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Pete F
30th Jun 2016, 09:25 PM
I don't know if this qualifies as a "project", but thought some may be interested in this. I needed a 60 degree dovetail cutter to cut some, well 60 degree dovetails.

The first job is to make a new Aloris style parting tool holder as my current blade holder is a holder within a holder and sticks out from the toolpost a lot. It creates a lot of twisting effect on the cross slide etc, so isn't as rigid as it should be.

A commercial 60 degree insert cutter would have cost me over $100, and I wasn't about to spring for that. So a quick turn and mill and out popped this. Not an especially challenging project, but there are a few things that are critical, hence why I thought it may be helpful for others.

I turned the body between centres to ensure it was concentric, then mounted in a Spindexer of all things. It was something that could get nice and close to the milling head, and I'd previously scraped it to be extremely accurate. The two critical operations are the angle and depth of the milling cut as this sets the angle of the insert. To get that I set the spindexer up with a sine bar and gauge blocks to the correct angle as I'd scraped the outside edges of the spindexer body parallel to the spindle. If the insert doesn't sit at the correct angle the angle it will cut will be out, more the point is the bottom finish will be horrible.

An initial brain-fart yesterday had me cutting the insert on the wrong side. Doh! It would have worked perfectly but only with the mill spindle running in reverse. I printed off a model so I would't make such a stupid mistake again and today had another go.

The only other thing is to ensure the insert clamping screw is set back towards the wall of the pocket a precise amount off insert centre. I don't have the figure to hand, but it's something like 0.17 mm IIRC. That pulls the insert back into the wall. Too much and it won't seat properly, too little and it won't be accurate. No biggie, but something that's a Goldilocks type of thing; not too little and not too much. When I tighten the screws the inserts basically click in.

It was slightly more challenging by having multiple inserts, as they need to track each other well to get a vibration free cut with a good finish. They were out slightly more than a ground commercial tool would be, but quite acceptable just the same.

That's about it. The moral of the story was simply that anyone considering buying something like this could also just as easily make one. The only caveat was that I only had TCxx inserts with a hole like this, and the "C" is only 7 degree relief. That's fine for a lathe, but won't be enough for a milling cutter, especially a very small one like this. I'll do the figures and work out if this will need D or even E inserts to get clearance. In the meanwhile I just ground some relief in the back of the insert by hand, just keeping back from the cutting edge. They still rub a little, but I'll see how they go in steel. I included a picture of some scrap aluminium I was using to check for rubbing. I was running the cutter through with no particular attention to speeds and feeds, but the chips were good and the finish quite ok.

Hope that helps somebody else making something similar.

Edit: According to my calculations I only just missed out with those inserts, and if my maths is correct in theory I need 7.7 degrees relief. It looked like it was rubbing a bit more than that, but maybe not. I'll get some Ds and that should well and truly cover it. Happy days.

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KBs PensNmore
30th Jun 2016, 10:27 PM
Excellent work on this Project. As far as I'm concerned anything that is made/repaired in a shed, is a project. It's great to see what the members on here make in the way of tooling. OK these things can be bought, but where's the fun in that.:2tsup:
Kryn

Pete F
30th Jun 2016, 11:04 PM
Thanks Kryn, the only thing I'll now add is to look in to the insert you intend to use when planning the tool, and confirm that clearance won't be an issue. As I said above, I'll just get some "D" inserts. Well, no I won't.

I was working off the inserts I had, triangular ones and I wanted them large enough to cut bigger dovetails in one whack if required. I don't use this particular style of insert much anymore, but still have many holders that take them, and try to limit the number of different inserts I need to buy. So it was a completely arbitrary choice without any further consideration than that. In fact I snookered myself with the insert size and thickness I used, so can't seem to get any "D" relief in a 32.5x size. Thinner, yes. Smaller, yes. the size I chose to use? No. :rolleyes:

I've ordered some "P" which is 11 degree clearance so we'll now have to wait and see. Theoretically they "should" work, but I would prefer more fat the 15 degrees would have given, as I would possibly use them elsewhere. It's not like I'll be going through these inserts like weet-bix each day, as the tool will rarely be used so relieving the back of the insert isn't a big deal, and the chances are the inserts will never need a change. It's just crappy designing on my behalf, and a poor choice. Oh well.

KBs PensNmore
30th Jun 2016, 11:36 PM
It's just crappy designing on my behalf, and a poor choice. Oh well.

I always do a rough draft before a masterpiece, but usually I'm happy to use the rough draft. I'm always told that God made man first as a draft then woman as the masterpiece.

eskimo
1st Jul 2016, 09:02 AM
I always do a rough draft before a masterpiece, but usually I'm happy to use the rough draft. I'm always told that God made man first as a draft then woman as the masterpiece.

you have been fooled?

Pete F
1st Jul 2016, 12:29 PM
I know everyone likes Happy Endings, at least I do, so below are some photos of this cutter through 1020 steel. I just took a piece of scrap round that's generally too short to be useful, but I'm too tight to throw away even that tiny amount, and ran the cutter through the end.

Before doing so I set up the T&C and ground approximately an 11 degree relief to mimic the inserts I ordered. Because I took it right to the edge, I probably affected the 60 degree angle slightly, as I didn't set it up with a sine system and just tried to get it as close as I could. It would be very close, within fractions of a degree, and in reality it's not that critical for this intended application anyway. The object of this exercise was merely to prove the inserts would be ok, and the ordered replacements will be exactly 60 degrees anyway. As I was holding the inserts in a cheap Chinese lathe tool holder, I took the opportunity to grind more relief off it, as it was not very useful for ID deburring due to the holder rubbing. With the new inserts I should be able to use that tool now down to reasonably small IDs without anything rubbing. The inserts don't repeat very well in that holder, and it's pretty sad to think I can get better results in a home workshop than they're capable of in their factory. Even though I have both cheap and high quality insert holders, I'd never thought there was anything wrong with going cheap for the holders, however when grinding the inserts I could see they weren't repeating. Anyway, just a random thought on that.

The finish off the dovetail cutter was excellent, and the reflection from the opposite face can be seen in the vertical wall in the photo (that's actually the floor of the dovetail). That was a 1 mm stepover and somewhat deeper than an Aloris AXA would be.

If anyone was doing this type of thing, I'd probably suggest considering the TDEX 322 (or the ISO equivalent) for this size insert. It's thinner and has 15 degrees relief, so there shouldn't be any issues with rubbing right down to relatively small tool sizes. It's the insert that's commonly used in similar Chinese dovetail cutter, something I would have realised if I'd be paying attention!

Anyway, that's that. A good quick little project and I saved over 100 bucks plus postage for my education. I'll do a few other cutters when I get some time a they're a great little filler job and I could use some other angled insert cutters.

Edit: Oh BTW, I looked at my notes, and the screw offset is 0.13 mm toward the pocket WALL. If you're doing a holder with two walls you'll need to do the trig if you're moving it to the inside corner. This is one of the most critical features to get correct, and is apparently why that Chinese holder wasn't repeating well.

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variant22
1st Jul 2016, 12:58 PM
I had a crack at one a while ago. Like Pete I only had the TCxx style inserts. Mine cut but rubbed badly (as mentioned). The dovetail was not perfect by any means. I made a few blanks to try different inserts but never got back to it. When I get back to it I will use the TDEX inserts.

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Pete F
1st Jul 2016, 01:26 PM
Just be aware that the TDEX inserts are probably a different thickness to the ones you're using now, so they won't be drop in replacements. I believe the inserts I used were TCMT 32.52, a very common size in triangular inserts and cheap Chinese tooling. It was one of the first insert lathe tools I bought (as a set) when i began this malarky, and I continued with that shape for a while until finding better alternatives, hence why I now don't use them. I think the TDEX are normally TDEX 322 in this size, which would mean you'd need to cut a shim to go under TDEX insert to bring it back up to centreline.

An alternative is just to take your current inserts and grind some relief in them by hand as I originally did. If you're careful and hold back slightly from the very edge, you should be able to get a reasonable result from them. I use a #400 diamond wheel and it grinds carbide well; a good compromise between speed and finish. Better yet, set up a jig with a holder at the correct angles and you can go right to the edge. It would be tricky to do that freehand or without a T&C grinder, but if you just keep the relief slightly back from the edge you can go nuts, as relief doesn't matter, just so long as it's enough.

KBs PensNmore
1st Jul 2016, 04:06 PM
Must be a pretty good setup to get the mirror finish in pic Dovetail 2.jpg. I've yet to see factory made tooling give a finish like that.:2tsup:
Kryn

Pete F
1st Jul 2016, 07:14 PM
Thanks Kryn, yes I was well pleased with it. I cleaned up the ends of the bar with a cermet insert (it's normally my tool of choice and what the cutter body was turned with) and I normally get good finishes off that, but the dovetail cutter left it for dead. It did sound as if it may have been slightly rubbing, but I marked the insert and couldn't see any evidence of any rubbing. The chips looked good, and there wasn't the telltale "dust" you generally get when something is rubbing, so maybe not. The flat base of the dovetail can't be rubbing, because of the insert geometry, and the finish on both sides was similar. Whichever way, I'll take a finish like that even if it was just pure dumb luck!!!

Incidentally I do get finishes like that off my cermet milling cutters. I have two, and the larger one leaves a surface like a mirror. The smaller one not so much, but I may just need to spin him faster. I'm a firm convert to cermets, the only downside is they like to run fast, like REAL fast, so I really need to sort out some shields etc to contain the chips, as they send a stream of blue chips everywhere in the workshop like a firehose!

PDW
1st Jul 2016, 09:10 PM
Nice work, but what happened to the 3 insert dovetail cutter?

PDW

Pete F
1st Jul 2016, 10:17 PM
Nice work, but what happened to the 3 insert dovetail cutter?

PDW

Some Bozo cut it back to front and I didn't want to run the mill backwards all the time :D

Seriously though, once I actually saw it popping out I thought it didn't have as much meat around the inserts as I'd like. I figured I'd instead go with two inserts on the next attempt. It was a good lesson that I should have printed a prototype off so I didn't do anything stupid. It didn't take long to print and used about 30 cents worth of plastic. Both are now on their way to Sydney's landfill ... at least the 3D print is biodegradable!!!

PDW
2nd Jul 2016, 05:12 PM
Some Bozo cut it back to front and I didn't want to run the mill backwards all the time :D

Ha ha ha - glad I'm not the only one that does things like that......

The results from the 2 flute one look excellent anyway so it's a win.....

PDW

.RC.
2nd Jul 2016, 06:31 PM
Some Bozo cut it back to front and I didn't want to run the mill backwards all the time :D



You could use that in both the southern and northern hemispheres.

eskimo
3rd Jul 2016, 10:09 AM
Some Bozo cut it back to front a

when did I visit....cant remember doing that...but I can when I made my first reverse rotation fly cutter.

even making these knurler arms i tripple check before drilling/cutting ...and still I wonder when when I am going to stuff up.....