Cutting Dovetails

I have a dovetail milling cutter.

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The shank is marked “20×8 60 degree HSS-E”, this is quite easy to understand. The base of the cutter measusres 20mm diameter, the vertical height of the cutter is 8mm. It cuts 60 degree dovetails and is made of HSS-E.

The box calls it a 20x12x8x63x60D 6FL D Cutter Flatted Shank, this is a lot more information.

  1. 20x – The base diameter
  2. 12x – The diameter of the shank
  3. 8x – The vertical height of the cutting surface
  4. 63x – The overall length of the tool
  5. 60D – 60 Degree Dovetail
  6. 6FL – Six Flutes
  7. D – Unsure, does this mean flatted shank?
  8. Flatted Shank – Means of holding. I’m using collets, so this isn’t perfect but still OK.

I purchased it from Axminster who were doing special offers – I paid £14.75 for it.

I need to cut a bunch of dovetails and I don’t want to spend ages faffing around. So it is worth spending a bit of time planning..

I’m aiming for a 5mm deep dovetail. The base of the dovetail cutter is 20mm, the flutes angle at 60 degrees, so over 5mm depth the radius will reduce by 5/tan60 = 2.89mm, so the width of the cut at the top would be 20-(2*2.89) = 14.22 mm.

Clearly, I’m not going to plunge a dovetail cutter right into the side of the job. It’s a fairly expensive cutter and easily damaged. I want to use it to remove the minimum amount of material.

The dovetails I’m cutting have a top width of 20mm, so it would be a good idea to open out much of this before using the dovetaill cutter.

Ideally, I’d get a 14.22mm end mill, cut a slot with that, move over by 5.78mm and make another pass, leaving a 20.0x5mm notch ready for the dovetail cutter.

However, I don’t have a 14.22mm cutter, and I’d have to change collets even if I did. I need to use a 12mm collet for the dovetail cutter, so that implies using a 12mm end mill.

So my milling procedure becomes….

  1. Set up 12mm end mill on surface of part.
  2. Back off the part and move down by 5mm.
  3. Start the mill and mill a slot through the part.
  4. Move left by 5.75mm
  5. Mill back through the part.
  6. Lift the head, swap the end mill for the dovetail cutter
  7. Drop the head back down to just touch the dovetail cutter to the milled surface.
  8. Mill back through the part.
  9. Move right by 5.75mm
  10. Mill back through the part.
  11. Take the part off and touch the dovetail corners with a file.

So, there we go, a simple way of milling a series of dovetails without too much measuring and faffing about.

I’d be really interested in any comments about how to do it better!

 

 

2 thoughts on “Cutting Dovetails

  1. From your description you aim for 5mm deep dovetail socket, with a base width of 20mm and from your calculations, 14.22mm wide at the surface.

    Point 1 – Your first step is to machine a clearance rebate using a 12mm end mill – surely step 5 would be to move left 2.22mm to achieve a 14.22mm wide square sided rebate?

    Point 2 – If you made a single pass with the 12mm end mill along the centre line of the intended dovetail this would remove the bulk of material. Then by changing to dovetail cutter would prevent having to find centre again.

  2. Thanks for your comment Jrcsh, I believe it is the first blog comment that I’ve had.

    You are perfectly right in what you say, however, I don’t think I explained the task very clearly. I should, as always done a quick drawing. I’ll probably update the blog post when I get a moment.

    The top width is 20mm, The bottom width is (calculated) 25.78 (I’m guessing it is supposed to be an inch).

    So you are bang on – your point 2 is exactly what I’m doing, removing the bulk of the material, then taking out the dovetail, but I’ve got to do it on both sides.

    So thanks for you comment, and I shall try and put more drawings in my posts.

    You’ve made my day 🙂

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