Recommendation? Dovetail Cutter Specs/Dimensions for Slipjoint Crescent Nail Nicks

[David Schott]

Hello,
My slipjoints are progressing to the point they are extremely clean but something I've always struggled with is a CRISP nail nick. I am not looking for a rectangular notch. I want that ultra sharp crescent look.

I am willing to put down some money for the right tooling.

I have a bridgeport mill but it is much older (1944) and the MAX shank I can put in there is 1/2".

I have seen others advising using a cup grinder or cutoff with a dressed angle cut in. I've never been able to locate the mandrel, cutoff types and such to do this and it seems itll end up costing or being enough headache the dovetail cutter route would take.

All will be generally medium to large sized blades.

I have seen advised a dovetail cutter that is about 1+3/8" to give the right radius to make this cut deep enough. Process straightforward once i have it.

Every dovetail cutter of any size I can find has a 5/8" shaft. Do large diameter dovetail cutters even exist with 1/2" shanks? Someone here may have some advice to work through this. I've failed at flycutters and dremel discs so far.

 

[AVigil]

Go to Birdvis instagram stories, he showed a big cutter he uses. You probably can get it from any tool house

 

[Ken H>]

I use a flycutter with the tool bit shaped to give the crescent look. A HHS tool bit doesn't last long at all, but carbide tipped lathe tool seems to work fairly good. The diameter required depends on how long you want the nick to be, and how deep you want it cut. I normally make slipjoint blades in the .090" range with nick cut about .040" to .045" deep making a nick about 3/4" long.

 

[David Schott]

I played with flycutters tonight and I think I'm onto something! I did this in 1095...I tried 154CM and didnt fair so well but I dont think I'm even sharpening the point correctly...I need to both look up a better shape to do this with as well as increase my diameter.

 

[Sam Dean]

Any tool grinder can run a tool shank down to the size you need. Or, you can always have a custom tool made. If there was enough interest here, and a standard diameter and angle could be defined, I wouldn't mind making a batch...

I really think 1-3/8'' is too small. A 1-3/8'' X 60° dovetail makes a nick 0.489'' long at 0.045'' deep.

You need to go to a 3'' cutter diameter to get a nick 0.729'' long, at 0.045'' deep.

A 60° single angle slitting saw & stub arbor is what you need.

 

[David Schott]

Interesti

A 60° single angle slitting saw & stub arbor is what you need.

Interesting! I see these semi-affordable but they all have what look like 1" holes so I assume thats the stub armor size I'd need but again I'd have to have someone turn down (I assume its hardened) the shaft to 1/2"

I do have an older logan 10" swing lathe....which would take any size shaft if I put the shaft in the chuck. I wonder if I could figure out a setup to hold the blade vertically and move it into a larger flycutter or the saw type you described above.

Here are a few terrible pics i found with the idea:

This one not a lathe but same concept, blade under cutter:

These two look like a lathe setup (horrid quality)

 

[Daniel Carraher]

They make 1/2” arbors for 1” hole size slitting saws

 

[Sam Dean]

Interesti


Interesting! I see these semi-affordable but they all have what look like 1" holes so I assume thats the stub armor size I'd need but again I'd have to have someone turn down (I assume its hardened) the shaft to 1/2"

I do have an older logan 10" swing lathe....which would take any size shaft if I put the shaft in the chuck. I wonder if I could figure out a setup to hold the blade vertically and move it into a larger flycutter or the saw type you described above.

Here are a few terrible pics i found with the idea:

This one not a lathe but same concept, blade under cutter:

These two look like a lathe setup (horrid quality)

You could definitely make the lathe setup work by fixturing the blade in the tool holder. The downside is that you lose 1 axis of movement compared to the mill, which might make positioning pretty difficult.

Your Bridgeport has a #2 Morse spindle taper, right? A #2MT to ER32 adaptor would let you hold up to 3/4'' shanks. https://www.toolots.com/chongde-mt2-er32-morse-taper-milling-collet-chuck-tool-holder.html

You could also find or make a #2MT arbor to hold any standard milling cutter. Even this might work OK, since you'd be taking such a light cut: https://www.ebay.com/itm/Slitting-S...8-Draw-Bar-Hold-From-1-2-1-Bore-/264619675129

 

[David Schott]

Your Bridgeport has a #2 Morse spindle taper, right? A #2MT to ER32 adaptor would let you hold up to 3/4'' shanks. https://www.toolots.com/chongde-mt2-er32-morse-taper-milling-collet-chuck-tool-holder.html

You could also find or make a #2MT arbor to hold any standard milling cutter. Even this might work OK, since you'd be taking such a light cut: https://www.ebay.com/itm/Slitting-S...8-Draw-Bar-Hold-From-1-2-1-Bore-/264619675129

I actually have a pretty old 1944 M-head that takes B&S#7 collets which max out at 1/2"...let me check out those other links

 

[David Schott]

Playing around a bit more I'm starting to have some success. I widened my flycutter channel to fit some of my lathe carbide tooling. This also let me widen the arc to about 3"

Here's one done with an upside down carbide insert that I believe is for threading...my only issue is its laking a defined "straight" edge so I need to angle the insert down even further to make the "bottom" flat. It is, however, insanely crisp so I feel like I'm on the right path:

 

[David Schott]

Success! I eventually figured out a weird setup with a carbide threading insert placed a bit offset into a flycutter arbor that I milled out to fit my lathe inserts. I believe this is about a 3.5-4" radius. It is 60% into the thickness of the blade and pretty GD crisp. I did this on my 1944 Bridgeport. Here's the tooling and result:

 

[Sam Dean]

That looks great!

 

[Josh K]

That looks fantastic!

I know many makers use a variety of setups to get a nail nick cut. I think Tim Robertson had a nice clip on Instagram of how he does it with a flycutter and a mill. I'm sure tooling is a big part of figuring out what you can do. There are some absolutely beautiful Dremel cut nicks out there.

Profile https://www.instagram.com/p/BynsIt9nRv1/ and an action shot https://www.instagram.com/p/BylOpf5Hztt/

And attached in case anyone doesn't want to bounce to IG

 

[David Schott]

That looks fantastic!

I know many makers use a variety of setups to get a nail nick cut. I think Tim Robertson had a nice clip on Instagram of how he does it with a flycutter and a mill. I'm sure tooling is a big part of figuring out what you can do. There are some absolutely beautiful Dremel cut nicks out there.

Profile https://www.instagram.com/p/BynsIt9nRv1/ and an action shot https://www.instagram.com/p/BylOpf5Hztt/

And attached in case anyone doesn't want to bounce to IG

That video and setup is almost exactly what I went with. Given that I was using carbide, testing showed me I really didnt need to slow my mill down much at all. I still fed very slowly but I ran the mill at the same speed I normally mill any other steel and had no issues. (this may or may not have been a good idea, I'm a machinist hack) I did 5-10 nicks on various test steels and the carbide insert is still razor sharp. I do wish the angle was a bit wider but the threading inserts are all less than that, i would think.

Now that I can put out a good one I can experiment and throw out the small box of various things i've made or tried in the attempts to master this. I also think simply making the angle I'm cutting at more extreme should widen things.

Slipjoints are hard enough without worrying about this detail!