Undercut Tool Question

A friend of mine asked me to mill a replacement handle for his rowboat that the manufacturer doesn’t make anymore. I have it modelled and it has a 5 degree inward draft angle on one of the walls. Does anyone know if there are endmills will a 5 degree outward taper that I can use to match this angle?

Might be faster (and cheaper) to make up a flip jib with registration pins and cut from both sides?

My inclination would be to mill up a set of fixtures:

  • cut bottom
  • cut top
  • hold top at 5 degree angle and make the angled cuts

Is he draft critical to the fit? Or is it a feature of the original manufacturing process (mold draft, for example)? If not critical, I’d ignore it. If it is critical for fit, the easy way is hit it with a file after machining. It’s a handle that bolts on to a rowboat. A Timex, not a Rolex, I would presume.

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Thanks for the ideas. The 5 degree angle is critical in order to match the shape of the rear of the boat so that the holes will line up and can be riveted in place. Will’s suggestion makes sense but I was hoping that there was an angled cutter out there, kind of like a dovetail cutter but with a more gradual angle.

My mistake, I thought you were referring to the handle itself, but now I see what you are trying to do. I suspect that holding the workpiece at an angle would cause the endmill to cut into the part of the plate with the holes, no? You could maybe mill it from the side, but then you’d have to worry about the inside corner which would take on the profile of the cutter diameter.

To answer your original question, the only cutter I can think of that might provide that would be a dovetail bit. Best I could find was a 7-degree: https://www.amazon.com/Freud-22-113-Diameter-7-Degree-Dovetail/dp/B00004T7EH

But, again, you’d run into that far wall which I believe you’re saying is a right angle.

How about 6061 aluminum plate bent to that angle, or a two piece design so you could cut them separately?

Any way you could cut it square and use a shim or something to get the angle? What are you making this out of?

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Not sure this is exactly what you need but you could try an undercut endmill. You would have to leave a radius on the bottom of the drafted wall.


They also go by the name spherical or lollipop.

I think the dovetail bit might be the way to go. I haven’t found a 5 degree yet but Harvey carries a 4 and 6 degree. I also found some more affordable ones from Amana Tool.

Thanks for the help everyone!