[TC28] Metal lathe (large scale)

[howitzer]

I have had the idea of a metal lathe bubbling in my mind for a long time, and this is the perfect contest to make it reality. Originally I thought it impossible to do properly as there was no way to make long enough screw for the feed but that changed with the release of 73763 with which can arbitrarily long screws be made.

Another significant problem was the need for a suitable main bearing which can take the weight of the spindle and has a large enough hole through for the bore. This was enabled by the hoop parts 3250 and 77107 along with the steel ball 99948. I tried GBC balls but as expected, the rolling was very rough and not what I wanted for this kind of thing.

While I'm not attempting to replicate any real product exactly, I'm showing here the lathe I bought years ago to give the general idea of what I'm aiming to make:

I intend to replicate most of the important functions such as:

• Variable speed for the spindle
• Centering chuck (not sure yet if three or four jaws but we'll see)
• Manual and automatic feed, manual cross feed and manual top feed
• Thread cutting with automatic feed
• Tailstock

It's a big project though and I have limited time available for building so there's no telling how many functions I'm able to build, but I hope to get it to some degree of completion.

So as the first part of my project I set out to make the main bearing from the aforementioned parts which is shown here:

Few more photos at https://imgur.com/a/RwcEqqJ

Wish me luck!

 

 

[2GodBDGlory]

The scale of that is really cool! Those are some seriously serious bearings!

Would a series of standard 2L worm gears not work for the thread cutting feed? Or maybe the 32L axle that would limit you to just wouldn't be long enough. I was planning on using 2L worm gears for that on my lathe project, but before figuring out whether I could make it work or not, I realized that I don't actually have enough worm gears left over either way, so I think I'll have to leave thread cutting out of my model, unfortunately. (Actually, as I type this, I'm realizing there's another option. Instead of having a full-length worm gear, I could have a full-length rack with a standard worm gear that translates along it. It wouldn't be realistic, but it might be workable)

I can't wait to see what comes of this!

[schraubedrin]

That's incredible!

I love the idea of such a machine built in Lego.

Looking forward to following your process.

[ord]

Nice!

How is the performance of the bearings? It looks like you've kept a 2L space between both the inner and outer rings?

[howitzer]

On 1/17/2025 at 2:31 AM, 2GodBDGlory said:

The scale of that is really cool! Those are some seriously serious bearings!

Would a series of standard 2L worm gears not work for the thread cutting feed? Or maybe the 32L axle that would limit you to just wouldn't be long enough. I was planning on using 2L worm gears for that on my lathe project, but before figuring out whether I could make it work or not, I realized that I don't actually have enough worm gears left over either way, so I think I'll have to leave thread cutting out of my model, unfortunately. (Actually, as I type this, I'm realizing there's another option. Instead of having a full-length worm gear, I could have a full-length rack with a standard worm gear that translates along it. It wouldn't be realistic, but it might be workable)

I can't wait to see what comes of this!

The limit of 32L axle indeed is the reason why I opted not to even try it with the old worm gears. It's true also that you could have the worm gear in the carriage and pair it with stationary rack gears but not being realistic I didn't consider it either.

8 hours ago, ord said:

Nice!

How is the performance of the bearings? It looks like you've kept a 2L space between both the inner and outer rings?

Yeah, the spacing is 2L. I haven't yet built a solid support structure for the bearings so I haven't tested them properly but we'll see when the project goes forward.

[howitzer]

A little bit of progress. I built the gearbox (8 speeds for now, I'm thinking of adding a hi/low selector to double the speeds but we'll see) and positioned it so that it can connect to the spindle. The black banana gears are where the connection happens and they're driven by a pair of 20T gears. I wanted to use 32T gears as that would be more efficient but there's no space between the banana gears and the spindle shaft. The gear shifters are the two DBG 24T gears at the top left, which I'll eventually route to proper shifting knobs somewhere in the front of the machine. 

The whole thing is still very wobbly due to the lack of supporting structure and I don't dare to try running it motorized but turning by hand it works fine. Next I'll get the support up and attach the motors and then we'll see how it works.

 

[Davidz90]

Wow, this is a huge project! Really curious how well will the bearings perform.

[howitzer]

A quick video to see if there's any obvious problem with the drivetrain. Apparently it works at least with slow speeds even with the current quite wobbly support structure. I'm powering it with the 9V train power supply which I intend to integrate into the build.

 

[howitzer]

Another update: I realised that having the spindle driven by both, variable speed motor (using 9V train controller) and multi-speed gearbox is a bit unrealistic, so I decided to drive the spindle straight from the motors with appropriate downgearing. On the other hand, the thread cutting feed requires a gearbox with several speeds so I decided to reuse the gearbox I had already built. The lead screw would also require a significant downgearing relative to the spindle and for friction reasons I decided that the downgearing must happen before power is fed to the gearbox (and from there to the lead screw) so I built a distribution gearbox on top of the spindle.

There's also a half-stud offset with the ring gear that's coupled to the spindle and that require some half-stud magic to get everything properly aligned with the distribution gearbox. The bearing frame and various gears also impose some serious restrictions on building so the frame of the distribution gearbox is a dense mess of connectors but it feels strong and secure. Here's a couple of photos:

 

Here's also a computer render of the distribution gearbox design to show the gearing (note that the 16T gear that drives the 40T gear is missing from the photos above):

[howitzer]

Haven't updated for a while but there's been some progress nevertheless. I've tinkered with the transmission line from motors to the gearbox and from there to the lead screw. I built a mockup of the downgearing needed to drive the gearbox, which I simplified by ditching half of the speeds and added a direction switch. The previous design had a high friction connection which is bad because there's a lots of gears  and thus lots of friction already.

Beside tinkering with the gears I've been attempting to build the chuck. This has been quite a challenge with the requirements of having three jaws and self-centering clamping. My solution is to drive the jaws with a worm gear+rack gear combo which in turn is driven by a ring of banana gears (yellow) sandwiched between more banana gears (black). There's quite a bit of friction but at least in principle it works. There's also some slack which requires idler gears to keep the ring gear in place so it connects properly with the gears which drive the jaws.

I also built a stand to raise the thing higher, though it's not yet connected in any way and just sits on the stand.

Here's a photo:

(Sorry about the mess, I couldn't be arsed to clean the table for photos as I'm going to continue building anyway.)

[Lego Tom]

Just like with metal parts, you can use lubricant to minimize the friction, as long as it's a lube that plays well with plastic. I have used a silicone grease that is allegedly plastic-friendly, and it can make a big difference, plus it reduces noise as well.  

[howitzer]

On 2/9/2025 at 5:39 PM, Lego Tom said:

Just like with metal parts, you can use lubricant to minimize the friction, as long as it's a lube that plays well with plastic. I have used a silicone grease that is allegedly plastic-friendly, and it can make a big difference, plus it reduces noise as well.  

The problem here was the connection of 28T <-> 16T gear which is slightly too tight and thus has high resistance so lubricant wouldn't be of any use there. Eliminating it helped tremendously.

---

Today I've been tinkering with the lead screw connection to the feed and while the 27266 makes for a nice sprocket for the screw to drive, the distance needed requires some annoying connections. Any distance achievable with whole- or half-stud or plate-height connections doesn't seem to work as the distance needed involves half-plate thickness. So I guess there's going to be some strange connections in the feed mechanism.

Here's a photo of the test connection I made:

[howitzer]

Since the last update I've been building with all the time I could spare and as the competition draws close I have attempted to get something presentable done. Here's a photo of my entry as it is now:

As you can see there's a lot missing, most importantly toolholder, tailstock and casing. But the things I was able to build do work to such an extent that I consider this project a success, even if there's much room for improvement.

The final list of features is:

• Spindle on ball bearings
• Motor control with 9V train controller for multiple speeds in both directions
• Gearbox with 4 speeds and direction switch
• Motorized longnitudal feed
• Manual traverse feed
• Self-centering chuck with three jaws

When beginning I thought that the ball bearings might be the most difficult thing to design and I was totally wrong - those ended to be among the easiest parts of the build. The chuck demanded some serious creativity and while it works in principle I'm not satisfied with it, as it has very high resistance and is hard to open or close. Some lubricant would probably help but at this point I don't want to stain my Lego. Another serious hurdle to my progress was the lead screw connection to the tooldholder sled. I made numerous attempts to connect it so that the lead screw can turn constantly and is locked for feed from a switch in the sled, but I couldn't get it to work at all so I had to settle for this less realistic version where the lead screw and the sled can't be disconnected and the switch between manual and automatic feed happens at the gearbox. The lack of casing also makes the whole thing wobblier than it should be, which doesn't prevent it from functioning but is apparent when you try to run it.

This whole project feels like I've been exploring the limits of what can be done with Lego and it has for sure been a great learning experience even if I'm not fully satisfied with the result. Anyway, I hope you like it!

Here you can find some more photos of the progress, also on the failed lead screw transmission thing: https://imgur.com/a/P548tFF

Here's more photos of the finished thing: https://imgur.com/a/kMXrnVE

Here's a video: 

 

[Heppu]

That is some serious amount of gearingin crammed into one block of intricate mechanisms

Since you mentioned it being an interesting challenge, I would like to see and better understand how the mechanism to attatch and fasten a work piece to the chuck works.

 

[Davidz90]

Very impressive! I'd love to see some details of the chuck as well.

[howitzer]

4 hours ago, Heppu said:

That is some serious amount of gearingin crammed into one block of intricate mechanisms

Since you mentioned it being an interesting challenge, I would like to see and better understand how the mechanism to attatch and fasten a work piece to the chuck works.

 

3 hours ago, Davidz90 said:

Very impressive! I'd love to see some details of the chuck as well.

I hope these two photos help to explain it:

In the first photo you see the "key" for adjusting the jaws, which drives both, the worm gear that connects to the jaws and the 20T->12T->20T->banana gear which rotates around the whole chuck, driving each of the jaws.

  

 

[2GodBDGlory]

Really glad to see your progress! I'm glad you managed to get enough put together to get something entered here. Do you plan to continue work on it to add a tailstock, etc.?

There's definitely a lot of complexity going on there!

[HydroWorld Outlook]

Amazing work! I have to say that your project is very well done, especially given the tight TC28 contest timeline. I am very interested in the large and sophisticated bearing system that you used for your metal lathe model. 

I am currently working on a very large colony ship aircraft with shrouded proprotor fan propellers that must spin at very high rotation speeds, faster than any normal LEGO axle would be able to spin inside of a pin hole before melting (due to the friction created when rotating). Therefore, mounting the propeller shafts on ball bearings seems to be the most promising solution for achieving higher rotation speeds with less friction generated.

I have been looking for the most economical way to build ball bearings using LEGO Technic pieces. I've watched the Akiyuki Brick Channel's video but I am very intrigued by your solution as well. Is there a chance you could post more photos of how you accomplished this system?

Thanks so much in advance and once again, excellent work on your model. :)

[howitzer]

12 hours ago, 2GodBDGlory said:

Really glad to see your progress! I'm glad you managed to get enough put together to get something entered here. Do you plan to continue work on it to add a tailstock, etc.?

There's definitely a lot of complexity going on there!

I'll have to see about it. The lead screw transmission is something of a bummer for me as I couldn't get it to work but I have an idea for alternate solution which I wasn't able to attempt as time ran out for the contest. Tailstock would also be an interesting challenge considering it's requires stuff that can't be easily made with Lego (such as drill chuck) so I'll see about it. Building a casing would also be nice.

11 hours ago, HydroWorld Outlook said:

Amazing work! I have to say that your project is very well done, especially given the tight TC28 contest timeline. I am very interested in the large and sophisticated bearing system that you used for your metal lathe model. 

I am currently working on a very large colony ship aircraft with shrouded proprotor fan propellers that must spin at very high rotation speeds, faster than any normal LEGO axle would be able to spin inside of a pin hole before melting (due to the friction created when rotating). Therefore, mounting the propeller shafts on ball bearings seems to be the most promising solution for achieving higher rotation speeds with less friction generated.

I have been looking for the most economical way to build ball bearings using LEGO Technic pieces. I've watched the Akiyuki Brick Channel's video but I am very intrigued by your solution as well. Is there a chance you could post more photos of how you accomplished this system?

Thanks so much in advance and once again, excellent work on your model. :)

You probably could reverse engineer my bearing design from the photos but I'm not sure if you should, considering that it is probably much too large for the project you describe and there's no way it could withstand the forces present when running several thousand RPM so I believe you'll have to think of something else. Unless Lego purism is an absolute must, you could try a third party liftarm with integrated ball bearing.

[HydroWorld Outlook]

3 hours ago, howitzer said:

You probably could reverse engineer my bearing design from the photos but I'm not sure if you should, considering that it is probably much too large for the project you describe and there's no way it could withstand the forces present when running several thousand RPM so I believe you'll have to think of something else. Unless Lego purism is an absolute must, you could try a third party liftarm with integrated ball bearing.

It's not too big at all. The futuristic aircraft I am building is a flying colony vessel and therefore very massively large, so bearings like the ones you've built would be perfectly-sized for my application. That said, however, I do get where your coming from with the RPM, and I am planning to primarily use magnetic bearings, with the steel ball bearings for additional support, to stablize each proprotor fan propeller while maintaining free rotation. Alternatively, if this doesn't work I may use a roller bearing setup with the "banana" gear racks like the one TLG developed for the 42082 Rough Terrain Crane, but reinforced and modified to effectively operate in a vertical (axial) plane when the shrouded fan units are tilted forward for horizontal flight.

Since the proprotor fan propellers will be mounted coaxially (they will contra-rotate) inside shroud units that will tilt 90 degrees, I may also consider using this setup to help support the weight of the shroud when swiveling between the vertical and horizontal flight positions. So even if the bearings can't spin at sufficiently high rotation speeds to work for the propellers, I believe they should at least be useful for the vertical-takeoff-and-landing transformation function, since the shrouded fan units themselves will not need to rotate in complete circles and can be geared down to a lower speed.

In any case I, unfortunately, will need to stick with just the LEGO parts I currently own when building all of this. I will already need to build the colony aircraft's fuselage out of PVC pipes due to the otherwise higher monetary construction costs associated with its massive size, so I can't (realistically) afford all the costs of going out and buy additional professional-grade materials on top of that. And I have explored third-party liftarms with ball bearings, but given the large sizes and weights of the centrifugally-reinforced propellers I am constructing, any Technic beam-sized bearing diameters would be too small and too weak to work effectively.

I don't mean to derail your topic, so I very greatly apologize if my posts appeared to do so (I wouldn't want Milan upset with me). Thank you so much for all the tips and I look forward to any further updates on the Metal Lathe. :)

Edited March 3 by HydroWorld Outlook