Bad day of threading

Just wondering if you were to get a known 5/8-11 bolt and study your tool in there and where
it makes contact and where it should not. And then you say you had a thread stop so its
pretty close to -0-. With a thread stop its not close= its dead on -0- unless its moving or
something. And then another fact sometimes you will come upon stock that just can not be
trained. I know my biggest habbit is junk pickin free junk and thats usually what it is,
unmachinable junk. very hard to break old habits. "problems understood always have a
simple solution, Hugo Young".. I just noticed that you are feeding .010-.020 then you will
have to know if your machine has a direct reading dial or not, which means the feed may
be a little too much for that lathe. Thats all I can think of for now. samuel
 
Shepherd said:
Cutter was on centre, would have to check the side clearance...I'll get a pic tomorrow night.

one other thought...the gearing was a particular hassle. Machine shows 72-120/127-33, Chinglish manual shows 72-120-33, and the Grizzly manual I have (much better written) shows 72-127-33....would this affect the shape of thread or the cutter picking up the thread on each pass, or just the pitch?
Click to expand...

If you have a compound gear in the train like 120/127, it will have a affect on picking up the correct lead. Does your lathe have a english lead screw or metric lead screw? On the other hand, if it is stepping up the lead screw 72:33 which approx. equals 2.1818 step up, meaning the lead screw is spinning 2.1818 times faster than your spindle. It could be very easy to engage the half nuts in the wrong place.

This is where you have to very quick to back off the cross feed screw to get the cutter out of the cut BEFORE disengaging the half nuts! To save your thread.
 
Thanks all...I'm fairly sure it's not my set up, but rather the gearing or backlash in my machine. Just not prepared to drop 3000 right now to buy a new lathe just to fabricate a rear axle for my bobber build.

ive got new stock chucked up and turned to size, ready for another attempt this weekend. Well report back then.
 
TomG said:
I've never been a fan of the 29 1/2º thing. If the compound is set to roughly 30º, the tool is essentially cutting on one side. When the thread is nearly to depth, the last few thousandths are taken with the cross slide. Once that happens, the tool cuts on both sides anyway and it doesn't matter where the compound was set (within reason). The theory behind setting the compound to 29 1/2º is that the tool will cut mostly on the left side and a very light cut on the right. This reduces the amount of force on the set-up and consequently reduces the possibility of chatter. Where the theory falls short is when the thread is nearly to size. It's a heck of a lot easier to figure out how far to feed the tool in for the final cut with the cross slide than it is with the compound when it's set to 29 1/2º.

Tom
Click to expand...

Quick FYI,
PITCH = 1/NUMBER OF THREADS PER INCH

American National Standard Slant depth formula;
1) External Thread= .750 X pitch
2) Internal Thread= .625 X pitch

American National Standard Straight depth formula;
1) External Thread= .64952 X pitch
2) Internal Thread= .541266 X pitch
 
Or if you find you need to remove another .003" from the pitch diameter, you move the cross slide dial in .003" and be finished. I'm old and lazy and don't want to remember conversion factors or refer to charts any more than necessary when I cut threads. :))

Tom
 
Kylisdad said:
The point was, if you choose to do it the Traditional way, the formula for the slant depth is just as easy to calculate as the straight depth...
Click to expand...

And my point is that there is no need to calculate anything. Just crank the compound in until you get enough thread to measure the pitch diameter with the thread mic or wires and take the remainder off with the cross slide. Also, the slant depth and straight depth calculations are only approximate, you need to actually measure the pitch diameter at some point to finish the thread.

Tom
 
TomG said:
And my point is that there is no need to calculate anything. Just crank the compound in until you get enough thread to measure the pitch diameter with the thread mic or wires and take the remainder off with the cross slide. Also, the slant depth and straight depth calculations are only approximate, you need to actually measure the pitch diameter at some point to finish the thread.

Tom
Click to expand...

What ever floats your boat ;) Some of us like having an idea where we are headed, and actually have those old formulas stuck in our head because we use them day in and day out to earn a paycheck... But if you prefer not to calculate anything, that's your prerogative. That's the beautiful thing about machining, there are a hundred different ways to do any one thing, and as long as the end result is correct, the boss is happy.. Have a nice day :)
 
I am doing some reading of the Busybee manual online (hoping it's been updated from my copy), and it indeed shows different gearing from my machine


My machine thread gear chart says (Motor gear-intermediate gear-spindle gear):

72 - 127/120 (with the spindle engaged with the 120) - 33 on the spindle

Grizzy says:
72-127-33

The Busy bee manual currently online says:
72 - 127 - 33 same as grizzly


I am getting the idea that the 120/127 combo gear is what allows one to switch beteen imperial and metric threading, just examining the charts. As busybee is sold here in Canuckistan, the dials on the machine have the metric readings closer to the "notch" than the imperial> I'm thinking that the factory misprinted the faceplate, assuming that the leadscrew on the apron was in fact metiric as well, but I'm getting the sense that otherwise, the guts of it are purely imperial, and should be geared accordingly (ie" using the 72-127-33) ratio specified in the grizzly manual.


thoughts?
 
You must log in or register to reply here.
Back
Top