ML7 Novice Questions

That's the way to do it. It is possible to make or, sometimes, buy handles that fit into the far end of the spindle. these make turning it by hand much easier. But they aren't necessary.

A reversing switch is quite simple to add into the motor wiring. I can't find a diagram on the interweb that doesn't make it look far more complicated than it is, but a double pole double throw switch should be used to reverse the supply to one of the two windings in the motor. The motor needs to be stopped before the reversing switch can have any effect.

One gotcha that I would add is that the tool should be retracted out of the thread before winding the lathe backwards. If this isn't done, the slack in the leadscrew and gears will cause the thread that has just been cut to try to push the tool rather than the leadscrew pushing the tool. This _will_ cause the end of the tool to be snapped off DAMHIKT.

Mark Rand RTFM

Got that wrong. It's 58% for 60 degree threads and and 52% for 55 degree threads. Sorry.

Forgot to mention, the "topslide travel" should be 15.5% more for 60 degree threads and 12.7% more for 55 degree threads than the required depth of cut for the thread (hope that makes sense) when using this method.

Ooops - sorry, too early on a Sunday.

Forgot to tell you also ... thread dial indicator is for imperial threads only.

on metric threads you got no choice you have to leave the half nuts engaged and reverse

believe that some myfords have a hand wheel on the end of the lead screw for reversing.........if not make one .buy one ....or take mark rands advice on setting motor up for reversing.

all the best.mark

Not sure on this....for myfords or not......but some lathes....the chuck comes undone when you reverse.....so also .... it is advisable to make some sort of alteration to the chuck to lock it onto the threads on the headstock... full details of this mod will be given by others.

this is a useful mod ....so you can have your lathe in reverse and cut angles with the compound slide facing towards you rather then having to lean over the lathe and grapple .

All the best..mark

Nope! It means putting a hand crak on the lathe spindle and cranking the spindle back to the beginning without disengageing the leadscrew halfnuts.

You leave the halfnuts engaged, withdraw the tool with the cross slide (important!) and crank back to the beginning of the pass.

If you build a suitably balanced cranking handle, it can be left in place as the cut is taken under power, or you can just disengage the drive belts and use the crank to turn the spindle in both directions, allowing very fine control, esp. for short threads.

Cheers Trevor Jones

Lathe"

Welcome!

One of the manuals was from the metalillness.com board, the other from practicalmachinist.

I can take credit only for passing them along.

Cheers Trevor Jones

On a metric thread, with an inch pitch leadscrew, the halfnuts and gear train MUST remain engaged (There are some ways around this, but somewhat complicated). When cutting an inch pitch with an inch leadscrew, safe is to use the same number. No worries, no having to remember which numbers are correct.

Now. If the pitch of the thread being cut, is evenly divisible by the pitch of the leadscrew (inch pitches , inch leadscrew again) there is no need at all for a thread indicator, as the thread will engage correctly at any point that the halfnuts will engage. Some pitches will require the use of only one number, others have several that will work.

Many lathes have the chart for the threads and the appropriate number to use, right on the machine near the thread indicator.

One lathe I use at work has no half nuts. Threading is done with a ballscrew, and the reverse lever by design. A bit of adaptation, to get used to.

Reversing the spindle, or even stopping it while the tool is in contact with the work, is deadly on insert tips. At 25 dollars/ 12 pounds or so per decent quality insert, I recommend staying completely away from the carbides, and sticking with the HSS. Learn to grind a tool, and you have the skill forever.

I make the apprentices at work hand grind their threading bits, to their satisfaction, then we look them over with a comparator. They have to grind a UNF threading tool with all the correct geometry, in order to pass. Most are quite capable of grinding a tool to dead nuts perfect once they practice a bit, whether they think so or not. Guys get all freaked out about grinding tools. It's dead silly simple, with a bit of practice. You don't get any practice by avoiding it, either.

Even most of the CNC lathes dont do this any more. It's very hard on tips, with some drastic loads applied.

Huh? That sounds like it makes life more complicated than it has to be. If it works for you, though...

That is the more common practice. Use slightly less than half the included angle of the thread, so as to cut primarilly on the one face, but apply a shaving cut to the other. If you use exactly the half angle, there is a possibility of leaving steps in the face that the tool runs parrallel to, causing a rough thread, with steps down one flank.

It is easy. To the point of being a bit boring. (ooh, lathe pun!)

The first thread I ever cut with a lathe was a acme thread on a mild steel 5/8 inch bar, to replace the leadscrew on my bench vise (unwisely used to press out too big a bearing). The threaded portion of the bar was 7 inches long, IIRC, and I ground the tool bit using a angle gauge and a micrometer to measure the tip width. Once I got that done, there was never any fear of cutting threads with a silly little V tip. :-) I did this before I had ever got any real training in the craft.

The recipe is thus:

Set zeros (or note dial readings) on cross and compound slides. Feed in compound (topslide) for depth of cut Engage halfnuts Cut Disengage halfnuts* Crank out cross slide Crank carriage back to start point* Crank in cross slide to zero Feed in compound for next pass Engage halfnuts* Repeat until final depth is reached.

The starred items will be skipped if you are hand cranking the spindle back to the start. You MUST pull the tool back from the work before reversing the rotation, though, or you get to learn how to pick up on a partially completed thread (less fun).

Threading, and grinding HSS tools, are dead easy. Only fear keeps guys from plunging right in and getting the job done. Practice is key. If you do not do it, you do not get any practice, now, do you?

Cheers Trevor Jones

I can understand now why I have never seen this method in use. :-)

Too many things to remember. :-)

Cheers Trevor Jones

You cannot usually drive the spindle backwards with the leadscrew handwheel. The geartrain does not allow it at the ratios used.

Cheers Trevor Jones

Simple answer, that has worked for well over a hundred years, is to not try cutting with the spindle running in reverse.

Avoiding going hard from forward to reverse (stop the spindle in between in between) is another way to keep the heart rate at a more reasonable pace.

Reverse is a bad thing at high enough speeds that you must worry about inertia removing a threaded chuck on startup.

IMO such modifications that would cause the chuck to stay in place, mostly serve to make life in front of my klathe just a little less enjoyable, as it complicates the removal and installation for little benefit. I have yet to see a good reason for running the lathe in reverse fast enough to spin a chuck off at startup.

I know it is standard on the new Myfords. I blame that on lawyers, not on common sense.

A better idea that I have seen was a spring catch that prevented the switch from being thrown straight through from the forward to the reverse position, so it had to be pushed out of the way to reverse.

Nothing as fun as a chuck going forward at 2000 rpm and the spindle going backwards! :-) Mostly only an issue with 3 phase power, as most single phase motor will not hard reverse, but must be brought down to a slow rpm before the start windings will kick the motor in the other direction.

Cheers Trevor Jones

I had an ML7 with a reversing motor on it. I now have a Super-7 with a simple on-off switch. It has not complicated my life at all to be without the reversing facilities.

I would rate it as something potentially handy to have, but by no means a requirement.

Cheers Trevor Jones

Get over the idea that grinding tools is any sort of black art.

By that logic, so is machining. Best left to those in the know, doncha know.

It is a skill, like machining, that one must learn by doing, rather than reading about.

Avoidance solves nothing and costs more.

The angles are, in general, open to interpretation, and capable of being varied (often by a huge amount) to see what works. Just as there are different angles given for HSS tools, there are even MORE variable in tips for insert tools. A Kennametal or Iscar catalog will set you right to work grinding HSS, esp. once you see the prices. In carbide tooling, you generally get what you pay for. You just have to know what you want, and why, to make them worthwhile.

A sharp edge with a little clearance in a couple direction will cut most materials well enough. Flat on top for brass and threading tools. A radiussed tip for a nicer finish, most of the time.

Grind a tool, try it, try different geometries to see what works. Some tools work quite well on many different materials, despite what the books say about how wrong the geometry is.

I use a lot of carbide tooling daily at work. I use a lot of HSS at work as well. More HSS than carbide. I turn steels from mild through some semi exotic stainlesses, Brass, Beryllium copper, titanium, graphite, plastics, and a few other materials. HSS works well for all of them.

I do not work in a production shop environment, rather in maintenance, where I have to make one or two of most of the jobs that come in.

Cheers Trevor Jones