Bit Diameter Auto-Measurement

A CNC owner seeks technology to speed up calibration of his equipment when switching among numerous tools with varying diameters. April 17, 2009

I was wondering if anyone knew of an electronic device/sensor that could be used for measuring bit diameters. Ideally I would like to mount this to my router and have the machine measure the diameters automatically, or at least run the bit by a sensor that has a readout for manual entry. Has this been done a million times and I am just in the dark?

Have devices like this been tried already and proven unreliable? Is there at least a table-mount device that can perform this? I understand that I can't measure all bits in this manner, at least just end mills and other straight tooling of the like.

Forum Responses
(CNC Forum)
From contributor M:
Length measurement is possible even as an aftermarket attachment, but I am with you, I have no idea why these machines do not calibrate diameters in a similar way. The increase in speed and accuracy gained with electronic touch tool is fantastic. It is standard on many machines, Multicam, Anderson and a dozen others. I miss the feature sorely on my Holz Her.

I am sure all of the manufacturers have a million reasons why but none I know of have addressed diameter compensation, but I can't see any valid reason it could not be done in a similar way to touch tool, and it would be a fantastic addition to any machine.

From contributor K:
How much more accurate than a digital calipers or micrometer do you want to be. If one hundredth of a millimeter is too far out for you then you should not be working in wood. If a bit is 18mm and goes away to be sharpened and comes back stamped as 17.8mm dia. then I reset to this and this is good enough for me.

From the original questioner:

I agree with you on just using what the re-sharpened value is, but our library of tooling is considerably large and keeping track of all the tooling is tedious. We change out tooling very often as our operations call for, which makes for a time consuming process to always stay on top of the correct bit sizing. We cut various plastics and wood products in all shapes and sizes, with quite a bit of oddball pocketing which makes the bit assortment and quantity difficult to manage. Automating the diameter measurement would eliminate steps in labor, speed things up, and produce more consistent results just as a start. I'm not out to get more accurate than with a mic, but at least get the same accuracy, just have the measurement process be part of automation as with the auto-tool length measurement - what a time saver!

From the original questioner:
To contributor Z: that sensor is right along the lines of what I'm looking for! I just need to see if I can fit it next to the tool length touch-off sensor and still fit it inside the dust hood around bit. Also, I wonder what its tolerance is to dust.

From contributor V:
Whenever our tools get sharpened i have the sharpening company measure and mark the diameter on a label on the tool case, this is especially helpful on three flute tools.

From contributor K:
Iím with you now. Having a big inventory of tooling can be a logistical nightmare and a recipe for ruined work during tool changes. In an ideal world we should have an infinite amount of tool holders and infinite room on the carousel for tooling.

From contributor M:
I also have my sharpening service mark the shank with the new diameter. It is not an issue I even think about anymore.

From the original questioner:
For re-sharpened tooling it is easier to know the diameter, but new tooling requires measurement also, as several threads on the forums have attested to. New tooling rarely comes in at advertised diameter. We could all "get by" by measuring tooling by hand and going off re-sharpened measurements, I am just emphasizing the point that an automated sensor would just be a big help and increase ease of use! If a sensor of this type is available and reliable, it would be a great help to see some options. Again, thank you for all the responses.

From contributor G:
We use a variety of machines to this, not just one and they are not inexpensive. When we send out any tool new or used ODís are marked on the package. We do tell our customers to reuse the same package when not in use, so they have an OD, when used again. Letís say we have just serviced a Diamond tool, we would have on record what the new OD was, plus the new OD .