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

I am having trouble understanding why it would require more power as you approach the headstock. Something must be binding. The cutting load really can't be changing or you would see some major discrepancy in the part. So that means that the additional load is coming from the carriage drive. Does it do anything like this when running but not actually cutting, just running the carriage?

Many years ago when I had my 12x36, I had a 1HP on it, and never stalled it. I did a lot of work with Inconel, really tough nasty stuff to work with.
 
how solid is the lathe? is it worn or does the carriage have excessive slop?
1/2 hp is way too light in my opinion and may be a source of your problems
 
The bed ways do have some wear. Idk maybe the motor I have is overrated. It's some hashimoto no name that the guy I bought the lathe from put on it. Says .4 kw on it. I'll check some things tonight and report back then I'm back to work for a week and will be away from the machine.
 
chevydyl said:
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?
Click to expand...

Instal ? It came with the motor. I have it struggle once taking some stupidly deep cuts but backed off as I was chicken.I have damaged it in the past where I bound the travel up on the spiral swarf shield and bent the travel shaft/pinion. I think the cross slide and tool post assemblies on these lathes could be stronger and that is where their limitations are as far as over powering the machine.

Accordingly I insure that tool over hangs and are minimized. I quite regularly part off stainless solid and tube to 50mm(2") with a HSS tool, with out any bother.The head stock gear train has always seemed noisy to me but, I can't be positive that as I have not seen any other gear head lathes of that size to compare to. The lathe will be shifted to its new home in the shed I have just built. So I"ll take some snaps when i can access the back of it.
Hope this helps
 
I have a 3/4 hp single phase motor, US made and connected for 240 VAC, on my 3996. In 30 years, I've never even slowed it down. Putting anything larger on the machine is a waste of money, plus if you ever have a crash, you will just break more parts. If the motor slows down in one area and not the other, something else is wrong. Try running coolant (oil) on the cutter.

Try flipping the part end for end. If you get the same results, the material isn't the problem. Put an AC voltmeter and an AC ammeter on the motor and check what the voltage and current are doing. Also calculate the HP input from those numbers. One thing that could be wrong is a bad splice.

If you do put a variable speed system on it, you should probably use a 1 HP motor as the motors tend to overheat when operated below their rated RPM and should be derated.
 
Ok so I just fired up the lathe it's 45 deg in my shop no warmup time and dialed in a .030 cut. No problems. Didn't even sound worked. And a great finish on the cut. I watched the pulleys and didn't see any issues. I also with the lathe off placed the carriage close to where it was stalling and engaged the half nuts and turned the belt by hand to see if I could feel any abnormal resistance. Just pulled a .040 cut without a hiccup.Then .050 and wow. That's definitely where the insert wants to cut at. Very nice pile of small chips. At .040 the chips were about an inch long. Now they are small chips like they should be. And still that perfect finish. No tears just that nice rainbowesque look. Hmmm....it seems to be cutting fine now. I made no changes.
 
Well dammit. Went out in the shop this morning and tried to take an .080 cut and cha-cha chaAaaatteeeerrrr!!!!!!! I may have spoiled the workpiece last nite on those deeper cuts. I was using oil not coolant. I'm not setup for that. The chips from the .050 cut were blue right off the nose of the insert so I am suspecting that I may have added a little hardness to the workpiece. Not sure how deep it went but is there any way to fix it or should I just scrap the part now. Honestly it was scrap to start with I was just cutting to see if I could make a shaft good enough for bearings... but I would like to keep going as 8 only need to remove about .400 to get to size.
 
Sumpin' changed. A change in performance ALWAYS indicates a change in something else.

I trust you are using a QCTP. No change in position, up or down? Cutter is on the center line or a thou below for external cuts?

Sorry I didn't discuss this yesterday.... Early on I found if my cutter was a tad above the axis of the spindle it would start to bind and stop the spindle as it approached the headstock. Why? The workpiece was bending upwards and away from the cutter - a normal response to the cutting operation - but as the cutter approached the chuck the workpiece could not flex upwards as much so the cutter began to hog in taking a deeper cut and this would stall the spindle. (BTW I keep my belt drive a little slack so the belt will slip under such conditions preventing serious damage to the machine.)

The cure was learning to get the cutter dead on the axis of the workpiece, or when in doubt a thou or two below the axis for OD cuts, and a thou or two above the axis for internal cuts. No more hogging in causing stalls! As I gained more experience and became more skilled at setting up the cutter I didn't need to offset below (for OD) or above (for ID) as much and rarely do this now unless taking deep rough cuts where precision is less important than time.

When cutting an OD the workpiece will tend to flex up and back just a wee bit while the cutter will tend to bend downwards. If the cutter is just a tad higher than the axis of the spindle (OD cuts) then as it gets closer to the chuck the workpiece can't bend up and back so the cutter starts hogging in and can jam. The same will happen on an ID cut if the cutter is a tad below the axis. Too far below for OD or too far above for ID cuts and it will chatter horribly if it cuts at all. There is a fine line between enough and too much.

In the absence of any reasonable explanation for the change in performance you might want to maintain a log book and record every measurement, setting, shop temp, and all other observations so you can go back and refer to previous notes if you see a similar problem again. Sometimes we are not able to nail down the cause of the change right away, but is sure is nice to have a record to review and sometimes find the root cause there later on.
 
Yes I am using a BXA qctp with a 1/2 inch shank sclcr tool. Ccmt insert. I faced the end of the work to dial in the height of the cutter. No nub. I changed nothing from last night. I made those cuts I spoke of. I made the .050 cut and shut the lathe off and went to bed. Came out the next morning dialed in an .080 cut and it left a terrible finish chattery finish. I decreased the depth and the same all the way out to .020 I think the material may have gained a little tempering from the last couple cuts from the night before. The chips were blue....
 
Yes, heat generated during turning, especially when taking deep or fast cuts, can slightly "work harden" the surface.
Keep up the good work!
 
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