Quill tilt

[compact8]

It's an EMCO FB2 bench mill, hobby grade. I have trammed the head so that when the quill and head is locked, the spindle is perpendicular to the table. When the quill is unlocked for drilling and boring operations, it will tilt as shown in the picture. The tilting is due to the play between the head and the quill. It's perfectly usable for drilling because it's just 0.04 mm over 36 mm. However, when I do boring, the tilt is 3.5 times of that. Any idea why the results of drilling and boring are so different ? The depth of cut in boring is very small, just 0.01 mm in the final pass.

The material of the workpiece is mild steel. The tools used for drilling is a short 5 mm carbide drill held by ER25 collet chuck. For boring, it's a carbide bit held by a Big-Kaiser precision boring head. The hole size is very accurate and the finish is good so the tools and holders should not have any problems.

I have tried sweeping the table surface with the DTI mounted on the spindle. To reproduce the setting for drilling/boring operations, the quill was unlocked and lowered with the position held by a piece of steel wire tied to the quill feed handle and the quill lock bolt next to it. The magnitude of the spindle tilt measured in this way is very close to that of drilled holes so this is consistent. The result for bored holes is really puzzling ......

The head was locked in all cases so variation in head tilt could not be the cause.

Would like to hear some thoughts.

 

[RJSakowski]

You obviously have play in the quill, leading to the different tram conditions for the locked and unlocked states. The boring tool is by nature, an unbalanced tool so the tilt will be greater.

I would suggest using the quill lock to take up some of the play. For critical operations, I will tighten the lock just enough that I can still move the quill. It works for me on my RF30 clone of forty years.