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Thread: How much power is really needed for threading? (or, speed controller OK?)

  1. #1
    Boolit Master

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    How much power is really needed for threading? (or, speed controller OK?)

    Hi guys,

    You guys are my go-to for machinist advice. Here is where I am at:

    I am threading with a hand crank on my toy lathe because my lowest speed setting is 150 RPM on the belts. This is OK, but can get tedious.

    I'm using a std 1725 RPM .8 HP motor, no 3-phase.

    I've seen the dial turn variable speed controllers for dremels and such which the lathe community says a resounding NO! Don't use! Because ostensibly the speed slows and so does the power. So I'm on board with that.

    But then I have to wonder, how much is needed just for threading? If I will only use the speed controller for slowing the lathe down to 30-40 RPM for threading, is it OK if I take a hit on power? It's easy to remove a variable speed controller when I'm doing every other operation.

    So: can I get away with one for threading? or is it best to stick with the hand crank?

  2. #2
    Boolit Master Any Cal.'s Avatar
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    I would say it would stink. Power would be so low that it would change speed drastically when the tool touched and then again when it was pulled away.

    I usually thread at least 150 rpm, even though my lathe goes down to 55. Just takes forever at that speed. Typically smaller lathes are doing higher thread counts, so bit isnt advancing very fast. Only matters when you have to disengage 1/2 nuts anyway, and at 20 tpi 150rpm, you have almost 1/2 second per thread, so plenty of time. I usually am doing 14 or 24 tpi, but 14 is usually not to a shoulder, so no biggie there either.

  3. #3
    Boolit Master

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    You will lose torque with a speed controller but remember with single point threading you are only taking a very small bite at a time. A DC motor of say 1 HP or so will thread just fine. In a standard AC motor changing the belting would be a better option.

  4. #4
    Boolit Master

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    As always, thanks guys

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    Boolit Master
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    add a jackshaft and reduce your rpm more will also increase torque

  6. #6
    Boolit Master

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    Some of the DC motors and controllers don't lose power near as bad as the AC do. I also thread at higher rpms than a lot do. 35 years in the trade practice allows this. While not a lot of power is needed it does need to be even power and speed as changing during cut may cause different patterns and tourque to distort the threads

  7. #7
    Boolit Master

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    The size and depth of the thread is going to dictate power needs more than anything. Not long ago I made a chuck back plate that was 1 3/8-6, had to finish it with a hand crank to minimize chatter. My Clausing 8000 has a 10 HP motor, so power wasn't the issue. Yesterday, I cut 52 tpi in 12L14 in three passes at 200 RPM in a Myford Super 7. Two very different styles of threading that had to be addressed by different techniques. Your lathe is likely fine without modification. Without seeing your lathe, I would imagine that you have to configure a gear train or have a QCGB. The speed could be variable at the input side and have no affect on the lathes ability to thread since the threading pitch is transmitted through the gear train. Likely the only thing that would likely be affected would be the finish of your threads. Just my opinion, others will likely differ. Good luck


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  8. #8
    Boolit Master
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    I feel your pain.

    I quit even trying to thread with my lathe powered up. Even though its slowest setting is 70 rpm, for the life of me I can't reliably engage the half nut on time to make clean threads. Everything else is simple enough; it's just that step of engaging the half nut in same place every time that doesn't work out for me.

    I've been using a home made hand crank for several years now. It's the only way I've been able to get over this hurdle. It's true that it is a PITA to do it this way but, it's even worse to not be able to do it at all.

    In regard to the power needed to turn threads; with this hand crank method I set my gears to the fastest rpm and turn the hand crank from that position. The effort needed to turn the crank is really pretty light and yet, I can still take fairly deep passes if I want to but, I generally take it easy when turning threads. I mention this because in my mind's eye I can't see how adding an adjustable weaker motor to do this very same thing would have to much of an impact. I have to admit though, I've never tried it myself so the more experienced guys here are most likely correct in their observations.

    HollowPoint
    Last edited by HollowPoint; 07-28-2017 at 11:29 AM.

  9. #9
    Boolit Master

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    You could leave the half nuts engaged, retract the compound at the end of the thread and run your lathe in reverse, reset your compound to zero when you clear the product. move your top slide in the amount required and begin your next pass. This is the technique used to cut metric threads on an imperial lathe or any lathe without a threading dial.


    We accumulate our opinions at an age when our understanding is at its weakest. Georg C. Lichtenberg

    At what point, then, is the approach of danger to be expected? I answer, If it ever reach us it must spring up amongst us; it cannot come from abroad. If destruction be our lot we must ourselves be its author and finisher. As a nation of freemen we must live through all time, or die by suicide. A. Lincoln

  10. #10
    Boolit Master
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    I doubt that a motor speed control would maintain speed if the load increases much when actually removing material. You could try setting the controller to a desired speed with the half nuts engaged but well away from the part. Start by just chasing the threads and repeat with incrementally heavier cuts to see if you can run slow enough without stalling out and sticking the tool in the work-piece.

    If it does stall just back off the compound a little and hand rotate to clean up the raised chip where the tool stalled out. Feed a touch of compound and repeat. I have recovered a couple threading jobs this way when the old flat belt belt slipped and things stopped turning during a cut.

    That said, I will sometimes hand turn the lathe anyway to minimize vibration or chatter when I want the best possible finish on a thread. It would be nice to have a more rigid machine, but with some thinking and perseverance one can work around a surprising number of limitations in a hobby machine shop.
    Last edited by BeeMan; 07-28-2017 at 06:19 PM. Reason: typos

  11. #11
    Boolit Master
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    Quote Originally Posted by Jeff Michel View Post
    You could leave the half nuts engaged, retract the compound at the end of the thread and run your lathe in reverse, reset your compound to zero when you clear the product. move your top slide in the amount required and begin your next pass. This is the technique used to cut metric threads on an imperial lathe or any lathe without a threading dial.
    Before I upgraded to my gunsmithing sized lathe I was using a cheapy little 9x19 metal lathe and this is exactly what I started doing with it whenever I needed to cut threads. I did manage to need to replace the on/off switch due to turning my that little lathe from forward to revers so often though. That spilled over onto my gunsmithing lathe so this is the way I do it no matter if it's metric threads or whatever. Using the same home made hand crank, it's the method I've gotten used to using.

    I suspect that with more practice I could eventually get the timing and the feel for using my metal lathe in the powered-up mode that it was intended to be used but frankly, I really don't do a lot of projects that require threading. The ones that do need threads are generally small enough that I use threading dies.

    HollowPoint

  12. #12
    Boolit Master
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    I have a repeating job where I have to thread to a shoulder and I usually do it at 110 or 200 rpm because it cuts better and goes faster. To keep from crashing, a 1" stroke dial indicator is bed mounted to pick up a surface on the carriage as it approaches the end of the thread. I position the carriage where the end of the thread is that will give me enough time to back out. Then the indicator is adjusted to compress for two revs and zeroed. With this reference, you can time throwing the lever and backing out at the same place repeatedly with a little practice. This also negates the need for a relief groove if you want because you will always back out at the same point and your thread will like like it was cut on a CNC.

  13. #13
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    Quote Originally Posted by country gent View Post
    Some of the DC motors and controllers don't lose power near as bad as the AC do. I also thread at higher rpms than a lot do. 35 years in the trade practice allows this. While not a lot of power is needed it does need to be even power and speed as changing during cut may cause different patterns and tourque to distort the threads
    Not only that but the finish you get on those threads if the speed fluctuates would be pretty bad. You need to thread fast enough to get a good finish and to have the spindle speed remain constant thruout the cut.

    I see way too many guys here being so afraid of their machines and wanting to do threading by turning the spindle by hand it blows me away. You don't have to have 30-40 years in the trade to be able to thread right.

    One thing you can do is,,, Thread from the inside out in reverse. IE: you don't have to sweat the pullout.

    When Single Point Threading you typically will put a "Thread Relief "at the end of the thread. This is normally where you would disengage the half nut and stop the carriage. You can also start the thread at the thread relief in reverse and thread out . This way you don't have to worry about not disengaging at the right time.

    Virtually all of the older machines that you's guys have are able to make threads as designed. They were all made early on and things like speed controls were fiction. You changed speeds with the pulleys on the machine and worked with what you had available. Lots of work got done like that,,, and you can do it too.

    Sometimes you need some instruction,,, Sometimes you just need to practice a little more.

    What you really need to do is get some instruction from a real person and then practice a little. Threading just ain't that hard to do, and inventing workarounds for your fears is not productive at all. It doesn't advance your skills one bit. Nobody was born knowing how to do this stuff. It was learned and you can too!

    Part of the draw towards being a machinist for me was learning how to do new things that enhanced my abilities to build more stuff. The more you know the more you can produce. "Production,,, is the basis of Moral!" Learning new stuff makes you feel good! For lots of us, "Feeling good" is in short supply. This is a way to make more of it happen.

    What you could to do is visit an Oil Field Machine shop and watch a guy threading 6" Drill Pipe with tapered threads up to a shoulder at 300 rpms,,, on a big manual Engine Lathe. That will convince you that it can be done. The guy who's doing it wasn't born with the knowledge and he probably didn't get it off the internet. He probably got showed how to do it, and then practiced until he was good.

    Believe me any of you can thread on a lathe just like it was intended to be used. You just have to try a little harder.

    Randy
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
    www.buchananprecisionmachine.com

  14. #14
    Boolit Master

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    Seversl tricks to high speed threading. grinding point off center so it has as much clearance as possible on the shoulder. It is nice to hand grind one on a 1/8" wide cut off blade. This gives a tall narrow blade that's stiff and solid. You only need enough flat to cut the vee and these will do up to 13 threads per inch or so. Another one is to grind the tool off set so I On centerline can be mounted upside down. You then set lathe up normally and cut in reverse feeding away from the head stock this gives more room to stop controls chip build up a lot better and allows oil to flow to tool better as the chips aren't carrying it away with them. an extended center makes this even better. It does allow you to see better whats going on and the tool better. With this type set up I would thread around 600 rpms. Draw back to this is the burr and sharp edge is pushed out off the end not into it. So you need to touch up the chamfer after threading. I actually prefer a hand ground or surface ground HSS cobalt threading tool that's been honed over carbide as it cuts cleaner and easier to me. A good center gage gives a way to hand grind the tools and also the depths of a given thread pitch. Very handy little tool. A well dressed wheel on a bench grinder will quickly grind a threading tool and a little stone work it will cut very nice clean threads. At work and in my box at home now I had a little block made up that allowed me to grind a small snap ring groove cutter or threading tool on the surface grinder Made a very nice sharp tool with proper angles and relief

  15. #15
    Boolit Man

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    Back in the day had a Daewoo engine lathe with ball lead screw. One you engaged the half nut on the ball lead screw you cranked the cross slide and reversed the motor and never disengaged the half nut until finished to size. Cut left and right hand threads for tire drum machines for Goodyear plant at Union City, Tn. These were acme single lead threads on a 1.5 in. stressproof shaft and run the lathe at 150 rpms , used regular lathe coolant and those threads would slick out like they were done on a thread grinder, course I was younger and a lot faster then. Worked at NNSBDC in Newport News, Va and cut six lead buttress threads on Submarine hatch covers. Run about 2 or 3 rpms using a 72 in. chuck lathe, slow, slow, slow work.

  16. #16
    Boolit Buddy
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    I have the same lathe you do , I never found it to be all that difficult to thread at 150 rpm
    I have also went the three phase motor and vfd route , I find that I tend to thread at speeds quite a bit faster then 150 rpm now that I can adjust speeds easily .

    But everyone's comfort level is differant .

    Your worried about power , take this into consideration .
    Your lathe uses a 3l size belt .
    Under normal tension that belt won't care if you have a 1/2 no or a 50 hp motor .
    It will only transfer so much power . I did the math awhile back and with the pulley sizes on your g0602 that equals just about 1/3 hp

    What's that mean? ... it really won't matter what motor or controller you use .. a.c. or d.c. or twelve hamsters in a cage .
    That 3l belt is the defacto power limiting part of your equation .

    Use a decent quality motor and don't worry about it .

  17. #17
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    Now if you really want a fool proof method of single Point threading the Hardinge HLV has it beat.

    The machine has a set of stops on a shaft that is hooked up to a single tooth Dog Clutch that allows the lead screw to run the carriage forward and then disengage and then reverse and back out independent of the spindle but still in time with the spindle. The carriage has a Retractable Compound that retracts the tool when you back out.

    Once you engage the half nut, it stays engaged until you are done with the setup. The stops are adjusted so that as the carriage approaches the end of the thread it automatically dis-engages the dog clutch and Centers the lever then you retract the compound and reverse the lever to back the carriage back to the starting position which also has a stop that disengages the clutch.

    Essentially you just run the carriage between the stops, and make offset adjustments on the cross-slide (X Axis) for thread depth. The beauty of this setup is that once setup(a 10 min job), a moron can make perfect threads and you can do it at 3000 rpms if you so choose. You can also take unlimited spring passes on the part to insure a perfect finish on the threads.

    I have made 10-40 lead screws for instruments that were 2" long and supported by a center and collet. Needless to say the part did flex in the center a few thou. However the ability to take 15 spring passes on the part with the same X offset made these threads come out perfect.. The part ran in a split bronze nut for a zero backlash system used to position a small part in a grinding fixture.

    This is one of the reasons why Hardinge machines cost so much. They are arguably the finest Tool Room Lathes ever made and I'm pretty sure they are still making them.

    Randy

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    Last edited by W.R.Buchanan; 08-02-2017 at 05:46 PM.
    "It's not how well you do what you know how to do,,,It's how well you do what you DON'T know how to do!"
    www.buchananprecisionmachine.com

  18. #18
    Boolit Master

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    Hardinge is still there making lathes. They make some really nice manuals and have some cnc controlled now. The ones we had at work had an 1 1/2" spindle bore also. The hardinge chuck mount is unique to as its a simple 1/4 twist and slide off or slide on and 1/4 twist. We had 5c collets with a lever closer, 3 jaw, 4 jaw and 6 jaw chucks for ours. Expensive yes, but for accuracy and finish they can be beat, and the solid bed is easier to clean when done.

  19. #19
    Boolit Master 303Guy's Avatar
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    Quote Originally Posted by W.R.Buchanan View Post
    ...

    One thing you can do is,,, Thread from the inside out in reverse. IE: you don't have to sweat the pullout.

    ...
    I've done this a few times but found it difficult to see what I was doing with the tool upside down on the opposite side of the workpiece. But the results were great.
    Just this evening I did some threading on mild steel .... Well I got it right and this after a long time of no practice. Threading the bore was the pain - I just couldn't see inside. Why did they ever invent mild steel? I learned to machine the stuff on a decent lathe - fast with deep cuts - but not on my cheapo home lathe!
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  20. #20
    Boolit Master

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    First lathe I ever ran was a South bend that had the motor way up on the wall and a flat belt going down. A drunk went off the road and hit the wall causing the motor and all the flat belt shifting to fall. His insurance bought a transmission and motor to mount on top of the lathe and got it running again. Most of the lathes that I have run have several positions for the belt to change the speed and also back gears to slow them down a bunch. A motor speed control sounds great but I think I would be looking for a small transmission, maybe something from an old motor cycle.
    John Taylor, Taylor Machine, gunsmith

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