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Cutting external dovetails in hardened steel, indexable vs solid carbide?

Joined
Sep 21, 2023
Location
Dallas, TX
I'm fixing to run some scope rails out of pre-hardened 4142 steel (~25RC) that have an external dovetail as shown in the attached picture. I did the initial run of prototypes using a cheap HSS dovetail cutter, which took forever. We're talking like, 45 minutes to do two passes per side based on what GWizard told me to do (and which I stuck with because I didn't want to trash the cutter mid-part). The parts came out beautiful, but for future runs I naturally want to decrease cycle time significantly. The obvious choice is carbide, but since I am inexperienced with dovetail cutters in general I wanted some opinions on whether a solid carbide cutter or an indexable cutter is right for my application.

This is the solid carbide cutter I am looking at: https://www.harveytool.com/products/tool-details-738032-c3

This is the style of indexable cutter I am eyeing: https://www.ebay.com/itm/234440202362

Which is going to allow for a greater material removal rate? Which will provide a better surface finish?

My "gut instinct" tells me the indexable cutter is more economical but is going to be slower and have a worse surface finish, but I am open to being corrected on this assumption. If a big 5/8"+ solid carbide cutter is going to be significantly faster than the indexable and provide a high quality finish, I don't really care if it costs more up front, but I don't know if there are tool life considerations that make that really not worth it.

Going with a larger diameter on the solid carbide cutter (say, to a 5/8" instead of 1/2") would be no issue as this is an external dovetail and I am not having to cut an internal dovetail in a corresponding part, so that could come with nothing but advantages over the smaller solid carbide option aside from cost of the cutter. Would this pay off economically in terms of increased tool life due to the thicker neck, or is this a case of diminishing returns?

Of the indexable cutters I have found, they seem to take one of either TDEX or TCMT carbide inserts. I'm a fan of Kennametal, and they only carry TCMTs. I haven't found a respectable "big name" brand that carries TDEX inserts, only no-name Chinese brands on eBay. I'm hoping someone with more knowledge on triangle inserts (which I normally never use) can chime in. I'm sure the type and grade of inserts plays a huge factor in the viability of an indexable cutter for my application.

Thanks in advance,
Tyler.
 

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Hi Sovereign Development:
You need to be able to cut a dovetail at 60 IPM minimum for roughing and to get a nice finish maybe 30 IPM for a finish pass in 4140 at 25 RC.
So maybe 5 minutes for a 6" long dovetail 3/16" tall.

I've had best success roughing with stepdowns and simultaneous stepovers on dovetails that were tall enough that you couldn't just take the whole height in one pass.
So I walk down the angled face of the dovetail taking a wider and wider pass on the face of the cutter, but nothing on the side of the cutter.
Once I'm down I take a kiss pass of maybe 0.002" to 0.005" to finish the sides of the dovetail.
If my cutter is fragile (small shank or small corner radius) I take a lot of shallow but fast passes, and I'll often confine my stepdown to less than one corner radius on the cutter, and bump up my feedrate to something nice and quick like maybe 100 IPM and a surface speed of 500 SFM (which is kinda pushing it for 4140 at 25 RC).
For a 4 flute cutter that makes a pretty aggressive chipload but the DOC is so shallow that there is little strain on the cutter so long as you keep the chips clear.
I've found it can handle it better than a bigger DOC and a smaller chipload, but I do mostly prototyping and others will have other strategies.

I can peel out a dovetail without ever pushing the cutter very much and so long as I stay in the "zone" for surface speed, the cutter will last forever.
I'm talking about carbide cutters of course, and I'm talking about milling them on a VMC, not a manual mill.

That has worked for me so I always do dovetails that way.
I usually use home ground 2 or 4 flute carbide cutters, but I have a good grinding setup.
You can buy solid carbide doves from Harvey.
I've never been happy with the results when I've tried insert dovetail cutters, but others may have very different opinions.

Cheers

Marcus
www.implant-mechanix.com
www.vancouverwireedm.com
 
Agree with Marcus the insert dovetail cutters don’t give a good finish
 
I've been using a Dorian Tool dovetail cutter for 4 years or so in aluminum. Mine is only 3/4" diameter because it has to fit between parts in a strip. It uses TDEX inserts which Dorian seems to make, I just looked. I've made a few thousand parts with it and never changed inserts and the finish is good. But I've never cut anything but aluminum with it. One thing that can be a pain for sight mounts is getting a cutter with the right radius. The tendency for many dovetail cutters is to make the radius too big for this application.
 
I used the Harvey / Helical solid carbide dovetail cutters for stock prep in Ti6Al4V-ELI, with good results. Single pass, but I wasn't holding a tolerance or worried about finish.
 
Production? I'd look hard at roughing with an indexable tool, then finish with solid carbide.

For the finisher, I would also seriously consider a custom tool with maybe 8-10 flutes.

I've never used an indexable dovetail, can't help you there.
 
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I've never gotten good results with my indexable dovetail cutter. It always leaves ripples in the finish and it sounds like its hammering in the cut.

My go to is Harvey solid carbide dovetail cutters, they leave a good finish and last a decent while as long as you don't overload them.
 
For the cost of that cutter, if its a repeat production part, I would figure out how to get a good(not that cheap one) indexable to do it.
If its a single order different story, get carbide.
AB Tools has good indexable dovetail cutters.
@Orange Vise can chime in, but I think he mentioned to me he uses an AB tool indexable cutter for the Carvesmart cut in his vises.
 
For the cost of that cutter, if its a repeat production part, I would figure out how to get a good(not that cheap one) indexable to do it.
If its a single order different story, get carbide.
AB Tools has good indexable dovetail cutters.
@Orange Vise can chime in, but I think he mentioned to me he uses an AB tool indexable cutter for the Carvesmart cut in his vises.
I also use an AB "dexi-dovetail" cutter to make steel vise jaws, and a few other things. It works great. Nice finish, and not too expensive.\

I've also had good luck with Ingersoll ChipSurfer dovetail cutters, if it's a high production job.

 
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I also use an AB "dexi-dovetail" cutter to make steel vise jaws, and a few other things. It works great. Nice finish, and not too expensive.\

I've also had good luck with Ingersoll ChipSurfer dovetail cutters, if it's a high production job.

I was gonna mention these but couldn't find them to link, I thought PhHorn had some also, but couldn't find them quickly either.
ISCAR Also.
 
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I was gonna mention these but couldn't find them to link, I thought PhHorn had some also, but couldn't find them quickly either.
ISCAR Also.

I have the Iscar MM GRIT. It is a fantastic tool. The insert heads cost a bit more than inserts on the Dexi, but you get 6 flutes instead of 3 plus a much smaller diameter resulting in much faster feeds/speeds. I also think the accuracy and cut quality is a bit nicer than the Dexi.

 
I've been using a Dorian Tool dovetail cutter for 4 years or so in aluminum. Mine is only 3/4" diameter because it has to fit between parts in a strip. It uses TDEX inserts which Dorian seems to make, I just looked. I've made a few thousand parts with it and never changed inserts and the finish is good. But I've never cut anything but aluminum with it. One thing that can be a pain for sight mounts is getting a cutter with the right radius. The tendency for many dovetail cutters is to make the radius too big for this application.
I also have a dorian dovetail cutter. Haven't used it in ages. I was cutting annealed 8620 and me and my customer were happy with the finish but he had to heat treat the part after I was done with it so surface finish was not a big concern and I can't remember if I though it was pretty or not. If I had a lot of work for it I get another and maybe use it as a roughing tool and a solid carbide tool as my finisher. Don't know if this helps. Picture for reference.
 

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Thanks for all the helpful input, gents. I will definitely look into the AB "dexi-dovetail" and Ingersoll ChipSurfer. A cursory search based on the recommendations here has lead me to believe these are promising options. I also sent an inquiry to Harvey Tool directly to see what they say, out of curiosity.

I realize now that I was fairly vague in terms of production numbers and tolerances required. This run is going to be low volume (around 20 pieces) but there might be a higher volume run in the future. For this reason the ChipSurfer seems like a very great choice in that the replaceable heads are actually cheaper than a solid carbide tool individually and they also have more flutes than the Harvey offering.

I will for sure report back when I run these parts with whatever I end up choosing.
 
@Orange Vise can chime in, but I think he mentioned to me he uses an AB tool indexable cutter for the Carvesmart cut in his vises.
Dexi for soft jaws.

Custom solid carbide for master jaws, 6-flute with helical geometry. I make my own now.

If I were buying, I'd go with the replaceable heads. Iscar and Ingersoll are both part of IMC Group. There may be overlap in product lines. I don't use their dovetails but their T-slot cutters are good.
 
Dexi for soft jaws.

Custom solid carbide for master jaws, 6-flute with helical geometry. I make my own now.

If I were buying, I'd go with the replaceable heads. Iscar and Ingersoll are both part of IMC Group. There may be overlap in product lines. I don't use their dovetails but their T-slot cutters are good.
I'm testing this one from Ingersoll right now:
450 Brinell material, 325 SFM, .002 IPT.
 
Gorilla Mill has off the shelf tools for this application. I've used a bunch of their tools in the past and the performance is incredible. Try these guys out and I doubt you'll look for anything else.
 
Gorilla Mill has off the shelf tools for this application. I've used a bunch of their tools in the past and the performance is incredible. Try these guys out and I doubt you'll look for anything else.
I just checked them out. It looks like they don't carry any dovetail cutters aside from the picatinny form cutters you linked, and the dovetail feature on my part is not a picatinny rail. I'll definitely keep them in mind for future projects though. Thanks!
 








 
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