Thread relief on tenon

alinwa said:
OK, let me just get this right.....Fitch you just HIT REVERSE with a couple hunnerd pounds in motion? (I realize that reversing force is probably only 20-30ft/lb but hey..... if it was hooked to my nose it'd hurt)

I know of hydrostatic drive heavy equipment where that's normal but that's because of bleeders and popoffs.. and routing. Does a three-phase offer such a smooth cushion that there's no shock or what?

al
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Years ago I worked in a shop that made hydraulic cylinders. They contracted to make a bunch of cylinders for a Japanese forklift company with all metric threads. I ran a large LeBlond Makino lathe and I was amazed to see the 12" chuck stop and reverse from 220 rpm with no fuss whatsoever. We cut metric threads just as Fitch describes and it works! I don't have that luxury with my single phase Jet.

Scott Roeder
 
frwillia said:
I've never tried it with a 3ph inverter (variable speed) drive. It might work, but I'd think it would have to be a programmed ramp down and back up, and it might not like it much - but it might work at low speed.

Fitch
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Actualy it works, and it probably works better than most rotary phase converters!
You are dead right about the programmable ramp down and back up, but that is only part of the story. Most modern VFD's offer dynamic braking and can be equiped with a suitable brake resistor. Once they are set up and configured to your motor and load, one can go from full speed forward to full speed reverse in complete safety and usualy VERY quickly. They are current limited so the drive will always protect it's self from damage (at the expence of ramp speed).
I have a 2.2KW VFD on my lathe (1.5KW motor) and i can go from full 1800 RPM to zero and back up to 1800 RPM reverse in less than 2 seconds in complete safety. Even with the 8" 4 Jaw chuck on (allthough limited to 1000 RPM with the 4 Jaw). At 300 RPM, reversal is pretty much instant! The brake resistor is about a foot long and nearly 2" dia and rated to 500W continuous power but still gets quite warm after several high speed reversals.
Combine this with the fact that i can dial up any speed between about 6 and 1800 RPM at the flick of a dial, a VFD is the only way to go..
With the cost of VFD's droping dramaticly over the last few years i cannot understand why anyone would be mucking arround with rotary converters.

Cheers
Leeroy
 
Leeroy said:
Actualy it works, and it probably works better than most rotary phase converters!
You are dead right about the programmable ramp down and back up, but that is only part of the story. Most modern VFD's offer dynamic braking and can be equiped with a suitable brake resistor. Once they are set up and configured to your motor and load, one can go from full speed forward to full speed reverse in complete safety and usualy VERY quickly. They are current limited so the drive will always protect it's self from damage (at the expence of ramp speed).
I have a 2.2KW VFD on my lathe (1.5KW motor) and i can go from full 1800 RPM to zero and back up to 1800 RPM reverse in less than 2 seconds in complete safety. Even with the 8" 4 Jaw chuck on (allthough limited to 1000 RPM with the 4 Jaw). At 300 RPM, reversal is pretty much instant! The brake resistor is about a foot long and nearly 2" dia and rated to 500W continuous power but still gets quite warm after several high speed reversals.
Combine this with the fact that i can dial up any speed between about 6 and 1800 RPM at the flick of a dial, a VFD is the only way to go..
With the cost of VFD's droping dramaticly over the last few years i cannot understand why anyone would be mucking arround with rotary converters.

Cheers
Leeroy
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Thanks for the update on inverters. Sounds good. I probably won't go shopping for one any time soon, but it's good to know they are out there.

Why won't I be getting one? Well, as good as inverters may be today, my rotary converter (built 20+ years ago), has never failed to do anything I designed it to do, is about as reliable as gravity, paid for, and isn't broken. If it ever breaks, I'll consider an inverter, but since I built the converter myself, if it ever breaks I can't imagine anything on it that I can't fix for twenny bux.

Fitch
 
Leeroy said:
Actualy it works, and it probably works better than most rotary phase converters!
You are dead right about the programmable ramp down and back up, but that is only part of the story. Most modern VFD's offer dynamic braking and can be equiped with a suitable brake resistor. Once they are set up and configured to your motor and load, one can go from full speed forward to full speed reverse in complete safety and usualy VERY quickly. They are current limited so the drive will always protect it's self from damage (at the expence of ramp speed).
I have a 2.2KW VFD on my lathe (1.5KW motor) and i can go from full 1800 RPM to zero and back up to 1800 RPM reverse in less than 2 seconds in complete safety. Even with the 8" 4 Jaw chuck on (allthough limited to 1000 RPM with the 4 Jaw). At 300 RPM, reversal is pretty much instant! The brake resistor is about a foot long and nearly 2" dia and rated to 500W continuous power but still gets quite warm after several high speed reversals.
Combine this with the fact that i can dial up any speed between about 6 and 1800 RPM at the flick of a dial, a VFD is the only way to go..
With the cost of VFD's droping dramaticly over the last few years i cannot understand why anyone would be mucking arround with rotary converters.

Cheers
Leeroy
Click to expand...

OK, now this is more concievable to me :):) modifications made, or machines made TO allow reversing on the fly are different IMO than just "hitting reverse" on your spinning lathe!

The first post about just hitting reverse just set my teeth on edge a liddle....... no arguments here, no attempt to argue with what IS, just hadda' question the idea a little. For the home hobbyist that's banging the hannle and wondering why the lights flicker.... :)

LOL

al

al
 
Just poke the button, or flip the switch. With a Bridgeport type mill it's damned near every day they're being direct reversed, sometimes all day, even all week long. Ya just gotta replace the drive pulleys every few years.

If you break your lathe or mill by reversing it, you need to buy better iron.

Most quality machinery today all have direct tapping capability, so tapping heads are not as necessary as they once were.
 
TRA said:
Just poke the button, or flip the switch. With a Bridgeport type mill it's damned near every day they're being direct reversed, sometimes all day, even all week long. Ya just gotta replace the drive pulleys every few years.

If you break your lathe or mill by reversing it, you need to buy better iron.

Most quality machinery today all have direct tapping capability, so tapping heads are not as necessary as they once were.
Click to expand...

I didn't think to mention it, but that's true. I have a tapping head but seldom use it. Instead I set the mill (a 3ph 2HP 16 speed belt drive 9x42 BP clone) for it's lowest speed forward and flip the switch to reverse if the tap starts to slip in the drill chuck, then back to forward. Works great.

Fitch
 
If you set up properly you can cut right up to the shoulder without a thread relief.

Note the shallow thread just to the left of the last full thread on the left. That shallow thread is a portion where the tool is being withdrawn in a coordinated movement of disengaging the half nut while turning the cross slide dial out.

The best way to do this is to position the tool to where you want the thread to stop. Then with the carriage in that position, make a mark with a felt tip marker against the left intersection of the carriage wing and the bedway.

Before starting the threading cuts, practice watching that ink mark on the bedway and the approaching carriage wing. i.e. instead of watching the threading tool, watch this point. Do this a few times before you start cutting threads.

 
I do it similiar to what Jerry is explaining, only I set the actual carriage stop.

I thread at 250+ RPM, to a shoulder. So you really do not need any fancy gimicks, you just need to learn how to do it.

As for Metric, none of our lathes will re-catch a metric thread if you dis-engage the half nut. But they do have an instant dynamic brake, on the Mazaks, it stops in an instant. But then, these machines are desined to take the shock. Some of the more popular "gunsmith lathes" being marketed might be suspect.......jackie
 
I set up a dial indicator and set it so the dial is at zero when the tool is as close to the shoulder as possible with a little clearance... when the carriage is backed away the needle rotates and stops in about 40 thou of movement... it is this needle I watch and kick the threading tool out and throw the engagement out at the same time as the needle 'hits' zero. I thread at 45 to 90 rpm depending on how close I have to get... it doesn't bother me if I have to cut a 50 thou relief cut on the tenon, but in the past I set some actions up on a mandrel and cut the relief in the action.
 
I understand there is some pride involved in cutting the thread to the shoulder. But IIRC, about three threads do most of the work, with another 3 or so doing some moderate work. The rest of them are there, as Bruce Thom describes it, "for alignment." From that perspective, you can set the barrel back a number of times before losing any strength.

Am I missing something?
 
The lasr four, or five barrel's, I have turned the cutting bit upside down, and run the lathe backward. This leaves nothing for the bit to run into, and you don't need lightning reflexes which I certainy don't have. I made a dedicated tool holder just for this job, and also made a thread grinding jig to keep everything straight. Grinding the bit down to root diamater on shoulder side, you can start the bit right at the shoulder. This method, with these made tool's has for me, made threading just another turning job.
 
B.Johnson said:
The lasr four, or five barrel's, I have turned the cutting bit upside down, and run the lathe backward. This leaves nothing for the bit to run into, and you don't need lightning reflexes which I certainy don't have. I made a dedicated tool holder just for this job, and also made a thread grinding jig to keep everything straight. Grinding the bit down to root diamater on shoulder side, you can start the bit right at the shoulder. This method, with these made tool's has for me, made threading just another turning job.
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When you are running your tool upside down and threading away from the chuck are you using a thread relief to start the tool before engaging the half nuts?
 
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WSnyder said:
When you are running your tool upside down and threading away from the chuck are you using a thread relief to start the tool before engaging the half nuts?
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perty much gottabe IMO

You can sure make the relief SMALL though!

:)

al
 
Threading to a shoulder is easy with one of these, acts just like the compound slide on a Hardinge HLV, also you can buy the blades for 60 deg and 55 deg threads.
Since my lathe is 3 phase and has a metric leadscrew I flip the lever to retract the tool and hit reverse at the same time..........Ian

Tool extended
Extended.jpg


Tool retracted by the flip of the lever
Withdrawn.jpg
 
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WSynder: The tool will automatically start it's own small relief. Since my lathes have all got threaded spindles I make sure the threads, and shoulders of the chuck, and spindle are clean, and mount with a small snap. I make small cuts with HSS, and measure when close with the three wire method. I have not ever had the chuck come loose, and wii remove with a slight snap as normal. The thing is making light cuts here. I use the same method cutting action threads, but the tool is upside right at the back of the work. This really works well on a blind hole where you certainly do not want to hit bottom.
 
I do it the same way Dennis does except I use more than one revolution on my dial indicator, that way I can watch the thing out of the corner of my eye. When I see it start to move I watch until it hits the zero the second time and desengage the lever and back out the cross slide at the same time. I can usually get to within .005 of the zero everytime and I ain't a young guy with great reflexes. When threading for a metric thread however, it is a different story; I disengage the pulley lever and back the cross slide out and stop the chuck from spinning with my hand, then put it in reverse. A little slower, but it works.

Jim
 
Ian_Owen said:
Threading to a shoulder is easy with one of these, acts just like the compound slide on a Hardinge HLV, also you can buy the blades for 60 deg and 55 deg threads.
Since my lathe is 3 phase and has a metric leadscrew I flip the lever to retract the tool and hit reverse at the same time..........Ian

Tool extended
Extended.jpg


Tool retracted by the flip of the lever
Withdrawn.jpg
Click to expand...

Do you have any drawings of the tool? I am used to the Hardinge at work, and would like to have the same setup on my South Bend at home.
 
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