[taconick]

Hello all, I have a LC4896 with the 5hp HSD ATC. I have broken 2- 1/4" single flute compression spirals, solid carbide. One was and Amana the other a Freud. They both broke 1/8" in side the collet. I am using 18000RPM, 150imp with .25" pass depth in hard maple. They were in two seperate collets any ideas? I can't afford to go through $150 worth of tooling a day. These collets (and the machine for that matter) are just over a month old. Any ideas?!? Thank you.

[RandK]

Depends some on the toolpath and if you are taking much of any full diameter cuts but with my 3hp HSD I would run less than 75ipm 20K with a 2-flute carbide up spiral .25doc. Some hard maple is really tough and I have some that has been case hardened and it is a struggle to resaw with my big Laguna and carbide tip blade. On hard stuff I use the biggest bit that will fit to rough it. Not sure about your single flute compression spiral as I have not used them. Single flute is going to be 2x the chip size of a 2-flute at a given feed & speed. Slow down and use your speed override to increase if it it too slow.

[ger21]

I'd use 2 flute downcut or upcut, and not compression spirals, unless you're cutting thin material.

Are you sure they are tight in the collet? I've never seen a tool break in the collet like you're saying. When I've had bad collets, they've broken right at the collet, but not inside.

[victorofga]

is your spindle on the programmed rpm when it start to moving?

sorry for this question... but 150 migthbe a little much, but couldnt cause the break..

unless your spindle not on the 18K yet it is in the acceleration yet, but machine start to moving... and a lot lower rpm

nigth be not this... but thinking on the 18K rpm and feed.. that looks normal.. i would use 2 flute...

[taconick]

the spindle is getting up to full speed before it starts the cuts. There seems to be no reason for it, I don't feel like I am pushing the bits too hard. Just out of curiosity why two flute bits, that is what I use for the finishing pass but I have found that the single flute does a much better job, less deflection, better cut quality, longer tool life, etc... As of now all of the stock that I cut is under 1" thick, what thickness would you recommend for the compression? I have had really good results with the compression bits in my other machines, until now, just confused. I think that the most frustrating thing is that the companies won't take them back even though they were both less than a day old. Oh well, I guess I just won't eat this month, I need to loose a few pounds anyway.

[louieatienza]

Maybe you're not pushing them enough, and they're jamming in the kerf from too small chips? I looked up Onsrud's 1/4" compression spiral and they recommend .014"-.016" chipload at .25" depth, which is about 75-100% what your chipload currently is. You might try either LOWERING you spindle speed or RAISING your feedrate, though I think lowering your spindle speed might be the better way.

Just to make sure, are the toolholders you're using balanced for 18K spindle speeds? Have you let your wood stock acclimate in your shop for at least a week and prefereably two? Are you plunging, or ramping into your work? Is there any debris or dust in the collet or collet nut that might cause the bit to wobble? Maybe excessive runout in the toolholder? Are you inserting the flutes or the flutes' fadeout into the collet? Just throwing out things to check...

While a 2-flute bit is stronger, the flutes have less volume, and chip extraction becomes more important.

[ger21]

As Louie said, 2 flute bits are stronger. I run them between 300-500ipm.

If you want to save some money, and you're cutting 3/4" stock, try these.
57 270 Onsrud 7 32" Solid Carbide Double Edge Downcut Spiral Wood Rout | eBay

Are you hearing a loud screaming noise? That's usually an indication of cutting too slow.

[chris_techno]

Something aside from the tool itself/cutting speeds; if your collet is oriented improperly in the nut it will cause unequal stress on the bit and may cause the fracture 'in the collet' as you're stating. ger21 is correct 99% of breaks caused by stress from material will shear off at the collet not inside, this is odd.

Here a quick document on proper spindle colleting:
http://www.docs.technorouters.com/im..._Colleting.pdf

Not saying it's the primary cause but it may be a contributor.

EDIT: Do you have any pictures of the broken tool? In or out of the collet.