threading problems.....

[mikey]

Bob, don't beat yourself up. Lots of folks thread with the cross slide and have no issues doing so. It would really help if you showed us some pics of your set up and your tool.

 

[T Bredehoft]

The reading on the compound is not cast in iron, it could be off by 90º. Many manufacturers don't take into account the "real" angle. Draw a line 30º on a piece of card stock, cut it out and use it to set the compound to that angle relative to the face of the chuck. In this case 30 is less than 45.

Yeah, use the compound to move the tool.

 

[Bob Kelly III]

The cutter matters too. HSS is the way to go for cutting threads at low RPM. It will cut much better than carbide when it is turning at a speed where catlike reflexes aren't required. Carbide will work fine when you get practiced with threading and can run the higher speeds, but at low speeds I have found it will tear up the threads instead of cutting them sharp.

well cutters have been a problem but I think I cured it a bit ago.... I made up a holder a long time ago for the 3 in 1 lathe that holds a piece of broken file with a 1/4"x 20 bolt ao I used a piece of broken file and made my thread cutter out of it and that seamed to work fairly well I don't have any HSS cutter stock( yet) but I will have eventually !
not using the compound to advance onto the threads i am sure is 90% of my problem ! that just slipped my mind !
..... all my threading up to now has been done with taps and dies and yes I've even resorted to making my own threaded rod before under duress !
but I have a lathe now and I want to make my own threaded rod on demand so far I've had no luck at all !
HAHAHAHHAHA
Bob.....

 

[Bob Kelly III]

I am wondering now if that "not using the compound " is the biggest issue here now......
that and my tool was ground by hand and may very well be too wide......

I'll try to snag the wife's cell phone and take a few pictures of the setup
.....
the thread dial :
I took it off and discovered I could hold the gear in my left hand and turn the dial easily with my right hand !
but it did take some force, so it's not very likely to have been the problem sense air is the only thing that would be trying to turn it !( or vibration)<grin> but I tightened it up anyway re set it and made sure it was point at a mark ( all I had to do was move the cross slide up or down the bed to do that ....so I don't think that is the issue, I engaged the half nuts this time exactly on the mark and it fell into gear just after the mark.... every time .
I was going at about half the speed I was before ( 15 on my VFD! ) which proved to be so slow the motor didn't have any power so if I do it again I will put it in back gears and slow it way down......
lots of little nuances in threading !
......
here I thought threading would be easy sense I have watched every threading video on Youtube a dozen times or more ! LOL !
but it's giving me hell !
.... tomorrow I will try it with a fresh grind on the cutter and Use the compound to advance the tool and see if I can get some decent threads or not !
thank you for the help guys !
.....
I think the addition of a reverse switch would cure all my problems in one fell swoop ! and just leave that half nut engaged during threading.
i think that is the easiest cure...
....
Bob........

 

[ttabbal]

Any idea what RPM you're running at? I usually thread pretty slow, about 100 RPM. Definitely try the back gear. If nothing else, timing for engaging the half nuts is much easier. For that, try starting at about half way between the two lines. Just get the lever moving and looser. Just before the line, add pressure and it will drop in at the right time.

You might try not using the compound. Set it for 90 degrees (perpendicular to the work) and use the cross feed. Just use lighter passes as you are engaging more of the cutter. Sharp HSS helps. I do it like this all the time as I usually don't have the compound installed, and I'm too lazy to get it set up for a quick thread. It's one less thing to remember as well.

If you suspect that the thread dial is not clocking properly, leaving the nut engaged is a good test. You do need reverse though. Can you enable it on the VFD directly? Good for testing anyway.

 

[mikey]

well cutters have been a problem but I think I cured it a bit ago.... I made up a holder a long time ago for the 3 in 1 lathe that holds a piece of broken file with a 1/4"x 20 bolt ao I used a piece of broken file and made my thread cutter out of it and that seamed to work fairly well I don't have any HSS cutter stock( yet) but I will have eventually !

I am wondering now if that "not using the compound " is the biggest issue here now......
that and my tool was ground by hand and may very well be too wide......

In my experience, faults in thread form are usually from the compound being at the wrong angle or engaging the half nuts at the wrong time or the tool is not ground at a 60 degree angle. Burrs are due to the tool and typically if the relief angles are too low or uneven or if the tool is dull.

Thread cutting is one of the simplest of lathe operations, Bob. Not much to it but your set up needs to be good and your tool must be ground correctly. You stand a much better chance if you grind a square HSS tool bit into a 60 degree threading tool and toss out the piece of old broken file.

 

[Joeman77]

I think you mean 60-1/2 degrees from spindle axis. That would be 29-1/2 degrees from perpendicular to spindle axis.

Tom

59, 60, 61 I could be off a bit, like T Bredehoft said it's not set in iron, as long as you're close it should cut threads. But yeah it needs to be relative to the actual angle of the threads & I've noticed some of the newer lathe compounds just aren't marked correctly.

 

[Bob Kelly III]

RPM ? probably about 40 or 50 RPM..... definitely less than 100 RPM
but no, the VFD does not give me any indication of RPM at all just percentage of power for motor speed, I try to run it at 60 sense I have it to where it can go 2 times that
..... Yes the forward reverse switch can be very simple to hook up...all I need is a 3 way switch but it is between paydays and I gott'a wait for the funds to get a switch ! it may be a switch or brazing rod but not both LOL...we'll see ! but a $5.00 switch shouldn't mean not eating ...Right ? LOL....
.....
60 degrees eh ?for the threading tool point ? well I went way past that to a needle point a few days ago that doesn't seam to last very long ! LOL
yah.... I know toss the crap and use good stuff, but when crap is all you have to work with , well you work with crap !
broken bits of files or busted drill bits are the only HSS stuff I have, I bought a box of carbide 1/2" shank cutters when I got the 3 in 1 about 15 years ago and still have about 3 left but they have a half moon of carbide brazed onto the tip and they are extremely hard to grind.... they eat my grinding wheels very fast ! LOL..... I don't have one for carbide.
but I have one that I took down to a center point a few years back I may well make it into a 60 deg point and use that !
I always put a healthy undercut on the lathe tools I make,...... maybe too much but they usually cut real good
the file does by the way.... it looks like I just put it in ! I hate chatter ! and discovered it was my grinding of the cutters with not much undercut or relief now I am very careful about that.
the more I play with this Logan the more impressed I am with that old 3 in 1 although I have to tighten every gib on it to get it to stop chattering even at slow speeds it does take deep cuts that gives the Logan a run for the money !
.....
OK one more question..... how deep of cuts should you take when threading ? I've been taking 10 thow to 15 thow for the first few passes then back off to no more than 10 thow then go to depth..... problem is it never seams to reach depth ! I thought I had a deep enough thread on a rod a bit ago but it would not go on the nut ! and that is the only thing I can think that it is .....
...... I watched a video where a guy took 5 thow cuts when threading ....is that NORMAL ???? my god, that will take you an hour to make a thread !!!
......it's possible I am hogging out too much at a pass ! LOL...maybe that is why their so ragged ! ripping them to pieces
....
Obviously I got a lot to learn with this thing!
....
I hear the raggedness is in the cutter ! I concur with that assessment ! I shall work on that !!!!!
maybe ordering some HSS tool stock is the best option here !
....
Thanks to all of you ! I appreciate the help !
I'll let ya know what I discover and learn in the process !
C ya !
Bob.......

 

[mikey]

Bob, the cutting tool used to cut threads on a lathe is essentially a form tool. That is, it has a 60 degree point that cuts a 60 degree thread. If the tool tip is not at 60 degrees then your threads will also not be at 60 degrees and your nuts or parts (that do have 60 degree threads) will not fit onto your part. Now, when I say it has to be 60 degrees, I mean 60 degrees, not 58 or 61. In order to grind a tool to a precise 60 degree angle you should use a template like the common Starrett C391 or the Mitutoyo 950-201. You grind the tool to match the fishtail shape of the gauge.

Alternatively, you can use inserted carbide threading tools (Carmex is good) or even inserted HSS threading tools from AR Warner.

You can have the lathe set up right and do everything else right but if the tool is wrong then you cannot cut threads on the lathe. I suggest you fix this first.

 

[Bob Kelly III]

Will do thank you !