Four jaw chuck for wood lathe

[Continuum]

This is still a WIP but first tests went well.

Second I am planning a guard to keep from getting smacked.

Here is the final build. I give a summary of the build below.

Basically I wanted a beefy four jaw chuck. This lathe is MT1 and four jaw chucks are very expensive, small size and seems to get bad reviews. I want a chuck I can attach to the head stock thread and not MT driven. I also wanted something I could change out chucks with. Planning a variant to the jaws to grip inside too.

This was a total acid test. This is hard maple. I made no attempt to get it cleaned for roughing. I wanted to see if I could clean it off without a live center. It really held firm the entire time. If this was driven by the MT it would certainly have spun and galled.







In the end, this turning became the nut for an MT1 chuck draw bar. This centered nicely. I really like the drawbar concept since it keeps the tapers from getting spun. Plus I can remove by loosening the thread and tapping lightly with a wood mallet.

[scsmith42]

Well done! How did you bend the round bar supports? They sure look more consistent than I could achieve.

[Continuum]

Well done! How did you bend the round bar supports? They sure look more consistent than I could achieve.

Thank you. The bars are 1/2 so cold bend is not really possible. I used my fabricated carbon arc torch to heat. I don’t have an OA rig so this is my go to, short of pulling out the forge. 90 amps AC for 15 seconds. Heat until it just gets pliable. I cheat a tad and bend all and cut to a common length.



If interested here is the build for the CAT

https://weldingweb.com/vbb/showthrea...rbon-Arc-Torch

[farmersammm]

I'm not at all familiar with wood lathes.

My first question would be how this might affect the spindle bearings over time. I figure you did the test without a tailstock just to see how robust the new chuck is,, but I'm not sure the lathe would take repeated use like this. Lot of stuff hanging out there in space without a tailstock.

[Continuum]

Agree. That thought had crossed my mind. My end-use is not this abuse. I’m planning some bowls and wanted a chuck to grip the rim. Once it’s roughed it’s pretty smooth. Of course imbalance will add some grief over time.

Re lathe difference: You’re clearly a top notch lathe operator so you’d know issues in metal lathes. I guess there really isn’t any difference. Only by degree. I had to align the way. The tooling and cutting geometry are no less important in my opinion. Wood is just more forgiving.

In prepping the machine (was my late fathers) the head stock bearing was very tight w no play. If it fails it will be under my hand.

I went back after for more testing and to make more nuts. This time I used a centering pin in the tail stock. So I have very positive drive and good pivot on the tailstock to take off bending moments. This machine is only MT1 and I would have spun the sprue for damn sure. Dad did gall the taper a bit so I’m fighting that until I can ream it clean.

[farmersammm]

I think you've hit it right. I've run across wood turning chucks sometimes on Ebay, and they're just about as expensive as the ones for a metal lathe.

I'd be a nervous wreck with that chunk of wood whacking away at the chisel That has GOT to take some getting used to

[Continuum]

I think you've hit it right. I've run across wood turning chucks sometimes on Ebay, and they're just about as expensive as the ones for a metal lathe.

I'd be a nervous wreck with that chunk of wood whacking away at the chisel That has GOT to take some getting used to

It’s not too bad. The tools are long. They’re designed to anchor against your hip. The roughing gouge is used to knock the corners off. Really no different than working square stock in your lathe.

Ran this this morning. Here I roughed the maple with the tailstock centering bit, then I parted the rough end, then removed tailstock center, changed to Forstner bit. The chuck held nice and square. I was able to make all drilling and even part the remaining two.

[farmersammm]

I used to work with wood quite a bit. Built most of the furniture in the place. Sometimes I miss it, but I really don't have a big enough house to add anymore furniture. And I'm not sure I have the patience anymore. I never used top quality wood................it was all about furnishing the old place, where I used to live 25yrs ago, in an affordable manner.

I built everything with benchtop tools back then. I didn't have a shop, and used to pull all the stuff out on the back patio, and get to it The neighbors never complained about the noise, but would call the cops in a heartbeat when I had folks over for tunes, and brews It's funny how people are. There's nothing more annoying than running a router.............but I guess they thought it was "productive" noise.

[John Koch]

Having done your build and testing, I would build your guard before you turn anything else. If you slip or have a micro second mental lapse, you won't get smacked, you will get shredded. Fully disassembled. I worked in a wood shop 40 years ago that had a chuck like this. When it came apart, it literally took out a whole wall. No one hurt, fortunately. Honestly, looking at your lathe and the rotational mass of this chuck makes me feel uneasy.

[Continuum]

Having done your build and testing, I would build your guard before you turn anything else. If you slip or have a micro second mental lapse, you won't get smacked, you will get shredded. Fully disassembled. I worked in a wood shop 40 years ago that had a chuck like this. When it came apart, it literally took out a whole wall. No one hurt, fortunately. Honestly, looking at your lathe and the rotational mass of this chuck makes me feel uneasy.

Hey John, no disagreements here at all. I’m just testing for now. Was in the co machine shop yesterday talking to the master machinist on some fab issues. Noted a fold over 1/2 acrylic shield on the acer lathe. Was thinking along those lines.

Curious about your design and the fail to learn more. Any pics or more you’d share about it? The web is replete w diy wood crafted chucks but not much in the welded steel realm.

Here is the backside welds. I’m pretty happy w the burn in. I have good fusion. Plus when the jaws grip they deflect outward due to elastic deformation. They return upon release. I estimate from wood denting and 6000 psi wood yield (pine) that the jaws bind at around 500 pounds each. So each arm has a 500 lb moment arm torquing backward.



Regards

[farmersammm]

Put an indicator on it to see where it's actually bending. I'd bet the arms are not bending............the plate is probably bending. At least, looking at it, that's where I'd expect it to bend.

The real issue, if there is any...............fatigue.

There's probably a lot goin' on when that thing spins, and the chisel impacts the wood. Micro movements with a very high frequency.

A failure, if it ever occurs, would probably be in the base plate where it meets the weld. You have a transition there. The weld, and round stock, are stiffer than the plate. So cracks, or deformation, will happen in this area I'd imagine. A failure might look like an under weld failure, making people blame the weld, but the failure is actually in the plate itself along the boundary.

Clamps of any kind are about diminishing returns. They yield as they're tightened, so the actual clamping force is less than the screw is capable of. You reach a point where all the force is dissipated in yield.

Given that we have a limit on actual clamping force, then we have to figure out where the safe stickout falls. In general, with metal, the rule of thumb is around 3 to 1..............or 3 times the diameter of the material. This depends on a lot of variables, but it's easy to remember.

The radial force applied by the tool remains constant, but as we go further from the chuck face, we're starting to deal with leverage. The tool force is multiplied. The workpiece will either tend to climb over the cutter, or the workpiece will deflect......giving a tapered cut. When cutting metal, this requires spring passes to overcome, dunno about wood turning.

So, in short............you go a long way in eliminating possibility of failure by keeping stickout to a minimum, keeping clamping force to a minimum(reducing deflection), and tool pressure to a minimum.

A long winded reply

[Continuum]

Put an indicator on it to see where it's actually bending. I'd bet the arms are not bending............the plate is probably bending. At least, looking at it, that's where I'd expect it to bend.

The real issue, if there is any...............fatigue.

There's probably a lot goin' on when that thing spins, and the chisel impacts the wood. Micro movements with a very high frequency.

A failure, if it ever occurs, would probably be in the base plate where it meets the weld. You have a transition there. The weld, and round stock, are stiffer than the plate. So cracks, or deformation, will happen in this area I'd imagine. A failure might look like an under weld failure, making people blame the weld, but the failure is actually in the plate itself along the boundary.

Clamps of any kind are about diminishing returns. They yield as they're tightened, so the actual clamping force is less than the screw is capable of. You reach a point where all the force is dissipated in yield.

Given that we have a limit on actual clamping force, then we have to figure out where the safe stickout falls. In general, with metal, the rule of thumb is around 3 to 1..............or 3 times the diameter of the material. This depends on a lot of variables, but it's easy to remember.

The radial force applied by the tool remains constant, but as we go further from the chuck face, we're starting to deal with leverage. The tool force is multiplied. The workpiece will either tend to climb over the cutter, or the workpiece will deflect......giving a tapered cut. When cutting metal, this requires spring passes to overcome, dunno about wood turning.

So, in short............you go a long way in eliminating possibility of failure by keeping stickout to a minimum, keeping clamping force to a minimum(reducing deflection), and tool pressure to a minimum.

A long winded reply

Hey Farmersam, Nope. Not long winded. Makes sense. I chucked up a knuckle to act as a drive surface to clean off a rotary tool holder. I used a center spur on the unsupported end. I tighten the clamps. As you indicated, they deflect once you bear into the wood. I looked and the 90 degree angles of the arms were preserved so as you’ve indicated the plate tips are deflecting. They are elastic and return to the undeformed state when I loosen the screws. So there are slight lifting and tearing loads on the welds. I don’t think the forces are more than 500 lbs on a screw based on the yield stress for wood. Not concerned w the welds letting go at those loads. The arms are 1/2” and the faceplate is 1/4 thick.

Good comments and rule of thumb unsupported per length. The plan is to use this as positive engagement and not run unsupported unless I am drilling w tailstock or cleaning off a bowl face.

My plan is to turn a series of billets w standard ID holes so I can grip small diameter stock.

Also I am running this on lowest speed 750 RPM only. No plans to go higher. At 4 inches radius, this is 63 g. Assume the arm weighs one pound and this is 63 lbf. Pretty low inertial loads. No consideration for tool impact, deflections etc.

Planning swing arm semicircular guard that lifts into position from the front. Guard noted in second line of post

Regards

[Xsbank]

Great idea but it gives me the collywobbles just looking at all that stuff spinning by. It's as bad as me attempting once to tighten the packing gland on my 2.5" shaft with it in gear and getting the wrench jammed and it getting red hot and sparks were flying instantly. I survived, the shaft did too and I learned a valuable lesson!

Don't use it until you've guarded it! Your �� is too valuable to sacrifice it to a sneeze.

[Continuum]

Updated chuck design here. Still needs one more mod to be able to grip a bowl tenon. Works nicely. I’m able to loosen one jam nut and tighten the other to get the work centered.

I turned down the 1/2 UNC and added a 1/4x20 thread to capture the jaw. That way I can tighten down without it spinning.




Here was some square bowls I made at Christmas. These are very much prototypes which is why they are made from pine. This was just to get a feel for the process and learn what works. I chickened out on going thinner.

[Continuum]

FYI guard is completed and in operation. Will post that next.

[Shootr]

David Barkby has a booth at a yearly pop-up art exhibit in my area. When it comes to dangerous turning - this dude takes the cake!

[Continuum]

David Barkby has a booth at a yearly pop-up art exhibit in my area. When it comes to dangerous turning - this dude takes the cake!

Maybe not...

[In Utopia]

Nothing wrong here, even got steel toe Crocks.

[Shootr]

Maybe not...

I stand corrected...

[davec]

Interesting ....and yowza! Yeah you need to guard the hell out of that. That will rip your arm right off if you slip. BTW, don't use acrylic. You want polycarbonate. Though they may look similar (aka clear plastic) PC has like 100x the impact strength of acrylic. No, I don't have the numbers handy and am too lazy to go look it up, but the difference is HUGE. PC is what you want when impact strength is important.