Facets in my 16 TPI Threads - Need some help!

[TX COWDOC]

I'll check the glass of water / harmonics. Thanks for all of the info.

I believe I have too much vibration when the lathe is running.

 

[TX COWDOC]

Hey neighbor
PM me an address and I’ll send you a 60* HSS tool to try

Hey Z2V - I sent you a PM. I'll try the HSS to rule this in / out. I just posted some videos with a glass of water sitting atop the Headstock at both 65 and 300 RPM. I also noted when I had a dial indicator / NOGA sitting up there as well that is had a vibratory buzz.

 

[Larry$]

29.5 degrees! I wonder how accurate the markings are?

 

[davidpbest]

This works much better if you use beer. Especially something dark and hoppy...

David- what is the point of the insert holder being tilted and counteracting the angle of the insert? Is this purely for clearance? This tool is labeled as an external threading tool by the manufacturer so clearance would not be an issue?
Robert

This Laydown threading type of insert has no clearance or relief angle - the cutting edge is perpendicular to the bottom of the insert. This improves the strength of the insert at the pointed end. To provide the necessary clearance the insert must be held in the toolholder at a negative rake, otherwise it would just rub rather than cut. External Laydown type toolholder has a 10-degree negative rake, internal have a 15-degree negative rake (to provide more clearance under the insert working inside a bore). Then to offset a negative rake (which would essentially tear or scrape away material rather than cut into it), the insert has a top surface geometry that reestablishes a positive cutting angle relationship with the part being machined.

Rather than hijack this thread further, I'll DM you.

 

[TX COWDOC]

29.5 degrees! I wonder how accurate the markings are?

I appreciate the spirit of your comment and will tell you that I removed the compound and marked the cross slide with a center punch after marking with a protractor. It's between 29 and 30.....so as close to 29.5 degrees as it's going to get. Whatever the issue is here, it's most likely not the angle.

 

[mikey]

I have the impression that the chatter is visible in the turned and faced surfaces in my pictures as well. ?

Doc, I have no idea why this pattern is occurring but you're right, there seems to be a chatter pattern on the faced work, too. This suggests that there is some harmonic going on, possibly from the motor? In the pic, you are using a negative rake tool that is not ideal for aluminum but, in general, negative rake tools usually finish well. Much depends on getting the work turning at the proper speed but still, there is something that is causing a regular defect. I've seen threads where this sort of thing turned out to be the motor so it was an electrical issue. Might be good to contact PM to see what they say.

 

[TX COWDOC]

Thanks Mikey. I emailed PM yesterday. They are usually pretty good with responses so I'm optimistic for a quick diagnosis / resolution.

 

[Z2V]

Hey Z2V - I sent you a PM. I'll try the HSS to rule this in / out. I just posted some videos with a glass of water sitting atop the Headstock at both 65 and 300 RPM. I also noted when I had a dial indicator / NOGA sitting up there as well that is had a vibratory buzz.

I did not receive your PM for some unknown reason.

 

[savarin]

I used to see that sort of pattern on my aluminium threading.
On my flexi 9x20 it was total lack of rigidity in the compound/topslide system, it could visibly be seen moving in some instances.
With a dial indicator on the top of the tool bit it flexed up and down like a yo-yo (bit of exageration but you get my drift)
I removed the compound and replaced it with a solid plinth, always use very sharp honed HSS and dive in at 90' now for all my threading with no problems.

 

[davidpbest]

I removed the compound and replaced it with a solid plinth, always use very sharp honed HSS and dive in at 90' now for all my threading with no problems.

Same here. Solid tool post mount was the single best improvement I made to my PM1340. Drastic improvement in parting and plunging in at 90’ when threading. I haven’t had the compound on the machine for almost two years.