Thread: Planing bit (sanity check)

Hi Yoboseyo

I tried that very same setup (same router, same bit) but didn't get a very good result. Went back to a 25mm bit and result was very much better. I think the 50mm bit spins too fast in the 3600BR and really needs a variable speed router at a slower speed to get a reasonable result. I was flattening a workbench top of hardwood approx. 2100mm x 900mm and found the 50mm bit burnt the krapper out of the timber and left the centre higher than the edges. The 25mm bit only left the occasional burn mark (operator error?) and flattened the top much better with no centre hump.

Hope this helps.

Regards
Twosheds

If you can't slow it down, 50mm is probably too big unless you can feed really fast. Also, don't be tempted by the 6-flute bits, you can't feed fast enough by hand to make them work, 2 flutes is plenty.

I flatten slabs with a 50mm x 12mm two flute bit. The router is a Makita 3612C. The C is the difference - variable speed 9000 - 23000 rpm.
The BR is a constant speed router, running at 23000rpm, this is way too fast for a 50mm cutter. Even a 25mm cutter would be having trouble in hard timber. For soft timbers I find I can work at a steady pass if the router speed is set to about 15000 rpm. For dense hardwoods I drop back to the 9000rpm. At this speed a 50mm cutter can be worked comfortably, without having to rush to prevent burning.

I have done a fair bit of surfacing work with my router, bought a $75 Torquata bit with 5 tct cutters and pretty much wrecked it first time out.
Ended up buying a Carbi-tool 3 flute bit which takes replacement 4 face tct inserts, It's an amazing cutter although costs $ 200.
I run this at about 12000 rpm you can get amazing surface finish if used carefully,

Thanks for the responses, all. I ordered a 1" bit and I'll take shallow cuts

Originally Posted by twosheds

the 50mm bit burnt the krapper out of the timber and left the centre higher than the edges.

How does this happen?

I think the centre of the workbench surface was higher because the 50mm planing bit was riding on top of the timber to some extent rather than cutting to its full depth, hence the severe burn marks as well. The edge portion was at the right height so to speak because the flutes of the bit cut into the edge at the correct height initially but gradually rode higher on top of the timber as I pushed it toward the centre of the benchtop. Well anyway that is what I think caused it.

All I did was change to a 25mm 2 flute bit while leaving the jig setup exactly as it was - hey presto.. flat surface with minimal burning.

Anybody want to buy a little used 50mm 6 flute HSS surface planning bit???

Regards
Twosheds

Before we start, please note that I am not having a go at you, this is a perfect opportunity to demonstrate how important bit selection is and some of the things to consider. This is the science side to machining that's often overlooked because people simply don't know about it.

Originally Posted by twosheds

6 flute HSS

There's your problem (actually, two problems).

1) The average cutter surface speed (how fast the tips of the cutter are moving) on a jointer or thicknesser with HSS knives is around 1500 m/min (give or take a few hundred), the surface speed of your bit was up at 3600 m/min - that's 140% over the normal speed. If it was carbide, you could get away with running that fast, but HSS can't handle it.

2) The average thicknesser takes about 0.3-0.4mm per blade at the slowest feed of 6-7 m/min. Assuming you feed your router that fast by hand (it's doable), you'd be taking 0.053mm per cut; at that point, you're scraping more than cutting. Scraping is bad enough for a cutting edge as it is (if you've ever used a chisel as a scraper to clean up a bit of glue squeezeout/staining, you'd know just how fast that sharp edge goes dull), now factor in all the heat being generated. Let's take a speed of 0.2 m/sec (12 m/min) as a ballpark speed for hand scraping. I'm sure you've felt how hot a scraper gets after just a few minutes of use, now imagine how hot it'd be moving 300x as fast. Now you've got a hot, dull edge whizzing around and there's your burnt job.

It all comes down to heat management; heat is the enemy of sharp edges, the hotter it gets, the shorter its life. When you're cutting and making chips, they're carrying some of the heat away, if you're scraping and making dust, all the heat is soaking into the tool and the job.

More flutes is NOT always more better. Extra flutes only help if you can feed the tool fast enough (or slow your RPMs) to make sure every one of them is still cutting effectively and keeping the heat at a level appropriate to the tool material.

I agree with you Elan. And that's a good explanation about the heat generated.

But I found out the hard way. Lesson learned.

Regards
Twosheds

I've used a 6 flute 50mm Carb i tool surface planer bit (TSS 13 1/2) in a TRA001 with no burning or ruination of the bit. But the TRA001 does have speed control and it was wound down to 14500 rpm.