Surface Finish Too Rough
I need to hold a certain surface finish and my parts are coming off too rough. I don’t have a finer grit wheel to try. What can I do?
1. Increase the wheel speed. This is the most common solution. Imagine you’ve got a little guy sitting out on the surface of the wheel with a shovel and every time that wheel comes around he takes a scoop. The faster you spin the wheel in a given amount of time the smaller those scoops need to be in order to take away the same amount of material. The smaller the scoops, the smoother that part is going to be.
So increasing the speed of the wheel should make your finishes smoother. That’s the most common solution. Unfortunately, in many cases when people are bore grinding they are already doing so at maximum rpm. So you have to do something else.
2. Increase Oscillation. Increasing your oscillation speed or the length of the stroke will make a smoother finish. This will increase the effect of the abrasive cutting at angles that are different from the wheel’s rotational direction, and will create more of a random grind pattern that should improve the effective surface finish.
3. Use Longer Sparkouts. The longer you dwell with no feed at the end of the cycle, the smoother your finish will be. This is because smaller and smaller “scoops” are removed each wheel rotation while the built-up forces within the grind system relax. This is likely to solve your finish problem but at the cost of longer cycles.
4. Make the Wheel Duller. This is counter-intuitive but if you still can’t get your part smooth enough, try using less aggressive dressing parameters to make your wheel duller and back off on your feed rate. You may lose a couple seconds on your cycle time but you will most likely get the surface finish you are looking for.
If you are running into this problem a lot, then it is time to consider purchasing a finer grit wheel; And look for part 5 in our top 10 bore grinding solutions…..fluctuations after dressing…in our next installment.