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Speaking of 555s...

Recently I added an air cylinder to a manual lathe that opens the half nut when threading by moving the proper lever. For those who don't know a manual lathe that can cut threads has a leadscrew that drives the carriage along the ways when a split nut-the half nut-is clamped around the leadscrew. When the carriage has traveled the desired distance the half nut must be disengaged. The faster the carriage is moving the less time you have to disengage the half nut. Failure to disengage the half nut in time typically results in scrap parts or worse. As I have gotten older my reflexes have gotten worse so I can't thread as fast as I use to. So to move the lever I added an air cylinder that is actuated by a solenoid valve that is switched by an inductive proximity switch. It works very well. But there is some drift after the half nut opens. I can set the carriage lock so that it drags some while threading and the lathe will stop repeatably within .004". But the faster the carriage moves the more overtravel I get. Plus I don't like having so much drag on the carriage. So now I want to add another air cylinder that locks the carriage for half a second or so whenever the half nut is opened. A 555 monostable timer seems to me to be the best option. I have some questions though. Because of the way the proximity switch works the trigger pulse to the 555 will longer than the time I want the carriage lock to be actuated. This longer pulse won't be a problem will it? My plan is to use the proximity switch to pull the

555 reset low whenever the switch is off. Then the switch will detect the carriage, the reset will go high and the trigger pulse will happen. Will this work? Do I need to just pulse the reset? I could do this with another 555, or just use a 556 chip. The whole reason for actuating the carriage lock for just a half second or so is that the thread being cut requires several passes and I want the carriage to stop and then be released so I can then wind the carriage back and prepare for the next pass. I don't want to fuss around with pressing reset buttons or anything. The way it is now threading is seamless and reflexive, the lathe is operated just like normal except I don't have to pull up on the lever to disengage the half nut. I want to keep it that way. Thanks, Eric
Reply to
etpm
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Seems to me I remember seeing a datasheet for the 555 that shows a capacitor coupled trigger to the trigger input.

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Figure 6 shows a complete 555 monostable multivibrator circuit with simple edge triggering.

Reply to
default

~Reset goes high, so and trigger is low out goes high, dicharge turns off and the cap starts charging.

when threshold goes high (or reset goes low) the 555 output turns off

if the discharge pin is not connected it will run a single cycle.

can the input connected to reset sink current?

.-------------------------------------------------------------. | This is an ascii schematic, if the diagram appears garbled | | try switching to a fixed-pitch font (courier works well) | | pasting it into notepad works well on ms-windows. | | or in google groups "show original" (in "more options") | `-------------------------------------------------------------'

+12 | . . . .|. . . . . VCC(8) . . . in --+-----------------RES(4) OUT(3)----- out | . 555 . +--[R1]--+---+----TH(6) DIS(7)-- | | . . | +----TR(2) CV(5)-- | . . === . GND(1) . C1 | . . . .|. . . . | | ---+--------------+------ C1 1uF R1 470K

After the signal is removed it'll take about 1 second to re-arm fully, This could be sped up by putting a diode parallel to R1

Another option would be to have a sensor on the slide that detects when the tool is backed out and then releases the carriage brake, or do reverse the lathe to return to the start?

--
  Jasen.
Reply to
Jasen Betts

Thanks for the link. It shows me how to do exactly what I want. Eric

Reply to
etpm

Greetings Jasen, I didn't consider another proximity sensor but your idea would work. Which is kinda dumb because I'm already using one and have several more in a drawer. No matter what the tool gets moved either in or out at the end of the cut. And that motion could be used to switch the solenoid air valve. Since I already have air lines going to the carriage it would be easy enough to add wires. Now I have two options to choose from, though yours seems at first blush to be the simplest. I just need to figure out how to mount the proximity switch and I will need to get one that has NC and NO contacts. I could use a micro switch but I like the proximity switches better for this application because they are non-contact. Thanks, Eric

Reply to
etpm

snipped-for-privacy@whidbey.com prodded the keyboard with:

Why not simply thread away from the chuck with the lathe in reverse. Of course you will have to put the threading tool behind the work. Otherwise it is no different and there will be no risk of running into the chuck.

I thread this way all the time. Fascinating to watch threads appearing at 300 rpm !

--
Best Regards: 
                      Baron.
Reply to
Baron

There are all sorts of reasons not to thread away from the chuck. For eaxmple, if you goof when engaging the half nut you have no chance of disengaging it before the work is ruined. And I thread fast, 600 RPM or more if I can to keep the surface speed up for a good finish on small diameter parts. And right now, with the air cylinder disengaging the half nut it is easy to thread parts fast. I can't believe I never thought of this before. It works so effing good. Eric

Reply to
etpm

Instead of the 555 circuits you may want to check out the Arduino processor boards. They are usually less than $ 5 and they have timers you can set and input pins that only need to go high or low logic. Easy to reprogram for different times and several inputs and outputs. If you only had 2 or 3 different settings you could set up a selector switch for that.

Reply to
Ralph Mowery

I also thank you for the link, I bookmarked it. I have a couple breadboards and bought some 555s a while back to play with but have yet to do anything with them.

--
Shaun. 

"Humans will have advanced a long, long way when religious belief has a cozy little classification  
in the DSM" 
David Melville 

This is not an email and hasn't been checked for viruses by any half-arsed self-promoting software.
Reply to
~misfit~

The 555 is a very handy device. If you look at the internal workings (comparators, flip flop, discharge transistor) and think outside the box, there's a lot of handy-dandy "off-label" uses it can be applied to. I've used it for thermostats, voltage regulation, battery charger, and a fail-safe heater control.

Reply to
default

That's part of the reason I bought some and decided that I'd like to play with them a bit. I just haven't got around to it.

Cheers.

--
Shaun. 

"Humans will have advanced a long, long way when religious belief has a cozy little classification  
in the DSM" 
David Melville 

This is not an email and hasn't been checked for viruses by any half-arsed self-promoting software.
Reply to
~misfit~

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