Work Zero Location? Centre or Edge

[Khalid]

Dear All,
Recently finsihed a Vertical Mill and now going to machine some metal...I have confusion in selecting work zero position (The position of initial Tool ) or Program Zero. What should I do?
1- Selecting the Centre Top of work piece as Zero
2- Selecting the Cornor as zero

Please guide me and help me what strategy is best? Considering subsequent tool changes what is best?

[txcncman]

What is best is what you decide. Indecisive people do not make good machinists or CNC programmers. Most jobs work well with edge finding for rectangular stock and center finding with round stock.

[Khalid]

Thank You txcncman
Actually I have a good experience with CNC woodworking where i always keep Program Zero at the centre of the part. The difficulty was the tool change and their i always have some error but in wood working 0.5mm error is nothing .The error was due to the fact that the wood en pocket machined at Programm Zero location.... Now as i am going to use Mach Screenset 2010 by Gerry, the tool zero will be perfect in my wooden router.....


I have seen that many CNC programmer prefer edges for program zero ... So, how can i make a simple probe or edge finder to get the edges zero on Milling Machines( No insulator)..

Regards

[txcncman]

You can touch a tool of known diameter to the edge of the material and then raise the cutter and move an addition distance of the radius of that tool so that the center of the spindle is aligned with the edge of the material. This location would be the zero point for that edge.

[Eurisko]

khalid,

I've admired your work for some time. Nice to finally get a chance to talk with you.

Manually finding the edge of a workpiece is easy. The least expensive way is to use the shank of a drill or end mill. Chuck the tool in your spindle. With the spindle OFF, position the tool close to the edge of the workpiece. A thin piece of shim stock (.005 in. or so) is inserted between the tool and the workpiece.
Repeat until the shim just clears. This technique can easily find the edge within .0005 inch.

Your distance from the edge is the tool radius + the width of the shim.

A variation of this method is to use an offset edge finder.

edge finders

This type of edge finder consists of 2 cylinders loosely held together. The edge finder is held in a RUNNING spindle, 500 rpms or so. The bottom cylinder is allowed to contact the edge of the workpiece and is pushed off center, providing visual feedback.

Your distance from the edge is the edge finder radius.

[Khalid]

Thank You Eurisko and txcncman
You have described the best way to getting the edges manually and thank you for taking time and helping me... I am looking for DIY type electronic edge finder similar as most of the people using on wood router and getting accurate Auto Tool Zero and edges in Mach3.
I am thinking of ways how to get either my workpiece or tool insulated on Metallic Milling machine to get the edges zeroed from the endmill or any tool in the spindle..

[RICHARD ZASTROW]

Often the lower left corner (closest to the operator side of the machine) is used to determine X-0 & Y-0. That way everything is a plus direction from zero. This applies to absolute programming.

Dick Z

[Eurisko]

...I am thinking of ways how to get either my workpiece or tool insulated on Metallic Milling machine to get the edges zeroed from the endmill or any tool in the spindle..

khalid,

The industrial CNC machines use a touch probe to zero a workpiece. The probe is loaded into the spindle with the automatic tool changer. The probe communicates with a fixed base unit via infrared emitters and detectors. The base unit detects the signals from the probe, and passes the information to the CNC controller.

Would be fairly challenging to build a system like this, and write the software to control it.

The workpiece only needs to be zeroed once before machining.
Zero the workpiece, machine it using whatever tools are required. Subsequent tools don't affect the workpiece zero.

[HelicopterJohn]

Hi Khalid,

Do you have a picture of your milling machine that you would like to share?

Do intend to machine only metallic parts, or will you also be machining plastics, wood and other metallic parts?

I am currently using the 2010 Screen Set on my Shopbot Router. It has included with it some probing routines. I have not implemented any of them yet but I think they would be of some help on your milling machine.

I use the 2010 Screen Set Semi-Automatic Tool Change and it is Awesome!!!! You have to install a fixed plate on which all tools are referenced if you want to use multiple tools in your program. It also has a system that allows you to designate a tool change position. On my router I have designated the tool change position at the front end edge near the center where I can easily change tools. The system directs you to touch off the first tool using a movable touch off plate on the top of the part, then it touches the fixed plate to establish a reference. Then each tool after that is referenced on the fixed plate to establish the correct offset in reference to the top of the part. They have a video on their website that shows this system in action.

I would think you would be able to adapt this system to your milling machine. It may require some easily removable fixture setup plates. If you using a vise they could possibly be attached with magnets etc.

I have a Renishaw Wireless Probe and Tool Setter on my HAAS TM-1P. One of the macros that it has one that checks the diameter of the tool while it checks the length. I would think one of you macro experts out there could develop one for use with Mach 3. One of the items in the macro turns on the spindle at say 200 rpms running the spindle in reverse so that it rubs the tool on both sides of the carbide setting devise instead of cutting it. It will not be as accurate as the Renishaw but might be something to look at.

Just a few thoughts that may be of some help.

John