COLLET BROKE, DOES ANYONE KNOWS WHY?

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enriquewoodcarver
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Joined: Wed Apr 20, 2011 2:23 pm

COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by enriquewoodcarver »

Few days ago I set my cnc to start with a rough cut something went wrong and suddenly horrible noise in my bit I stop the machine than I raised the Z axis, accidently tap the bit n it fell off (http://www.cncsharktalk.com/viewtopic.php?f=2&t=4298), but today I was going to do another test and I saw that the collet of my Bosch bolt palm router was broken so I'm not so assure that could've been the problem of the gap it made because after I raised the Z axis the bit fell off but oh well, but I also wanted to know if Anyone knows what could've been the problem the collet broke? Any advices, tip or suggestion I'll be happy to hear Thank you.
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Rando
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Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by Rando »

It's somewhat unusual in a router at high RPMs (I'd expect more catastrophic failure earlier) to "break" a collet. There are three pieces involved, not including the bit. There's the router shaft...which I assume did not break....are there horrible marks inside the bore? Next up is the collet (insert) that grips the bit. Is THAT the part that broke? And then finally, did the collet NUT break? A broken collet nut would be something to make me wear a bulletproof vest around the router!

So, I'm going to assume it's the collet INSERT that broke. When I add in your mentioning that the bit had fallen out with a mere "tap" when removing the dust shoe, I will tentatively conjecture that the bit and/or collet insert were not really well seated. Like how a small bit can be "held in place" in a drill press chuck, but at the same time be not at all centered. My guess is something along those lines happened, and when you tightened it down, it was only really tight in a skewed place. Maybe the dust boot hid the spinning nightmare from view? The collet insert might have failed because of the skewed stress on it being clamped wrong, and then the waggling bit added enough stress to break it. The breaking would have provided some more slop around the bit, that could have then made it fall out with that last little nudge.

In your case, is there one (two) collets for all size bits the router can handle? I'm a convert to DeRosa's MuscleChuck and their very close-tolerance, single-shaft-size collet inserts. But with a collet that can accept, say, everything from 1/8" up to 3/8", that's a lot of space between the fingers, possibly allowing for a skewed bit seeming to be held propertly, but skewed in reality.

One way or another, however, a collet insert should not fail, and even if it WERE your fault, I'd call the manufacturer and demand a replacement so you don't call the Attorney General and get a lawyer specializing in product liability laws. Think McDonald's coffee in the lap ;-). If the cost to them is a $0.50 part instead of escalating exchanges, they'll almost always ship the part just to end it with a good-faith gesture on their part.

Sound truly scary. Bits coming lose, broken collet (inserts), yikes! I'll take lions tigers and bears, heck even snakes over that ;-)
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enriquewoodcarver
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Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by enriquewoodcarver »

Rando wrote:So, I'm going to assume it's the collet INSERT that broke. When I add in your mentioning that the bit had fallen out with a mere "tap" when removing the dust shoe, I will tentatively conjecture that the bit and/or collet insert were not really well seated. Like how a small bit can be "held in place" in a drill press chuck, but at the same time be not at all centered. My guess is something along those lines happened, and when you tightened it down, it was only really tight in a skewed place. Maybe the dust boot hid the spinning nightmare from view? The collet insert might have failed because of the skewed stress on it being clamped wrong, and then the waggling bit added enough stress to break it. The breaking would have provided some more slop around the bit, that could have then made it fall out with that last little nudge.
Thank you Rando for your reply, I really appreciate which I'm still a rookie. Yes it was only the collet, not the collet nut. Yes there's a lot of lines marked inside the collet. No, is not a Derosa's MuscleChuck Im using the original collet that came with the router. I had this router since June 2011 and I think it was the shaft or something inside that melt and made it stop like 6months ago but I had another Bosh colt palm router but it didn't had a collet so I used the same collet from the broken router, and maybe the collet was already ware out because the broken router worked in some projects for 15hrs without stopping and maybe took rest for 6-8hrs, even thou you were able to hear a rattle noise inside on his last 2yrs of use. Yes thanks god no flying object occurred.

Does it also has to do with the bit size? my router only takes shanks of 1/4, but the cutting length or overall length does it has to be specific?
I been reading other topics to find a similar problem as mine but didn't seem to match but I heard many mention about precision collet, do you know if those are good to use?
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Rando
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Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by Rando »

The internal cone shape of the shaft is often subtly (or significantly) different between manufacturers, models, and even years of the same model. Maybe what happened is the older collet insert didn't really fit properly in the newer unit? I seem to remember the guys over at DeRosa mentioning that one manufacturer very slightly changed their shaft-to-collet mating surface so that the MuscleChucks for that model didn't fit, and people were having issues. Somebody figured out all they had to do was take a diamond file and "open up" the new opening some very small amount and it worked. I guess at high speeds and high loads, having a good fit means having a GOOD fit.

There could be some variation in bit shank size, e.g., with no-name brands from eBay that are actually 3.10mm or something (no direct experience; conjecturing). Each collet insert has a min and max limit to what it can clamp, with more issues on the smaller-shaft size. That's because the gaps between collet fingers are pressing on each other, and not pressing on the bit shaft. It will feel like the normal tightness, but the actual pressure on the bit will be far less. That said, if your router collet only accepts 1/4" bits, there should be some reasonable margin, say like it will accept a 3.0mm or 4.0mm shaft for the metric markets. Okay, anywhere but the US ;-).


As you mention, insertion depth is important. Typically with router bits that have a large body at the end of the 1/4" shaft, "in as far as it can go" was the rule, or there was often a minimum insertion line. I'd go with "the straight part of the shaft should be held in place at the outside and the inside ends of the collet insert, with maybe a little more overlap at the inside.

That said, with more-modern endmills and such that don't have the large bit-body, but instead have flutes that cut right into the 1/4" shank diameter, you don't want to clamp the bit with those flutes too close to the collet. Well, keep track of the total insertion length, to be sure. But, those cut flutes do somewhat weaken that end of the bit. You can think of it like a nice strong part attached to a less-strong part. That spot where the two meet represents a place where the bit will bend "differently" between the two. So, if the bit is inserted so the "weaker" part is close to the clamping location, more of the stress will be taken up in the weaker part, and little to none in the strong part. The bit's overall ability to hold up under load will be "lower" because all the flex is put on the weaker section. It's not zero, nor 10%, but probably more like 90+% as strong. So, having 1 to 1.5 diameters (0.250" to 0.375") of shank between the collet bottom and the flutes start might make it a little less prone to breaking.

With the router-style bits, there seems to always be a slight radius where the shaft leaves the body, so definitely don't clamp that radius into the collet. That won't cause the problem you saw, though. Instead, the bit will mock you by falling out pretty much as soon as the router starts up and it touches anything. ;-)

Regards,

Thom
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enriquewoodcarver
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Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by enriquewoodcarver »

Rando wrote:As you mention, insertion depth is important. Typically with router bits that have a large body at the end of the 1/4" shaft, "in as far as it can go" was the rule, or there was often a minimum insertion line. I'd go with "the straight part of the shaft should be held in place at the outside and the inside ends of the collet insert, with maybe a little more overlap at the inside.
The collet did fit pretty good because the 2 router looked similar. Well about the Shank size I think I didn't had a problem with that because the first time I put in my bit it was tight but by the time I used it I didn't struggle to change the bit. I've been using a 1/8 in Dia x 2in Overall Length end mill and between 5/8-3/4 is what is clamped in the collet and everything its been doing a good job for Roughing and for Finish I use a 1/16 Dia. x 3in overall length ball nose and it goes in like around 1 1/4 inside the collet. Like around 6 month ago I bought some bit for roughing with the same measurements as the finish and since than I upgraded to Control Panel 2, I started it to have this issues, so I inserted the bit all the way in because I thought it'll be better clamped and safer, and one thing that I wasn't noticeable is if my bit was slipping down. So there's many things that could've been happing that maybe it was the collet not holding tight enough because the longer size of the bit or I should've not put my bit all the way in, so I don't know its kind off confusing, well for me maybe because I'm a rookie
Precision collets been reading about it but what can you tell me about it?
Thank you Thom for your replies.
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Rando
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Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by Rando »

Well, you're a braver man than me :D. I don't think I'd use a collet from one machine on another unless I knew they were both an industry standard size, like say an ER-20 or ER-16.

Collets, eh? Well, they are cool; there is that. When replacing an existing collet setup, there are roughly two types you can go with, depending on the form of the router/spindle shaft. The first is what I'd call the custom-fitted collet replacement, and the second uses a set of narrow-range collet inserts onto a standard collet.

When you're going from an actual router, those seem to almost never have an industry-standard collet size, opening, or threads. So replacing a router collet would be one of those custom-fitted jobbies. The MuscleChuck is the most-recent version of a design that was goes back some (10?) years now. The original design patent was sold/licensed, and I think the (Whiteside?) Eliminator is the name of that product. The MuscleChuck is an improved version, designed by the same engineer, but directly produced by him (and maybe some indentured children spread around the shop; I think his son is doing much of the work these days ;-) ).

In general, the good characteristics include:

- Much easier bit insertion with just a 4mm allen wrench. No more two-wrench juggle, or finding that darned shaft-locking button on the router.
- Much closer tolerances on bit fit; The collet inserts are for specific standard sizes, and aren't intended to be used more than a tiny bit outside that range. But very accurate clamping.
- Engineered to correctly fit into specific router shafts very accurately. This is probably the best feature: when John DeRosa says it works with a router, you can be assured that it really will fit, and it really will fit well.

Some of the tradeoffs include:

- You'll generally lose 1/2 to 1" of vertical range, since the new one has more internal stuff than the original router one. Some might be more, some might be less. Depending on your setup, sometimes that height can be regained by moving the router up in the clamp, but that then effects its stability in the clamp, and so on....
- A somewhat limited and not-inexpensive ability to use non-standard shaft sizes. I had to have Mr. DeRosa make me a 3/16" collet insert. It was fast and no more expensive than any other of their inserts, but when I originally inquired, that size wasn't available. So, if for some reason you someday need to use a weird bit shank size, make sure the replacement chuck can handle it. Sounds like that won't be a problem for you if you're using just 1/4" and 1/8" shank bits.
- You'll need to be at least a little more aware of whether your bit shafts really are what they say. This is almost never a problem on the high-end bits ($40+ each) used in, say, aluminum-cutting end mills, but cheap bits from the hardware store, purchased at 930pm on a Sunday night when the real stores are closed....
- If you do decide to use a replacement chuck, avoid using reducers or anything that doesn't come from the chuck manufacturer. Their collet inserts clamp into, and around the bit in specific ways to ensure very high quality clamping. Using things like a shaft (opening) reducer is just asking for trouble...of the kind that started this thread :D.

I love my MuscleChucks. I got the first one for my DeWalt D618 router, and then when I changed to an "actual" spindle, I got a Type-6B MuscleChuck, which fits the ER-20 end. And, I can use the same collet inserts between the two, so I didn't have to get a redundant set of those.

Now that I've mentioned ER-20...if at some point you end up with a spindle that uses them, you'll find online huge sets of "ER-20 collet inserts". Those provide narrow-range inserts that will typically only fit one drill or bit size and no other. I've seen them in sets of like 20 collets. Now, if you're drilling using twist-drills that don't have standard-diameter reduced shanks (say, a 7/16" drill with a 1/4" shaft up where it goes in the chuck), and instead you're trying to use a 7/16" drill bit, you'd select the 7/16" collet and use that specific one. But, in situations like our's, where we typically have 1/8, 1/4, 3/8 and 1/2" shanks, there's no need for the 20 piece kit. Sadly, buying 4-5 individual inserts can cost more than a complete set...that you'll never use most of. Luckily, the 4-5 individual ones (being all green and not wanting to waste metal) often cost in the same ranges as a nice MuscleChuck or similar. Go figure.

Well, that's my data dump for Saturday. Hope your weather is as gorgeous as it is here in Seattle today. Light breeze, 68F, not a cloud in the clear blue sky. Mount Rainier is in full view with only a little haze....and she's like 70 miles away :D.

Regards,

Thom
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ThomR.com Creative tools and photographic art
A proud member of the Pacific Northwest CNC Club (now on Facebook)

enriquewoodcarver
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Joined: Wed Apr 20, 2011 2:23 pm

Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by enriquewoodcarver »

Rando wrote:In general, the good characteristics include:

- Much easier bit insertion with just a 4mm allen wrench. No more two-wrench juggle, or finding that darned shaft-locking button on the router.
- Much closer tolerances on bit fit; The collet inserts are for specific standard sizes, and aren't intended to be used more than a tiny bit outside that range. But very accurate clamping.
- Engineered to correctly fit into specific router shafts very accurately. This is probably the best feature: when John DeRosa says it works with a router, you can be assured that it really will fit, and it really will fit well.
I was searching to look forward on buying a musclechuck for my Bosch Palm Router PR20EVS and they don't make for 1/4 shank it has to be for 1/2 shank, that's no good, because I don't think I can fit a bigger router on my CNC Pro plus, if you know any website where I can find it'll be helpful

By the way nice weather out there here in TX its crazy on Saturday and Sunday was hot on its 80-90 but today it was cold in the morning on 50s so right now is on its 70
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Rando
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Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by Rando »

Ah, very true. There is this:

http://www.ebay.com/itm/Craftsman-1-4-i ... 5357&rt=nc

The fact that they ARE on eBay but NOT at the actual Sears.com site, well, that must say a lot right there. Like you, I'm not seeing a whole lot of other options. I guess the market on them isn't all that competitive...yet! :D.

Thom
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enriquewoodcarver
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Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by enriquewoodcarver »

Rando wrote:Ah, very true. There is this:

http://www.ebay.com/itm/Craftsman-1-4-i ... 5357&rt=nc

The fact that they ARE on eBay but NOT at the actual Sears.com site, well, that must say a lot right there. Like you, I'm not seeing a whole lot of other options. I guess the market on them isn't all that competitive...yet! :D.

Thom
Alright thank you Thom for all the help and your time, I'm going to take a look at them. I really appreciate all the info you provide me.
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TDA
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Re: COLLET BROKE, DOES ANYONE KNOWS WHY?

Post by TDA »

Wish I could have responded to this ealier but hopefully this is still useful.

The colt collets have always been brittle. However, the main issue was probably switching to the other router. The new colts use a different armature and the taper of the router bore is not as long. This causes the collet to get "pinched" in the back. That "pinch" causes higher runout, faster wear, and less tool grip. If you want a DIY solution to this see BillK's post here (Link).

While I don't like to comment on what could be interpreted as competing products. Be extremely careful with those quickchange adapters. They were originally made for the carvewright/compucarve (even they have moved away from these) and were prone to many issues. I wouldn't recommend using them on any cnc system.

If there is anything I can help with please let me know.
John Torrez
Think & Tinker / PreciseBits

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