I have a 3 hp router installed on a router table and I have been using several different router bits to carve out some crown molding. The table I have was purchased at a woodworking show many years ago. One problem it has is the seemingly excessive distance from the top of the router chuck (at max hieght setting) to the surface of the table (about 1 1/4″). Using 1/2′ shank bits, I even then have to be careful not to set the bits too far into the collet. The max insertion depth I have to use is only about 1/2′ into the collet. I have used several different bits in this configuration for several passes on the router table without problems. But last week I installed a bit at the same depth I had used it before. I turned on the router and watched the bit fly up about three feet and curve over to land at the other side of my workshop. This happened twice so I shut down operations until I could figure out the problem. Any thoughts? I know the bit insertion may not have been deep enough but why did it work for so long before. I always make sure the chuck is tightened but might there be other causes of the fly-away problem?
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Replies
I wouldn't personally use the router with a bit inserted maximum 1/2" into the collect. I had one fully inserted less 1/16" once using it to route a simple round-over on a deck stair rail edge when the bit jumped the collect and launched. The problem in that case was an internal knot. Could be your problem? Might have been running a larger bit (you didn't mention how large it was) too fast.. or taking too much in one pass.. a worn collect on the inside or the outside of bit sjhank.. saw-dust or grit in the collect not giving good grip..
Or possibly a combination of or.. all of the above?
You may never know really but.. I would start by putting yourself into a position of not having only 1/2" of the shank inserted into the collet. Whatever that takes to correct as I personally see that as "it's not gonna happen that way in at my shop".
Good luck...
You've been warned
Let's just put it this way - you received notification that this isn't the way it should be set up. I'd say you've been lucky it hasn't happened before and sent you on a trip to the hospital.
Modify your router table in whatever way is needed to remedy the basic problem.
Get a new collet.
JR,
I suspect that you have belled the collet end by inserting the bit to an insufficient depth in past operations, as well as overtightening it to make sure that mere 1/2" of bit-shaft you gave it was gripped like a Reiver with a sheep.
If the collet is so-belled, it has no real chance of subsequently gripping other bit-shafts correctly and so the bit takes an excursion. Now, what if the cat had been sat 'blootin' just where that bit flew? Cat's are not forgiving and if it survived the whizzing tool you might well have found something unpleasant in your slippers that evening.
Lataxe, who understands how much angular momentum there is in a rotating router bit and why said momentum should not be allowed to go linear.
A Belled Collet?
What's a belled collet? Some sort of distortion?
JR,
Yes, a belled collet is one in which the entry end has flared slightly, trumpet-fashion, because of distortion caused by tightening it when there is insufficient bit-shaft through the collet to spread the tightening forces evenly, so the empty part is squished in a bit. When the collet nut is slackened-off and the bit is taken out, the distorted collet flares at it's end because of the squish at the other end..
Wear through slippage or ill-made bit-shafts can also cause the collet mouth to become distorted. A router collet & bit-shaft contain an enormous amount of angular momentum when at full-whizz; and suffer a lot of extreme forces when biting the wood. They need to stay within very small tolerances, near to perfectly-round, and once out of shape the end of their ability to grip the shaft approaches quickly.
Here is some text from a machine-tool maintenance blurb:
"The Collet. It is the piece that grips the tool . It is sacrificial - in that it is a wear component. It needs to be checked and replaced regularly. It is subjected to a lot of lateral pressure and over time will start to 'bell' which destabilizes the tool. One easy way to check for collet wear is to look at the tool shank. If there are any lateral lines on the shank replace the collet. Also if you look at the shank and it is clear the shank is being gripped over a small area relative to the shank length, replace the collet. Collet wear, more than any other mounting problem will reduce tool life and deteriorate finish cut. And, again it will harm the machine if allowed to get too worn. Collets wear out regularly depending on the load they are subjected to. Buy the best collet you can find (that usually is the most expensive - and none cost a lot) because those are the ones that are designed for the high RPM's of a router.
A poorly mounted tool will give poor results from the first inch of cutting and will wear out a lot faster. The problem is the progression of deterioration is so slow often it isn't noticed until long after it should have been corrected".
Lataxe
I think I'm beginning to see what is happening. I had no idea I should be replaceing collets, and this one is many years and many revolutions old. Your info is very helpful. Thanks.
JR
You can get an extension to go into your router. It was specifically designed for this problem. It is a 1/2" shaft with a new collet on the end. Gives about 11/2 - 2" added length to your router bits.
wot
Do you know where such extensions might be available?
Extensions
JR
I purchased the extension bit I use in Oz, I don't know of sources in the US but I know CMT bits are available there, this is the one I have. The CMT part numbers are:
1/2" 796-001-00
1/4" 796-001-01
CMT recommend that you use only bits under 40mm in dia. and only in a router with variable speed control.
I haven't had any problems with the device however take note of Lataxe's posting. Though he has a proclivity to drinking warm beer and cider the pearls that fall from his mouth are worth heeding
Wot,
I have a-one of those collet extensions you mention but no longer use it. I got it because the Dewalt 625 router I used in the roiuter table didn't project some bits far enough above the table. Also, it helped poke the bit down a bit further when using the 625 in the woodrat.
However, the extra noise and less-clean cuts quickly convinced me that this extension is not such a good idea. If you think about the mechanicals of the arrangement, you realise that this gubbins will be amplifying any slight run-out of the collet or bit; and may be introducing some additional run-out of its own.
In fact it did seem to greatly accelerate collet wear amd I replaced the 625's 1/2" collet in a matter of days. As you may know, the Dewalt 625 collets are of high quality and good design (multi-splits rather than just one) so faster collet wear would be an issue. (I think they're about £30 each).
I replaced the Dewalt 625 in the router table with a Triton, as this has many features that suit life in a router table, including a lot more projection of the bit above the table, so no collet extension needed. I would advise anyone to avoid these extensions unless they have a one-off operation to do and/or are prepared to replace worn collets a lot more frequently.
Lataxe
Well, i guess I have joined the "never choke up" club.
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