Author Topic: Mechanical Limits  (Read 616 times)

Offline PK

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Mechanical Limits
« on: April 14, 2017, 07:59:26 AM »
Remember boys and girls, without mechanical stops, you're only one GCode typo away from a ballscrew rebuild!
G0Y820..... What was I thinking?

Offline PekkaNF

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Re: Mechanical Limits
« Reply #1 on: April 14, 2017, 08:20:03 AM »
OUTCH!

Ballscrew snapped? What else?

We had one design with two sycronized ball screw jack. Two limit switched connectod servo ennable. Worked like charm: If user mannaged to coax the transfer device to HW stop, they had to power down the servo, remove one guard (two bolts) and manually turn coupling (and servo motor) until switch was made (pilot litght came on). Great. Worked every time. BUT users startted to complain that once a year of doing this is too hard. OK. We installed a push-button to override the HW limit and two push-buttons to control locally the transfer. Worked only 50% of the time. Some people panic and hit every button in random order when something rare happens.

My point? Even smartest people make mistakes, but recovery is less painfull than on general public.

Pekka

Offline awemawson

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Re: Mechanical Limits
« Reply #2 on: April 14, 2017, 08:25:04 AM »
 :bugeye: PK I feel your pain  :bugeye:

Software limits would also be a 'good idea' perhaps
Andrew Mawson
East Sussex

Offline PK

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Re: Mechanical Limits
« Reply #3 on: April 14, 2017, 08:26:35 AM »
OUTCH!

Ballscrew snapped? What else?

Nah, it just wound the screw all the way out of the nut and deposited all those little bearings in 6 years of accumulated swarf and muck under the table.. I think I recovered them all.. :-(

You can see in that pic that I've already tapped the end of the screw to take an M8 bolt, that'll hold  a plate that will stall the stepper if I try the same trick again...


It took 5 minutes to drill and tap that screw. It'll be an hour or so to rebuild the screw and reinstall it....
How does it go? " No one has time to do anything properly, but we all have time to do it twice!"

PK

Offline PK

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Re: Mechanical Limits
« Reply #4 on: April 14, 2017, 08:32:16 AM »
Software limits would also be a 'good idea' perhaps

Yep, a hole drilled in the base and nail hammered in to limit travel would have worked too.. Hell, just about ANY amount of thought and effort could have prevented it!


Offline philf

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Re: Mechanical Limits
« Reply #5 on: April 14, 2017, 11:04:17 AM »
Remember boys and girls, without mechanical stops, you're only one GCode typo away from a ballscrew rebuild!
G0Y820..... What was I thinking?

PK,

To quote yourself from August 2016:

To rephrase:
Basically, you don't need limit/home switches on a basic machine.

Limit switches would have saved you some work! :(

Phil.

Phil Fern
Location: Marple, Cheshire

Offline awemawson

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Re: Mechanical Limits
« Reply #6 on: April 14, 2017, 01:33:53 PM »
 :lol: :lol: Bitch  :lol: :lol:

Poor old PK don't rub his nose in it  :clap:

At least he had the integrity to admit what had happened  :thumbup:
Andrew Mawson
East Sussex

Offline philf

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Re: Mechanical Limits
« Reply #7 on: April 14, 2017, 02:06:06 PM »
:lol: :lol: Bitch  :lol: :lol:

Poor old PK don't rub his nose in it  :clap:

At least he had the integrity to admit what had happened  :thumbup:

I just couldn't resist it! Sorry PK.  :thumbup:
Phil Fern
Location: Marple, Cheshire

Offline PK

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Re: Mechanical Limits
« Reply #8 on: April 14, 2017, 05:44:48 PM »
 :doh:It's a fair cop...