Table top isolation and crash detection question

[Michael Simpson Virgina]

My new CNC has a aluminum table. I was thinking of isolating it from the rest of the machine (all metal). This way I could detect of the bit ever touches the table. If it does I could force an Estop. This could be quick enough to prevent major dammage to the table and bit.

[Paul Grothouse]

Techno uses this technology to to do bit length touch offs, it works very, very well.

My Andi however would a shove a bit through the other side of the table before this technology could decelerate it quickly enough. I have personally experienced this first hand because of a improper bit offset.

The best way I have learned to not have this problem is to set my origins in CAM to the bottom of the part. They I quickly scan the NC file to assure there are no negative Z moves, if there are then I know to go back and figure out what I did wrong.

[Jim Underwood]

One of my pet peeves on this subject is that you can spend over $120,000 on a machine, $30,000 in software, pay an operator $20/hr (or whatever), and none of them can tell you at all times where the end of the flippin' bit is...

If we can put a man on the moon, you'd think manufacturers would come up with a way to prevent a bit from hitting the table...

[Michael Simpson Virgina]

I use a probe to reference to the top of my material. The problem is If I make a mistake in my CAM software I can mill through my waster board into my clamp table. On my KRMx01 I use a MDF clamp table so its not a big deal. Its happened a couple of times.

On the KRMx02 the clamp table is aluminum. If I hit it, I am going to do more dammage, Most likly I will probably break the bit. Its not IF this is going to happen its WHEN.

The good news is that the table is made up of 80/20, 1030 strips. Very easy to replace one of them.

[Ross Moshinsky]

Put an adjustable limit switch on your Z axis?

Otherwise adding another MDF is a simple and easy way to protect yourself.

[Rob Wright]

if you can use a touch plate probe without attaching a second lead to your router bit ( I can do this with my hitachi - can't with my porter cable )- what about just assigning a B axis (or any other unused switch or input) limit pin to the table and connect a lead from the table back to the controller. actually, it could be run in series with your other homes and limits without any issue in Mach3. At that point anytime that limit was activated then mach3 would estop

[james mcgrew]

the camaster controller sets a low z limit, bit gets there it stops and notifies of an error!

[Mick A Martin]

My new CNC has a aluminum table. I was thinking of isolating it from the rest of the machine (all metal). This way I could detect of the bit ever touches the table. If it does I could force an Estop. This could be quick enough to prevent major dammage to the table and bit.

Are you running Mach3 or WinCNC, WinCNC has built in protect as Jim stated

[Gerry Grzadzinski]

Mach3 has Z Inhibit, which does the same thing. But you'll need to adjust the value whenever you zero the Z axis.