1340gt surface finish problem

rherrell said:
The photos above are 770rpm and a .005" feed rate, I've tried them all and nothing helps.

These next photos are the same piece of aluminum with half of it turned at 475rpm with the slowest feed rate of .0027".
Click to expand...

WAY WAY too slow on the spindle speed. Aluminum likes speed.

RPM = 4*sfm/D = 4*500/ (5/8") = 3200 rpm!
sfm for Aluminum with carbide 500-1000 (1/4 that for HSS)

If you don't like doing math, then get HSMAdvisor or G-Wizard.

The above is really for using with coolant, but I would be cutting that 5/8" aluminum rod at a minimum of 2000 rpm. Aluminum likes high speed, and it doesn't like low speed.

What about DOC? Start with at least a 0.030" DOC, and you will get a mirror finish... except when you run the carriage back to the right, you will get a spiral on it. Then take a spring pass.

Try a feed of 0.004ipr (too small a feed rate can be just as bad as too high a feed rate.... you end up rubbing instead of cutting, and that destroys your surface finish).
 
qualitymachinetools said:
Yes another good idea, and also I think it was already mentioned, make sure the tool post is pulling down tight. Just saw a machine this morning that has an Aloris on it, the T Nut was a little too thick, so it was tightening down on the T Nut, but not actually sitting tight on the top of the compound, so you could tap it back and forth. Similar problem, fixed that immediately.
Click to expand...

tmarks11 said:
WAY WAY too slow on the spindle speed. Aluminum likes speed.

RPM = 4*sfm/D = 4*500/ (5/8") = 3200 rpm!
sfm for Aluminum with carbide 500-1000 (1/4 that for HSS)

If you don't like doing math, then get HSMAdvisor or G-Wizard.

The above is really for using with coolant, but I would be cutting that 5/8" aluminum rod at a minimum of 2000 rpm. Aluminum likes high speed, and it doesn't like low speed.

What about DOC? Start with at least a 0.030" DOC, and you will get a mirror finish... except when you run the carriage back to the right, you will get a spiral on it. Then take a spring pass.



Try a feed of 0.004ipr (too small a feed rate can be just as bad as too high a feed rate.... you end up rubbing instead of cutting, and that destroys your surface finish).
Click to expand...
 
I locked everything down, no difference. The toolpost is down all the way and tight.


This lathe has a top speed of 1800 rpm, I've tried that speed at .010", .020", .030", .040", .050"and .060" doc, no difference.
 
I'm having the same issues with my South Bend 9c, but it appears to only happen with I feed with my compound. I haven't messed with it to see what's going on. The lathe is well used (early '35-'47 model I believe), and it's done it for as long as I've had it (not quite 1 year yet).

No suggestions for you, but I'm following along to see what you find.
 
I believe he fixed it if anyone is wondering, said he put some washers on the motor mounting plate. New motor was sent and changed out, a motor that was tested good here, didnt change anything so that was not it, he can comment more on the details, but since people keep emailing me about this, wanted to put an update on here.
 
Thanks for the update.

DrAsus

Sent from my XT1575 using Tapatalk
 
The rubber washers took about 50% of the ripples out but it's still not right. I'm going to try a 3 phase motor with a VFD , I've tried everything else and nothing has worked. I'll get back here in a few weeks to let you know how it went.
 
Make a list of everything thats been checked if you would, headstock bolts, and any other bolts, check spindle bearing tightness, and the stand its mounted on.

Also try a different chuck, but make sure to check everything thats been talked about, and list it if you can.

If the washers helped, and thats a known good motor that was checked on another machine here, something is loose somewhere there, thats all it can possibly be. Yes of course a 3 phase motor/vfd is always better, but if it didnt do it on a machine here, and it does there, it isnt the motor, something is loose somewhere. And there are only really 4 things to check between the motor and the part, you already changed the belt, so the motor mount, the headstock mounting bolts, the spindle bearings, the chuck, and the stand its mounted on.
 
Matt, everything you have listed has been checked. All the bolts are tight, and it does the same thing with a collet chuck or the 3-jaw.

When I push on the chuck with moderate pressure the deflection in only .0005", when I push as hard as I can it's .0015".

The only other variable is the stand.
002.JPG


001.JPG



The stand is made from 2"x2" steel tubing with 2"x4" steel tubing for the uprights. The stand is NOT sitting on the wheels, I jacked it up and put 3" round solid steel under it. There are adjustable feet threaded into the steel rounds but you can't see them in the photo. The floor is 2x10 studs with 3/4" plywood that has been reinforced under where the lathe sits. It also sits on a piece of 3/8" solid steel plate.

Let's all not forget the elephant in the room, when I turn the lathe using a drill motor I get a perfect finish. To me that says it's electrical.
 
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