Frequently Asked Questions

How many times can a spindle be requalified?

After the spindle has been requalified 5-6 times, do I need to buy a new shaft?

How often does a spindle need to be requalified?

My spindle crashed.  I need my machine ASAP.  Can I hand-grind the machine just to get back into operation until you can get here?

How much space on the machine do you need in order to requalify the taper?

What does the axial deflection information on your Inspection Report mean?

What is the correct draw-bar pressure?

Does the brand of retention knob make a difference, i.e. does it affect the quality of the match between the tool holder and the spindle?

What causes retention knobs to break?

Is there such a thing as too much draw-bar pressure?

 


How many times can a spindle be requalified?

On a typical machine it can be done 5 or 6 times before any extemporaneous steps need to be taken.  It is necessary to check the gage line to the face of the spindle and the draw-bar pressure before and after each spindle requalification.  This is a part of the service that we provide, and should be done by anyone who requalifies your spindles.  As a reference it should be ౵" from the face of the spindle.  Various machine manufacturers may deviate from this number.  If the gage line is negative more than .015", make sure that the draw-bar pressure is adequate and that the tool changer does not have any conflicts.

 

After the spindle has been requalified 5-6 times, do I need to buy a new shaft?

Not necessarily.  The most palatable solution is to disassemble the spindle and hard chrome the taper.  This process adds additional material in order to bring the gage line back to the original specification.

 

How often does a spindle need to be requalified?

In normal use, it should be checked every year, or if you are having problems.  Premature deterioration can be caused by heavy milling, worn tool holders, foreign material getting into the spindle, declining draw-bar pressure, or "bumps in the night."

My spindle crashed.  I need my machine ASAP.  Can I hand-grind the machine just to get back into operation until you can get here?

We ask customers to not "help us too much."  Hand polishing to remove the gaul that results from spinning a tool in the taper should be undertaken with extreme care in order to not subvert the parent surface.  The material that has been "welded" as a result of the spun tool will be extra hard.  While trying to remove the weld, make sure not to remove too much material from the parent surface.  If you don't have to hand-grind, please don't.  If is very difficult to hold a tolerance of .0001" by hand.

How much space on the machine do you need in order to requalify the taper?

On a vertical machine:  We need approximately 17-1/2" of height under the Z axis and a space on the table to bolt to that is about 14" long and 8" wide.

On a horizontal machine:  We prefer to bolt to a blank pallet.

On all machines:  The spindle needs to be able to turn at approximately 100 rpm and the retention system needs to be operable.  If a machine is equipped with a rotary screw draw-bar that protrudes into the taper, then it needs to be pushed back out of the way or it needs to be removed.

What does the axial deflection information on your Inspection Report mean?

It's generally used as a baseline number to determine whether or not the spindle bearings are losing their pre-load through wear.  Contact the machine manufacturer to find out what their recommendations are for the axial deflection on your machine.  It can vary significantly even for different serial numbers of the same model machine due to internal feature changes by the manufacturer.

What is the correct draw-bar pressure?

This can vary greatly even by serial number in the same model machine.  We simply try to report what the actual value is and suggest for our customers to contact the manufacturer.  Most of the draw bars contain Belleville Disc Springs (also know as Belleville washers, disc springs, conical compression washers, and spring washers), which are cycle sensitive.  The more times they are flexed, the sooner they will go away.  If the retention pressure is too low, you will need to replace the Belleville Disc Springs in the machine.

 

Does the brand of retention knob make a difference, i.e. does it affect the quality of the match between the tool holder and the spindle?

This is a little-known fact in the industry.  Yes.  It makes a difference.  Use retention knobs that are ground on the surface that matches the top of the tool holder.  Also the surface where the collet lands on the retention knob needs to be ground.  If ground retention knobs are not used, it can pull the tool off to one side and affect the coaxiality.

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What cause retention knobs to break?

In the best circumstances, the tool holder, the retention knob, the collet, and the spindle all turn together simultaneously.  When the tool holder taper doesn't have a good match, the retention knob becomes the flexure point.  You simply work the tool holder (it bends) and breaks due to fatigue.


Is there such a thing as too much draw-bar pressure?

As a practical matter, no.  Only to the extent that you start to stretch the retention knob would it become too much pressure.  For instance, a Haas style retention knob is well capable of withstanding 9000 pounds of draw-bar pressure and not stretching the knob, if it is made from any reasonable material.

     

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Disclaimer:  We make no warranties as to the results to be obtained from the use of this information.  Always defer to the wisdom of the machine manufacturer who understands exactly what has been engineered into their system.