Re: [Emc-users] Emc-users Digest, Vol 118, Issue 61

[Gene Heskett]

On Tuesday 16 February 2016 08:15:43 Robert von Knobloch wrote:

> On 16/02/16 14:02, emc-users-requ...@lists.sourceforge.net wrote:
> >> Pass over the switch might be possible?
> >
> > No. The datasheets I've read all say the same that you must activate
> > the plunger straigt on. Any angle will give you bad performance. Any
> > sideways stress on the plunger can kill the plunger assembly.
> >
> > The only alternative is to use a level-based micro-switch. That,
> > however, will probably make it less accurate. Especially when you
> > move over it side-ways. The angle of attack is too small with
> > respect to the travel distance.
> >
> > -- Greetings Bertho
>
> Bertho,
>
> FWIW I made mine by using small, round bar magnets (ca. 6 x 15 mm) and
> reed switch capsules. I milled out small (25mm) pieces of 10 x 10mm
> aluminium and epoxied the switches and magnets each in one. These, I
> glued to the machine with cyanoacrylate such they slide past each
> another horizontally, with a small gap (no contact at all) . I haven't
> measured the repeatability but it seems pretty good and they are cheap
> and sealed against junk getting in.
>
> Cheers,
> Bob
I used the round buttons Grizzly put on the tables for hard stops but 
took the stops off and the button just rolls the wheel in the end of the 
lever as they go by for X, and put a pointer on the head sled to hit 
the roller on a post mounted switch. All 3 can go on by without damaging 
the switch.

On the toy mill when I put some teeny ball screws in it, I put a switch 
with a plain lever to sense when the screw was about to come out of the 
nut by letting the lever come out as the end of the screw passed the 
root of the lever.  That made a quite decent homing switch, so I then 
set the software limit to stop it a few thou before it hit the hard 
stops at the other end of the travel.  But on that mill I have never 
tried to put a switch on the Z.  It has the whole post to play on, so 
there aren't any sw limits and I just touch it off where ever I need it 
to be.

On the lathe, Z switch is about an inch from the empty chuck to the empty 
toolpost, and X switch trip is about 5 thou from the X maximum backout, 
so I remove the tool holder from the QC post, and the ctl+home sequence 
finds X first, then since that will clear the tool post with anything 
under 2.5" in the chuck, goes & finds that Z home & then parks it at 2" 
away from the chuck.  All 3 machines seem to have pretty good.  On the 
lathe of course both measurements are completely arbitrary since there 
is not a way to put a tool point so it blocks a beam of light thats 
exactly on the centerline.  Repeatability is more important, and that 
seems to be adequate. More important when turning is taper, and the best 
way to control that is to map X against Z but LCNC cannot to that so I 
have to put it in the gcode. And that works about 75% of the time, 
depending on the direction and backlash, but .002" accuracy is do-able 
for about 3 or 4" of Z travel.  Then bed wear sets in and I've not tried 
to compensate for that, yet...

However, hint hint, if X could be mapped according to Z, that would be 
the cats meow. Use one map when running in the chuck, and another when 
using a tailstock too.

Any axis to any other axis would be the ice cream on the pie. Those are 
my major sources of error on all 3 machines.

Accuracy of the screw thread itself hasn't appeared to be a problem, with 
acme or ball screws within my ability to measure it, but that would be a 
bit crude to do with my limited range indicator tools.

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] Emc-users Digest, Vol 118, Issue 61

[Robert von Knobloch]

On 16/02/16 14:02, emc-users-requ...@lists.sourceforge.net wrote:
>> Pass over the switch might be possible?
> No. The datasheets I've read all say the same that you must activate the
> plunger straigt on. Any angle will give you bad performance. Any
> sideways stress on the plunger can kill the plunger assembly.
>
> The only alternative is to use a level-based micro-switch. That,
> however, will probably make it less accurate. Especially when you move
> over it side-ways. The angle of attack is too small with respect to the
> travel distance.
>
> -- Greetings Bertho
Bertho,

FWIW I made mine by using small, round bar magnets (ca. 6 x 15 mm) and 
reed switch capsules. I milled out small (25mm) pieces of 10 x 10mm 
aluminium and epoxied the switches and magnets each in one. These, I 
glued to the machine with cyanoacrylate such they slide past each 
another horizontally, with a small gap (no contact at all) . I haven't 
measured the repeatability but it seems pretty good and they are cheap 
and sealed against junk getting in.

Cheers,
Bob

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Monitor end-to-end web transactions and take corrective actions now
Troubleshoot faster and improve end-user experience. Signup Now!
http://pubads.g.doubleclick.net/gampad/clk?id=272487151=/4140
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