Where to start? Vertical Mill CNC conversion.

I have got hold of an Elliott Omnimill vertical mill (missing horizontal arbor).

I was thinking of converting to x,y CNC with a z drive on the quill, if I get that far.

So where to start? Should I use the dimensions of the existing leadscrews as a basis for new ballscrews or should they be larger diameter?

I suspect the most awkward part will be fitting the ballscrew support bearing holders to sufficient accuracy. (especially without any milling equipment!)

I do have a small emco lathe if that helps!

If this is going to be more or less impossible without significant machining of the knee and table, I may just have to settle for a DRO kit!

Any advise is welcome no matter how discouraging!

Cheers!

The big problem with converting manual mills is mounting the ballscrew nuts.
A ballscrew nut typically takes up a lot more room than a leadscrew nut, so mounting new nuts can be a challenge.

My advise, is if you are serious about it, is strip it, do lots of measuring, and see if you can physically fit ballscrews/nuts in. If you can, reassemble it, machine the bits you need, then strip and rebuild it again with the new parts.
Other than the weight of bits, especially the table, which you can often get away with just sliding along far enough to get access without completely removing it, mills aren't that hard to dismantle.

My first and second attempts at converting my mill seemed somehow wanting because I always wanted MORE!
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Eventually I figured out that I wanted zero backlash on all 3 axes, no power supplies to go wrong, (I had problems with power supplies), my own setup to locate the tool and work piece. When finished it was fricking incredible, but then I moved house, it got moth balled and I really miss it.
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What I lacked was a clear idea of what I wanted the mill to do. That could be a good starting point :thumsup:

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Originally Posted by Robin Hewitt

My first and second attempts at converting my mill seemed somehow wanting because I always wanted MORE!
.
Eventually I figured out that I wanted zero backlash on all 3 axes, no power supplies to go wrong, (I had problems with power supplies), my own setup to locate the tool and work piece. When finished it was fricking incredible, but then I moved house, it got moth balled and I really miss it.
.
What I lacked was a clear idea of what I wanted the mill to do. That could be a good starting point :thumsup:

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To be honest, as long as it still works, I'll be happy! I don't want to destroy it.

I'm not too worried about the drivers side of things, more the mechanics of fitting the ballscrews.

As m_c said - you need to know whats in there.

I converted my Bridgeport to CNC and I love it, made a good machine even more useful. Don't forget that when finished, it will still be an Omnimill - it will not take bigger cuts or drill bigger holes :) It will just do what it did a lot better and repeatably.

Provided the ways are not shot, it can be done. The ball-screw nuts are much bigger than bronze ones, on the BP they fit into a yoke that joins the X & Y screws under the table, does an Elliot have similar or are the two nuts totally separate?

The BP screws were 1-1/4" dia IIRC and the ball screws I fitted were 30mm - this made the nuts very large, a lot of conversions use 25mm screws so the nuts are almost the same size as the old bronze bushes. I ordered a custom made yoke built to fit which made the job easy.

30mm ball screws are very oversized i think as a BP can only take relatively light cuts anyway due to its flexible design, 25mm would be just as good as the loading figures on ball screws are amazing.

Stepper motors would work ok on the Elliot i think, servos probably overkill but nice still ;)

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Originally Posted by Robin Hewitt

What I lacked was a clear idea of what I wanted the mill to do. That could be a good starting point :thumsup:

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Robin,
That's a fantastic point and an excellent idea for a starting point!
Nice One! ;-)

I still don't know but i did end up with a machine that does most of what i want :wink:

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Originally Posted by Davek0974

I still don't know but i did end up with a machine that does most of what i want :wink:

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Having converted a number of mills to CNC (with varying degrees of success:-)), I suggest that the Elliott Omnimill is one of the easier machines to convert.

I have noted the quotes about ballnuts being larger than leadscrew nuts and this has caused me issues in the past. However, I am just in the early stages of converting an Omnimill (or rather, I am re-engineereing a machine that was previously "semi converted"). There is cavernous space for a ball nut housing under the table and I am moving up to a 25mm x 5mm ballscrew whereas the previous owner had only gone to 20mm.

I will be driving directly with NEMA 34 motors and the table geometry allows these to "overdrive" the X axis and increase the travel from the original machine configuration.

This weekend, I am machinng the brackets and spacers to fit a 60v geared motor to the knee lift which was previoulsy a long handle manual type engaged in a dog. The geared motor will drive through bevel gears with a speed controller and a momentry switch with an "up/ down" switch to allow easy rise and fall of the knee (at my age, I don't want to be spinning too many handles manually!). The switch panel for this motor will be mounted on the front of the saddle where the original gearbox housing was.

Basically, I wish I had found Elliott Omnimills years ago - they make the best CNC conversion for this size mill that I have found in 20 years.

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Originally Posted by Ali Kat

This weekend, I am maching the brackets and spacers to fit a 60v geared motor to the knee lift

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Are you incorporating the plumbing for an automated lube system too?
I have a long term project that I'm incorporating ball screw and way lube plumbing into.