Smoking Sparking Routers used for Desktop CNC

When might a single spiral flute half inch shank be to much for a router?
Is there a better bit to be used on firm rubber like plastics?

The guy that runs the Nextwave Branded CNC (just retail marketed DIY stuff) insists that a job we do, cutting these soft rubber like plastics, must be done with the 1/2in single flute. That while other bits can be used, they can only be smaller, meaning longer time per cut. The trouble is we also insist on using ONLY routers that Next Wave signed off on as being acceptable for use on the Shark CNC machine, so a particular model of Porter Cable is the only one we use. But since they upgraded the model, it now catches fire when using the half in bit. Sometimes sparks, sometimes smoke, sometimes it just stops spinning. I speculate the bit is pulling to much strain on the bearings and in turn is effecting the load on the internal power regulator, which is likely just powerful enough to handle the expected load and not power through. It’s the best theory I have. I know router doesn’t have the same quality of parts that a spindle does.

Although I don’t like the controller, or the drivers. I do not believe they are at fault with this failure. I do think the Router model is a problem, but thats more an internal argument. Though I don’t mind if you have tips, or experience to share on the mater. I can pass it back and hopefully we can move on.

Not by any means an expert…

Do the bits flutes get clogged with melted plastic?

Never milled plastic with a 1/2 bit but I do know that plastic is very easily melted and can clog a bit quickly. This is usually because the feed and spindle rpm are two fast for plastic. At the right combination of feed and speed the bit should create plastic chips rather than melting the plastic.

I use this as a starting point for themoplastics like PVC, ABS, acrylic or polycarbonate: F = 0.03 x D x No. flutes x RPM (3% chipload per flute)


This stuff whatever it is, will burn, but the bits don’t seem to make it melt. It flakes off cold. No lubricant, just compressed air. I can carve it with a finger nail, but it is also durable enough to be used outdoors and in commercial industrial applications. The first time a router went up, we just assumed it was worn out. It took several months before we happened to be cutting the same parts, and using the same bits, again when I realized the pattern. Later confirmed with the death of a third only just new from the box days before.

Ok that is weird!

This is probably not going to be helpful but…

You have no idea what the material is called?

  • If you knew, our resident chemist @NedMan might provide some insight.
    Does its manufacturer have any advice?

The router catches fire?

  • I have a Porter Cable router and run it hard on wood with 1/2 bits without any fires?
  • It’s unusual for a modern power tool to catch fire?
    • Its most likely an over-load (as you point out) but that should be curable by getting the right combination of speed, feed.
    • I have never been able to overload my Porter Cable.
    • I am surprised the material as you describe it (soft) would be a larger load than wood?
    • If you’re getting cold chips that sounds like its cutting correctly
    • … something unrelated to load causes the fire…
      • Is it possible that cutting this material is giving off flammable or corrosive vapor.
      • How long is the job running before the router catchs fire?
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No idea what the material is. If I had to guess, some kind of TPU. But that there are so many kinds of everything out there, it’s a needle in a haystack to me. Manufacturer is, Made in China.

Did a little digging and found only this generic entry, “injection molded polyurethane plastic”
and again I know from experience polyurethane comes in more blends than I can shake a 1000 sticks at…

Operational time varies. This particular material we will make a few cuts per part, stop, change the tool, restart. Stop, reset the tool and the materials. By this time the router is often scorching hot and you have to use gloves to handle the bits and chuck. Compressed air is used, to clear the feed path, 120spi. We do not use it direct into the router vents do to water in the lines, despite removal tools. One cut runs about 12 min and the smaller 5 min. It only takes 3 cycles to get it hot.

No gasses that I know of. Would have to assume that it generated corrosive or explosive vapors we would have seen other signs or had an actual fire.

If I could recall the particular model of router, I would. Like I said the ones that burned out seems to be these upgraded versions. We managed to wear out 1. We ran it as long as we could. It had different parts inside but was otherwise identified as the same model. However all of them have had failures while using the 1/2 single flute bit.

Day one when the Shark was new, the very first cut, it smoked up the box. the covers bowed out and the thing looked like it was about to blow. We took it down a for a few weeks. But this behavior was not seen again until the bits started causing burn out.

I would like to know if there is solid alternative to a single flute for soft plastics. Like I said the guy thats generates the patterns insist this is the ONLY bit or smaller. That of the many other bit types for what we are cutting, this is it.

My opinion is that a better balanced bit would reduce wear on bearings and in turn keep the power regulator cooler. Of course maybe if we used coolant on the bits and the material that would help too. But the whole set up is more standard for wood sign carving than plastics or metal…

I am sorry to pester you both on this.
@donkjr @NedMan

Other than an explicit following of the formula or say a slower feed rate at RPM.
Any other words of wisdom here? for a rubber like “polyurethane”?

I am sure a better spindle is a good starting place. Hopeful I can drive then to use a different bit that doesn’t vibrate as much. What are your opinions?

You’re not bothering us, we are here to do our best to help, at this point this is a strange and irrational problem…

It’s hard to give good advice until we know the mechanism for failure.
It just doesn’t make sense that routing plastic would be the culprit for smoking routers.

I would try some experiments/measurements to see if we can pin down the source or at least get to a more rational understanding of the elements of the problem.

Potential sources of the problem, [what we know]:

The router is defective.
[ multiple routers would have to be defective]

The material is overloading the router:
[cuts with proper looking chips]
[does changing speeds/feeds/cutting depth lower the load?]
[does changing the bit size lower the load?]
[does changing the bit-type (more flutes, upcut, downcut) lower the load?]
{Does the same speed/feed, bit, and router overload with a different material like wood]

The material gives off gases that destroy the router:
[no smell or other evidence of a gas]

Measuring the load on the router:

What can we measure that helps us understand the problem?

The load on the router!

The load on the router can be measured by monitoring its current.
The router’s electrical load can be easily measured with a clamp ammeter.
A clamp ammeter like this can be used:
This type of clamp meter needs to be placed on one leg of the AC line.

You can make a cheater cable where the cable sheath is pulled back to expose the wiring and the meter can be clamped on one leg.
You can also buy an adapter:

Create a test job for measuring loads

Create a short duration test job for use with various materials especially including the problem material
This job can include a few objects (lines, circles, squares) that are milled a various speeds/feeds/depths.

Measure the Router current under differing loads:

Measure the router load during jobs that do not damage the router
Measure the router load on the subject job while routing
Measure the router load on the test job
Compare the loads against each other and the current spec on the router.

[hope this data provides a hint to the problem]

As an Amazon Affiliate, I earn from qualifying purchases.

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Quick reply from work if this posts. Router is Porter Cable 8902, 890 router. The bit used was Amana Tool 51428: 1/2D x 1/2SHK upcut plastic spiral carbide single flute.

We use Dewalt DWP611, and only change brushes. They don’t normally just die. But the shank is also smaller.

Oddly today the CNC guy ran a cut on 1/4 aluminum paneling. Cut out two parts. The bit ran very hot. Discolored. The material is rough. The tech says this hasn’t happened before.

I assume to much to fast on a bit getting dulled without lubrication. Using a 1/4 single flute carbide.

What are the job parameters for the failing job:

  • Spindle speed
  • Depth of cut
  • Cutting feed rate

With that router, the current should not be above 7 amps (see measurement suggestion above)

Those details… working on it. CNC guy not as forthcoming. Also we don’t have a clamp type meter. We do DC stuff but rarely any inhouse AC. Promise to add details as soon as I get them.

You can get a clamp meter on Amazon, link above.

Boss said he’s going to get one. Amazon no less. Thanks for the link. However it doesn’t show over the email for some reason.

If we have to train the CNC guy to use the camp type to monitor load. You can be sure it will happen. It’s a chore to pull a router out and re-feed the cables and the bosses don’t like having to buy new routers.

Edit: Wrote on phone at work. Spell check is a smart ass and changes words sometimes more often than I misspell them. Also I at home I can see you are referring to your third reply, with regards to the link. So I can see it now.

Do you need them again??

I think that the meter (clamp) would NOT be needed once we find out the problem. Just testing to find the problem.

I like the idea of the clamp or even an inline ammeter as we can see when the system exceeds a load that is considered a limiter, in order to protect our tools. I have copies of some of the files. I will need to look and see if the headers contain any data useful. But as I recall they just contained the maker of the hardware, safe height, the tool used, etc.

Boss came and said the clamp on meter works if and only if we can separate the wires. Which does sound about right. He says we cannot just throw it over the cable. So he hasn’t ordered anything yet… I probably just need to source out a cheep digital inline that can handle the through load with catching on fire itself.

I don’t have the exact data but I think I can guesstimate some of this. The bits tear down about 3/16in. They don’t move seriously fast but I would estimate about 1"/s. The RPM, I think has been set to peak, since it is router the controller does not effect the RPM (32000?), it has no means of reducing voltage or current such as a dimmer on a light switch can…

See the post above it explains how to make a cable that the clamp can fit on only one leg.
It also links to a device that servers that purpose.

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