CNC Vertical Milling Machine

Hi All

I am working on a new CNC Mill that I intend to publish... In MEW if it fits the magazines publishing criteria or in any event here on the forum.

The frame of the machine will be fairly simple to build.... made from Laser cut steel plate sections bolted not welded together, this eliminates a lot of the distortion introduced into a structure by welding.

While not essential it will be designed to be filled with an epoxy aggregate for extra vibration damping and stiffening as used by the major machine builders these days. It is intended to test the prototype with and without it and compare the difference.

The cad files for the frame will be made available to individuals free of charge. not commercial resellers.

I am encouraged to build it after the success of the small CNC router I posted on the Mach3 thread on this forum. you can see a short video and a few pictures here....

http://www.model-engineer.co.uk/forums/postings.asp?th=74182

As before Mach 3 and smooth stepper for software and interfacing.

Having spent many of days on AutoCad making a number of different 3D solid model concept designs I think I have a viable plan!

Now a few questions that need answering:

I would appreciate any constructive comments.

What size should the work area be, (the area that can be reached by the cutter). Length width and height I will add 100 mm to the height for the tool itself.

Tentatively for travels I have used 512L x 312W (12mm is for a 12mm cutter to cut the sides a rectangle 500 x 300)

For height 200+100 for the tool itself under the spindle.

There is enough room for a 4th axis on the table

The overall size is a consideration.

Currently the bench area needed is about 1000 x 600 allowing for table travels.

The table will be drilled and tapped M10 at 40mm centres. Alternatively builders wit a larger manual mill can make a T slotted table. Ideally to be sent out and surface ground.

Spindle?

Should a difficult to make but useful int 30 or 40 ball bearing spindle be used? or something a lot simpler using a Chinese ER Collet holder. it is assumed the builder has a lathe of adequate size.

What sort of drive should be used? These days a VFD and a 2800 rpm induction motor is Ideal.

direct drive 1425 RPM Motor Maybe for 500rpm to 2500 rpm? Maybe a step up and down pulley giving a wider speed range Say 1.5 to 2 KW

Or maybe a Chinese water cooled high speed spindle? (not very useful for steel but good with non ferrous metals, and wood)

The machine is driven by Rolled ball screws on all axis. Hopefully with backlash eliminating nuts. 

Cost: Not cheap, substantially less than many extruded aluminium machines I have seen on the net. It will depend on how well you source the components. The good news being that the competition is fierce these days... linear bearings, ball screws, step motors and drives are all getting cheaper.

And then there is the pleasure of building a machine from the ground up...Yes it will require a lot of time, precision fitting and measurement to align and set it up.

I would really appreciate feedback

Thank you

Cheers

John

Edited By John McNamara on 24/02/2013 11:59:27

John.

You state milling machine but given bed sizes and details above it still sounds like a router style or bed mill.

This seems to follow a trend , probably started on Ebay of calling every CNC machine however built a milling machine.

A working footprint of 500 x 300 cutting steel will require probably more mass than a bolted assembly can handle.

Now if we drop down to a router cutting alloy then it will probably be quite suitable.

Hi John,

I haven'tdone any calculations, but my immediate thought is that you plan quite a large machine. Compared to a wood routing machine, tool loads will be much higher - if you use 13mm cutters it will have to be rigid to avoid distortion, which will mean very heavy construction, in turn meaning more powerful motors, leadscrews etc.

The alternative is to reduce the depth of cut/feedrates, but you would even need to do this for small parts.

You might consider slightly reducing the size so it's more comparable to benchtop machines?

Neil

Hi John

I am aiming for a steel cutting milling machine not a router. The frame is heavily ribbed internally, It may have to be filled with epoxy concrete. or other to damp vibration. It should be stiff enough. It will use the jointing system I used on the router posted. It will not be like the Ally tube jobs you see on ebay.

And yes smaller is better to keep the material cost down, Hence my questions: How big is big enough for most of the recreational work we do?

Cheers

John

Edited By John McNamara on 24/02/2013 13:23:32

Edited By John McNamara on 24/02/2013 13:30:21

Hi Stub Mandrel

I guess the question is how small can it be and still justify the effort.

What would you consider the work area should be.

X3's start at about 400 x 150 table travels is that too small? Is that big enough to attach a 4th axis?

Cheers

John

So a mill configuration and not a moving gantry router ?

300 mm travel in the Y is a big machine, that's the same travel a Bridgeport BOSS 1 CNC has and it weighs 1429 Kg.

X3's can easily hand a 4th axis.

Hi John

Its not a moving gantry. nor is it a Bridgeport knee mill style.

Cheers

J

Hi John

Is it a portal machine where the table moves in the X and the spindle moves across in the Y rather than the table.

I used to make bits for water cooled spindles with air bearings. I doubt anyone on here could afford one.

They used to run at 360,000 RPM and they were working on 500,000 RPM a few years back.

A simple 1/8 or 3mm collet used to cost £125 + vat.

regards David

To get a better idea what David means about a portal milling machine watch this video of a Huron.

**LINK**

Pay attention to the ram which is actually the Y movement.

Hi John.

Nup! Keep thinking on it?

Cheers

J

I would like Davids Air Bearings!

Cheers

J

Hi There

This is a portal milling machine.

This is a slow link but it does work.

Look at the lower of the 3 pictures, all will become clear.

I disagree with the Huron John.

A portal is supported at both sides I think.

Replacement spindles on the Brigeport version were £30,000 +VAT.

No doubt due to ceramic bearings.

We had three of these Bridgeports working 24/7 at one place I worked.

I don't know if they were ever put into production by Bridgeport as we had the only three prototypes.

regards David

Edited By David Clark 1 on 24/02/2013 14:56:36

I would say X3 travel at 360 x 145 is plenty, a bit more Y would be nice, but not essential. But travel of 500 x 300 mm suggests a table perhaps 700mm long by, say 350mm wide to get X3 bedway lengths and that seem a bit of a monster to me.

The big challenge is keeping the head steady, you can have as much X as you want and it won't make much difference (as long as the table isn't so long compared to the bedways that it distorts the bed), but for more Y you need to increase the 'throat'. If 'visibility' isn't an issue with CNC, why not design in a front brace for the head, or even some form of gantry arrangement.

I think this is a good idea, but I think a home build would best aim to be cheaper than, say an X3, with similar specification, rather than similar price but greater capacity. That way it becomes a very big investment, very, very heavy and a major challenge.

If you do want extreme travel with compact size and reduced cost, how practical would a travelling head arrangement be?

Neil

Hi David

You are on the right track!

The question is what working area would be the Ideal size?

Cheers

John

Portal is just another name for a bed mill or what we know as a moving table router.

Gee Its 2am this side of the pond

have to see you tomorrow.

Cheers

John

Hi John

I would make a decision on the working Y axis travel.

This is the critical decision.

The x axis can be varied depending on the constructor's needs.

Most mills can only be moved by maximum of 9 inches (230mm).

I would think a 12 inch width of table should be ample.

For small mills, the x axis should be a minimum of 12 inches bearing in mind this would make the machine's length at least 24 inches plus.

A portal machine would be long and thin.

regards David

Just out of interest, I've seen a CNC machine for routing wall panels for prefabricated houses. It has a roller bed some ten metres long and three or so wide and seems to be able to work panels up to about 20-30 cm thick. The whole factory was laid out so that panels can be shifted along as they are made up. Apparently it was fundamentally a scandinavian machine, but they built the factory and workflow layout so it can handle bigger panels than the originals. It was able to 'flip' big panels so the other side can be worked, and with modest staff levels. Very different from metal working!

I can only find a picture of one of the panels:

Neil

Hi John

"For height 200+100 for the tool itself under the spindle"

Presume that you will be using the machine for drilling holes as well as milling - if so I think that you might find the height under the spindle very restrictive once you add in the height of the vice and a drill chuck / holder of some description.

Regards

Roger

Hi Roger

A vexing question? As the Z axis travels down it moving down and away from its support creating an overhang in the vertical plane. It is easy to add height as long as stiffness is not compromised. I will work on it. (Remember this is not a knee type mill the spindle assembly moves up and down)

What is the height of the typical work piece we work on? And what is the maximum height of all but 1% of the work we have actually worked on. in other words the 99 percentile.

I am trying to keep the size of the machine, and the cost down.

Maybe in the end it will have to be in two size versions to fit the needs of various builders.

For want of better words a micro and a maxi.

Cheers

J