cooling

[alarants]

Hi,

I am new in woodworking but I made a CNC and experimenting with it. It is cool but top of my router bit gets burned. I am woodworking pine with low router speed and velocity 250 mm/min (sorry, no inches this time) which is almost maximum speed my machine can take. Still the top burns. Before the wood got burned too but after increasing velocity it does not happen any more. Only top of the router bit gets burned. The problem is heating I believe. How to avoid it? Should I use some liquid cooler like water or...?

[BigDaddyG]

Alarants,
I would suggest experimenting with different cutting tools. If the wood is not being taken away quick enough, then it will stay and burn. A better cutting tool will act in the same way as slowing down the speeds, by allowing the wood chips to be removed.
Good luck.

[ynneb]

What diameter bit are you using?
One or two flute?
Have you tried spiral up cut or down cut bits?
Do you have a vacuum system on your machine?

It has been advised to me to also turn the router speed down, but I have found the opposite also works for me. I think it must get rid of the junk a lot better and make smaller particals that dont clog up. That last advice is unconventional, but at least give it a try and see if it helps.

[alarants]

Hi,

Thanks, at least I've got some ideas:
1.Install vacuum closer to remove wood chips fast. It is possible but not much.
2.I now use two flute HW bits diameter 6 mm. Never tried spiral bits but I will if you say that it helps.

As I understand my great idea about liquid cooler is not practical?

[kong]

Liquid cooling will damage the wood. Try the spiral up-cutting bit since they will disperse the dust upwards, hopefully into the dust extractor. A lower spindle speed should help too, but like Benny said, sometimes it is the reverse.

[Patrick2by4]

Sounds to me that the router is moving too slow. When I router material by hand, I would move the router about 70mm per second or 4200mm per minute (about 3" per second or 15ft per minute which is kind of slow for a 1/4" bit). With a router speed reduction to 10000rpm, I would still move at the router at a pace of 1700 mm per minute.( 5 1/2 ft per minute or 1" in per second). Any slower and you risk scorching the material.
At 10000 rpms. you're moving at 10" per minute or less than 1" per 4 seconds, just too slow.

[RandMan]

I have experienced this with straight bits (2 flute carbide tipped) when machining woods that have a high sap content like some maples and definately with pine. Spiral bits don't do it. I still use some straight bits because I need smooth profiles that a spiral which is great for pockets won't give me. I think it is the sap creeping up the warm bit and forming a crust up by the collet where it continues cooking. It's a problem if I later need to plunge down deeper and hit the crust. Otherwise I just soak the bits in some pitch remover (for saw blades & such) and it comes right off.

As long as you are not scorching the wood you are going fast enough.

My 2c

[alarants]

I have just tested one flute spiral bit. It works much better. It goes warm but not burnning hot. Even cross the grain the cut is normal. I can take now more material at the same time. I tested up to 25mm (1 inch). This is not optimal but works. Thanks everybody who replied. I have got real help fro this forum.

Alar

[ger21]

NO matter what you do, you'll probably be experiencing some burning. It may mjust take longer to notice it. One thing that will help a LOT is to not plunge straight down into the wood. Try to always ramp in at an angle. On our machine at work, we cut 3/4" plywood at 300+ ipm at 15-16K rpm. When we first got the machine, we used to always plunge straight down. Bits would get burned very quickly. Since we started ramping, we get much better tool life.

Even at the speeds we cut at, tools still get incredibly hot. Heat dulls bits, dull bits run hotter... vicious cycle.