Small face mill using tangential cutter

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I recently made a small face mill that uses a 3/16" diameter HSS rod for the cutter. The idea was to replace an indexable face mill with something that would handle interrupted cuts better (I always seem to chip the inserts). I like the concept of the tangential cutter because they're dead easy to sharpen. To simplify some of the machining steps I made the face mill in two parts -- the arbor and the holder for the cutter. I started with a 3/4" rod of HRS for the arbor and some 1.25" diameter 4140 for the holder. The photos below show a few steps in the process of making it, after I did the initial lathe work to turn the 3/4" rod down to 11/16" to fit my R8 collet and smoothed/faced the holder down to a .486" thick disk (there was no specific thickness target, it just ended up that thick).

This photo shows the holder in my angle vise. The vise is set to 12 degrees from horizontal, and I'm milling a flat preliiminary to drilling the 3/16" hole for my HSS rod.
The slot (machined in a previous step) is .1" deep and .5" wide, and matches a tang milled on the end of my arbor. With this approach the bolt that joins the two pieces doesn't have to resist the torque produced by the cutter when it's removing metal....and I can make different-sized holders as needed. To make it easy to accurately rotate the holder 90 degrees, before breaking down the previous setup I also milled two flats on the side of the holder. That gave me a nice secondary reference plane.
making hole for bit.JPG

The photo below shows the holder and arbor assembled to make sure they fit OK. This photo actually predates the first one shown above. My old drafting ruler is there to provide a sense of scale. I was able to machine the slot and tang accurately enough to get a friction fit. 'Course, if I hadn't done so well I wouldn't have mentioned it :rolleyes:.
Cutter A.JPG

Below shows the finished product, complete with a shortened hunk of HSS that's been ground to 30 degrees on the end. I wrote a spreadsheet to calculate the offset necessary to place the tip of the cutter so it is exactly tangential to the circle swept out by the tool, when the cutter is projecting .1" below the bottom face of the holder. I also used the same spreadsheet to determine where I needed to drill/tap the hole for the set screw.
After grinding the HSS I did notice a small burr on the end so I honed it with a 600 grit diamond file. That produced an edge that would easily shave my fingernail.
end mill with cutter.JPG

Below shows the result when I tried my face mill on a piece of 6061. I also tried it on some HRS with a .01" depth, full .75" wide cut and it worked just fine. No chatter, nice smooth surface. This was done on my Sieg SX2 mini mill, not the most powerful beast around, so I call it a success.
I was concerned that the cutting forces would push the cutter into the holder but that wasn't a problem. Not so far, anyway....
trial run.JPG
 
Nice work ! Proof is in the pudding ! The finish is very tasteful and looks excellent, nice design work !
 
Thanks for all the positive responses!

I have attached the spreadsheet I used to calculate the locations of the holes used to hold the cutter and set screw. I tried to make the program as generic as possible so the design could easily be scaled up. Downsizing it might be difficult, unless you also reduce the size of the arbor or drastically reduce the length of the HSS rod so it doesn't protrude through the top of the holder. As it was, I had to reduce the length of the rod so I could grasp a decent length of the arbor in my R8 collet. The piece I used is long enough to be resharpened quite a few times before I would need to replace it. Another alternative I just thought of would be to make the holder thicker (taller), to accommodate a longer rod.
 

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  • Tangential face mill calcs.xls
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not sure i get it. what part of the rod is the cutting edge?
 
Grinding the end of the rod at an angle produces an elliptical facet. The cutting edge is the narrow end of the ellipse. The relief angle(s) are produced by tilting the rod at a 12 degree angle and the 30 degree grind on the end of the rod.

The next-to-last photo in my original post shows the rod installed in the holder.

I'm thinking of making a holder for my lathe's QCTP to use a similar style of cutter. It will be interesting to see how that performs, and the holder will be much easier to make compared to the tangential designs I've seen. However, unlike the tangential designs it won't be able to turn to a square shoulder.
 
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I really like this idea, great work.
Flycutters freak me out a bit as they whirl around looking unbalanced and ready to fly apart.




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Very imaginative and beautiful work.
Just to be sure I understand, with a 12 degree hole and a 30 degree grind on the end, relief at the cut would be 18 degrees?
What maximum depth of cut would you try on steel?
Please keep us posted on what you come up with for use on a lathe.
Thanks for sharing.
 
Very imaginative and beautiful work.
Just to be sure I understand, with a 12 degree hole and a 30 degree grind on the end, relief at the cut would be 18 degrees?
What maximum depth of cut would you try on steel?
Please keep us posted on what you come up with for use on a lathe.
Thanks for sharing.
Yes, that's how the relief angles work out. I tried a .01" depth of cut in some HRS and got a nice finish, with no complaints from the tool or mill.

It would be easy to try a grind angle less than 30 degrees (as long as it's at least 12 degrees). I had thought of trying something like 20 degrees to get a more robust cutting edge....that is, if the 30 degrees turns out to be a little too fragile. So far so good though.
 
I really like this idea, great work.
Flycutters freak me out a bit as they whirl around looking unbalanced and ready to fly apart.




Sent from my iPhone using Tapatalk
Thanks for the kind words!
I've got a flycutter as well but it really is too big for most of the stuff I do. And like you I'm pretty paranoid about that big, unbalanced thing spinning around. The tool I made is similar to a flycutter, in that it's a single cutter spinning 'round but much smaller and the geometry of the cutter itself is different.
 
"Grinding the end of the rod at an angle produces an elliptical facet. The cutting edge is the narrow end of the ellipse. The relief angle(s) are produced by tilting the rod at a 12 degree angle and the 30 degree grind on the end of the rod.

The next-to-last photo in my original post shows the rod installed in the holder."

thats what i figured. why then do you call it tangential?

o.k., maybe i get it now: the two angles are not in the same orientation. is the 12° from axis of rotation? but then the narrow end wouldnt be the cutting edge. on the pict. it looks like the angles line up (30-12=18°)

this is a cutter i made:

ball cutter 031.jpgball cutter 031.jpg

its originally for a radius attachement but it cuts and faces wery well.

(how to delete the second pict.?)
 
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