mill requirements

How useful is a tilting Z axis?

Are ballscrews needed to get around 1/100 mm overall finished parts accuracy for a cnc mill? Would good leadscrews do instead?

Thanks,

Reply to
Peter Fairbrother
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I have a tilting Z axis on my mill but have yet to find a use for it. Mind you, it has saved the occasional end mill by allowing the column to tilt rather than break the tool when I have taken too heavy a cut...

Whether it is useful to you wil depend on what kind of machining you plan to do...?

Ballscrews are primarily chosen for efficiency rather than for precision; a ballscrew can be up to 95% efficient, whereas a conventional Acme thread is probably down in the 30-40% range. This makes a difference when it comes to choosing suitably sized motors to drive the mill.

There is nothing magical about ballscrews from the accuracy viewpoint; you can get high precision screws in a variety of styles of thread; by the same token, you can get ballscrews that are not terribly high precision (generally rolled thread ballscrews are not as accurate as ground thread).

So, there's no reason why you shouldn't use conventional leadscrews if you can obtain them in a suitable grade.

There is also not necessarily a direct relationship between the accuracy of your leadscrews and the accuracy of the mill. For example, if you use a closed loop control system with linear scales/encoders on the ways providing the positional feedback, then the system's accuracy will depend on the resolution and linearity of the scales, not the accuracy of the leadscrews.

There are also CNC controls around (but probably out of reach of the average home constructor!) that allow each axis to be calibrated so that the software can compensate for inaccuracies in the leadscrews.

Regards, Tony

Reply to
Tony Jeffree

Reply to
Airy R.Bean

One things for sure,when you've gone to the trouble of tramming the hea

in you'll be very reluctant to move it.

Alla

-- Allan Waterfal

----------------------------------------------------------------------- Allan Waterfall's Profile:

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Reply to
Allan Waterfall

Parts for small rocket engines, from 316L stainless and Inconels mostly. Max dimension is about 50 mm, the kind of complex 3-d shapes you need CNC for - maybe even a turbine wheel with blades. Need about 1/100 mm overall parts accuracy.

They can be made in sub-parts and then diffusion brazed together though (some will have to be) which allows multiple brazings, ie I can braze two bits together then braze another bit on, and so on.

[snip]

Thanks for the informative answer. Is there a standard for accuracy of ball/leadscrews?

I have about £500 available to buy a small manual mill, which I will later convert to cnc - I do know electronics and computers, and am just finishing my second 4-axis cnc hot wire foam cutter - any suggestions/ tips?

The Peatol mill is the same thing as the Taig mill (apart from being more expensive, but already here in the UK) isn't it? Would that do the job?

How about the Chester Conquest or a similar Chinese mill? A Sherline? Any others? I'd prefer a metric version.

Thanks

Reply to
Peter Fairbrother

In article , Allan Waterfall writes

LOL!

This is very true.

On the other hand, I've once had a need to tilt the head on my Bridgeport where no other way would have worked.

It was boring a *hugely* corroded exhaust stub out of a small motorcycle engine. I could only hold the head flat(ish) on the table, so I tilted the head to match the exhaust port angle and had at it. Got the bugger out in the end, cursed the mate who brought it to me, and re-trammed the mill head.

Any cylinder head material that might have been removed in the process was filed under "gas-flowing"... ;^)

Reply to
Nigel Eaton

motorcycle

tilted

bugger

process

Yep - been there - had to do almost the exact same thing on the power valve port on my sons RD350 - without the tilting head the job would have been a nightmare.

AWEM

Reply to
Andrew Mawson

Well if you bought a *decent* mill like an Elliott or Beaver instead of a Yankee mill/drill you would get a tapered fitting that locked the head knob on vertical. No ear of bat or tongue of newt trying to tram it in.

Bridgeport's are like Myfords, they have a reputation that far outstrips their capabilities.

-- Regards,

John Stevenson Nottingham, England.

Visit the new Model Engineering adverts page at:-

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Reply to
John Stevenson

Well that's handy to know! I did see the dowels on the lathes.co.uk information pages, but haven't had time to collect my Beaver yet, hope to 'beaver off to Brum' this week, weather permitting. I don't want to trailer it back home in a salt and snow-laden atmosphere and leave it under cover up the farm sweating away....

Peter

-- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk

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Reply to
Prepair Ltd

In article , John Stevenson writes

Yeah, good point.

I should chase up the cynical trader I bought it from and complain. I've got his phone number here somewhere... ;^)

Reply to
Nigel Eaton

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