There has been a lot of discussion about how well made the IH mills are, and particularly about the quill runout. I thought I would take a couple of measurements on my machine (received at the beginning of the year) and share the results. YMMV.
Over the entire travel of the quill, 5", I measured a maximum deflection of 0.0075" on my Interapid indicator, which is much less than the 0.020" in 1" some others have experienced with early versions of the mill. Quality controls must have improved with time.
A couple of other important things to note. A huge amount of that deflection was in the last bit of maximum travel, backing off just 1/2" and using 4.5" of travel, the max deflection falls to 0.005". Over the course of an inch, it is slightly over 0.001", which ought to be fine for most HSM boring operations, but is still not great. For comparison, I found a copy of the Wilton B'port style mill manual somewhere on line and it lists the equivalent spec for that knee mill as being 0.000984", which is less, but not hugely so.
I was also curious how the Z-Axis was behaving, and so took the same measurements moving the Z-Axis with the quill retracted. The results are dramatically better. With my setup, I was only able to measure over about 1/2 the travel, or 10" (need to find a nice big cylindrical square to do better). Over that distance I got a maximum deflection of 0.00075", which I though was quite good. Note that I have not squared the machine (i.e. shimmed the column mounting bolts for squareness), but I had just trammed the machine in very carefully. The equivalent spec for the Wilton is not nearly so good, as they are quoting 0.002362". Another comparison is Tormach, which lists a figure of 0.001378" for 5.9" of travel in their QA spec document, so the IH would have qualified well within that spec.
I took all of the measurements a half dozen times, and found them to be completely repeatable as well.
It seems to me that quill operations can be handled just fine on the IH Mill, but if an extra measure of accuracy is desired, use the Z-axis and these mills are pretty darned good. I suspect an enterprising HSM might find some ways to tune up the quill so it performs better. My mill's future lies with a CNC conversion, and I will definitely look to drive the z-axis off the column rather than the quill for best performance.
I hope this helps those who are interested in understanding this mill's capabilities. I am pleased thus far with the mill's performance, and looking forward to continue to test its limits.
Best,
BW  |