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CNC screw cutting lathe advice
« on: June 29, 2009, 01:25:23 PM »
Hi All

I am not sure if this is the correct place to post but I am looking for advice on purchasing a small CNC screw cutting lathe/system. I am looking for something out of the box that requires minimal set up and it is mainly to be used for cutting stainless steel.
I have seen this system
http://www.cadcamcadcam.com/sherline4400-cnc35x17cncreadylathe.aspx
and they do a spindle encoder that allows cnc screw cutting but what do you guys think or are ther alternatives.

All advice much appreciated.

Brian

Offline RICH

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Re: CNC screw cutting lathe advice
« Reply #1 on: June 29, 2009, 04:31:31 PM »
Brian,
What is small? How big of a screw thread do you want to cut? How much money do you want to spend? Industrial use or home shop use? I use a Sherline and I would say anything past 20TPI is starting to tax it even though i have done up to 12 TPI and down to 80TPI. Nice for model work, but for the price I would retrofit one of the mini bench lathes putting ball screws and larger steppers along with the longer bed as it would be a lot more roburst than any Sherline, but, that's not out of the box.
All comes down to what you want to do with it and to what degree.
RICH  
Re: CNC screw cutting lathe advice
« Reply #2 on: June 29, 2009, 04:54:53 PM »
Hi Rich

Thanks for the reply. Probably the biggest thread would be M12 but mostly M8 and M10 with 1 mm pitch. It is for my busness www.ebolt.co.uk

The main problem I have is the time to retrofit to something existing. I already have a mill that I am trying to get round to converting to CNC.

The lathe I have posted the link to comes out at about £1500 plus. I already have a good old style lathe that could be converted but as i say I dont have the time to do it myself so another alternative would be to pay someone to do it for me.

Brian

Offline alenz

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Re: CNC screw cutting lathe advice
« Reply #3 on: June 30, 2009, 02:40:19 AM »
Brian, you are showing 12 mm stock but the Sherline spindle only has a 10 mm thru hole although I believe they will provide a larger bore on special request.

http://www.sherline.com/specs.htm

al
Re: CNC screw cutting lathe advice
« Reply #4 on: June 30, 2009, 03:13:22 AM »
Hi Al

I think this one should fit between centres on the 4400. But it is still something to bear in mind.

Brian

Offline simpson36

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Re: CNC screw cutting lathe advice
« Reply #5 on: June 30, 2009, 05:36:05 AM »
Couple of thoughts:

There are lots of places that sell pre-converted asian mills and lathes. You are not restricted to Sherline for off-the-shelf small CNC machines.

If you are starting with hex stock, you should consider getting a lathe large enough to pass the stock thru the head, otherwise you are committing yourself to pre cutting each piece and the resulting waste in stainless material and manhours may cost more that the lathe itself.

Of you are willing to precut your stock and don't care if it can pass thru the spindle, you can consider doing the threading on your mill.

For many years I did extensive machining of all of the stainless grades including Inconel and Monel. I would wager that you will have zero success cutting anything except perhaps 303 on a Sherline in a production environment. Stainless work hardens pretty much instantly so you need enough power to keep cutting at ALL times. For this you will need not only the HP, but a very rigid machine, even for 12mm shafting. You are also goint to need flood cooling.

Single pointing 316 is one of the trickiest things I ever had to do. Unless there was an absolute need for single point (reverse thread, odd size or pitch, thread to a shoulder, etc ). I always used threading dies . . up to about 25mm, using a die holder in the tail stock. The low speed also eliminated the need for flood coolant. A squirt of threading oil was sufficient.

You make some beautiful parts, incidentally.  How are you cutting the hex pocket in the drain bolts?

 
« Last Edit: June 30, 2009, 05:46:37 AM by simpson36 »
Re: CNC screw cutting lathe advice
« Reply #6 on: June 30, 2009, 06:53:18 AM »

Thanks fro that Steve; I am coming to the same conclusion regarding the Sherline. I am now looking at a WARCO http://www.warco.co.uk/Metalworking-Mini-Lathe-D4121A9297.aspx# and I have been talking to Lester from MEDW about fitting this system to it http://medw.co.uk/wiki/index.php?page=ELS+Price+List it means I will have to make some mountings for the motors etc. but it will be no problem. Also mit means I can source it all in the UK.

Do you have links to the asian lathes you mentioned?

Any thoughts would be appreciated

p.s. the drain plugs a re an off the shelf item I buy in.

Brian

Offline simpson36

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Re: CNC screw cutting lathe advice
« Reply #7 on: June 30, 2009, 07:27:02 AM »
Note that I am not endorsing any of the following, just FYI here is a link to lots of other links:
http://www.mendonet.com/cnclinks/index.html
An example of an outfit that puts all of the controls together for you into a functioning system:
http://www.lowcostcncretrofits.com/

If you need to do more than simple turning, you can follow my thread here on a 'mini machining center' that I am developing. Currently I am looking for the right sero drive and getting ready to start making the final new head:
http://www.youtube.com/watch?v=NzY-OqckqpI
Re: CNC screw cutting lathe advice
« Reply #8 on: June 30, 2009, 12:38:15 PM »
Thanks for that; your machining centre looks very good. I have an existing manual mill (a converted Taylor Hobson engraver) with DRO but I don’t think it is suitable as the extra weight on the table could cause problems but also I think I prefer separate machine. Something like your machine would perhaps be a step too far as I am hoping to get up and running with minimal effort by me.

I also have an old Portass screw cutting lathe that might be worth converting that will allow me some funds to convert the mill.

I have been looking further into the ‘Electronic Lead Screw’ kit but I am concerned it only has limited facilities for other CNC turning such as form, diameters etc. I would prefer to go down the Mach3 route but I am hearing there are possible problems with screw cutting??

I am hoping to make some decisions in the next few weeks so I will keep reading and hopefully I can get system that will meet my needs.

Brian

Offline simpson36

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Re: CNC screw cutting lathe advice
« Reply #9 on: June 30, 2009, 01:14:53 PM »
My little project is not ready for prime time . . just something I'm dinking around with for the fun of it. The capability of it is dependent to a very great degree on the mill it is sitting on.

You make a very good point.  MACH does seem to have problems threading, although not using Mach turn at all,  I am not the one to comment on the extent of that.

If all you are doing is the kind of item you posted, I'd have to really question how much time savings CNC will be to you, vs the cost of hardware, software and learning curve.

I am an engineer with many years experience in machining and designing prototypes of all mannet of machanisms and it has taken me months to get a simple CNC retrofit to perform adequately . .  and I'm not done by a stretch. Not intended to scare you off, but if you are busy running a successful business, I would not recommend you dive into your first CNC retrofit if you need any product off it in the coming months, or if you have other things to do besides becomming a full time student again   :P

Out of curiosity, what started you thinking about CNC in the first place?