Cutting Metric Threds

[eww1350]

I have a Birmingham LUX-1340 lathe that will supposedly cut metric threads. but I have heard that cutting metric threads requires that the halfnut stay engaged and that I would have to reverse the headstock after backing out the tool etc...

Anyone have a similar lathe and have cut metric threads on it.??

Eddie in Texas

 

[Scott Harris]

I have a Birmingham LUX-1340 lathe that will supposedly cut metric threads. but I have heard that cutting metric threads requires that the halfnut stay engaged and that I would have to reverse the headstock after backing out the tool etc...

Anyone have a similar lathe and have cut metric threads on it.??

Eddie in Texas

You are correct, keep the half-nut engaged and run the lathe in reverse to reset it. Your gears still need to support metric threads. My lathe comes with gears that I have to swap out. It also has a metric gear chart.

 

[eww1350]

My lathe has the metric gear combo installed already.. according to my manual and inspection of the gear set..

 

[butchlambert]

Eddie, I really think you need to check further.

 

[MDSpencer]

Their is a trick to it. Yes you can disengage the half nut. Stop the machine without the half nut going around. Reverse and engage the nut at the same mark as you engaged it at. Run back and don't disengage.

 

[MDSpencer]

Go to YouTube and look for Ox Tools. Great video on this.

 

[Ggmac]

Just googled his machine , it does say cuts both without changing gears . It's made in Taiwan . Taiwan is now China isn't it .

 

[GrocMax]

Can someone explain what makes a lead screw strictly metric or imperial as far as the dial is concerned? Have a junky Chinese lathe at work that will cut metric and imperial using the dial in a normal fashion with just a gear change.

 

[Auto-X Fil]

Can someone explain what makes a lead screw strictly metric or imperial as far as the dial is concerned? Have a junky Chinese lathe at work that will cut metric and imperial using the dial in a normal fashion with just a gear change.

If the lead screw is an inch pitch, then there will be a simple ratio between the number of lead screw turns and part revolutions.

For instance, with an 8tpi lead screw, it'll turn 1:1 with the part when making an 8tpi thread. It'll turn half the speed of the part when cutting a 16tpi thread, and 1/4 when cutting a 32tpi. For those even ratio pitches, you can lock the halfnut anytime and it will chase the threads correctly.

If you want to cut a 13tpi lead screw, the part spins 13 times for every time the lead screw turns 8 times. This is where the thread counter comes in - there are usually 8 teeth on the gear, so it takes 8 turns (1 inch) to get the dial all the the way around. That means if the dial lines up, the lead screw will have moved some integer multiple of 8 revolutions, which means the part will have moved some multiple of 13 revolutions, and they will sync back up at the right spot if you engage the half nut at that point.

If you want to cut an M1.0 thread, which is the same as a 25.4tpi thread, you need to engage the half nut after the part has spun a multiple of 127 times (127 is 25.4x5, which is the smallest integer multiple of 25.4)

So, the only way to make a thread dial work for both metric and imperial is to use multiples of 127, which would mean a large gear-box thread dial (they exist) and waiting forever for the next alignment.

Your cheap lathe can't possibly have a simple thread dial that works on metric and inch threads. Try cutting a 1.00 mm thread, and a 28tpi thread. One will fail. (Or just measure the lead screw pitch).

 

[GrocMax]

Imperial gears- 40T/127T/40T
Metric gears- 30T/127Tx120T/40T
lead screw 8TPI

It works for both 28tpi and 1.0mm

The dial does not have any even numbers, 1/3/5/7 then lines between.
Can't find the dial instructions but there was something goofy about it in relation to metric threads not of a 1.0 multiplier (1.0, 2.0, 3.0 etc.)

Near as I can tell the unit was set up for the N. American market.

 

[butchlambert]

China and Taiwan are not one and the same.

 

[Ggmac]

Thanks Butch , I never was good at geography. I thought I remembered stickers on stuff that said made in Taiwan , ROC . Wich I thought was republic of China .
Anyway thanks for answering an off topic question .
Gary

 

[butchlambert]

ROC is the Republic of China, but China calls themselves The Peoples Republic of China.

 

[eww1350]

OK, again my question is what is the process for cutting metric threads on a lathe that has the correct gears in place to thread metric.. ?? Does it require me to mark the thread dial, reverse the headstock after each pass, etc..??

 

[Auto-X Fil]

OK, again my question is what is the process for cutting metric threads on a lathe that has the correct gears in place to thread metric.. ?? Does it require me to mark the thread dial, reverse the headstock after each pass, etc..??

Two options:

1) leave the half-nut engaged all the time, and use the brake the stop the lathe when you're in the relief. You can even do this without a brake if you put your tool upside-down and thread from the chuck towards the tailstock, since that gives you plenty of room to stop the lathe (unless working between centers, when the tailstock/center gets in the way.)

2) re-engage the half-nut in the exact same spot on the lead screw every time. This isn't all that tricky - look at Oxtool's video on YouTube. The downside is that if you mess up, there's no (easy) way to get back in sync. On a part from raw stock that's no big deal. On a barrel that would be bad.

 

[jdh47]

Eddie you can back the tool out at the end of the cut and reverse the lathe then advance for another cut leaving the half nuts engaged. It is the easiest most foolproof way of cutting metric threads on a lathe having an imperial leade screw. My Clausing Colchester 15x50 has the hi-lo gearing that does not use change gears and that is the way I cut metric with it. My Harrison M300B does use change gearing and it cuts the metric threads the same way. It is just what we must go through to cut metric threads on lathes with imperial leade screws.

Joe

 

[Clark]

A new adventure for me.
I cut 1.5mm pitch metric threads on an Arisaka barrel this week with my PM1236 Precision Matthews lathe.

I practiced on a piece of scrap, and could almost get away with opening the half nut, but it was a little off. So I followed the internet folk lore and kept the half nut closed and ran the lathe backwards.

 

[GenePoole]

A new adventure for me.
I cut 1.5mm pitch metric threads on an Arisaka barrel this week with my PM1236 Precision Matthews lathe.

I practiced on a piece of scrap, and could almost get away with opening the half nut, but it was a little off. So I followed the internet folk lore and kept the half nut closed and ran the lathe backwards.

What do you mean by a little off? There are discrete steps on the thread dial and you can only engage it in those exact steps. I have a 6tpi lead screw so that means that there are 6 engagement steps between say "1" and "2" on my thread dial, or only 3 steps between "half" marks. With about a 1 inch diameter wheel on the thread dial, it's hard NOT to get it in the right slot--even in reverse.

 

[Clark]

What do you mean by a little off? There are discrete steps on the thread dial and you can only engage it in those exact steps. I have a 6tpi lead screw so that means that there are 6 engagement steps between say "1" and "2" on my thread dial, or only 3 steps between "half" marks. With about a 1 inch diameter wheel on the thread dial, it's hard NOT to get it in the right slot--even in reverse.

My mechanical reasoning is top 1%, I normally do not have trouble. But when I read I could not open the half nut, I figured I would make a cut with the thread dial on "1" and roll the carriage to the right, and close the half nut when the thread dial said "1" again. That is off by at least 0.010" for 1.5mm gear box settings on my lathe.
I think I know where my mind went wrong. I can close the half nut on different numbers when cutting 16TPI for a Rem700. I figured that would wash out if I just closed on "1".
Re reading the internet folk lore, the lead screw is an inches lead screw. That is it has a pitch in inches.
We can fool with the gear box until the carriage is moving in mm per spindle rotation, but we do not have phase lock on the lead screw.

 

[GenePoole]

All Correct.

I thought you were having trouble with the method described by MDSpencer above. You can disengage the half-nut as long as you re-engage with everything at the exact same spot. This is easily achieved at the speeds we normally thread at. Make a sharpie mark on the dial if you want an extra reminder. Disengage just as you would for any other threading, but after disengaging, let the lathe spin a bit in forward, and you'll see that the dial move pretty slowly past your mark. You have plenty of time to reverse the lathe--even if you have to stop the motor first. Once your rolling in reverse, watch the dial spin back around and re-engage at the same spot on the dial when it comes back to your mark (if you go past a little, just go back to forward and hit the mark when it comes around and then back to reverse). Let it run in reverse until your clear of the workpiece, then (while still running if you want) restore your cross-slide, and advance your compound (and add cutting oil or anything else you want) and just switch back to forward. As long as you don't let the dial go too far while dis-engaged, you can easily restore your gear-train geometry every time.