CNC tooling slippage
I was advised to take the 12-13mm collets and replace them with true 1/2" collets. The tool that has slipped (on more than one occasion) is a 1/2" upcut 3 fluted spiral chip breaker. Is this bit too aggressive or should we stick to a twin flute? Obviously, circumstances determine the tool needed, but some of this changes with the use of a flat table and spoil board. Our rates for the current tool that slipped were S18000, VF3 and a feed rate of 8. We were cutting solid 19mm maple and penetrating 17mm with one pass. We’ve also tried scuffing the shanks to remove the polish.
Any advice on tooling? I’ve had more success with up/downs, but they’re not the best choice when not fully penetrating.
Make sure that the shank of the tool goes all the way through the collet to get maximum grip on the tool. You do not want a tool only part way through, as the back of the collet can collapse and loosen the grip of the front part. Definitely throw the range collets away and use a true 1/2" collet of the correct length for your tool holder. Yours may be a little too long and bottoming out before properly gripping the tool.
You were correct in replacing the collets for a true 1/2". Many manufacturers of collets claim they have a 1mm collapsibility. The truth is, with feed speeds going up, true IDs are a requirement for collets, as well as bearing collet nuts. You did not advise to the RPMs and helix angle of the tool. Once this info is provided, I can assist you. I believe you are machining at 8MPM, which should be at 13-14,000 RPMs. If you are penetrating at 17 mm, you can achieve faster feed speeds with an up/shear tool. Using one of Courmatt's CRU-500-1 1/2 x 1 1/4 x 4"OAL x 3 flute, machining speed would be at 20MPM+ at 17,000 RPMs.
I hesitate to mention this because I haven't tried it, but I saw an ad in a metal working magazine for collets that gripped milling cutters with a solid collet. You put the collet in a specially designed heat chamber. This expanded the metal. You insert your bit and when it cools down, the bit is solid within the collet. (I may have this backwards - cooling versus heating - but you get the point.) I assume that the loads on a metal cutting application would exceed woodworking.
Have you tried a hydro collect? We have a Biesse Rover 30. We machine solid 30mm tops with a 16m 3 flute up roughing spiral cutter, feed speed 12mpp without any slippage. Only problem is that hydro collects are costly.
From the original questioner:
We had another bit slip this morning. This time it was a 6.35mm 3 flute upcut (happened while cutting through 13mm veenered flk). Has anyone else had these same problems? Should it be mandatory to re-tighten each HSK cone each week? Has anyone used tooling with "matte" shanks? I was informed that Southeast Tools have tools with a duller shank. Currently we have been purchasing solid carbide tooling from Vortex. Could it be the HSK holders that are the problem? We are still using stock Biesse HSK holders. We have purchased some after market holders and I'm going to try a couple.
If you haven't replaced your collets yet, you haven't attacked the root of the problem. I make sure that my guys really clean out the collets and holders when changing bits. I also purchased a torque wrench so that every time any of the guys loads a tool, the force to tighten the collet nut is exactly the same.
I read an article in Modern Woodworking (Jan. 2002) on a Teflon-coated collet nut by Techniks that claims to be 40% better at holding.
When we first had our Rover 27 installed, the tools slipped a lot until we clamped down on them more.
From contributor E:
I have a Biesse Arrow, with HSK63F tool holders, ER40 collets. I suspect this is the same as you are using. I have only experienced tool slip on two or three occasions, which could be explained by other circumstances. I regularly push the envelope on feeds and speeds. It is not the tool holder! A Technique's Torque wrench and nosepiece adapter will ensure that you are tightening the nosepiece enough. There are a host of options for nosepieces, from ceramic coated to ball bearing style, and they run a wide range in price. You have been advised about the importance of collet care, cleaning and sizing issues. Unless you are using something different than HSK63F with ER40 collets, you should really try replacing the collets with proper size and style collets for the tools being used, and make sure you Torque the nosepieces properly. If your nosepieces are showing galling on the contact ring (where the collet contacts the inside of the nosepiece), you will have to replace the nosepieces as well.
Just to review a couple of points about tool holders and collets:
b) Changing tools: Completely disassemble the three components, and clean every one with a non-residual cleaner like alcohol. Do not use WD on the inside of the collet - WD and similar products attract and hold dust, while what you want is a clean, dry fit between the collet and tool shank. Technically, you should not use WD or equivalent on any mating surfaces in the tool-tool holder-spindle equation. I find that a little WD on the nosepiece threads and contact ring help ensure a good tightening, and protect against galling of the collet or nosepiece.
2) Collets are a wear item. The are subject to wear from normal use, and can be damaged in the case of tool breakage or dropping or improper torque - too little and the tool slips and degrades the inside of the collet, too much and you may damage it or the tool holder. Fortunately, there is an acceptable torque range. Collet style and tool holder nosepiece will dictate proper torque values.
3) Collets have two contact surfaces, both of which are critical to the proper mounting of the tool. The visible outside is what mates with the collet pocket in the tool holder, and must be free of dirt, debris, burrs, pieces of paper towel, etc. Rust is definitely not your friend here either. The inside of the collet is harder to deal with, but is probably the most abused. Acquire a selection of bore brushes (copper or brass work pretty well) and use those every time you change tools. An ultra sonic cleaner is on my wish list, but the object here is to make sure the bore of the collet is clean. If it is blackened with resin, you will not get a good grip on the tool and the tool with not run true. If you have a tool break off inside the bore of the collet, throw away the collet! If your tools regularly show little dark marks where the collet grips, you are having tool movement - this is not a good thing.
4.) Collets are designed to grip a tool shank, but not just 1/4” of the end of the shank. The best case is to have the tool shank long enough to be gripped along the entire grip-able length of the collet. In practice, if you get 75% of that, you're doing okay. If less, use a “collet buddy” or other plug at the rear of the collet to keep the grip surface parallel. The plug must be a precision piece. Follow the instructions on use and placement.
5.) Nosepiece. The collet and nosepiece are designed to snap together on the standard Biesse HSK tool holders (and every other tool holder I have ever seen except one, an ultra high precision, very high speed nosepiece, and I am fairly sure that nobody in the wood industry uses them). The Biesse tool holders that I have use an eccentric relief retainer in the nosepiece. You get the collet in by tipping it a little and pressing it into the nosepiece. It will “snap” in and then you can thread the nosepiece onto the body of the tool holder and insert tool, etc. I point out this last issue because many years ago, when I first had a collet and nosepiece (for an old Perske 5 or 7 hp collet spindle), I did not know about that snap-it-into-the-nut-before-you-tighten-it-up. That makes for a tough time getting the collet out of the spindle. It was several tool changes later when somebody educated me.
6) HSK63 tool holders, and HSK in general, is a very robust, rigid, axial constant repeatable tool system. However, it is also very finicky when it comes to cleanliness. Do not use WD or similar protectants on the cone or contact flange - use only the recommended dry protectant that Biesse (or your machine's manufacturer) recommends. The HSK system is sensitive to contaminants that get where they don’t belong, and compromise the otherwise excellent accuracy and rigidity of the system.
Summary: Clean everything every tool change - tool, collet, nosepiece and body. Every time. Use alcohol on mating surfaces, not WD. Use quality collets - the issue of on size collets can be argued as optional, but they will provide the best grip, and the better accuracy. Inspect tools for signs of collet wear - distinct “etching” like scallops on the shank of a carbide tool indicate slight movement of the tool in the collet - the more pronounced, the worse the condition. Onsrud publishes a very excellent article on collets and their care.
Heat shrink collets are available, but are pricey, and can only be used with carbide tooling. If you fit a steel-bodied tool into a heat shrink, you now have a permanent steel-bodied HSK tool. The heat shrink technology works on the simple principle of differing coefficients of expansion - as the tool holder is steel, the tool better be something with a lower Ce like carbide, or they will not be separable. This type is pretty neat, but a hydrolock seems more applicable to the wood/plastic/aluminum cutting we do on routers. I do not own any hydrolocks for the router, but I have been involved in their use on moulders. They are much better than slip bores, but when they fail, and they inevitably do, they tend to thrash things a bit more than a slip bore. I will defer any recommendations for or against the use of hydrolocks to those who actually use them. Ditto on the shrink fits.
I've got an Anderson Statos-sup. I've used profiled tools 3-4" diameter, 2 cutting edges, 250-350ipm, 12-14,000 rpm, and taking some meat out of MDF, and not once had a tool slip. I just tighten them well - you know when to stop when you get the feel of it.
One of the major contributing factors for tool slippage in the collet is as follows. When the tool is put into the collet it should not bottom out in the holder. When the tool is bottomed out, the collet cannot collapse properly around the shank of the tool. If the tool bottoms out in the holder, the tool should be pulled back about 1/8 of an inch to allow the tool to be pulled up as the collet collapses. This is a problem when tools are put into holders that are turned upside down for tool installation and tightening.
From the original questioner:
I’m beginning to think that it’s the actual HSK holders from Biesse or the nuts. We have replaced the collets to all 1/2” and have been “surgically” cleaning the holders and all components. I was told that another tool slipped yesterday afternoon (this was with a new 1/2” collet, surgically cleaned, etc.) We have had two previous Biesse machines prior to this (using ISO30 cones) and never had any notable issues for 6 years. We purchased a few Guhdo HSK holders that I’m going to try next. If this resolves the issue, the cones or nuts are the problem. In that case, credit for (7) faulty cones will be on my list of follow-ups.
With nearly 20 years in the CNC arena (mostly metal), I must agree with contributor E. The information he presents is in keeping with advice from any reputable tooling manufacturer. You would be well served to follow his philosophy. Or, you could take the less scientific approach. Torque it 'till it strips and back off a quarter turn!
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Comment from contributor T:
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