[aarongough]

Hey all!

The mod:
The mod basically replaces the rack and pinion gear on the carriage with an ACME leadscrew for moving the carriage. The carriage handwheel now lives on the right hand side of the lathe, underneath the tailstock, much like it does on the Sherline lathes.



A pair of bearing blocks were made up for each end of the lathe to support the leadscrew, with the block at the headstock end sporting a pair of thrust bearings to support the cutting forces.

The mod replaces the powerfeed (see below for why) and allows very accurate control of feedrate and produces really nice surface finishes. It also allows you to stop bashing your hand into the cross-slide handwheel when moving the carriage and vice-versa.

Here's a picture of the surface finish my lathe is putting on 6061-T6 after my mod, much better than I was able to get before:


The backstory:
A few months ago I got the 7x12 lathe which I had been hankering after for a long time. The first thing I did when I got it was disassemble it and start thinking about how to CNC it...

Then I slowly realized that for normal users CNCing a lathe is far less important than CNCing a Mill, CNCing a mill adds so much capability, whereas for small hobby and custom jobs a manual lathe seems to be fine.

With this in mind I went to put my lathe back to factory setup and realized I had thrown out my change gears and leadscrew... what a silly idea that was.

While looking for a solution I realized that I didn't have much need for machine threading, but I definitely had a need to produce fine surface finishes, and the carriage handwheel arrangement was making that very hard, hence the leadscrew.

The next step: A semi-automatic lathe
The next step is to fit a spindle encoder and to built a stepper mount for the leadscrew. I know what you're thinking: "didn't you just say you didn't want a CNC lathe?"... While this is true, being able to have an easily controllable/adjustable powerfeed and the ability to single-point threads would be very nice. The basic idea is that I'm going to write up a microcontroller program that will read the pulses from the spindle encoder, and then drive the leadscrew according to a feedrate specified by the user on a small LCD interface. This will allow different threads to be cut without changing gears as well as easy and fast fine-tuning of feedrates for different materials. It will also allow the concept of an 'electronic carriage lock' by using the stepper holding torque to maintain carriage position rather than a mechanical device...

Basically this lathe is going to become a test-bed for a bunch of ideas I have about a lathe that I want to scratch-build.

Anyway, I realize this post has gotten a little long. All feedback welcomed, I plan to continue to update this thread with my progress.

-Aaron

[hoss2006]

I liked the hank crank there much better too.
The stepper idea is good, imagine you can have the program pause before each threading pass then hand feed in on the X.
Hoss

[ame=http://www.youtube.com/watch?v=lz3BRnzINWA&feature=plcp]5C Collet Lathe.wmv - YouTube[/ame]

[aarongough]

I liked the hank crank there much better too.
The stepper idea is good, imagine you can have the program pause before each threading pass then hand feed in on the X.
Hoss

5C Collet Lathe.wmv - YouTube

Thanks Hoss! I'm pretty happy with the handcrank there too... I may experiment with a faster screw soon (maybe something like 5TPI or so).

I'm looking forward to trying out the stepper idea, there's definitely going to be problems that I haven't thought of yet, but luckily I have the knowledge now to get past most of them I think.

One thing I'm definitely going to do is setup up a carriage stop that is also a limit-switch. That way I'll be able to run the power-feed right up against shoulders without having to 'catch' it at the last minute... Much less stressful for those final passes :P

[aarongough]

I liked the hank crank there much better too.
The stepper idea is good, imagine you can have the program pause before each threading pass then hand feed in on the X.
Hoss

5C Collet Lathe.wmv - YouTube

Also, with the treadmill motor on your lathe: what is the low-end speed and torque like? What is the ratio you have between the spindle and the motor? I was thinking of making a setup very much like yours with no hi-lo box and a belt-drive hooked directly to either a treadmill motor or some other continuous-duty motor...

[hoss2006]

I still have the stock motor on there with a belt drive, 2:1 iirc.
I was thinking of using the controller and motor off of my g0704 on this for better low speed power.
I can't use the hi/low gears with mine because of the 5c spindle but would like to have that
low speed option.
Hoss

[aarongough]

I've been using the lathe for a week or so now with the carriage leadscrew, and so far I'm VERY happy.

I encountered a problem today when knurling a piece: the locking collar I was using to hold the leadscrew in place wasn't able to hang on tightly enough to deal with the forces created by knurling... Luckily I had some 1/2" ACME locking nuts on hand that I bought from ENCO when I bought my cheap leadscrews. This seems to have worked quite well!

I used the lathe today to prototype a pen design. It's such a pleasure to use now as I never have to worry about the dimensions of the part being off due to the carriage rocking, and the surface finish is much improved. Here's a photo of one of today's parts after a light touch with 600 grit sandpaper.



Now I just have to get an anodizing rig setup and I'll be set!

[B-RAD]

I need an anodizing rig to, are you going to buy a kit or make your own? Do you have anything picked out yet?

[aarongough]

I need an anodizing rig to, are you going to buy a kit or make your own? Do you have anything picked out yet?

I'm probably going to go the home-brew route... Turns out you can anodize quite nicely with Sodium Bisulfate: Anodizing and dying aluminum without battery acid - Observations

HomeDepot have the chemical in question (called PH MINUS), and I already have several power supplies, so I'm just going to give it a go!

If you've seen other anodizing kits that are better then let me know!

[B-RAD]

I haven't looked into it much, but I have Sodium MetaBisulfite, wonder if its acts similar? I have it laying around from my gold scraping days.... I'll dig around and learn more about it soon.

[aarongough]

I haven't looked into it much, but I have Sodium MetaBisulfite, wonder if its acts similar? I have it laying around from my gold scraping days.... I'll dig around and learn more about it soon.

Sounds good! I'm looking forward to getting some parts anodized, mainly so they don't scratch so easily...

[SCzEngrgGroup]

If you want a GOOD anodizing kit, look at Caswell Plating.

Regards,
Ray L.

[aarongough]

I've heard a lot of good things about their kits...

[aarongough]

I managed to get the first part of the 'electronic leadscrew' working. Yesterday I built a tachometer using a microcontroller, and it seems to work fairly well!

The video below is a quick demo of the prototype in operation:

[ame=http://www.youtube.com/watch?v=P_8k3yZrnNs]Prototype Lathe Spindle Tachometer - YouTube[/ame]

The next step will be to get a decent stepper and driver, hook them up to the carriage leadscrew and work on getting some synchronized motion! I hope to have results within a couple of weeks!

[pws]

Hi aarongough,

If it's not too much trouble, would you mind posting some of the details of your Hand Wheel / lead screw mod? I am interested in doing something similar, so I would like to know what you did and perhaps, what you might do different having done it!

Thanks,
Paul

[aarongough]

Hi aarongough,

If it's not too much trouble, would you mind posting some of the details of your Hand Wheel / lead screw mod? I am interested in doing something similar, so I would like to know what you did and perhaps, what you might do different having done it!

Thanks,
Paul

Hey Paul!
What info were you after? For the leadscrew mod or for the tachometer?

I have already made a page for the tachometer which is here: Gough - A Spindle Tachometer for the Lathe

I'll make another page for the leadscrew modification and get back to you with the info!

Be aware that link is to a website that is only a few days old, it's hot off the press and only partially complete! So if there's any issues just let me know.

-A

[B-RAD]

I got your reply on your video, I have an arduino, just need the led display, thanks.

[aarongough]

I got your reply on your video, I have an arduino, just need the led display, thanks.

I literally *just* updated my website a few minutes ago with a bill-of-materials: Gough - A Spindle Tachometer for the Lathe

Towards the bottom of the page there is a link to the LCD screen and the sensor.

[aarongough]

I got your reply on your video, I have an arduino, just need the led display, thanks.

It should also be noted that the tachometer is just a prototype right now. If you need a super-accurate tacho then it's probably not for you... If you want to be able to hack it as required, then it probably is for you!

[pws]

Hey Paul!
What info were you after? For the leadscrew mod or for the tachometer?

I have already made a page for the tachometer which is here: Gough - A Spindle Tachometer for the Lathe

I'll make another page for the leadscrew modification and get back to you with the info!

Be aware that link is to a website that is only a few days old, it's hot off the press and only partially complete! So if there's any issues just let me know.

-A

Yep, looking for the leadscrew - I will look for your update on it!

Thanks!
Paul

[aarongough]

Yep, looking for the leadscrew - I will look for your update on it!

Thanks!
Paul

Hey Paul!
Sorry I took so long to get back to you on this, I've had a lot on my plate!

I've put together a blog post with the drawings and BOM for the leadscrew mod. The blog post can be found here: Gough - Carriage Leadscrew for the Mini-Lathe

Let me know if you have any questions!
-Aaron