Keep crashing internal threads on Grizzly 4003 lathe

[ridgeway]

Guys...thanks a ton for all the suggestions. I may give it one more try and keep in mind of the suggestions.

Ray...its 304 SS...i think its the lighting in my garage casting the tint.

I will cut a relief groove in the next on and maybe raise my bit a tad bit above center.

I am thinking toward the end of the cut, I may inadvertently travelling in a few thousands before lifting the half nut and backing the bit away causing a disruptio. Or the flow of chips following the cutter and bottoming out. I dunno...frustrating. LOL.

No biggie with the part...i can live without it. The purpose of this tool was to thread onto various barrel tenons and have indexing marks to locate where to engrave the caliber on the barrel so it lines up in the correct position. That way I dont need to screw the barrel on the action, mark the location and take it back off

 

[Ray C]

OK, first, with SS, it is not cooperative. You must do spring passes on every second pass unless you have a beast lathe. Trust me on this. I do SS threading 3 times a week at least. I'd venture to say this is the smoking gun. Next best guess is the relief on the cutter. Also, with SS, you must have dark cutting oil or it grabs like crazy.


Ray

Guys...thanks a ton for all the suggestions. I may give it one more try and keep in mind of the suggestions.

Ray...its 304 SS...i think its the lighting in my garage casting the tint.

I will cut a relief groove in the next on and maybe raise my bit a tad bit above center.

I am thinking toward the end of the cut, I may inadvertently travelling in a few thousands before lifting the half nut and backing the bit away causing a disruptio. Or the flow of chips following the cutter and bottoming out. I dunno...frustrating. LOL.

No biggie with the part...i can live without it. The purpose of this tool was to thread onto various barrel tenons and have indexing marks to locate where to engrave the caliber on the barrel so it lines up in the correct position. That way I dont need to screw the barrel on the action, mark the location and take it back off

 

[ridgeway]

shor...thanks for taking the time to make that video. One of my tries, i did have my compound set wrong...actually twice. LOL. I also had 29.5° set on the wrong axis doing external threads...you can only imagine what they looked like, LOL.

 

[DAN_IN_MN]

ridgway

From your info on your first post, it does sound like you know how to turn a thread and something is giving you the run for your money on internal threading.

Have you tried turning the same thread in mild steel? How about cutting the same thread in SS without being a blind hole?

Like others suggested, you might be bottoming the cutter out and the carriage pushes the cutter back in the tool post so not it's not in sync with the thread groove.

Another thing you could do, and it will take more time, is to shut the lathe off and manually turn the spindle with the half nut engaged and watch the cutter to be sure it lines up with the threads. If it lines up, without disengaging the half nut, hit reverse and back up the carriage, advance your cutter for a deeper cut and make the cut. Do this until you discover the cause for the cutter misalignment.

I suppose after checking to make sure the cutter hasn't moved, you could engage the half nut using the threading dial. I think you know what I'm trying to get at here.

 

[ridgeway]

Dan, I crashed the threads 2 times in mild steel and twice with stainless. Wasted 4" of good 304!

I don't think turning the spindle by hand in low gear would be a pleasant experience, lol.

Anyhow, i will try this again on mild steel. I will bore to minor diameter. Then I will bore a large relief inside and thread inside out. I only need .750" worth of threads. I should be able visually see what I'm doing atleast, lol.

Might not be for awhile, but I wi report back if im sucessful at this.

 

[ridgeway]

Well guys...I am happy to report back that I suceeded in turning inside threads, sort of. I set up to thread from the inside out. I counter bored relief inside so I only threaded half the length, which is totally fine for this tool. I did manage to break the carbide threading bit though. Not sure why, maybe chips or burr? I was set up to make my last pass, engaged the halfnut and boom, broke turning bit the first three threads. Good thing I had my hand on the crossfeed to back out in a hurry. The break upset the tool bit and wasnt about to replace the bit and rechase the threads. So I pulled the part out and almost chucked it into the scrap bin. I looked at the threads and blew them out with air. Gave it a whirl and it magically threaded. Im like good and chucked it back into the lathe to counterbore the damaged threads away. While I was at it, I went ahead and finished and put a super light knurl on it. Threw a coat of cold bluing on it to help with rust.

 

[wallyw]

After many years of threading and several years on my G4003 ran into a problem. Threads were just not up to snuff. Checked all the usual fixes. After an hour or so found that the cap screw opposite the halfnut engagement handle had loosened. Tightened it. Good threads again!

Wally