Holy Cow Metal Lathe Threading

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FGarbrecht

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Just tried fussing with the change gears on my 7x12 mini-lathe to teach myself lathe threading, and what a major PITA! The nut/bolt adjustments to get the gears into position are essentially unreachable if the gears are actually in place, and getting them to mesh without skipping and/or grinding is a hair raising adventure. I was getting so anxious I had to stop. Just ranting, but if anyone has tips I'd love to hear them.
 
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1shootist

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Some folks can throw down threads on a mini metal with ease...I am not one of them. I have tried to teach myself on a couple minis but soon quickly went back to tap & dies.
Good luck !
 

magpens

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Been there, done that !! . Agree with "PITA". . And sometimes you have to calculate gear ratios, etc., also ! . Oh, and units conversion too ?
 

More4dan

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Just tried fussing with the change gears on my 7x12 mini-lathe to teach myself lathe threading, and what a major PITA! The nut/bolt adjustments to get the gears into position are essentially unreachable if the gears are actually in place, and getting them to mesh without skipping and/or grinding is a hair raising adventure. I was getting so anxious I had to stop. Just ranting, but if anyone has tips I'd love to hear them.
I have the 7x10 version. I use open end wrenches and reaching nuts hasn’t been too bad. I just hold the gears together as I tighten the adjustment. Occasionally I’ve had to readjust if I got them too tight. White lithium grease also helps. I even made some knurled grips I press fitted to the cap screws to speed up the gear changes. You’ll get a feel before long. All that said, it’s still a PITA. Since getting the tap and die guides from LMS I haven’t turned a thread on the lathe. I mostly used it for making specialty taps for kitless fountain pens.

Danny


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FGarbrecht

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Starting to get the feel of it. Finding a 3 gear combo is easier than trying to get 4 gears aligned. Lathe stalling out at low speed, I think because the leadscrew is not turning very freely and it gets worse when I engage the autofeed. Need to take things apart and adjust.

I managed to experiment a little bit. I'm trying to turn an 8 tpi thread onto the end of a 1" rod (for mounting a chuck or collet chuck). I'm not sure how you stop the threading cut in the same place every time.
 

More4dan

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For continuing the threading I never take it out of the drive mode. I thread toward the head, turn the speed to zero at the end. Reverse the cross slide a couple turns. Hit the reverse switch and drive back to the tail stock and stop. Advance the cross back to the starting point. Advance the compound set at 30 degrees about 0.010” but back in forward and repeat until the thread is cut.


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FGarbrecht

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For continuing the threading I never take it out of the drive mode. I thread toward the head, turn the speed to zero at the end. Reverse the cross slide a couple turns. Hit the reverse switch and drive back to the tail stock and stop. Advance the cross back to the starting point. Advance the compound set at 30 degrees about 0.010” but back in forward and repeat until the thread is cut.


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I had the compound set so the tool is at 90 degrees to the rod. Should I change the angle?
 

More4dan

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It helps to cut only one side of the thread at a time. Reduces drag and chatter. At 30 degrees you build the 60 degree thread wall as you go deeper.
For the last pass you advance the cross slightly (0.001-0.002”) to clean up the final threads.

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More4dan

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The tool is at 90 degrees to the rod but you advance the tool into the material at half the thread pitch with your compound. The tool should then only be creating chips on the left face. Results in half the drag and load on the tool and motor.


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lorbay

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If you are using carbide tooling just go straight in forget the angle. It must be true Joe Pie said so. Oh and another thing he always threads away from the head stock. It’s also way easier . You don’t have to have your butt cheaks squeezed together hoping to disengage the half nuts.
Lin
 

More4dan

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If you are using carbide tooling just go straight in forget the angle. It must be true Joe Pie said so. Oh and another thing he always threads away from the head stock. It’s also way easier . You don’t have to have your butt cheaks squeezed together hoping to disengage the half nuts.
Lin
Will that work with a 8 tpi cut on a 7” mini lathe? You would be removing a lot of material in the final passes.

Cutting toward the tailstock sure makes sense, removes all the drama at the end of cut. You could also cut at higher speed improving the threads surface finish.

Danny


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howsitwork

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I can’t comment on working plastics but for metal you can use a handle to hand drive it so yo sto0 at exatly the same place every time. This works well on fine threads but 8 Tpi might be a bit “athletic” but it builds upper body strength !

Plastics should be easier to cut. As for plunge vs compound angled cutting see which you prefer. I use compound angle but there going straight in is easier to set up and measure the thread depth.

By using a handle I mean a cranked handle with an expanding end that inserts up the rear of the headstock bore . You then expand the end ( like a rawling bolt anchor end action) and it grips inside the headstock bore allowing you to manually turn the work.

If you,look for G H Thomas , “The model engineers workshop manual” it shows exactly what I mean and has dimensions for making one to fit a myford Ml7 lathe. I just adapted it for mine. This book is a gold mine for useful gadgets for metal work lathes .
 

FGarbrecht

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If you,look for G H Thomas , “The model engineers workshop manual” it shows exactly what I mean and has dimensions for making one to fit a myford Ml7 lathe. I just adapted it for mine. This book is a gold mine for useful gadgets for metal work lathes .
Must be a good book. $353 on Amazon. Up to over $600 on Abebooks.
 

howsitwork

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What !!!

It’s not cheap over here but I thin’ it’s still in print at about £60 new. Surely the exchange rate is not that bad !!
 

More4dan

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yes. I’ve done it many times. You just take lighter cuts on the final passes, as well as spring cuts. The whole angled compound method is unnecessary when working plastics.
I believe he is cutting 1” x 8 tpi threads into steel. I agree that for plastics it doesn’t really matter.

What are spring cuts?

Danny

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rherrell

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Starting to get the feel of it. Finding a 3 gear combo is easier than trying to get 4 gears aligned. Lathe stalling out at low speed, I think because the leadscrew is not turning very freely and it gets worse when I engage the autofeed. Need to take things apart and adjust.

I managed to experiment a little bit. I'm trying to turn an 8 tpi thread onto the end of a 1" rod (for mounting a chuck or collet chuck). I'm not sure how you stop the threading cut in the same place every time.
Turn your threading tool upside down and run the lathe in reverse, this way you start on the left and end up on the right out in space so there is no PANIC STOP. Here's a YT video on the technique...


I changed over to this method and LOVE IT!
 

bmachin

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Fred,
glad to see that it's getting easier. Here is a link to a couple of items that can improve your mini lathe, both of which you may be able to 3D print.


I had always intended to build the banjo but never got around to it, but it would certainly make your gear changes easier. The fine feed would much improve the finish of any power feed finishing.

Another suggestion. I don't know what your plans are for the threading that you're doing, but when you finally get there, don't thread raw stock. True it up before you start. That may involve buy-in oversize stock to begin with. Also, I would stay away from Big Box store material. Instead, buy some cold roll or, better yet, some 12L14 or similar. Just makes life easier.

FWIW,
Bill
 

FGarbrecht

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Fred,
glad to see that it's getting easier. Here is a link to a couple of items that can improve your mini lathe, both of which you may be able to 3D print.


I had always intended to build the banjo but never got around to it, but it would certainly make your gear changes easier. The fine feed would much improve the finish of any power feed finishing.

Another suggestion. I don't know what your plans are for the threading that you're doing, but when you finally get there, don't thread raw stock. True it up before you start. That may involve buy-in oversize stock to begin with. Also, I would stay away from Big Box store material. Instead, buy some cold roll or, better yet, some 12L14 or similar. Just makes life easier.

FWIW,
Bill
May have to see about 3d printing that fine feed attachment banjo.

One of the reasons I'm doing (or trying) my own threading is because the big box store threaded rod is SO SLOPPY. Goes to prove the old adage, if you want it done right then do it yourself, no matter how many attempts you have to make.
 

More4dan

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Frederick, here is a good tool for calculating threads including the different tolerance types if your looking to do something “tighter than standard.



You could also turn ACME threads. Look at the way the brass.threaded block on your cross slide works and how to adjust it to take up the backlash. It is something you may be able to incorporate in your design. Tilting the female block takes up the slop.

Danny


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FGarbrecht

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The thread calculator that Danny linked to is AWESOME, it's my go to reference whenever I do any threading.
Wow, this is so frustrating. When I put on the gear combination for 8 tpi, I think the lathe motor just doesn't have the torque to power feed the carriage. I'm going to tear down and readjust/lube the carriage to see if I can get it working, but suspect I'll need a spindle crank to just do it by hand. Rick, any chance you could make me one (Chinese 7x12)? I know LittleMachineShop has one but seems expensive for how junky it looks.
 

More4dan

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You will get more torque out of the motor at faster/full speed. I believe the speed control for this DC motor is resistor based so you get reduced power at lower speeds. You might get better results turning away from the head, in reverse, with the tool upside down. You could then run at faster speeds with higher torque.
You are at the ragged edge of what this little lathe is capable at 8 tpi. You may have to engage the half nuts while turning at speed using the threading dial to stay aligned. Worth trying without the cutter engaged to see if you can get it to move And engaged at the right point consistently. Loosing up the carriage gibs a bit might also help.

Just read an article that states that the speed controller isn't resistive and preserves torque at lower speeds. Here is an article on how to slow down the lathe even more for cutting lower TPI threads and increasing torque from the motor by adjusting the motor controller settings.


Proceed at your own risk.

Danny
 
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FGarbrecht

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You will get more torque out of the motor at faster/full speed. I believe the speed control for this DC motor is resistor based so you get reduced power at lower speeds. You might get better results turning away from the head, in reverse, with the tool upside down. You could then run at faster speeds with higher torque. You are at the ragged edge of what this little lathe is capable at 8 tpi. You may have to engage the half nuts while turning at speed using the threading dial to stay aligned. Worth trying without the cutter engaged to see if you can get it to move And engaged at the right point consistently. Loosing up the carriage gibs a bit might also help.

Danny
May try the upside down trick. I loosened the carriage gibs and cleaned out the gunk and that helped a little bit but at slow speed I get about 1/2 turn into the piece and it stalls. I think I screwed up this piece of stock though; got some passes done (by running until it stalls and then switching off / on again to get it through the whole 1.5 inch of stock in little increments). Even advancing the tool 0.0005" stalls it out. And then, the banjo shifted a little bit and the change gears were spinning without driving the feed. And then, the piece started spinning because I guess the collet wasn't tightened quite enough. Pretty much everything that could go wrong has gone wrong. Lots of opportunity for learning with this one 😅 . Thanks for all the suggestions! Try again tomorrow (or whenever I can get another piece of round stock).
 

More4dan

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Frederick, what are you making? Are you using steel, maybe aluminum would work and be easier to machine. Cutting fluid might also help.

“Rherrell” could make you one for a fair price I would bet. Maybe even less than material and tooling. Certainly less than a blown speed controller.


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FGarbrecht

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Frederick, what are you making? Are you using steel, maybe aluminum would work and be easier to machine. Cutting fluid might also help.

“Rherrell” could make you one for a fair price I would bet. Maybe even less than material and tooling. Certainly less than a blown speed controller.


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Hey Danny,
I'm making a threading jig (to do wood threading, similar to the 'Incredible Threading Jig' in the resource section here). The problem is that the threaded rod I've gotten is so sloppy that once a spindle adapter is threaded onto it the runout is ridiculous and way too big for pen threading. I thought that if I got some nice straight and round steel rod and threaded it myself I could solve the slop problem. The only 'precision' threaded rod that I've been able to find has been Acme threaded, and that's no good for a spindle adapter or a lathe / collet chuck. Aluminum is probably a great idea, and is no doubt cheaper. Cutting fluid also good idea. I was using a piece of steel rod because I happened to have a short piece the right diameter. I guess if I can find a commercial spindle adapter that is not internally threaded (smooth bore attaching with hex nuts or something) I could make that work without the hassle of threading. I'll see what I can find. Thanks for the suggestions

Addendum: It looks like PSI has a 1x8tpi to 5/8" spindle adapter (for Shopsmith) that connects to the spindle using a setscrew instead of spindle threads. This may work for what I need.
 
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bmachin

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Fred,

Why are you putting yourself through all of this? You already have a metal lathe. Mount your live cutter to your tool post. Set your change gears for the thread pitch you want. Add a crank. Mount your blank in your 3 jaw or collet chuck. Turn on the Dremel. Turn the crank. Job done.

Somewhat oversimplified, but not much.

Bill
 
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