Re: [Emc-users] correct x error from bed wear

[Phillip Carter]

On 9/9/18 1:14 pm, Gene Heskett wrote:

On Saturday 08 September 2018 22:34:06 Phillip Carter wrote:


On 9/9/18 5:18 am, Gene Heskett wrote:

Greetings all;

I am about to give up on this bedwear comp project.

How I determine the amount of correction needed has been tried by
watching the dial as Z is moved, taking notes as to which way the
center of the wobble (the spindle is running about 15 rpms) moves,
and putting that DRO's RAD in the hal files lincurve "setp" list.
Makes it worse, change sign of lincurve y-val, still worse.  Seems
like the correction is being multiplied by 3 or more.

I have run it to a lincurve X-val-nn point, and using the jog dial,
centered the dials wobble on zero, then put the obtained rad into a
y-val-nn, again making it worse with either sign.

So how do you folks derive the correction needed?

I'm assuming the offset itself is in radius, not diameter. In which
case the needed radius correction max's at about 2.5 thou. And that
the sign is the "tricky" part.

Thanks everybody.

This lathe bedwear may be a good candidate for the
dgarr/external_offsets branch.


Humm, can't say I've ever heard of that.  URL?


https://github.com/LinuxCNC/linuxcnc/tree/dgarr/external_offsets

Cheers, Phill

Thanks Phill.>


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Re: [Emc-users] correct x error from bed wear

[Gene Heskett]

On Saturday 08 September 2018 22:34:06 Phillip Carter wrote:

> On 9/9/18 5:18 am, Gene Heskett wrote:
> > Greetings all;
> >
> > I am about to give up on this bedwear comp project.
> >
> > How I determine the amount of correction needed has been tried by
> > watching the dial as Z is moved, taking notes as to which way the
> > center of the wobble (the spindle is running about 15 rpms) moves,
> > and putting that DRO's RAD in the hal files lincurve "setp" list. 
> > Makes it worse, change sign of lincurve y-val, still worse.  Seems
> > like the correction is being multiplied by 3 or more.
> >
> > I have run it to a lincurve X-val-nn point, and using the jog dial,
> > centered the dials wobble on zero, then put the obtained rad into a
> > y-val-nn, again making it worse with either sign.
> >
> > So how do you folks derive the correction needed?
> >
> > I'm assuming the offset itself is in radius, not diameter. In which
> > case the needed radius correction max's at about 2.5 thou. And that
> > the sign is the "tricky" part.
> >
> > Thanks everybody.
>
> This lathe bedwear may be a good candidate for the
> dgarr/external_offsets branch.
>
Humm, can't say I've ever heard of that.  URL?

> Cheers, Phill

Thanks Phill.>
>
>
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-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 


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Re: [Emc-users] correct x error from bed wear

[Gene Heskett]

On Saturday 08 September 2018 22:03:21 jeremy youngs wrote:

> Gene , can you mount a probe on the carriage and probe a lathe
> alignment bar ( or drill rod )?

I don't have a probe per sei on it. What I'm doing is sticking a mag base 
to the top of the toolpost holder base that has replaced the mangled 
compound, with atm a dial indicator riding a 21" bar of .500 diameter A2 
rod. Theres a thou or so wobble right at the er40 adapter, and the 
center dimple on the other end is off center about 2 thou riding a live 
center in the tailstock barrel. The A2 is slightly bent so I get about a 
10 thou wobble in the middle of it, but with the spindle turning, the 
true center is easily seen. I have used the lathes x motor to try and 
straighten it better, but by the time I  get enough bow in it to make a 
diff, the rod shortens and pops the end off the live center.

I would do it according to demagnetizeing rules by pushing it far enough 
to bent it back, with the spindle turning, and once I have evidence that 
I am actually bending it, the let it run while I slowly back off the 
push, which should make it run pretty true. But w/o a socket instead of 
a center in the tailstock, I can't get up enough pressure to actually 
bend it straight. A half inch of A2 20+ inches long is still pretty 
strong stuff.

I should buy another 36" piece of 3/4" A2 which would obviously be 
stiffer. But I wouldn't wager it would be straighter. So I'd still have 
to deal with the wobble. And that much A2 isn't cheap.

Setting up a contact probe would trigger on the peaks of the wobble, and 
that measurement would be meaningless w/o knowing the p-p wobble at each 
probed point. I can get that accurate with a dial. I think...

>From what I have observed so far, I think the huge majority of what I 
need to correct is in the first 8" from the spindle, the rest looks like 
a fairly straight line, IF the tailstock is on center. The major error 
once the sled is pulled to center, is vertical. 50 thou off at least.

Thanks Jeremy.
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-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 


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Re: [Emc-users] correct x error from bed wear

[Phillip Carter]

On 9/9/18 5:18 am, Gene Heskett wrote:

Greetings all;

I am about to give up on this bedwear comp project.

How I determine the amount of correction needed has been tried by
watching the dial as Z is moved, taking notes as to which way the center
of the wobble (the spindle is running about 15 rpms) moves, and putting
that DRO's RAD in the hal files lincurve "setp" list.  Makes it worse,
change sign of lincurve y-val, still worse.  Seems like the correction
is being multiplied by 3 or more.

I have run it to a lincurve X-val-nn point, and using the jog dial,
centered the dials wobble on zero, then put the obtained rad into a
y-val-nn, again making it worse with either sign.

So how do you folks derive the correction needed?

I'm assuming the offset itself is in radius, not diameter. In which case
the needed radius correction max's at about 2.5 thou. And that the sign
is the "tricky" part.

Thanks everybody.

This lathe bedwear may be a good candidate for the 
dgarr/external_offsets branch.


Cheers, Phill



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Re: [Emc-users] correct x error from bed wear

[jeremy youngs]

Gene , can you mount a probe on the carriage and probe a lathe alignment
bar ( or drill rod )?

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Re: [Emc-users] correct x error from bed wear

[Gene Heskett]

On Saturday 08 September 2018 18:30:42 Chris Albertson wrote:

> This has already been done on Merlin.  Merlin is the software that
> interpret g-code for most 3D printers.
>
I see, but that also is dealing with what effectively is a plain one 
dimension rendered in 3d.

A lathe is a slightly different critter, and the major src of the error 
is the tilting of the carriage in and out due to different amounts of 
wear front and rear, so the correction consists of moving a dial along 
the centerline height, and measuring this in and out wobble the tilting 
creates and applying an in or out correction of 3 thou maximum, so the 
cutting tool effectively follows a straight line.

Due to the wear createing a height of tool motion, its acknowledged but 
unless working on a eighth inch or smaller part, this height change is 
surely under 0.001" in effect on the part unless its super teeny.
 
> The way it works is there is a distance sensor on the print head and
> it probes the entire bed in a grid pattern.  It ALWAYS finds that the
> bed is not level and not flat.   There are several kinds of probes
> sorted.   One is a simple microswitch.
>
> Then after probing the bed and seeing that  it is not flat or square
> it computers a transformation matrix and then later all X,Y,Z values
> in the g-code are transformed.  In the end you have a part that is
> perpendicular to the bed but maybe not vertical.Depending on where
> on the bed your part is it might be leaning in a different direction.
>
Again, an effect that on a lathe, that is quite miniscule, and with only 
stepper motors to microstep control, plus the lash in the ball nuts and 
thrust bearings, is quite low. So low that its a non-problem if not 
working on the hubble mirror.

> It works well within reason.  Actual errors need to be only a few
> thousands.  In my case the bad is slightly bowel shape with the
> =center being about 0.2mm deeper than the corners.  This level of
> error is easily corrected.

I assume you meant "bowl" shaped. :)
 
Do we have a receiver/logger module for the digital output of a scale I 
intended to put on the tailstock barrel, one of Shar's lower cost models 
with a remote display. This, fed to some math to detect the high and low 
spots and how high or low which would allow the error to be logged. I 
could mount it in a tool holder and put a teeny ball bearing to ride the 
calibration rod, and rubber band its slider toward the rod.  Its a 
thought anyway. I'd have to obtain the data cable, or just log it from 
its own display every 1/4" if no recording module is available.

At least I would have a good starting point, which may in fact be "good 
enough for the girls I go with".

Thanks Chris.
>
> On Sat, Sep 8, 2018 at 12:23 PM Gene Heskett  
wrote:
> > Greetings all;
> >
> > I am about to give up on this bedwear comp project.
> >
> > How I determine the amount of correction needed has been tried by
> > watching the dial as Z is moved, taking notes as to which way the
> > center of the wobble (the spindle is running about 15 rpms) moves,
> > and putting that DRO's RAD in the hal files lincurve "setp" list. 
> > Makes it worse, change sign of lincurve y-val, still worse.  Seems
> > like the correction is being multiplied by 3 or more.
> >
> > I have run it to a lincurve X-val-nn point, and using the jog dial,
> > centered the dials wobble on zero, then put the obtained rad into a
> > y-val-nn, again making it worse with either sign.
> >
> > So how do you folks derive the correction needed?
> >
> > I'm assuming the offset itself is in radius, not diameter. In which
> > case the needed radius correction max's at about 2.5 thou. And that
> > the sign is the "tricky" part.
> >
> > Thanks everybody.
> >
> > --
> > Cheers, Gene Heskett
> > --
> > "There are four boxes to be used in defense of liberty:
> >  soap, ballot, jury, and ammo. Please use in that order."
> > -Ed Howdershelt (Author)
> > Genes Web page 
> >
> >
> > ___
> > Emc-users mailing list
> > Emc-users@lists.sourceforge.net
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-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 


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Re: [Emc-users] correct x error from bed wear

[Chris Albertson]

This has already been done on Merlin.  Merlin is the software that
interpret g-code for most 3D printers.

The way it works is there is a distance sensor on the print head and it
probes the entire bed in a grid pattern.  It ALWAYS finds that the bed is
not level and not flat.   There are several kinds of probes sorted.   One
is a simple microswitch.

Then after probing the bed and seeing that  it is not flat or square it
computers a transformation matrix and then later all X,Y,Z values in the
g-code are transformed.  In the end you have a part that is perpendicular
to the bed but maybe not vertical.Depending on where on the bed your
part is it might be leaning in a different direction.

It works well within reason.  Actual errors need to be only a few
thousands.  In my case the bad is slightly bowel shape with the =center
being about 0.2mm deeper than the corners.  This level of error is easily
corrected.

On Sat, Sep 8, 2018 at 12:23 PM Gene Heskett  wrote:

> Greetings all;
>
> I am about to give up on this bedwear comp project.
>
> How I determine the amount of correction needed has been tried by
> watching the dial as Z is moved, taking notes as to which way the center
> of the wobble (the spindle is running about 15 rpms) moves, and putting
> that DRO's RAD in the hal files lincurve "setp" list.  Makes it worse,
> change sign of lincurve y-val, still worse.  Seems like the correction
> is being multiplied by 3 or more.
>
> I have run it to a lincurve X-val-nn point, and using the jog dial,
> centered the dials wobble on zero, then put the obtained rad into a
> y-val-nn, again making it worse with either sign.
>
> So how do you folks derive the correction needed?
>
> I'm assuming the offset itself is in radius, not diameter. In which case
> the needed radius correction max's at about 2.5 thou. And that the sign
> is the "tricky" part.
>
> Thanks everybody.
>
> --
> Cheers, Gene Heskett
> --
> "There are four boxes to be used in defense of liberty:
>  soap, ballot, jury, and ammo. Please use in that order."
> -Ed Howdershelt (Author)
> Genes Web page 
>
>
> ___
> Emc-users mailing list
> Emc-users@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/emc-users
>


-- 

Chris Albertson
Redondo Beach, California

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[Emc-users] correct x error from bed wear

[Gene Heskett]

Greetings all;

I am about to give up on this bedwear comp project.

How I determine the amount of correction needed has been tried by 
watching the dial as Z is moved, taking notes as to which way the center 
of the wobble (the spindle is running about 15 rpms) moves, and putting 
that DRO's RAD in the hal files lincurve "setp" list.  Makes it worse, 
change sign of lincurve y-val, still worse.  Seems like the correction 
is being multiplied by 3 or more.

I have run it to a lincurve X-val-nn point, and using the jog dial, 
centered the dials wobble on zero, then put the obtained rad into a 
y-val-nn, again making it worse with either sign.

So how do you folks derive the correction needed?

I'm assuming the offset itself is in radius, not diameter. In which case 
the needed radius correction max's at about 2.5 thou. And that the sign 
is the "tricky" part.

Thanks everybody.

-- 
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Genes Web page 


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