Constant home position

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chessnut
Posts: 3
Joined: Tue Jan 02, 2018 11:20 pm

Constant home position

Post by chessnut »

Does anyone know of a way to establish a permanent x,y home postion on a Shark HD4 with pendant? I've been trying to figure out if you can set the x,y to a constant coordinate so that even you've powered the machine off, you can power up and have the router return to the same position. Or another use would be if you normally set your datum postition in Vcarve to the lower left corner, then have to change it to the center for a job. When you mark the workpiece in the center, and move the router to that center point and zero the x,y, and z, then the default x,y becomes the center of the workpiece. I would like to be able to return to a specified position in the lower left corner after that job so the x,y will be in the lower left corner when I start another job. Or, have a home button that would send the router to a default position. I haven't been able to find a comprensive guide to the various options available when you tap the "Apps" button on the pendant. Some cnc's have the "home" capability. Any ideas?

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Kayvon
Posts: 515
Joined: Tue Oct 21, 2014 11:46 pm

Re: Constant home position

Post by Kayvon »

I think limit switches are the biggest missing features on Sharks. Not only can they prevent the machines from trying to tear themselves apart, but they would provide a constant home position, even between power-ups. Start a project today, finish it next week.

Sadly, I don't have an answer to your question, but I feel the pain.

Janettx
Posts: 13
Joined: Sun Apr 02, 2017 9:46 am

Re: Constant home position

Post by Janettx »

I watched the Controller video and he mentions you can do this but for the life of me following his instructions do not work for me. :( Anyone else able to set a new default home?

Rando
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Location: Boise, ID
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Re: Constant home position

Post by Rando »

There is a common misunderstanding of the function of LIMIT switches versus HOME switches.

The function of a limit switch is to tell the machine that it is about to CRASH. The normal function
of these switches, when tripped, is to trigger an ERROR and immediately stop movement in the machine.
That is how the limit switch inputs on the shark controllers work. Or at least that's how they seem to
work the one time I tried to use them. They're a bust for the purpose you're looking for.

So....what you're looking for are NOT limit switches, they are HOME switches, which are typically set about
1/2 to 1" inside the travel, near the most-negative limit switch. The machine is supposed to approach the
home switches at moderate speed. Once detected, it's supposed to move back away from the home switch,
then slowly approach the home switch to get an accurate Zero for each axis. But, that would require the
controller to actually understand HOW to approach and then use the home switches.

But, no matter what you call them, the sharks do NOT have the capability of HOME switches, only LIMIT
switches.

But, all is not lost. You CAN create a very simple system that will let YOU reset your X0Y0 to a preset location.
Well, the system is simple...implementing it might not seem so simple, depending on your experience level.

You first need to learn how to use an edge-finder. Whether you choose the less-expensive mechanical ones,
or an electrical one is up to you, but the plan is the same. See the image at the bottom of this post if you're
not familiar with what they look like.

Start with an aluminum block, about 3" on a side, 1" thick.

Take a block of aluminum, say 1" thick, and cut an L-shaped slot in it. The cut-out only needs to be about
1/4" or so deep, but needs to be about 0.3" wide on each arm. Leave the ends of the arms rounded, but the
angle of the L as a sharp angle. Cut this with nice slow (but proper) feeds and speeds, and use two finish
passes. That means rough with a margin of about 0.015, then a finish pass leaving 0.005, and the final pass
taking the final 0.005". This should, even on an old shark-ii like I have, a nice straight edge on the L-arms.
Do several roughing passes to get to depth, but do the finishing passes to the full depth. Deburr the edges
at the top if they need it, but don't relieve down more than about 0.010"

You'll want to also drill at least one hole through the block so you can FIRMLY attach it using the t-slots.
If you want to use the electronic edge finder, add a small hole to screw down a wire that goes up to the spindle
body, so the edge finder will get conductivity. (Not needed with a mechanical edge finder.)

Next up, you need to attach the newly made zero-block to your bed using a hold-down bolt through the hole
you drilled, into a T-nut. Countersinking that hole for the bolt head will help you avoid crashing the finder
into it. use a flat washer under the bolt/nut head. Those two edges of the inside of the L will become your
indicating surfaces for X0 and Y0. Ignore the fact that they're going to be actually 0.1" (half the diameter
of the edge finder's cylindrical sensing part) from "true zero".

Now comes the precision part: you need to PRECISELY align the INSIDE edges of the L to the X and Y of your
machine. Use a dial test indicator with 0.001" resolution, and moderately tighten the block down. Attach the
dial test indicator to the z-axis carriage and gently lower it into the L. Watch out for cosine error. Jog the
machine back and forth along the 1" or so of the arm's STRAIGHT length, and use a hammer or the end of
a screwdriver to tap it into alignment. You should only have to do one axis, but check the other. When you've
got it within 0.001" along that length, final-tighten the hold down screw. Test it again to make sure you
didn't move the block.

When you're satisfied with the alignment, use the edge finder to "get" your X0 and Y0 off those inside
edges of the L, about 0.2 - 0.3" away from the sharp inner corner.

If you're practiced with an edge finder, of either form, you should be able to re-get X0Y0 within 0.001" quite
repeatably. When you reach the edge, just click the X0 or Y0 buttons as appropriate.

And, there you have it: a constant X0Y0.

I use this method when I make fixtures that hold parts I want to machine precisely and repeatably. And yes,
I can un-mount parts, and remount them later, months later, and it will still be as accurate as the first time.

In the pictures below, the first shows a bunch of the fixtures where I've used this method...for over
five years now, so don't imagine this is some "experimental crap"...it's tested and works perfectly. And
yes, every one of those fixtures and the parts on them were cut on a shark hd-ii, so don't complain
you somehow can't cut it.
L-shaped X0Y0 features in multiple fixtures
L-shaped X0Y0 features in multiple fixtures
The second picture shows three examples of edge finders: two mechanical "wiggler" models, and one
Fowler electronic edge finder. That one has red LEDs that light up. Whatever you do, do NOT spin them
above about 900 RPM, especially the mechanical ones.
Three edge finders
Three edge finders
Yes, it's possible to do this in wood (minus the electronic edge finder, as that requires conductive material, duh),
but be sure to use VERY hard wood, and realize that wood changes shape with moisture, and will eventually
need to be replaced as the friction against the edge finder will change the contact location. Whether that
adversely affects your X0Y0 repeatability is up to you.

Sorry, I'm not going to explain how to use the edge finders here...there are lots of tutorials on YouTube
showing the technique. Just be careful you don't break off the end (that's why I prefer the mechanical ones
these days).

There...now you know how to get a constant X0Y0.

Regards,

Rando
=====================================================
ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

tonydude
Posts: 1558
Joined: Tue Aug 17, 2010 9:23 am
Location: Buffalo,NY

Re: Constant home position

Post by tonydude »

It will only work with the HD 5
home.jpg
also here is a youtube video on it, watch it at the 41:08 mark on the video. https://www.youtube.com/watch?v=Q-SPLo-JXWE

Tony
Buffalo,NY

"What will matter is not what you bought but what you built; not what you got, but what you gave”

Aspire 10.017, photo vcarve, cnc mako shark extended bed with the new upgraded HD 5 gantry with Led pendent.

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