[hedgehog23]

hello everyone. this will be my build log , and from time to time ill look upon you guys for help and suggestions.


the mill will be built from steel. thk linear ways and ground ball screws (all from ebay)

iv started on the Y axis. thk 25 linear rails , and a ground ball screw 14-5 pitch

here are a few pictures.






the base has been machined all around and will be flat ground when i get it over to my friends grinder. one side of the base has a ridge/rail machined into it and will become the master ala 5 bears


for steppers i was thinking direct drive from

http://kelinginc.net/CNCNEMA23G540Package.html

G540 3 axis package (One G540 + Three
KL23H284-35-4B (1/4” Dual shaft with a flat) 387 oz-in + one KL-350-
48 48V/7.3A 115V /230V power supply: $494.95


please feel free to add comments or suggestions

[hesham morsy]

happy hunting for the rest of your part

[hedgehog23]

oh and for travel im hoping for

x = 15"
y = 8"
z = 15"

[hedgehog23]

i was hoping someone would chime in on my stepper choice. all my ball screws should be around the same size and pitch, and all with be ground.

is direct drive the way to go? I was hoping so to simplify the build and keep the cost down.

Enough torque? Options?

Thanks

[muddobber76]

What type of spindle do you plan on using? I am slowly doing a mill build myself. Depending on your setup, 380oz stepper may be lacking in torque for the z axis. The z axis column will get heavy very quickly, wich is good for rigidity but a strain on undersize motors. My build will be similar to yours in travel and I am going to incorporate both steel and aluminum to combat this. I am using 640oz for the z. Keep posting and we can work together. Good Luck.

[muddobber76]

Here is the spindle and housing I built. The housing is made from 7075 alum. and the collet is an ER32 design. It will be belt driven.

[jalessi]

Hedgehog23,

What is the TPI of your ballscrew?

By looking at the picture of your ballscrew some sort of reduction will be necessary.

Pulleys and belts are very inexpensive.

Add an additional 20-30 dollars per axis will be money well spent.

Bigger motors = bigger stepper drives.

Jeff...

[hedgehog23]

5mm lead

and im not sure about the spindle. i was thinking of making it removable so i could use a router and a mill head from a mini mill. but i like the looks of the homemade job.

[hedgehog23]

What type of spindle do you plan on using? I am slowly doing a mill build myself. Depending on your setup, 380oz stepper may be lacking in torque for the z axis. The z axis column will get heavy very quickly, wich is good for rigidity but a strain on undersize motors. My build will be similar to yours in travel and I am going to incorporate both steel and aluminum to combat this. I am using 640oz for the z. Keep posting and we can work together. Good Luck.

i plain on using aluminum as much as possible. where ever i wont need to grind. iv also read that others have used larger motors on the z axis

Thanks

[hedgehog23]

5bears went direct drive, any reason why i cant?

[jalessi]

Hedgehog23,

5Bears used really high end servo motors.

There is a big difference between a servo and a stepper.

Stepper motor torque falls off fast as the rpm increases.

You may get away with direct drive with light cuts, and small tooling.

The weight of your Z axis may also become a issue.

Jeff...

[hedgehog23]

are the timming belts zero backlash? i would think some backlash would be interduced with the belt.

what would be the minimum stepper size you would recommend for direct drive?

arie kabaalstra also used direct drive for his machine, although he did say small he would be machining small things, small cuts

[jalessi]

Hedgehog23

Many industrial CNC machines are factory fitted with drive belts.

Backlash is not a issue as long as the belts are tight.

The KL23H284-35-4B will be fine for the X and Y axis, the Z may be a issue depending on the weight of the finished axis with spindle assembly.

Jeff...

[bad bearings]

You could get yourself an air spring for the z axis to reduce the gravitational load. SPC or an auto supply store would have one--for a trunk.

[veteq]

Hey,

in my opinion direct drive with the 380 steppers will do and is in most cases overkill, but offcourse it all depends on your application and design.

imagine you want a perfect system, no tolerances and backlash, a belt always brings backlash in time and it gives an extra travel error to the system
(same as c3 or c5 or c7 ballscrews, the tooth profiles are not ground and precision parts)

Big vmc`s cann use them because they use a servosystem with encoders on the motor and also a linear encoder (scale) next to the table, the computer is constant calculating and adjusting the servo to keep the table in the right position. (thus canceling the backlash and travel error in the mechanical parts.

If you look at the x and y axis, gravity isn`t a problem, since the axis of freedom is in a different direction (in z axis the gravity works in the same direction as the axis off freedom, so the stepper continiusly has to overcome the gravity and less torque cann be used to accelerate and deliver force to mill).

For x and y axis,
the stepper will give torque, this is by the ballscrew converted to a force.
- This force can be used to accelerate (F = m * a)
- Overcome the force generated by milling (difficult formula, but always low force)
- Overcome the resistance to rotate the ballscrew, accelerate.
( moment off inertia http://en.wikipedia.org/wiki/Moment_of_inertia )

imagine, you`re table weights 20kg and you want 10 m/s^2 acceleration,
(This acc. is the same as a fast expensive vmc!!!)
force=mass*acceleration so, 20*10= 200N off force (nothing)

The force needed for the real milling is very low and lets say, never higher then 200N.

Then the force for rotational acceleration off your ballscrew, offcourse it takes more torque to accelerate a 40mm ballscrew then a 14mm diameter.
Most force gets in rot. acc. off the ballscrew.

A ballscrew with a lead off 5mm will generate with your 380 steppers around 2800N off force on the table. so, 2800 - 400 is 2400N left, or 2,4Nm for overcoming momentoff inertia.

This 3 parameters off force cann be easely calculated after a weekend off reading some lecture. This are the main calculations needed for a mill with linear bearings, ballscrews etc. (for the z axis gravity comes in to play f=m*a
a = 9,81m/s^2).

So it will all depend on the weight of your moving parts, needed acceleration and diameter off the ballscrews. For highest speed look at the point in the torque curve off the stepper where it is the same as the needed total torque you calculated. then take a FOS.

Remember that resistence off the linear bearings and ballscrews are almost 0.

regards,

Roy B.

[hedgehog23]

interesting read , thanks Roy. anyone else think the 380's will cut the mustard?

[LeeWay]

I used the keling old style 495's. They are better than the newer ones I've seen there. I used 203V's and a 72 VDC PS. Everything else I used is much the same as yours. I found these are great for X and Y, but was lacking on Z. I wound up using a timing belt and gears from https://sdp-si.com/eStore
Then I was satisfied with it all. Plenty strong now. The other day I was using a 3/4" end mill and found that I bogged the spindle motor before any missed steps. It was bad coding on my part and shouldn't have used it the way I did. Making a 7/8" hole in 1 3/8" thick CRS bar. Smaller EM's work much better.
I was hogging .05" and running it at 3200 RPM @ 25 IPM. Wayyy too much for my little motor.

[hedgehog23]

a few update pictures. im on holidays for a bit so i should get some real work done.





need to pick up some metric hardware , and make up a block for the ballscrew nut.

[hedgehog23]

just looking for some feedback on some spindle considerations.

http://littlemachineshop.com/product...ory=-269978449



combined with a Tormach tooling system basic kit



http://www.tormach.com/Product_TTS_sets.html

then a homemade air actuated draw bar.

top it all off with a belt drive , dc drive vari speed motor.

comments welcomed

[hedgehog23]

im a little concerned over the two speed plastic gears in the housing. id like to use something off of the shelf to save build time but i have my doubts on this one.