What's a decent cut for a 9x20 import?

durableoreo said:
I've got a bunch of parts to make that require boring out a 2.1" diameter bore to 0.813" in annealed 4140. I've been taking 0.015 per pass. I'm using a 1/2" carbide boring bar with some insert---if it's important, I'll post more details about the tool. No chatter but there's some deflection when I reverse the tool.

Curious what the experienced hands would do in this situation.
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durableoreo said:
Changed the insert, which reduced the spring. A dull insert was causing the boring bar to deflect, I think.

At 0.015, it is very slow going. And the cuts don't sound good. I bumped up to 1000 RPM, which is great at 2" diameter, close to 550 SFM. At the beginning of the job, where my drills top out, top speed (2000 RPM) is only 327 SFM... a little low for carbide.

I tried one of those speed/feed calculators. A cut of 0.020 at 2" diameter, 0.005 in/rev (520 SFM) is about 0.5 HP at the motor. So I guess that's an answer to the original question. The same cut, but 0.033 deep is 0.75 HP. So it seems that I'm limited by motor power, not rigidity.

The insert seems to last better at higher surface footage.
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Ditch the calculators and find what your machine will do.

With a properly ground HSS tool you should be able to do much better than .015.


Inserts and machining calculators are not your friend in that sized machine.
 
durableoreo said:
Changed the insert, which reduced the spring. A dull insert was causing the boring bar to deflect, I think.

At 0.015, it is very slow going. And the cuts don't sound good. I bumped up to 1000 RPM, which is great at 2" diameter, close to 550 SFM. At the beginning of the job, where my drills top out, top speed (2000 RPM) is only 327 SFM... a little low for carbide.

I tried one of those speed/feed calculators. A cut of 0.020 at 2" diameter, 0.005 in/rev (520 SFM) is about 0.5 HP at the motor. So I guess that's an answer to the original question. The same cut, but 0.033 deep is 0.75 HP. So it seems that I'm limited by motor power, not rigidity.

The insert seems to last better at higher surface footage.
Click to expand...
I cut 4140 Annealed at around 550 RPM at 0.03In/rev 0.030 depth of cut on PM1236.
 
RaisedByWolves said:
Ditch the calculators and find what your machine will do.

With a properly ground HSS tool you should be able to do much better than .015.
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Hell, my 7x16 with a 500w / 0.67HP Brushless motor, using the leadscrew to drive the carriage (standard reduction ratio of 0.0625) I can get a ten thou' (0.010) cut in mild steel and twenty thou' (0.020") cut in ally if I want to, not that I do very often, though on some 2" ally I was machining earlier today, I did run 20 thou' passes to get down to the diameter I wanted due to not wanting to waste time, not that I recommend it.

Depending on the wattage of @durableoreo lathe motor and reduction to leadscrew, they should have a little more capability, not least because of better rigidity and more than likely a more powerful motor.
 
verbotenwhisky said:
I hate 300 series stainless....
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Must admit, I don't "love it", but I don't mind it. I purchased a 25mm bar of 316 intentially, just to turn a couple of hand-wheel bushes up before turning any other material on my mini. A bit of patience with it, using suitable feeds, speeds and DOC and good results can be had with zero stress. Actually, I enjoyed machining it more than I do mild steel.

As for ally? That stuff can be bloomin stringy and I really do not like having to deal with that.
 
GrifterGuru said:
Must admit, I don't "love it", but I don't mind it. I purchased a 25mm bar of 316 intentially, just to turn a couple of hand-wheel bushes up before turning any other material on my mini. A bit of patience with it, using suitable feeds, speeds and DOC and good results can be had with zero stress. Actually, I enjoyed machining it more than I do mild steel.

As for ally? That stuff can be bloomin stringy and I really do not like having to deal with that.
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4" Deep 8.625"Diameter 304, like making grass burs.... Hot Grass burs....


Ready.jpg
 
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