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Author Topic: Mach 3 toolchange for dummies???  (Read 60511 times)

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Re: Mach 3 toolchange for dummies???
« Reply #50 on: March 10, 2011, 05:31:46 PM »
Also, this is from the first post:
Quote
I have removed the original toolchange internals and now have an 8 position turret that raises and lowers with a 4way solenoid. I have just finished making an 8" .375 pitch timing pulley that fits around the base of the original rotating turret (for stepper motor indexing of the turret)
Seems there must be some reduction going on here ?
Not clear how it is actually set up. (or I overlooked it)
Even if the latch timing is OK, there is still a pretty chunky mass there to start and stop !

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Re: Mach 3 toolchange for dummies???
« Reply #51 on: March 10, 2011, 05:38:32 PM »
Cant be much of a reduction I wouldnt have thought or the rotation would be a mile out, but if there is then yes steps per degree will need re-worked.
Will just have to wait for Nate to clue us up on things :)

Hood
Re: Mach 3 toolchange for dummies???
« Reply #52 on: March 10, 2011, 06:11:31 PM »
I agree. It's either two 8" pulleys, not likely, or that big chunk is coupled directly to the motor shaft.
Inertia out the ying yang !
Russ
Re: Mach 3 toolchange for dummies???
« Reply #53 on: March 10, 2011, 09:07:15 PM »
I am working on uploading two parts of a 2 minute video that will explain better.

The first design was the big ring design with the 70tooth pulley and a 10 tooth pulley driving it.

the design now has 2, 10 tooth pulleys driving the original internal gear train (three gears). this will nessicitate a detent arm to positively locate each position before locking down of the turret.
Re: Mach 3 toolchange for dummies???
« Reply #55 on: March 10, 2011, 10:47:09 PM »
Nicely narrated video.
With the micro stepping and the evident reduction through the original gear train, I would think that the arm you speak of would not be necessary.
That is if you are sure there is no loss of steps with the motor.
It should be dead nuts for each index.
I would count the teeth in the gear train and determine the exact ratios and set the steps per accordingly.
There is probably enough backlash through the gears (you can also create a little with the belt not super taught).
Can you access the gears to count the teeth easily ?

Re: Mach 3 toolchange for dummies???
« Reply #56 on: March 10, 2011, 11:44:57 PM »
The internal gear train (3 gears) has all of the three gears with the same number of teeth.

I have locked the last gear in place for testing and have found that I have about 3 degrees of slop at the turret. That's about 1.5 degrees of slop at each gear mesh point (2 mesh points in a three gear train.

So, the stepper will locate the turret numerically accurately, but the turret can be +- 1.5 degrees when it stops. depending on how fast the turret decelerates, it can be + 1.5 degrees or -1.5 degrees. if the turret is not located +- .5 degrees of the indexing location, it will not lower down onto the locating dogs correctly.

My location problem turned out to be not having the A axis homed. now, the locating accuracy problem is purely mechanical backlash, as the stepper is going exactly where it should. I am positive that the issue (currently) is that even though mach 3 and the stepper locate the first gear in the train accurately, after 2 gear mesh points, enough slop is introduced to have the turret off just enough to only lower down onto the dogs about half of the time.

if I make a detent arm, the detent arm will snap into each of the detent locations (8 total) with accuracy which is entirely dependant upon how much accuracy the detent locations are machined to. This assumes that the detent arm does not itself have any slop (backlash)

Fortunately, cutting detent locations on my mill will be very accurate as I have a high resolution Peiseiler 4th axis. The detent arm can be made to have almost zero slop if I make it right. I plan on having the detent arm made with the spring tension being adjustable. I think the detent slots should be V shaped for positive location locking.

I hope all this makes sense. 
Re: Mach 3 toolchange for dummies???
« Reply #57 on: March 11, 2011, 06:54:28 AM »
Yes, I understand better now.
3* is quite a bit, must be quite a bit of wear.
Probably be too much involved in replacing the worn parts, common size gears/bushings are available from MCarr and others pretty cheap.
You've considered this of course.
Good luck,
Russ
Re: Mach 3 toolchange for dummies???
« Reply #58 on: March 11, 2011, 01:35:51 PM »
Their is virtually no wear on the gear train. It was designed to rotate via air motor and stop location (index) was accomplished by an air cyllinder with a stop arm. The turret was designed with gear train backlash. It was designed to overshoot, only being halted by the stop arm...

I have come to the conclusion that a detent arm or pin is a must to completely allign the position after positioning by stepper motor, so that when the turret lowers, it will engage the locking dogs correctly. if the position is not very close, the turret lowers onto the dogs incorrectly if at all.

time to make some sort of detent locating arm...

 
Re: Mach 3 toolchange for dummies???
« Reply #59 on: March 11, 2011, 06:37:57 PM »
Ah, now it makes even more sense, more and more details coming to light.
I'll leave you be now, you're on a roll !
 Be sure to post pics/vid of your final design, I'm certain it will be unique and interesting.
Russ