12x36 hp issues..... need advice or recommendations

[chevydyl]

So today I was turning a piece of 4140 turned ground and polished 2 in stock at about 400rpm taking .030 DOC and when I got closer to the headstock it would stall out the motor. Using carbide. So I lightened up to .020 and it still stalled. Using power feed with the shortest cut per rev. So I upped the rpm a little and it no longer stalled. However I realized that to get to my final od is gonna take FOREVER. Has anyone increased their hp and by how much? What are the risks of the extra power? I would assume the little cheapie gears would be at risk. I have access to a 1.5hp 3 phase motor that I am seriously considering installing. Using a VFD to control the motor. BTW my lathe currently has a 1/2hp motor wired 220v. The motor I could use is a little longer than the current motor but I have no problems with cutting a hole in the cabinet to make room for the new motor. My lathe is an underneath drive. looking at picture my lathe was made the year before they added the lever to the power cross feed. Mine has the pull knob. Other distinctive features like the compound add to the time period.

 

[Rbeckett]

At lower RPM's you will find the smaller motors would stall and overheat. to eliminate the problem you are on the right track with the 1.5 HP Motor. I think you will find that will cure most if not all of your stalling issues at low rpm. Good luck and let us know that you solved the problem and how.


Bob

 

[chevydyl]

Thanks for the reply. My concern is overpowering the rest of the components in the machine. I ripped the teeth off a gear cause my leadscrew was too tight at the far end. Took 2mo of searching ebay to find that stupid gear lol. But I guess I'm not really gonna be taking huge cuts because of the rigidity issues of these lathes. Tired of having my big drills stall out also. it sure will be nice to drop or raise the rpm with a button though. Within reason of course. Not sure how the motor would react to overspeed. I wonder if it's more of a bearing issue to on the motor when you increase the speed.

 

[Ozwelder]

I also run 12 x36 lathe.It has a 2 hp 240 volt motor. I have owned it for 8 years and never had problems relating to over stressing the components due to motor size.
If you have any specific questions about operation of my lathe,I am more than happy to answer them for you.

 

[chevydyl]

Thanks Oz welder that's what I wanted to hear. You have a picture of the install? And have you ever actually used all that power? Or has it been enough power that you've never really had to push it's limits?

 

[Mondo]

I am concerned that the machine stalled as you got closer to the headstock. What would the position relative to the headstock have to do with the forces involved? The forces for a given DOC at constant feed and constant speed should be constant from start to finish. I think there is something wrong with the setup or the cutter is dulling rapidly as it cuts due to incorrect positioning of the cutter.

Make certain the leadscrew is clean and free of chips and swarf and properly lubricated. Make cerain the carriage gib screws are properly adjusted and it isn't binding up due to uneven bed wear. Be certain the bed is properly lubricated, too. SAE 20 non-detergent is recommended for that lathe, you can use Way Oil on the ways if you wish.

Check your cutter setup against the textbook recommendations for the material. Check relief angle, rake angle, etc. You did not say what make of carbide cutter you were using, or if you were using it as-is out-of-the-box or if you sharpened it yourself before use. There are a lot of inexpensive carbide cutters out there and I doubt any of them are ready for use out-of-the-box. Make certain the cutter is properly sharpened before starting the cut. Inspect with a stong magnifier, use a diamond hone on the carbide cutter if necessary.

That lathe is rated for 3/4HP motor maximum. You should need nothing more powerful than that. Certainly not for a .030 DOC!

 

[Round in circles]

Nice post SC.. it took me a while to discover why the carriage on my old ( circa 1943) lathe was tighter at the head stock than four inches from it.
On carefully looking with a magnifying glass I noticed a slight change in the colour of the ways there was a glazed & slightly sticky patina of ancient old dried up oil causing it to stick .

I ended up using a stainless steel knitted pans scrubber and WD40 to loosen it up then a used clean green Scotch Bright kitchen pan scrubber to follow on with some clean detergent engine oil to deep clean the ways on the top , sides and underneath . It's now as smooth as silk from end to end for both carriage & tail stock .

I've also taken to following the old engineers habit of wiping and then oiling the ways whether Ii use the lathe or not and keep it covered in some canvas sheeting to keep any dust / moisture off it when I'm doing other things close by .

 

[Ulma Doctor]

i don't think 2 hp is unreasonable to put on a 1236.
i'm gonna put 3hp on mine:nutsi have one laying around)

i'll relate it like this...
top fuel dragsters scatter drive trains routinely,
just plan on working on your lathe if something goes wrong.

 

[chevydyl]

Sorry I was using a brand new Kennametal insert ccmt 21.52 for roughing. The carriage feeds nicely. With no binding. My tails to k is off a thou but it's larger od at the headstock. And I must say that the finish of the cut is absolutely gorgeous. I can spin the leadscrew by hand. She's always well oiled with sae20. The only thing I can think of is maybe the.l carriage Gibs are too free maybe causing it to bind. Start of cut you can hear the motor start to work then the rpm gradually drops until it would stop.

 

[mws]

I thought the same thing, that carriage position should have no affect on loading. But if what your saying is that the crudded ways were enough to stall the machine I'd say a motor upgrade is in your future. I have an 11x36 and it has a 1hp on it. If I think I might get into some trouble I just don't lock the belts down on the cone pulleys underneath. I only snapped a taper pin on my leadscrew once, but 1 horse has been enough for me so far.