G0709 gearbox: cutting wrong thread pitch

[mcdanlj]

Would it be possible for you to show a picture for the Change Gears from both a Face View and Edge View?

Most definitely the F configuration! Here it is:



@mksj I didn't know the difference between this quick change gearbox and a Norton. I'm new to this, thanks for the correction! I have another rabbit hole to go down now!

Another naive question - any chance you're engaging the power feed instead of the halfnuts?

That would easily explain it if I did!

I had just minutes before been doing some work on the mini-lathe before where there's only a halfnut for both feed and thread, and I wonder if I did just that?

The chance that a dial is newly-misaligned without me noticing it seems very small relative to the chance that I transferred the wrong control while focusing on the gearbox. And because I wasn't disengaging it between passes, it would be easy not to notice it from one pass being horribly misaligned with the prior pass.

I think I just used the magician's trick of redirection on myself. Good job me!

I don't think you succeeded in asking a naive question. Thank you for bringing an open mind to the question of what I might have done wrong.

I'll have to try again this evening, but I would be shocked if you didn't hit the nail on the head.

I'm embarrassed but relieved by this likely explanation, and if I find out I was wrong I'll be back for a second round.

 

[BGHansen]

FYI, threw my G0709 into FARW8 and touched off on a Dykem'd piece of Delrin. I got 0.7 mm for the thread.



Scratch pass is spot-on 0.70 mm pitch as it should be



Just to verify your "8" spot, maybe try a scratch pass on FCTY8 for a 28 tpi thread?


To a post above's point, this one is the half-nut lever for threading (just in case). The one to the left is the Feed Selection Lever (not for threading).



Couple of warnings about threading in general and in particular metric threading. Once I engage the feed direction knob (presumably Tail stock to head stock direction for a RH thread), I do not disengage the knob until threading is completed. Once you throw this knob, the gears on the head stock get sync'd with the gears on the quick change gear box. It's a little easier to see what's going on a lathe with an open quadrant like a South Bend or Clausing. Naturally, the head stock rotational position must be in sync with the carriage which is doing the cutting or you'll split the thread. If you disengage the feed direction knob and rotate the spindle at all, you'll very likely be out of sync when the feed direction knob is re-engaged.

On metric threads, I don't use the thread dial at all. With metric, once you engage the half-nut lever, it stays engaged. No "hitting a number" for a second pass as we have English lead screws on our lathes. Since you engage the half-nut and leave it engaged, there's really no purpose for the thread dial, so I don't loosen the cap screw and bring it into the lead screw.

On metric threading (and English), I start with the compound at a touch past the 60 deg. mark on the scale (just off the scale by 1/2 deg). A lot of import lathes (like the Grizzly) have their compound angle reference rotated 90 deg. as compared to older American models. On my Clausing 5418, 0 deg. puts the compound in line with the cross feed. On my G0709, compound at 0 degrees is in line with the longitudinal feed. There are a variety of "camps" out there: 29.5 deg., 30 deg. or straight on (cross feed only) for threading. I use 29.5 deg., relative to perpendicular to the spindle axis. On my Clausing, the compound gets set to 29.5 deg., on the Grizzly G0709, just a shade past the 60 deg. mark.

Some guys struggle with this on their import lathes as it's pretty common so set your compound to 30 deg. If you chuck up a standard bolt, the compound angle should be set so the tool will parallel the thread face on the RH side of a "V". If you set your compound on a typical import lathe to 30 deg., you'll see that the side faces of the compound and the face of the thread are off (by 30 deg.). Some guys set a 30 deg. or 29.5 deg. angle block against the face of their chuck and rotate the compound until it touches off on the opposite face of the angle block, then tighten the compound.

Anyway, once the compound is set to the proper angle, I turn the compound crank until it's at a "0". The micrometer dial is on a clutch on the G0709, just my personal preference, but I turn the crank until it's at "0" instead of turning the micrometer dial.

My cross feed micrometer dial has been modified so it uses a more conventional thumb screw. I loosen the thumbscrew so the micrometer dial turns freely. I start the lathe and advance the threading tool until it just touches the work, then set the cross feed micrometer dial to "0".

I back off the cross feed one revolution and back the carriage off the work towards the tail stock. Once off the work, turn the cross feed back to zero. Start the lathe to make sure it's in back gear, not open spindle, and turn the compound in 0.003" for a scratch pass. Engage the half-nut and power down the lathe just short of the end of your thread. You may even want to just use jog button to thread. I usually turn a relief at the bottom of the thread to just past the full thread depth before starting to thread so you have some wiggle room for stopping the lathe. If you are a little short, either jog or rotate the chuck by hand to complete the thread.

At the end of a pass, DO NOT DISENGAGE THE HALF-NUT. Turn the cross feed back out one turn (or more depending on the coarseness of the thread) and lift up on the Spindle On/Off lever which will run the lathe in reverse (run the carriage from the head stock towards the tail stock). Run it until your threading tool is just past the start of your thread and stop. Advance the cross feed one turn back to "0" on the micrometer dial. Advance the compound with a comfortable number. You'll read posts here where guys will "go for it" and advance 0.025" per pass though most are probably using a more conservative number like 0.003" - 0.005" depending on the material.

Make your next pass by either holding the jog button in or throw the Spindle On/Off lever to down or forward direction. Repeat the procedure above until you've got your thread.

If you've got an M4 nut handy, that'll work as a good gauge. Otherwise, there are other methods like thread wires, thread triangles or thread pitch micrometers. It's not uncommon to run a flat file over the thread when it's finished as the OD of the work will likely grow a little from threading.

Hope you get 'er figured out!

Bruce

 

[mcdanlj]

It's sobering to me to discover complacency at the lathe. In aviation, it's known that one of the most dangerous parts of a pilot's career is after hundreds of hours of experience, when they start getting really comfortable with their skills. I think of using the lathe like purposely standing right next to a spinning propeller, and try to be completely present while running the lathe.

I am now fully confident that I engaged the power feed instead of the half nut. I tested tonight and it's working just fine. It appears that my brain was about as well engaged as the half-nut yesterday. I was so focused on the gear train that I failed to check the most obvious problem.

This isn't the first time I've single-pointed threads, but I think it's the first time I've made this mistake.

I hadn't specifically thought about the feed direction selector losing sync, but it makes sense, and I do run the lathe in reverse to back up for the next pass.

 

[BGHansen]

Glad you got it figured out for basically FREE! Anyone on this forum who says they NEVER made a mistake is like watching a campaigning politician. You can tell they're lying to you if you see their lips move.

My dad flew Mooney 201DH. It's a high-performance single engine plane with retractable gear. Line is there are pilots who've done a gear up landing and others who haven't, yet. He always went through a checklist before landing he called GUMPPS: gas (fuel pump on), undercarriage, mixture (rich), prop (pitch), pressure (I think a look at manifold pressure?) and seat belts. He was landing at Capitol City Airport in Lansing, MI. Had "only" been flying out of that airport for 35 years. He was on final and had clearance to land on 28 left, but there was a commercial plane on his tail who'd have to circle before landing, so he radio'd that he'd do a loop-around instead. Did his loop around the field and was flaring when he heard a bad noise. Tried popping the power to pull up but too late. Slid to a stop in probably 150 feet, radio'd the tower that he'd done a gear-up landing, was turning off the master power and was getting out of the plane. It was after that that he realized he'd actually landed on runway 28 right's taxiway. FAA examiner had done my dad's bi-annual flight reviews for over 20 years, said my dad was the only pilot he'd every flown with who he figured he would only see for a bi-annual review. Dad got out of his routine and had an incident, but fortunately walked away unhurt.

Not to belabor it, but I've had 3 mess-ups while threading and have single-pointed well over 1000 threads.

First one: Made a scratch pass which checked fine. Made my second pass and thought, "this thread looks like crap". Yeah, that's what happens when the compound is at 45 degrees. . .

Second one: Was threading to a shoulder, nothing special. Came up a little short, but instead of jogging the lathe, I for some reason grabbed the feed direction knob instead of the back gear/open spindle lever. It's easier to hand rotate the chuck in open spindle, but I grabbed the wrong lever/knob. Rotated the chuck by hand to finish the cut, backed up and promptly split the thread on what should have been the last pass.

Third one: Was threading a metric screw for a bench vise, something like 5" of threading. Was making conservative passes of something like 0.003" per pass. Stopping the lathe, backing out the compound and running the lathe in reverse with the half-nut engaged. Took forever (it seemed) to get back to the start point in back gear. So I started doing the reverses after putting the lathe into open spindle; around 450 RPM instead of 70. Much to my chagrin, I failed on one pass to put the lathe back into back gear at the start of a pass. Glad it was 5" of thread as I had time to stomp on the brake and stop the lathe before it crashed.

On the plus side for you, nothing got broken, no one got hurt and we all learned something!

Bruce

 

[projectnut]

Glad you got it figured out for basically FREE! Anyone on this forum who says they NEVER made a mistake is like watching a campaigning politician. You can tell they're lying to you if you see their lips move.

My dad flew Mooney 201DH. It's a high-performance single engine plane with retractable gear. Line is there are pilots who've done a gear up landing and others who haven't, yet. He always went through a checklist before landing he called GUMPPS: gas (fuel pump on), undercarriage, mixture (rich), prop (pitch), pressure (I think a look at manifold pressure?) and seat belts. He was landing at Capitol City Airport in Lansing, MI. Had "only" been flying out of that airport for 35 years. He was on final and had clearance to land on 28 left, but there was a commercial plane on his tail who'd have to circle before landing, so he radio'd that he'd do a loop-around instead. Did his loop around the field and was flaring when he heard a bad noise. Tried popping the power to pull up but too late. Slid to a stop in probably 150 feet, radio'd the tower that he'd done a gear-up landing, was turning off the master power and was getting out of the plane. It was after that that he realized he'd actually landed on runway 28 right's taxiway. FAA examiner had done my dad's bi-annual flight reviews for over 20 years, said my dad was the only pilot he'd every flown with who he figured he would only see for a bi-annual review. Dad got out of his routine and had an incident, but fortunately walked away unhurt.

Not to belabor it, but I've had 3 mess-ups while threading and have single-pointed well over 1000 threads.

First one: Made a scratch pass which checked fine. Made my second pass and thought, "this thread looks like crap". Yeah, that's what happens when the compound is at 45 degrees. . .

Second one: Was threading to a shoulder, nothing special. Came up a little short, but instead of jogging the lathe, I for some reason grabbed the feed direction knob instead of the back gear/open spindle lever. It's easier to hand rotate the chuck in open spindle, but I grabbed the wrong lever/knob. Rotated the chuck by hand to finish the cut, backed up and promptly split the thread on what should have been the last pass.

Third one: Was threading a metric screw for a bench vise, something like 5" of threading. Was making conservative passes of something like 0.003" per pass. Stopping the lathe, backing out the compound and running the lathe in reverse with the half-nut engaged. Took forever (it seemed) to get back to the start point in back gear. So I started doing the reverses after putting the lathe into open spindle; around 450 RPM instead of 70. Much to my chagrin, I failed on one pass to put the lathe back into back gear at the start of a pass. Glad it was 4" of thread as I had time to stomp on the brake and stop the lathe before it crashed.

On the plus side for you, nothing got broken, no one got hurt and we all learned something!

Bruce

I think we're all safe here. That is unless you make video's filming yourself as the narrator showing your face with you're lips moving. Then there are a few who say they've made a mistake, but then qualify it by saying the "mistake" was the one time they thought they'd made a mistake, then later found out they hadn't.

I'll admit I've made a few threading mistakes along the way. A while ago I was making a new back plate for a chuck on my older lathe. I was actually using the machine to make the part. I looked up the change gear combination and thought I'd double checked everything. When all was finished I was so proud I'd made the plug in record time with no mistakes, or so I thought. When I went to check the threads by attempting to screw on a chuck off the shelf it was obvious something was wrong.

It worked about a turn then stopped. I checked the profile and thread depth at least a dozen times and just stood there scratching my head. I finally had enough and left the shop for the day. The next day I came back still pondering the problem. After a few more measurements I finally went to the tool box and pulled out the thread gauge. Big OOOps. I had inadvertently put on the gear combination for an 11 1/2 pitch thread. So much for no mistakes and record speed.

I keep the plug in a prominent place as a reminder that I'm not nearly as perfect as I once thought I was.

 

[Larry$]

For those that have not watched Joe Pie's threading videos, I highly recommend them. His explanations are excellent. He is a professional machinist mostly making medical devices. Some of the things he recommends are simpler approaches than the traditional. Examples: thread away from the chuck, plunge straight in (no 29.5+-,) use only one thread wire, not the miserable 3 wire system, and yes you can disengage the feed doing metric on an imperial. And yes they all work just as well and are definitely easier. For those of you that have threaded chucks there are ways of making a draw bar so you can run in reverse. Not covered in Joe's videos but available on YouTube.

His many other videos are all very well presented, usually a white board followed by a run video on the tool. When I got my rotary table his videos helped a lot. Life's to short to do it the hard way!

 

[mcdanlj]

@BGHansen most of my hours are in a retract, and so far no gear up myself, though I picked my dad up after he had his only gear-up, also in a Mooney. (He was luckier than your dad; he heard the prop strike, popped it up, and successfully dropped the gear, so no belly work, "just" a new prop and engine rebuild, top and bottom.) I'm taking a break from flying because I keep working instead of flying and want to be safe, but when I get back to it I'll probably be flying a retract again. I have had other "I learned about flying from that" opportunities. I'll save those for another forum though!

I'll say that threading towards the headstock can be about as intense as short final on a gusty crosswind day!

@Larry$ yeah, I've watched several of those.