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All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Topic started by: happymecanic on February 04, 2023, 11:03:48 AM

Title: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 04, 2023, 11:03:48 AM
I've had this idea for a while, I'd like to be able to cut left-hand threads on my King KC1022ML (same as Grizzly G0602). Problem is, there's no provision to do so with the original gear arrangement. I need to make a reverse tumbler, and saw topics on different hobby machinist forums. But the guys do it using smaller gears to reverse the rotation of the lead screw, which in my view change the final ratio:

https://www.hobby-machinist.com/threads (https://www.hobby-machinist.com/threads) ... ler.37795/

https://www.rcdon.com/html/the_reverse_ (https://www.rcdon.com/html/the_reverse_) ... oject.html

Am I missing something? The plastic gear that gets power from the spindle is 60 tooth, and is somewhat worn, I think I could make 2 new ones (lots of work, but doable). I'd need to make a cutter that has the same exact profile as the teeth on the OE gear, and I'd like to make the new gears out of metal instead of plastic. I do have nylatron (MDS) of the correct size, but I'd rather use bronze or steel. Anyone ever attempted this?

The red arrow shows the gear I need to make:
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: sb327 on February 04, 2023, 11:47:52 AM
It’s hard to tell how the gears are actually changed by the picture. The easiest way to change direction is to place a gear between two meshed gears. If you move the two meshed gears apart and place ANY number of teeth gear in between, it will not change the ratio, it only changes the direction.

Dave
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 04, 2023, 01:08:31 PM
Thanks for chiming in Dave!

Is it true only for same size gears, or it's also good for different size gears? The spindle (drive) gear has 40 teeth, the driven gear has 60 teeth, hence my confusion ??? .
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: sb327 on February 04, 2023, 02:41:27 PM
It’s the same. Consider this.

Example.

Drive is 10 tooth

Idler is   5 tooth

Driven is 20 tooth

If drive turns 1 turn, it  ‘outputs’ 10 teeth into idler. The idler turns 2 times and  ‘outputs’ 10 teeth.

The driven intakes 10 teeth and turns 1/2 turn in the same direction as drive.

Take the idler out and direct mesh, drive one turn, driven 1/2 turn but in opposite direction.

So no matter the arrangement, the idler only ‘output’ the number of teeth the drive ‘inputs’ into it.

Hth,
Dave
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: JPSAXNC on February 04, 2023, 04:39:15 PM
You don't need different gears to cut a left hand thread. If you push the thread (cutting toward the head stock) you get a right hand thread, if you pull the thread ( cutting away from head stock) you get a left hand thread.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: sb327 on February 04, 2023, 05:50:52 PM
Here is an adapter currently unavailable

https://www.amazon.com/CFU-TOOLS-REVERSE-IDLER-G0602/dp/B01N4SG3SR (https://www.amazon.com/CFU-TOOLS-REVERSE-IDLER-G0602/dp/B01N4SG3SR)

It seems it would be simple to build.

Dave
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 04, 2023, 06:01:39 PM
It’s the same. Consider this.

Example.

Drive is 10 tooth

Idler is   5 tooth

Driven is 20 tooth

If drive turns 1 turn, it  ‘outputs’ 10 teeth into idler. The idler turns 2 times and  ‘outputs’ 10 teeth.

The driven intakes 10 teeth and turns 1/2 turn in the same direction as drive.

Take the idler out and direct mesh, drive one turn, driven 1/2 turn but in opposite direction.

So no matter the arrangement, the idler only ‘output’ the number of teeth the drive ‘inputs’ into it.

Hth,
Dave

Oh yes it helps Dave, thanks A LOT!
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 04, 2023, 06:13:21 PM
You don't need different gears to cut a left hand thread. If you push the thread (cutting toward the head stock) you get a right hand thread, if you pull the thread ( cutting away from head stock) you get a left hand thread.

On my lathe the lead screw is driven by the spindle. If I ''pull'' the thread the spindle rotates counter-clockwise, cutting right-hand threads. I actually cut my threads that way since I don't have a foot brake. I set the tool bit upside down when I do this. I really need to reverse the rotation of the lead screw to cut left-hand threads. I know what you mean though, this is how they do it at the shop where I work. I wish I could do that at home, but I only have a small hobbyist machine. See the picture in the link Dave posted ;).
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: WobblyHand on February 05, 2023, 05:04:17 PM
You don't need different gears to cut a left hand thread. If you push the thread (cutting toward the head stock) you get a right hand thread, if you pull the thread ( cutting away from head stock) you get a left hand thread.
At least on a Grizzly G0602 type lathe without an idler, this is not true.  As a matter of fact you will cut a right hand thread if you put the lathe in reverse and cut outward.  I did that to cut the threads on a cast iron back plate for a set tru ER40 chuck.  I used a left handed tool, turned the lathe in reverse, and I made a perfect 8 TPI right hand thread, that exactly matched my spindle thread.  To cut a LH thread, you need an idler gear to change the rotation of the lead screw relative to the spindle.  If you reverse rotate a RH screw, it doesn't turn into a LH screw.  If you call Grizzly and ask them if the stock G0602 will cut a left hand thread, they will tell you it is incapable of cutting left hand threads.  You need an idler gear.

That being said, instead of installing an idler, I designed an electronic lead screw of my own.  It can cut any thread I like, metric or imperial at the touch of a touch panel display.  No changing gears at all.  Wrote all the code myself.  This thing works great.  The first picture is of the electronics being assembled.  It has a 3.2" touch panel display.  It also integrates DRO's if you have them.  Second picture is it fully installed on the lathe and cutting a 5/8-11 thread, just because I could.  (If you zoom in on the picture, you can see 11 TPI on the display.)  If I wanted to, I could program it to cut a unique thread, oh, like 3*pi TPI, or 1.89mm, if needed.  By touching the Right Hand button, I can toggle it to Left Hand, or toggle it back to Right Hand.  Pretty convenient.  (But not on the fly!  Only when the spindle is stopped, do I allow changing thread or feed pitch, or handedness.)  Even managed a 4 TPI thread as a test, and 100 TPI while I was testing this, along with the equivalents in metric.  Feeds are selectable by touching the display as well.

I made that cast iron back plate threading outwards and in reverse, as I described in the first paragraph.  I machined the back plate it before making the ELS.  Started out with a raw chunk of cast iron.  The back plate locks up to the spindle beautifully.  No run out that I can measure, since I machined it on the spindle.  The ER40 Chuck has 0.0002" TIR mounted on the back plate.  I could probably do better, but chasing the last few tenths is hard.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: Rob M on February 05, 2023, 09:30:53 PM
good topic.. and its the same on my g4000 , i dont even bother , i just buy the chinese dies on amazon , especially for small size left hand threads.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 05, 2023, 10:17:05 PM
good topic.. and its the same on my g4000 , i dont even bother , i just buy the chinese dies on amazon , especially for small size left hand threads.

I would have gone that way for a small job, but I need to make two left-hand screws of different sizes and a bronze nut. Also it's a good ''school'' to learn about gear cutting, plus after the mod I'll be able to cut many a metric and SAE threads without spending more money ;).
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: KWK on February 06, 2023, 12:02:59 AM
That's good. Single pointing makes great threads and not hard at all with a little practice. You can create the class thread you need.
This is a setup I used to make a left hand Acme thread for a tailstock feed screw. I needed a longer one so I could put a dial from a South Bend 10k on to my SB9. SB9's don't have a dial. Only the scale on the quill. I made an Acme thread form bit and set it up on the back side so I could feed toward the headstock. Ran the spindle in reverse. Of course, I had to reverse the lead screw. The screw I made has only .002 backlash.

(http://)
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: KWK on February 06, 2023, 12:03:07 PM
You don't need different gears to cut a left hand thread. If you push the thread (cutting toward the head stock) you get a right hand thread, if you pull the thread ( cutting away from head stock) you get a left hand thread.
At least on a Grizzly G0602 type lathe without an idler, this is not true.  As a matter of fact you will cut a right hand thread if you put the lathe in reverse and cut outward.  I did that to cut the threads on a cast iron back plate for a set tru ER40 chuck.  I used a left handed tool, turned the lathe in reverse, and I made a perfect 8 TPI right hand thread, that exactly matched my spindle thread.  To cut a LH thread, you need an idler gear to change the rotation of the lead screw relative to the spindle.  If you reverse rotate a RH screw, it doesn't turn into a LH screw.  If you call Grizzly and ask them if the stock G0602 will cut a left hand thread, they will tell you it is incapable of cutting left hand threads.  You need an idler gear.


That being said, instead of installing an idler, I designed an electronic lead screw of my own.  It can cut any thread I like, metric or imperial at the touch of a touch panel display.  No changing gears at all.  Wrote all the code myself.  This thing works great.  The first picture is of the electronics being assembled.  It has a 3.2" touch panel display.  It also integrates DRO's if you have them.  Second picture is it fully installed on the lathe and cutting a 5/8-11 thread, just because I could.  (If you zoom in on the picture, you can see 11 TPI on the display.)  If I wanted to, I could program it to cut a unique thread, oh, like 3*pi TPI, or 1.89mm, if needed.  By touching the Right Hand button, I can toggle it to Left Hand, or toggle it back to Right Hand.  Pretty convenient.  (But not on the fly!  Only when the spindle is stopped, do I allow changing thread or feed pitch, or handedness.)  Even managed a 4 TPI thread as a test, and 100 TPI while I was testing this, along with the equivalents in metric.  Feeds are selectable by touching the display as well.

I made that cast iron back plate threading outwards and in reverse, as I described in the first paragraph.  I machined the back plate it before making the ELS.  Started out with a raw chunk of cast iron.  The back plate locks up to the spindle beautifully.  No run out that I can measure, since I machined it on the spindle.  The ER40 Chuck has 0.0002" TIR mounted on the back plate.  I could probably do better, but chasing the last few tenths is hard.

 
Really cool electronic lead screw.
FWIW  I have never heard of the terms "pulling" or "pushing" on a machine tool.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 18, 2023, 09:19:34 PM
Update on the project: Today I was able to make some chips!

I made the mandrel, or arbor if you like, that'll be used for both machining and using the cutters. It’s made from a piece of scrap 4140 CrMo steel. The small end has a 0.6235'' OD x 1/2'' long bearing surface for the cutter, threads are 5/8''-18 NF, 3/4'' long. The shank is 1/2'' and has a concentric 60° center hole in the end. I still need to make a nut and a washer/spacer, and re-machine the big end of the arbor.

I also had two 1 1/2'' x 3/8'' pieces of O1 tool steel cut to make the gear cutters, and found a good ''scrap'' piece of bronze for the spindle gear. Also shown is the Stressproof steel blank for the idler gears. Still a lot to do, but it's coming along 8).
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 19, 2023, 06:28:38 PM
The arbor is finished, ready to use. I made two spacer washers and a flanged nut, again with scrap 4140 steel bar. The nut has a recess so it can be treaded deep on the arbor, allowing me to use very thin cutters/saws if I want. The thickest can be up to 5/8''. I made a shoulder on the big end so it'll butt against the chuck's jaws, that'll make the arbor rock-solid with the live center tightened, no side play allowed  8) .

Next step is to machine the cutters.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 25, 2023, 01:41:30 PM
Update to my last post :

I said the arbor was finished, I was wrong. I forgot to machine the keyway, and make a key.

So I just did that; I used a HSS 4 flutes 3/16’’ endmill with lots of cutting oil, spinning @ 560 RPM and hand-fed to make the keyway. The key was made from 3/16’’ square stock I had. I made it 9/16’’ in length and one end is rounded.

So now the next step is to make the cutters, and then broach them and the washers. Will post about that soon.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on February 27, 2023, 03:09:52 AM
I started on the cutters and did some good progress. I first had to make a keyway cutting bit, I used a broken Guehring tap reground into a straight tool, 0.190'' wide. I installed it in my milling attachement on the lathe, and chucked the first cutter blank with its backside flat on the chuck's face.

I then centered the toolbit and took many, many a pass to cut the keyway, slowly increasing the depth of cut on the ''Y'' axis until the arbor fits. My lathe is not the most rigid machine, so I need to work with that. Anyways the keyway is cut, has a nice finish and is well within my specs. Now to do the other cutter blank and the spacer washers.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on March 04, 2023, 09:00:29 PM
Today I finished broaching the other cutter blank and the two spacer washers. Glad it's done, as it's quite long and hard on the hands. O1 tool steel seems a little easier to hand cut than 4140, but I got cramps in my hands nonetheless lol!
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on March 05, 2023, 06:42:05 PM
The first cutter is profiled, I used a forming tool again made with a broken Guehring tap, then used #220 wet/dry sandpaper to smooth the surface. Still have to rough cut the teeth, harden it and sharpen it. The arbor I made is pretty rigid, there was no chatter when forming the profile 8).
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: Rob M on March 05, 2023, 07:10:56 PM
looks great , ever consider extending the travel on any of your lathe tailstocks ? I considered it at one point , but quickly realized it was quite the project
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: sb327 on March 05, 2023, 07:51:05 PM
Amazing the process you’re going through for this. I took the lazy way out and 3D printed some gears for my micro lathe.

Awesome work.

Dave
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on March 06, 2023, 01:43:17 PM
looks great , ever consider extending the travel on any of your lathe tailstocks ? I considered it at one point , but quickly realized it was quite the project

Thanks Rob!

Yes I considered extending the travel of the tailstock, I'm currently gathering parts for that. How would that be related to making gears on my lathe?
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on March 06, 2023, 01:54:53 PM
Amazing the process you’re going through for this. I took the lazy way out and 3D printed some gears for my micro lathe.

Awesome work.

Dave

Thanks Dave!

I don’t have a machinist course, so I use my projects as a ’’school’’ to learn. No better way to learn than to do it I believe. My ’’school manual’’ is the Machinery’s Handbook, lots to learn from it.

Cheers!
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: Rob M on March 06, 2023, 06:54:55 PM


kwk posted a tailstock leadscrew, and i got mixed up lol
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: KWK on March 07, 2023, 10:33:13 PM
Ok, I'll take the blame. LOL

This really is an interesting post. All this with a china lathe and milling attachment. Industrious man. Keep going.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on March 08, 2023, 04:59:05 AM


kwk posted a tailstock leadscrew, and i got mixed up lol

OK I understand now ;). Interesting coincidence that I also want to use a leadscrew (from my old mini-lathe) to move the tailstock 8).

Ok, I'll take the blame. LOL

This really is an interesting post. All this with a china lathe and milling attachment. Industrious man. Keep going.

Lol! Thank you Karl!

I've checked the prices for gears, and I'd be in for over 250 Cad. bucks if I'd buy them, and this is for plastic gears. The reverse tumbler itself isn't even commercially available, so I have no choice but to make it. This must be my most elaborate machining project yet, and probably the most interesting :D.
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: KWK on March 08, 2023, 12:02:18 PM
Do you see here how this reverse tumbler set adjusts lash? From a South Bend 9. Very handy. I have the end gears on my 1947 South Bend running quieter than my 1960's version with the non-adjustable plunger style. I can't stand a jingly lathe in my home shop. Especially if it doesn't have to be that way. I tried plastic but found no improvement over well adjusted steel gears
(http://)
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: happymecanic on March 08, 2023, 03:12:29 PM
Do you see here how this reverse tumbler set adjusts lash?

I think I do see grub screws in the ends of the slot, isn't it? I agree it's a good way to adjust lash. Thanks for posting the picture, I'll try to include that feature in my tumbler!

I tried plastic but found no improvement over well adjusted steel gears

Totally true!
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: KWK on April 13, 2023, 11:47:54 AM
How's it coming?
Title: Re: Cutting left-hand threads on a Chinese small lathe?
Post by: WobblyHand on May 23, 2023, 09:57:25 AM
It's been a while, any progress?