Metric Threading on Standard Modern 1334-MIL

[nabison]

First post! Desperate!

I have at 1334 MIL lathe that I use for my side machining business. I have single-tooled many a inch threads no problem. Now I have a job calling for metric threads, M65x2 and I'm stumped. See from attached pictures from my machine that I have the metric capability. I can select the correct feed from the quick change gear box to get 2mm pitch no problem.

However, as has been well documented that since I have an inch leadscrew and inch travel dial, I must leave the half nut engaged throughout the threads. That's where my problem comes in.

1) My first inclination was to engage half-nut, make my first cut, and switch the direction of the leadscrew using upper left lever on the head stock while it's running. During the reversal process, there is a brief pause of the leadscrew while the reversal happens, all the while the spindle is turning. Thus I lose my timing. I've verified this by attaching a pen to my tool holder, and the pen lines DO NOT match up.

2) After scouring the internet, I found this method (

) and gave it a shot. Same issue happens, when I reverse the spindle, the lead screw noticeably pauses when switching directions. In this video, the lead screw speed is 100% synced to the spindle, mine is not. Using the pen check, again I lose the sync using this method.

3) Lastly, I found this video of a standard modern lathe that goes into detail about the "Lead Screw Reversing Mechanism."

. Im 99.99% sure I don't have this "Lead Screw Reversing mechanism mentioned in this video.

4) What really bothers me is that my manual says I have a lead screw reversing mechanism which allows the half nut to stay engaged. So, I called up Racer International (aka Standard Modern) and they were not helpful. They pointed out that the lead screw reversing mechanism is the lever on the head stock. Well, it definitely reverses the lead screw direction, but as I noted previously, the lead screw will pause briefly while spindle is still turning which to me is absolutely useless when making threads.

I'm somewhere between a newbie and a wannabe machinist, so I assuming I'm missing something. But it seems to me that the lead screw reversal on this particular lathe is non-typical. I really need to get this figured out for this customer. Does anyone have experience machining metric threads on a 1334-MIL? Many thanks.

 

[tailstock4]

Real lead screw reverse involves either electrical or electromechanical reversal of the spindle thereby reversing the leadscrew. Or another method is a mechanical leadscrew reverse which in my opinion is the best method. The latter involves dual clutches and a dog to maintain synchronization.

On your lathe when you try to reverse the leadscrew by going to the headstock and reversing the leadscrew direction even though the half nuts are still engaged, you are switching gear trains in the headstock there by losing your synchronization.

What you need to do is leave the headstock engaged in either left-hand or right-hand (whichever one you are using). Then reverse by electrically reversing the spindle direction or if you have forward/reverse clutches in the headstock, it can be done that way. This will maintain your synchronization.

 

[nabison]

I tried your suggested method. I engaged half nut, reversed spindle, and you will see there is a dwell period where spindle is now rotating in a different direction, but the lead screw takes a while to catch up.

 

[markba633csi]

There is unavoidable backlash and you must pull the cutting tool out when reversing back to your starting point. Keep track of
your cross slide setting. The backlash zeros out when you switch the spindle again to forward.
I'm pretty sure you don't have the fancy instant reversing feature as mentioned in the second video- you have the conventional type of machine
so the spindle drive must be reversed instead; the tool must be pulled back after each pass

 

[Ischgl99]

I tried your suggested method. I engaged half nut, reversed spindle, and you will see there is a dwell period where spindle is now rotating in a different direction, but the lead screw takes a while to catch up.

When you go forward again, it will take up the backlash and the tool will be at the same spot as the last time you were going in the forward direction. You don't need to worry about the backlash when reversing since you are not cutting in that direction. As Mark says, make sure you back your tool out of the thread when going backwards to your starting point, you do not want to be cutting in that direction. You also want to make sure you go back far enough from the start of the thread that when you go forward again, all the backlash is taken up.

 

[RJSakowski]

You can't reverse the lead screw while threading without losing sync. You have to reverse the spindle direction to back the carriage out. The problem is you have to stop the spindle which can be an issue when threading to a shoulder. The solution offered by Tom Lipton works. Another solution is to run the swindle in reverse and thread towards the tailstock.

 

[markba633csi]

When you reach the end of each cutting pass you can either stop the machine then pull the tool out, or you can do the opposite.
I usually do the former; I can judge pretty well how the machine will coast to a stop. Some folks do both at once with two hands. Whatever you feel most comfortable with.
It can be hairy when you are threading up to a shoulder, or making an internal thread in a blind hole. Fast reflexes are needed
One trick I did recently was put a Sharpie mark on the bedway as a "do not cross or you'll crash" point

 

[nabison]

Thanks gentlemen. I will try reversing the spindle tonight and see if the backlash is properly accounted for. I will use a fine tooth sharpie to test these theories before the real cutting begins.

 

[SteamWilly]

Sorry, but the FIRST thing I do when confronted with ANY metric thread, is find out the reason it cannot be simply changed to a U.S. standard thread in an equivalent size!

YIKES!

THREADING IS THE ONE IMPORTANT THING THAT ALL THE "METRIC YAMMERERS" IGNORE WHEN DISCUSSING THE SUPPOSED SUPERIORITY OF THE METRIC SYSTEM.

You are faced with diddling with a metric thread, or else you can just go out and buy a metric tap and die in the appropriate size. This would be MY choice if there was no way to make this thread a standard U.S. thread of some type. Those are the two best possibilities for this project. Or you can, as you are doing, fiddle with it and hope it comes out.

This is a fairly sizable metric thread 2.5" (Or would be a U.S. thread of 2. 562", 2 9/16", or any thread pitch in that size) so it might be hard to find a tap and die in that size, unless you order it special, in which case you are looking at somewhere north of $400.)

Any possibility of re-tapping the hole in a U.S. Standard thread size, and cutting a U.S. Standard thread on the part that fits into it?

Please DO POST on how you solved this problem!

I am very blunt with anyone who wants a metric thread on something I make. Unless they have an EXCEPTIONALLY good reason, I insist on a change to a Standard U.S. thread, or tell them either: "Sorry, I can't make that." Or, I give them the option of paying for the necessary tap and die in metric form. (And I keep the tap and die after the work is complete!) (because; What are THEY going to do with it?!? It is useless to them.)

You have already probably spent enough time on this circus to lose money on this job.

Unless this is a Bugatti, or a German Fighter from WWII, this job will NOT be worth the time and effort.

Just my 2 pfennigs.

Some jobs, you are better off just turning down.

Or sometimes, you have to straighten the customer out about what he REALLY wants!

 

[Ischgl99]

I am very blunt with anyone who wants a metric thread on something I make. Unless they have an EXCEPTIONALLY good reason, I insist on a change to a Standard U.S. thread, or tell them either: "Sorry, I can't make that." Or, I give them the option of paying for the necessary tap and die in metric form. (And I keep the tap and die after the work is complete!) (because; What are THEY going to do with it?!? It is useless to them.)

Because they’re paying you isn’t a good enough reason? I’ll gladly take those customers from you if you are unwilling to learn how to thread metric. Most of what I do is metric, so it makes no difference to me which system someone wants to use, their money is green either way.