Machine Tool No 50 Taper

[DelMuir]

I am trying to find information regarding a recommended Maximum Radial Moment which can be applied to a No. 50 Machine Tool Taper. We have a Grinding/Cutting application working at the moment that is showing a lot of fretting between the Spindle and Tool at the Taper. Is there such a figure available.

 

[EnglishMuffin]

First, a question. Is this the same problem being discussed on this thread : Automatic Tool Changer Problems.
thread281-81884 ? (Just curious)

It's not quite clear what you mean by "Maximum radial movement". If you mean relative radial movement between the tool and the spindle, that should be almost immeasurable, at least at the front. However, if fretting is occurring, there will be some very small amount of movement. If you look at the standards for a 50 taper tool and the corresponding spindle taper, you will find that the tolerance on the taper is .001" per foot on both, but that the male taper tolerance can only be applied in the direction which increases the rate of taper, and the female taper tolerance in a direction which decreases it. This means that, assuming the tapers are 3" long, that there could be, in the worst case, a clearance of .0005" on diameter at the small end of the taper. If you notice more fretting there, that is most probably the reason. Since only the spindle taper geometry is controllable from the point of view of a machine builder, the very best that can be achieved is .0025" at the rear. When the tool is pulled into the taper, the front of the spindle expands slightly, and this has the effect of reducing the rear clearance, possibly to zero. The amount of this expansion is of course dependent on the drawbar pull and the design of the spindle. Some spindles have a relief in the central part of the taper, so that the tool only contacts on front and rear lands. Whether this helps is questionable. If, with enough drawbar pull, you can achieve a perfectly fitting taper, then you should be able to eliminate any possibility of fretting. However, tool ejection is another problem you can run into with high drawbar pulls.

 

[EnglishMuffin]

Sorry - ignore my post - I've just noticed that you said "Maximum radial moment", not "maximum radial movement"! I was thinking about that other post !
However, my comments are not totally irrelevant. In the mean time, I will think about the "maximum radial moment" question. Sorry !

 

[EnglishMuffin]

I could be wrong, but having done a few rough calculations, it would appear to me that with enough draw in force (which in some cases can go as high as 10000 lbf), and an accurately fitting taper, you should not get any tool pull-out with purely radial static loads of any magnitude before failure of the tool/taper interface. Under vibratory conditions and a weak drawbar pull, all bets are off. With Ott drawbars, the pull out force is theoretically limited by the draw rod stiffness only, since they have a self-locking wedge action. So I think the question you need to ask is whether you have vibratory loads, a weak drawbar, a poorly fitting taper, or some combination of these.

 

[EdDanzer]

Any time you have two parts connected there will be a level of non linearity. Even though this could be modeled in FEA, I don’t think you will get results that will be the same as measured. The best choice since these are common parts is to do a static deflection test to determine when an unacceptable level of deflection, or when non linearity is reached.
Kennametal originally published deflection values for their KM joint based on FEA results. Until we did a static test and found the numbers wrong they would not believe the joint was weaker then originally published. Kennametal did take back the defective parts for full credit and do not publish a load value.
So I doubt anyone will have good moment load information.