Modifying a 3 jaw chuck for better grip -- Why not?

[Derek Eder]

Hello,

I recently bought my first lathe, a Swedish (Ejca) cast iron battleship from the 60's. Among the vintage accesories was a 3 jaw chuck, clearly a metalworkers chuck which crushes wood effectively but offers no gripping power. I feel like a hockey goaly using it because I have taken several sharp shots to the face (mask) using it.

While it would be trivial to add protruding pins to the jaws by drilling and fitting sharpened carbon steel pins are there any possible dangers with this I wonder?

 

[john lucas]

Well I suppose you could but a better remedy would be to either buy a good wood working chuck designed for that purpose or simply use a faceplate. I turned for years with just faceplates before I ever got a chuck. Modifying tools to do what they weren't supposed to do is almost always a half way measure.

 

[odie]

Hello,

I recently bought my first lathe, a Swedish (Ejca) cast iron battleship from the 60's. Among the vintage accesories was a 3 jaw chuck, clearly a metalworkers chuck which crushes wood effectively but offers no gripping power. I feel like a hockey goaly using it because I have taken several sharp shots to the face (mask) using it.

While it would be trivial to add protruding pins to the jaws by drilling and fitting sharpened carbon steel pins are there any possible dangers with this I wonder?

In the early days, and up to the 80's, it was very common for woodturners to use metal working chucks, but they never worked as well as modern wood lathe chucks do.

I'd be willing to bet those metal working chuck jaws are hardened.....which would be a difficult thing to drill into. If not, it could be done, I suppose. You may also want to consider using a file and putting some ribs on the surface of the jaws.

What is your spindle thread size?

I would have to agree with John......get a woodworker's chuck.

ooc

 

[Gerald Lawrence]

Well I suppose you could but a better remedy would be to either buy a good wood working chuck designed for that purpose or simply use a faceplate. I turned for years with just faceplates before I ever got a chuck. Modifying tools to do what they weren't supposed to do is almost always a half way measure.

John has it right . I have seen some folks very good at metal modifications, But unless you have a unique idea it is still a makedo. You can get a good wood turning chuck starting at $140 better for 180 and up even more over 250. If you get the cheap one it is still usable when you buy better. This will eliminate frustration and make you feel better about your work.

 

[Hu Lowery]

Another viewpoint

If you have odd threads on your spindle or simply want to use your old chuck I have never seen any reason not to use a metal working chuck on a lathe meant to carry it. Most are considerably heavier than a wood chuck and also considerably more precise. The answer is soft jaws. They may be readily available for your chuck or it may be easy to make some out of something like 6061 T6 or 7075 if I remember that second number correctly. Talking good grade aluminum alloys, still far stronger than the wooden tenon going in them.

What you need is more surface area for your jaws so you don't crush wood as I'm sure you recognize. Usually the existing jaws have threaded holes to attach soft jaws or the outer jaw is easily removable to replace with soft jaws.

I think you are talking about drive pins and turning between centers, this is another option with a big center pin also. This is the way Glen Lucas does his "production" bowl turning and the video's are on youtube showing him doing this.

Wood chucks are readily available now and fairly cheap if you don't have spindle size and thread issues. Adapters are available and you can make your own too. However if you have a quality metal chuck and a lathe meant to spin it I think modifying it is a viable option. I have turned wood and soft materials in metal chucks for years and pattern makers did it for decades judging by the images of old pattern makers lathes I have seen.

Faceplates are another route and there are good arguments they are the best route when turning all but very moderate sized pieces of wood. Lyle Jamieson has video on youtube addressing why he never uses a chuck.

Still pretty green myself but I find that the chuck and faceplates both have their places for me. If I had it to do over I would probably have invested in more faceplates instead of a chuck. Still might spend a day turning my own faceplates out of some 6061 T6 I have laying around from old projects.

Hu

 

[Bill Boehme]

I will disagree with the notion that a metal chuck is OK, especially for a beginner. The amount of modification to make it safe is more than the effort to buy the right chuck. There are two main reasons for using a woodturning scroll chuck as opposed to a metal turning chuck:

• The first is surface area to distribute the pressure on the tenon. The forces created between the tenon and chuck jaws can be considerable and pressure being force per unit area means that small jaw area means that the pressure can be great enough to crush wood fibers. If thew wood is green then is even more significant. Once the wood is compressed even the slightest amount, the tenon becomes loose in the jaws.
• The tenon must be captured. This means that the jaws must wrap around the tenon so that it will be held even if it becomes loose. Also it needs either a dovetail or other means such as the Oneway design to hold the tenon securely.

If your turning skills are highly refined then you might be able to get away with using a metal chuck, but everybody I know who has used them back when there were no real woodturning chucks say to forget about trying to use them because it is a very good way to get a serious injury or even kill yourself.

 

[Richard Coers]

I've never seen metal working chucks with hardened jaws nor have seen any with bolt on jaws. I would just have a shop make a threaded adapter from your lathe shaft to a common wood chuck thread. One really big hit to the head would make that adapter a relative cheap option compared to medical bills or lifetime handicap.

 

[Hu Lowery]

the catch is weight

I will disagree with the notion that a metal chuck is OK, especially for a beginner. The amount of modification to make it safe is more than the effort to buy the right chuck. There are two main reasons for using a woodturning scroll chuck as opposed to a metal turning chuck:

• The first is surface area to distribute the pressure on the tenon. The forces created between the tenon and chuck jaws can be considerable and pressure being force per unit area means that small jaw area means that the pressure can be great enough to crush wood fibers. If thew wood is green then is even more significant. Once the wood is compressed even the slightest amount, the tenon becomes loose in the jaws.
• The tenon must be captured. This means that the jaws must wrap around the tenon so that it will be held even if it becomes loose. Also it needs either a dovetail or other means such as the Oneway design to hold the tenon securely.

If your turning skills are highly refined then you might be able to get away with using a metal chuck, but everybody I know who has used them back when there were no real woodturning chucks say to forget about trying to use them because it is a very good way to get a serious injury or even kill yourself.

Bill,

You bolt soft jaws on a chuck and shape them to suit. They can be identical to any set of dovetail jaws on a wood chuck other than the advantage they are custom fit to your lathe. Soft jaws are typically mounted on the lathe they are to be used on and then cut to suit. Decide the size you want for optimal hold, set the jaws there with something deeper in the chuck mechanism to hold pressure outwards or use a spider and cut to fit. Because the jaws are custom fit to that lathe it will run truer than anything you can buy off the shelf except by purest fluke.

A set of soft jaws on a chuck with a matching tenon on the wood is a safer set-up than a wood chuck which isn't nearly as stiff and generally has far more runout. When the bearings on the lathe are in good shape the runout on soft jaws is basically zero, you can measure it in ten-thousandths of an inch.

The only disadvantage to a metal lathe chuck with custom jaws is the weight. If a lathe is designed to handle the weight a metal chuck with dovetail jaws is likely to be superior to a wood chuck with dovetail jaws in every way.

360 degree support from the jaws on a metal chuck compared to 360 degree support on a wood chuck the only differences are that the metal chuck is likely to run truer with less vibration. You do get more of a flywheel effect with the heavy chuck but that is often a good thing when roughing irregular shapes.

Soft jaws often in no way resemble the hard jaws people think of when they think of a metal lathe chuck. The soft jaws are often cut to fit one piece of material perfectly for production runs. Cutting a set of 360 degree hold dovetail jaws would be little different. It isn't complicated, I could have cut a set of dovetail soft jaws in the time it took to write this post if I already had the blanks.

This is a set of full round eight inch soft jaw blanks, viewed from the back looks like. Usually made from 6061 T6 they are strong and very easy to machine to suit.

Hu

 

[Bill Boehme]

..... A set of soft jaws on a chuck with a matching tenon on the wood is a safer set-up than a wood chuck which isn't nearly as stiff and generally has far more runout. When the bearings on the lathe are in good shape the runout on soft jaws is basically zero, you can measure it in ten-thousandths of an inch.

360 degree support from the jaws on a metal chuck compared to 360 degree support on a wood chuck the only differences are that the metal chuck is likely to run truer with less vibration. You do get more of a flywheel effect with the heavy chuck but that is often a good thing when roughing irregular shapes. ......

I don't know what run-out you are talking about. If you see the chuck body not running true then it probably means one of two things -- that it is a cheap chuck and not a Oneway or Vicmarc or other quality chuck -- or, it might mean that your lathe spindle is bent or has a bearing problem. If you are talking about the scroll, how would you determine whether it isn't running true? You do realize that the axis of rotation will be about the spin axis which has nothing at all to do with the chuck. I'm sure that you have seen chucks such as the Escoulen that allow you to shift the tenon away from the spin axis. This is normally used for multi-axis work, but you can also turn a piece of wood perfectly round when the tenon is off center.

Anyway, I have a large assortment of Talon, Stronghold, and Vicmarc chucks and they all run perfectly true. When I got my first lathe, a Delta 1440 Iron Bed, the chuck wobbled like crazy, but it wasn't the chuck, it was the lathe spindle. Delta sent me a new spindle and then the chuck ran perfectly true.

Unless you are fortunate enough to have a good buddy machinist who will do the machine work on his bosses nickel, the cost of having a machine shop modify a metal lathe chuck will make the cost of even an Easy Wood chuck seem cheap.

The angular moment of inertia of your load (chuck + wood) when reflected back through the drive train to the motor armature winds up being much smaller than the motor's moment of inertia -- which is a good thing when talking about electronic drives because a large load moment of inertia would make the drive system unstable. The bottom line is that your flywheel effect really isn't significant, but if it were that would not be a good thing.

We all do things for no reason other than the fact that we want to show that we can. I did it when I turned my Delta lathe from a sows ear to a silk purse. Was it smart? No, because nobody other than me would have that Franken-lathe.

 

[Hu Lowery]

sorry

I don't know what run-out you are talking about. If you see the chuck body not running true then it probably means one of two things -- that it is a cheap chuck and not a Oneway or Vicmarc or other quality chuck -- or, it might mean that your lathe spindle is bent or has a bearing problem. If you are talking about the scroll, how would you determine whether it isn't running true? You do realize that the axis of rotation will be about the spin axis which has nothing at all to do with the chuck. I'm sure that you have seen chucks such as the Escoulen that allow you to shift the tenon away from the spin axis. This is normally used for multi-axis work, but you can also turn a piece of wood perfectly round when the tenon is off center.

Anyway, I have a large assortment of Talon, Stronghold, and Vicmarc chucks and they all run perfectly true. When I got my first lathe, a Delta 1440 Iron Bed, the chuck wobbled like crazy, but it wasn't the chuck, it was the lathe spindle. Delta sent me a new spindle and then the chuck ran perfectly true.

Unless you are fortunate enough to have a good buddy machinist who will do the machine work on his bosses nickel, the cost of having a machine shop modify a metal lathe chuck will make the cost of even an Easy Wood chuck seem cheap.

The angular moment of inertia of your load (chuck + wood) when reflected back through the drive train to the motor armature winds up being much smaller than the motor's moment of inertia -- which is a good thing when talking about electronic drives because a large load moment of inertia would make the drive system unstable. The bottom line is that your flywheel effect really isn't significant, but if it were that would not be a good thing.

We all do things for no reason other than the fact that we want to show that we can. I did it when I turned my Delta lathe from a sows ear to a silk purse. Was it smart? No, because nobody other than me would have that Franken-lathe.

Bill,

The cost to machine softjaws is zero if blanks are available, do it on the wood lathe. I routinely cut 6061 with wood saws without carbide tips, no reason to think decent wood turning tools wouldn't cut it easily. I would clean up wood chuck aluminum dovetail jaws in the same manner. The metal chuck that came with the lathe already mounts to it so that is a nonissue. No assembly has zero runout including your lathe and chucks, cutting the jaws in place compensates for a lot of runout issues. Just writing about this has persuaded me to change to dovetail jaws on my Talon to allow me to compensate for angular runout it seems to suffer from.

In general metal chucks are considerably superior units as they should be being considerably more expensive too. The advantages of faceplates over my wood chuck are impossible for me to debate after using both. I am moving away from using a chuck. However if I purchase a chuck to use on a wood lathe in the future it will almost certainly be a metal holding chuck. Greater strength and stiffness, more compact, by being able to use a smaller diameter unit I think any weight disadvantages are negated.

I gave this some thought and originally wrote at considerably more length. After experience with both I am more sold on the metal chuck for use with all materials than ever. Install soft jaws to match a wood chuck, faceplate mount it to allow a maximum precision install, enjoy the best of both worlds.

Hu

 

[Bill Boehme]

Faceplates are what I use for very large heavy things that are at the limit of what I can lift (not the limit of what the late can handle). I managed to mount a piece of wet mesquite that extended about 20 inches from the faceplate and weighed about 75 pounds before I got it round. I also used a faceplate on a very large piece of box elder that started out about 28 inches across the largest diagonal and weighed a mere 55 pounds. I later bought a Vicmarc 120 chuck and 7 inch jaws and must say that it is a beautiful piece of machined work. It runs perfectly true and everything is very tight -- no loose jaws. I'm not sure how heavy that thing is, but it is really good exercise hefting that thing around. Currently I am turning an 18 inch tall vase out of mesquite mounted on a Stronghold chuck. I was a little apprehensive about not using a faceplate, but the chuck with large jaws is doing a great job.

Regarding types of jaws, I prefer the Oneway profiled jaws over the dovetail jaws. The reason is simple -- the shape of the profile jaws provides greater contact area over a range of tenon diameters while dovetail jaws provide optimal holding at only one diameter.

 

[Dale Miner]

I've never seen metal working chucks with hardened jaws nor have seen any with bolt on jaws. I would just have a shop make a threaded adapter from your lathe shaft to a common wood chuck thread. One really big hit to the head would make that adapter a relative cheap option compared to medical bills or lifetime handicap.

I have never seen a metal working chuck that did not have either hardened jaws or master jaw/top jaws (bolt on) or both. Not saying that there are not chucks out there with soft one piece jaws, just never have seen them, and I have been around a LOT of machinery. Some of the smaller three jaw chucks have two sets of jaws, one for external gripping and one for internal. These jaws have the teeth that engage the scroll incorporated into the jaw. Larger chucks that use the master/top jaw configuration have the teeth that engage the scroll on the master jaw, and the top jaws are reversible and replaceable. Unless the top jaws is a 'soft jaw' both the master and the top jaw are harder than can be easily drilled. The master jaw is always hard. If the master or two set type jaws were not hard, the scroll would quickly strip the teeth off the back of the jaw.

A three jaw chuck with machinable soft top jaws would not give the holding power of a four jaw wood working chuck. The three jaws will not have as much contact area as a four jaw. The three jaw chuck will not be able to compress the grain evenly like a four jaw will. That is, with a four jaw it is possible to orient the piece so that each jaw is opposite the same portion of the grain structure. With only three jaws, two jaws will always be in a harder portion of the grain than the third jaw. There are four and six jaw scroll chucks available, but the cost is substantially higher than a three jaw scroll chuck.

The modern wood turning chucks are task specific, and are designed to do what woodturners do. They grab round stock, and also grab square stock. Pretty hard to beat in my book.

 

[Syd Sellers]

I don't know what I would do without my very old 3 Jaw chuck I got from Busy Bee at least 25 years ago....I use it on a daily bases. I also have 2 4 jaw chucks. But to grab something quickly and spin it, you can't beat the 3 jaw. It also allows we to go from 3" dia. all the way to 5/16" with out changing jaws... I do all my Salt & Pepper sets using it to drill all the holes. If you don't want to mark the wood, I have made up a series of metal and rubber rings that you put around the wood and tighten gently. Works for me!!! It always is dead on for centering the piece and I can hold up to 8" long spindles without tail stock. Yes, it has it's limits but don't through away a very useful chuck because it allows you to do stupid things....

 

[Richard Coers]

I have never seen a metal working chuck that did not have either hardened jaws or master jaw/top jaws (bolt on) or both. Not saying that there are not chucks out there with soft one piece jaws, just never have seen them, and I have been around a LOT of machinery. Some of the smaller three jaw chucks have two sets of jaws, one for external gripping and one for internal. These jaws have the teeth that engage the scroll incorporated into the jaw. Larger chucks that use the master/top jaw configuration have the teeth that engage the scroll on the master jaw, and the top jaws are reversible and replaceable. Unless the top jaws is a 'soft jaw' both the master and the top jaw are harder than can be easily drilled. The master jaw is always hard. If the master or two set type jaws were not hard, the scroll would quickly strip the teeth off the back of the jaw.

A three jaw chuck with machinable soft top jaws would not give the holding power of a four jaw wood working chuck. The three jaws will not have as much contact area as a four jaw. The three jaw chuck will not be able to compress the grain evenly like a four jaw will. That is, with a four jaw it is possible to orient the piece so that each jaw is opposite the same portion of the grain structure. With only three jaws, two jaws will always be in a harder portion of the grain than the third jaw. There are four and six jaw scroll chucks available, but the cost is substantially higher than a three jaw scroll chuck.

The modern wood turning chucks are task specific, and are designed to do what woodturners do. They grab round stock, and also grab square stock. Pretty hard to beat in my book.

Maybe it's our interpretation of hard jaws. The vintage 1950s Hardinge toolroom lathe I ran for 15 years showed lots of impact dings from impacts between the cross slide and the jaws. There was no indications of chipping. In my experience, hard steel doesn't dent or "wipe" over like that. I've never Rockwell tested the jaws, just went by the dents. I was also taught that the jaws were on there to be machined as needed. I never had to grind then, just machine them. That is the 3rd lathe I have used. None of them had bolt on jaws. Maybe I'm just an old guy that has worked on machines that are as old as me and older. Come to think of it, that Hardinge was the newest one I ran.

 

[Dale Miner]

Maybe it's our interpretation of hard jaws. The vintage 1950s Hardinge toolroom lathe I ran for 15 years showed lots of impact dings from impacts between the cross slide and the jaws. There was no indications of chipping. In my experience, hard steel doesn't dent or "wipe" over like that. I've never Rockwell tested the jaws, just went by the dents. I was also taught that the jaws were on there to be machined as needed. I never had to grind then, just machine them. That is the 3rd lathe I have used. None of them had bolt on jaws. Maybe I'm just an old guy that has worked on machines that are as old as me and older. Come to think of it, that Hardinge was the newest one I ran.

If you were able to machine the jaws, then I would classify them as soft jaws. Hard jaws need to be ground. Accidental contact between carbide tooling and hard jaws will take a bit of the jaw before destroying the carbide, but actually machining hard jaws with carbide is not usually done. Typically hard jaws will be trued by grinding when new, and occasionally to retrue as they wear from use. Soft jaws are used where they will intentionally be machined to a hold a
specific part/diameter so that when the chuck is tightened the part will run true. I am not familiar with a scroll chuck that incorporated soft jaws that did not use a master/top jaw configuration, but they may be out there. It seems like the teeth that engage the scroll would rapidly wear if not hard and lose accuracy as a result.

 

[Raul McCai]

I think the law of physics are your enemy

Putting teeth in a three jaw chuck meant for metals won't likely provide you with much more grip.
Some yes, but enough to prevent spin out? Prolly not.
YA see the problem is all about surface area and angle.
Good chucks have a dovetailed gripping jaw surface and they have a very wide jaw to grrip with, so they make it doubly hard for a piece to spin out of the chuck.

All little teeth will do is grip better than before, but in a highly localized area thus be subject to tearing away.

In the alternative if you could weld little plates to the jaw tips and machine them to have dovetailed geometry to trap work you might have something.

 

[hockenbery]

Good chucks have a dovetailed gripping jaw surface and they have a very wide jaw to grrip with, so they make it doubly hard for a piece to spin out of the chuck. All little teeth will do is grip better than before, but in a highly localized area thus be subject to tearing away. .

I like dove tail jaws. I use them for most of my bowls and especially if I'm using for shorter tenon on natural edge bowl.

Another excellent choice are the ONEWAY profile jaws. These provide better grip on square stock and spindles than the dovetail jaws.
These jaws give eight wide grip points with small teeth to bite in.
The profile jaws grip bowls really well on tenons close to the height of the jaws. I don't like using them on tenons that don't catch at least three teeth.

The dovetail jaws have eight tiny grip points on square stock. These work okay on most woods an will always be fine when the tailstock is in place.
Dovetail jaws consequently grip much better when the tenon diameter Is close to the closed jaw diameter.
The ONEWAY profile has a much better grip on tenon wider than the closed jaw diameter.

For anyone working with square stock. The profile jaws are excellent.
The profile tower jaws give even more grip surface for spindles and square stock.

 

[john lucas]

Al A friend called me one day. He was looking at chucks and one of them (a famous brand but I won't mention the name because I may have it confused with another) said that you shouldn't use a dovetail tenon because it weakens the tenon. Well I suppose in theory it does. I've been using Vicmarc chucks with dovetail tenons ever since I bought my first chuck. In fact the only chuck I've used where we had problems with bowls staying in the chucks was a chuck that doesn't have a dovetail. It was a brand name chuck as well. I was teaching at the Folkschool and one lady had constant problems with the piece coming out of the chuck. I gave her my Vicmarc and the problem went away.
Anyone else hear that dovetail tenons weaken the hold. I think it was Mike Mahoney who showed how he was able to core bowls with an extremely small (as in depth) tenon using Vicmarc dovetail jaws. Then tenon was about 4" in diameter but probably only 1/8" deep. Coring as you know puts a lot of force on a bowl.

 

[hockenbery]

Al A friend called me one day. He was looking at chucks and one of them (a famous brand but I won't mention the name because I may have it confused with another) said that you shouldn't use a dovetail tenon because it weakens the tenon. Well I suppose in theory it does.

I have not seen any problem with dovetail tenons being "weak"
I have also heard people say tightening a tenon too much will tear it off.
I tighten as hard as I can and never tore a tenon off ( I guess if the dovetail on the tenon is cut at too small an angle closing the jaws might crack the tenon)

I trust a dovetails on a short tenon. I have done quite a few bowls with tenons an 1/8" long. I still get surprised that they hold.
They may not hold up to a catch.

We use dove tail jaws on the strongholds most of the time for bowls and I love the Vicmarc chuck.

The ONEWAY profile jaws are great too.

 

[Owen Lowe]

I have not seen any problem with dovetail tenons being "weak"
I have also heard people say tightening a tenon too much will tear it off.
I tighten as hard as I can and never tore a tenon off ( I guess if the dovetail on the tenon is cut at too small an angle closing the jaws might crack the tenon)

I think when folks experience a failed tenon, it’s probably due to it being too small in diameter in relation to the diameter of the bowl. Up to 10†or so, I’ll go with about 2-2.5†tenon; from there up to 16†I’m comfortable with 3-4â€. For me, it looks like the tenon is about 1/4 the overall bowl diameter.

Another issue may be including portions of the bark layer or other weak material in the tenon.

 

[Bill Boehme]

Both types of jaws have advantages and disadvantages depending on the particular situation. That is why a well known brand of chuck made in Canada also offers dovetail jaws for their chucks. Another well known brand of chuck made in Australia now offers jaws with ridges addition to their dovetail jaws. Their jaws with ridges are not the same as the well known band of profiled jaws, but they also have advantages in certain situations.

The profiled jaws are excellent when you have enough wood to make a longer tenon. I typically go for a length of around 3/8". They also are nice because the profile isn't simply concentric with the jaw circle. They are profiled with a variable diameter type curve that provides a good match for tenon diameters that are within the range of the jaws operation. This means that each area of contact is wider than a small point. Also, to counter misinformation often stated about the profiled jaws, they do not have sharp ridges -- the ridges are rounded over. I have seen the short tenon and shallow mortises that Mike Mahoney uses when he was at our club a couple years ago. Seems like I recall that he didn't tighten the chucks very much, either. I'm like Al, I really honk down on a tenon. I'm a bit more cautious when tightening in a mortise.

There are various reasons that a tenon might break or that the wood will split if expansion chucking, but I would not attribute that to the design of the jaw for either type. It's either not paying attention to the wood or getting a bad catch.

BTW, John, why are we not mentioning brand names? I'll never be certain which ones we mean ...