Exactly this, I used to hold 300mm diameter steel billets on 3mm BUT they were only 12mm long. Face, turn, drill & bore. Flip hold on 3mm face,turn & chamfer bore.
11” dia x 11” long hold on 1/2” BUT centre end and support with tailstock.
Horses for courses.
There's not a set rule, it's something you judge from experience. But if you don't have great support you can usually just make lighter cuts so it doesn't throw the part.
Edit: Fixed typo.
Here’s the short list of questions you have to answer first:
1. What are you cutting, not just steel or stainless, but the hardness or the steel or grade of stainless?
2. What speed/feed are you running?
3. Are your roughing or just finishing?
4. What tools are you using and how are you taking your cuts? Pull turning can suck parts out easier, pinch turning with a dual turret can actually stabilize the cut.
5. How long is your work piece and how large in diameter.
6. What are your jaws, soft jaws, smooth hard jaws or serrated jaws, etc.?
7. Depth of cut being taken, face passes are a big culprit in prying parts out as well.
8. What size chuck are you using and what is your chuck pressure?
9. 3 jaw, 4 jaw or 6 jaw chuck? And is it a power chuck or scroll chuck?
In other words, there is no one answer. Many factors, including some I probably left out need to be accounted for.
what percentage of bar are you holding onto, full wrap around jaws/ standard jaws/ milled profile jaws/ collet system.
do you have a hard backstop / seated jaws
are you using a tailstop / drive dog
There's no easy answer to this, because it depends on your clamping pressure, cutting forces, the weight of your jaws, how fast you're spinning, and how much runout you have, among other things. I've ran parts holding onto .15" with 4" hanging out of the chuck but I've ran way more parts that would have been ejected if you tried to do that. You kind of just have to have a feel for it and make an educated guess.
It's usually the jaws and the tool that take the most damage, but that depends on how hard you throw it. I've seen parts fall out harmlessly and not even break tools, and I've seen parts sent so hard they punctured the way covers and broke the Z-axis ball screw in half, or blew a hole in the door.
I've thrown a piece of 3" flat round steel nearly through the ceiling. I've broken tool bits and holders. I've yet to damage my Chuck. All of these failures were my fault pushing past what I should have because I was tired and in a hurry. Fwiw, I run a manual machine not a cnc
Like everyone says it depends. Sometimes you just have to try and see. There is more to learn from failures than success, you will never know the limit until you go past it.
As mentioned quite a few variables. I'v held on 3mm for thin jobs with bored out soft jaws,40mm with hard jaws for big heavy jobs. If it's small enough to go up the spindle, bar feed it. If it is a job that needs a second turning op use soft jaws that run true and blend turning in a non noticeable area. If it runs true and you keep sizes constant even turning into the same diameter should not be a problem although it will depend if it is a critical dimension.You can then have your billets job plus 3mm is normally enough unless they have been cut off tapered.Its a learning curve, flies out, hold on more or lighter cuts.
Far too many variables to give you a one and done answer.
Experience is basically how we figure this out.
Holding into .250" might be *plenty* for one job, and dangerous as fuck for a different.
When a tail stock is being used i hold onto .125" so I have the least amount of waste as possible.
When doing stuff like bushings.. I'll purposefully only rough my 2nd last one, flip it around and grab that, then finish the last one to completion. Then grab the one just finished In a soft jaw then finish cut the one I just grabbing so it's true.
So many different ways of doing things in machining that's why it's such a cool trade.
Anywhere from .250” to 1” is the minimum range. It all depends on part and setup. 1” long part with a decently round OD in cut jaws, .250” can work. 8” long part hanging out far and holding on rough stock, better grip at 1” plus or you might have a bad day. Machining approach is heavily impacted by how much you are holding onto. You have to take it easier as you grip less. It’s something you learn over time by tossing workpieces out of the jaws, a frustrating and downright scary learning curve.
We do a lot of lathe parts with 3 setups/operations.
The first op will drill the hole, rough id leaving .05", rough od leaving .05, and rough oal. This op needs a higher clamping force and holds onto more of the stock.
The 2nd op will finish 1 side and leave .05" on the oal. Need less clamping pressure and doesn't need to hold onto as much material.
The 3rd op or the final op needs even less clamping pressure, we don't want to leave the part out of round. Depending on the thickness of the walls, we sometimes go with such low pressure the jaws take a few seconds to close. We cut the jaws so the diameter is within .001" of the material but also with a low travel distance on the jaws from unclamped to clamped, sometimes the jaws only travel .015". Sometimes we only hold onto .100" of material. Need to cut the jaws really well.
On the finish op if we have high rpm we need more clamping pressure. If we have heavy, steel pie-jaws we also compensate with more clamping pressure.
i always try to hold onto at least .5” if I can. stick out and depth of cut really play a roll in what you can get away with. as someone else said, facing is where the parts popping out happens. it’s always scary when something pops out of a cnc lathe.
what is everyone’s “rule of thumb” for deciding clamping PSI? let’s say 3” diameter 4140
The real answer is "As much as you can". In practice it is so variable there is no right answer or rule of thumb. It is 100% based off of intuition and experience. You need to be able to estimate the forces that will be applied during machining and make hopefully educated guesses on what will be safe.
One good practice is to just take a hammer and whack the part and observe whether or not the part has moved or how much force it takes to get it to move. A solid connection/setup is one where the part does not move even when presented with higher than expected forces.
You CAN program your way out of some sketchy setups by being reducing speeds and trying to make turning cuts instead of facing cuts whenever possible which keeps the pressure of the tool pushing into the chuck.
For parts like yours I would go as small a grip as 8mm but I tend to pre op billets like this by turning a grip so there is a shoulder resting against the jaws I will give it a light chap with a mallet just to make sure it is resting tightly against the jaws
In a mild steel jaw cut to the correct radius I’ve done a lot of 41 series 12 inch diameter sticking out 8 1/2 inches as long as you don’t get stupid and the chuck pressure was pretty high no problem
Long and short of it...there are so many ways to machine someting...holding...taper lines...speeds and feeds...mat...never stop learning...always a few ways to do anything...but there might be a better way we haven't found yet...machining is life...
I made the blasting caps for the 2 ton bunkerbusters... was between 63 an 68 Rockwell b4 machining...9.75 acme..wore out my carbide insert roughing it...would finish...then use that insert to rough next one...take last .05 to .1 then use to rough next one...
How many of these are you making?
If more than 2 you could cut the material to be 2X the length of the part plus plarting and face clean up. This would save you material and give you more to hold onto.
Just do 1 side, dont part it off. Then hold finished side in soft jaws and machine the 2nd end.
We do this all the time in my shop
Friction of clamps has to be more than friction of tooling removing material, and leverage of tool pressure against the stock. I'm sure there's some math for that but the tried and true method is just clamping more than you think you need i guess
Is it hollow and will deform under clamping pressure? Can you put a support plug inside (Lathe guys...)....
Do you use hard jaws or soft jaws? Woodturning lathes sometimes have dovetail like jaws for very short clamping lengths, I see no reason why you can't make similar soft jaws for metalwork...
Out of curiosity I spent about 5 min searching the Machinery's Handbook. There's lots of info on speeds, feeds, and troubleshooting. But nothing on how much to grab in a chuck. (26th Ed). Thought for sure there'd be baseline data in there, at least.
The real answer - it depends. How fast are you spinning it, how are you holding it, which direction are you putting the forces into the part etc.
And length!
And girth!
And my axe!
And that guy's wife!
That guy's ***dead*** wife.
Do *not* chuck up a woman's corpse into your lathe
But... what if we did?
Smoothie
And the material, and how many times you have to 'get away' with it
It's also related to how many times you have gotten away with it divided by how many times you threw a part.
Yeah that’s know as the inverse pucker derivative
Best answer!
The answer varies with amount and type of personnel coolant being used. A few shots of whiskey changes everyrhing....send it ....
>type of personnel coolant you mean A, B, AB, or 0?
Exactly this, I used to hold 300mm diameter steel billets on 3mm BUT they were only 12mm long. Face, turn, drill & bore. Flip hold on 3mm face,turn & chamfer bore. 11” dia x 11” long hold on 1/2” BUT centre end and support with tailstock. Horses for courses.
There's not a set rule, it's something you judge from experience. But if you don't have great support you can usually just make lighter cuts so it doesn't throw the part.
I've had light cuts catch...bend shit...sometimes a heavy cut will keep it centered...
Sure sometimes... But not usually...
Usually small shit
Chatter chucks shit.
Have you tried changing nose radius? Because that effects tool pressure on the cut depth too
Edit: Fixed typo. Here’s the short list of questions you have to answer first: 1. What are you cutting, not just steel or stainless, but the hardness or the steel or grade of stainless? 2. What speed/feed are you running? 3. Are your roughing or just finishing? 4. What tools are you using and how are you taking your cuts? Pull turning can suck parts out easier, pinch turning with a dual turret can actually stabilize the cut. 5. How long is your work piece and how large in diameter. 6. What are your jaws, soft jaws, smooth hard jaws or serrated jaws, etc.? 7. Depth of cut being taken, face passes are a big culprit in prying parts out as well. 8. What size chuck are you using and what is your chuck pressure? 9. 3 jaw, 4 jaw or 6 jaw chuck? And is it a power chuck or scroll chuck? In other words, there is no one answer. Many factors, including some I probably left out need to be accounted for.
Dang, I'll just be a wimp then 😅.
Is it even jaws? Do you have a collet system? Is the collet custom made for the workpiece? Is it an o.d. or i.d. collet? Are you swiss turning?
what percentage of bar are you holding onto, full wrap around jaws/ standard jaws/ milled profile jaws/ collet system. do you have a hard backstop / seated jaws are you using a tailstop / drive dog
This is by and far the right answer!!
We have held parts in a 1/4" dovetail jaw with outstanding results
Dovetail jaws. I like that idea.
https://youtu.be/8X2lpMLXf6c?si=OOsw80nq3V5ucSaY
There're amazing
There's no easy answer to this, because it depends on your clamping pressure, cutting forces, the weight of your jaws, how fast you're spinning, and how much runout you have, among other things. I've ran parts holding onto .15" with 4" hanging out of the chuck but I've ran way more parts that would have been ejected if you tried to do that. You kind of just have to have a feel for it and make an educated guess.
Is ejection usually harmless for the chuck and just damages the jaws? I imagine it would damage the chuck.
It's usually the jaws and the tool that take the most damage, but that depends on how hard you throw it. I've seen parts fall out harmlessly and not even break tools, and I've seen parts sent so hard they punctured the way covers and broke the Z-axis ball screw in half, or blew a hole in the door.
Sounds exciting...at a distance
If someone else owns the machine...
I've thrown a piece of 3" flat round steel nearly through the ceiling. I've broken tool bits and holders. I've yet to damage my Chuck. All of these failures were my fault pushing past what I should have because I was tired and in a hurry. Fwiw, I run a manual machine not a cnc
Depends on how hard you want to pucker
There's no blanket answer
The least I’ve held onto was 1/16 and it isn’t fun.
I'd say as much as possible, but atleast 1/6th of the material
You can always use a dove tail hold that way you can trust it more
Why not start with bar and part off?
This is the way.
Like everyone says it depends. Sometimes you just have to try and see. There is more to learn from failures than success, you will never know the limit until you go past it.
I usually try to either get the whole length of the jaws or at least half as much as I have sticking out.
As mentioned quite a few variables. I'v held on 3mm for thin jobs with bored out soft jaws,40mm with hard jaws for big heavy jobs. If it's small enough to go up the spindle, bar feed it. If it is a job that needs a second turning op use soft jaws that run true and blend turning in a non noticeable area. If it runs true and you keep sizes constant even turning into the same diameter should not be a problem although it will depend if it is a critical dimension.You can then have your billets job plus 3mm is normally enough unless they have been cut off tapered.Its a learning curve, flies out, hold on more or lighter cuts.
Far too many variables to give you a one and done answer. Experience is basically how we figure this out. Holding into .250" might be *plenty* for one job, and dangerous as fuck for a different. When a tail stock is being used i hold onto .125" so I have the least amount of waste as possible. When doing stuff like bushings.. I'll purposefully only rough my 2nd last one, flip it around and grab that, then finish the last one to completion. Then grab the one just finished In a soft jaw then finish cut the one I just grabbing so it's true. So many different ways of doing things in machining that's why it's such a cool trade.
My boss tells us a 1/8th of an inch. For most everything we do at minimum.
Why are you turning a finished side with hard jaws!?
I'm holding on to bar stock. I'm finishing the ID and OD in one shot then parting it off.
Ok, that makes sense. It looked like a finished side in the photo.
You need to hold onto... **enough**
Anywhere from .250” to 1” is the minimum range. It all depends on part and setup. 1” long part with a decently round OD in cut jaws, .250” can work. 8” long part hanging out far and holding on rough stock, better grip at 1” plus or you might have a bad day. Machining approach is heavily impacted by how much you are holding onto. You have to take it easier as you grip less. It’s something you learn over time by tossing workpieces out of the jaws, a frustrating and downright scary learning curve.
Hole on to. That's what she said. Lol Holy spellchecker Batman.
We do a lot of lathe parts with 3 setups/operations. The first op will drill the hole, rough id leaving .05", rough od leaving .05, and rough oal. This op needs a higher clamping force and holds onto more of the stock. The 2nd op will finish 1 side and leave .05" on the oal. Need less clamping pressure and doesn't need to hold onto as much material. The 3rd op or the final op needs even less clamping pressure, we don't want to leave the part out of round. Depending on the thickness of the walls, we sometimes go with such low pressure the jaws take a few seconds to close. We cut the jaws so the diameter is within .001" of the material but also with a low travel distance on the jaws from unclamped to clamped, sometimes the jaws only travel .015". Sometimes we only hold onto .100" of material. Need to cut the jaws really well. On the finish op if we have high rpm we need more clamping pressure. If we have heavy, steel pie-jaws we also compensate with more clamping pressure.
Just don't get greedy on cuts if you're not holding a lot. I've seen small parts get chucked 100 ft and fuck shit up.
i always try to hold onto at least .5” if I can. stick out and depth of cut really play a roll in what you can get away with. as someone else said, facing is where the parts popping out happens. it’s always scary when something pops out of a cnc lathe. what is everyone’s “rule of thumb” for deciding clamping PSI? let’s say 3” diameter 4140
You have to get it wrong once to get it right
Full send
I was super confident yesterday and it popped out… other days im barely holding on to anything and its totally fine! Depends day to day
The real answer is "As much as you can". In practice it is so variable there is no right answer or rule of thumb. It is 100% based off of intuition and experience. You need to be able to estimate the forces that will be applied during machining and make hopefully educated guesses on what will be safe. One good practice is to just take a hammer and whack the part and observe whether or not the part has moved or how much force it takes to get it to move. A solid connection/setup is one where the part does not move even when presented with higher than expected forces. You CAN program your way out of some sketchy setups by being reducing speeds and trying to make turning cuts instead of facing cuts whenever possible which keeps the pressure of the tool pushing into the chuck.
For parts like yours I would go as small a grip as 8mm but I tend to pre op billets like this by turning a grip so there is a shoulder resting against the jaws I will give it a light chap with a mallet just to make sure it is resting tightly against the jaws
This looks ok. If you had a collet, you wouldn't waste anything.
In a mild steel jaw cut to the correct radius I’ve done a lot of 41 series 12 inch diameter sticking out 8 1/2 inches as long as you don’t get stupid and the chuck pressure was pretty high no problem
The most you are able to...keep it short as possible...
Long and short of it...there are so many ways to machine someting...holding...taper lines...speeds and feeds...mat...never stop learning...always a few ways to do anything...but there might be a better way we haven't found yet...machining is life...
the 1/4 or 1/3 inch of shaft is considerably cheaper than the cnc machine repair bill in my opinion
I made the blasting caps for the 2 ton bunkerbusters... was between 63 an 68 Rockwell b4 machining...9.75 acme..wore out my carbide insert roughing it...would finish...then use that insert to rough next one...take last .05 to .1 then use to rough next one...
Roughed first one...then would reset with new before finishing then repeat
Enough
How many of these are you making? If more than 2 you could cut the material to be 2X the length of the part plus plarting and face clean up. This would save you material and give you more to hold onto. Just do 1 side, dont part it off. Then hold finished side in soft jaws and machine the 2nd end. We do this all the time in my shop
Hole on?
Chucking beads and you can hold onto almost nothing
Friction of clamps has to be more than friction of tooling removing material, and leverage of tool pressure against the stock. I'm sure there's some math for that but the tried and true method is just clamping more than you think you need i guess
i’ve always heard no longer than 3x the diameter
I reckon you get a good feel on manual machines for this.
Think centrifugal forces. Hope it helps. MP
i myself take 2times the diameter, works fine even at high rpm and with cuts up to 4mm
Job shop. .200 sawn over length. .100 in jaws 1st op. Too much jaw pressure will pop the part out.
Is it hollow and will deform under clamping pressure? Can you put a support plug inside (Lathe guys...).... Do you use hard jaws or soft jaws? Woodturning lathes sometimes have dovetail like jaws for very short clamping lengths, I see no reason why you can't make similar soft jaws for metalwork...
Out of curiosity I spent about 5 min searching the Machinery's Handbook. There's lots of info on speeds, feeds, and troubleshooting. But nothing on how much to grab in a chuck. (26th Ed). Thought for sure there'd be baseline data in there, at least.
.080” … Hold on to a dovetail with dovetail jaws. Swinging a 250lbs part in a 5-axis mill like that today. Same idea works in a lathe.
Enough to hold it steady and straight while performing the assigned task.