Todays Project - What did you do today?

[PixMan]

Got back from a business trip to Nashville (and a stop ay my brother's place in Durham NC on the way back) yesterday, headed to the shop today to try and salvage the screw I had started making for Darren. No hope, as the threading insert had dug in too deep on the load side of the thread flank. And that was my second attempt.

Third time a charm, thankfully!

As I'd done with my second attempt, I first turned a wide groove in the area of where the gear will eventually sit. This gives me a generous landing spot for pulling out the half nut while threading a 5 thread per inch thread at 120 rpm.

Here's a shot of the piece after I finished threading and before I cleaned the coolant out of it:


This close-up shot is so detailed it looks somewhat rough, but it really is quite nice and not a trace of chatter despite the 18.7" of thread length. My machine doesn't have a follower rest, so that's hard to do!


Here's a shot of the three flats I had first milled on the end going in the 3-jaw chuck. When I made my first attempt, the finished 20mm diameter spun in the chuck from having too much tool pressure as I threaded. I probably should have cleaned off the cosmolene gunk from the 8 year old (but still new) 12" 4-jaw independent chuck I have that's never been on the machine. Too lazy to drag it out when this worked fine both times.


I'm just happy to have this part of the project done, finally! Finishing up the diameters, thread and keyways will be simple, despite the interrupted first cut I'll have.

I think I'll leave it as is and start on the mating bronze nut. This way I won't worry about damaging the finished 20mm diameter nor the M12x1.75 thread.

[Mayhem]

Thread looks fantastic from here (Dubai International Airport). I can't wait to see the next post! Thanks again!

[stevec]

Ken, I'm amazed that you were able to do such a beautiful job without a follower rest. Did you perhaps film a video of the operation?
( I will refrain from suggesting that when you test the screw in the nut that you thread it all the way, just in case, just kidding. )

[PixMan]

Steve,

I had made a 52 second video of a single pass on the last attempt, when I was about halfway done. I didn't want to "jinx" it this time, just wanted to "Git 'er dun".

No fears about test fitting the screw all the way into the nut I'll make. I am quite confident that there's not more than .001" variation in thread pitch diameter.

[stevec]

Great Ken, your success is an obvious testament to your knowledge of and selection of cutting tools.

[krv3000]

well dun

[TomG]

That's a good looking thread Ken. Darren will be thrilled.

Tom

[f350ca]

Beautiful work Ken. Sure nothing to fault on that finish.

[PixMan]

Thanks given to all!

It was quite a chore, probably 40 passes to get it done right. The carriage was flying. With rpm at 120 and threading feed at .200" per rev, that means 24 inches per minute rate. A little puckering every time the tool got close enough to the chuck to clear the threaded section and land in the 1/2" wide groove I made. If I had a CNC lathe like Russ, I would have run at about 500 rpm. At 120, that's only 39 surface feet per minute, far too slow for carbide inserts in most cases. Fortunately for me the threading inserts are made with a high cobalt content binder to give the insert higher toughness, a little more shear strength.

I needed that shear strength because I had smashed one corner of the insert when I engaged the half nut haphazardly and it plowed into the first thread, shearing off the insert and part of the supporting anvil. The anvil under the insert had to be changed from the standard 1.5º to a 3.5º one because of the high 2.915º lead angle of the thread.

Here's what the insert edge looked like after the first couple dozen passes, at .080" deep on the compound slide infeed:



Indexed to a new edge, this is after finishing the thread, about .132" deep on the compound slide infeed:



And a shot of the Vardex threading insert holder in it's 250-401 QCTP tool holder block:

[Mayhem]

(03-17-2014, 06:04 PM)TomG Wrote: ...Darren will be thrilled...

Will be? Already IS