Years ago, we were working with a VERY LARGE company on optimizing their tooling. They were having severe fretting on the tapers, One thing we noticed is that their pull studs could not be screwed into the toolholders by hand. This is a tell tale sign. We brought in a ring gage to prove that the knob threads were out of spec. But, it could also have been the toolholder, so inspecting incoming holders and pull studs with a thread and ring gage is a good practice.
Additionally, the guy in the tool crib (I hope he has retired and is not on LinkedIn) welded a 4 foot cheater bar to the retention knob socket. To remove a knob he installed, we had to heat the shank in a shrinker. Despite what we told him, he wouldn't even consider using a torque wrench. So, the next time we came in, we brought with us a NASCAR logo'd pneumatic impact wrench with a retention knob socket, but in between we installed what is pictured below, a torque limiting adaptor (they are known as torque sticks). They are made with different shaft OD's and will twist when its designated torque rating is reached. The tool crib guy wailed away on the knobs with his new gun and the problem was fixed.
"Variable Processes produce Variable Results" My favorite quote from Dr. Scott Smith of UNC Charlotte. If you want to create a truly lean, repeatable and error free process you must eliminate variability. Single purpose and preset. One product that can benefit from this is the very popular ER collet chuck. An ER spring collet is indeed a spring. If you drop one it will bounce. Like any spring, its properties change with how tight you compress it. If you under-tighten the collet the tool may slip or pull out. If you over-tighten the collet it will twist and distort the shank angle creating runout. Dynamically, the stiffness and damping properties of the tool assembly change with the collet torque, thereby changing the location of stable speed lobes. Yet, you rarely see users torque collet chucks. Recently when searching the internet, I came across this product from a company called the iSWISS CORPORATION. These are preset torque wrenches, one for each ER collet nut type (spanner and hex). They are inexpensive and with nothing to adjust and no socket to change, all variability, all chance for error have been removed. Find them here: https://lnkd.in/dSAVNc2
Staying on the dreaded side lock endmill holder theme, there is a significant quality gap, though this was not a comprehensive test. We measured two 3/4" stub length toolholders from two suppliers with a 3-point bore gage. After calibrating off of a ring gage, the first bore measured 0.751" and the second 0.75005". We also measured ten random 3/4" carbide blanks (as we did in the earlier post with 1/2" blanks). We then loaded each of the ten blanks in each holder (tightening the screw on the round blanks, no flats) and measured the total indicator runout (TIR) in a high end tool presetter. Toolholder #1 ranged 0.0011" to 0.0012" in TIR and Toolholder #2 from .00020" to 0.00030".
Side lock toolholders are still in use because, they still work in some applications. As we pointed out in an earlier post: https://goo.gl/gEaNuP
by design endmills are trying to twist and pullout of toolholders. Many other toolholders are held by friction only. Think of it this way; if you wanted to drive a gear or a sprocket from a motor shaft, would you rely on a press fit? You would use a key and a screw (or a spline). Dynamically, side lock holders can be made very short (1.75" gage length minimum) with significant damping.
Draw your own conclusions.
Before toolholder experts start throwing up their hands that I am discussing side lock endmill holders, the fact remains it is likely still the most popular toolholder is use today (rivaled by the ER collet chuck), therefore including them in our research is both relevant and responsible.
When measuring runout on a side lock holder once, we noticed extreme runout. We had measured both the bore of the holder and the shank of the endmill, but this runout was TWICE what it should have been based on those measurements. AND, it was perpendicular to the screw hole, not inline as we expected. What we found was the flat on the endmill was ground so the bevel of the screw made contact with the angles of the flat. We get what they were going for here, a more accurate taper to taper contact, but when we applied prussian blue and reassembled we found uneven contact points.
The tightening of the screw made contact on the center line as intended as shown by the lower arrow, but the twisting and downward force of the screw cause the tool to pivot in the bore. The end of the toolholder bore acted as a fulcrum.
Two of the four endmill brands tested had these narrower flats. Amazing what you find when you measure stuff.
As Professor Scott Smith from UNC Charlotte likes to say, "Random processes produce random results". If you have been following our posts you will have learned that a milling tool is a flexible beam and that changing the length of that beam, even a small amount, will change its frequency and can impact the tool's performance. You will also have learned that rotating a spiral fluted endmill in a toolholder can change the balance of the assembly significantly. If you have something running really good, you want to keep it that way.
Most toolholders other than side-locks use friction to hold the endmill shanks. So you need help to get repeatable tool changes. We found these wrench-free aluminum shaft collars from Ruland Manufacturing. The aluminum won't damage the cutting edges and holds up to the heat of shrinkfits. You can also use steel set screw collars or drill stops.
Set the tool projection from the tool tip, not the back end. Overall length is not a tightly controlled spec in ISO or ANSI, so measuring from the back or using backup screws will not give you a repeatable tool stick-out. You can use a caliper depth rod or depth micrometer to set the projection, just subtract the collar thickness.
Also, use the slot in the collar to orient the tip of one tooth, like a gunsight. This will retain balance. Look through the slot and rotate the tool until the tip lines up with the slot. If you are using variable pitch endmills, identify tooth #1 and set to that each time. Put a witness mark on the end of the toolholder and use that as your target when orienting the new tool with the collar's slot. Balance the tool assembly first, place the collar on the tool while still in the holder and line up the slot to a tooth. Mark the toolholder at the slot with a center punch or drill point. For a collet chuck, torque the nut to the proper value, then mark the nut just as above.
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