Dovetail Cutter

[Geoff]

Hi Folks,

I ripped up a 60 Deg. Dovetail cutter for the mill. It uses a triangle carbide insert with positive rake to provide relief. This was a test run for me as I wanted to see how well the inserts that I have work and to see how my mill handles it. I just used a scrap of 1018 steel and I'm fairly happy with the result. Now i'm going to make another one from 4140.

After I finished the cutter, I wanted to test it. The reason I am making this is to make a bunch of tool holders for my QCTP. So I just placed a few marks on a chunk of 1' square stock and away I went. Surprisingly without doing any measurement, it actually fit in my QCTP first try (I wasn't expecting that!!)

I should have captured photos of the complete build and the photos i have are not the best, but here is the idea...

A few changes for the next cutter:
4140 steel
Longer shank
I'm going to change the insert to TPGB with 11 deg rake angle and no chip breaker.

 

[PeterT]

That worked out ok. Were you detecting flex or chatter vibration, or why the next one using 4140? Some youtube vid I saw, the guy made a very similar dovetail cutter from I think a throwaway bolt from a Sikorsky helicopter or something. It machined beautiful & logically would be high tensile stuff. I tucked that tidbit in my brain, might be cheaper to buy a good quality 3" bolt at whatever preferred diameter from BoltSupply than a 1-ft chunk of whatever at MetSup with the prices & min $$ rigamarole.

Also, what sort of depth cut were you able to traverse the cutter at?

 

[Geoff]

Hey Peter! Yes that was Randy Richard and that is where I got the inspiration. He sells them for $95 USD! Mine was definitely louder through the cut compared to his and those bolts that he was using were very hard. I figure I may be getting a bit of flex so I thought I would try some harder material. Also, it doesn't look like the back of the insert is rubbing through the cut but it is extremely close so I want to use an insert with 11 deg. Relief angle. That will ensure clearance! I took some decent size cuts and it didn't seem to make much difference if I was taking 50 thou or 10. I think it actually preferred the slightly deeper cut though.

I have some 4140 on hand so that's why I'm going to give that a shot but the idea of getting a big bolt isn't bad!

Cheers!

 

[Janger]

Nice! Where is a good place to get inserts?

 

[Geoff]

Nice! Where is a good place to get inserts?

Ebay!!

 

[Geoff]

TPGB are the inserts that I'm going to use... Want to split a pack of 10?

 

[sorrelcreek]

Nice job always great when everything works out when your building something that you haven't built before and it has a complex setup that takes time to set up.

 

[Geoff]

I have been working on the second Dovetail cutter! I'm using 4140 this time around in hopes for a more rigid cutter. I also have some new (quality) TCMT 321 inserts which Matt kindly hooked me up with! I should be done tonight and will post the results.

I few things I'm doing different this time... I turned the 60 Deg. Taper down to a smaller OD this time because the first cutter actually made contact with both sides of the milled slot on the QCTP holder that I am making.
My setup for milling is slightly different this time as well. For the first cutter, I stuck the shaft into a 5C collet which was held my my spindexer. Since I'm not rotating the part at all, I decided to hold it in the vise. Unfortunately I don't have any v-blocks or a collet block so I quickly milled a piece of aluminum with a 'V' and placed it in the vice to help hold the shaft secure. I then used a 30 Deg. Angle block to indicate the vice at the right angle for the milling op. That's where I'm at right now. I'll post some pics this evening!

 

[Geoff]

Finished the new dovetail cutter tonight. As mentioned, it is made from 4140 alloy. I took a bunch of pics, although I forgot to take photos of the turning and setup to turn the 60 Deg. taper. I did have one hairy moment while drilling the hole which secures the insert... The drill broke on me right when it popped through. This is a tough spot to drill since it is popping through on the tapered surface. I was lucky and the broken piece of drill just pushed out the bottom and I was able to continue to the next op which was tapping.

One part of the setup that I have not described is how I locate the exact position for the screw hole which secures the insert. What I did was turn a pin to the exact size of the hole in the insert. I then mount the pin into an ER32 collet, place the insert in the approximate position, lower the pin into the insert hole and then fine tune the exact position where the insert should be by adjusting the mill table. Once I am in the spot, I move my table about .001 - .002 towards the inside edge of the dovetail cutter. I do this to ensure that when the screw is fastened, the countersink of the screw pulls the insert tight against the inside wall of the cutter. Once I am happy with the insert location, I lock the x and y table axis and replace the pin with the tap drill.

Also, before all of that, you need to mill out a section of the cutter which accepts the insert. This part is very important because you need to mill just enough so that the insert sits about .040 - .050 over the ends of the cutter. This is necessary so that the cutter does not rub while making the cut. You also need to ensure that the top of the insert, once mounted, is at exact center height. In my case, I have to go down exactly .838 and the width of cut was .495. Those measurements depend on the size of the insert as well as the largest OD of the cutter.

Anyways, here are a bunch of photos (including the little piece of aluminum which i placed in the vice to secure the cutter for milling). I will be testing the cutter in the morning, most likely.

 

[PeterT]

Nice job again. Have you found much difference cutting in terms of the insert nose radius? For example is sharper better, or maybe that's too fragile? Also, I'm guessing you first relieve the bottom of the dovetail slot with a straight end mill so the bottom edge of the insert only has to cut the minimal face amount there? Which dovetail cutting direction works better, climb milling or, sheesh - what's the other direction even called? ...ploughing? Do you see any benefit to a dual insert or just one cuts fine? I haven't done any dove tailing yet, but I'm sure its in my future.

 

[John Conroy]

Nice work Geoff, looks like a fun project.

 

[Matt_b_m]

Nice work Geoff!

 

[Geoff]

Hi guys, thx for the comments. After giving this one a rip, it's pretty clear that I'm going to need inserts with 11 Deg relief. This new one is performing very similar to the first and I think the biggest issue is that as the insert travels through the radius of the cutter, the back of the insert rubs and I have even chipped a few. The inserts I'm using have 5 Deg relief so I'll have to buy some with 11 Deg relief (TPxx). After making these 2 cutters, I don't think it really makes a different on the material. Maybe once I get some inserts that fit the purpose better, I will be able to distinguish.

Peter, I haven't noticed a different with nose radius but all of the inserts I have tried have a very small nose radius. Also, I do cut a relief of about .020 so the dovetail cutter is cutting minimal material on the bottom edge.

I'll post more results after I track down some TPGx inserts.

Cheers!

 

[Geoff]

Well I have been at it again with the dovetail cutter!! I wasn't overly happy with the performance and how hard the cutters were hitting so I got some TPGB 321 Inserts and turned out yet another cutter. I had to make another one because the through hole in the TPGB Insert is smaller than the TCMT and will only fit a 4-40 screw. I can knock them out pretty quick now though . This one came out quick and i used a chunk on scrap 1045 steel.. This one turned out the best so far and I was able to cut a perfect fitting dovetail for my QCTP. I find that when taking the full depth of cut, it still hits pretty hard but you just have to take your time and I also helps to use lots of cutting oil. At full depth of cut, it doesn't seem to make much of a difference if i'm taking .005 or .020 so I take bigger cuts so I don't need to do as many passes. The TPGB inserts provide enough relief angle (11 Deg.) so that there is no rubbing. Attached is a few pics of the 3rd cutter and the dovetail that I cut out of a block of cold rolled... I'm going to batch out some more holders soon so that i won't always be changing to tools that I have installed in the 2 standard toolbit holders that I currently have.

 

[PeterT]

Another similar cutter to what you are producing is a chamfering tool (typically 45 deg) to make nice beveled edges on milled parts. Those shanks/insert packages tend to be expensive which I've never understood. They have about the same amount of machining in the pocket as any insert lathe tool. Maybe the offshore cloners just haven't gotten to it yet. I think I've seen one tool that uses one of the unused faces on a trapezoidal lathe tool, which is kind of smart because you get some extra utility out of the insert before tossing them. The other consideration if you decide to make one is the tool cant be too chunky if you also want to also do internal chamfering (vs. just externally around the edges). I'll take some pics of my little connecting rods soon, the chamfering makes a huge aesthetic difference & actually is required for some motion clearance. I'm using a 0.375" multi-edged carbide tool that looks kind of like a pointy end mill though. I don't know if the finish would be different from a single edge insert cutter.

 

[Geoff]

Hi Peter, on the topic of using the unused edges of inserts, I have 2 face mills that take APKT Inserts and one of them uses the insert in the vertical orientation and the other face mill used the inserts in the horizontal position. Its very convenient to have both of these face mills and i certainly get the max out of the inserts. I have heard of similar face mills that do the same with CNMG Inserts.

For Chamfering, SorrelCreek gave me the idea about grinding HSS end mills. I have a bunch with slightly chipped or worn corners so i'm going to grind a few of them (45 Deg on both flutes - 2 flute end mills) and give that a try.

 

[thriller007]

Well I have been at it again with the dovetail cutter!! I wasn't overly happy with the performance and how hard the cutters were hitting so I got some TPGB 321 Inserts and turned out yet another cutter. I had to make another one because the through hole in the TPGB Insert is smaller than the TCMT and will only fit a 4-40 screw. I can knock them out pretty quick now though . This one came out quick and i used a chunk on scrap 1045 steel.. This one turned out the best so far and I was able to cut a perfect fitting dovetail for my QCTP. I find that when taking the full depth of cut, it still hits pretty hard but you just have to take your time and I also helps to use lots of cutting oil. At full depth of cut, it doesn't seem to make much of a difference if i'm taking .005 or .020 so I take bigger cuts so I don't need to do as many passes. The TPGB inserts provide enough relief angle (11 Deg.) so that there is no rubbing. Attached is a few pics of the 3rd cutter and the dovetail that I cut out of a block of cold rolled... I'm going to batch out some more holders soon so that i won't always be changing to tools that I have installed in the 2 standard toolbit holders that I currently have.

I know this is an old post but do you by chance have a drawing for your cutter with dimensions? thanks