What size dovetail cutter? Mitutoyo test indicator

[Janderso]

You got it. Chip clearancing can be as aggressive as it needs to be to help chip removal- something especially important with aluminum. With such a fine cut, you don't want to be dragging chips and gumming things up. When you rub soft metal chips under great speeds and pressures between the back of the unclearanced cutting tool and the work, it turns into smeary caca. That is the technical term for it.

Keep in mind, you can take as much metal off to clearance the tool as you want, as long as you preserve the cutting edge and leave enough material to provide adequate strength. I would leave the bottom dished at 1 degree like an end mill for some clean-up action on the base of the cut, but that only needs to include half of the tool diameter to work- the back half of the tool does nothing but support the cutting edge and get in the way of exiting chips. Split the difference between the two to suit the job,

The reason the neck of the dovetail isn't coming out well is that part of the tool isn't clearanced as you did with the base of the tool. The way I make my d-bit clearance cuts is really simple using the dividing workhead on the Sheckel (Shars cloned Deckel). It is going to take a wall of six dollar words without pictures and videos, but I can give it a shot. It might be better than trying video on my phone. I am pretty sure Stefan Goetteswinter covered the technique in his introductory d-bit Deckel video, though. You grind the back side and meet the point. Conceptually it's that simple, but there are some setup tricks to pulling it off with the Sheckel as it's equipped. I kinda pick stuff like this up without much input, so I don't have too bad a time navigating areas that are sparse in documentation. The Deckel manual is the gold standard on this subject. There are several models and manuals over the years, so looking at them all and aggregating the information is helpful. Then Harold Hall covers cutters well beyond the d-bit chapter in his workshop practice book. Some of the good texts that cover d-bits go back 120 years, I like to look up the tool and cutter chapters in any shop manuals I find. Kurt Moltrecht is easy to read, he has a chapter on d-bits too.

I guess the only equipment consideration is the wheel; that small profile might be easier to cut with a sorta cheap 1/16" CBN cutoff wheel. A tool that small can be ground on three edges of the CBN wheel, and its narrow kerf would make grinding the cutter's waist easy. I have a $24 Shars wheel that I double-mount with a flaring wheel (2 wheels, one mount) for those critical gash cuts on the faces of end mills- the ones you can't sharpen the mill without. That's what I'd reach for if I were grinding your d-bit pattern.

Last comment since finish is important (and I'm avoiding feeds and speeds because we all own mills here) is to not just stone the tool, but hone it. Hone it until you cut yourself, then go for the next finer stone. You want to be afraid of that tool when you touch the edges.

Nawww, not the last comment. 50 HRC is just fine, it'll cut right through aluminum. If you want a longer lasting tool you can aim for more hardness, but for a few short, slow cuts there is nothing to worry about.

Love it. Thank you.
I’ve been practicing on aluminum, the part to be cut is annealed A2.
Cleaning up that upper edge will be tricky.
I don’t like this small work.

 

[Janderso]

I hope this helps, I used this to create a dovetail for my Mitutoyo test indicator years ago. I'm hoping the geometry will help you.
View attachment 434192View attachment 434193

Nice!
Was that an end mill?

 

[woodchucker]

Nice!
Was that an end mill?

it's a commercially made cutter. I did not make that, I got it in a lot of tooling. Was hoping you could gleam what you need about it. Notice that the section behind the cutter is mostly relieved, it's rounded to provide support, but it is no where near the circumference of the cutter.

The pics don't do justice to the corner that it cuts. It's sharper than it looks. But not pointy like the pinwheel type cutters.

One more thing, and maybe some of the pros here can comment. In woodworking we cut the dovetail in two operations. First a straight cutter down the middle for the minor diameter, then we run the dovetail in. I do the same in machining to A) clear the chips B) the dovetail cutter is delicate to it helps relieve the cutting forces. (especially when you use a pinwheel since those are very delicate)

 

[Janderso]

Got it.
The angle plate is square. It’s my standard.
The 2-4-6 block came out if my home fire. I knew it wouldn’t be close to square. Now I can measure the differences.

Next step, heat treat and grind all components.

 

[Parlo]

If you flip the 2-4-6 block over the indicator will show double the error out of square without needing a standard.

 

[Janderso]

If you flip the 2-4-6 block over the indicator will show double the error out of square without needing a standard.

Good point.

 

[Janderso]

One thing about hobby machinist’s, we make mistakes even though we think we know what we‘re doing.
There is no substitute for experience.

I learned another lesson today. I was quenching this part in oil, the container was not quite big enough meaning it didn’t hold enough oil to stay cool enough throughout the process. I thought I would just finish off the cool down in my little stream.
I heard a cracking sound.

The best part, I get to make another part that will fit better than this one.
Mc Master, tomorrow.
Start over.

I should add, don’t use a plastic bucket when quenching. If you drop the part, it will burn a hole in the bucket and the oil will flow out all over your wife’s concrete .

Boy am I in trouble. I’m use to it.

 

[twhite]

That sucks. At least it was not the base.


Cutting oil is my blood.

 

[Janderso]

That sucks. At least it was not the base.


Cutting oil is my blood.

Ha ha, yeah. The base cracked too.
I just don want to deal with this right now.
I’m in a bad mood.

 

[twhite]

Ha ha, yeah. The base cracked too.
I just don want to deal with this right now.
I’m in a bad mood.

YIKES


Cutting oil is my blood.