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Suggestions for homing on a pin
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10106&t=32361		 Page 1 of 1
Author:  Sheldon Dingwall [ Sat May 28, 2011 6:52 pm ]
Post subject:  Suggestions for homing on a pin
I've developed a preference for homing on an index pin rather than the edge of a fixture. This is going to be a little more difficult with the new machine due to the distance from the pendant to the pin. Any suggestions for a trick way of homing X & Y on a pin?
Author:  Chris Pile [ Sat May 28, 2011 7:16 pm ]
Post subject:  Re: Suggestions for homing on a pin
I used to swing in the pin with an indicator in a collet (never a drill chuck), or used an "Indicol" device to hold the indicator. There are several versions and methods you can use. I had quite the collection of devices I either bought, or assembled in the shop to fit whatever situation I was presented with. Helps to have a mirror when you check the rear of the pin, too.

Swing in the pin, and enter G54X0Y0 - done!

Of course, your programming dimensions will be determined from the pin in most cases.
I assume you were using an edge finder for 2 perpendicular edges to find X0Y0?
Author:  Andy Birko [ Sat May 28, 2011 8:11 pm ]
Post subject:  Re: Suggestions for homing on a pin
Sheldon,

Have you seen this thread: viewtopic.php?f=10106&t=31205

This might be just what you're after.
Author:  BobK [ Sat May 28, 2011 8:25 pm ]
Post subject:  Re: Suggestions for homing on a pin
Does your machine have a touch plate for setting Z height? Here's a link to some updates for Mach that allows for individual X and Y locations plus a center finder using a similar technique to the touchplate. Just make a simple jig like the one shown in picture 3 only add a hole centered in the base that precisely fits your locator pin. As long as your touch ring is truly round and centered relative to the locator pin hole you should get good results. I use 1/4" drill rod and a 3/4" copper pipe connector and get decent results, but I need to have someone machine a replacement ring at some point.

http://www.cnczone.com/forums/mach_wiza ... ation.html

Bob


Edit: What Andy said...
Author:  Chris Pile [ Sat May 28, 2011 10:43 pm ]
Post subject:  Re: Suggestions for homing on a pin
Man.... that video makes a simple operation so complex......
Author:  Sheldon Dingwall [ Sun May 29, 2011 9:32 am ]
Post subject:  Re: Suggestions for homing on a pin
Thanks for the replies.

I assume swing in means a zigzag pattern in X as you're sneaking up on Y and vise versa?

I'll need to dig deeper into the Fadal control to see if you can use a macro similar to the one these guys are using for Mach 3. I'm kind of hoping you can.
Author:  Chris Pile [ Sun May 29, 2011 10:52 am ]
Post subject:  Re: Suggestions for homing on a pin
Quote:
I assume swing in means a zigzag pattern in X as you're sneaking up on Y and vise vers


Well, I swing the indicator around the pin. Your spindle moves in a circular motion.... You want your indicator to read zero steadily when you are centered over the pin.
Author:  Kevin Waldron [ Sun May 29, 2011 6:49 pm ]
Post subject:  Re: Suggestions for homing on a pin
None of you guys mentioned this............. Laser Center/Edge Finder..........

http://www.lasercenteredgefinder.com/

kevin
Author:  Chris Pile [ Sun May 29, 2011 6:54 pm ]
Post subject:  Re: Suggestions for homing on a pin
Which is simply a more expensive variation on the simpler themes mentioned above.
Also, a laser does NOT make it any more accurate than an edge finder or indicator.
Author:  Bob Garrish [ Mon May 30, 2011 6:35 pm ]
Post subject:  Re: Suggestions for homing on a pin
The most accurate way I've found to find an X,Y, and Z location is to use a gage block for the Z and then swing an indicator on a proper bore (ie: round through use of a boring head or a reamer). Using an indicator to find center is a hassle, since you need to read the face in all four quadrants of rotation, but it's dead accurate if you have a decent indicator (0.001" for a router, 0.0001" for a mill).

Finding bore center with a probe would be faster, but there's no way to be sure your probe is centered in your spindle without things getting really complicated. I've had a Renishaw from eBay sitting in a drawer for a few months until I get time to set up the stuff to calibrate it.
Author:  npalen [ Mon May 30, 2011 8:16 pm ]
Post subject:  Re: Suggestions for homing on a pin
Using the pointed end of an edge finder extended down into a tooling hole is fairly fast and reasonably accurate.
Even a center punch mark can be picked up easily with this method also.
Bring the spindle down slowly and it's easy to see when to stop
I run the spindle at low RPM when doing this which makes any runout very visible.
That was important when using a router but not so much when using a precision spindle.
Here's a center finder for anyone not familiar. http://www.wttool.com/index/page/category/category_id/17502/?utm_medium=cpc&utm_source=SiteChampion
Nelson
Author:  Stuart Gort [ Mon Jun 06, 2011 9:40 am ]
Post subject:  Re: Suggestions for homing on a pin
I'd use an electronic edge finder to touch off each side of the x and y and then average each to find center. If it's a wooden or foam tooling plate you could run a wire from the pin to a ground.

As you can imagine finding center on an aircraft propeller is pretty critical. That's the technique I used to find center on about 20,000 propellers. :) I've also applied that technique on pins and bosses but for tooling plates made of wood or foam I use a premade aluminum rectangular insert with a wire that runs to ground and I use the corner of that as an origin. It's easier to find a corner point than a circle center.
Author:  Jeffkos [ Fri Jun 17, 2011 12:44 am ]
Post subject:  Re: Suggestions for homing on a pin
I don't know if this will work for you or not, but here's a trick I use.
I'm assuming you're trying to line up the axis of the spindle with the axis of drilled / machined hole.
I like using 1/4" steel dowels; so I'll insert a dowel pin or a piece of a 1/4" precision shaft in the hole in the work piece. I'll then stick a 1/4" shaft in the collet of the spindle, and try to get it close to the shaft in the work piece, in X, Y and Z. Before I get too close though, I'll slip a 1/4" precision bronze bushing on the spindle shaft (although you could also put it on the work-piece shaft). Then I'll micro-jog the spindle to get it to align with the work-piece shaft. When you get within a couple thou, you can get the bushing to slide from one shaft to the other. As you get close, you can actually cheat and bend the shaft in the spindle (assuming you left a couple of inches of shaft hanging out of the spindle) and get the bushing to transfer. And the direction you had to bend it, is the direction you need to keep micro-jogging.

This usually gets me to within a couple thou of being dead-on. And for the type of wood-working I do, where I know I’ll have to do sanding afterwards, this is typically good enough…and pretty quick.

Hope this makes sense.
Let me know if it doesn’t.

Regards,
Jeff

KOZM Guitars
Author:  Sheldon Dingwall [ Fri Jun 17, 2011 11:08 am ]
Post subject:  Re: Suggestions for homing on a pin
That's a good one.

Slight change of direction here. Since a lot of our setups are going to be repetitive once they are dialed in for production. Does it make any sense to use dowel pins on the fixtures that locate on edges of the T-slots and end of the table to consistenly position the fixtures. Then just use the Cold Start position as home instead of homing locally on the fixture?
Author:  Bob Garrish [ Fri Jun 17, 2011 8:53 pm ]
Post subject:  Re: Suggestions for homing on a pin
Sheldon Dingwall wrote:
That's a good one.

Slight change of direction here. Since a lot of our setups are going to be repetitive once they are dialed in for production. Does it make any sense to use dowel pins on the fixtures that locate on edges of the T-slots and end of the table to consistenly position the fixtures. Then just use the Cold Start position as home instead of homing locally on the fixture?


That's essentially what the factories using Fadals do, except that they have dowel pin holes bored into the table. Mine is bored like the ones at Taylor, and has 1/2" holes with inserts at 5" or 10" centres in the middle of some of the lands between the slots.

That said, it only works if you re-calibrate your cold start position regularly. If you have a resolver machine the cold start position will drift over time. I'm not sure if it's an issue on the encoder machines, as they likely have an index pulse.
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