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Author Topic: I want to buy a lathe, please advise  (Read 1181 times)
fourchette
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« on: January 10, 2018, 06:01:22 am »

Hello,

I run a small r&d lab. we design things with cnc, laser cutter and 3D printers.

I've been struggling for a while without a lathe. No dig deal, I can often find an alternative solution. but it's often a waste of time.

some typical example
* can't "tap" this 1m long 20mm diameter steel shaft at ends.
=> so instead of mounting the shaft by screwing it directly on the main body, i have to design a specific holding part in my cnc miill to securely tight the shaft instead.

* can't put a flat on a shaft so that my time pulley will hold securely on the shaft (but maybe it's my ignorance and i should have been able to mill it, it's just i don't like to mill steel, i'm scared of damagind my mill) => instead I drill the shaft and tight the pulley on the shaft with a screw and hope I pulley have the position correct Cry

* can't transform a aluminium threaded shaft into a plain flat shaft. (or reverse... but i never encountred the situation)
* can't increase the internal diameter of some existing aluminium time pulleys. or can't make the shaft hole an aluminium time pulleys (sometimes, small ones are sold without the hole and the customer is expected to make it)
* can't make my own time pulleys (except some 3GT/5GT tooth profile)


and the list goes on...

Now that I understand better turning operations through cambam documentation, youtube and this forum. I feel like I want to buy one (and not make one). I know that I would rather stay in the 5000 - 10 000 EUR/USD range, possibly cheaper. I will use it only for my own shop in order to gain autonomy. I will use it for steel, aluminium and plastics (delrin). I want it to be natively using metric units and I want it CNC not just manual.

The company who sold my cnc mill does not sell lathe. I will request one supplier soon, but he sells exclusively proxxon machines and I want an outside opinon

What do you suggest?

thanks
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kvom
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« Reply #1 on: January 10, 2018, 11:43:20 am »

From my own experience in looking for a CNC lathe, it seems that there's a big price gap between models based on mini-lathes and ones that are suitable for production or close tolerance work.  That said, from your description you don't need a CNC lathe.  A good quality manual lathe will fit your budget and will in fact be easier to use.
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fourchette
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« Reply #2 on: January 10, 2018, 20:38:38 pm »

True, but i prefer to have a CNC model because i want to be able to repeat operations on a systematic way once i'm happy with a part.

One supplier offered me the PROXXON Precision lathe PD 400/CNC
https://www.proxxon.com/en/micromot/24500.php?search

So far, so good. It's CNC and all. It seems to be well suited.

However, the guys suggests to add Mill/drill head PF 230 (ref 24104)... which is manual...
i'm confused. Is there sense in using a manual tool on a CNC machine?
(after all, on my CNC mill, i can't pilot the speed of the spindle from GCODE, I have to manually select it on the button, the GCODE merely turns on/off the spindle... maybe it's a somehow similar use case?)


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Garyhlucas
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« Reply #3 on: January 11, 2018, 00:57:18 am »

Some thoughts for you.  I have a big bed mill, cat 40 spindle at work with CamBam installed. On the big bed mill we have a Cat40 mounted 5" lathe chuck.  It also has 10" chuck on an 8" 4th axis. 

I have a homebuilt Minimill with R8 spindle at home with Cambam. On the Minimill I have an R8 mounted 4" chuck.  I also have 7x14 minilathe bed with headstock Morse 3 taper, tailstock and a large stepper motor, no carriage.  The minilathe has a flange mounted 3" chuck.  My machine has a couple of other unique features.  The bed doesn't move and is a heavily ribbed 205 lb hand scrapped surface place.  The milling head rotates 90 degrees making it a horizontal mill, great for deep cavities.  And because the table doesn't move I can clamp down a 400 lb 4" bar and drill and mill right on the end! I have two spindles, one minimill with treadmill motor and a Hitachi 2-1/4Hp router. Oh yeah it has an extruder and heated build bed for 3D printing too.

If you adjust your point of view a little bit by tipping your head to the right about 90 degrees both mill look an awful lot like a gang tooled lathe!  That is how we use them for parts that fit the chuck and are 4" long or less.  A tooling block bolted to the table holds an 0XA tool post from Tormach and that holds turning tools.  Another gang tool style block holds chucks, boring bars etc.

Now this sounds pretty great and it works, but we do lots of plastics and plastics on a lathe just sucks with chip wrap.  So we now circular mill most stuff making tiny chips, and for long parts we use the 4th axis to turn the part between centers and use a milling cutter to do the turning.

On my home machine the big stepper on the minilathe makes it a pretty decent 4th axis.  I can put the chuck on, and by using 80 volt dc stepper drive from a 68vdc supply and a low inductance motor I get a good reliable 1000 rpm turning with the 0xa tool post mounted to the milling head.  So I think your 20mm shaft fits through the spindle so I could drill that and even rigid tap it.


* IMG_0504.JPG (2030.79 KB, 3264x2448 - viewed 47 times.)
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Gary H. Lucas

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 http://a-little-business.blogspot.com/
dave benson
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« Reply #4 on: January 11, 2018, 02:24:32 am »

Hi Fourchette

According to your requirements stated in your  previous posts, This machine will not meet them.

I went to the website and could not find a quoted “Spindle Bore Diameter” so you won't be working with your 1 metre shaft.

Also the machine won't be able to thread  “out of the box” as it needs a encoder upgrade kit purchased separately.

I have a Generic Chinese Import Lathe (9x20) with a Spindle bore that can accept 20 mm shafting, so as long as the work diameter  is less than 20mm, then I can machine work longer than the centre distance of the bed.

I  converted the lathe to cnc late last year and then made a Auto tool changer a few months ago
and am very happy with the result.

I use Mach3 as a controller, and use the Wizards to program mostly (Very easy to use) and for
some work I use the “Ezilathe Program” Freeware to do more complex work.

On the whole I wish I had done this earlier, as it was well worth the effort.
Some short videos of the lathe in operation I uploaded last week.

 here: https://www.youtube.com/channel/UCD5wr4jG94pGyldBCPLnGYw/videos

The only thing I wish I had done  is buy a lathe with a larger Spindle Bore (should have bought the 10x40)  with a Spindle Bore of  nearly 40 mm, which for the extra $500 was a far superior machine in every way.

Just as an example of what you can get for the budget you have, I looked at some vendors of OEM used cnc machines in Europe  and found this one https://www.surplex.com/en/machines/c/cnc-lathes-4328.html

At the bottom of the page there are a few machines that would fit your budget (inc dismantling and shipping).

Of course you need  the space and 3ph (I use Inverters)  so these may not be suitable for your situation at all, but I just posted it as an example of how much machine you can get for your money.

In summary I think that the Proxon lathe is a little small for you needs and you would quickly outgrow it.
 
I sometimes see Lathes (10 by 40's)  already converted to cnc, either (Mach3 or Linuxcnc) on ebay and other sales sites  as well, all within your budget and so if you have the time to wait to find one this may be the way to go.

Dave
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fourchette
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« Reply #5 on: January 14, 2018, 21:39:39 pm »

thank you very much for your feedback.

Gary, your machine sounds and looks beautiful. indeed the idea of being able to turn the spindle 90 degrees so you can horizontally mill something, while at the same time being able to horizontally hold a bar so that the extremity of the bar is accessible to the cutting tool...
=> assuming (1) you can somehow securely find the center of the bar (that leaves me with https://en.wikipedia.org/wiki/Wiggler_(tool) to read very attentively i guess) and (2) you don't need to cut too deep
=> well i agree that you could indeed tap my 1m long 20mm diameter steel shaft.

A friend of mine says he has seen a few people having a "hole" somewhere on the table so that the bar could fit in there. maybe not a 2m bar, but a 1 or 1.2m it could work. I guess it's a somehow similar story.

Now for the rest of your answer. if i understand right -- I lack tons of vocabulary and experience in machining sorry -- you somehow manage to hold a minilathe inside the machine and somehow hold a lathe cutting tool on the cnc spindle...
wow... i am confused.

But i do know that I don't feel like hacking my CNC mill for sure. What we do with it is so successful that she seems to be milling stuff most of the day. We queue to use it. We'd really be in the sh*t if we broke it.


It's so frustrating...
In order to know what i need for a lathe, i should be skilled in turning already. But in order to build the skills to use a lathe, I must have one already... talk about chicken and egg issue Cheesy

For the record, after my discussion about time pulleys and 4th axis (http://www.cambam.co.uk/forum/index.php?topic=7046.0), I was convinced enough to request a quote to my supplier. He offers a 4th axis (from original manufacturer) for 1100 EUR and i think i'll order it.
But i really have the intuition that we should buy a lathe as well.

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fourchette
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« Reply #6 on: January 14, 2018, 21:41:21 pm »

Dave,

You're right about the missing encoder. I spotted it also and requested the quote to be updated.

The 20.5 spindle bore does exist. it's documented on the non-CNC version of PD400 that is supposedly mechanically identical (https://www.proxxon.com/en/micromot/24400.php). Honestly i would feel more comfy with a spindle bore in the 40mm range and a size in the 10x40 inches as you suggested (250x1000mm if i'm not mistaken) so i feel future-proof. But i can say at the same time that it's a bit big too. And i do have the space for such a machine. What's 3ph btw?
Unfortunately PD400 seems to be their biggest lathe in catalog. My supplier claims he can find bigger lathe from another manufacturer but he didn't name it and says i wouldn't need it anyway with i described him (same thing that i put here)


Your suggestion to go surplex and buy a used machine makes a lot of sense. Problem is, one of my goal is solve my ignorance. So I'm likely to pest the vendor with a few phone calls at the beginning. So i would rather buy something where I know the vendor get moneys for support. I would also be very happy to buy such a second hand machine from a shop nearby that would help get up and running. But all i remotely know are complex, super precise, super big machinery in the 100 000 EUR range, mostly for aerospace industry, far far away from my usecase. There are more and more newbies/wannabes that buy small cnc mills, some of us use this forum. But within this market segment, ppl who want a lathe like I do seems to be non-existent.

If I shouldn't go Proxxon, where should I get my lathe from?
=> Can you suggest a 10x40 lathe from europe -- say a german manufacturer -- in my price range ?
=> a chinese import would do but i would rather avoid it. and maybe it would be wiser to buy a cheap too small chinese cnc lathe, so that i build the skills to later know exactly what to buy? I could even donate it to a fablab nearby.

Also, what is the benefit of the manual mini-milling machine on a CNC lathe? (the guy suggest a "Mill/drill head PF 230 for lathe PD 400" but also confirmed it's to be operated manually... on a CNC?... go figure)

I think I also need advice for my turning skills too. But it's another topic i'll hopefully create very soon Cheesy


thanks for your help

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dave benson
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« Reply #7 on: January 15, 2018, 03:29:16 am »

I don't know enough about your market there, to make an informed  opinion

“3ph” just means 3 phase power (most purpose built  OEM  cnc lathes) would have this.

I guess that a CNC Lathe's superpower, is to mass  produce Identical  parts on a production basis.

And if you look at a OEM production machines with the same work envelope as the Proxxon you'll be staggered at the sheer massiveness of the machine.

The Proxxon is  a well made machine (I believe the lathe's,mills and some other hand tools are sourced from Taiwan not China).

Quote
But within this market segment, ppl who want a lathe like I do seems to be non-existent.

Yes there seems to be a gap in the market for people with your usage case (I include myself here)
and that's why I retrofitted my existing lathe. There are complete cnc retrofit Kits available for this.

Haas and Emco make machines that might be worth a look at.

I had a look at the software and it seems ok and is pre-programmed for the threading and 4th axis.

One thing, I didn't see any conversational programming or wizards like Mach3, and I have to say
that at the start of using (my newly cnc'd)  lathe I couldn't see what good they were, after all I could just use CB or Ezilathe to cam a program up and off I go.  Couldn't I ?

But in practice this is far from the truth.
Quite often I only want to clean up a shaft or the thread on it, or simply turn some diameters on a shaft which is (much quicker) and easier with the Mach3 wizards rather than taking the time to sit down at the computer and writing a small cam program to do this.

There are times like now, when  machining the spindle shafts for my auto tool turrets, where the material is expensive and there are lots of different types of operations to do on the part, then I use the cam programs.

Quote
Also, what is the benefit of the manual mini-milling machine on a CNC lathe?

If you go here http://latheexperts.com/top-5-best-metal-lathe/ , look at the bottom of the page, there is a grizzly (similar to the Proxxon) lathe with a mill attached to the saddle, this means (if you have a spindle lock) that you can machine T5 pulleys or  splines ect. see picture
EDIT: after seeing a few more pic of the lathe,I don't think the milling head is attached to the saddle, in which case it's usefulness is questionable.
Quote
and maybe it would be wiser to buy a cheap too small chinese cnc lathe, so that i build the skills to later know exactly what to buy?

This could be a wise move and could save you some money in the long run.


Dave


* proxon mill head.PNG (566.61 KB, 596x487 - viewed 36 times.)
« Last Edit: January 15, 2018, 03:52:11 am by dave benson » Logged
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