Threading Issue on new manual lathe

[Nyfabshop]

Hello everyone,

I recently acquired a lathe with no documentation and no real labeling that would point me to any specific manufacturer. All that I can see on it is the label "Maxturn JL183" and have found nothing on the internet about it. Everything seems to working well but when I try single point threading, I am not getting the TPI that I would expect.

I have the change gears in the "D-E-F" configuration on the chart. If I am understanding this chart correctly, if I want to cut 20 TPI, I would put the settings to "G-N-III" with the lever to the threading symbol on the left. When I try to cut the threads, it is not correct.

Am I simply misunderstanding this chart or missing something? Or does what I described make sense and this lathe is not functioning correctly?

I circled some formulas on the chart that I don't understand and perhaps that may be the issue. It also seems like the thread dial is not bringing me back to the same spot.

Any help would be greatly appreciated as this seems like a great machine otherwise and would love to start using it to its full potential.

-Steve

 

[Cole2534]

Couple things

1) skip the thread dial for now, just reverse the spindle. it'll make problem solving easier.

2) how much off are your threads?

 

[Booze Daily]

Do you have the correct change gears in there? Looks like you need D,E,F.
Those letters correspond to the letters in the bottom row which I would suspect is the number of teeth.

 

[Nyfabshop]

Yes I have the correct gears in.

The last test I tried at 40 TPI and I got about 14 tpi on the part.

 

[Mike C.]

You're going to have to go old school and figure this the hard way. Measure the leadscrew pitch and then figure what gear combination is going to make up 20tpi. Good luck. Looks as bad as the Summit here at work that changes thread pitch with speed range. Slowest you can cut 20tpi is 250rpm on that one.

 

[Nyfabshop]

Any tips on the math for that?

 

[Nyfabshop]

The last test I tried at 40 TPI and I got about 14 tpi on the part.

 

[CalG]

Second hand lathe? Make sure there are no shear pins that have been over loaded. Go through the ENTIRE gear train. Make sure everything is solid.

Voice of experience....

 

[K Barton]

I would look inside the cover to the gear train to see if there is a selector shaft to change the gear ratio that goes to the Norton style gear box.
The Summit 20 X80 that the company I retired from had such an arrangement. If it was not in the correct shift position none of the thread pitches were correct.

Ken

 

[partsproduction]

Since your lathe has a DRO one quick way I check my selections is engageing the half nuts with the gears in neutral, first use a paint pen to make a make on the gearbox adjacent to the back of the collar that the chuck is attached to, so you pull the chuck over by hand and when you get to the mark zero the Z scale. Then turn it another turn and the readout will shown what your gear selection is moving the carriage. For TPI divide 1 by the number of threads, for instance 20 TPI equals .050, the DRO readout should be very close to that, within a few tenths.
I wish I could stand at the lathe and help you figure out what's going on.

 

[steve-l]

The gears are in the wrong place. Someone had the machine apart and reassembled it incorrectly. Arithmetic is your friend!

 

[Nyfabshop]

Thank you all for your suggestions. I will go through each and see what I come up with. Parts production- where are you located?

 

[jariou]

My hunch is that the settings you are looking at correspond to a worm to match a gear with diametral pitch of 40. If I am correct, that would result in an effective pitch on the "thread" of 1/(40/pi) = 1/(12.73")

You say that it looks like 1/14, but 1/12.73 is not far from that. If you measured precisely the movement of the carriage with an indicator as you spin the spindle 10 times, you should get a pretty accurate measure of what the effective pitch is. If it's closer to 12.7 than it is to 14, then I would bank on my being right!

I think that you instead want to look in the 4 rightmost gear setups. The first one of those, whatever letter it corresponds to (I can't read the fine details on that chart), with GN-II. That should give you the 20 tpi, me thinks!

That's my wild-ass/educated guess.

Good luck,

Jacques

 

[Nyfabshop]

Hi Jacques,

I will check that. So are you saying that if I am using the D-E-F gear configuration, I cannot go by the TPI numbers on the chart, but rather calculate what they actually are? If so, how would you calculate that accurately? Also, are you saying if I use the gear configurations on the 4 rightmost setups I can trust those numbers? Just trying to make sure I understand what you are saying.

 

[jariou]

Well, what I am saying is that you can trust the numbers on the chart but you have to understand what they mean.

Typically on larger lathes, you have 4 kinds of "threading" modes. SAE/English threads, metric threads, and the corresponding thing for making worms using either diametral pitch, or module pitch.

So you have 4 sections of the chart. I suspect that the first section is for module pitch worms, the second is for metric threads, the third one is for diametral pitch worms, and the 4th section which has 4 gear setups is for inch/SAE threads.

The worm pitches are defined in terms of the pitch of the gear they match with. Gears in the non-metric world are dimensioned in terms of diametral pitch, i.e. how many teeth per inch of diameter. So a 20 diametral pitch gear with pitch diameter of 1" will have 20 teeth, and a gear of the same pitch but with pitch diameter 1.5" will have 30 teeth. Gears of same diametral pitch have the same size teeth so they can mesh with each other. They can have different diameters and therefore different number of teeth, but the size of the teeth are the same.

Now, take a gear with diametral pitch of 40. It means that there are 40 teeth in a gear with diametral pitch of 1". How wide is each tooth? The pitch circumference is 1" x pi, so each tooth is (1"/40) * pi wide from base to base. So the worm pitch that will match that gear has to be the same, i.e.

(1"/40) * pi = 1" / (40/pi) = 1" / 12.73239545 = 0.07854"

But that last couple of numbers are not that important.

If you want to make a worm, it will be specified with the numbers on the chart.

If you want to make a thread, it will be specified with the numbers on the chart.

You just need to know what you want and what each section of the chart means.

I am absolutely convinced that the 4 sections mean exactly what I said. And what I am describing in my previous post about putting a DTI to measure the movement of the carriage when you do 10 turns of the spindle is just a way for you to prove to yourself what the reality is exactly.

I am convinced that if you take an hour to set up the 4 different configurations you have in there and measure the effect on the pitch, you will be 100% confident of whatever you will discover. You don't need to believe me. You just need to believe the machine. It will tell you exactly what it is doing.

I hope I made the matter a little clearer. If something is a little hazy still, come back and ask or send me a pm, we can have a chat on the phone. But do yourself a favor first, and measure the pitch as the machine will tell you. I believe it will answer all your questions better than I will ever be able to.

Good luck having that conversation with your lathe! ;-)

Jacques

 

[Nyfabshop]

Hi Jacques,

Thank you so much for all this information. This is extremely helpful. All of your numbers checked out. I tested both gear configurations and your numbers were spot on. This will open up so many more possibilities for using this machine. I am very grateful!

Best Regards,

Steve

 

[partsproduction]

Parts production- where are you located?

About half way up the I-5 corridor where all the homeless hitch hike, short of Portland go left about 45 miles (There are no right hand turns allowed in oregon, and the closer to portland or salem you get the fewer reasons to think at all, just re imagine whatever you want).
You should be able to determine what the output of the lead screw should be, 8 TPI with an 8 TPI leadscrew should be 8 turns. But when I saw the gear cluster at the bottom of your leadscrew indicator that made me wonder if you have a metric leadscrew.