Dear PM,
please advise on this. I had to make 4 long screws with 250 mm of 19 mm OD shoulder and 230 mm of M16 thread. For strength, we opted to use a prehardened steel, specifically Impax Supreme from Uddeholm, which is at 34 HRC.
I used my Colchester Triumph 200 for this (Clausing 15").
It turned out much more complicated than I had anticipated.
- turning down the shaft from 22 mm bar stock, was not trivial. I set up the follow rest (traveling steady) which, I was not able to use properly. Here is the setup:
Some times, I was setting the roller for light touch and after a while I was getting chatter that when away if I removed the roller so that it wouldn't touch the shaft. Chatter like this:
Then I would try without the roller touching. Then I could get chatter again at some point, which went away if I moved the roller to lightly touch! Crazy stuff.
Was using at CNMG insert, running at 625 RPM and tried several feeds.
I never got the chips to break at all:
- as for the thread....what a nightmare. There were clearance issues so I wasn't able to use the follow rest. Tool was a ground carbide one. Feeding from the top slide at the correct angle.
The thread came out torn, dull, with burrs.
To my understanding, there must have been vibrations since I didn't have the follow rest on, but I am not sure if this was the reason for the lousy finish.
I run the (2 mm pitch) at 250 rpm, though I did try a bit faster as well.
So, I am wondering:
- my problems at thread cutting were mainly due to the dimensions of the part? If the part was short and fat one could get a nice, accurate and shiny thread on pre-hard? This thing, in regular conditions machines very nicely, but you have to take a bite. I am not sure if this is possible when single pointing a thread.
- would it make sense to switch to HSS (that would have the benefit of not chipping so easily) and go nice and slow?
Any advice welcome.
Thanks in advance.
BR,
Thanos
please advise on this. I had to make 4 long screws with 250 mm of 19 mm OD shoulder and 230 mm of M16 thread. For strength, we opted to use a prehardened steel, specifically Impax Supreme from Uddeholm, which is at 34 HRC.
I used my Colchester Triumph 200 for this (Clausing 15").
It turned out much more complicated than I had anticipated.
- turning down the shaft from 22 mm bar stock, was not trivial. I set up the follow rest (traveling steady) which, I was not able to use properly. Here is the setup:
Some times, I was setting the roller for light touch and after a while I was getting chatter that when away if I removed the roller so that it wouldn't touch the shaft. Chatter like this:
Then I would try without the roller touching. Then I could get chatter again at some point, which went away if I moved the roller to lightly touch! Crazy stuff.
Was using at CNMG insert, running at 625 RPM and tried several feeds.
I never got the chips to break at all:
- as for the thread....what a nightmare. There were clearance issues so I wasn't able to use the follow rest. Tool was a ground carbide one. Feeding from the top slide at the correct angle.
The thread came out torn, dull, with burrs.
To my understanding, there must have been vibrations since I didn't have the follow rest on, but I am not sure if this was the reason for the lousy finish.
I run the (2 mm pitch) at 250 rpm, though I did try a bit faster as well.
So, I am wondering:
- my problems at thread cutting were mainly due to the dimensions of the part? If the part was short and fat one could get a nice, accurate and shiny thread on pre-hard? This thing, in regular conditions machines very nicely, but you have to take a bite. I am not sure if this is possible when single pointing a thread.
- would it make sense to switch to HSS (that would have the benefit of not chipping so easily) and go nice and slow?
Any advice welcome.
Thanks in advance.
BR,
Thanos