Testing a carbide insert slab flattening bit.. (SB25-2)

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This 1/2″ shank bit clears the surface of your Spoilboard, creating a base surface that is perpendicular to the router motor. This tool measures 2-1/2″ wide and comes with 2 carbide inserts installed plus an additional pack of 10 carbide inserts for a total of 12 that can be used on all four cutting edges, giving you a total of 24 complete blade changes! That comes out to $16.00 per blade change. Compare that to the cost of a typical carbide-tipped flattening bit that must be resharpened when dull.


  1. This was very helpful. How do you determine the thickness of the slab to feed into vcarve? the slab is not 100% flat so you even if you have a 3 milled slab there might be a section or two that are higher than 3″ off your spoil board. Second, and just point me to the article or help file but how do you get vcarve toolpath to go the length of the slab. I can only get my toolpath to be across
    thanks, Jay- super glad you are doing more with the CNC.

    • I don’t worry about that in VCarve. I just make the file so it will take off one pass and the Z-0 point on the material surface. At first, I manually jog the machine to get rid of the high spots until I’m satisfied with letting the machine work on its own. Then I zero the Z axis and run the file. From there it’s hands off. If the cut is complete and I need to go deeper I use MDI (manual data input) to jog the machine down the exact depth of cut the file completed, zero the Z again, and run the file again.

  2. I wonder if a version of this bit (smaller maybe) would work with my big router and my flattening sled jig? About 30 years ago I worked in a cabinet shop where we used a double tooth carbide cutting head, 3” diameter, in a radial arm saw, set vertically to flatten some odd boards. It was a terrifying operation. The cutting head was from Sears. Good times. Anyhow, I might need to visit bits and bits and pick up one of these cutters. Then I’ll just have to get a cnc.

    • While I’ve never personally done it myself I don’t see a reason why I wouldn’t try it. Obviously, it’s a bigger bit and therefore can have a bigger catch so I would have to be very mindful of not getting too aggressive. I would also be very mindful of having good control of the router and sled as to not let it get away from me.

  3. Thank you – as a complete newb to CNC, this content is very valuable. I just got the motor cables and proximity sensors for my Avid CNC 4848 this week and am hoping to get power to the 8.7 hp spindle today.

    • Nice! Are you running the 8.7 on 3 phase? I have that spindle in house but haven’t installed it yet. I’ll be on 240v single phase so it will be 4.7kw or 6.3hp.

  4. You might take a look at g-wizard (now cnccookbook.com). They purport to enable you to know your optimum speeds/feeds for just about any tool in any material. I’ve been reading about them for many years but haven’t actually used it yet.

  5. Hi, Jay – Have you thought of using a variable frequency drive to give you 3 phase power? It would have the advantage of full power and speed control as a bonus.

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