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before the toolholder hits the table.all you lose is an endmill

Last night I was about to decide on where to put the limit switches on
the mill's Z-axis...
the top switch is ok, but how about the bottom switch?
I really can't see any benefit from having this switch.

Here is what I found (many of you will have been her long time ago):
Activate the switch when:
-spindle hits the table
-tool holder hits the table
-tool hits the table

Can't find any of these all that usefull...whatever selection it will be
wrong and useless in other conditions
e.g other tool lengths.

So what do you milling guys do? Do you even fit this switch?

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Eirik Karlsen

How about if your tools too short and then you will stress out some
mechanical part trying to go further down than it can.

This assumes you have soft limits out of wack.


Thanks,

Lee.

Lee K. White
Premier Pattern Equipment Ltd.
9725 - 60 Ave
Edmonton, AB T6E 0C4
Phone: 780-430-1549
Fax: 780-430-1526
Website: www.premierpattern.com

I made my lower Z switch adjustable allowing it to be set for what ever table height you have.

Marty

Well, on this machine its not a problem because the spindle itself (no
toolholder) stops at the table, and
it the table wasn't there the spindle could go a further 10-15cm down.
However the table
can not be moved sufficiently X-Y for that to happen. So Z can reach the
table even without any tool.

So wherever I'd place that switch it would either allow a mech. crash
with the table, or with a shorter
tool there wouldn't be sufficient Z travel towards the table. Either way
the limitswitch would just be a nuisance.

Only solution I can see is if that switch was adjustable so it could be
adjusted to match the length of the tool
in use at the time. Probably not too practical with an automatic
toolchanger, but I'll be using manual toolchange
so this might be a way forward.

I believe there are plenty of 'cnc-millers' on this list and they must
have run into this problem and possibly solved it.

I could go for a movable switch right now but would like to avoid it if
possible...tricky mechanics.
Would like some more input on this problem.

Thanks
E.K





Lee White wrote:

How about if your tools too short and then you will stress out some
mechanical part trying to go further down than it can.

This assumes you have soft limits out of wack.


Thanks,

Lee.

Lee K. White
Premier Pattern Equipment Ltd.
9725 - 60 Ave
Edmonton, AB T6E 0C4
Phone: 780-430-1549
Fax: 780-430-1526
Website: www.premierpattern.com
----- Original Message -----
From: <mugen121@...>
To: <mach1mach2cnc@...>
Sent: Thursday, January 26, 2006 9:31 AM
Subject: Re: [mach1mach2cnc] Whats the point with a Z bottom
limitswitch ?

before the toolholder hits the table.all you lose is an endmill






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Regards
Eirik Karlsen

My Denford mill has an easily adjustable Z switch - very simple mechanics. I can upload a picture if you have a hard time figuring out how to implement it.

Often the part is held by a vice and far above the plane. Also most of my tools are almost equal in length, so it's relatively easy to set a relevant negative Z limit. I have never needed it so far, but one day I'll thank Denford.....

/Torleif.

Eirik Karlsen wrote:

Thorleif,
Machines are different so pix are probably not all that useful.
I'll ponder a bit more about this, may use a movable cam instead and
leave this switch fixed like the rest of them.

Thanks


Torleif Jensen wrote:

My Denford mill has an easily adjustable Z switch - very simple
mechanics. I can upload a picture if you have a hard time figuring out

how to implement it.

Often the part is held by a vice and far above the plane. Also most
of
my tools are almost equal in length, so it's relatively easy to set a
relevant negative Z limit. I have never needed it so far, but one day
I'll thank Denford.....

/Torleif.

Eirik Karlsen wrote:

Well, on this machine its not a problem because the spindle itself

(no

toolholder) stops at the table, and
it the table wasn't there the spindle could go a further 10-15cm

down.

However the table
can not be moved sufficiently X-Y for that to happen. So Z can reach

the

table even without any tool.

So wherever I'd place that switch it would either allow a mech.

crash

with the table, or with a shorter
tool there wouldn't be sufficient Z travel towards the table. Either

way

the limitswitch would just be a nuisance.

Only solution I can see is if that switch was adjustable so it could

be

adjusted to match the length of the tool
in use at the time. Probably not too practical with an automatic
toolchanger, but I'll be using manual toolchange
so this might be a way forward.

I believe there are plenty of 'cnc-millers' on this list and they

must

have run into this problem and possibly solved it.

I could go for a movable switch right now but would like to avoid it

if

possible...tricky mechanics.
Would like some more input on this problem.

Thanks
E.K





Lee White wrote:

How about if your tools too short and then you will stress out

some

mechanical part trying to go further down than it can.

This assumes you have soft limits out of wack.


Thanks,

Lee.

Lee K. White
Premier Pattern Equipment Ltd.
9725 - 60 Ave
Edmonton, AB T6E 0C4
Phone: 780-430-1549
Fax: 780-430-1526
Website: www.premierpattern.com
----- Original Message -----
From: <mugen121@...>
To: <mach1mach2cnc@...>
Sent: Thursday, January 26, 2006 9:31 AM
Subject: Re: [mach1mach2cnc] Whats the point with a Z bottom
limitswitch ?

before the toolholder hits the table.all you lose is an endmill

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Regards
Eirik Karlsen







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Regards
Eirik Karlsen

Hello Guys,
The main reason for "hard" limit switches is to keep the machine
from tearing itself apart whenever it reaches end of travel (either
extended or retracted). They are not normally designed to prevent
the tool, tool holder, or spindle from crashing into the table,
fixtures, or parts. This is why a "bad" g-code program can destroy
so many different things..... ie. parts, tooling, or worse a machine!

Thanks, Tim Bostic

ps. That is why it helps when you can become a good programmer &
machinist instead of an operator/button pusher.(See where the
machine "thinks" it wants to go & stop it before total
destruction!!)


--- In mach1mach2cnc@..., Eirik Karlsen <eikarlse@o...>
wrote:

Thorleif,
Machines are different so pix are probably not all that useful.
I'll ponder a bit more about this, may use a movable cam instead

and

leave this switch fixed like the rest of them.

Thanks


Torleif Jensen wrote:

My Denford mill has an easily adjustable Z switch - very simple
mechanics. I can upload a picture if you have a hard time

figuring out

how to implement it.

Often the part is held by a vice and far above the plane. Also

most

of
my tools are almost equal in length, so it's relatively easy to

set a

relevant negative Z limit. I have never needed it so far, but

one day

I'll thank Denford.....

/Torleif.

Eirik Karlsen wrote:

Well, on this machine its not a problem because the spindle

itself

(no

toolholder) stops at the table, and
it the table wasn't there the spindle could go a further 10-

15cm

down.

However the table
can not be moved sufficiently X-Y for that to happen. So Z can

reach

the

table even without any tool.

So wherever I'd place that switch it would either allow a mech.

crash

with the table, or with a shorter
tool there wouldn't be sufficient Z travel towards the table.

Either

way

the limitswitch would just be a nuisance.

Only solution I can see is if that switch was adjustable so it

could

be

adjusted to match the length of the tool
in use at the time. Probably not too practical with an

automatic

toolchanger, but I'll be using manual toolchange
so this might be a way forward.

I believe there are plenty of 'cnc-millers' on this list and

they

must

have run into this problem and possibly solved it.

I could go for a movable switch right now but would like to

avoid it

if

possible...tricky mechanics.
Would like some more input on this problem.

Thanks
E.K





Lee White wrote:

How about if your tools too short and then you will stress

out

some

mechanical part trying to go further down than it can.

This assumes you have soft limits out of wack.


Thanks,

Lee.

Lee K. White
Premier Pattern Equipment Ltd.
9725 - 60 Ave
Edmonton, AB T6E 0C4
Phone: 780-430-1549
Fax: 780-430-1526
Website: www.premierpattern.com
----- Original Message -----
From: <mugen121@a...>
To: <mach1mach2cnc@...>
Sent: Thursday, January 26, 2006 9:31 AM
Subject: Re: [mach1mach2cnc] Whats the point with a Z bottom
limitswitch ?

before the toolholder hits the table.all you lose is an

endmill

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Regards
Eirik Karlsen



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Tin;
Thank you for posting this, short and to the point

Message: 2 Date: Fri, 27 Jan 2006 01:12:40 -0000
From: "Tim" <luvindaddy@...>
Subject: Re: Whats the point with a Z bottom limitswitch ?

Hello Guys,
The main reason for "hard" limit switches is to keep the machine from tearing itself apart whenever it reaches end of travel (either extended or retracted). They are not normally designed to prevent the tool, tool holder, or spindle from crashing into the table, fixtures, or parts. This is why a "bad" g-code program can destroy so many different things..... ie. parts, tooling, or worse a machine!

Thanks, Tim Bostic

ps. That is why it helps when you can become a good programmer & machinist instead of an operator/button pusher.(See where the machine "thinks" it wants to go & stop it before total destruction!!)

You can always tell the "operator/button pusher" from the "cnc machinist/programmer" by the holes cut in the machines table.

Carl

Hi Erik:

Usually, you dont put in a lower switch, only plasma guys do that to signal torch has hit the bottom..

Thanks,
Art
www.artofcnc.ca

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