CNC Vertical Milling Machine

Apart from making loco frames 2 or 3 times in their life how often does a model engineer work outside a 6 in cube?

If going to the trouble of making a whole machine the extra work for a special low profile tool holder and buying a few short drills to compensate for a short z axis is minimal effort to significantly improve the rigitity.

John;

Just a thought - if you want to keep the costs down, why not as an option use LinuxCNC? Cheaper than Mach3, and can use soft-stepper sw reliably, as it uses a real time kernel. If you need help configuring it, there's lots of people to ask (including me).

Anyway, thank you for proceeding with this design. I'll be following it with interest.

John A. Stewart

Ottawa, Canada.

Hi Bazyle;

I'd agree, but making the boiler formers for my 7-1/4" "Stourbridge Lion", I needed a bodge to get the size required. These formers would not work well on this design of machine.

Somewhere on my blog:

http://cnc-for-model-engineers.blogspot.com

are my Stourbridge Lion formers after initial CNC routing. It required a "open" mill to machine.

I think there's going to be a few areas where a 6x6x6 envelope might be exceeded, and this is a small locomotive for 7-1/4". I'm certainly not disagreeing with you, just pointing out one place that tripped me up with my little mill.

(just getting back from holidays - this going away from the workshop certainly curtails progress!)

Another JohnS.

Hi John,

A German individual is offering the frame of a CNC portal milliing machine which could

be interesting:

http://www.mineralgusstechnik.de/prod_fs3mg.html

Cheers

Edited By John Stevenson on 17/04/2013 00:06:09

Thank you hans

Yes he is doing great work. I have kept an eye on that site for a while.

Now all I need is some time to get stuck into mine.....

Cheers

John

Hi John,

Found today a video for a polymer concrete milling machine which sounds quite good.

https://www.youtube.com/watch?v=fDiEi2bOXgs

Cheers,

Hans

Thank You Hans

Yes a great build. I clearly shows the advantages of the material. I have collected all the slides and many of the parts to make a new machine myself. Trouble is the time needed to do it Hmm.

The link below is to other videos by the same poster.

**LINK**

Regards
John

HI John,

Today I searched with "Tobias Merten CNC" and found a lot of videos AND

the link for written report about the polymer concrete vertical 3-axis mill in German:

http://www.grundig-akademie.de/cms/uploads/pdf%20download/fs_technik_nuernberg/schuelerprojekte/2013_cnc_portalfraesmaschine_merten_guenther.pdf

Tobias Merten is the co-author.

Wish you happy reading.

Cheers,

Hans

Hi John,

I've got a few pointers that might be of help based on my experience using a similar sized machine to the one you are proposing, its a Sieg KX3 CNC which i've been using for the last 5 years. So if i had a wish list for your mill:

1) Spindle speed - the lack of rigidity for a small benchtop mill means that 'big' cutters, and when i think of 'big' this is anything larger than about 8mm in my case, gives rise to lots of vibration and poor finish. To compensate for the lack of rigidity, increase the spindle speed to as high as practicle for the bearings planned and use smaller cutters , <6mm. These small carbide mills can deal with huge surface speeds and have been a game changer for me. Increasing the KX3 to 6500RPM has enabled some useful removal rates with a 6mm 3 flute high angle cutter in 6061 Al with feeds of 600mm/minute and 4mm depth. At this speed and these cutters there is virtually no vibration and excellent finish. I would aim for 10,000 RPM if you can, using a poly V belt drive and VFD, you'll need plenty of HP for this, 2HP would be good starting assumption. There are numerous websites which have online apps to calculate the HP needed for cutters, materials and feedrates. If you want to do engraving, which is something that i found myself want to do quite often, for letering on panels, aim for 20,000 or a separate engraving spindle.

2) Rigidity - A rigid as is feasable!. Polymer concrete would be an ideal base, it adds 'dead' mass which helps with natural vibration. My father used to design machine tools and these used polymer concrete for super accurate, low vibration machines.

3) Accuracy - Most jobs are making parts that would be a pain or impossible to make by manual milling, or your making a lot of them. I'm not going to use it to bore holes expecting a bearing fit, so for me accuracy has not been something that has mattered as much as i originally thought, i get better than 0.05mm on all axis and this has been adequate, using rolled ballscrews and normal nuts (not the double ones).

4) Axis speed - i get about 2000mm/min max, which is already too frightening. so unless the machine is going to be used for production i would say this would be a good number to aim for. Microsteppers are quite adequate for this.

5) Y axis travel - Most manual mills dont seem to have much travel in the Y direction, probably because parts are often moved between operations. But for CNC you'r trying to do all or as much of the machining in one go with tool changes, so i would go for as much as you can. The KX3 has <150mm, which i guess came from the fact that it was an adapted manual mill, and this has been limiting , 250 mm would have covered almost anything.

Cheers

Tom Chapman