A schedule of preventive maintenance will help keep your spindle operating at peak performance.
Keep the spindle housing, fans and ductwork clean to allow free movement of cooling air. Clean tool tapers, collet cavities, shafts and collets clean using denatured alcohol. Never use lubricants or oils on tooling items. Failure to keep tooling clean can cause tool misalignment, imbalance, tool slip and poor-quality cuts.
Electric spindles need a warm-up period for best performance. Do not apply loads to a cold electric spindle. For warm-up, run the spindle at 9,000 rpm for 10-15 minutes or until the spindle bearing supports reach 98º F (human body temperature). This allows bearings, bearing supports and the spindle shaft to reach their designed dimensions and preloads through thermal expansion. Applying loads to a cold spindle will cause premature bearing failure.
If a spindle has been kept in stock for more than six months without rotation, it is imperative to perform an extended warm-up procedure before applying any load to the spindle.
Allow cooling system (fan, compressed air or liquid) and bearing pressurization (if used) to run for 10 minutes after stopping work. This minimizes condensation and prevents contaminants from being drawn into the bearing cavities.
Keep tools sharp to reduce forces, heat and to maintain cut quality. Monitor increases in electric current to the spindle to detect loss of tool sharpness. Heat generated from tools can overheat bearing grease, evaporate its essential components and lessen bearing life. Maximum bearing temperature of bearing supports is 150º F. Excess heat will cause tool holders to jam in automatic tool change spindles. Be sure all spindle sensors operate properly to avoid damage.
CAUTION: All PDS electric spindles with ATC are designed to accept only ISO or HSK style tool holders. BT tool holders are not interchangeable. Use only balanced tools and tool holders and rebalance all tools after each sharpening. Vibration from unbalanced tools can rapidly destroy bearings. Replace any worn, scratched or deformed tool holders and collets with new items to prevent tool slip and imbalance from run-out. Normal collet wear life is < 700 hours. Tool slip leads operators to over-tightened collet nuts and damaged threads.
Broken shafts, seized bearings, “welded” tooling, all can be prevented. Prevention = money in your pocket or more precisely, money you get to KEEP in your pocket. Let’s start with spindle basics. These bearings just don’t fail in one instant. They have been failing for some time. You’re just not paying attention. Most bearing sets in today’s spindles are rated for 6000-7000 running hours. Now there are a lot of variables here; material, chip load, balance, all have an impact on bearing life. Obviously the lighter the work load and the better the tool balance, the longer the bearing life. During every tool change the operator should carefully spin the shaft and see if there is anything that does not feel right. It takes about 5 seconds so don’t worry about wasting any time.
Typically, if a bearing is failing you will start to feel a drag or a rough motion. It may not “free wheel” like it used to. You might also notice an obvious decline in the cut and finish quality. These are symptoms of an expensive repair in the making. Now is the time to get the spindle off the machine and in for repair. If you are pro-active, you can schedule for some downtime. Dominate downtime, don’t let it dominate you!
Very often we see bearings destroyed and the result carries over to the shaft or the bearing housing causing catastrophic damage to the assembly. These usually come in with the spindle housing bluish/black in color. Now that spindle got noticeably hot before it came to a halt. Someone was not paying attention as this had to be making an incredible noise before it seized. Had it been sent for repair earlier, it may only have needed a bearing replacement and a balance. Remember that “money in your pocket” idea from earlier?
I’m not going to spend any time on tooling balance other than saying it’s one of the most crucial factors in long spindle life. Follow the manufacturers guidelines for the particular tooling you are using and make sure loose knives are all within 1/10th of a gram of each other.
Make sure the spacers and locknuts all are in excellent condition and the mating surfaces are free of burrs and nicks. The objective is that they all push squarely on the tool body, so everything is spinning perfectly and not running out of round and out of balance.
We see many failures that are mostly related to poor operation and maintenance. Always use the safety collar on your hydro tooling. It’s there for a reason. It prevents the tool from being welded to the arbor shaft when the hydro pressure drops during operation. We see more of this than you can imagine come through the door. Most of the time we can save it, but not always. Either way, it’s expensive.
Outboard bearings are the next in line for most failures. On most machines, the assembly is designed to “float” in the mounting plate so an axial spindle adjustment does not put any unnecessary preload (side load) on the bearing itself. For some unknown reason, some maintenance personnel or the operator alone feel these should be rock solid and tighten them down in the housing, so they can’t move. If the hydro-sleeve is pressurized when the operator makes an axial adjustment, it won’t take long for that bearing to fail. Again, a preventable expense.
Here is a common failure. It is predominately reserved for bottom spindles, but any location can fail if the alignment is not perfect. On most machines the outboard bearing plate is a slotted assembly on the bottom spindles. Meaning, the operator must break loose the plate BEFORE making a radial adjustment, so it can float with the spindle. Too many times the operator forgets or disregards the basic instructions and adjust the spindle without doing this. Now think of a paperclip that you bend back and forth until it breaks. That’s what is happening with every revolution of that spindle. The shaft is going to break in the same place every time. Right at the shoulder of the spindle housing. If you see this, I will almost guarantee this is the culprit. Avoidable!!
If you see this on the upper spindles, have a qualified professional check the alignment of the complete spindle/outboard bearing assembly. If you have multiple machines that are alike, make sure every OBB plate is in its original position (on the correct machine) and never swap them around.
Now here is where it gets interesting. There is a myriad of things that can go wrong on these. I don’t mean to discredit them, HSK is an excellent tool holding interface used in almost all of the most critical of material removal machines.
Dirt and dust! HSK does not like either of them. Keep the cone area free of these. Make sure the cone-clean feature is working and if you are not using a spindle on a particular set-up, put in the cover plug. Always!
This is what holds the tool in. If the spring tension is not within specifications, it must be adjusted. This is for both safety and cut quality. There are drawbar gauges and testing kits available for end users if they feel comfortable making the adjustments, otherwise, leave it to a trained professional. The spindle does not need to come off the machine to service this. And while we are on the subject of spring tension, avoid leaving the tooling in the machine when it is at rest overnight or over the weekend. When the tooling is loaded in the spindle, the springs are compressed. The longer they are compressed, the shorter their life. Simple!
This is also a key area not to be overlooked. The clamp group (which is the segmented assembly inside the end of the spindle) has a very specific adjustment. First for tool holding and cut quality and second for safety. If any of these segments are missing, cracked or severely worn, the tool cone will not be held securely in the taper. It could fly off, that’s the worst case. Secondly, it could lead to premature bearing failure. And the least issue – bad finish quality. Should you notice any of the last two, get the spindle off the machine and in for service. Something is wrong.
I bet you don’t think too much about this expensive little assembly? Out of sight – out of mind, right?
Do you have bad cut quality? Tear out when you should have chip-free cutting? Unusual vibration you never had before? Don’t be too fast to blame the blade. It could be the arbor. Bearings are not the only part that can wear. The arbor post, both flanges and pins can and do wear.
Have a close look at the pins as these take the most abuse. If they are worn out of round they need to be replaced. If the arbor post is supposed to be 40mm in diameter, is it? How about the flange surfaces? Are they nicked and worn? Many manufacturers do not have or want rebuilding services and would prefer to sell you a new assembly. These units are VERY rebuildable and for about 25% of the cost of a new one. Do your homework and find a rebuilder that has surface grinding and balancing capabilities. Keep that money in your pocket!
This is the next generation of preventive maintenance just making its debut in the wood industry. I recently spoke with Mr. Darcy Duggan of Techworkz Solutions, Inc., who has been instrumental in placing many of these monitoring systems in operation. I asked him to describe the concept; “In a nutshell, wired or wireless sensors are placed on critical machine components like router spindles, moulder spindles and arbors. These monitor bearing frequencies and temperature in real time and relay the data back to a central monitoring service. Should a monitored component report any abnormality, the service notifies the user by text message or email according to chain of command so immediate action can be taken.” Duggan said. This alone can save your company thousands of dollars per year in unnecessary repair costs. These sensors can also be used on any other critical piece of rotating equipment in the plant-like compressors, blower motors and vacuum pumps.
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