Router bit of-the-month (January)

The router bit-of-the-month featured in Episode 19 is a raised panel bit from Carb-i-tool and has their typical quality features: low friction coating, high quality carbide, anti-kickback design and importantly, accurate dimensioning of the shaft. I have quite a few Carb-i-tool bits, as you may have gathered from other posts, and I always have a great deal of respect for the quality of the bits (and the subsequent quality in finish they produce), as well as the (for me) very important fact that it is a local manufacturer turning out such a good product.

There are a number of profiles available for the raised panel, it is a matter of choosing which one you feel suits the product you are making (and one that complements the rail and stile profile). This cutter is a horizontal style cutter, as opposed to a vertical raised panel bit. In other words, the panel you are routing is presented to the cutter horizontally, ie resting on the router table. I tend to prefer this type of bit, as it means the workpiece is fully supported by the router table, and I don’t have to balance the panel against the router fence. This is particularly important for large panels. So that is the positive aspect, and I feel this is the preferred orientation. However, it does mean the router bit itself has to be huge (and the raised panel bit is often the largest router bit you’d ever own). It is a huge chunk of steel and carbide that the router needs to spin, and as such, you need a strong, heavy duty router to cope with it, and essentially, one that is variable speed. (Check a post I made recently about matching router bit speed to the size of the bit).

If your router cannot cope with such a large bit, then the vertical raised panel bit is the way to go, as it is nowhere near as large a diameter bit, and the router can cope with it much easier. You do need a good, high fence to support the panel then, so that is the compromise.

I tend to use an unbearinged raised panel bit, as it leaves my options open for exactly where I position the fence, and I can centre the fence on the bit, or have it as far forward as I’d like. If the bit had a bearing, I would be limited to just how much of the profile I could expose with the fence. In any respect, I am always going to use a fence with this bit (and a router table). It is way too large to ever consider handholding the router.

Also, given the amount of material this bit can remove, it is highly advisable to take multiple passes to remove all the material. You can achieve this in 2 ways. Either by moving the fence, starting with only a little of the cutter exposed, then expose more for the second pass, then set the fence close to the final position for a third pass and finally set it for the full depth pass so that one is a very light pass (ie removing very little material) which really improves the quality.

The other method is to set the fence in the final position to start, then raise the router bit each time instead, until it is at the correct depth for the final pass. For some reason this is my preferred method, but either is perfectly valid. Both have the problem that if you want to produce another panel later, you need to reposition the fence and the bit depth exactly, so obviously, ideally, you’d have all the panels ready to go, and do the same pass on all the panels one after another before changing bit depth (or fence position), so each panel is at the same stage when you set up for the final pass. It is worthwhile also running a bit of scrap wood through the process at the same time, so that you can set it aside, and use it to help reset up the fence and bit depth if you ever do need to produce another matching panel at a future date.

Episode 19 Router Bit Review Raised Panel Bit

Raised Panel Bit. To complement the rail and stile bit featured last month, the raised panel bit is used to produce the panel that fits into the frame created by the rail and stile. The result is a very traditionally styled raised panel, used for cupboard doors, drawer fronts, and even the sides of some types of furniture.

Woodwork 101 – Router Bit Speeds

A question that comes up on a regular basis, is how fast do I have the router for the different bits?

Obviously, this is only really applicable for variable speed routers. It doesn’t mean that the information here is not applicable for fixed speed routers, but instead indicates at what point (ie at what bit-size) that the fixed speed router should not be used.

What we are really concerned with is the tip speed – ie the speed at the outside edge of the bit.

For example, we have 2 bits – one 80mm diameter (approx 3″) (a panel raising bit), and a 13mm bit (approx 1/2″) (a straight cutter). Our router is set at 22,000RPM.

The tip speed of our 13mm bit will be around 54km/hr (33mph). Whereas our 80mm bit has a tip speed of 330km/hr (206mph).

The large bit is therefore running way too fast for optimum performance and safety. However, it is not a matter of running every bit at dead-slow. A router after all is a high rotary speed tool – the bits are meant to run fast. If you run too slow, you risk chatter, kickback, and tearout. If you run too fast, you risk burning of the wood, and catastrophic failure of the bit.

Here are some suggested (maximum) router speeds, which can be used as a starting point for determining the optimum bit speed. Now unlike any other table that I’ve seen for router bit speeds, mine gives plenty of overlap. This is because I have researched the various recommendations out there and the general consensus seems to lead to a suggested tip speed of 100 – 150 km/hr. If you are uncomfortable with higher speeds, or are going to make a heavier pass, removing large amounts of material, then tend towards the lower end of the scale. For final passes removing very little material, tend towards the upper range.

I have also based them around a router with a speed range of 8000 – 22000 RPM.

00mm – 35mm: 22000 RPM
20mm – 40mm: 20000 RPM
30mm – 45mm: 18000 RPM
35mm – 50mm: 16000 RPM
40mm – 60mm: 14000 RPM
45mm – 70mm: 12000 RPM
55mm – 80mm: 10000 RPM
65mm – 90mm: 8000 RPM

Determining the final speed also needs a few other things to be taken into consideration. Sharpness of the bit, quality of the bit, quality of the router (the bearings, and the collet), density of the material being routed, and material feed rate. (I refer to material here, rather than just wood, as it is feasible to use a router on some metals (such as aluminium), and plastics. However, I am not covering the other issues involved in routing different materials. Even wood has a phenomenal range in material characteristics that I can’t take into account here.)

It is generally a very good idea to make test cuts until you are familiar with the working properties of the material.

Another point is how much material to remove in any one pass. A straight 1/2″ cutter can generally handle a single pass (in softer material such as pine), but taking 2 passes leaves a better finish, and places less load on the router and the bit. In some instances (such as dovetails), multiple passes with the same bit isn’t possible, but even then, you can use a small straight cutter to remove the bulk of the material before switching in the final bit.

For something like a panel raising bit (80-90mm diameter), you may think that running it dead slow and going in one pass is the answer (with a slow feed rate). It isn’t though. The tip speed may be high (150km/hr at 8000RPM), but the centre of the bit is only running at 15km/hr – not enough for a good finish (and never mind the huge load placed on router and bit removing all that material in a single pass). The only answer then, is multiple passes (or removing some of the bulk material on the tablesaw or bandsaw).

A final hint? Listen to the bit – it sound ‘funny’ when at the wrong speed. You get used to the sound that a correctly set router bit makes.

Oh, and one last thing. Any bit over 50mm is a router table job only. Even smaller bits benefit significantly by being used in this manner. Sometimes handheld is the only way, but if I have a choice, I use the router table every time.

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