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Author Topic: Backlash not applied during manual JOG?  (Read 10641 times)

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Re: Backlash not applied during manual JOG?
« Reply #20 on: January 20, 2016, 05:00:57 PM »
t, i don't think we're in the realms of breaking physics. as a secondary, a typical arrow band o2 sensor is a closed loop system, it feeds back enough information to allow the engine to operate within parameters and try to keep a predefined air/fuel mix for the most efficient idle burn in terms of emissions output, it does not just indicate an error. this is what fuel trims are. some cars have closed loop all the way to WOT and will trim, as we advance ECU's and use faster cpu's we're moving away from archaic open loop systems with precomputed tables and trims, to directly using the sensors to determine correct fueling an advance etc, the whole engine moves away from being an open loop system to closed loop, the sensors can feed back enough info to do this properly, if a major fault appears that is something else, but to compare backlash to a loose steering wheel is another thing entirely, but i feel like this comparison may have run its course but we're in agreement of what an O2 sensor does i believe, and why its a good thing.

trims vs compensation for a failure, two different things.  the ecu will say, hold on we're getting a tad crazy with these trims here and throw a warning code to the operate, backlash compensation to me is the same thing, agreed tolerances and where it can, and can't work, it does work in some scenarios, not in others, not having it means it can never work.

you seem to be looking from the point of view worst case, i'm looking at from the pov of best case, in where it is a useful feature, sure maybe thereis some thing i can learn that i can write gcode or cam up so that i no longer need it, but i'm not there yet, to me i'm still in the realms of i can draw a circle that turns out to be an oval, i can draw on oval that becomes a circle, which of course is a gross oversimplification of it, but thats my pondering over coffee and not being an experienced machinist. I do get that experienced machinists say remove all the mechanical slop and stop dreaming about backlash compensation, but that takes a while to achieve, i'm ok with working within the limitations as i improve the build and race towards 0.

roger, we're doing an incremental build, and are at stage 1 as it were, with 7.62µ of backlash at the moment. the idea is to keep improving the parts we're making with each incremental build of the machine, and improving it, the goal being not to need backlash compensation at all, but for now its extremely handy.

we could be the guys in the pits arguing about splitfires and monster cables, or the guys on track drifting around corners in a beater.

Offline rcaffin

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Re: Backlash not applied during manual JOG?
« Reply #21 on: January 20, 2016, 05:23:07 PM »
Quote
roger, we're doing an incremental build, and are at stage 1 as it were, with 7.62µ of backlash at the moment. the idea is to keep improving the parts we're making with each incremental build of the machine, and improving it, the goal being not to need backlash compensation at all, but for now its extremely handy.
Sounds good to me.

Cheers
Roger

Offline Chaoticone

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Re: Backlash not applied during manual JOG?
« Reply #22 on: January 20, 2016, 05:42:22 PM »
charliex, we do agree on somethings but you are clearly not getting what I am saying. That does not bother me in the least. What does bother me is others may see this and some will hear what they want to in your post and believe it.

Quote
if a major fault appears that is something else

This is almost funny. To a machine controller backlash is this something major. It does not get much more major than this. There is no degree of backlash only varying amounts. It either exist or it does not.  Backlash is the distance the driver went around the course with the steering wheel disconnected from the shaft. No control!  ;D  Backlash is the additional length of wire needed so that the O2 sensor you keep talking about can be connected. Backlash is the length of fuel line needed to connect the fitting on the tank to the fuel pump. Backlash is the distance between the connecting rod and the crank when there is no rod bearing installed. Backlash is that tick you hear when a pushrod gets bent. Believe me charlie.............. backlash can be some serious juju.

I really am on your side, you just haven't figured that out yet. Do not underestimate the implications a "little backlash" can have.
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!
Re: Backlash not applied during manual JOG?
« Reply #23 on: January 20, 2016, 05:59:13 PM »
So if you could show me at what point i said backlash doesn't matter i'd be happy to be on your "side" ? i'm pretty sure i've said exactly the opposite, and gave an example of it, just as i gave the example as to where it works for me. You cannot argue against that no matter how much you try, since all i'm saying is, in my specific circumstances/setup the backlash compensation is something i'd like to have, whilst also understanding why its a bad thing, perhaps not to the extent that you do, but thats ok since i know its bad and am trying to get rid of it. I also like the idea of screw pitch adjustment over the length of the axis.

again i'll repeat, i'm looking for a recommendation on a mach3/4+controller that supports backlash compensation, not if backlash is good or bad, people who read this thread and all the others will come up with their own line of thought regardless of whatever either of us says, thats just how it is, neither of us will live long enough to change that aspect of humanity.

and i quote
"but it works in some scenarios, not all, its a bandaid, fix your machine,we get it. but sometimes we can only go so far and having the option is nice."

and that option is when i'm end milling out circles. it does work for me, on my setup, in that case that is undeniable, i'm not going to assume that other people aren't also able to use it to their advantage in some way, maybe i'm wrong to have such an opinion.

cheers

Offline dude1

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Re: Backlash not applied during manual JOG?
« Reply #24 on: January 20, 2016, 06:05:19 PM »
backlash is a monster, backlash comp is a big monster get it wrong and it will bite you hard, A person on the yahoo forum spent some time on this, he got it in the end but it was hours and hours of hard work.  he fixed the problem mechanically as best as he could first, before backlash comp was even tryed what was hours and hours of work.
is it worth spending hours and hours on it, and not cutting anything for days or weeks hell no.

Offline RICH

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Re: Backlash not applied during manual JOG?
« Reply #25 on: January 20, 2016, 06:31:46 PM »
charliex,

Quote
i'd like to be able to keep fitting bearings after an endmill

I used BC for a long time with MACH 3. Yes you can use the mill that has backlash and be able to just slip that bearing into what is cut,
but, you need to adjust both the BC settings and your code, and even with dong that,.....it's only good for a particular operation.

I don't know where BC implementation is relative to MACH4 or current external motion controllers. So can't help you there.

Take this advice:
Your machine is what it is, you either accept it's limitations or make improvements. Do yourself a favor and get rid of the
BC ( oh, BTW, there is no such thing as "0" backlash ).

RICH

 

 
Re: Backlash not applied during manual JOG?
« Reply #26 on: January 20, 2016, 06:48:39 PM »
RICH,  "roger, we're doing an incremental build, and are at stage 1 as it were, with 7.62µ of backlash at the moment. the idea is to keep improving the parts we're making with each incremental build of the machine, and improving it, the goal being not to need backlash compensation at all, but for now its extremely handy. "
Re: Backlash not applied during manual JOG?
« Reply #27 on: January 20, 2016, 07:00:32 PM »
There needs to be a mention of what backlash comp can and can't do. Like a manual machinist it can take out the backlash that happens when an axis reverses. Like a manual machinist it can't allow you to climb mill no matter how careful it is. We had an acme screw Spindle Wizard knee mill that used a spring to turn a second nut slightly eliminating the backlash. It climb milled with no problem ever. The down side was that the considerable friction this introduced meant it was limited to 40 ipm.

Offline RICH

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Re: Backlash not applied during manual JOG?
« Reply #28 on: January 21, 2016, 06:20:28 AM »
Quote
with 7.62µ of backlash at the moment

That's 0.00000762"  so how did you measure that?

Maybe your units are incorrect since that's almost impossible to accurately measure.
Using a mounted 500x microscope with fical micrometer as compared to a calibrated u line scale I had trouble
measuring to down to 0.000040".

If you preload axis thrust bearings to that you won't have movement / stall. There is no such thing as "0" backlash,
maybe min BC would be  better term.

But improving to a practical min BC is certainly desirable.

FWIW,

RICH
  

Offline rcaffin

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Re: Backlash not applied during manual JOG?
« Reply #29 on: January 21, 2016, 06:28:04 AM »
Hey Rich

7.62 microns is very likely metric.

Cheers
Roger