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Threading issue

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Hukshawn

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#1
I need to cut a thread bigger than my lathe has an option for...
I need to cut a 6 tpi acme thread but my lathe only goes to 8.

Am I up the creek?
 

Bob Korves

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#2
It is all a matter of gear train ratios. See if you can cobble one together that advances the lead screw twice as much as for a 12 pitch thread... It might well be possible with what you have.
 

British Steel

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#3
If you're cutting coarser than the lathe's designed to do, take *light cuts* to avoid extra strain on the leadscrew, half-nuts, gears etc. - try to take off as little as you would for each pass of 8 tpi. I have some 3 ipt (yep, inches per turn) to cut at some point, I may have to threadmill on the lathe at the 45* helix angle...

Dave H. (the other one)
 

RJSakowski

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#4
If you have external change gears, you may be able to come up with a gear combination that will give you 6 tpi.
 

Hukshawn

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#5
It is all a matter of gear train ratios. See if you can cobble one together that advances the lead screw twice as much as for a 12 pitch thread... It might well be possible with what you have.
It's a gear box with a small banjo to switch between imperial or metric. How do you calculate all the gear ratios?
All my lathe gearing has been posted here before when I was sorting out my first threading issue. But I'll post the pictures again in a minute.
 

Ulma Doctor

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#6
divide the drive by the driven to find the ratio
you may need to change to a larger headset gear and your threading chart will not be the same.
 
Last edited:

Hukshawn

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#7
So, the 34 is the input from the fwd/rev selectror
the 74/51 gear train is the imperial output to the gear box.
The 34/62 is metric.

IMG_20170909_233214.jpg
IMG_20170909_233153.jpg

Does this help at all?
 

Bob Korves

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#8
The 74 is meaningless for the imperial setup, it is only acting as an idler and does not change the ratio at all, only the direction. The gear ratio is from 34 to 51. You would need to use the AZ4 gear box setting (12 TPI), and then double the change gearing ratio to double the gearbox input speed, for instance, change the first drive gear from 34 to 68 teeth, if that is indeed possible on that lathe. You could also use the AZ2 gear setting and increase the existing change gearing by a ratio of 3:2, a 150% increase. That could be done by replacing the 34 tooth drive gear with a 51 tooth gear and leaving the existing 51 tooth gear for a 1:1 ratio. You could also use any two gears with the same tooth count to achieve that 1:1 ratio. Again, the center idler does not change anything unless set up for compound gearing. I assume you only have the four change gears shown in the two charts, and they alone will not do the job for a 6 pitch thread.
 

Hukshawn

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#9
Correct. I have no other gears. I would have to make them, which I have no method of doing.

So, I'm up the creek then.
I have to make screw legs for an oven. I did a kitchen reno and the counter tops are higher than the flat top stove the client bought. The damn legs aren't tall enough. I have the stove propped up on pieces of plywood, to add insult to injury, yesterday when I was caulking the backsplash, I slid the stove out slightly to get behind it and snapped the two back legs off like twigs nudging the stove back in place. The legs were cheap plastic... Useless...

Monday is my last day there. I have one of the broken plastic legs in the garage. I was reaaaaaaaly hoping I could just make some new longer ones from aluminum bar.
I may try to make a thread at 8tpi and try it. The thread in the bottom of the stove is just a piece of formed sheet metal, maybe engages 1-1 1/4 threads, tops. Maybe I can just force it...
Uhhg...


Edit: I should mention, I spent a combined 3.5 hours on the phone Friday trying to find longer legs. I can find replacements, at $30 a pop... But not longer ones.
 
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francist

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#10
Drill and tap them all to accept standard 5/16" or 3/8" appliance leveller feet? Kind of like a telescoping thread.

-frank
 

dave_r_1

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#11
seconded...drill it out and tap it for what you can make. Alternately, you could get a 6 tpi die for the diameter and do it manually instead of using your lathe.
 

Hukshawn

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#12
The original legs are plastic and only about 5/8" thick. I really believe it would just chowder under the weight.
I have a friend with a bigger lathe, I asked him what his goes to. If all else fails I have two options, try the 8tpi and see if it fits, or buy an acme die.
 

epanzella

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#13
If it only engages 1 1/4 thread does that mean you can get to the other side? If so use a smaller SAE thread and put a nut on it.
 

Hukshawn

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#14
It's for leveling a stove.... While that is extremely feasible to use jam nuts and any threaded rod, the method of leveling the stove in place is impossible. I don't have 36" long wrenches.

My friends 12" lathe will do 6tpi. I'm going to use his tomorrow probably.

I need to home up on my acme threading.
 

Hukshawn

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#15
Used a friend's lathe. A craftex ct043n. It goes down to 4tpi.
So, this is the first time (as an adult) I've used another modern lathe. I have to say, I'm pretty stuck on mine. Maybe it has more to do with I'm used to mine. I know it's moods, the way it breathes, when it's on its time of the month. Whatever, I didn't like his lathe.
His lathe is bigger than mine (10x28. His 12x36). But it felt cheap. The way the gear levers are set up is just foolish. Mine, everything is sequential. Click a lever further you speed up, click it back you slow down. His, is just all over the place. Its almost like figuring out a combination lock just to set the speed and feeds. He's let it get rusty. The ways are rusty beyond the first 8" of regularly used travel. Made me kind of upset... He also has an old bridgeport that he's let go crappy too. Breaks my heart. I'd love to take the Bridgeport off his hands.

Anyways. Took me almost an hour to figure out the combination of change gears and gear box settings. The manual was useless, referred to the similar grizzly manual, no luck, then realized I was an idiot and the name plate gear table makes perfect sense I just didn't see it at first... Duh... seems I do that quite often...

Anyways again. Threaded the parts. Cut them in reverse with the tool upside down so I could feed away from the chuck. Completely chowdered the first attempt cause I missed the thread dial and half nut and the part was slipping in the jaws. The rest came out great.

Now I'm home finishing off the bases. Getting them glued and screwed together. Reasonably happy.
Best oven leveling feet you'd ever see...

IMG_20170911_220056.jpg
 

q20v

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#21
Nice job! Feels good to use the hobby machines to fix domestic things, eh. What kind of lathe do you have?
 

Hukshawn

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#22
Nice job! Feels good to use the hobby machines to fix domestic things, eh. What kind of lathe do you have?
A relatively unknown Enterprise 10. 10x28". It's an Indian lathe made by a company called Mysore Kirloskar i believe... a long lost company.


Edit: lathe name correction.
 
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