Shop Efficiency Part 5 : Re-Thinking Your Height Offset Strategy

As we have been stressing throughout this Shop Efficiency Series ... keeping your spindle running and the green cycle light lit is one of the main keys to making money and profits. In Part 5 we're going to shift our attention back to the VMC and HMC world and send out some thoughts regarding Tool Height Offsets ... "touching off" tools ... and how to get that inevitable task done quickly, easily and efficiently ... so that the spindle stays running and the tools gets in the chip.

Tool breakage or the need to replace dull or ineffective tools can cause huge loss of cutting times and spindle on time. With the implementation of the simple system we outline below ... you can insure that replacing or setting up your tools for machining can be done quickly and efficiently with as little disruption to cutting time as possible. There are some initial costs involved ... but the ROI is fast and you'll see the results immediately.

We'll take you through the Set-Up and Process first to show you how it works ... then highlight some of the Features and Benefits that can achieved by utilizing this system. The basic idea is to utilize a MASTER TOOL to set the part Z0 position ... and use the HEIGHT OFFSETS to calibrate the distance difference from the MASTER TOOL and EACH CUTTING TOOL. This system leaves us only the MASTER TOOL to re-calibrate for each workpiece ... and allows us to leave the cutting tools unchanged no matter what part we're running. Setting up ONE tool is obviously faster than setting up multiple tools.

What You'll Need :

1. Height Gauge ... digital gauge will obviously function the best.
2. Master Tool ( more details below )
3. Tool Holder Adapter or Setting Fixture

The Master Tool :
In order to utilize the features of this system, you'll need to create a MASTER TOOL. What we refer to as a master tool would be a piece of stock, say a piece of turned, ground and polished stock or drill rod loaded and secured into a tool holder. It should be secure in the holder ... the best way is with a shoulder butting against the tool holder face so it has a positive stop. Another feature is to make this master tool close to the length of the machine specs longest tool. This way you'll know that no cutting tool can be longer than this master tool.

Tool Holder Adapter or Setting Fixture :
Once you have created your stable Master Tool ... the next stable component should be your setting fixture. With a little thought and work you can turn a standard tool tightening fixture ... such as the ones pictured below ... into something suitable for this purpose ... with the main criteria being the stable repeatability of the tool holder positioning.

The Process :
On a surface plate, set up your height gauge and tool holder adapter to allow for the measuring of your tools. To measure a tool :

• Place the MASTER TOOL in the setting fixture and set zero at the top of the master tool.

• Place a cutting tool to be measured in the setting fixture and record the reading at the top of the tool's cutting edge. This is the distance from the master tool tip to the cutting tool tip. This dimension is the value that is to be entered in the machines height offset table for the measured tool.

• Repeat the second step above for each tool to be measured, recording the value on the height gauge for each tool.
• Load the tools in the magazine and enter the measured height offset values from Step #2 above into their respective height offset table positions.
• Using the MASTER TOOL, touch the Z0 surface of the workpiece and record the value from the home position to the Z0 location. This value should be entered in the Z table for the work offset (G54 - G59) to be used in the program.

That's it. 

Your program is ready to run. Your program will call up the G54 - G59 work offset or similar and will know the distance from the master tool to the Z0 location. Using the H value call in the program, the machine will calculate the difference between the master tool and the measured tool and adjust as required.

Now that we've set the thoughts and ideas in your mind ... feel free to deviate and expand on the basics outlined here.

Some Features and Benefits :

1. Let's suppose you're going to set up a new job next but will utilize some of the tooling from the previous job. The only set-up required is to use the Master Tool to touch the new Z0 surface, changing the value in the work offsets with this new value. Your cutting tools and their height offsets can remain the same. Save time by touching off one tool instead of many.
2. You can set-up a spare tool or replacement tool off the machine using the master tool and the height gauge ... insuring that your spindle will be back in the cut faster.
3. You can load say a nice cutting carbide mill in the magazine and use it for a variety of different jobs. No need to touch it off all the time, just use the master tool to get your work offset in Z.
4. Measuring tools becomes easier, allowing more people to assist with the tool setting . Setters don't need to know how to operate the machine.

From experience, once you try this method you'll find it saves you all kinds of time. The best advantage is being able to call out set tools that stay in the magazine. This really speeds up the set-up and changeover process.

Please come back for our next installment in our series on Shop Efficiency.

Until next time ... Happy Chip Making !!

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