Router Bit Longevity

[GregS]

I seem to be going through 1/4" straight cutting bits at a very fast rate. Typically a bit will do me about three cutouts in 3/4" plywood for a 12" speaker before it's toast (literally).

I tried doing cutouts in two passes as well (one at 1/2 depth and the next the rest of the way through) as I thought the bit would be less likely to overheat than doing the whole thickness at once.

I am running the router at the 2nd slowest speed it will run at so I don't think excessive RPM is the problem either.

The bits are not cheap either which is why I'm concerned about going through them this fast.

Is this normal for them to wear out this quickly or is there something I'm doing wrong?
What are other's experience with this?

Thanks,

Greg

[Jazz P Bass]

Cutting wood is basically the same as cutting metal.
In metal working there is a feed & a speed for every metal.
I do not know the specs for wood.
It might pay to research it.
Tool life depends on proper feed & speed.

[riz]

Are you using carbide-tipped bits? What are the speed settings on your router? Slower is not better when cutting wood with a bit of that size, unless the slowest speed is around 20K rpm. I'm suspecting two things: you are using HSS bits, and you are not trimming out the waste first with a jigsaw, just leaving an 1/8 or 1/16" inside the perimeter of your speaker cut-out. If you do so, then you are only trimming off a small amount of material with each pass, instead of immersing the bit in the channel it's cutting. Do you follow me? I would expect a lot more life from it, if it's carbide. I occasionally have to abuse some of my bits, and they still seem to last a long time.

[GregS]

Thanks for the replies.

Are you using carbide-tipped bits?

I don't think so but am not totally sure. I'm not at home where I can check right now.

What are the speed settings on your router? Slower is not better when cutting wood with a bit of that size, unless the slowest speed is around 20K rpm.

The router ranges in speed from 11K rpm to 25K rpm with 6 speed settings. I am running it on the 2nd speed setting which I would estimate to be around 14K given the range and the 6 speed settings. So perhaps I'm running it too slow? I would have thought the opposite as it seems my problem is that the bit is overheating (the bit is charred after use). Wouldn't running it faster cause the bit to heat up more?

I'm suspecting two things: you are using HSS bits, and you are not trimming out the waste first with a jigsaw, just leaving an 1/8 or 1/16" inside the perimeter of your speaker cut-out. If you do so, then you are only trimming off a small amount of material with each pass, instead of immersing the bit in the channel it's cutting. Do you follow me?

HSS bits means high speed ?? What does the other S mean?

I'm not quite following. I'm not using a jig saw at all. The way I'm doing it is I'm using a circular jig that I fabricated to guide the router in a perfect circle. It pivots on a hole drilled in the very centre of the cutout. So I'm cutting a 1/4" swath (the width of the bit). I've tried both cutting the whole 3/4" thickness of the plywood at once and doing it in two passes cutting half the thickness in each pass. After the first pass I clear out any saw dust in the groove from the first pass.

Greg

[Kazooman]

Router Bits

HSS means high speed steel. These bits do tend to dull pretty quickly if they are overheated. Too slow a router speed, too fast a cut, not clearing the shavings, and the glue in plywood all contribute to this.

You really should invest in good carbide bits. They will last much longer than HSS bits. You should also consider a spiral upcut bit like this one

1/4" D x 1" L Solid Carbide Spiral Upcut CMT Router Bit, Power Tool Accessories - McFeely's

The spiral helps lift the cuttings out of the groove allowing the bit to run cooler.

Take you time with multiple passes and as mentioned above use enough speed on the router. Use a shop vac to clean out the groove before making another pass with the bit lowered.

[defaced]

HSS bits means high speed ?? What does the other S mean?

High speed steel. HSS is a very common steel cutting tools are made of. They're usually pretty basic in quality, but work well enough for typical light home use.

Bit charring can be as much about what you're cutting as it is about the temp of the bit. Depending on what the plywood is made of, it may contain a wood with some amount of sap and then glue, both of which char when they get hot.

What Riz is saying is that by cutting the full bit width, you're really taxing your bit unnecessary. Get the hole close to size with a jig saw, and then finish off the hole with the router to get the nice edge you need. Divide and conquer.

[GregS]

Thanks for the replies.

You really should invest in good carbide bits. They will last much longer than HSS bits. You should also consider a spiral upcut bit like this one

I'll look for bits of this nature.

What Riz is saying is that by cutting the full bit width, you're really taxing your bit unnecessary. Get the hole close to size with a jig saw, and then finish off the hole with the router to get the nice edge you need. Divide and conquer.

The problem I have with doing that is that once the centre of the cutout is gone I have nothing to guide the router with so the edge of the cutout would be wind up being irregular. It's only at the very end of the cut when centre piece breaks free that I get a slight notch that I can easily sand out.

Greg

[Kazooman]

One way to get a perfect circle after making the jigsaw rough cut is to use a template and a bit with a bearing. For the template you would just use a piece of plywood (1/4 or 3/8" would do) in which you had carefully made a perfect circle (probably by the method you are using now with a trammel arm and a center pivot point. You then lay out the cutout you want, do the rough cut, clamp the template in place and then clean up the hole using a bit with a bearing on it such as this one:

1/2" D x 1" L FlushTrim Freud Router Bit with Top Bearing, Power Tool Accessories - McFeely's

[riz]

Yeah, the others cleared up what I was trying to say! I know what you're saying about using the circle template technique. I actually do it that way a lot, too, but usually when making a template to then do it the other way I described earlier. I use a 1/4" carbide end mill and take light cuts. If you don't know what an end mill is, google it. With a light enough cut the waste gets a chance to escape, and the end mill spirals to help clear waste as well. If you were using HSS then step on up to carbide and stop wasting your time! You'll be happier! I don't know why they still sell those things, carbide is cheap now.

[riz]

P.s: If you're not doing a lot of this work, like, every day, just do it with the circle jig and an end mill like with the technique you're already using, taking lighter cuts than you are now. Step down maybe 4 times. I have a pin router, which is a BIG router that runs a template from a pin under the bit, so it makes sense for me to make templates first. If you're just doing a couple here and there, a carbide end mill in a hand-held router should last a long time.

[GregS]

Thanks a lot for the tips!

The template and the bit with the guide bearing is a great idea! That never occurred to me. It would also ensure consistency from cut to cut. If I ever get into significant volume of cabinet making I'll definitely do that! I'll make sure to get the carbide bits for the time being.

Just one last clarification: I should be running the router significantly faster than about 14K rpm for what I'm doing? That's the impression I have from some of the responses here.

Thanks again for all the help and advice.

Greg

[cminor9]

another thing you should do when you are done with a router bit is clean it. Anything with a lot of resin or sap (like pine, which is a popular material for guitar amp cabinets) will gunk up your bit and cause it to heat up more. Heat is the enemy. Soak it in mineral spirits or something and wipe it off.

Got that tip from a book I bought with my router. Seems plausible.

I also find that they type of bit determines wear. My roundover bits seem to be as good as new. The straight cutting bits (like you'd use to cut a speaker hole, trim up an edge, etc) are starting to get a little dull. They are carbide tipped, too.

[pdf64]

Callaham advises that cryo treatment extends cutting tool life!
Callaham Vintage Guitars and Parts (Cryogenics / Pickups)

[GregS]

another thing you should do when you are done with a router bit is clean it. Anything with a lot of resin or sap (like pine, which is a popular material for guitar amp cabinets) will gunk up your bit and cause it to heat up more. Heat is the enemy. Soak it in mineral spirits or something and wipe it off.

Got that tip from a book I bought with my router. Seems plausible.

I also find that they type of bit determines wear. My roundover bits seem to be as good as new. The straight cutting bits (like you'd use to cut a speaker hole, trim up an edge, etc) are starting to get a little dull. They are carbide tipped, too.

Yeah, I notice that buildup on mine too. Didn't know how to clean them though. Thanks for the tip.

I don't have much problem with my roundover bits either.

[the great waldo]

Hi

Use good quality carbide bits, stay clear of cheap chinese bits they are crap and wear out in no time. I use bits from trend which really last a long time http://www.trend-uk.com/en/DE/produc...uter_bits.html The speed depends on the cutter diameter small diameter = high speed large diameter = slower speed.

Cheers

Andrew

Andrew