[dataway]

Got in my first set of linear guides today .. jeez these things are great. Huge advance compared to dovetail ways. I got some cheap Chinesium examples but they appear excellent, can't imagine how my little project would need anything better.

PAV thanks again for getting me on this track ... already working on drawings for a new design using linear guides.

[dataway]

Mini-Mill version 2.0 in the works.

This is a whole new machine. Plates made of 3/4" 6061, 20mm linear rails with four carriages per axis. I got a 2.5hp VFD combination motor/spindle with an ER20 collet. Will still use the original cast iron table top.

So far so good ... the motor/spindle is going to be questionable for steel, I've heard they don't live long cutting steel. Next version may use a BT30 CNC power head under driven 2:1 using the same motor.

Rendering of the design and a pic of what's done so far. Will use the same stepper motors used on the first version.

[Pav8427]

Looks good. If its like any other machime tool, the first job for it will be too big and you will wish you made it just that much bigger.
That will be fun to play with.

[dataway]

Yep, that's already happening in my head as I build it

I have to constantly remind myself this is just a proof of concept machine and I'll be lucky if it machines wax without destroying itself.

I basically drew the line by only using metal I had in stock. Coming up with large dimension thick plate can get expensive fast.

[dataway]

Picked up a 3D printer recently, finding it very useful for fabricating the necessary small bracketry, spacers etc. for the CNC project.

Here is a Molex MLX patch panel ... didn't want to spend $500 for a molex panel punch for each size connector so I got the specs for the punch out and printed up this test piece. I want to have all my cables detachable from the outside of the CNC controller box, so I can now hack whatever size hole is needed in the enclosure and print up a panel with the appropriate punch outs for the cables I want to use.





Printed up this caddy for the stepper motor drivers so I can mount them in the enclosure all in one piece. Drivers are stepped to the rear so I can access all the top terminal screws.





And ... made this small screwdriver holder ... the base comes off and serves at a top cover so it can be thrown in a tool box without losing everything.

[dataway]

Latest update. The CNC controller cabinet is almost done. Made from an outdoor electrical enclosure. Contains the spindle power inverter, axis motor power supply, axis motor drivers and the motion controller CPU. Aviation connectors for the power connections to the axis and spindle motors. 3D printed handle, cord holder, spindle control face plate and various other components inside. Still need to add the spindle power switch, axis motor power switch, limit switch aviation connectors, coolant flow relay etc.

Lots of wires and a lot more to add. Left room to squeeze in a 4th axis if I want to ... although that's kind of an optimistic dream.

Trying to make the whole system portable so I just have to carry my laptop and this controller down to the shop and hook it up to the milling machine.

[Shiny]

wow...

[dataway]

Amazing how much of this stuff is sort of plug and play when you find the right info on the internet .. lots of folks taken this path before I did.

[Shiny]

Understood you aren't flying blind, but still impressive to see you take it on and making so much progress. My prior life required building and programming test equipment that used stepping motors so I appreciate the challenges. Never as easy as following a recipe and takes time to learn when you have little experience. Deadlines didn't help for me, so hopefully doing it as a hobby is more fun and less stress.

Mike

[dataway]

Lots of fun so far. And yeah, a year ago I didn't know the first thing about steppers or servos .. or microprocessors for that matter.
Spent some time watching the oscilloscope monitoring the various signals to the motors and between that and the driver programming began to understand how they work.

About a week or so away from testing the X/Y on the new machine. Then the long project of sorting out the Z axis ... which has to be really, really right to work well.

[dataway]

X-Y hardware is finished and ready for testing. Need to test how fast it can move before stressing the motors, and check the current draw on the motors, check backlash (appears to be zero at the moment). Eventually I'll have to change the table I think ... it's got quite a bit of metal removed on the bottom side ... overzealous tightening of a hold down clamp could fracture it ... but, slabs of pre ground cast iron aren't cheap.

[Pav8427]

Looks nice. If that spindle motor is what I presume it is, sounds like it might work decent. The size of tooling you would be running, there wouldnt be any real load. Not like you are going to be removing pounds of steel per minute. Most tooling should cut pretty free.

[dataway]

I'd be overjoyed if the spindle can handle a 3/8 endmill reliably, even 1/4" should do for most of what I have in mind. Have no idea how long a chinese product like that will last even under no load. It will turn 24,000 ... I'll probably never use it above 12,000 unless I was using a super small mill. Will be interesting to see how the cheesy water cooling works. I've run it dry for a bit and it does warm up quickly at higher rpms.

Should start on the Z axis before long ... looks like I'll be welding one up out of 1/2" flat mild steel, 4" wide is the widest I have in my shop so that will have to do for the forward facing part of the column ... and I'll probably have to mill off 0.060" of that to get it flat. Would have like to go with 6" wide to get some more separation between the linear guides ... but, trying to keep the costs down at the moment and avoid the two hour round trip to the metal supplier. I'll try to design it in such a way that it can be swapped out for 6" wide if I feel it needs it in the future.

[Shiny]

Originally Posted by dataway

X-Y hardware is finished and ready for testing. Need to test how fast it can move before stressing the motors, and check the current draw on the motors, check backlash (appears to be zero at the moment). Eventually I'll have to change the table I think ... it's got quite a bit of metal removed on the bottom side ... overzealous tightening of a hold down clamp could fracture it ... but, slabs of pre ground cast iron aren't cheap.

That looks like a lot of progress!

Would it be possible to use steel for the base and avoid the fracture risk? I'm not sure what part you're talking about...

As to current draw and speed, your application seems "bursty" as opposed to continuous movement (ie fast translation won't happen continuously). Do your drivers have a means of limiting max current? I'm thinking the drivers might limit you more than the motors in terms of "max" stress. With the loads accelerating, the drivers may get pushed if they don't have a lot of margin??

[dataway]

Yep, the drivers have setting to limit current to protect the motors. The motors are about 4amp, 24 vdc ... I oversized them a bit to make sure they would work. And yes the big deal with the motors is fast wind up, and slow down, and "transport" speed when not machining. It's not like they are forcing the metal into the spindle with a lot of force, it's more about the ability to accelerate.

When I was testing them with very little load I couldn't get them to draw more than about 0.20 amps, so seems like plenty of margin.

I guess another thing that is important is "holding torque" ... bear in mind that the motors are what keep the bed in place when the spindle is engaging the work.

I will probably end up replacing the table with steel at some point, I can get 1" thick precision ground steel way cheaper than cast iron. Kinda wanted cast iron for the rigidity and vibration dampening but it's not a deal breaker. And, most CNC machines have moved to drilled tables (beds) instead of the old school slotted type.

I'm trying to seriously over build this thing for something with about a 6" x 10" work area. I'd like it to be very accurate for small detail work, I've got a manual Bridgeport for the large stuff. The closest equivalent I've seen is a Tormach desktop machine ... about $7-8000 ... about 500 lbs I think ... this will only be 150 lbs when done at most .. so I'll have to bolt it down to something heavy

[Shiny]

Good deal on the software-selectable current limit...

It sounds like you will have LOTS of margin unless you start trying to hurl tungsten bricks across your shop.

I would not expect the holding current to stress anything. If the motors are rated for 4A they ought to be bulletproof at less than 1A.

As to the steel vs cast iron, it seems you are talking about the work-table where you will clamp your workpiece. The density of steel and iron are close and so is the stiffness so if dimensions are equal, the only difference may be whether you like slots or threaded holes. The damping is better with iron but spinning at 12K to 24K I doubt it will have any effect on accuracy or stability. I think we had that tawk and you convinced me...

Mike

[dataway]

You're right ... didn't think of that, at those RPMs I wouldn't think it would matter.

[dataway]

Posted a video of the new machine testing the X-Y axis. This about 200" per minute feed rate.

https://www.youtube.com/watch?v=hb9ANtkOLx8

Now on to the Z-axis.

[Shiny]

Congrats on that milestone.. should make you happy!

That looks very beefy for a tabletop machine.

Does the controller handle the accel/decel or are you programming this?

I'm assuming there are no encoders. Do you use mechanical switches to zero and/or prevent overtravel?

[dataway]

I've got open loop steppers so no position feedback ... when I researched that I discovered it's kind of like an "oil thread" on an auto forum. Personally I would like positive feedback on machine position .. but for most the opinion is that if you size your motors and program your stepper driver properly it should never lose a step so the software will always know where the machine is. And since closed loop steppers/drivers cost about three times as much ... I have no encoders

The accel/decel settings are in the g-code machine setup, so you configure them in software ahead of time ... the commands get interpreted by your motion controller (in my case a Teensy 4.1 microcontroller) which then sends the appropriate signals to the driver boxes. So I never have to actually write the code, just set parameters in the software and it generates the code.

When I finish the Z-axis I'll be figuring out the limit switch placement for zero'ing, homing and over travel. I'll get to use my 3D printer to make up little mounts for them. Going to be a definite necessity on this machine ... checking it last night I found that the Y axis travel is about 4 3/8", Z will be about 5", X about 10" ... so very easy to exceed that. Why so small? That's a function of using whatever heavy stock I had in the shop ... if I really like the machine I can get some larger stock for the base and use all the same parts ... should get it up to 6" on the Y, which is what I wanted when I started.

Yep I wanted it as beefy as possible for a small machine ... wait till you see the column, will be a welded up square out of 1/2" steel plate ... weighs more than the rest of the machine. Hoping with some creative shimming I can get accuracy to about .001". Would love it if it will make some nice looking emblems, maybe "engine turned" gauge pods, scale model parts etc.