[hub]

Hi,

Finally got my first prototype working! And did some successful cuts in wood! :cheers:

I built the prototype as fast as I could, as cheap as possible. Success so far.

My plan is to then build a "proper" one and upgrade components. I'm on a tight budget (like most people I guess) which means compromises.

Ok, here is the current prototype:
[Sorry, I'm from Europe so I design in metric units]

General:
- 3 axis'
- Steppers, 3Nm
- Using cheap-o-threaded rod (I'm amazed how accurate the machine works with them, I thought they would be a lot worse than what they are)
- Wood/aluminium/steel construction
- Spindle: 0.75kW VFD, fully controlled by Mach 3. Motor 3 phase 0.75kW
- ER 25 collet


X-Axis:
- Threaded rod, M10
- "slides" 2 x 1000mm length, travel 500mm (bad I know, compared to the length of the rails, but my DIY ball bearing idea was not rigid enough so I had to make them apart by 450mm)..
- square tubing + bearings for linear slides

Y-Axis:
- Threaded rod, M10
- Slides 2 x 1000mm, fully supported 25mm hardened round shafts
- 4 x 25mm Linear bearings, open type
- travel about 800mm

Z-Axis:
- Threaded rod, M12
- Slides 2 x 500mm, fully supported 25mm hardened round shafts
- 4 x 25mm Linear bearings, open type
- travel about 100mm (gantry height not enough to do more)

That's about it in short..

So... here is my "real" machine specs:

- Fully aluminium/steel construction
- X axis 1500mm fully supported 25mm hardened round shafts + 4 x 25mm Linear bearings, open type
- Y axis 1000mm fully supported 25mm hardened round shafts + 4 x 25mm Linear bearings, open type
- Z axis 500mm fully supported 25mm hardened round shafts + 4 x 25mm Linear bearings, open type

- Will still be using the same steppers for now, will upgrade to servos some day

- Ball screws on all axis'

- Rigid enough to mill aluminium with as good accuracy as possible

- A MT3 spindle

I will update this thread when I make progress, but I'm expecting the progress will be slow, since this is only a hobby & I have lots of other things to do as well.

Any advice/help/opinion/anything is appreciated

Added some photos to give some idea of what I have done so far.

[koaDave]

Wow! Looks nice. I guess you have more money in your budget than I do
(0). I work next to a metals recycler, and have been scrounging aluminum and steel to make mine. The foreman there looks out for me and lets me know if something good comes in. I buy it for scrap price. I will use 1/2" MDX (exterior grade waterproof glue) for whatever metal doesn't cover. Where did you get the spindle? I think I can get a VFD motor, and was wondering how to get a collet on the end. Your setup looks like just what I am looking for. Thanks for sharing.

Dave

[hub]

Thanks!
This one is built from "scrap" too. For example, I got the al-extrusions for free if I would disassemble a old machine!
The spindle is at the moment: an ER25 "collet chuck" with a 20mm shaft. From hong kong 15eur + shipping.
Two standard "UCP" bearings from Germany, about 5eur each.
Will be upgrading all this soon...

This might be a good option..:
LittleMachineShop.com - Spindle, 3MT

Hub

[hub]

A closer photo of the spindle, which is currently taken off because I'm assembling the new base. And a couple of pics of the new Z ball screw that just arrived.

[hub]

And the original proto design pics for anyone interested.. It worked but not rigid enough for the spindle weight.. Would maybe work ok with a light router.

[koaDave]

Thanks so much, Hub, for the info and pictures. Also for highlighting the weight factor. I'll check out Little Machine Shop.

Dave

[hub]

This is the design so far, the frame. Lots missing.. The build is actually ahead of the CAD design, I can't remember that happening before LOL.
The reason is that I'm using parts & assemblies from the prototype.

The height of the gantry is adjustable, it will be set pretty low for starters to make more rigid because most stuff I will be machining won't need a lot of Z height. But I can later adjust it higher if more height is needed up to max 500mm (19.7 in).

The whole Z axis' weight is "a lot". Any suggestions on a good way to "fight gravity" and help to lift the mass? Gas spring, mechanical spring, or..?

[hub]

Thanks so much, Hub, for the info and pictures. Also for highlighting the weight factor. I'll check out Little Machine Shop.

Dave

You're welcome!

They have good stuff. Delivery cost me "a fortune" from there to Finland but was very fast.
Also, if you don't have a motor etc. This would be worth considering maybe:
LittleMachineShop.com - Mini Mill Head Assembly 3MT Spindle
Includes everything, spindle, motor, speed control, housing, bearings etc etc.
Would buy it myself, but the shipping is too much to Fin cos of weight..
So I ordered some spindle parts & bearings etc from Germany.

[hub]

Some progress..
Put the X and Y framing together, installed the rails and linear bearings and squared everything using a dial indicator. The squaring took time to get it within +- 0.025mm, the best I could get. I think the aluminium extrusions are not "high precision" but pretty good.

Installed and aligned a temporary X screw (threaded rod) & plastic nut for now.

[koaDave]

I was waiting for the "big boys" to weigh in, but maybe not. My suggestion is only based on thought and not experience, not having built one of these before. I would use springs. Enough tension to hold the carriage at the top of its range, but not such heavy springs that the stepper has trouble moving it down. That way, if the stepper is off, the springs will overcome the lead screw and lift the carriage away from the work. We have a couple of non-cnc machines at work that rely on a gas shock, and after a few years, the shock is shot and useless.

[hub]

I was waiting for the "big boys" to weigh in, but maybe not. My suggestion is only based on thought and not experience, not having built one of these before. I would use springs. Enough tension to hold the carriage at the top of its range, but not such heavy springs that the stepper has trouble moving it down. That way, if the stepper is off, the springs will overcome the lead screw and lift the carriage away from the work. We have a couple of non-cnc machines at work that rely on a gas shock, and after a few years, the shock is shot and useless.

Thanks a lot Sounds like a plan.
The gas springs also require mounting approx double the length of their stroke, which would be a bit of a problem in my case..
I'm guessing "pulling" type springs would be better in this case?

[koaDave]

Yes, pulling springs. Funny, that was clear in my head, but not so much on paper. I don't know much about springs, so cannot suggest size, material, diameter of wire, etc., but should be able to find something. Do you have "big box" hardware stores like Lowe's and Home Depot in Finland? That's where I go for inspiration. And once in a while I find a clerk who really knows about stuff and can suggest things.

I'll check out the mill head. I like the idea of getting everything as a whole unit, although I usually don't like the price. I will have access to a large Ballestrini linear profiler with 8 heads that my company is scrapping out later this year. I will use the rails, linear bearings, ball screws, AC servos, amplifiers and power supply. This is big boy stuff. The individual heads weigh hundreds of pounds and the 18 horse motors spin 8 inch high cutterheads! The ball screw for the main table is about 1 1/2 inches in diameter and about 22 feet long. I say this because these things will be free except for the sweat to remove them. Since my budget is $0, this is good. I'll cobble together what I can, and will just have to ante up for what I cannot. But looking at what is available pre-packaged, and/or individual parts stimulates the ideas, and now junk I see has new possibilities. Thanks for the leads.

[koaDave]

another idea for balancing Z: Quoting Romanlini in "5-axis build full steam ahead" in this forum;

"To balance the Z without adding an equal mass counterbalance I would use a strut or thin piston connected by a hose to a air resevoir, and keep the air resevoir at X PSI to dial in the exact amount of lift. Provided the air resevoir is significantly larger than the piston's total displacement then the pressure will remain pretty constant (within a few percent) and the lift at the Z axis will also remain constant so you can dial it in very nicely..."

A little more work, but elegant, light weight and easy to adjust.

[RomanLini]

Hey! I said that!

Actually I was just browsing through the thread and trying to think of a good way to balance the weight.

A more expensive style of gas-lift strut has a resevoir attached that is significantly larger than the piston displacement, so they provide a relatively constant lift force. The cheaper gas struts like they use of car hatchbacks don't have the resevoir and they have a big difference in lift depending on the stroke position. Of course if your total stroke is only small (3 inches?) then the non-linearity won't matter that much.

Once suggestion I would make is to ditch the cast iron motor and get a much lighter router motor. There are many good routers on the market and most have variable speed control which is another bonus.

[hub]

Thanks for the ideas!

Yes we have a quite a few hardware stores here in Finland, but none with springs the size required. Online stores have some though. Been having a nice easter & not thinking much about this the last few days :cheers:

The Z travel is about 500mm ( 19.5 inches)... Springs would be available that size I think. Gas springs are a bit hard to find with that long a stroke. And those that might have a total length of.. (too much)
Same with compressed air cylinders. I haven't tried to find any, but it seems like a lot of stroke & total length.. Plus my current compressor makes lot of noise, would like to avoid using air in the machine if possible.
I'm still leaning towards the springs so far..

The motor, yes a nice light spindle motor would be nice, but the ones I have found are rated 5.000-30.000 RPM and are quite expensive (I'm on a budget). Also my VFD's max freq is 200Hz, they seem to want 400Hz..
I really don't want anything faster than 10.000 RPM. Why? Because if I have too much RPM I would have to have a very fast feed with very powerful steppers/servos.. That would work well with "softish" wood, foam etc. only I think. ?

I'm not planning to do any high volume production. So, if the machine is slow that's fine with me.
I would like to have decent accuracy though, it's more important to me.

And WOW Dave! That's some serious stuff! You're very lucky!! Keep me updated what you do with them please, would like to see what you make of them
If I'm lucky, hope so..., I'm getting 7 big servos & drives from an old robot being updated. I have to pay something, but practically free. Keeping my thumbs up!

[hub]

Got the machine assembled to a point it can do some cutting (test cuts only, it's not adjusted properly/precise yet except for the X axis).
Works fine so far
Lots of temporary solutions though.. which will be changed one at a time. Like the nice wooden bearing blocks for example! lol

The Z axis works very well without any springs or anything to fight the weight. No problems there. I'm worried that the ball screw or nut would wear quickly if it has that much weight to lift all the time?? If that's the case, I'll put in some springs to help lift it.

Also, I think I have made a design error. With the current design, I'm not able to adjust squareness/parallelism of Y and Z separately. If I loosen the bolts in the gantry it will loosen both Y & Z axis. (Trying to adjust Y square to X & the table; and also Z square to the table).
At the moment it's "ok", but not accurate at all.

And some pics of the current situation.

[hub]

To save money, I'm going for this design, check the picture.., (one less ball screw, ball nut, belt, 2 pulleys, bearings, blocks etc).
This would work I think? Has anyone tried this? If so, is there problems in accuracy and would it be rigid enough?
The steel wire can be tightened pretty hard and will hold a lot of force/weight.

Or is this a bad idea? Should I just go for a second ball screw and connect both with a belt? Or some other idea?

[koaDave]

Wow, Hub, great progress. Also glad the Z weight is not too great for the mechanism. (Yet) As for the steel cable idea, I had a table saw once that used that to keep the fence square. It was rock solid and reliable. Of course, who is measuring thousandths of and inch in woodworking? If the pulleys and mounts were sturdy, I think it would work, but since I have no experience. . .

Dave

[hub]

Thanks Dave
I'm definitely going to try the wire "thing" to see how well it works, unless someone tells it's a no-go

[hub]

I have done some adjustments and further tests. Runs pretty good so far.
Started to mount the wires to fix both sides of the gantry. I have only had the time to start it. I still need to design and machine the four wire rollers.
Will do some more work on it tomorrow I hope.

Some pics to keep it more interesting