Home/Limit advice, please

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03 Jun 2020 21:53 - 03 Jun 2020 21:57 #170021 by blockbuffer
Hi!

I've gotten to the point in setup where I have XYZA motors moving expected amounts in expected directions, and now on to the next challenge...homing (or not...).

This is a simple hobby setup - a Taig mill, with steppers, G540, 7i92, and NO limit/home switches. While I've certainly had to give pncconf some nominal 'home' positions, I'm still left with the matter of actually getting and keeping the various axes PHYSICALLY in the home position - but wondering whether it even matters and whether just orienting to the workpiece is sufficient and I should just move on to a little G-code practice...

What say you?

Thx!

- Bob
Last edit: 03 Jun 2020 21:57 by blockbuffer.

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03 Jun 2020 21:59 #170023 by tommylight
G-code practice is always nice, so go on...
As for limits, you can get away without them and never need them, until you set the home in the middle of the table and set a part to move beyond the table on one side and let the machine rip, just to be a bit later wondering "what is that screeching noise coming out of the machine". :)
Adding them is quite easy, and makes the machine much safer and pleasant to work with. Also saves a lot of material anytime you rush a job.

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03 Jun 2020 22:05 #170027 by blockbuffer
That sounds like a vote for limit switches for safety, but not home switches. Correct?

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03 Jun 2020 22:14 #170031 by tommylight

blockbuffer wrote: That sounds like a vote for limit switches for safety, but not home switches. Correct?

Same thing, really, you can use the same switch for home and limit, or of mounted to the moving part of the axis, one switch can do homing and both sides of the limits.
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04 Jun 2020 08:35 #170083 by bbsr_5a
Replied by bbsr_5a on topic Home/Limit advice, please
why dident yoiu read bevor buying NO
With NC you only woudt lose one PIN on all 10Switches if you want
XYZ you can have HARD limits on the Taig and a REF so its 9Switches BX inductive
and a Index at the Rotary

all wired as a Chain (CHERRY Switch) or as inductive the Black together
This gives you also the advantage if one switch fails the whole machine will not start ((inductive fail will bring a red light to one switch))

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04 Jun 2020 14:30 #170097 by blockbuffer
bbsr_5a,

I'm having a little trouble parsing your post, but I think I see two key points:

1) Scolding me for not having read (presumably the manual), before buying. Well, I did. And it was about what I expected to find. Long on description of individual features, and very light on guidance for new users who just want to get their installation working. I knew what I was getting into, based on experiences in other settings. The software would work, but setup would be painful.

My guess is that linuxcnc users who are already familiar with motor control and machine tools are fairly ok with the doc, as they bring a lot of understanding in with them. And as shareware/freeware goes, the breadth of doc coverage is impressive.

But for the new user who's just arriving on the scene and doesn't come in prepared with that background? Sorry about the dumb questions, but it's a rough go...

2) I think you're advising me to use switches that are wired serially so that the whole machine halts if one trips. This is an interesting tip, and will send me back into the doc. Absolutely - if one axis bangs into something, you certainly would want the whole machine to halt while you sort out what went wrong. Thank you!

- Bob

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04 Jun 2020 15:01 #170098 by Clive S
Replied by Clive S on topic Home/Limit advice, please
Are these switches you have NO ie (normally open contacts) and are they the sensor type.

For a small mill just 3 would be ok one at the top of Z (Z should be -ve going down) and one each for X and Y they can be setup as a home switch including soft limits.

Now you have your mill working it is better to edit the HAL and INI files by hand. Or make a new config with the switches in, then copy and paste the relevant bit sto each of the two files.
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04 Jun 2020 15:49 #170100 by blockbuffer
Clive,

Well, I don't have switches at the moment - I'd have to source those.

But...I would think that Normally Open would be what you'd want for individual switches, but if wired serially, as bbsr_5a was suggesting, then surely I'd want Normally Closed?

- Bob

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04 Jun 2020 16:09 #170101 by PCW
Replied by PCW on topic Home/Limit advice, please
Normally closed is usually suggested since a broken wire
will result in a fault and stop
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05 Jun 2020 12:46 #170250 by andypugh
Replied by andypugh on topic Home/Limit advice, please
For a Taig mill you probably can just push it to the hard stops when turned off, then home it when you start up (in no-move homing mode)
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