Thread chatter only with carbide

JonathanK

JonathanK

New member
I recently purchased a Nikcole mini-grooving holder with a TIN carbide 60 degree threading insert. I really like this type of setup but I am getting chatter, I normally set my compound to 29.5 degrees going in with the compound and use the cross-slide to back out where I want to end my threads. I run the spindle at 65rpm. I have tried moving the compound, different rake and different heights of the tool. I have also tried going in with the cross slide. I havent tried different spindle speeds yet as Im still learning and not quite ready to thread faster. Im thinking it may just be that my pm1236 isnt quite heavy enough to thread this slow with carbide. When I change back to HSS it cuts nice and clean. Also does anyone know where I can find hss inserts for the mini-grooving holder?
 
I have to thread at 115 min with carbide to get decent threads . Under 100 i believe HSS is you best bet
 
Ok thanks...I just got off the phone with Arthur R Warren Co. and they carry the hss insert for the mini-groover
 
I received my Warren hss insert the other day, and it seems to have fixed the issue. I plan on getting Warren inserts for all my indexable tooling.
 
Just so nobody goes off on a wild goose chase, it's the Arthur R. Warner Co. And, yes, I have their stuff too.
 
Is the spindle loose? Check the outboard lock nuts. I'm Serous. We have a similar machine at work. Spindle came out on poor old Merl, while he was polishing.
 
spindle seems ok and has very little runout....Im pretty sure the issue Im having is the same issue as many Chicom machine owners have expierenced, vibration from the motor. I have dampened the motor bracket and got it very small chatter marks when running at 65rpm and none when running at 100rpm, Im still trying to get that last little bit out. I thought it was a carbide issue, but it was only kind of masking the issue when I switched back to HSS. The chatter was there when looking at the threads from the side with a loupe, and they seem to worse where the leading edge is cutting. When I make a pass with the motor off just turning it by hand the threads look good.
 
JonathanK said:
spindle seems ok and has very little runout....Im pretty sure the issue Im having is the same issue as many Chicom machine owners have expierenced, vibration from the motor. I have dampened the motor bracket and got it very small chatter marks when running at 65rpm and none when running at 100rpm, Im still trying to get that last little bit out. I thought it was a carbide issue, but it was only kind of masking the issue when I switched back to HSS. The chatter was there when looking at the threads from the side with a loupe, and they seem to worse where the leading edge is cutting. When I make a pass with the motor off just turning it by hand the threads look good.
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Not that it makes any difference in the results but you may be getting "faceting". Faceting is caused by material moving too slow across the carbide cutting tool. Chatter is caused by a looseness or limberness somewhere in the machine/cutting tool/workpiece combination.
 
Im having the same issue with HSS, and the more I mess with it the more Im sure the issue is from the motor. I can run it with the belt off and I can still feel the vibration at the carriage. The motor does make some noise when turned by hand with no load, Im gonna call a local electric motor specialist tomorrow and see if they can help. If any one has any other ideas pleasel let me know.
Thanks
Jonathan Kuykendall
 
Can you take a good sharp close up picture of what the cut looks like when it's doing what you call chatter?

Jerry is right, there is a big difference between faceting and chatter.

If it is torsional vibration caused by the single phase motor, and you can do it, you would be much better off with a 3 phase motor and a rotary converter or a single phase to three phase variable frequency unit. Three phase motors have no torsional vibration like single phase motors.

Note: Running a 3 phase motor from cheap "starter" that uses a capacitor to create the third leg for starting purposes, and then runs the motor single phase, won't be any different than running another single phase motor.

Fitch
 
JonathanK said:
...... very small chatter marks when running at 65rpm and none when running at 100rpm,.
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Couldn't you just thread at 100 or more ? Once I figured out that faster was better I quit messing around with low rpm threading. 200 to 300 rpm is my normal threading speed. I cut a small thread relief and all I have to do is disengage the half nut just as the tip of the cutting tool enters the relief. Another thing I do to simplify the process is to engage the half nut before turning the motor on. This way the only things my brain has to process [ under time pressure :) ] for each pass is to turn on the motor and then disengage the half nut at the right time.
 
I will put some pics on here this evening, as far as threading faster that is option Im considering but I want to get the machine functioning as best I can
 
On his lathe he should not have to disengage the half nut just hit the foot brake when the tool passes into the thread relief at the shoulder . Lathe stops dead. Back out and engage reverse.
Go back to start and engage stop. Wind in to next cut depth and engage forward. Repeat until thread is right fit. That's how I run my foot brake lathe anyway .
This way you can work at a higher spindle speed because you can stop the lathe instantly before you hit the shoulder .
Also the 1/2 x1/2 tool may be not rigid enough as this lathe usually takes larger shank tooling. If you look at surface feet per minuet guides for carbide inserts they are working as much as 800% faster speeds than 50 years ago in some cases .
Also you may have the job too far out of the chuck. Also try the insert going straight in at 90 degrees as I found mine cut better that way then with the compound on the angle .
Nothing beats big solid rigid tool posts and strong shank tooling with no packing under them .
 
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JonathanK said:
Im having the same issue with HSS, and the more I mess with it the more Im sure the issue is from the motor. I can run it with the belt off and I can still feel the vibration at the carriage. The motor does make some noise when turned by hand with no load, Im gonna call a local electric motor specialist tomorrow and see if they can help. If any one has any other ideas pleasel let me know.
Thanks
Jonathan Kuykendall
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Brace the gearbox sturcture of the lathe, this will virtually reduce all oscillating movement from all various sources of top heavy, table top, asian lathes mounted on sheet metal boxes and chip pans.

Simply run a metal brace arm from any flange on/near the lathe gear box structure over to an ajoining building wall/2x4, bolt or lag in place.
 
thread chatter issue

2011-06-27_224111.jpg


Heres a pic I took tonight after rough cutting at 65rmp, yes I know they are sharp and jagged but this is just a piece of barrel stub I have been using to troubleshoot with. You can see lines parallel to the threads and the chatter is very faint now and can barely be seen with naked eye. I started out with pretty deep chatter marks so as ugly as these are it is an improvement and when I step it up to 100rpm they look a lot better. I feel I almost have this thing whipped, i can still feel a slight 60hz hum on the carriage but its better now after dampening the motor bracket and bolts with rubber. I will try bracing the gearbox and I have thought about moving the motor off the machine all together
 
NASTY.... Have you removed one of the drive belts?

How deep were you cutting?

Better yet, what thread depth strategy do you use ?

You can usually see the cause of chatter problems.

Remember that rigidity is gold when machining, keep your cutters and your work as close and supported by as much mass as possible.

Also anything much under a 3/4 in tool holder is destined to cause problems, 1/2 and 3/8 best left to watchmakers lathes.
 
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I have removed the second belt, I have been setting the compound at 29.5 and going in .005 4 3 3 3 till I get close and then 2 1 1 1 and then usually .0005-.001 in on the cross-slide. This method seemed to work great untill recently when I started getting chatter.
 
JonathanK said:
I have removed the second belt, I have been setting the compound at 29.5 and going in .005 4 3 3 3 till I get close and then 2 1 1 1 and then usually .0005-.001 in on the cross-slide. This method seemed to work great untill recently when I started getting chatter.
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Here's a dumb question - Do you need to change the cutter? How does it look under bright light and magnification?
 
thread issues

I finally got it cutting decent threads again after some more tweaking of the motor mounts and sharpening and properly setting my tool. I still am suspect of the motor as it makes some strange sounds from time to time and gets pretty hot (cant hold finger on it for more than a second, the machine is in my garage which is 80-85 degrees but dont think it should get this hot) I plan on taking it to a motor specialist tomorrow to see what they think. Hopefully if needs work the company I bought the machine form will help me the charges as it is still under warranty. If I had the extra money I would upgrade to a 3hp 3 phase motor and a VFD. Let me know what Yall think. Heres some threads I cut today.

IMG_20110628_203705.jpg
 
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