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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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.
363069
363070
363071