# Computer guy playing with wood



## foxkid (May 31, 2012)

Hi.

I'm an embedded software guy these days, dabbling in mechanical engineering, CAM, and woodworking. I built a 6 axis CNC router, wrote the software to run it, wrote the software to make tool paths, and now I'm trying to do some routing.

My first question is: How long do 1/8" solid carbide up-spiral bits last? How much wood will they cut before they must be replaced? I need to figure out if I need to be changing bits int he middle of a job, one bit per job, or if I should expect to have one bit last for "a long time".

The best answer would be something like: You can remove xxx square inches of cherry at 18K RPM with a feed of 60 inches/minute -- or something else vaguely specific. This is a CNC machine, it may be operating with the lights out (no operator present), and I can't tell from how the router feels in my hand if the bit is still sharp enough.

-- Carl


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## dherbert (Oct 28, 2011)

As a retired metal machinist and novice woodworker,my 2 cents of advice is,"it all depends on many variables." Carbide is extremely brittle. My guess is you will break at least a dozen of them before you hit on the proper combination of speed and feed.Metalworking CNC mills use flooded coolant in the gallons per minute to cool and wash away the chips.Obviously,you cannot do this with wood, so you must use a constant blast of compressed air to remove the chips,or else they will load up your cutter and break in a heartbeat.Good luck, but be prepared to break a lot of cutters until you find the magic combination.


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## bobbotron (Jan 7, 2010)

foxkid said:


> Hi.
> 
> I'm an embedded software guy these days, dabbling in mechanical engineering, CAM, and woodworking. I built a 6 axis CNC router, wrote the software to run it, wrote the software to make tool paths, and now I'm trying to do some routing.
> 
> ...


I think they'll last quite a while if used correctly. 1/8" is quite narrow though, if you could step up to 1/4" for the bulk of the operations you'd probably speed up your jobs and tool life quite a bit.

I believe if you contacted a company like onsrud, they should be able to give you specifics as to how long to expect a bit to last, feed rates, etc.


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## kartracer63 (Jan 19, 2009)

It really depends on what type of material you'll be cutting. Your bits will last a lot longer cutting a soft wood like cedar vs. cutting marble.

Your spindle speed & feed rate also figure in bit lifespans. A feed rate too slow is almost as bad as too fast. Too slow builds heat and shortens bit life. Too fast increases your chances of snapped bits ( or missed steps ).

Make sure you buy nothing but carbide bits (avoid high speed steel).

The larger diameter... the better, as far as I'm concerned.

Good Luck!


Eric


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## bcfunburst (Jan 14, 2012)

*Cheap Router Bits, NO Savings*



bobbotron said:


> I think they'll last quite a while if used correctly. 1/8" is quite narrow though, if you could step up to 1/4" for the bulk of the operations you'd probably speed up your jobs and tool life quite a bit.
> 
> I believe if you contacted a company like onsrud, they should be able to give you specifics as to how long to expect a bit to last, feed rates, etc.


I agree with using Onsrud bits. You'll get ten times the use from superior router bits. I've had some bits that last only five small cuts in Western Maple. You don't save anything buying cheap router bits.


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## foxkid (May 31, 2012)

*Speeds and feeds*

Is there a good reference source for speeds and feeds for wood working? (Actually, maybe I should check my Machineries Handbook.)

I am using the Porter Cable 7519 router (variable speed, ~ 11K - 19K RPM). My max speed with current electronics is about 350 inches/minute. I'm using a 0.300" depth of cut using 1.5" total length 1/8" micrograin carbide mill bits.

I'm getting good cuts. I wonder about tool life, and how to tell when bits need changing (before I've messed up the work).

Where would I go to gain wisdom from the experience of others?

-- Carl


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## bobbotron (Jan 7, 2010)

foxkid said:


> Is there a good reference source for speeds and feeds for wood working? (Actually, maybe I should check my Machineries Handbook.)
> 
> I am using the Porter Cable 7519 router (variable speed, ~ 11K - 19K RPM). My max speed with current electronics is about 350 inches/minute. I'm using a 0.300" depth of cut using 1.5" total length 1/8" micrograin carbide mill bits.
> 
> ...


I think Onsrud has that kind of reference if you hunt around their website or email them.

Periodically cleaning the pitch off of your bits before it builds up too much helps prolong their life. Pitch = heat build up.

I'm not sure there's a formula to predict exactly when a bit will kick the bucket, expect some trial and error ahead.


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## darsev (Feb 3, 2012)

Carl,

As has been said many times already, the life of your bit depends on too many variables to be able to answer the question definitively. What I can tell you though at our factory (cabinet making) we expect 12mm carbide compression bits to last about 150 sheets when our CNC router cuts cabinet panels out of them. Sheets are 2400 x 1200 (or 8ft x 4ft) We had a major investigation when one batch of sheets were so rough that we only got 80 sheets per cutter. We had the rep out to explain why etc. etc. If we think that cutting up 80 sheets is poor performance, then I think you would be very unlucky if you only got one job out of a bit. 

Darryl


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## Phil P (Jul 25, 2010)

kartracer63 said:


> The larger diameter... the better, as far as I'm concerned.


As Eric says, the bigger the better. The larger the bit the longer it takes for the bit to get hot. Rather than talking in terms of using a blower normal industrial practice on CNC routers and point to points working timber products is to have dust _extraction_ which helps keep the cutter cool as well as removing swarf before it can start churning.

I'm with the rest on both feeds and speeds and cutter life - there are just too many variables to give any sort of accurate answer. If you are forever breaking cutters then your feed speed is too high or the cut too aggressive (too deep)! Though that isn't often a problem with spirals where feeding too slow probably causes more bit breakages than anything else. One partial solution is to wire an ammeter into the spindle. When the amperage drawn for a given cut starts to climb rapidly then that cutter needs to be replaced. A few of the industrial manufacturers actually offer this as an option on their machines. I think the main thing is to keep a book on tool usage which details cutter, cutter life, material, depth of cut, quality of cut, etc (including failures) so that when you next get a similar job you have a ready reference point from which to start.

Regards

Phil


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