Thread: Hottie Catcher

Anything that catches something hot is going to catch sawdust so it kind of defeats the purpose.
What are you specifically concerned about?

If you are really worried about this then a smoke detector with a sensor inside any sort of DC enclosure and the alarm outside may be worth considering

I'm currently using it on the CNC and when machining ply or MDF at any sort of speed it seems to create these little red lumps of material that create a fire trail when sucked up into the pipe. I bought a Shop Vac the other week and proceeded to catch it on fire with said hotties found their way into the bag and filter.

I cant be the first person to have this problem, so wondered what others did to prevent fires.

Originally Posted by HeadScratcher

I'm currently using it on the CNC and when machining ply or MDF at any sort of speed it seems to create these little red lumps of material that create a fire trail when sucked up into the pipe. I bought a Shop Vac the other week and proceeded to catch it on fire with said hotties found their way into the bag and filter.

I cant be the first person to have this problem, so wondered what others did to prevent fires.

Might be best to ask in the CNC forum?

Originally Posted by HeadScratcher

I'm currently using it on the CNC and when machining ply or MDF at any sort of speed it seems to create these little red lumps of material that create a fire trail when sucked up into the pipe. I bought a Shop Vac the other week and proceeded to catch it on fire with said hotties found their way into the bag and filter.

I cant be the first person to have this problem, so wondered what others did to prevent fires.

While CNC waste can get quite toasty, I've never experienced it getting so hot as to self-ignite.

What's your setup and cutting parameters (bit type, rotation speed, feed speed, etc)?

Also bear in mind that CNC routers need a LOT of suction to effectively clear waste from the cut (especially if your machine has a vacuum table) which will also reduce the temperature of the bit and the waste.

I'm a bit of a newbie when it comes to a CNC (i.e. I have just built it) but I greatly suspect that some of my configuration is probably causing some of the issues I am having. For one I think I am spinning the spindle too fast ~24000 rpm (need to read the book shortly to see how to lower the frequency) using a 4 flute 6mm cutter, feed rate I am slowly increasing but up around the 1000mm per minute, otherwise it I going to take forever to get anything done.

On a side note, the plus side of drinking a bottle of wine before dinner has helped reduce lost letters in my post immensely. Not sure what is with this forum, but it misses a lot of what is typed.

Ive had sawdust begin to smolder from a cnc when machining a deep pass (45mm deep) on western red cedar. A combination of high rpm and slow feed speed and dull cutter = enough heat to create embers which then fall into the pile of sawdust beneath the panel.

U can see the effect of slow feed and high rpm quite well when using forstner bits in a drill press, even the good shavings have a lot of heat in them.

Using 4 flute cutters at only 1000mm/min has a tiny chipload, you are really just rubbing the surface rather than giving the cutter something to cut through. You need to speed up the feed, reduce rpm or change to a 1 or 2 flute cutter. At 1000mm/min I would I only use a 1 flute cutter.

Originally Posted by HeadScratcher

I'm a bit of a newbie when it comes to a CNC (i.e. I have just built it) but I greatly suspect that some of my configuration is probably causing some of the issues I am having. For one I think I am spinning the spindle too fast ~24000 rpm (need to read the book shortly to see how to lower the frequency) using a 4 flute 6mm cutter, feed rate I am slowly increasing but up around the 1000mm per minute, otherwise it I going to take forever to get anything done.

On a side note, the plus side of drinking a bottle of wine before dinner has helped reduce lost letters in my post immensely. Not sure what is with this forum, but it misses a lot of what is typed.

Didn't know they made 4-flute that small. 24k rpm is pretty fast (probably too fast for a 4-flute) and 1000mm/min is definitely too slow for that. The formula is:

Feed speed (mm/min) = Number of flutes x RPM x chip load (how much each tooth is taking off)
So, your current setup is: 4 flutes x 24000 rpm x 0.35 (recommended chip load for a 6mm bit in MDF) = a feed rate of 33,600 (not a typo) mm/min

The general rule for feed rates is that you go as fast as possible until one of the following happens:
Motor gets bogged
Bit snaps
Piece moves
Finish is not acceptable

Worth having a look here for more details:
http://www.cncroutershop.com/uk/calculate-feeds
http://www.pdsspindles.com/engineering-speeds

You should also throw that 4-flute bit in the bin; aside from not being suitable for what you're doing, it's probably completely blunt from all the heat.

Thanks for the replies guys. Yes feed rates are definitely way off. I had a quick look through various feeds and speeds websites the other week and I am definitely running the spindle too fast and not enough feed speed. Problem is I have only just semi finished building it, I am still dialling things in. At the moment I only have one X axis screw in (hence why I am keeping feed rates down) and I have been replacing parts as I make them.

I have dug out the VFD booklet to visit turning down the frequency which shouldn't be too hard, and hopefully that alone should be enough to stop the hotties. Guess when it all said and done once I drop the spindle speed it may stop doing it and therefore remove the need to catch hotties if there are none.

Started a new thread here https://www.woodworkforums.com/f170/spindle-speed-194079 to discuss spindle speed, appears I am only turning at half the speed thought I was.