Grain Size Wheel Profiles haas multigrind

Scra99tch · Oct 30, 2018

Hi,

I am thread grinding on a haas Multigrind. My thread profile has a .001 radius but the wheel I am using a 38A180 is breaking down way too fast. From my understanding the grain size on a 180 wheels is about .003".

How many grains should be at the point in order to hold form before the bond breaks down and ejects the grains, collapsing my radius? Should I look into using something J or harder or maybe even an M bond strength?

Thank you

Conrad Hoffman · Oct 30, 2018

If it's anything like holding a corner on a surface grinder, and if the manufacturer's data can be believed, you might need a 600 grit wheel to do 0.001".

Scra99tch · Oct 30, 2018

Yup, exactly what I was thinking, now trying to find an 8+ inch wheel in that size is going to have a loooong lead time. Just fyi how many grains should I have in the radius 1,2....10?

CarbideBob · Oct 30, 2018

A rule of thumb is that you need 3 grains inside the rad to be held.
Bob

Robert R · Oct 30, 2018

Scra99tch said:
Yup, exactly what I was thinking, now trying to find an 8+ inch wheel in that size is going to have a loooong lead time. Just fyi how many grains should I have in the radius 1,2....10?

The Norton tool room catalog lists wheels up to 220 grit in aluminum oxide and the SG abrasive.. The catalog says that the minimum radius for a 220 grit wheel is .0026 "

The V form CBN wheel is a stock item from other suppliers. A quick look shows that they are available in 600 grit. I do not know if "available " is the equivalent of " in stock".

Robert

CarbideBob · Oct 30, 2018

How are you checking a .001 radius?
We are at over 300X optical when doing this and I would be in micron graded wheels.
I can't do a .001 inside rad with a 800 grit.
Bob

Scra99tch · Oct 31, 2018

preliminary checking is on a comparator. With the thread normal view we measure the pitch of the thread. We see that the radius is positioned right at what our pitch is supposed to be, we then model this and find instead of a .001 we end up with close to a .003.

We also have a Microvu unit and I could try cutting into a block of graphite to see where our wheel just off dressing is cutting if need be. I feel somewhat confident from our grind that the wheel is just breaking down from lack of bond at the tip.

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