3 Tips To Grinding Round Parts With A Centerless Grinder
When looking at a centerless grinder, it may seem impossible to grind a part into roundness when compared to how center type grinder operates. In center type grinders such as an OD Grinder, the part is held into place between centers used at each end of the part to be ground. The grinding wheel is moved into the part and the high points of the part where it is out of round is ground smooth eventually creating a round part.
In centerless grinding the part literally floats between the two grinding wheels and is supported by a work blade as it is being ground. It would be impossible to grinding the part round when the part is set up improperly. However with the right set up, one can create a high tolerance round part.
Here are 3 tips to creating round parts with a centerless grinder:
(1) The centerline of the work piece should be placed as high as possible on the blade. If the part were to be placed on a flat blade and placed on the centerline of the grinding wheel and the regulating wheel the part would triangulate. The high point of the part when riding against the regulating wheel pushes the low point against the grinding wheel causing the triangulation. This is why the work rest blade is set at an angle, usually 30 degrees.
The angle of the blade allows the part to set up higher on the blade and also allowing the centerline of the part to be placed higher than the centers of the grinding wheel and regulating wheel. When the part now rotates, there is a gap between the work piece and the grinding wheel when the highpoint of the part rides against the regulating wheel. Eventually, the high point of the work piece is ground down and the part moves into roundness. Generally speaking, the higher the work piece is placed on the angle of the blade the quicker the rounding action.
(2) If and when the other factors, the blade angle and the work piece location above centerline of the grinding and regulating wheels, are set up properly, then the speed of rotation of the part can be helpful in creating a round part. The faster the work piece rotates, relatively higher speeds work best, the faster it will come into roundness. One thing to look out for is the work piece chattering because the rotation is set too fast. Manipulate the speed of the regulating wheel until you find the proper combination.
(3) Thrufeed grinding brings an additional factor to the table. The speed of traverse across the grinding and regulating wheels must be adjusted as well to help keep the part in round. It is necessary to adjust the feed slower to make a bar that isn't perfectly straight round. Sometimes, because the bar is so bent, it is better to straighten the bars first to help the centerless grinder to make the bars round.
Following these tips in your set up and while adjusting your speeds will help you make a part round or keep it in round.
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