FAILSAFE option needed

[myxpykalix]

I have a request from a wood carver who has a piece of African Mahogany that is 3'x5' and he simply wants me to rout out a 2.5'x4.5' square that is .25 deep so he can place a piece of glass over the carving when he is through with it and it will be handcarved by him to different depths.

The issue I have is that the piece is 2" thick and even with a short bit and a .10 height over the material I am afraid my Z height might top out and the bit fall into the material and ruin it. The material is valued at $475.00 and i don't want to have to pay for it if it does.

I need to figure out some type of failsafe "catch" that would prevent the router from losing position and falling into the material.

I was thinking of maybe somehow securing some strong wire that could connect to the carriage or something like that. If it was my wood, i would take a chance but i am superparanoid when it comes to other peoples property. I don't want to have to pay $500.00 loss for a $50 job.

Anyone have any suggestions?

[knight_toolworks]

the material is only 2" thick? that's not much. I have cut 3" material with 3.25" of bit and used .25 safe height. all you have to do is set it all up and do a test run without wood and see if anything bottoms out. for safety sake I would glue up some mdf in the same size and do test run.

[Gary Campbell]

Jack....
The "Failsafe" in a CNC operation is the operator. The operator should be able to audit the file and see the highest z movements and test, prior to cutting, if that height is workable.

In reality, there is no way to invent an intelligent failsafe. That said, there is only one intelligent part in the CNC chain, the operator. If you do your homework and feel the file can be cut, cut it. If not, pass and let someone else do it. Or, you could sit in the corner and wait for someone to invent a free failsafe program for you.

[bleeth]

You have 6 plus inches of z height Jack. This is a quick and easy that you shouldn't be too paranoid about. I'd chuck up my 1 1/2" mortise bit (Whiteside) and do it in two 1/8" passes with a 90% stepover. Plenty of guys would nail the whole 1/4" in one pass and frankly that shouldn't be a problem. If he needs the corners square let him chisel them by hand. Since he's a woodcarver this part is nothing. With the years you have had your machine I darned sure wouldn't worry about doing a "practice" piece. It is, after all, a simple area clear. Use offset strategy starting from the outside. When it starts cutting you'll go "Doh-this is just like surfacing my spoilboard!!"

Gary: Is "fell" anything like "feel"?

[zeykr]

Mostly watch your z height and Z home when you setup your material to make your toolpaths.

The other gotcha on thick pieces is your zzero routine - you may need to modify it so it doesn't raise too high after zeroing and hit the stop.

[nat_wheatley]

My only advice would be to not pause and restart the file at any point. I've had a number of issues with incorrect depths, and in retrospect, I think that all have been attributed to stopping/starting files midstream. Zero your bit and have at it, but don't pause.

This is a glitch in the control software that has yet to be ironed out.

[coach]

I just completed a job cutting 3" thick eps foam and used a 5" ball nose bit.
I have a 6" Z height but had room to cut this job.
Dave

[zeykr]

I've found you certainly don't want to pause and restart in the middle of a command such as CR. I have a problem anytime I do that, so I always move home and restart the CR.

[myxpykalix]

I did a test cut with a .75 endmill 3" length on a scrap piece of 2" walnut and the Z height wasn't an issue I guess i am just afraid of ruining an expensive piece of wood since just previously i was cutting some .75 mdf molds and the Z topped out and ruined a piece on me mysteriously.

I guess i explained it incorrectly in that i figured in a normal situation it would handle the 2" material but just incase i had one of those mysterious "gotchas" where the machine does something crazy...and it does happen without operator error, i wanted to try to be prepared so as not to ruin the material.

[Brady Watson]

Guess what? If you worry about it long & hard enough, you WILL screw up what sounds to be a total cake job. Stop worrying and doubting yourself & get it done.

A $500 piece of material is nothing. Try getting a $4000 sheet of material right on the 1st go.

Be deliberate & clear headed....You've been running your machine long enough now to not need all this support and coddling. Your nerves will get the best if you if you allow it.

-B

[myxpykalix]

My apprehension was only due to my previous "****-out" the other day and nothing i was spazzing out over.

I seem to recall a picture of a guy who cut a floor inlay out of metal and i'll bet you held your breath and said your prayers first!

[srwtlc]

If ya need a safety net, it wouldn't be too hard to setup a mechanical stop to limit the travel.

Other than that, just "Git'er Done". ;)

[Brady Watson]

You bet I held my breath...Thousands of dollars in special order brass & tight scheduling demanded nothing less than perfection.

Just do an air cut 1st. Then cut it for real. Easy, breezy, beauty-ful.

-B

[Gary Campbell]

Jack...
Looks like you got the job. The light in your room makes you look younger than I remember! :D

[curtiss]

How many times in the past few years have you lost position and had the z plunge into the material ??

If a problem, I would think only two options,

1) something physical on the z tower to the y car that would prevent a drop. or

2) something more FUN made out of a few electric eyes from your garage door connected to the E Stop. :)