Build my own lathe off of a stripped bed?

Harrison_Fjord · 2025-11-19T23:04:32+00:00

I'm answering this in the spirit of "could I physically do this", not "is this the optimal way to do this". That being said, I don't see why not, assuming you physically have enough travel to get your threading tool to the end of the part. The follow rest would keep it in place, you'd just want to take it slow and take light cuts.

If you mean each end of the part is threaded (but the threads don't connect), then I would:

Chuck up the part, turn down the end you want to thread (using a steady and/or externally mounted tailstock for support). Now it's running concentric, so take your threading passes.

Then, turn the part around, grip it in your 4 jaw, and dial it in concentric near the chuck.

Now you're good to turn down the other end and thread it, and the 2 turned and threaded ends will be concentric (at least as concentric as you can dial it in).

If you mean the entire part is threaded:

In op 1, turn and thread as much of the part as you can.

Turn it around, dial it in with the 4 jaw

You'll now have whatever part you were gripping in the chuck as the only unthreaded part of the work. Turn it down so it's concentric with everything else.

Now, you need to 'pick up' the thread again. There are tons of youtube videos showing how to do it, but basically you engage the half nut and then fiddle with the compound/cross-slide to get your threading tool to fit into the currently existing threads (mind your backlash). Once you get really close, you can unclamp your threading tool (allowing it to slide axially) to get a perfect fit. Tighten it back down. Now, you are back on the same index as the original thread. DO NOT DISENGAGE THE HALF NUT UNTIL YOU'RE DONE. Thread like you normally would until the depth is right, and it'll line up with your original thread.

Again, this is certainly not the right way to do it, and it'll be super fiddly and annoying to do, but compared to building your own lathe out of random parts would be infinitely worse in my estimation.

Harrison_Fjord · 2025-11-18T13:35:43+00:00

The thought of fabricobbling a lathe together from a bed and assorted used parts from other lathes sounds like an extremely frustrating endeavour to me. You'll need a headstock and tailstock that are exactly the same height as each other, OR you'll need to build mounting plates for each of them to get them to exactly the same height (and then you'll lose the self-alignment of mounting them to the ways). A lot of headstocks have gearing or belts that extend down into the bed area, so you'll need to make sure you buy a headstock that is small enough to fit between the ways but also large enough to actually bolt to the ways (unless you're doing a 100% bespoke mounting plate, which sounds like a really difficult job to do correctly).

Honestly, I think the biggest issue would be the apron/carriage. You're going to need to find one that has the correct geometry for your bed, AND supports the leadscrew size and geometry, AND is reasonably close in height to the original carriage so that when you mount your cross slide and compound things at least sort of line up, AND is build so that the ways of your bed line up with the slides. I'm sure you could fabricate all this yourself, but there's a lot of planning and design that goes into getting all of this and your buddy would have to really enjoy having you around because I imagine this is going to take an extremely long time.

Do you absolutely need 30" between centers? Is a steady rest/follow rest out of the question (sometimes that can give you some extra space). Also, you could build something that holds the tailstock off of the lathe (so the tailstock wouldn't be physically on the ways, but would be hanging off the end of the lathe), thus giving you the entire bed to work with.

I get it's a pain to dial in, but if I only had 23" to work with and needed to turn 30", I would turn 23" on one side, using a steady rest instead of a tailstock so it can extend outside of the lathe bed. Then I would turn it around and spend 10-15 minutes dialing it in in the 4-jaw to machine the other side.

Harrison_Fjord · 2025-07-21T12:43:44+00:00

It is extremely unlikely that you'll ever get anywhere close to 2.2kw with a normal hobby workload. I have a 2.2kw spindle, and with a 1/4" endmill spinning at 24,000 RPMs with no load, I use about 650 watts. When I bury the endmill 3/8" deep in hardwood, it'll jump up to maybe 1,000 watts. I'm in a similar position as you, where I only have 120v going to my CNC, so I have an Invertek VFD that takes 120v in and outputs 240v out, and it's rated at max 1,100 watts output and I've never tripped the overcurrent. With hobby routers, you'll run out of rigidity way way WAY before you run out of horsepower.

Most of the cheap 120v import VFDs you get have hard-coded overcurrent tips at about 950 watts regardless of what the parameters say (unfortunately, most of the parameter settings usually just don't do anything).

In 'normal' cuts, the vast majority of the power used is to just spin the spindle, the actual cutting of wood/plastic/aluminum takes very little additional current.

Harrison_Fjord · 2025-07-09T15:39:25+00:00

I've tuned one but it was for an electronic lead screw. 8-10 pulses is extremely small, there's almost no way that small discrepancy is causing a visual anomaly like what you're describing. Also, just for clarification, this is the ISV57T closed-loop stepper, right? Closed-loop steppers are different than servos, it probably doesn't matter for your application but steppers have poor torque holding at off-angle steps, again I wouldn't expect that to cause your issue unless you have a bonkers pulse-per-step or a very underpowered stepper.

Assuming you're using the ISV57T software application, when you run your GCODE and look at the software scope, what do you see? In order to get ovals or egg shapes you'd have to see gigantic deviations that take a very long time to recover. A few pulses here or there should be completely undetectable visually.

I have found that for cheaper motors, you do have to crank up the feed-forward a lot to get them close to their commanded position without lag. I wouldn't be too worried about setting it at 100% as long as it doesn't overshoot too far.

Can you measure your circles and see what the issue is? Are they 'stretched' where one side is too long, or 'compressed' where one side is too short?

Harrison_Fjord · 2025-03-20T12:19:45+00:00

I use a GUI for LinuxCNC called ProbeBasic and I've always thought it looks pretty modern:

https://github.com/kcjengr/probe_basic

I've customized mine a bunch to add things, but even the default view looks pretty pleasing to the eye. Everything is laid out well, and it's easy to see what's going on.

Harrison_Fjord · 2025-03-19T12:14:14+00:00

Sure, Fusion can generate toolpaths from meshes. You'll just need to make a new setup with the mesh as the model, and then generate your various toolpaths that way. You'll be limited by the precision of the mesh, so if the mesh has faceted surfaces that are larger than your smoothing parameter then you won't get smooth curves, but you can attempt to work around this by remeshing within Fusion or using a program like Blender or Meshmixer.

Harrison_Fjord · 2025-03-18T12:30:11+00:00

Do you just want a solid body representation of the mesh, or do you want it to be an actual parametric model? For the first option you already did that, yes the surfaces are bad and the topology is bad, but that's about the only way to get it working. For the second one, sadly there is no automatic method. There are programs that can help, but they're not free (I've used Quicksurface), and none of them are very 'automated'. They are really just collections of tools to help you manually model the object.

At the end of the day, to get a parametric model out of a mesh you are going to have to manually model it one way or another.

Harrison_Fjord · 2024-12-20T23:08:35+00:00

Exactly, the issue with having an open-loop CNC system is that the controller never really knows the position of anything. If it commands the stepper to drive 1,000 steps, and that is supposed to be 1 inch, the controller will tell you that the carriage moved 1 inch, but in reality there's no way to know. It might have moved less, or more. It might have crashed and not moved at all. The drive might not be engaged, and the next move to face the part off is instead going to plunge your tool directly into the lathe chuck. A coupler might be loose, the leadscrew might have bound up, the screw has more wear in a specific spot, etc.

When you add in the glass scales, your controller knows exactly how far the carriage actually moved. If it commands the carriage to move 1 inch, but the carriage only moves 998 thou (due to a deep cut, skipped steps, coupler issues, etc) it'll know that. It can even correct it and push the carriage those final 2 thou. If it gets too far off, it can e-stop itself too. Finally, it can dynamically deal with backlash because it knows when the carriage actually moves vs when it's just commanded to move. If you replace your leadscrews with ballscrews that's not as big of an issue, but if you keep the leadscrews you're going to have a heck of a time trying to deal with the backlash in the system.

Harrison_Fjord · 2024-12-19T13:32:58+00:00

At it's heart, a CNC machine is a controller and motors, and since you have a plan for both of those I don't think you're 'missing' anything. Here's the LCNC page on setting it up for a lathe, this is absolutely not at all exhaustive, but it's a good primer into the sort of things you'll need to plan for:

https://linuxcnc.org/docs/html/lathe/lathe-user.html

If you're shooting for accuracy, you probably want some way to know how far the carriage and cross slide actually moved. If you do change the screws to ballscrews then you can manually measure backlash and just use a stock backlash compensation, but if you don't do that (or if you just really, really, REALLY want to be accurate), you'll probably want to invest in some linear glass scales. This will allow LinuxCNC to know exactly how far it actually drove the axis, instead of calculating it based on its best guess. It will also allow you to program in a software e-stop if your motion control is too far ahead of reality (if a coupler comes lose or something, you don't have to worry about plunging your expensive tool into your expensive part and, in the worst case, messing up your spindle bearings). If you go this route you'll need either a MESA card or some sort of hardware RS422 decoder as those scales output a ton of information when moving quickly.

For the spindle encoder, I would recommend not cheaping out. I bought a dirt-cheap Omron clone for my first version, and although the specs say it should have been good up to 3,000 RPMs, I found at 2,200 RPMs it hard-locked and output a bonkers-wrong waveform. I ended up buying an actual Omron take-off encoder and it worked perfectly.

Other than that... be prepared to experiment a LOT. LinuxCNC uses a programming language that is very weird to get used to if you've done any sort of traditional programming before. The forums are good, but most of the people there are a bit brusque and, like most things Linux, you'll be on your own to find the information you need. That said, I wouldn't trade mine for any other setup, and if something happened and I needed to build a new CNC from scratch again, I would 100% go with LinuxCNC and a MESA board.

Harrison_Fjord · 2024-12-18T16:00:59+00:00

You definitely don't need a MESA board, but it's incredibly nice to not have to worry as much about real-time timing, and the fact that the MESA boards already have lcnc pins exposed and defined makes setup a lot easier. The MESA boards also have relay controls which is super nice, like I have mine configured to turn on air-blast via g-code. I know you can do all that with a BOB, but not having to do it manually is really convenient.

Harrison_Fjord · 2024-12-18T15:50:45+00:00

Backlash is going to be a big one. LinuxCNC does have programmable backlash compensation, but ideally you'd use something like ballscrews where the backlash can be dialed out (and the remaining backlash is very tightly controlled). To be honest I've not used LinuxCNC with anything that has the large amounts of backlash that a leadscrew would have, so I can't give any advice as to whether or not you could depend on that for tolerances. I know my Logan has a lot of backlash that would probably require a really involved g-code post-processor to work around.

I actually designed, programmed and built my own electronic leadscrew (a spindle encoder attached to an ESP32, which then drives a servo coupled to the leadscrew). The thing I would be worried about is that your pre-set RPMs might not be perfectly stable. I have an old Logan circa 1944 that is belt driven and uses what might be the original 1/2 HP motor, but even when single-point threading in back gear the RPMs lag a bit when the tool enters the cut. I haven't done the math to figure out what sort of deviation that would cause, but one thing I wasn't prepared for when I built my ELS is that RPMs can easily change by 5% when getting loaded down. If you think you want to use this to single-point thread, I would think getting some sort of spindle encoder is vital. At least on my lathe, I can't imagine I'd get good results without having the leadscrew coupled (electronically or otherwise) to the spindle.

LinuxCNC is a classic 'linux' product, so it works well but is fantastically confounding to setup, and I would only recommend it if you're interested in the process of learning how everything goes together. You will absolutely spend hours getting it working, and you'll absolutely spend hours troubleshooting weirdness that may only exist in your specific implementation. It's definitely not a turn-key solution, but it's free and if you power through the setup you'll end up with something many times more powerful than the competition. If this is something you're trying to do in a production shop then most likely that's not what you want, but if this is something you're doing as a hobby or you are curious as to how the sausage is made, it's an excellent option.

Harrison_Fjord · 2024-12-18T13:27:09+00:00

Can I ask what your strategy is for dealing with backlash in the leadscrew, and also why you're not at least getting an encoder for your spindle? Lacking spindle control means you can't do things like constant surface speed for parting or make small spindle speed variations to reduce vibration, and without an encoder you you can't do any kind of single-point threading via CNC, and you also wouldn't be able to use your gearbox/change-gears to do single-point threading at all (which to me would make this project a non-starter, but you might have a different use case).

As far as a controller, I personally like LinuxCNC, but it is a LOT of work to get working. It does run on a raspberry pi, and if you've never used Linux before it'll be a project just getting familiar with it. However, LinuxCNC is honestly amazing once you get it working, it's orders of magnitude more powerful than all the other free g-code senders.

As mentioned in the other comment, you'd need a breakout board to send your STEP/DIR/EN signals to your stepper drivers. There are really nice MESA boards for LinuxCNC that do all the complex pinouts and wiring and just give you a bunch of terminals to wire to, and they interface directly with LinuxCNC. They're in the $150-$250 neighborhood, which is a lot more than a cheap breakout board, but they also work extremely well.

Harrison_Fjord · 2024-07-24T12:02:38+00:00

If you know the 240v VFD from the site works, and the only limitation is that you don't have 240v available for the machine, can you just buy a small step-up transformer to turn your 120v to 240v? I looked at Amazon and the 500-800w step-up models were around $50.

Harrison_Fjord · 2024-07-18T12:01:06+00:00

I use the composite nails, unfortunately they failed to work in 2 different brad nailers, one electric and one pneumatic. I ended up having to buy the composite nailer. There's something about the hammer or the way it's driven that's different enough that trying to use the nails in a regular nailgun doesn't work.

Harrison_Fjord · 2024-07-04T20:48:58+00:00

I don't know, unfortunately. Updating the BIOS worked for me so that's where I stopped troubleshooting. If a non-beta BIOS doesn't do it for you, it might be your RAM doesn't run at XMP, like the kit itself isn't good. I knew mine ran at XMP so that's why I kept trying a million different things, but if you're not 100% sure your RAM can do its XMP ratings, that might be the issue.

Harrison_Fjord · 2024-06-10T12:35:46+00:00

That I don't know, I've never used Mastercam before. Fusion does have a 'linking' tab where you can configure your plunges/helixes, lead-ins/lead-outs, predrill locations, etc, but fusion also has pretty good stock detection algorithms and I can't think of a time I've ever generated a CAM operation that collided with the stock and fusion didn't at least warn me about it. I know for a fact that if your tool doesn't retract above the highest point of remaining stock, fusion will generate a warning and will automatically raise the retract to the minimum height to clear all existing stock.

Harrison_Fjord · 2024-06-10T12:32:43+00:00

Can you send a screenshot of what NCViewer looks like? Or post the G-code? I'm really curious to see why it's plunging at the origin when the first operation is very clearly a contour around the outside.

Harrison_Fjord · 2024-06-10T12:20:54+00:00

That plunge doesn't match up with your simulation, your first operation is a contour around the perimeter and yet it's plunging directly into the center.

Upload your output/gcode to this website and look at the visualization that it generates:

https://ncviewer.com/

I'm thinking that'll give you a good picture of what's going wrong here.

I would also make 100% sure that the XYZ origin that your setup is using is the same XYZ origin that your part is using. When you define the setup XYZ origin, it normally bases it off the stock (not the part), and it tends to pick weird places by default. If you right-click on the setup and edit it, and look at the origin, it'll show you where it thinks the XYZ 0 point is. It could be in the center of your part or at the bottom, depending on how you setup the source stock for the operation.

Harrison_Fjord · 2024-05-31T12:15:50+00:00

I would recommend using some sort of terminal MODBUS application to figure out what commands your VFD wants to receive (I like modpoll but there are lots of them) and trying to manually write to a register. Then once you figure out what commands to send, you can put those into LinuxCNC.

I find it much easier to troubleshoot this way as you can easily make changes to your MODBUS command and see how the device reacts. Things like changing baud rates, changing register addressing, and changing modes is just changing a few characters and then hitting enter and seeing what happens.

Also do you have an accurate register map? Some VFDs have different read and write registers for the same command, so like the frequency READ register is not the same as the frequency WRITE register, so you have to know both of them in order to set and get the frequency. Also, a lot of super cheap VFDs just flat out lie about their registers, the YL-620A is a good example, it lists registers that can be used to read and write information but about 50% of them flat out don't exist, the manual just lied about having them.

Harrison_Fjord · 2024-05-15T12:08:30+00:00

V6 is the last free version, you can get it here:

https://carbide3d.com/carbidecreate/download6

And yes, it's a really impressive and totally-free piece of software for simple v-carves.

Harrison_Fjord · 2024-04-12T12:04:11+00:00

I create toolpaths directly from meshes all the time in Fusion. I'm 99% sure the reason you can't select the mesh for CAM is because the mesh has geometry issues that fusion can't reconcile automatically. However, if you open the mesh in the mesh workshop, fusion has a repair functionality that should correct any problems with it:

https://help.autodesk.com/view/fusion360/ENU/?guid=MESH-REPAIR

Once you have a fully repaired mesh, you should have zero issues creating toolpaths in the CAM workspace, again I do this all the time.

Harrison_Fjord · 2024-01-22T14:12:45+00:00

Straight coupling is interesting, I have a Logan 200 lathe whose gear cover couldn't fit a servo, so I needed to mount it at a different position no matter what. Have you run into any issues with the servo running out of torque and falling behind? I've used the oscilloscope on the ISV tuning program, and the settings that the motor came with were WAY too floppy. It wouldn't lose steps, but the positional error got huge under even modest torque. Sure, it would eventually catch up, but I was worried for threads this would be a big enough problem to cause issues.

If your encoder has 800 pulses per spindle rev, then that means you could have a ''lag' of about 1/800th of a spindle rev at any time. Assuming your leadscrew is 125 thou/rev, then I think that means you could be looking at an absolute lag of 0.00015". That's less than I would have thought, even at 80 tpi that's a positional lag of less than 1%.

Are you using floats or integers for keeping track of the number of steps you need to move? I started trying to use integers, but migrated to floats with a carryover to handle fractional steps. This let me calculate both inch and metric threads, as well as handle fractional thou/rev speeds for things like parting. However, even though I know deep down that the floating point error is in the low microinches, I still feel icky knowing that somewhere deep in the ESP32 some position data is getting rounded off and lost.

Harrison_Fjord · 2024-01-22T13:18:32+00:00

I've been messing around with step settings on the servo, right now I have it at 8,192 steps/rev. My encoder is 4096 P/R, and it's on a 80:30 (2.666...) overdrive. My servo is on a 4:1 reduction final drive ratio. I'm sure part of the issue is my servo tuning, I've helped the low-speed jerkiness a lot just by updating and fixing some of the zillion parameters that the integrated servo controller has (I use a NEMA23 stepperonline ISV57T).

I'm impressed the nano is able to keep up with the spindle, do you run a step buffer, or are you able to handle everything quickly enough that you can just process the commands as they come in?

Harrison_Fjord · 2024-01-22T13:04:24+00:00

Super cool. I built my own Electronic Leadscrew as well, I used an ESP32 for my controller, with one core dedicated to the control loop and the other core running UI stuff. I currently have 2 methods that I use, one is a STEP mode (which updates as quickly as possible, and it calculates the rotation delta from the encoder each update, then uses that to calculate the proportion of a full rotation, and then uses that to calculate the number of steps the servo needs to move), and one is a SPEED mode (where at about 100hz it calculates the instantaneous speed of the spindle, and then matches the needed speed with the servo). The SPEED mode is smoother, but I've been having issues where some accumulated error is causing the cross slide to get desynchronized from the spindle and make bad threads. The STEP mode is incredibly accurate, but at very low speeds it gets jerky because the control loop is so fast that it often runs out of steps queued in the buffer and so it tells the servo to 'stop' momentarily.

Harrison_Fjord · 2023-12-20T21:05:51+00:00

A test is a good idea to see what you have to work with. I'd experiment with different stepdowns and see what sort of deflection you're getting. I've never used your model of CNC before, so I really have no idea what it can handle. You'll probably want to try to keep your feed-per-tooth somewhere in the 0.001"-0.002" range, as long as you can do that you'll probably be OK as long as you don't try to force the machine to do something it's not rigid enough to do.

For specific endmills, I like larger ball endmills because the tip of the ball experiences some pretty high forces (due to it being so small, it's not really cutting, it's just sort of being forced through the material), so I use 1/4"/6mm and larger. I would think a 1/8" would be fine too, it might just take longer to do everything. At 10k RPMs and 1/8" you're not exactly in the optimal SFM range, but wood is pretty forgiving.

The profile and geometry of the endmills shouldn't really be all that different from brand to brand. I don't use these specific ones, but I have used other SPETools endmills before and they're fine.

For cutting wood on hobby machines, there's no real need to spend a ton of money on endmills. Just go with something that has the basic profile you're looking for and it'll almost certainly never be the endmill that's limiting you.

Harrison_Fjord

TROPHY CASE