Jonny's CNC portal mill

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jonnybischof
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Re: Jonny's CNC portal mill

Post by jonnybischof » August 11th, 2016, 3:52 am

For those who are designing their own CNC mill as well:

The most important thing that I've learned about designing CNC linear systems:

The good thing about precision linear rails is that they have play tolerances in the 5-15 um range, maybe a bit more for the usual cheaper quality stuff. The bad thing about that is, that you will have to align these rails in the very same accuracy range - because there is virtually no play, which means no room for error. Say you have a 0.1mm parallelity error between two rails of the same axis. For one, the axis will not run smoothly, and might even get stuck. And the other thing is, the balls inside the carriage will be worn out quickly and the carriage will get stuck and break eventually.

Now, it's easy to design stuff in CAD 100% accurately aligned. But you have to be able to build that in reality. In my case, I have two 1000 mm long rails that are 710 mm away from each other. How will I get these two perfectly aligned against each other? Note that the frame in between is made up from many different aluminum extrusions, which doesn't help at all :)
This is the main reason why I don't like those "raised gantry" type machines. It's even more complicated to get the rails aligned up there.

Professional machines solve that problem by just making one large cast iron base, and precision-milling the mounting faces for the linear rails, effectively creating nearly perfect reference planes. I decided to try and build my frame able to be aligned instead of face-milled. That will be much more difficult, but I don't need access to a huge CNC work center that can work with such a large piece.

So, what's my plan to get the thing aligned?

step 1.png
I start off with two beams. These are 40x80 mm Misumi HFS8 alu extrusions. They are strong like a tank, and completely impossible to deform with human strength. I put these together, but not tightened 100% yet.

step 2.png
View rotated horizontally by 90° clockwise
Now I add the build platform piece by piece (30x90 mm extrusions) into the frame.

step 3.png
step 4.png
Part flipped around 180°

The build platform parts are linked together using these 2.5mm steel brackets to ensure that they do not bend upwards or downwards.

step 5.png
Add all the platform beams and links, and then tighten everything down, making sure that the angle between the 40x80 mm beams is 90° and the frame is not warped in it's horizontal plane.

step 6.png
Part flipped back 180°
And then add the next 40x80 mm beam (not tightened 100% yet)

step 7.png
Now, these two 40x80 mm beams will hold the X axis rails (added as an illustration). So they need to be aligned perfectly parallel to each other, or my portal will get stuck or be hard to move on one or the other end of the machine.
What I plan to do here is to fix the left 40x80 mm beam and build platform to the rear 40x80 mm beam in a good 90° angle. Then adjust the right 40x80 mm beam (later when fixing it to the frame) until the two opposing beams are perfectly aligned.

I will measure that using a dial gauge (0.002 mm resolution) mounted on an aluminum extrusion beam:
length measurement tool.png
But first I need to add the last 40x80 mm beam, in order to be able to fix the previous one.
Now, the problem about these extrusions is, they are cut with 0.5mm length tolerance (which is already pretty good, but it's not perfect).

step 8.png
Because of this, I made the 30x90 mm extrusions 0.5mm shorter than the 40x80 mm ones. I will then add 0.1mm thick shims to get them within 0.1mm of the 40x80 mm beams.

step 10.png
Then add the final beam. The right side (in this view it's actually the rear side) is still not fixed 100%, because now it's time to do that alignment and secure the frame in place.
Now, the sides marked with red arrows have to be aligned perfectly. The other sides marked blue do not. The shims I added earlier are not needed to make the frame parallel, but to prevent the beam from deforming by more than 0.1mm when tightening down all the screws.

And of course the whole frame can't be warped in its horizontal plane, which is why all of this has to be done on a perfectly flat surface. I know, my reference plate is a bit too small for that, but I have to make do with it. I will also try using a water bubble to check the levelling.

All in all, the plan is not perfect and it will be difficult to do it. But I hope this will work...

/edit:
On most other machines one would first assemble the whole portal, then use the portal as a reference for aligning the rails. I will probably have to leave one of the X rails loose until the portal is mounted and then do that alignment with the portal as well. But for this to work, I need to have the reference faces correct. Other machines would actually leave the whole frame loose and tighten it around the portal, aligning the frame "into" the portal. I could do that as well if nothing else works.

/edit2:
By the way, one very important thing to consider is that during all of this, the ballscrews are not mounted yet, and have to be adjustable to whatever final result there will be. Make sure to consider that as well, because it's just as bad to have a misaligned ballscrew than having a misaligned rail.
The ballscrew has to sit loosely and be aligned by moving the axis up and down all the way, then tighten the ballscrew mounts piece by piece until everything runs smooth. In my case, the ballscrews are mounted with steel brackets that sit on the 40x80 mm beams. These brackets can be shifted to align the screw and then tightened down where they are.

/edit3:
One more thing for me to think about:
Once that frame is all tightened down, it must be strong enough to never deform. The question is - will it be?
I think it will help a lot when I cast 50 kg of concrete into the whole underside of the frame. It will fill all these notches and hold everything together. Once that has dried out, the frame should be solid and super tough. Will talk to my brother about that concrete, he is a construction foreman..
Best regards,
Jonny

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Re: Jonny's CNC portal mill

Post by danilius » August 11th, 2016, 4:16 am

I absolutely love this, thanks for that and keep it coming! As you know, I'm designing a CNC router as well, so in fact all I'm doing at the moment is sitting back and nodding and saying: "Yup, get all my thinking done for me".

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Re: Jonny's CNC portal mill

Post by jonnybischof » August 11th, 2016, 4:25 am

Hehe, it's motivating to know that someone will be interested in the topic ;)

One more thing I could add from my experience so far:
I've had an igus rep in house (I do this stuff from my workplace :) ) and evaluated igus rails. I loved the idea of having a dry linear system without lubrication, and which would be impervious to dust and dirt. Also, their double rails are easier to align because you already have two rails in parallel, in one part.

But there is one drawback to igus that turned me off: These parts have a huge amount of play compared to the Misumi linear rails. The igus website calculated a to-be-expected "wiggle" play in my portal of up to 0.3mm which is completely unacceptable.
While it's possible to reduce play in an igus system, this will also increase friction (because it's plastic rubbing on metal, not balls rolling on metal) and make the whole thing very... unelegant?
Best regards,
Jonny

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Re: Jonny's CNC portal mill

Post by danilius » August 11th, 2016, 4:36 am

I had an igus rep come round to my place and had a look at those rails. What appealed to me was the fact that that they can handle dust and so on without a problem. They won't get gunked up because they run dry. They can also be adjusted, but I found that if they were really tight, although they did not move, they were very stiff. Once they were running loose they were too wiggly.

One thing about your design is that the ball screws are exposed to all the dust and whatever else will be coming off the mill. I have seen this on many other designs as well. Why isn't this an issue?

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Re: Jonny's CNC portal mill

Post by jonnybischof » August 11th, 2016, 4:43 am

Oh it will be an issue :P
I'm not done drawing up all the dust protection thingies. I hope I can make something good that keeps the dust and chips off the linear systems. I also want to add a tube to the mill head that connects to a vacuum cleaner to suck most of that dust right off the machine before it can pile up. This could be problematic with aluminum chips though, but on the other hand these large alu chips won't get through my dust covers (hopefully).

What I can tell you, definitely, DEFINITELY! make sure that all the rails stay accessible for cleaning. I have to put my CNC mill into the middle of the room so that I can walk up to every side of it and clean it. I will also have to learn to use these lubrication fittings on the linear rails. I hope they will all be accessible in practice. Some of them are not in the best spots...
Jonnys workshop 1.png
Jonnys workshop 2.png
Is it obvious that I love drawing up that stuff? :P

/edit:
The table in the rear left is for manual woodworking. There's a disc grinder and a miter saw.
In the middle of the room there's the CNC and table with storage and controlling PC next to it. And there's the black reference plate.
The large rack in the rear right holds 2 3D printers in enclosed compartments and lots of storage for filament and stuff. In the front there's 3 tables, one is a massive workbench with my BF30 manual mill.
Best regards,
Jonny

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Re: Jonny's CNC portal mill

Post by drayson » August 11th, 2016, 5:05 am

Whow... of course, there are people who's interested !!

Great work dude.
Love to build one too but - I guess, you know - there's a little hurdle in budgeting....

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Re: Jonny's CNC portal mill

Post by jonnybischof » August 11th, 2016, 5:58 am

Yeah the budget really is a problem...

I guess my project won't be any good for most people, because many of my ideas really work only when you get these high quality parts from Misumi.
And I also didn't tell you yet that you also need a manual mill in order to prepare the alu extrusions. I did add some complexity into these extrusions so that I wouldn't have to make actual CNC milled parts. These modifications are simple and don't need to be super accurate, but you will need a mill with an XY table. A mere drill press won't suffice.

Example:
portal front beam.png
It's simpler than it looks. I just cut out a square hole with a 10mm mill. There's 0.5mm error tolerance to this so it's really hard to do it wrong.
And of course there's lots and lots of drilled holes (they are all just key holes for screwdrivers, so no need for pinpoint accuracy again) and tapping of these alu extrusion center holes.
y slider with z axis mounts.png
And another part where manual mill work is needed. The Y slider with the Z axis rail mounts. I decided to just slap these together using epoxy glue, then putting them on my mill and make those precise reference faces (green) where the Z axis rails and the ballscrew are mounted on. This is a small part that fits on my mill, and it's the best way to do it. Don't forget that a lasercut 2.5mm steel part will not be 2.500 mm thick but actually have some variance in the 0.1 or even 0.2mm range.

It's really difficult to keep track of where parts are accurate, and where you have to be careful with tolerances...

/edit:
Ofc you can just order that slider part in one piece from a professional shop. But that's expensive. I'm taking steel over aluminum because aluminum will not produce clean faces when milled on a manual mill. Steel is actually easier to machine in this regard (only taking off very little material at a time)
Best regards,
Jonny

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Re: Jonny's CNC portal mill

Post by LePaul » August 11th, 2016, 10:13 am

It looks like you're doing everything right

I was using my friend's CNC machine he built and snapped a few photos for you. You can see the water cooling around the spindle and of course the R2-D2 data panel pieces I made. :)
image.jpeg
image.jpeg
image.jpeg

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Re: Jonny's CNC portal mill

Post by martin-bienz » August 11th, 2016, 10:49 am

@Jonny, this is fantastic! A great design! If I only had the space... :)

I am not going to post a picture of my CNC here... It would be embarassing. It's an MPCNC (Mostly printed CNC http://www.vicious1.com/, based around 25mm conduit) that is mostly for wood, plastic, acrylic... For me, it does the job and cost around 10 times less then yours (so far).

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Re: Jonny's CNC portal mill

Post by drayson » August 11th, 2016, 1:48 pm

Great to hear that it works (MPCNC)...

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Re: Jonny's CNC portal mill

Post by jonnybischof » August 12th, 2016, 3:20 am

@LePaul, that is a nice looking machine there :)
Good ideas on the dust protection, I think I might borrow something from that :P
The spindle holder seems a bit minimalistic to me. Does that hold up well? I on the other hand might have gone a bit overkill using 2x 80mm high holders that pretty much cover up the whole spindle... :P
I will most likely use an MDF plate on the build platform as well. Very easy to handle and you can just mill away any scratches or holes in the surface.

@Martin, you can always come by if you need something made. Once the machine is finished ofc
Best regards,
Jonny

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Re: Jonny's CNC portal mill

Post by LePaul » August 12th, 2016, 9:43 am

The dust protection across the top works great. It's just like Venetian Blinds with some overlap...string ties them together so they slide around as the spindle moves across the X axis.

We have a LOT of time on that spindle and it has held up extremely well. Honestly, we are amazed it has. We've checked for replacement spindles just in case the day comes it fails

My friend also has a huge industrial size CNC machine but the spindle only goes to 3000 rpm. Great for really hard metals, not so great for aluminum

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Re: Jonny's CNC portal mill

Post by jonnybischof » August 15th, 2016, 2:39 am

Well I hope the regulation on my spindle will work well (using an Omron something frequency converter). That is a key component to getting good milling results...

The first Misumi order will arrive tomorrow, but I won't have time to do much with it this week. Still working on expanding the room's infrastructure (there was only ONE mains socket in the entire 26 m2 room...).
Btw. I already received a 10 kg package filled with nuts and bolts. xD
Best regards,
Jonny

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Re: Jonny's CNC portal mill

Post by danilius » August 15th, 2016, 4:16 am

Where do your order Misumi stuff from? I applied for an account from Misumi Europe and they turned me down.

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Re: Jonny's CNC portal mill

Post by jonnybischof » August 16th, 2016, 2:17 am

I have to luxury of being able to order from my workplace.. So I can order directly from Misumi <3
Best regards,
Jonny

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