I am milling 1.5" construction grade lumber. So I am using a upcut bit with a 2 inch cut depth. I have back my feed rate to 50 inches per minute and my pass depth is a quarter inch. There is really not much chatter at all by after a while the collet loses it’s grip on the bit shaft and it starts to slip out. Does anyone have an suggestions? On another forum someone recommended ER 11 collets. I am open to anyone else who has insight.
@kendallcaputo What router/spindle are you using? How far into the collet is the end mill?
Edit: Also, while you don’t want to overtighten, be sure to use two wrenches to tighten the collect nut, and not the red button/one wrench method.
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I like to clean the shank on the bits with rubbing alcohol before putting in the collet. Also clean the collet with alcohol, and like Grant said properly insert the bit to proper length.
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@kendallcaputo To elaborate on what @gwilki asked about how the far into the collet the bit is, I learned the hard way that you can’t put the bit into the collet as far as it can go. When you tighten the collet it squeezes the bit by pushing the collet up into the router and if the bit is already bottoming out it could damage parts or just not get a good grip on the bit causing it to be fine for awhile but then slip out at some point.
I ran into this when using a long bit on thick stock and with a 2" cut depth I’m assuming your bit is pretty long.
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Well, I came up with a solution that works. I superglued the a collet insert onto the shaft of the bit. It works great! Who would have thought?
How many times have you had a problem with bits moving in the router? I am wondering if you have actually squished the nut enough that you have misshapen it to the point that it won’t hold the bits? I would buy a new nut for it before relying on crazy glue to keep your bits in place. Actually buy a new nut and the insert for it to be safe. You shouldn’t have to wrench down real hard on them to secure them .
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Great suggestion. It is certainly easy enough to replace. But for the record. I am only having the problem with one project. I am cutting many parts out of 2x construction grade lumber for outdoor furniture. The wood is pretty wet, unstable and has a lot of tension in it and I am cutting some compound shapes that really pushes the limits of a bench top CNC. I have to use an upcut bit with a two inch cut capacity, the combination of the wood and bit results in a tremendous amount of vibration even with very conservative feed and depth of cut settings. I can cut hardwood for signs or trays etc., without any issues.
@kendallcaputo It’s good that you have fixed your problem. I will say, though, that you may want to keep an eye on things. A CA bond between metal is extremely brittle and prone to snapping/shattering. In your application, if that were to happen, the results could be dangerous.
Usual preface, I’m with PreciseBits. So while I try to only post general information take everything I say with the understanding that I have a bias.
You can’t use these. I have no idea where it come from to try and swap in “close” ER sizes in routers (not counting routers with ER chucks). The issue is that all these systems are based on compression of tapered section. This means that the taper angle in the router/spindle needs to match the collet. If it doesn’t, at best you will “pinch” the front or back of the taper and only get compressive force from that “pinched” area. For reference all ER collets are an 8° taper.
If you are having to do this to keep the bit from slipping then you almost certainly have a sprung collet and should replace it as it’s not only letting the bit slip but increasing runout. Using something like super glue will also almost certainly cause additional runout.
If you’re not aware runout is how much the tool will spin off the center axis of the router/spindle. Most people don’t give this as much weight as they should. I’ll give an example as to why.
We’re going to need a basic understanding of chipload for this. Quick, incomplete explanation of chipload is that it’s the width of the chip each flute is cutting per rotation. Or another way to think of it is that it’s the amount each flute is moving “forward” each rotation. It’s probably the most important cutting factor in CNC milling. It’s what all feeds and speeds are trying to get to and one of the primary factors in cut quality, tool life, and cutting force.
We need more data than you 50IPM. So let’s say that we are going 10KRPM and this is a 2 flute cutter. That works out to a chipload of 0.0025". Now let’s say that we have 0.002" of runout. In the worst case what will happen here is that the chipload will be added to one flute and substracted from the other. So now we are taking a 0.0045" chipload on one flute and 0.0005" chipload on the other. Or, we are functionally cutting 90IPM on one flute and 10IPM on the other. This is much less than ideal. Once the runout exceeds the chipload x (flutes -1) the worst case becomes putting all your chipload (feed) on a single flute.
Hope that’s useful. Let me know if there’s something I can help with.
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Same issue. Same job, several months apart. Bit slips about 1/4" over 6" cut for a 3-1/2 hr job - verified after job completion and back to home position. First time was with Sienci Precision Collet. Second time with Mak collet. Sienci 1/4" tapered 1/16" BN both times. S/W says exactly same depth.
Did you remove all sawdust from the collet and cutter shaft? I myself tend to forget doing that but sawdust can act as a lubricant of sorts which can cause slipping.
Also, I don’t think many people realize that a collet is a consumable item.
Lastly, collets that aren’t high quality , could have wrong dimension and/or runout.
That shouldn’t apply to a Sienci Precision Collet but crap can happen.
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Thanks. Yes. SOP to remove/clean nut and collet on bit change. Also shop vac router shaft. Puzzling that almost identical outcome several months apart (not much use in between). Cuts at correct depth for first 10% of the cut and then a fairly linear slippage. The the first time, when I noticed depth change, I paused the job and snugged up the nut - no difference. Also do not want to overtighten. Suggestions?
@Retiree Just out of curiosity, is the bit an upcut?
2 flute upcut according to Sienci
@Retiree I’m afraid that I don’t have a solution. I was just curious. Upcut bits, by design, are always trying to pull themselves out of the router. Since this seems to be happening to you at some frequency, if I were you, I would replace the collet. They do wear out through use. Yours is likely worn more than “normal”, owing the slippage.
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Thanks for practical advice. Has only happened on the same job a couple months apart. Other jobs (not as long a cut) I had no issues with same collet/bit. You got me thinking…I had a more careful look at my job, and noticed that the surface was flat where the bit was traversing the backplane on a shallow raster cut, and the sloping began when the bit started biting into the raised relief portion of the material (I had done a roughing cut first). This supports your notion that the upcut had enough force to slowly pull the bit out of the collet. Besides replacing the collet, what about roughing up the shaft of the cutter to increase the friction of the hold?
@Retiree You shouldn’t need to roughen it. Cleaning it may help, though. Be sure that you have enough of the shaft in the colletthat it protrudes a little from the top end of the collet, too.
Appreciate the advice. Never considered the top end. Just checked: I insert bits so that top of flute to collet clearance is same as bit shaft diameter, ie., 1/4". On the bit I am using this gives over 1/4" protrusion at the top of the collet. Next time will clean thoroughly. Can also consider a new bit. Will take time to get to a new project. Thank you
One other thought, I learned the hard way that you can insert a bit to far. If the bit is in to far, as the collet is pushed into the shaft when tightening, the top of the bit can bottom out in the shaft and then you don’t get the proper squeeze on the bit even though you put the correct amount of torque into tightening.
Don’t know if this is your issue but I had it happen twice before a kind soul on here pointed out my mistake, so it’s worth keeping in mind IMHO.
EDIT: Oops, I already mentioned this earlier in the thread but didn’t realize it as I only read the new posts.
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Makes sense - must hit the “sweet spot”.
Thanks