Dovetail cutting suggestions

[SirLesPatterson]

I want to clean up part of a 60-degree dovetail after doing some welding repairs. Most of what I will be cutting is MIG weld material which I typically machine with carbide. For this task I bought a HSS Chinese 3/8" diameter "HHIP" cutter off amazon. It was $18 lets just say I don't have a high expectancy for its life span. Because of this I am seeking advice on making the cut as I have never cut a dovetail before.

Specifically cutting speed to start but any other advice would be welcome. I need to cut about 2 linear inches all together, 1 inch on each side.

Thanks.

[Toolguy]

I would only run the cutter 300 - 400 rpm. Dovetail cutters, especially the smaller sizes, are kind of fragile anyway. Use a good cutting oil. It's easy to burn up or break flutes off. Also, feed gently. If you typically use carbide you may need a carbide cutter for this too. When cutting a dovetail from solid, always use a straight end mill to cut out the middle and only use the dovetail mill for the undercut part.

[Deus Machina]

Any time I have to cut a dovetail, I mark it out first and then cut away all I can before getting the specialty cutter at it.
Straight end mills for the center, then I tilt it to just-about-right in the vice and cut out with a broad slot saw or something.
I'm just used to my tiny mill, where dovetailing was a pain.

[Axkiker]

I milled Mig weld one time and thought I was cutting ubotanium. Even with a solid carbide endmill.

good luck with all of that

[SirLesPatterson]

Ok, thanks. It was the RPM's that I was mostly wondering about. I typically just use carbide for welds and HSS for most everything else. I only need this HSS cutter to last for this one task so I'll baby it and see what happens. As you folks have suggested I already cut all the meat I can off with a regular end mill. Thanks.

[digiex_chris]

I've cut a few miles of weld bead with HSS tooling. Infact because of the typically intermittent surface quality of weld bead, I prefer HSS in some situations to carbide because it seems to be more tolerant of impact. Used to be the only way I could get chunks of metal big enough for my projects was to weld pieces of scrap together.Treat it like heat treated 4140 or similar kinda hard material. Maybe 40 - 60 SFPM (400-600 rpm, but the suggestion of even slower than that is a good one because of those fragile tips), and keep moving without jerky movements on the dials. Be VERY smooth on the feed, when you're slow on the rpm like that it's easy to overload the cutter with feed. It's a different challenge than stainless in that it won't really work harden any more than it already is, but because of the typically uneven composition and surface condition of a weld, you can suddenly get too much chip load. Smooth and slow, not much of a big deal for HSS. A stinky dark cutting oil seems to help the edge, stinkier the better.

I find it helpful to have a second cheap cutter around, for when I inevitably underestimate the material and smoke the first one on a material I haven't cut before.

I've abused plenty of cutters on the stuff. It's not that bad. And remember, once you've broken a few teeth off the dovetail cutter, you can always grind half of them off and keep going with reduced feed with the remaining ones, if that's what it takes to get 'er done.

[Arcane]

This little calculator might be useful to some of you.

https://www.carbidedepot.com/formulas-milling.htm

[oldtiffie]

Why not use a shaper as its slow and powerful - relatively robust too - and all that is needed is a good HSS tool bit.

It could be or is said that shapers and dove-tail cutting were made for each other - which is good advice.

[SirLesPatterson]

Why not use a shaper as its slow and powerful - relatively robust too - and all that is needed is a good HSS tool bit.

It could be or is said that shapers and dove-tail cutting were made for each other - which is good advice.

The answer is quite simple. I don't have a shaper, yet.

[oldtiffie]

H-m-m-m.

That is a bit of a problem.

Carry on - as you were.

[DATo]

An "outside the box" solution you might want to consider would be to cut the angle of the dovetail from one long piece of bar stock, cut the bar into two pieces, and then bolt the two pieces to the base of the the part to be dovetailed. i.e. imagine just the angled parts as separate pieces bolted to a base. I've used this approach successfully many times. The advantage is smoother surfaces with a lot less work, a HELL of a lot less cutting, and the ability to jockey the pieces to form an absolutely perfect dovetail geometry. After bolting in place you might also consider pinning or tac welding to maintain the precision.

[SirLesPatterson]

An "outside the box" solution you might want to consider would be to cut the angle of the dovetail from one long piece of bar stock, cut the bar into two pieces, and then bolt the two pieces to the base of the the part to be dovetailed. i.e. imagine just the angled parts as separate pieces bolted to a base. I've used this approach successfully many times. The advantage is smoother surfaces with a lot less work, a HELL of a lot less cutting, and the ability to jockey the pieces to form an absolutely perfect dovetail geometry. After bolting in place you might also consider pinning or tac welding to maintain the precision.

You are correct this idea is outside the box, I like it. It would work very well for this situation and may serve me in the future. I will file this away in my brain where unfortunately it may be lost forever - but hopefully not.

[Paul Alciatore]

Why do you need to grind the broken teeth off? With reduced feed you don't need any more chip space. Actually the dovetail cutters I have used had no problem with chip space. Is there some other reason?

I've cut ...<snip>...

I've abused plenty of cutters on the stuff. It's not that bad. And remember, once you've broken a few teeth off the dovetail cutter, you can always grind half of them off and keep going with reduced feed with the remaining ones, if that's what it takes to get 'er done.

[digiex_chris]

Why do you need to grind the broken teeth off? With reduced feed you don't need any more chip space. Actually the dovetail cutters I have used had no problem with chip space. Is there some other reason?

you're probably right, it would probably work just fine. I just look at the new tip created from the break as often having no more tip relief. Probably wouldn't make a single bit of difference either way.

I've made a slitting saw with 1/3 of it broken off get the job done. Sure wasn't fun, sure was noisy, but I didn't grind and adjust anything there either and it worked. Not the kind of thing I'd do if I were doing it for a living, that's for sure.

Reminds me of the first endmill I broke on my heavier horizontal mill. I had no idea it happened, and continued with the job and only noticed it had broken all but one flute off when I went to change cutters.

[alsinaj]

If you can accurately tilt the work, you can cut dovetails using a normal endmill. You end up with an undercut on the flat side that's the width of the endmill. If the dovetail is large and your endmill is small, it just makes a nice relief groove that traps dirt instead of letting it jam in the corner.

Regarding built-up dovetails, one old-time technique was to bolt the dovetails onto the base, but with a fluxed brass shim in between. Throw the whole thing into something warm enough to melt the brass, and voila! brazed dovetails.