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Why are CNC lathes more expensive than a CNC Mill

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Ian Johnson 122/07/2019 01:01:02
99 forum posts
19 photos

I have a Sieg KX1 milling machine and have been considering a new little CNC lathe to compliment the Sieg. But what I can't understand is why the CNC lathes are more expensive than the CNC milling machines!

After all, the lathe has one less axis to equip with a motor and ball screw and controllers etc. And a lathe is relatively simple to make with a bed and head stock, it may not even need a tail stock, and a manual tool change would be okay with me.

In the UK I have a limited choice of new machines, Wabeco CNC are over priced, so Axminster Tools and machinery are probably the place to go to, but their small machines start at £9,799 rising to £16,659 also a bit too much for what they are! Their Mills start at £6,675 (KX1 in a metal box) to £14,998.

I've been following Roger Webb on Youtube with his excellent Mini Lathe CNC conversion so maybe this is the way to go.

So as the thread title asks - does any one know? why do CNC lathes cost more than CNC milling machines? Can we compare like for like?

Ian

Paul Lousick22/07/2019 03:38:27
1123 forum posts
485 photos

Not sure, but CNC mills are more common than CNC lathes. The higher price could simply be because of production costs for smaller quantities.

Paul.

not done it yet22/07/2019 05:09:24
3128 forum posts
11 photos

I don’t know but do these lathes have a separate feed shaft and lead screw to control?. That might make three sets of controls? How do they incorporate change-overs from long to cross travel? How do they manage both axes at the same time? Seems there may be more complications than first thought?

Edited By not done it yet on 22/07/2019 05:09:48

Baz22/07/2019 06:06:43
223 forum posts

Agree with Paul, CNC mills are more common than lathes, many years ago after purchasing a CNC mill I wanted a CNC lathe and could not find any so ended up buying a little lathe from Warco and converting it myself, I cannot remember Warco model number but it was cheap as they were discontinuing it, it is identical to the Sieg C1 on Arc eurotrade site.

JasonB22/07/2019 06:57:10
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Moderator
15711 forum posts
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1 articles

Sherline may be cheaper if you don't want it too big.

Michael Gilligan22/07/2019 07:50:36
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13531 forum posts
586 photos

Ian,

Permit me a little speculation here, please ...

1. Our introduction to the underlying concept of CNC was the XY plotter, and there is an obvious evolutionary path from that to CNC routing or milling.

2. The 'Holy Grail' is the full 5-Axis CNC machine : **LINK**

https://www.engineering.com/AdvancedManufacturing/ArticleID/11930/The-What-Why-and-How-of-5-Axis-CNC-Machining.aspx

3. Development effort progressed along that path.

4. A simple [2-Axis] CNC lathe can only produce a small range of shapes

5. In terms of 'perceived value' [i.e. is it worth developing and marketing this machine?] the lathe comes at the bottom of the list.

... Feed those thoughts into what Paul wrote.

Of course, however: Your perception of usefulness, and therefore 'value for DIY effort' might differ greatly from that scenario ... Making the CNC lathe an excellent home-brew project.

.

Jason's comment is, I suggest, consistent with this ... because Sherline is 'the amateur' raised to a power !

[and I mean that as a compliment]

Have a look around the Sherline site, and see them using their own machines to make products that they sell.

MichaelG.

Edited By Michael Gilligan on 22/07/2019 07:57:04

John Haine22/07/2019 07:56:35
2569 forum posts
133 photos

Lathe is technically simpler than mill, one less axis to control, but production volume is far smaller so costs have to be amortised over fewer sales. Worth looking at cncyourmyford for another approach. In industry CNC mills today do many of the jobs that would once have been done on a lathe. If you have a lathe why not convert that? I switched my Super 7 to CNC several years ago and don't miss the manual capability at all.

John Haine22/07/2019 08:08:31
2569 forum posts
133 photos

And of course if you only have an occasional requirement you can turn in the mill by putting the stock in the collet chuck and clamping tool to the table!

Ian Johnson 122/07/2019 09:53:04
99 forum posts
19 photos

Good answers thanks. I'd not thought about Sherline. And as for a five axis milling machine that would be nice, I already have four axis on my KX1.

Whether I get value from my machines is not so important because it is a hobby and I seldom get commissions for work, so I have the luxury of messing about in the workshop without worrying about a return on assets.

But the Mini lathe CNC conversion option is looking more attractive. I have a spare Hobbymat MD65 maybe I can butcher that into a CNC?

Ian

Jon Freeman 222/07/2019 10:38:05
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8 forum posts

There's one good reason for CNC lathes being more complex, therefore potentially more expensive, than milling machines - screw cutting.

Cutting screw threads requires accurate synchronisation of spindle speed to the speed of in particular Z axis movement. This adds cost of a rotary encoder on the spindle - not a huge cost in itself perhaps (£74 from zappautomation.co.uk), but this needs to output three signals - an index pulse to identify one 'home' spindle angle, plus a pair (e.g. step and direction) enabling the controller to keep track of the angle of the spindle at any instant. This should have many pulses per revolution, otherwise the controller can not be made aware of any spindle speed change at any point through the cutting pass. Software and digital electronics to keep all this sweet is non-trivial. LinuxCNC does a pretty good job, Mach3 not.

The only way around this would be to use a hugely more expensive servo motor driving the spindle, in the hope of maintaining constant spindle speed with minimal angular error, while cutting.

Vasantha Abey22/07/2019 10:43:33
13 forum posts

Hey Guys,

Having converted over 12 used original scrap cnc lathes and cnc mills let me give my experience about this.

Buy used machines mills or used at rock bottom values may be pound per kilo if you can like me here in Sri Lanka.

Make sure the bed ways are not excessively worn out. You can check ont he gibs for play and adjust. Checkthe ball screws for play and if you can remove the buts, its always a double ball nut means you can adjust backlash by either grinding a small shim between the ball nuts or putting in a shim. An empty bear can cut with a seamstress sissors will help. Check if you have the power supplies usually for a retrofit you will require 24 volt DC, 5 volt DC for relays and logic and for powering up the motors 30 to 60 V DC ,

Go for the best control system now in the market Centroid cnc Acorn Controller and software. Just go to the website Centroidcnc.com.

I am not a commission agent but talking from my experance. any questions please email me for help. vasanthtime@yahoo.com

Andrew Evans22/07/2019 11:12:51
245 forum posts
1 photos

As has already been said I think it's down to economies of scale as there is a higher demand for CNC milling machines for the hobby market. A CNC mill is great as you can do one offs, machining shapes that would be hard on a manual machine. I feel a CNC lathe is more about making multiple parts - a less common scenario at home so it's less of an advantage over a manual lathe.

John Haine22/07/2019 12:15:54
2569 forum posts
133 photos

Hmph.

Mach 3 actually does quite a good job of screwcutting with one pulse per rev, in my experience, provided you don't push the cutting depth too much. This is on my S7 with the standard motor at 215 rpm.

The old Denford Orac only had a 100 ppr encoder. You don't need direction as well because lathes generally only go one way and you will know which. You can use a quadrature pickup if you want to get double the pulse rate. but I don't know actually just how critical for example LinuxCNC is on rotational sampling rate. An alternative is a Hall Effect sensor on a gear wheel. So I don't think the spindle sensor is a critical cost element.

Once you have a source of spindle pulses the software takes care of everything, no additional electronics is needed.

I think the point about CNC being for multiple parts, made about both lathes and mills, is incorrect. Once you have a CNC lathe, you will use CNC for everything, all the simple jobs like turning, facing, tapers, curves, spheres, threading etc have wizards, you seldom have to write gcode, and of course once you're using cad/cam it generates the code directly.

It all comes down to supply & demand I think.

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