Welcome to LinuxCNC.org

I'm trying to arrange the project tasks in a prioritized manner, and for now, turning the spindle and moving under CNC control is the priority, but I do have bellows-style way covers in my shopping cart and I selected some that were wide enough to protect the headstock end of the lead screw.

I doubt I'll use anything close to the full 24" between centers. I anticipate short run production work consisting of 1.5" to 2" long parts turned from 1" or less diameter steel bar stock, and even the incidental shop uses for the lathe will probably be short pieces, bushings, etc. However, I'll try not to have the CNC conversion eat into any of the lathe's capacity.

Speaking of capacity... I was hoping for 6" of cross slide travel and that was the first thing I checked when I made the trip to purchase the lathe. I was ecstatic to find 8.25" of travel. I can get a true 8" of motion in the X direction, and that's going to greatly benefit my ability to use gang tooling for nearly instant low cost tool changes.

Despite the lack of curb appeal, I was also very happy to find tight gibs with free movement but no apparent slop or play, and no obvious evidence of saddle wear, at least to my inexperienced eyes.

Thank you to all who have been contributing ideas and suggestions for my first CNC conversion. I hope to make some positive contributions to this community when I have some experience that would be useful to others.

BruceLayne wrote:
Converting the X axis is much more difficult than the Z. (In fact Z axis conversion is so easy that I can see strong arguments for doing it with a manual lathe just to eliminate the changegears)

FWIW This is how I did my lathe:
www.cnczone.com/forums/mini_lathe/63621-...ide_ballscrew-2.html

You look to have a lot more space above the leadscrew than I had, so might not be quite so tight for space.

I also had a lack of room at the back, so a rear-mount motor wasn't possible.
If you can rear mount a motor then a very rigid solution which doesn't limit the screw size by what ball nut will fit between the doetails would be to rigidly connect a ballscrew to the cross slide (using a bracket in place of the existing nut), then have a belt-driven, rotating, ballnut mounted on the back of the saddle in angular-contact bearings. . A simple tube (also, optionally, rotating) sticking out the back could protect the ballscrew.

I/O Electronics Ordered!

Mesa Electronics

5i25 $89.00
7i76 $119.00
10' DB25M to DB25M IEEE-1284 cable $12.50

The 5i25 is fairly new. The goal is a product that's more optimized specifically for CNC applications, so it has the features we need, not a lot of capability we don't need, and the cost is a bit less because we aren't paying for features and added flexibility in excess of what we need. It's a solution that's a bit more integrated, and down the road that should translate into less complexity getting it to run with EMC2 or the controller of your choice.

Basically, the 5i25 plugs into the PC bus and has a DB25F port on the back of the computer. The cable connects the 5i25 in the PC to the 7i76, which will be in the electronics panel, which in my case is in the big drawer in the bottom of a roll around cart. The PC and monitor and keyboard are on the top of the cart, and lathe tooling, manuals and measuring tools are in the other drawers. There will be connectors on the bottom back of the cart with cables running to the lathe. The cables power the X, Z and spindle motors, carry encoder signals back to the CNC electronics, carry the end and home limit switch signals for X and Z, etc. The 7i76 card has screw terminals so making connections should be easy.

I've designed a lot of machines, including some big systems with a lot of PC based I/O (Opto 22, etc.), and I don't remember fretting over the hardware decision like I did this time. I entered this thinking EMC2 liked bit banging on the parallel port and the I/O would be easy. Just get one or two inexpensive optically isolated breakout boards for one or two parallel ports and program the EMC2 configuration file to know what hardware was where. Not so.

I probably made it harder than it needed to be. I'm glad I finally have the I/O hardware on order. That's the last big unknown checked off the list. All that's remaining are many little details - custom motor mounts, sensor brackets, lots of wiring, and later on, some ball screws... PLUS, all the big gotchas that I can't see from here.

Lots of work left to do, but I'm well under way. Thanks to Peter at Mesa Electronics for some hand holding and pre-sales technical advice in a couple of phone calls. Thanks also to those online who took time to help me.

I'm meticulously documenting this project, so hopefully I can provide a step-by-step guide that will save those attempting CNC retrofits some effort and a lot of the head scratching I did. I may not produce the very most optimal solution, but hopefully it'll be a good solution that others can emulate if they like.

The 5i25 I/O board is brand new, and Andy is apparently just finishing up the drivers. Thank you Andy! I'll need to do a little double clutching to get EMC2 to like it. I'll need to upgrade from 2.4.3 as installed on the live CD to the new version 2.5, but I'm fairly comfortable with Linux. I wasn't going to network the EMC2 machines, but in anticipation of the need for EMC2 version 2.5 and probably a couple of profile downloads, I ordered a three pack of Ubuntu friendly USB WiFi dongles from eBay last night. Those have gotten cheap while I wasn't paying attention. They're about $5 each! The next live CD version of EMC2 should support the 5i25 board without any upgrade hassles.

I need to devote some serious time to this project. I've been piddling around an hour or two a day, and adding more to the To Do list than I'm crossing off the list. At this rate, I'll never finish.

BruceLayne wrote:
Aye, that seems to be the way. I don't recall the last time I looked at my own retrofit.

It's all a hobby for me, though, so whether it is writing drivers or fettling castings, it's all good.

I hope to be making parts that I can SELL using my new CNC lathe. Writing drivers may be a hobby to you, but it could substantially help put food on my table. No pressure. I should send you a check for the 5i25 driver!

I do hope to pay some of this forward, and be a contributing member of the EMC2 community. I don't want to be a leech.

With the Mesa I/O hardware on order and about ten other orders inbound, it does feel like I'm over the big hump, but it's still a long way to the finish line. I probably won't post a Look At All The Stuff I Did Wrong project thread, but I will post some details of the finished project with an eye toward making it easier for the next EMC2 traveler. Realistically, I'll probably reach a point (or two!) once I dig into EMC2 where I need a little more help beyond what I can learn from reading the voluminous EMC2 documentation and scouring the info on this site. If nothing else, the newness of the 5i25 hardware will probably throw a curve or two at me, but I'll try not to wear out my welcome here. My long term goal is to give more than I take.

On the plus side.... Once I have it all figured out for the lathe, the CNC conversion of my G1006 Grizzly bench mill should be a lot easier, with a lot of cut and paste. I'm already ordering extras of many small parts like connectors, with the milling machine conversion in mind. I'd sell my old Grizzly and buy a well used Bridgeport class mill, but I can't tolerate the idea of moving the Grizzly out of the basement and a Bridgeport into the basement. I don't think I have that in me, so I'll CNC the import mill that I have.

Thanks for your posts as you go through your retrofit. I'm going through the retrofit of an Emco 120P lathe, and have been wrestling with the same sort of I/O issues. Sounds like the 5i25 and 7i76 combo is going to be a good one - it seems expensive at first, but given that it will replace a breakout board with optoisolation, a relay driver board, and provide enough I/O to replace the secondary control board I was considering having to build, all while being reliable, and providing smoother step control, it starts to sound pretty appealing. In my case, the Emco has a gad-zillion inputs and outputs, 5 inputs and 2 outputs alone to operate the 8 position tool turret, not to mention lubricant pumps, indexers on the ball screws, limit switches, etc. 32 inputs sounded liked a lot at first, but as I built my list of required I/O, I think I'll need it.

I'll definitely be following along with your thread, and I'm interested to hear about how it goes, and the process for writing the EMC interface stuff to interact with all that I/O.

-Sam