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Scratch Built CNC Micro Slant Bed Lathe

shooter123456

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Jan 20, 2016
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#1
A few months ago, I realized that I am constantly needing fasteners and other small parts that halt a project in its tracks. Everything from your regular 1/4x20 screws to things like M12x1 lock nuts. I spend a lot of time trying to find these, pay too much for them or buy them in large quantities, then spend more time cutting them to length. I started thinking about a small lathe that would be able to make fasteners for me so that I didn't need to stop projects when I am on a roll and wait a few days to order a fastener or search hardware stores for them. So I started drawing and doing a few simulations and pricing things out and I think I came up with something that will work.

My requirements were:
-Single point threading in steel
-Turn at least 1" in diameter
-$250 or less
-Make a 3/8x16x1" socket head screw in 4 minutes

For the spindle, I am using 2 deep groove ball bearings, an aluminum housing, and a faceplate to mount a custom chuck. I haven't decided what kind of chuck I will use, but it will probably be an ER collet system. For the spindle motor, again not decided but I have been thinking about using a Nema 34 stepper. It isn't the ideal solution, but using a 3:1 pulley, I should be able to get enough speed and torque out of it and threading will be easy at low speeds.

Linear motion for the Z axis will be on a Rexroth 25mm linear rail I got for $30 shipped on eBay. It is 9.25" long and will give me roughly 5.5" of travel. It will use a Nema 23 stepper and an acme lead screw for motion. I want to make one from 12L14 just because I haven't done any acme threading before, but I may just buy ground leadscrew stock and make it with that.

The X axis is still up in the air. I haven't been able to find a pair of small linear rails for a decent price. I will keep looking though. It will either use a Nema 17 stepper or a smaller Nema 23. I will use a leadscrew on the X as well.

I don't need fast rapids for this machine since it will only have about 5" of Z travel and 3.5-5" of X travel. Cutting at 10 IPM with .01" coming off per pass, the 3/8x16x1" screw will need 10 passes to turn it down to thread size, each pass will take 6 seconds, so that will be about 1 minute 30 seconds to turn it to the right diameter. This leaves me 2 minutes 30 seconds for the threading and parting to meet my goal. I am either going to use some kind of gang tooling or a turret for tool changing. I haven't decided entirely yet.

So far my costs and estimated costs are:

I already have
-Spindle bearings - $20
-Z linear rail - $30
-Various stock - $15
-Thrust bearings - $10

Estimated costs to come
-Spindle motor - $40
-Z axis motor - $20
-X axis motor - $15
-X axis rails - $30
-Z axis leadscrew - $5
-X axis leadscrew - $5
-Power supply - $20
-Spindle motor driver - $30
-Z axis driver - $15
-X axis driver - $10
-Breakout board - $10

Motor for tool changer - $15
Driver for tool changer - $5

This has me a bit over budget, but my initial budget didn't include the tool changer. To get the budget reduced, I have a few ideas. First is with the spindle motor. I might pick up a treadmill for $20 or less and take the motor out of that. Then make an encoder. That would give me more power and cut the price down $50. I have also been thinking of using dovetails on the X axis instead of rails. This will cut the cost by about $25.

Here are some pictures. I welcome questions, criticism and suggestions if anyone has some.

Here is the 3D model of the machine. It is about 14" long.


Here is the spindle machining in progress.


Here is the mostly complete spindle. That is a AAA battery for scale.


Bearings on the spindle.


For the spindle housing, I JB welded 4 .75" pieces of aluminum together. They were cleaned thoroughly, degreased, and roughed up beforehand. They will secured to the base and the spindle bearings will squeeze them together. I am not worried about it pulling apart.


Then I squared it up on the mill.


Then mounted in the lathe 4 jaw to do the majority of the boring for the spindle. That would have been a pain in the butt doing that on the mill.


Here it is bored out before I cut the bearing seats. I did that with the CNC and they both fit well. I indicated on the bottom each time so that they will be perfectly perpendicular to the bottom.


Bearings seats done and spindle base mostly machined. I just need to drill the holes for the screws to mount it to the table.


Here is where it is now. pardon the mess, I was cleaning a set of nasty linear rails I got online and went out to snap that picture really quick. Once I find some suitable rails or figure out dovetails for the X, I can press on.
 

shooter123456

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Jan 20, 2016
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#2
Quick update on this project.

I selected the X axis rails, they are going to be CPC 9mm rails with 3 bearings, 2 in the front and 1 in the rear. I also ordered the motors, I will be using 84 oz in Nema 17s which should have more than enough holding force and torque for the tiny cutting forces this lathe will see. I decided to go with the "600 watt" spindle motor from my X2 to run the spindle. That should have more than enough torque, and it will be pulleyed down from 6000 RPM to 2500 RPM. I am also going to hold off on a tool changer for now. It will use gang tooling and should have plenty of room for a profile and facing tool, a threading tool, a spot drill, and drill holder. That should cover everything I need this machine to do.

I have made the apron for the machine out of .5" aluminum plate and drilled and tapped it for the rail mounting and drilled and counterbored it for the M8 bearing screws. I messed up when generating the toolpath in fusion because I modeled the holes for 8mm which wouldn't give me any clearance. I set the radial stock to leave to -.025" to give me some clearance and it automatically set the axial offset to the same. I didn't realize it had done that so it cut the top face down for now reason. It looks bad, but it will never be seen and doesn't effect the functionality so I am just going to leave it. Please pardon the condition of the shop floor, everything was getting moved around to make room for a car oil change and stuff got jumbled.


Next up is the work on the base plate, drilling a bunch of holes, some tapped, some countersunk. Then I will make the plates that will set it at an angle and the bottom plate. After that it is just motor mounts, cross slide, and the toolholders.
 

shooter123456

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Joined
Jan 20, 2016
Messages
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#3
I have made a bit of progress on this little project as well as gotten some more parts.

First, a latest model based on some design decisions and such. It now has a T slot table and will use gang tooling at least to start. That will give me enough room for a turning and facing tool, a threading tool, a parting tool, and 2 drills, while working with a part .6" or smaller. Given that this machine will mostly be making parts around .375", that will be fine.


I made the table out of aluminum and it has 4 parts and 9 screws in it. I cut the T slot parts from the bottom, then attached them to the bottom of the table and squared them up, and finished machining all of it once it was screwed together. You can't even tell that it is multiple pieces.


I made the 2 leadscrews out of 12L14 steel on my lathe. They are .5"x10 TPI threads. I went with a 60 degree screw just for ease of machining. I think they will work well enough for the purpose I have. If not, I will learn how to do an acme thread and get the thread guages for that and remake them. The stock only cost $1/foot so I can afford to make a few mistakes with them. If acme doesn't cut it, I will probably just get some 1204 ballscrews, but I don't think it will come to that. I also got 2 84 oz in nema 17 motors. For the small amount of force I need and the low speeds, I anticipate them doing the job just fine. I also decided on the "600 watt" motor from my X2 (it was replaced with a 1000 watt treadmill motor) to run the spindle. I will probably do a 3:1 reduction to get the top speed from 6000 to 2000 and bump up the torque a little bit.


I am halfway done with the chuck for the spindle now. It will be an ER20 collet with a backplate that attaches to the spindle face. I made it out of 2 pieces since I didn't have any 2.5" steel stock and I didn't want to spend a ton of time cutting it down. The backplate is aluminum and is threaded in the middle to accept a the chuck portion. It will be turned around and then the collet nut threads and the taper will be cut. The fit between the spindle face and backplate is excellent.


Here is where the little lathe is now. I propped it up on the mill motor so I could see what it would look like once it is slanted.


Here is another picture to show the scale.


I am still waiting on the drivers, breakout board, and a few belts. Hopefully those get here soon and I can get this thing moving.
 
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