Questions about a tool height touch probe

[Smokingman]

Many of my designs require several tool changes. Most of my time seems to be spend setting the Z-height of each tool. Because of this I've decided to automate it as much as possible (without investing in a auto tool changer).

I'm working on making a tool height probe, and I would like to get some opinions of what direction I should go in. I can think of 2 simple ways to do this:

1. A metal "button" with a plunger spring (so the tool won't crash into is during deceleration) that's connected to an input pin. When the tool touches it the pin is pulled to ground. The advantage of this is it's simplicity. The disadvantage is the normally-open nature makes it not fail-safe.

2. A simple normally-closed momentary switch plunger switch.This is more electrically isolated from the frame and is fail-safe, but requires a switch that always brakes contact at the same exact point.

Does anyone have any experience/suggestions on which way I should go? Or am I going in the wrong direction with both of these methods?

The next step will be writing a tool change macro for Mach 3, but I think I can handle that. I have programming experience, just not a log of CNC experience.

Thanks in advance,
Chris Esser

[jemmyell]

I would be very interested in a viable design for this also. What I would like to throw into the mix is the ability to work with router bits as small as .008. I regularly use bits in the .031 to .015 range but need to go down to .008 on occaison.

Anybody thought about an optical sensor?

Proximity switch maybe?

-James

[Smokingman]

I thought about optical as well. I guess I'm like you; I'll go from a 3/4" roughing bit to a .023" fret slot cutting bit in the same run. I can't think of a way to make an optical sensor that would accurately accommodate both extremes. It would need to be fine enough to sense the tiny bits, but big enough to accommodate the larger ones.

I was thinking if the landing zone was stable enough to be accurate and at the same time had enough give to prevent damage to the extra fine bits, it would work in all (most) cases.

-Chris

[jemmyell]

Hi Chris,

Maybe two (or even three) different optical sensor stations? One that was 1/4" for 1/8" microtools, one that was 1/2" for 1/4" shank tools and one that was 1" for all others?

Or maybe just the 1/4" one for the 1/8" shank microtools. The larger tools should be robust enough to use a spring loaded touch sensor if you could guarantee an electrical connection to the router bit.

The 1/8" tools I use come with depth setting rings so they would be close when they were mounted, but I reall need very precise Z depth control.

-James

[Smokingman]

Actually, that gives me an idea.

My 1/8" micro tools also have rings. If they all have the same ring (offset) depth, It wouldn't be too hard to write a tool change macro that checks to see if the new tool number is within a certain range (say 50-75). If the tool is within that range, then skip the probe and use the known length. Otherwise, use the touch probe.

-Chris

[jaybird22]

I have a Mazak CNC Lathe, and it has a tool setting touch probe. It typically is right on the money with accuracy to well under .0005. Why not get a replacement probe head, and use that to build your set-up. It will already be a sealed unit, and be sensative enough to accurately do what you're looking to do. Sorry if I'm off base on this. It's just an idea that popped into my head while reading your post.

[jalessi]

Smokingman,

The Auto Tool Zero in Mach3 works flawlessly.

We use it to set tool height on a .005 diameter cutter several times a day for years with awesome results and no tool damage.

Read the attached thread it is very informative.

Another Aussie Auto Tool Zero Setter

Jeff...

[hemsworthlad]

Dont know if this is any use to you or could be modified to do what you want.?

This thread Another Aussie Auto Tool Zero Setter

Also checkout the Vid for how sensitive it is, he use's a tiny bit without trouble. "http://www.youtube.com/watch?v=DOBxt9MIbFo&feature=channel"]YouTube- Auto Tool Zero

[shadowvoice]

For sure You can use quite installation seen on that video and I believe quite enough preciseness can be achieved. Just because of I hate an idea to attach separate wire to mill by clip and being extra lazy man - I went a way to create quite simply unit utilising end-switch to close a circut. I've made a touch probe producing repeatable measurements within 0.004mm which is more than enough for my job.
"http://www.youtube.com/watch?v=5Hwgx9aogdU"]YouTube- Tool length measuring block for CNC router

The biggest issues You will face creating that stile surface probe is:
1. Selection of right switch with perfectly repeatable action;
2. Design and machining body of surface block to maintain precise measurements in case of tool touches surface not in same point every time;
3. Dust-proof and tool safe design.

PS - as I dont have a time to follow posts here - pls mail me in case of questions.

[Stubby1]

If there a probe or a way to make a probe that is in continuous contact with the material to keep the bit at a precise height to the material? I engrave in sheet metal and it is not always perfectly flat so it would be neat to have a probe that continuously adjusts the tool height depending on the metal surface.

[shadowvoice]

If there a probe or a way to make a probe that is in continuous contact with the material to keep the bit at a precise height to the material? I engrave in sheet metal and it is not always perfectly flat so it would be neat to have a probe that continuously adjusts the tool height depending on the metal surface.

For that kind of jobs You need an "floating" spindle - see that unit.

[jalessi]

Stubby1,

Take a look at a spring loaded engraving tool.

[nomedia="http://www.youtube.com/watch?v=gjVpr_u0PVo"]YouTube - cnc spring loaded engraving tool scorpion[/nomedia]

Jeff...