Router Runout?

[bigz1]

Just machined a cylinder 120 diameter by 30mm thick in MDF. Unfortunately it sides have a taper making it a truncated cone is this due to router runout? The piece widens the lower the tool cut. Taper is equal all the way round.

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[ger21]

How much is the taper? I'd say it's unlikely due to runout, and more likely from machine flex. Is it consistent all the way around?

[bigz1]

Yes its consistent all the way around. Approx deviation in diameter is 0.5mm. The bottom of the cut is more accurate. Normally I use a slight increase to the diameter of the tool for shallow cuts but I wasn't too concerned about the tolerance on this piece. But would like to nail this problem for future work.

[stevespo]

Use the largest diameter bit that makes sense for the project. I'd probably use a .25" upcut. Take lighter cuts and slow down your feed rate, until the taper disappears. Let us know what you're using for tooling, feedrate, spindle speed, etc.

You could also try a multi-step roughing cycle, leaving the part .010" oversized. Then come in with a single full depth pass to bring it to final dimension. You'll need something with a cutting edge at least 30mm tall. These are all worth a try.

If your router does have some runout, you might discover you have to enlarge the part slightly (or alter the toolpath) to compensate for a .25" cutter actually removing .252" worth of material. It all depends on what kind of accuracy you need to achieve.

Steve