CNC tool height gauge

[Janger]

A frequent concern with CNC milling is making sure the top of the stock is known correctly and the tool in the spindle is set to the correct length. If either of these is wrong then you can ram the tool into the stock or table all too easily. I designed a height gauge to help confirm these details are correct. Below in the program line N55 moves the tool to 0.2" above the surface to be milled. Typically you step through the program to that line and then check the height. CAM programs typically generate this command before every new operation. Rulers are awkward to verify and just eyeballing it can be wrong. I don't know what other people do but I let the program slowly move the spindle to this height and then check it with the gauge. I started with a plastic one 3d printed which was very effective. Just recently I made one from aluminium. The step height on each step is actually a little under the nominal height so the gauge will just slide under the tool.

O00902 (Height Gauge side 2)​

(Using G0 which travels along dogleg path.)​

(T4 D=0.25 CR=0. TAPER=90deg - ZMIN=-0.007 - spot drill)​

(T9 D=1.9587 CR=0.005 - ZMIN=-0.01 - face mill)​

N10 G90 G94 G17​

N15 G20​

N20 G53 G0 Z0.​

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(Face1 2)​

N25 T9 M6​

N30 S1024 M3​

N35 G54​

N40 G0 X1.2731 Y0.0475​

N45 G43 Z0.4 H9​

N50 T4​

N55 G0 Z0.2 <- STOP THE PROGRAM HERE AND CHECK HEIGHT​

N60 G1 Z0.1859 F15.901​

N65 G18 G3 X1.0773 Z-0.01 I-0.1959 K0.​

N70 G1 X1.​

N75 X-9. F24.182​

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Figure 2 showing the CAM milling operations.

 

[Janger]

Picture 1 shows the tool 0.2 above part supposedly. Picture 2 shows the machine thinks it’s at 0.2”. Picture three shows the gauge just under 0.2” so yes it is correct. Also the old plastic gauge in the foreground.

 

[Janger]

So what do other people do? Just eyeball it?

 

[RobinHood]

No CNC here, but I do use paper on the manual mill to find the height. Or just touch with the rotating tool if it is a non-critical part.

Great idea for a height gauge. Looks nicely done as well.

 

[YotaBota]

I have been just eyeballing or just touching off as per Robinhood. I hadn't thought of using a piece of paper to get close. I just checked the lined paper in the shop and it averages .003 so that will be my newest tool in the shop.

 

[Tom O]

On the Craftex I’ve been known to use the cig papers for Z when lazy though to pick up x,y I run the cutter backwards so it doesn’t cut and look listen for the rub. The same idea is used on the Haas measuring tools.

 

[Tom Kitta]

I usually touch off and take off tiny bit.

Haas uses the paper method - you can get it very accurate that way - you lower the tool till you cannot easily move the paper under it. This should get you within 0.001.

The only more accurate method is using expensive gizmo. The gizmo is usually electrically connect spring surface to which a probe touches. Accuracy is very high - I guess its well within 0.0001.

I actually have a small step gague like the one you made - I just have to look for it.