Need a little help with lathe chuck questions

[tominboise]

Looking at the current Logan Actuator page it seems like your lathe would be in the 200 series. I'd suggest jointing the Logan Group page which is owned by Scott Logan. You could also call Logan Actuator and talk to Scott to make sure which Logan model number corresponds with your machine.

This is the main page for Logan Actuator:

Logan Actuator Co. - Lathe Department

This is the section on the different models.

Logan Lathe Model Number Table

This is the Group page where a lot of the owners share info:

Lathe-List groups.io Group

*********************** Logan Lathe Users Group *********************** For discussion and announcements related to Logan Lathes. Hosted by Scott Logan, Logan Actuator Co. ( http://lathe.com ) Question about Back Gear Adjustment? See https://groups.io/g/Lathe-List/message/146 See our online...

groups.io

If yours turns out to be in the 200 series, this should work:

SPL Logan Lathe 200/800 series Spindle Lock Wedge Block To Remove Tight Chucks | eBay

The Spindle Lock must be slid in from the gear face. With slight pressure, the lock will slip in place. The spindle is then rotated allowing the block to wedge in place. The chuck is removed by placing a wrench on a jaw and turning it off, or your preferred way.

www.ebay.com

I believe you are correct. I actually messaged the seller of the lock you link there, and he confirmed that it will work on my machine. So I clicked the button and got one coming. Thanks for the help.

 

[Jimsehr]

For starters, I think the 4-jaw is more than enough chuck for that lathe. As mentioned, 4-jaws tend to be lighter because they've simply got less parts. I wouldn't hesitate to use that chuck at all. I haven't weighed them, but I know the 8" 3J on my 16" victor weighs more than the 10" 4-jaw I have for it. I have a 10" 3J for it as well, and that's way heavier than the 10" 4J.

As far as the 3-jaw, you've got a couple of things going on. It's hard to tell exactly from the pictures, but looks a touch big for that machine. I'm probably a bit biased, but at one point I wound up with an extra 6" 3J adjustable structure chuck and got an adapter to use it on my 14" Logan. I though the machine ran a bit smoother, with the 6" 3J on it than the 8" 3-jaw, and 10" 4-jaw.

I will say, whoever fit the backing plate for the 3J didn't really do what I'd call a proper job. For starters, having the adapter plate be larger than the OD of chuck simply adds unnecessary weight....and it looks goofy to my eye. They also seem to have left the adapter at full thickness and there's a long way from the face of the plate to where the spindle nose sits. Reducing the thickness of the plate will reduce the amount the chuck sticks out from the spindle and will help prevent chatter. The farther the chuck sticks out, the more likely you are to get chatter when doing things like parting where the's a lot of pressure on the cutter. You could face off something like 1/4" to 1/2", still have enough meat for the bolt heads and plenty of clearance to the front of the spindle. Next up, they didn't turn a hub for the back of the chuck where it has the recessed section. Adding a hub will help keep the chuck centered and you won't get chips in there like you do now (picture of the back of the chuck shows where those chips wind up.

I would turn it down to the OD of the chuck, then face off the extra meat and add a hub for the chuck to fit over. That will get the chuck closer to the headstock, save weight and simply work better.

You could also bore the back plate a bit bigger then the chuck and drill and tap 4
Places and make the chuck into a set true chuck.

 

[RaisedByWolves]

For starters, I think the 4-jaw is more than enough chuck for that lathe. As mentioned, 4-jaws tend to be lighter because they've simply got less parts. I wouldn't hesitate to use that chuck at all. I haven't weighed them, but I know the 8" 3J on my 16" victor weighs more than the 10" 4-jaw I have for it. I have a 10" 3J for it as well, and that's way heavier than the 10" 4J.

As far as the 3-jaw, you've got a couple of things going on. It's hard to tell exactly from the pictures, but looks a touch big for that machine. I'm probably a bit biased, but at one point I wound up with an extra 6" 3J adjustable structure chuck and got an adapter to use it on my 14" Logan. I though the machine ran a bit smoother, with the 6" 3J on it than the 8" 3-jaw, and 10" 4-jaw.

I will say, whoever fit the backing plate for the 3J didn't really do what I'd call a proper job. For starters, having the adapter plate be larger than the OD of chuck simply adds unnecessary weight....and it looks goofy to my eye. They also seem to have left the adapter at full thickness and there's a long way from the face of the plate to where the spindle nose sits. Reducing the thickness of the plate will reduce the amount the chuck sticks out from the spindle and will help prevent chatter. The farther the chuck sticks out, the more likely you are to get chatter when doing things like parting where the's a lot of pressure on the cutter. You could face off something like 1/4" to 1/2", still have enough meat for the bolt heads and plenty of clearance to the front of the spindle. Next up, they didn't turn a hub for the back of the chuck where it has the recessed section. Adding a hub will help keep the chuck centered and you won't get chips in there like you do now (picture of the back of the chuck shows where those chips wind up.

I would turn it down to the OD of the chuck, then face off the extra meat and add a hub for the chuck to fit over. That will get the chuck closer to the headstock, save weight and simply work better.

He’s kinda got part of that baked in with how the chuck mounting bolts are countersunk.

I would want at least 1/4” of land under the cap heads after cutting the register.

I do t mind the backing plate sticking out like that, but it’s a bit of an odd duck all the way around as is.

ETA: yes, that is a nice 4 jaw and will be a good size for that lathe.

 

[G-ManBart]

He’s kinda got part of that baked in with how the chuck mounting bolts are countersunk.

I would want at least 1/4” of land under the cap heads after cutting the register.

I do t mind the backing plate sticking out like that, but it’s a bit of an odd duck all the way around as is.

ETA: yes, that is a nice 4 jaw and will be a good size for that lathe.

True, without seeing it in person and taking some measurements it's hard to be able to tell how much could be removed, but I think there's some room to reduce the stick out and still have enough under the bolt heads as you suggest.

For most work having the chuck sticking out like that won't cause a problem, but I noticed a big difference between two otherwise very similar chucks on my 13" Sheldon. Both were 8" and weighed about the same amount. One was vintage and had the adapter plate really, really close to the register to minimize stick out...it was that old style you see where the chuck is right up against the headstock. That adapter plate was the kind that's flat on the back and has a recess bored for the spindle register rather than a raised section for that purpose. That was also a solid jaw chuck so the work was even closer to the headstock.

I bought a modern 8" 3J that had master jaws with reversible top jaws, and matching adapter plate and it was a lot more like what we see here. The first time I tried parting something with my previous technique I got terrible chatter and had to drop one or two speeds for everything to work smoothly. I did a bit of reading on the topic and the only thing that was different was how much farther the chuck stuck out...simply had more leverage I guess. I went back and took a bit more off that adapter plate and it helped a bit. Now when I fit an adapter plate I leave plenty of meat for the bolt heads and threads, but don't have the chuck out any farther than necessary. My current lathes are bigger and I might not even notice any difference, but I figure it can't hurt to minimize the stick out without going overboard.

 

[RaisedByWolves]

True, without seeing it in person and taking some measurements it's hard to be able to tell how much could be removed, but I think there's some room to reduce the stick out and still have enough under the bolt heads as you suggest.

For most work having the chuck sticking out like that won't cause a problem, but I noticed a big difference between two otherwise very similar chucks on my 13" Sheldon. Both were 8" and weighed about the same amount. One was vintage and had the adapter plate really, really close to the register to minimize stick out...it was that old style you see where the chuck is right up against the headstock. That adapter plate was the kind that's flat on the back and has a recess bored for the spindle register rather than a raised section for that purpose. That was also a solid jaw chuck so the work was even closer to the headstock.

I bought a modern 8" 3J that had master jaws with reversible top jaws, and matching adapter plate and it was a lot more like what we see here. The first time I tried parting something with my previous technique I got terrible chatter and had to drop one or two speeds for everything to work smoothly. I did a bit of reading on the topic and the only thing that was different was how much farther the chuck stuck out...simply had more leverage I guess. I went back and took a bit more off that adapter plate and it helped a bit. Now when I fit an adapter plate I leave plenty of meat for the bolt heads and threads, but don't have the chuck out any farther than necessary. My current lathes are bigger and I might not even notice any difference, but I figure it can't hurt to minimize the stick out without going overboard.

Understood.

Given what’s there, I would reduce the back plate thickness by half and redrill/tap/clearance the bolts up one size while adding the register and bringing it to size with the chuck.

As I said it’s an odd duck as is, but then again I like to complicate life like that.

ETA: Lol, I just went back and reread only to realize you had already proposed what I just mentioned.

Great minds and what not.

ETA#2: went and looked at the chuck again, it does seem a tad big for that machine.

 

[verbotenwhisky]

So, here is my curiosity question, why do lathes ship with smaller 3 jaw chucks for example 6" 3J and an 8" 4J?

 

[G-ManBart]

So, here is my curiosity question, why do lathes ship with smaller 3 jaw chucks for example 6" 3J and an 8" 4J?

I don't consider myself an expert, but at least one factor is that for the same size stock in the jaws on a 3J stick out farther than they will from a 4J. As an example, if you put an 8" 3J on a 10" lathe you can run out of room between the ways and the outer edges of the chuck jaws pretty easily. With an 8" 4J there's a fair amount more clearance between the ways and the jaws. A bonus is the lighter weight of a 4J lets you run a bigger chuck without adding any additional stress on the headstock bearings, etc.

 

[verbotenwhisky]

I don't consider myself an expert, but at least one factor is that for the same size stock in the jaws on a 3J stick out farther than they will from a 4J. As an example, if you put an 8" 3J on a 10" lathe you can run out of room between the ways and the outer edges of the chuck jaws pretty easily. With an 8" 4J there's a fair amount more clearance between the ways and the jaws. A bonus is the lighter weight of a 4J lets you run a bigger chuck without adding any additional stress on the headstock bearings, etc.

Good thought, but my 12" lathe came with a 6" 3J and an 8" 4J and I have an 8" 3J I am building an D1-4 adapter for it I think I will not have clearance issues.

 

[RaisedByWolves]

I don't consider myself an expert, but at least one factor is that for the same size stock in the jaws on a 3J stick out farther than they will from a 4J. As an example, if you put an 8" 3J on a 10" lathe you can run out of room between the ways and the outer edges of the chuck jaws pretty easily. With an 8" 4J there's a fair amount more clearance between the ways and the jaws. A bonus is the lighter weight of a 4J lets you run a bigger chuck without adding any additional stress on the headstock bearings, etc.

You’re pretty much on point with that, however I’m not sure if weight is an issue with the cutting forces involved. Just my opinion.

The real issue is being able to utilize the capacity of the money you spend on the chuck.

There is a limit on jaw extension, but there’s no sense having a larger chuck if you can’t extend the jaws fully.

The 4 jaw is a different animal and is larger as you sometimes need one jaw to be way out there and if it were similar size to the 3 jaw you would be limited in that regard.

 

[G-ManBart]

Good thought, but my 12" lathe came with a 6" 3J and an 8" 4J and I have an 8" 3J I am building an D1-4 adapter for it I think I will not have clearance issues.

Okay, but you didn't ask about a specific machine, so it wasn't a specific answer, just a general concept of why the 3J is usually smaller. You'll probably be fine with an 8" 3J but that's probably the max you'd want to try.

I'm sure different companies have different theories on what size chucks are best for their machines. It seems pretty common for modern 12" lathes to come with a 6" 3J as standard and most companies don't seem to put 8" 3J on until the 14" models.

I actually liked a 6.5" 3-jaw on my 14" Logan best of all for most normal work. The machine seemed a touch smoother, there was less chuck to work around and it was a lot nicer to take on/off. I had 8" 3J and 6J and 10" 4J chucks for it, but didn't use them if I didn't have to.

For my 16" Victor I've got 8" 3J, 8" 6J, 10" 3J, 10" 4J, and 12" 4J....I'm honestly thinking about getting another of the 6.5" 3J for it like I had on the Logan. Set-true style so it was super accurate and so much nicer to take on/off!