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12-21-2005, 06:18 PM #1
I have been doing alot of surface grinding with a manual abrasive 1 1/2 that uses a rack and pinnon method of sliding the table back and forth. This wasn't no big deal until I stand there for 3 hours at a time going back and fourth, my arm feels like its going to fall off. I know what everyone is going to say, go buy a hydraulic machine, well that what I want but right now this one is going to have to work. Has anyone ever rigged up a way to "automate" a manual machine. I have thought about a cheap steeper motor retrofit on the x and y axis. I could do it for 600 or less if I could use small steppers like 250 oz motors but I not for sure if it would be fast enough. I have seen where the rack and pinnon was disabled and the table was left free to slide back and fourth. Two single stage air cyclinders were used to shoot the table back and fourth. A cable was attatched to each one and when it got it the end of travel the cable would operate a valve that would close one cyclinder and open another. So the machine shot back and fourth, the speed was controlled by how much air was applied. Worked really nice, it was built by a retired machinist. I just cant figure how he made it index over each pass, any ideas? I really like the air idea the best.
12-21-2005, 06:31 PM #2
I've got one I thought about rigging up with a DC motor to move the table. It originally HAD a motor, and cout be run by hand, but now it's just hand. I don't even know the brand of this grinder. I got it in a trade, and had to even fit up the spindle motor that's on it now. The guy I got it from was one of those nuts that takes something apart, gets bored, and never finishes it.
12-21-2005, 07:32 PM #3
you can do this with a double acting air cylinder ideally a cable or rodless style, simple air limit switches and a 4 way valve and a flow valve on each port will work pretty good, if you need fine speed control you can add a hyd check cylinder. A rodless cylinder might be 250 bucks or so new, the valves etc should be cheap surplus.
12-21-2005, 07:57 PM #4
Instead of a stepper to move the Y axis, you might be able to set up a dc motor going extremely slowly. You'd end up with a slight V pattern, but that might or might not matter.
12-21-2005, 08:17 PM #5
When I said DC motor, I should clarify I meant one with a gearbox or "gearmotor" as they're often called. That would be slow, and have torque enough to do the job.
If anyone has such an animal, with a planetary-type gearbox, I'd like to hear about it.
12-21-2005, 08:45 PM #6
The air-stroke is a good idea, except that it will eat you in compressed air costs.
I'd say the simplest control system I can think of is a small 3phase AC motor, geared way down, possibly with a VFD, and controlled with a reversing motor starter and 2 limit switches.
Save your air cylinder and solenoid for a cross-feed ratchet mechanism (can be as simple as a real hand-ratchet adapted to the cross-feed ).
One final limit to inhibit any further movement when the cross-feed is "maxed out" so you don't crash.
If you have more interest in this idea, I'll attempt to cook up a ladder logic diagram.
12-21-2005, 09:03 PM #7
Thanks for the brain storming fellas. Got a few questions. What is a rodless air cyclinder? All the one's I saw looked like hydraulic cylinders. I wonder how big of a cyclinder it would take for it, I think the one I seen was 3/8" rod. They seemed pretty small to me :rolleyes: I only index about 1/8" at the most taking .006 at a time so its not being put under any real stress, I don't use any coolant so can't take much of a bite. Like I said in another post this is purly for a cosmetic finish and nothing else.
Matt, can you elaborate on the hand ratchet method you are speaking of? Whats going to move the ratchet to move the crossfeed?
12-21-2005, 09:08 PM #8
Sorry Mule, just use say a 3/8" square drive hand-ratchet. Attach the square drive with an adapter to the cross-feed screw. Adapt a standard air cylinder to the end of the handle thru some kind of a yoked linkage.
The amount of stroke you allow the cylinder to have determines "how many clicks" you will gain with each cycle of the air cylinder...have to play around to see what you really need.
Also, the easiest way to mechanically change the stroke of a fixed-stroke air cylinder is to make a long bushing (drilled rod) that fits over the cylinder rod, and limits reverse travel. Weld or cut the long bushing to dial in the stroke, the original air cylinder is undamaged.
Also use flow controls so the air cylinder doesn't hammer back and forth.
Assuming with an air cylinder hooked to the business end of the ratchet, you have enough leveage to tear something up. An electrical limit switch must stop all automated feeding and stroking processes when the max cross-travel has been reached.
12-21-2005, 09:53 PM #9
So...here's my idea for the system.
The logic looks intimidating if you're new to this but it's fairly simple stuff, just wire 1 line at a time.
I'm interested on any critique on the logic...it works just great in my mind However we don't want to send a man to tear his hair out with a schematic that doesn't work!!!
12-21-2005, 10:55 PM #10
You might consider incorporting a "C" band satelite dish actuator in the system. There should be plenty of them around since direct TV has virtualy replaced the big dish. You could use the original electronics with programable position capability.
12-22-2005, 12:35 AM #11
Eee, program stopped running in my mind and wouldn't restart [img]redface.gif[/img] Small problem in the logic...if the table were to stop in the middle, there's nothing to "kick" it off dead center so to speak other than manually tweaking one of the limits which is undesirable.
So, I added an additional contact to the start pushbutton in the 2nd line which should resolve that.
12-22-2005, 12:41 AM #12
PLCs rock! I like Direct 05, 06, and 205, 305 from automationdirect.com. Get some steppers or servos and the amps and go. I want to do this for my BoyarShultz 612. --Doozer
12-22-2005, 02:11 PM #13
What was you looking at to time the crossfeed with the x feed? Maybe a trip lever on the return stroke to activate the air cyclinder.
12-22-2005, 07:05 PM #14
I think what you are asking is how is the cross-feed ratchet timed.
The surface grinder will "wait" at LS2 after completing a FWD & REV cycle until the ratchet feed is completed (LS3 changes states) before the next cycle begins (in line 2, LS3 is what starts the next FWD table cycle).
LS = limit switch if I am speaking in too much code.
12-23-2005, 11:38 AM #15
A little playing with my new/old 6x12 KO Lee has me thinking about grinder automation too. I was thinking steppers, drivers, and some custom PC software, but haden't considered PLCs since I've never used one. But cheap PLCs would move this project a lot higher on my priority list.
12-23-2005, 12:17 PM #16
What I've proposed here doesn't require a PLC. Just 2 relays which could be $10 ice-cube relays. BTW: The $99 brick PLC is that, but you have to buy the software and cables to interface with it.
PLC or cheapo relays, you'd still have to get pushbuttons, limits, motor starters, air cylinder and a solenoid valve, but those parts would be required no matter if you choose PLC or not. It would take a little scrounging for the rest of the shopping list but I think one should be able to round most of the stuff up on ebay or other.
12-23-2005, 03:57 PM #17
how is the 3 phase gear motor going to react to being constantly reversed and forwarded? Would you do this through the vfd or a device similar to the rotary drum switch like on an old lathe or mill. Sorry for all the questions but electronics is not my strong side, It stretched my abilities to build a push button start 10 hp rotary phase converter
12-23-2005, 09:36 PM #18
if you could figure out a way to get "air over oil" such as a hydro check type device like i use on my centerless grinders for in feed,i think you would have a much better feed system.
problem with air is the compresability
to get a good constant feed out of air would be tough.
i guess you could jack the pressure way up and then throttle the exhaust side of the cylinder, but even that can be somewhat unpredictable in an inconsistant load situation.
if you ran you air cylinder on one side of the table and then had a closed loop oil circuit on the back for feed control might work
12-24-2005, 10:51 AM #19
Richard. I semi automated my B&S Micromaster with a 1hp Pacific Scientific permanent mag dc motor. No reduction gearbox. The armature voltage is 90 volts but I only need 0-24 volts for it to work for my machine.
Even at 12v input you can't hold on the shaft when on the bench. The power supply has to be beefy, 8 amps or better for it to perform well. I Ebayed a 0-24v 25a one for 60 bucks.
I was able to modify my crank handle shaft that runs the table and get the motor hooked up to it via a timing belt. Forward and reversal is done manually with a drum switch hence semi auto. But it sure beats hand cranking.
I have pictures of my installation and if I ever take the time to learn to post I'll get them up.
12-24-2005, 02:02 PM #20
I think "plug reversing" a small AC motor would be OK, it might get a little warmer than normal, but a 3 phase industrial motor is a pretty tough cookie, and the load it is pulling is not severe. If you are worried, add overload heaters and they will tell you when it's had too much.
This is where a PLC would come in handy...one could add short timers to allow the motor to coast before reversing direction.
A VFD should do the same thing, instead of sending signals to the motor starter, one could simply send the fwd and rev signals to the VFD's input terminals....some don't have their own internal power supply and possibly might require 24vdc instead of 110vac.