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Big Mama CNC Mill

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Dr. H.

Tue Nov 11 2014, 07:19AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day all

Thanks for the nice words Thomas

The X axis starting to take shape.

Best Regards

Mads Barnkob

Tue Nov 11 2014, 09:45AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

That is some hobby undertaking to build a machine that big! One thing that I wondered about, "how are Huben ever going to get that thing out of the house?"

I can see you can take it apart, but that will be some work to align it all when putting it back together, it certainly is easier to just level out a complete machine :)

Are you planning on some more cross beams to stiffen it up from rocking around in the X-axis?

Dr. H.

Tue Nov 11 2014, 09:57AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi Mads

Whoops this is the Y axis on the upper picture. About the X axis - a bit more steel is planed to be added. The vertical struts are prone to some rocking due to the nature of the bottom beam. It will be closed and perpendicular beams are going to be added to solve the issue.

When the X axis frame is bolted to the struts the rocking disappears - but just to be safe hee hee.

If you like you can add a picture showing where you suggest more beams - always nice to have constructive feedback.

Cheers

Dr. H.

Mon Nov 24 2014, 08:58AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi guys,

the Z-axis is slowly taking shape.

Cheers

Dr. H.

Tue Dec 02 2014, 06:42AM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Hi guys,

moving forward

P.S. There is a "good" reason to be on top of the mill - measuring the vertical deflection of the axis .... around 0.005mm with 100 kilos (if you look closely you will see the indicator below the Z-axis) - good enough

Cheers

Justin

Thu Dec 04 2014, 06:20PM

Registered Member #46164 Joined: Wed May 07 2014, 08:16AM
Location: California, USA
Posts: 89

Looking great, I'd love to do something like this when I have a larger workspace, keep up the good work.

Thomas W

Thu Dec 04 2014, 08:10PM

Registered Member #3324 Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276

I've packaged up those IGBTs for you, They should be off by friday ;)

Hazmatt_(The Underdog)

Fri Dec 05 2014, 03:00AM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Once it's all together, are you going to fly-cut the mounting surface to ensure that everything is true?

I'm just curious how you're going to deal with surface irregularities during your first setup. Like when you get a new machine, you assume that it is true.

Kizmo

Fri Dec 05 2014, 07:25AM

Registered Member #599 Joined: Thu Mar 22 2007, 07:40PM
Location: Northern Finland, Rovaniemi
Posts: 624

I have been setting up several commercial machining centers over the years and it is amazing how many geometrical problems these things can have. Milling the table surface does next to nothing.

In commercial world we test machines with ballbar test. Results will look like this:

These ballbar tests are usually performed in x-y plane but they can be done in any plane (X-Y (full circle), X-Z(half circle), Y-Z(half circle) )

Here are most common geometrical problems i have seen:

1. Spindles axis of rotation is not perfectly perpendicular to table. This error will cause steps in surface if you have to machine it in several passes. Also surface wont be flat since one side of the cutter is deeper than the opposite. I prefer better than 0.01mm / 200mm diameter circle.

2. Axis are not square to each other. This error is usually most noticeable in X-Y plane. Circles come out out of round and 90 degree corners are not 90 degree and so on. Commercial machines are tweaked until they are 0.005mm/meter

3. Table not being level over the whole travel. This one is hard to measure without precision level. And this is the one that causes table being not flat if you mill it in place. I have seen 0.15mm/500mm twist in 240000euro machines y-axis and it was pain to tweak to manufacturers specification (0.005/500mm)

If i was to build my own machine i would invest into precision granite square ($200 to $300 from ebay). It will help tremendously with setting axis to be square with each other. Also the square has usually 45 degree side so you can perform 45 degree test to ensure that your axis are in balance :)

Dr. H.

Fri Dec 05 2014, 03:02PM

Registered Member #931 Joined: Mon Jul 30 2007, 05:25PM
Location: Bulgaria
Posts: 486

Good day guys

Halfdead - thank you for your kind words.
Thomas - big thanks for your help

Hazmatt, Kizmo - those are nice questions and suggestions. Due to budged limitations and not trying to compete with a professionally built machines my standards are a bit lower. I use a indicator clock and a big precision ground right angle. I mount the indicator in the spindle and move it around and correct the axis alignment. I've never built something so big so I am not sure what the result will be at the end. Every "important" surface has been turned on a lathe to ensure flat surfaces for mounting the linear guides. I will be really happy to get into the 0.1-0.2mm error for the whole table.....
One of the big challenges in the moment is that I am making an automatic tool change spindle - so I don't know how accurate that will be .... will see in 1-2 weeks. Plan to make a disk using a lathe, mount on it the indicator clock and screw it in the spindle. Will rotate and aligned to the table. Again will see....

For the X-axis - a hight adjustment is planned(to increase the max height of the work piece from 200 to 300mm) so an adjustment "mechanism" will be incorporated (well... a nut and a bold

) that will also be used for aligning the axis to the table.

For the right angles - I cut a piece of material and measure the angle.

When I have the mill on it's final position, and aligned as best as possible will most likely "mill" the table to make it as flat as possible to the spindle.

This project is more of a learning experience - trying to push the limits of what I've learned through the years from my previous hobby mills. Like building those things hee hee.

Cheers

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