Munkul
Jack of some trades, Master of none
- Messages
- 7,371
- Location
- Cumbria
Been making some bushes over the last few days and I'm having fun with it, seeing how hard I can make my lathe work!
The steel is EN5/EN8 I think, it's pretty nice stuff to machine, finish is great and chips no problem with the right feed and DOC on the outside tools.
My problem is boring... I can't get chips to break, and I end up with long stringy messes. If I push the DOC too hard I get hot strings that are thick enough to choke an elephant.
There's no chatter at all from either of my bars, and the finished bores are spot on. My centre heights are good.
I have a 16mm carbide STFCL bar to open up from 25mm drill with these inserts https://www.sandvik.coromant.com/en-gb/products/pages/productdetails.aspx?c=tcgt 11 02 04l-k 1125
Using at 0.75mm DOC and 0.2mm/rev I can't push it any deeper or harder, or i just get thick string (I'm inside the operating envelope according to above). I'm only at about 60-80m/min surface speed, could this be the problem?
Once opened to around 40mm I switch to the 32mm SVUCR bar with a VCMT 1604 insert I'm not sure what grade, they came with the bar. Looks like a 0.8mm nose rad. Same again - if I push the DOC beyond 1mm, I just get hot thick strings, and it fouls the tool. which is the worst thing. I've tried faster, slower rpm between 500 and 1000, I've went between 3 TPR to 12 TPR (0.02 to 0.33 mm/rev), no difference. Seemed to work best around 0.3mm/rev and 650rpm, and 0.75mm DOC which seems wrong, this tool should be capable of way more than that. Maybe its the insert since I've no idea what it is, but it looks and feels capable.
What do we think? I'm getting the job done, but the small bar should make chips, and the big bar should be able to take much deeper cuts!
Could it be that I'm machining dry?
The steel is EN5/EN8 I think, it's pretty nice stuff to machine, finish is great and chips no problem with the right feed and DOC on the outside tools.
My problem is boring... I can't get chips to break, and I end up with long stringy messes. If I push the DOC too hard I get hot strings that are thick enough to choke an elephant.
There's no chatter at all from either of my bars, and the finished bores are spot on. My centre heights are good.
I have a 16mm carbide STFCL bar to open up from 25mm drill with these inserts https://www.sandvik.coromant.com/en-gb/products/pages/productdetails.aspx?c=tcgt 11 02 04l-k 1125
Using at 0.75mm DOC and 0.2mm/rev I can't push it any deeper or harder, or i just get thick string (I'm inside the operating envelope according to above). I'm only at about 60-80m/min surface speed, could this be the problem?
Once opened to around 40mm I switch to the 32mm SVUCR bar with a VCMT 1604 insert I'm not sure what grade, they came with the bar. Looks like a 0.8mm nose rad. Same again - if I push the DOC beyond 1mm, I just get hot thick strings, and it fouls the tool. which is the worst thing. I've tried faster, slower rpm between 500 and 1000, I've went between 3 TPR to 12 TPR (0.02 to 0.33 mm/rev), no difference. Seemed to work best around 0.3mm/rev and 650rpm, and 0.75mm DOC which seems wrong, this tool should be capable of way more than that. Maybe its the insert since I've no idea what it is, but it looks and feels capable.
What do we think? I'm getting the job done, but the small bar should make chips, and the big bar should be able to take much deeper cuts!
Could it be that I'm machining dry?
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