... You don't want to have to make an accurate "push" when there is a problem.........

spkrman15
05-24-2008, 11:15 PM
Doc what a neat idea. I would have never thought of that.

I also took some time to look throught your whiteboard. Had some good laughs

J T. Good suggestion.

Rob :)

Doc Nickel
05-24-2008, 11:26 PM
JT- Thought of that, but it's not necessary. The "stop" signal requires a constant connection through a normally closed switch. If that connection is broken, the motor stops. You can push both buttons simultaneously, while it's running, and it'll still stop.

Also, I'm considering mounting a second "stop" button on the drip tray, down and to the right of the operators' usual position, giving a second option for an E-stop in case, for example, a big wad of swarf gets wrapped up in the chuck and is whipping around.

Doc.

Bruce Griffing
05-24-2008, 11:59 PM
Doc-
Mine is similar, but I also included a reversing switch and a speed pot, in addition to start and stop. I really like being able to adjust the speed while facing. Worth a thought.

J Tiers
05-25-2008, 12:40 AM
JT- Thought of that, but it's not necessary. The "stop" signal requires a constant connection through a normally closed switch. If that connection is broken, the motor stops. You can push both buttons simultaneously, while it's running, and it'll still stop.



Yes, it WILL stop if you press BOTH.

if you MISS the stop, it won't, of course.

And, if you LET GO of the start button LAST (after pushing both), it may re-start. That is the reason it is a standard OSHA requirement, and present on every such setup........... worth thinking about even if you HATE OSHA

Doc Nickel
05-25-2008, 12:59 AM
And, if you LET GO of the start button LAST (after pushing both), it may re-start.

-Yessir. As I said, I'm considering a separate E-stop button mounted away from the spindle.

For that matter, I've also recently considered making a sort of "electric micrometer stop". A switch that mounts to the bedway, and when the carrige hits the switch, the motor stops.

That'd help some on repetitive tasks like boring or long turning jobs- not so I can go do other things (as in leave the lathe) but so I could, for example, deburr the previous parts, or other minor tasks.

That's kind of iffy, in that it can lead to sloppy practice, so I'll need to think on it some.

Bruce- Both reverse and the speed adjustment are used so infrequently that having to reach over to the control box itself isn't a big deal. I'd considered trying to make a full "control panel" but I didn't really have a place to mount something that size.

Doc.

macona
05-25-2008, 06:56 AM
Doc, I did the thing on my lathe that you are thinking of. Works well in test so far. I am using a AC Brushless servo so my performance is going to be different than yours.

I used a microswitch with a couple rare earth magnets glued to the side so it sticks to the ways. My drive is set up to use the drum switch built into the lathe. One common wire and one for fwd and rev. I used the switch N.C. in series with the forward lead so when the carriage hits the switch the spindle shuts down.

I chucked up a piece of 1-1/4" PVC in the lathe and put a fine tip sharpie in one of the toolholders. At about 600 RPM the carriage will stop usually less than .001 of the same spot at max feed. 9 times out of 10 within .0005. This translates to stopping the spindle within +/- 1/16" on the circumference of the PVC pipe. Thats about the backlash of the drive.

At higher speeds it takes longer for the drive to decelerate so it actually pushed the switch down the ways before it came to a stop.

Monarch actually has an option like this called ELSR (Electric Lead Screw Reverse) and there are cams set on a rod to stop the lathe, I think.

Heres a vid I took this week of my lathe drilling. At the end you can see how fast my lathe stops. A VFD wont stop this fast but you can help it by adding brake resistors if your drive supports it.

Evan
05-25-2008, 09:55 AM
OSHA requires the start to be guarded and the stop to lock in the off position so that it must be manually operated to reenable the start function. Same rules here in Canada too.

Although you can do what you like in a home shop I decided to follow the rules when I designed my CNC controller. As you can see the main power is guarded as is the motor power. That also controls spindle power. The E-stop locks in and must be rotated to release it so that the motor power switch can be used again to enable drives. If the E-stop is locked in nothing will run until it is released even if the main power is cycled. If power fails and comes back on it starts up disabled.

http://vts.bc.ca/pics3/switches.jpg

RobbieKnobbie
05-25-2008, 11:11 AM
I got all the components for my mill's control box from automation direct. the buttons, legend plates and pre-drilled box were all pretty cheap-less than ten bucks each. The only expensive part was the speed pot at $35. (but it came with a professional mounting and fit right into the 22mm holes in the box.

http://i286.photobucket.com/albums/ll117/dawnndummy/machine%20stuff/_MG_4584.jpg

It's mounted with a piece of bent up angle iron which also holds my el-cheapo goose neck desk, err, work lamp.

Alistair Hosie
05-25-2008, 01:01 PM
well done DOC a little ingenuity goes along way looking good or should I say to an engineer such as your good self engine youity:DAlistair best regards

Alistair Hosie
05-25-2008, 01:03 PM
Robbie how did you do the printing?Alistair

pcarpenter
05-25-2008, 01:07 PM
Evan-- I think that the same "off until on is pushed again" implemented electronically must also be acceptable. In effect, you have this with most any magenetic motor starter (as soon as either the stop is hit or power goes off, the motor remains off until the start button is pressed again). My guess is that the same thing exists in an RPC.

Still, that having been said, I would sure make a "guard ring" for that start button. Those pinball "flipper button" microswitches I am familiar with have nearly no resistance to their return spring. It wouldn't take more that the brush of a sleeve to inadvertantly start that spindle running. A guard of this sort could be easily fabricated from a piece of thick-walled tubing and some tiny screws to hold it to the faceplate.

paul

Evan
05-25-2008, 02:06 PM
Purely electronic implementations aren't acceptable. There must be a mechanical element that keeps the circuit open. A relay or other magnetic contactor or a mechanical locking switch meet the standard. A triac with a logic input doesn't. Every machine I have ever worked on with Xerox, and that was something like 70 different designs, have a physical disconnect for the main power, usually a relay coupled to a low voltage ac interlock circuit for all panels and doors that can be opened without tools as well as the main power off button. There are also rules about how much coast is allowed if rotating elements are at all accessible.

Doc Nickel
05-25-2008, 05:03 PM
At higher speeds it takes longer for the drive to decelerate so it actually pushed the switch down the ways before it came to a stop.

-I figured there's be a tad of "overrun", I have the decelleration time at... I think a second or a second and a half. Default was three seconds, as I recall. No braking resistor, but this model supports it, I think.

I figured I'd make the switch holder actuated with a rod, and the rod has a step and a spring. The step actuates the microswitch, and gives a bit of "play"- the carriage can move another 1/4" or 1/2", say, before starting to shove the switch mount itself.


The E-stop locks in and must be rotated to release it so that the motor power switch can be used again to enable drives.

-That's the kind of switch I'm looking at for the secondary E-stop I mentioned.


Those pinball "flipper button" microswitches I am familiar with have nearly no resistance to their return spring.

-These aren't quite that soft. They're definitely easier than some heavy industrial controls I've used, but they're "firm" enough that it'll take quite a bit more than just a brushed sleeve to light it off. The button itself moves a full 1/8" before it trips the switch.

The spring is also replaceable- there's a big one in the body of the button, as well as the microswitches' internal return spring. I'd considered dropping a slightly stiffer spring in the "start" button- and may still- but I want to run this combo for a while and see what, if any, changes need to be made.

Doc.

Evan
05-25-2008, 05:14 PM
You need to find some real safety switches Doc. The guarded push button on my control that arms the motors and spindle requires about a five pound press to energize. You really have to mean to turn it on. Your switches look nice but they aren't safe. They would be fine for switching accessories such as a coolant pump or similar.

Doc Nickel
05-25-2008, 05:56 PM
I have another 3-phase machine on the way (that Nichols horizontal mill) and I'm strongly considering upgrading the Logan to a 3Ph/VFD as well. I might, also, go with 3ph motors and less-featured VFDs (basically just to get the soft start) on the two shapers.

So I may well wind up eventually "standardizing" all the controls- size, orientation, position relative to the operator, etc.

But for the moment, this setup gets me up and running with something easier to use than the membrane switches, and only cost $7 including the screws, some junkbin parts, and half a day's labor.

And hey, if I do end up replacing it with a "proper" box and controls, I can always turn it into an Emergency Party Button (http://www.plasma2002.com/epb/). :D

Doc.

RobbieKnobbie
05-25-2008, 10:18 PM
Alistair: I got the legend plates from automation direct (here (http://web2.automationdirect.com/adc/Shopping/Catalog/Pushbuttons_-z-_Switches_-z-_Indicators/22mm_Metal/22mm_Pushbutton_Accessories/Legend_Plates)). They're unbelievably cheap and look a lot better than home made.

I think some of us may be confusing a stop function with an e-stop function. A regular stop button can be wired into a logic control. It can be a plain old button that doesn't require any twist-to-unlock.

An emergency-stop on the other hand has to be hard wired in to a control and must disable all motion. It cannot initiate motion in any way (meaning you can't re-start a motor by pulling out the e-stop.)

J Tiers
05-25-2008, 10:34 PM
I think some of us may be confusing a stop function with an e-stop function. A regular stop button can be wired into a logic control. It can be a plain old button that doesn't require any twist-to-unlock.

An emergency-stop on the other hand has to be hard wired in to a control and must disable all motion. It cannot initiate motion in any way (meaning you can't re-start a motor by pulling out the e-stop.)

yep, that is correct......

ONLY the E-stop needs to be locked. And there are specific rules on e-stop size, shape etc, IIRC, which is why they are all so similar.

But an ordinary stop button only needs to be easily used, while a start button needs to be guarded so you "mean it" if you push it.

However, a stop should stop either if power goes off, OR if pushed, and if power drops and comes back on, the machine must not start.

You can do whatever you like. However some things just make sense.