Tool Measure

[gcoding]

I am thinking of purchasing a Shopbot, I just have one question. If I make manual tool changes, is there so sort of tool measure switch other than the zero plate. The table I use now has a tool measure switch. I have the program wrote up to cut the router off, wait for the bit change then automatically measures the bit and goes back to work. Without having to program gcode for each tool change or stopping in the middle of a file. etc...

[bcammack]

The Z Plate is tied to Input #1 and the clamp is tied to Ground. Presumably you could tie one side of the tool measure switch to ground and the other to Input #1 and effect the same result.

Is the program you wrote for a ShopBot or for something else? That's a little unclear from your post.

It'd be fairly easy to have your production programs FP a standalone sub-program that stops the spindle, waits for user input (after they change tools), goes over to the measure switch and does the measurement, then reenables spindle start, prompting the user to hit "Okay" after the spindle is running.

[paul_z]

Jeremy,

I hope I understand your question. I have a PRT Alpha and I change bits all the time without reregistering the current placement of the router. I move the router to a convenient location (making certain the bit is raised enough to clear everything). Being a tad cautious, I disconnect the power to the router, change the bit, reconnect power to the router, and do a “home” command. Even if I were to move the router (which is really hard to do and has never happen to me) the controller would move the router back to where it should be.

I think the PRT (non alpha) would be just as difficult to make an uncommanded move but it won’t automatically recover. (At least that’s how I understand the PRT to work.)

If you turn the shopbot off and change the bits, it would be extremely likely that you would alter "current position" and have a mess on your hands.

Hope this helps.

Paul Z

[richards]

More details about the tool measurement switch, please.

Do you rapid move to a point directly above the switch and then move the z-axis toward the switch until contact is made? Then, do you set the z-axis height to zero? And finially, do you raise the z-axis to the height of the material you're cutting and then zero the z-axis again? That procedure, or something similar to it, could easily be programmed into your SBP files.

[gcoding]

My program calls in a sub program when a tool change comes up in the gcode. The router moves to a preset position Then the router shuts down. I change the bit then I hit enter the bit moves over "above" the tool measure switch slowly lowers until the tip of the bit hits the switch. When that happens the sub program accounts for the bit lenght offset. Then it raises back up and waits for the command to start again by hitting enter the router starts back up again without loosing my place or having to do anything else. I have to zero to the top of the material one time in the begining "one time"

This is the way I do it with the table I have now. I was just wondering how shop bot does it. Because I do not want to have to zero in the material top everytime I make a bit change. That is just waste full in time.

Remember guys I am thinking of purchasing a Shopbot

[richards]

Jeremy,

When you code for the Shopbot, you would follow amost exactly the same procedure.

1. Mount a contact point somewhere off the cutting area of the table that is still easily accessible to the cutter. Connect the contact point to an unused input on the controller board.

2. Install and use a z-zero plate (either purchased or home-made) to determine the top of the material. Connect the z-zero plate to an input on the controller board. (Or use a caliper to physically measure the thickness of the material).

3. Do everything else in software.

There are variables that you can access at any time to show the current position of any axis.

Your code could so something like this:

1. Z-zero the first cutter to the top of the material.
2. Make cuts with first cutter.
3. Turn off router/spindle (SO,1,0)
4. Move router/spindle to be directly over contact switch/plate
5. Move z-axis down until contact is made with switch/plate
6. Read z-axis true location from Shopbot variable and store it in your local variable
7. Move router/spindle to cutter change position and change cutter
8. Move router/spindle to switch/plate
9. Move z-axis down until contact is made
10. Set z-height to value that you stored in step six
11. Move z-axis to safe height
12. Turn on router/spindle and continue (SO,1,1)

With appropriate pauses entered into the code, your only intervention would be to zero the z-axis at the beginning of the program (or enter a pre-measured thickness for the material) and cutter changes. Everything else would happen as commanded by the code.

[paco]

Jeremy,

this can be done too with the Bot. You can do this with a fixed Z-plate or a switch like you use now or whatever sensor you can think of that would detect the touch (tip) of the tool bit. Some of us use this sort of zeroing technique but, for me, it has prove to save time only on long project (over a single material/sheet good) with more than say three (four-five-) tool changes. Other than that, I haven't saved much time (considering the time I spent to code the routine, the time it take to run the routine slowly enough to be accurate, the time I take now to zero with the Z-plate). As you mentioned, you still have to zero once at the start of the day (or whenever the control software crash) to index either the spoilboard surface or whenever the surface of the material change... Since I've installed this upper Z limit switch, I now never hit the limiting bolt that keep the Z rail assembly to disengage (going further than the rack length) which has improve a lot the system. One still have to be careful when changing from a very long tool bit to a very short one...

Can I ask how accurate this switch as prove to so far? Any pix of your setup?!

It's all up to you to decide on to get a Bot or not... but there's more than the Z zeroing aspect to consider about... you know that right? ;-)

[gcoding]

Thanks for the replies, I have no problem using the Z plate off of the material at bit changes, it sounds like it would be really accurate maybe even more accurate than my tool measure switch. I just wanted to know how the process works. The main concern is having to break up the file to switch bits. I have friends that had to run files for each tool change ie: rough, finish, v bit and so on.

Once again thanks for the replies on this matter, but while I have a few of you here how is the 3D speed, and has anyone ever had the z axis lose count at high speeds. What is the average speeds used for 3D machining...

[paco]

Depends a lot on the relief. If it has pronounce step (vertical walls or close to) then it'll slow more from any set speed. 3D ramp threshold (from VR command; set the value to a higher number like say 300 to 500) has prove to be what I was looking for to speed up 3D toolpaths in soft materials. This make tool (Alpha) very aggressive. Set it back the 100 (or close to) after 3D toolpath to make sure it doesn't create problem with tabs...

Still, with small brittle tool bits, you won't push it much ... unless you like to snap carbide!