Wire cup brush-how/where do you measure them?

[mart]

I have just bought a couple of new wire cup brushes off flea bay. Size 65mm, or at least that is the size on the box.

The disappointing thing is that the length of the bristles (18mm) are not much longer than the one on my angle grinder at the moment, that has had a fair bit of use is and is worn down a fair bit (13mm left on bristles).

I phoned a tool shop and asked where do you take the measurement from on the cup brush to check the size i.e. establishing brush is 65mm 80mm etc? The guy said that you measure the bell part I have measured my old one and the new one at this point and the dia is 50mm on both.

I am assuming one of the following:
Either the new ones are lesser quality ones with shorter bristles or, i have a smaller brush in a 65mm brush box. Is there such a thing as a cup brush that is smaller than 65mm?

 

[gordon stephenson]

I would imagine the 65mm will be the dia including the bristles. just like it says on the box.

 

[mart]

Hi Gordon.
On cup brushes, the bristles come out at an angle. So, the longer the bristles the wider the dia size at the bristles. For example, if my old cup brush measured 50mm at bell base (which it does) but measures say 80mm at the end of the bristles that is where the confusion is.(Maybe my old brush was an 80mm brush)

If what you suggest is correct, then some different sized cup brushes must have the same bell for several of the brush sizes-maybe 65 to 80mm for example, then the bell size increases after that?

 

[gordon stephenson]

Hello Mart,
Yes I know the bristles are angled, But the wires are usually a standard sort of length, No good having them too long at the speeds that angle grinders spin, too long and they would centrifuge outwards too much and not present the bristle ends to the work surface,overall dia seems like a good way to size them
Cheers Gordon.