Boring problems

[kong]

Thanks metlmuncher, I am running between 1350 and 800 rpm for my cuts, the lathe has speeds from 150 - 1800 rpm. My feed speed is around 100 - 150 mm/min, although I can go faster, off the top of my head, to around 1000mm/min. The reason I switched from a boring motion to facing was due to the incredible amount of swarf wrapping around the bar inside the hole - which prevented a clean cut, and stopped the coolant reaching the tip. I figured the facing motion would allow the swarf to clear itself, without a lot of thought (and experience) to the stresses on the bar itself.
I would appreciate some pointers as to feeds and spindle speeds, but like I said, I will also try some air blasts to clear the chips.

[Zep]

blind hole boring can always be a problem. Looking at your part I'd figure the biggest hurdle would be to rough it out. In that case I would step it out working in from the face. high rpm high feed (assuming setup is rigid) to break chips , lots of coolant to flush. Finishing high rpm again light cut .02 on dia .005 to .01 on face. insert style i would use a vnmg stle profiling insert with a large lead angle. Reason for this is, smearing is caused by chips being trapped between bar and work damaging surface. try to keep area directly around the bar clear of pinch points. This style insert works well for finishing with a small toolnose rad (.015); less prone to chatter . keep bars short as others have suggested .I have had good results using VNMG style inserts for finishing. Most suppliers will reccomend a grade/geometry to suit your needs
good luck

[RotarySMP]

How many of these do you need to make? The easiest solution might be to put a dwell on each retract and remove the swarf from the tool tip with a hook.

[kong]

I have loads to make unfortunately, like a hundred or so. I have just got my car fixed (damn stupid thing) so I will have a go this afternoon, after a nice coffee

[RotarySMP]

Is the alloy critical? How about changing to a leaded free machining Alloy?

[kong]

Fairly critical, these will eventually become alloy wheels for small rc-cars, so I am using 6082 for it's strength, corrosion resistance and ability to be pollished easily. Also, there is not the range available in the UK as in the states, so I think I have a choice of about 3 alloys which are readily available! Anyhow, I have jusu re-programmed the part to use a higher feed, and a boring motion. Just gotta drink the coffee now!

[RotarySMP]

I have been doing a lot of boring on my little cnc converted mini-lathe and tried a carbide insert bar with a thin carbide shaft, a larger diameter steel bar with a sharp HSS bit and a well used brazed carbide bar. I was really suprised that the brazed carbide bar gave by far the best surface finish and chatter resistance.

In your position I would try the variety of bars you have on hand. Not very scientific, but easier faster and cheaper than ordering new ones

[kong]

HA! Got it.
I ran a faster feed, lowered the spindle speed, and took a shallower cut so as not to stall the lathe. Unfortunately, I never left enough of material for a decent finnish pass, so some of the roughing marks are still visible. There is also a tiny bit of chatter on the inner most radius, you can just make it out in the second picture.
I ran
Spindle - 550
Feed - 300mm/min
DOC - 0.25mm
Hopefully I can take a bigger cut, and up the feed a bit more, since the motor wasn't struggling at all (stop laughing all you guys with 20HP lathes ).
The chips were different altogether. Some breaking up, and some a tighter curl, a bit thicker than the last lot. So a big thankyou to you guys