Kielwood shafts snapping during turning, strange oscillation.. can't seem to figure it out.

If the shafts are snapping, something is wrong and as you see from the responses it can be a host of things and it can also be a combination of things. I think finding the source of the vibration should be your first priority. What type of spur driver you use isn't really clear and I would look at the connection there, is it room for movement?
Shaft tension, cutter height, how precise and sharp your cutter is and then feeds and speeds all play a part.
Buy some cheap wood you can sacrifice in order to figure these things out.
 
You've gotten a lot of good advice, I'll try not to repeat any advice.
Have you measured the 150 RPM turn rate?
Do you back off the spur collar for EVERY new blank that you put up and only position the spur AFTER after the dead center seats and the tailstock pressure is set? If the spur contacts the blank before the dead center fully seats, bad things could happen.
What are you using in your tailstock? Is there any runout in your live center? You could try a 2nd dead center in the tailstock with a drop of BLO or some cue wax in the hole. There will be zero runout.

I'm curious as to why you are using 1.5 x 1.5 blanks for making shafts? Why not use 1 x 1 blanks? Are you going from 1.5 x 1.5 to final size in one session?
 
Mike Rys said:
You've gotten a lot of good advice, I'll try not to repeat any advice.
Have you measured the 150 RPM turn rate?
Do you back off the spur collar for EVERY new blank that you put up and only position the spur AFTER after the dead center seats and the tailstock pressure is set? If the spur contacts the blank before the dead center fully seats, bad things could happen.
What are you using in your tailstock? Is there any runout in your live center? You could try a 2nd dead center in the tailstock with a drop of BLO or some cue wax in the hole. There will be zero runout.

I'm curious as to why you are using 1.5 x 1.5 blanks for making shafts? Why not use 1 x 1 blanks? Are you going from 1.5 x 1.5 to final size in one session?
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Yes, I've measured the turn rate, I have a DRO for the rpms

Yes, I back of the spur collar every time. I seat both centers, and then engage the spur. I use Chris' spur driver

I've used both dead and live centers in the tailstock. Same issue. I do use some beeswax in the hole

I use 1.5x1.5 blanks because with a 1" blank and a .840 final diameter, I only have .160 (theoretically) to get to size. If my center is off even a little bit, or if the 1" blank arrives slightly undersized, I have no material left to work with.

No, I don't go to final size in one session. I typically take about 10 passes spread over a month or so.

Again, I've turned hundreds of shafts without issue. This phenomenon only started happening when I started turning terrified blanks..
 
Kielwood is more brittle, but those issues are of concern only when cutting threads in my experience.
Any pictures of your setup and the broken shafts?
 
tg_vegas said:
I have a batch of Kielwood square blanks that I'm turning now. About 25% of them are failing on the lathe. The rest are fine.

I am turning them from 1.5 x 1.5 x 31 squares. I took off the corners on my router table like I always do.

Then the rough turns. 1" Freud 2-Blade straight bit, brand new. 4-5 shafts turn clean, no issues.

Then the last two. I get down to about .650 on the tip end during the tapering passes. Turn starts out fine, but once I get to mid-shaft, I can feel and even hear a slight harmonic oscillation start to build that I can see in the shaft, like waves. Once I start to get closer to the headstock, it goes away.

However, on the two I did today, the oscillations got so bad that it drove the shaft into the router bit and snapped the shaft. WTF?

I'm on a Cuesmith Deluxe. 145-150 rpm rotation speed, feed rate of <4" per minute, total pass is 8 minutes. .050" cut.

I've turned a 100+ shafts with no issues in the past few months but the latest ones have me at a loss. I can't feed any slower and even at smaller cuts, I have the same harmonic situation. You can actually hear it as a humming sounds that builds up to a vibration you can see in the work.

Any clues from the experts??
Click to expand...

Are you climb cutting or conventional?
 
To minimize chatter, I would first make sure you have as little tool engagement with the material as possible. So, tool height is critical as has been previously mentioned. Then decrease the rotational speed of the shaft and increase the feed. I would also progressively decrease the depth of cut as you get closer to finish diameter. It has been my experience that the rigidity of the blank can vary greatly even when turning same type of wood. As a general rule I have found that chatter seems to propagate more as rigidity decreases.
 
tg_vegas said:
I have a batch of Kielwood square blanks that I'm turning now. About 25% of them are failing on the lathe. The rest are fine.

I am turning them from 1.5 x 1.5 x 31 squares. I took off the corners on my router table like I always do.

Then the rough turns. 1" Freud 2-Blade straight bit, brand new. 4-5 shafts turn clean, no issues.

Then the last two. I get down to about .650 on the tip end during the tapering passes. Turn starts out fine, but once I get to mid-shaft, I can feel and even hear a slight harmonic oscillation start to build that I can see in the shaft, like waves. Once I start to get closer to the headstock, it goes away.

However, on the two I did today, the oscillations got so bad that it drove the shaft into the router bit and snapped the shaft. WTF?

I'm on a Cuesmith Deluxe. 145-150 rpm rotation speed, feed rate of <4" per minute, total pass is 8 minutes. .050" cut.

I've turned a 100+ shafts with no issues in the past few months but the latest ones have me at a loss. I can't feed any slower and even at smaller cuts, I have the same harmonic situation. You can actually hear it as a humming sounds that builds up to a vibration you can see in the work.

Any clues from the experts??
Click to expand...
That's what prompted me to build my tapering machines. I understand people are building complete cues on taig lathes and early on I got a lot of advice how to avoid what you're going through when all I had was my cuesmith. After a few barber poles on the final cut I said screw this thing and made something less finicky.
 
Canadian cue said:
To minimize chatter, I would first make sure you have as little tool engagement with the material as possible. So, tool height is critical as has been previously mentioned. Then decrease the rotational speed of the shaft and increase the feed. I would also progressively decrease the depth of cut as you get closer to finish diameter. It has been my experience that the rigidity of the blank can vary greatly even when turning same type of wood. As a general rule I have found that chatter seems to propagate more as rigidity decreases.
Click to expand...

So I'm cutting off the side of a 1" two-blade straight bit. When you talk about tool height, are you wondering where on the side of the bit I am cutting? Does it make any difference??
 
tg_vegas said:
I must admit my ignorance here, I'm not a cue maker or machinist. I don't know what Climb Cutting or Conventional means.
Click to expand...
tg_vegas said:
So I'm cutting off the side of a 1" two-blade straight bit. When you talk about tool height, are you wondering where on the side of the bit I am cutting? Does it make any difference??
Click to expand...


This link explains it pretty well: https://engmachineshop.wustl.edu/people/climb-milling-vs-conventional-milling/

While they touch briefly on backlash, what they don't explain is what can happen in a machine that has a significant amount of backlash. When climb cutting the cutter can pull the router sled faster than it is being fed until the backlash in the feed is met. What will end up happening is that the sled will lurch a short distance and bounce back (this is all very small, but it can really screw with things). This is easily (and potentially dangerously) demonstrated if you have ever used a router by hand--if you cut counterclockwise, things work fine, you are always pushing the router. If, however, you cut clockwise, the router will run away from you (and climb out of the material) when you push it into the cut.

This involves your second question to CC, the side of the bit you are cutting on combined with your feed direction results in the type of cutting you are doing. CC is asking literally about the height of your cutter in relation to the axis of the shaft. Since you are using a double carbide straight cutter, this is moot--you are cutting on the center line of the shaft, by definition. CC is assuming that you are using a wing cutter with thin carbide (I use 1/8" carbide wing cutters).

If you are using the machine with the rack-and-pinion drive, never attempt to climb cut, there is just too much backlash.

Feel free to pm me if you'd like to talk more about this in private.
 
Coos Cues said:
That's what prompted me to build my tapering machines. I understand people are building complete cues on taig lathes and early on I got a lot of advice how to avoid what you're going through when all I had was my cuesmith. After a few barber poles on the final cut I said screw this thing and made something less finicky.
Click to expand...

Rigidity in structure and eliminate backlash in the drives. It's the reason I built my cnc with ballscrews and profile rails. I run a lot of my stock removal passes at about 22in/min and my finish passes at 6-9in/min. With the machine running using a 3hp spindle two people can have almost have a normal conversation five feet from the machine.
 
tg_vegas said:
So I'm cutting off the side of a 1" two-blade straight bit. When you talk about tool height, are you wondering where on the side of the bit I am cutting? Does it make any difference??
Click to expand...
When trying to minimize chatter you need to minimize tool engagement. So if you were cutting something conventionaly with single point tool you would use a cutter with as small a radius as possible at the corner of your insert. When cutting with live tooling or a router in our case same rule applies. So when setting the hieght of top edge of the cutter in relation to center axis of material. I set the top corner on center, or if I am turning with the spindle in reverse I set the bottom corner on center. The material is feeding into the cutter the same way as it would if I was using a single point tool. I use a slot cutter so my cutters only 1/8 or 1/4 of an inch. If you are using a 3/4" by 1in cutter say and you have the shaft running through the center of your cutter you have a great deal of surface area in engament with the cutter. That type of cutting will be much more conducive to chatter. And when your shaft starts to oscillate it can quick self destruct. I much prefer to use slot cutters for shaft work smaller cutters I only use for cutting larger diameters.
 
I want to thank all of you for the comments and one person in particular who reached out to me via PM and helped me sort this issue with Kielwood out. I made a number of changes based upon his recommendations and am now back to turning really nice shafts and nearly 75% less time!

I kept my turning RPMs to 150. I increased my feed rate to 4x what I had before. I replaced the 1" straight bit with a 1/16", 2" diameter, slot cutter. Amazing improvement and I now can make a full pass in 2 minutes vs 8 minutes before with no oscillation and really nice, sanding ready results.

Thanks AZB family for the support. In particular, you know who you are!

Best,Tom
 
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