[Jdubya]

Hey everyone! This is my build thread. There are many like it, but this one is mine!

I've been lurking here for a while now.... watching, reading, learning, waiting.... I worked in a aerospace CNC shop for a few years, many moons ago and I want to get back into CNC machines. I finally started ordering parts for my build earlier this month. Everything is here now and I started fabrication this week on the base.

Parts:
C7 RM1605 ballscrews
SBR20 supported rails
Nema 34 motors / drivers /power supplies
1.5kw water cooled spindle
mach3 windows pc

Plan:
A) I have a plan to run 2 ball screws and 2 drive motors on the Y axis for the gantry since I've read here you can slave the Y and A axis together in mach 3 . (This would be good.)

B) My other option is to run the signal from the breakout board into 2 separate power supplies and drivers for each motor on the y axis and pray the screws are close enough matched that there is no binding. (this seems problematic as I can't calibrate travel for each motor separately)

C) Just use a single screw down the middle and live with it. (i'm not making airplane parts here)

I know my motors are big (1600oz) I had originally went with the Nema 23 425oz but the seller convinced me my machine was too large for them and I needed bigger. I've read a few solutions here to getting decent rapids from Nema 34's, so I'm not too worried here. (ok, i'm a little bit worried,)

Both of my ball screw threads appear to inter lock with each other really nice so I cant imagine they are far off from each other to cause any binding? (I could be wrong here)

Someday, I may add a small 4th and 5th axis, so option B would be more appealing here to me if it worked alright.

I had a lame drawing but it has already changed a lot since I started building the base. I'm using 3" x 2.5" steel I beam (free drops from work) for the base and my gantry will be 1/2" aluminum plate.

I may post some pics as progress moves forward.

I appreciate any help or suggestions you may have as I still have a lot to learn here.

Thanks.

[Jdubya]

No replies, Thats probably not a good sign..

Or, maybe i'll be ok.

[automationtechinc]

you can use this machine as your reference

https://www.automationtechnologiesin...ne-cnc-router/

Contact me, I will help you

[Jdubya]

.

[Jdubya]

you can use this machine as your reference

https://www.automationtechnologiesin...ne-cnc-router/

Contact me, I will help you

Thanks, we have already been talking. You were the one who talked me into the nema 34's vs the nema 23's.

Edit, your link shows several machines?

[Jdubya]

Progress. The plywood is temporary and just for checking rail movement.

[ninefinger]

Look into LinuxCNC, I'm pretty confident you can slave together 2 axes.

[Jdubya]

Look into LinuxCNC, I'm pretty confident you can slave together 2 axes.

Thanks, i have read alot of good things about linuxCnc. Its good to have options. I am totally unfamiliar with linux systems however.

[Jdubya]

Trying to decide if my ballscrews should go on the outside of my i-beam for stability or on the inside of the ibeam to keep it clean looking. . See pic above.

[Jdubya]

I decided to put the screws on the inside of the ibeam. Then if i switch to a single center screw later, i will be in the right area already.

[skrubol]

I decided to put the screws on the inside of the ibeam. Then if i switch to a single center screw later, i will be in the right area already.

How will you mount the table?
Also, is the 60x40" overall dimensions or travel?

[Jdubya]

How will you mount the table?
Also, is the 60x40" overall dimensions or travel?

The table will have to be mounted from the ends of the y axis, from the ibeam. Once I'm sure i can get the dual screws working, i will work on the table. 60" x40" is the size of my rails and ball screws, (overall machine size) cutting area might be 54" x 34" ,,, best guess.

I got both ballscrews mounted and ready to connect to my rail blocks.

[skrubol]

With the 60" 1605's keep in mind your max RPM on the long axis (critical speed) will be around 800 RPM, 600 with safety factor, around 120ipm rapids. Not terrible, but that's about 25 seconds to traverse the table.
So you aren't going to have any cross members connecting the rails to the table? If so, you're giving up a ton of rigidity, especially when working in the middle of the table.

[Jdubya]

With the 60" 1605's keep in mind your max RPM on the long axis (critical speed) will be around 800 RPM, 600 with safety factor, around 120ipm rapids. Not terrible, but that's about 25 seconds to traverse the table.
So you aren't going to have any cross members connecting the rails to the table? If so, you're giving up a ton of rigidity, especially when working in the middle of the table.

Thanks for the Rpm information. Is it the diameter of the screws that will limit my rpm's? Do they start flexing or whipping?

I will be adding another piece of 3" ibeam down the long axis of the machine that the table will sit on, there will be cross bracing under the table that will tie into the sides.

Thanks for the help!

[Jdubya]

Looks like i can swap out the 1605's for 2005's if my long axis is too slow for a few hundred bucks if needed to gain more RPM's. Are 2005's big enough for that 60" length @ Skrubol for higher rpm's?

[skrubol]

This is where I got my info from:
https://www.zappautomation.co.uk/ecalculators.html

There's a sizeable fudge factor on those calculations I think, so info doesn't always agree, but looks like the RPM limit is linear with the screw diameter. At the 800 RPM (1000 critical,) you could run 2005's, I'd think the torque of the steppers would become the limiting value.

[Jdubya]

This is where I got my info from:
https://www.zappautomation.co.uk/ecalculators.html

There's a sizeable fudge factor on those calculations I think, so info doesn't always agree, but looks like the RPM limit is linear with the screw diameter. At the 800 RPM (1000 critical,) you could run 2005's, I'd think the torque of the steppers would become the limiting value.

Thank you Sir! I am not against replacing the motors either if i need to. I fell into the bigger is better group on my motors. I can always sell them.

[skrubol]

If you want significantly higher RPM's, you'll need servos (or fancier steppers.) Do you have torque curves for your steppers?
Normally for a router if you want faster speeds, you use a coarser pitch screw or rack and pinion (or equivalent.) Trying to get fast speeds with 5mm pitch screws, you end up with impractically large diameter screws. The router I'm building I'm targeting 1100 IPM rapids, but my long axis is only 36" (travel,) and I've got a 3610 screw and plan to use 1.5kw servos.

[Jdubya]

If you want significantly higher RPM's, you'll need servos (or fancier steppers.) Do you have torque curves for your steppers?
Normally for a router if you want faster speeds, you use a coarser pitch screw or rack and pinion (or equivalent.) Trying to get fast speeds with 5mm pitch screws, you end up with impractically large diameter screws. The router I'm building I'm targeting 1100 IPM rapids, but my long axis is only 36" (travel,) and I've got a 3610 screw and plan to use 1.5kw servos.

This is just a fun project to keep me busy. If i can run a 1/4" endmill on aluminum, i'll be happy, even if its a bit slow.

Here is the torque curve image

[skrubol]

If that's full-stepping and my math is right, looks like that graph ends around 800 RPM. My guess is you've got plenty of torque, especially if you're going to have 2 of those. At 600 RPM, it's around 3Nm of torque, so around 3700N of linear force before drag, figure around 3kN per screw with drag. If you've got 2 steppers/screws, that's 6kN force, so.. plenty for a lightweight router.