Sharpening counter sinks

[Ken S]

Excellent work, Jan!

Ken

[Jan]

Thank you, Ken! 

To set the lip relief (clearance) angle Tormek uses the DBS-22 setting template. This may be used in our case only if the height of the countersink centre above the USB is near to the corresponding height of the DBS-22.

My clearance angle setting method takes the drill bit diameter or height of the countersink centre above the base/USB into account. http://forum.tormek.com/index.php?topic=3226.0

Jan

[Serge Nelissen]

Prototype almost ready!
Pictures follow soon.

Serge

[Serge Nelissen]

Here it is!

Assemble 2 tool supports like this...
Pic 1 normal view
Pic 2 top view
Pic 3 front view
Pic 4 side view
Pic 5 bottom view

A steel tube, 12mm external, 10mm internal diameter
Pic 6

Place the tube in the upper tool support. Stick out in front 1mm to avoid friction with the tool support. Pay attention that the tool support has been shortened 15mm (otherwise long counter sinks won't fit)
Pic 7

The tube should stick out about 15mm at the back.
Pic 8

Make an 'L', as wide as the sharpening stone, height 77mm, as deep as the tool support. And 2 bolts 3mm diam. Pay attention to the white line, this will be the reference to the top of the tool support.
Pic 9

Fix the 'L' to the upper tool support. The height of the 'L' above the upper tool support must be 51.5mm (explanation later)
Pic 10

Make a ruler, 30 cm long, 4 cm high, 4-5mm thick and provide a hook.
Pic 11

This is the ring between the grinding stone and the machine. We are going to use it to set a correct angle of the tool support so that the axis of the countersink goes through the axis of the grinding stone. This ring is 36mm in diameter And the height of the axis of the countersink is 33.5mm. 33.5 + 36/2 = 51.5mm. This is the height of the 'L'.
Pic 12

Now, use the ruler you made, put it on the 'ring' and align the tool support with the ruler. Now we are sure the axis of the counter sink goes through the axis of the machine. This is needed to correctly set the horizontal angle for the counter sink conus.
Pic 13

Then, take a steel bar, 10mm diam. ⅜ thread in front for a chuck, M10 thread at the end. Fix a chuck as short as possible (I found one from Makita).
Pic 14

Place the steel bar with chuck in the jig.
Pic 15

Place a spring, a washer and a nut.
Pic 16

Assemble and fix a hand wheel. Ready!
Pic 17

Pictures: https://www.dropbox.com/sh/veofqyl9pnkzfcq/AACdxjfexZaYbzP5bZqOfHeoa?dl=0

How does it work? Tomorrow...

Serge

[Serge Nelissen]

Oh, I forgot the last picture... This is how it looks like as a whole:

https://www.dropbox.com/s/htttsm12riyq7r4/Jig-18.jpg?dl=0

[Serge Nelissen]

Since the jig can't move sideways during sharpening and because countersinks are hard, a standard grinding stone soon shows scores. Therefore I think a black stone is recommended.

I did a few tests... although the cones are perfectly sharpened, the sinks don't cut well. I know why: in between 2 flutes, the sink drops to the grinding stone and the cutting edge is rounded. I see 2 solutions:
1 after sharpening the cone, sharpen the inner side of the cutting edges with the jig in a 90° position and at the edge of the grinding stone. Difficult to do well!
2 modify the jig so it retracts the sink just at the cutting edge. I don't know yet how to do that

[Jan]

Serge, excellent countersink jig, congrats!.
Thanks for posting the detailed description and many pictures. Appreciated. 

In my opinion the reason why the countersinks do no cut well may be absence of sufficient relief behind the cutting edges. Similarly to drill bit, countersink cutting edge must have a relief angle also (typically 5 to 8°). Relief behind the cutting edge has even to be slightly larger and must continue around the "conical" surface segment of the countersink's tip. Strictly speaking it is not an exact right cone!

I have used the marker method to find spots where additional steel has to be removed. 

Good luck in tuning the final details!

Jan

[Serge Nelissen]

Hello Jan,

Any idea how a m

[Serge Nelissen]

Hello Jan,

Any idea how a relief angle can be achieved? I have no idea (yet).

Serge

[Jan]

Serge, in my case there was some play in the jig, so it was sufficient to apply more pressure behind the cutting edge.

In your case the jig play is probably much smaller and so you can proceed similarly as when grinding a secondary facet on a drill bit. It means you enlarge the clearance angle by some 10 degrees and grind off segment of the "conical" surface behind the edge. It may be necessary to repeat this procedure for larger countersinks.

Use the marker, blacken the whole countersink surface and make a test countersinking. If the marker is removed from the conical surface you need to remove more steel here.

Jan

[Serge Nelissen]

You were right about the relief angle Jan! It now cuts like crazy

Here is the proof with the marker: https://www.dropbox.com/s/dn9dwqv05fwynkv/jig-19.jpg?dl=0

Serge

[Jan]

You are welcome, Serge, I rejoice with you that the added relief helped to resolve the issue! 

Jan

[RickKrung]

In my opinion the reason why the countersinks do no cut well may be absence of sufficient relief behind the cutting edges. Similarly to drill bit, countersink cutting edge must have a relief angle also (typically 5 to 8°). Relief behind the cutting edge has even to be slightly larger and must continue around the "conical" surface segment of the countersink's tip. Strictly speaking it is not an exact right cone!

Jan

Hello Jan,

Any idea how a relief angle can be achieved? I have no idea (yet).

Serge

Serge, in my case there was some play in the jig, so it was sufficient to apply more pressure behind the cutting edge.

In your case the jig play is probably much smaller and so you can proceed similarly as when grinding a secondary facet on a drill bit. It means you enlarge the clearance angle by some 10 degrees and grind off segment of the "conical" surface behind the edge. It may be necessary to repeat this procedure for larger countersinks.

Use the marker, blacken the whole countersink surface and make a test countersinking. If the marker is removed from the conical surface you need to remove more steel here.

Jan

I didn't really follow the above conversation.  But, I believe what you need is some sort of cam that guides the countersink in that conical path, although it is a gradually changing conical shape and needs to continue for around 270 deg. in the case of a single fluted countersink.  This is how Drill Doctor does it (see photo) (except the DD photo shows a cam designed for a two fluted drill, so it is much shorter.

Rick

[Jan]

Rick, you are, of course, correct! 

My approach was guided by the idea to keep the solution versatile (e.g. what concerns the number of flutes) but as simple as possible. My intention was to replicate the existing edges only. Countersinks are usually made off hard steel and so my wish was to remove minimum amount of steel.

In my opinion the cam guiding approach may result in in re-grounding the countersink.

Jan