Homebrew CNC Lathe

[Deviant]

I'm starting to research building a CNC lathe. I'm thinking 2x3'ish steel tubing with 2 linear rails to support the carrage, with a slot between the rails for an extended arm that will attached to a ball screw which is hidden in middle of the 2x3. ((if that explains what I'm planning on doing))

I have a few concerns at the moment.

1: what should I plan for the top rail that the tailstock locks into/onto? One a normal 7x14 type lathe, the way is cast on the the way.

I was thinking that it might be possible to get someone on here to mill out a set of rails that would be mounted on top of the 2x3 and welded in place? Does this plan have any flaws, asided from my in ability to machine anything that large.

2: I was looking at using a 7x14 style head assembly, but I was wanting to get a large through hole. Is there a comparable head assembly that can be ordered that would fit my needs?

Does anyone have set of prefered links for homebrew type cnc mills?

Sorry if my description sounds vague. I'm still in the thought process.

Any concerns that experienced builders see? Will it work or a bad design from the start?

[MrBean]

I too want to have a go at a homemade CNC lathe. I made a 3D model of some ideas I had. I've not done anything like this before, so the ideas may be crappy, but It keeps me busy when I get stuck indoors.

I havn't seen many homemade CNC lathes. One actually. So I'm guessing about the design.

Regards Terry.....

[Deviant]

I'll try to draw up my idea a little later. I notice on yours you don't have any means to mount the tailstock or the support for working long materials.


I haven't been able fine many details on homebrew either. Only a few links on retro fitting existing mills.

[MrBean]

I had some ideas for the tailstock. I'll add one of the ideas to the model in the next 4 or so hours. (too busy at the minute.) Would be good to see some drawings of your ideas.

Regards Terry.....

[WayneHill]

Follow this thread for a CNC lathe conversion.

http://www.cnczone.com/forums/showth...ight=cnc+lathe

[MrBean]

I already have two lathes. I wanted to make a smaller one (CNC). Maybe 6 - 8" between centres. Yes I could buy another one and convert it, but that's not so much fun. I have most of the stuff I'd need already. Just waiting for that "inspiration" and some free time of course.

Regards Terry.....

[Torsten]

Originally Posted by WayneHill Follow this thread for a CNC lathe conversion. http://www.cnczone.com/forums/showth...ight=cnc+lathe

This is a conversion of a Lathe, has nothing to do with building one.
While i am at it I like to comment as much as I like
to build stuff there is a cost\effect ratio that may be though
to justify.
With all those cheap china lathes on the marked that are available
in various sizes it makes it very difficult to justify building one.
It is a lot easier to improve and build on a existing one then it is
to build from scrap.
The ground Bedways and dovetails are no match to any linear guides
a hobby builder may come up with in strength and ridity.
After doing some cost analises and getting a realistc look at what
you will end up with most decide to buy one.
Building stuff is more fun but it has to make sense, something that
you can't buy or only at horror prices.
But then again I am not allways right, good to know there are people
out there that can prove me wrong.

[kong]

It is a valid point Torsten. Stevie has built a fantastic little cnc lathe which is great for what it was designed for - very small parts. If you want to turn anything large - ie over 2" diameter, then even the 9x20 lathes are going to be stretched.
I have recently bought an old 550Kg lathe, and now I have it, it makes me wonder why I bother keeping the chinese one in the shop. The quality that can be had in old, and usually cheap iron, is not worth the hastle of trying to build one.
I don't mean to put anybody off, if you want to make small parts, then your homebrew lathe may be just the job, give it a go and most of all, enjoy yourself!

[Deviant]

I've considered going to the conversion route and honestly may end up that way.

However I have a china made mini mill. While I think think it was worth the money I paid, I think I'd rather build my own. I'm very intruged with using the linear rails like the on swede's mill.

As for the Lathe, I'm looking at something in the 9x20'ish range. Using THK type linear slides to carry the carriage. I'm looking at doing some very precision working..

ie, 100 mm lengh, turn down in several places to as small as 2mm, with +/- .02mm.

I'm afraid that I might not be able to get the precision that I need out of the china made lathe. ((Although, I'm sure it's possible)) Also the through hole on the chuck is a limited factor for me also, since I'd like to turn a few parts that are in the 2inch range. Ie, crowning on rifle barrels.

I'm planning on getting most of the parts used via ebay. The steel, I can get for free.

I'm not sure how much it will cost to have it face milled. I'm also unsure of the how true it will be, or if it will flex etc.

Does anyone see any flaws in my idea, aside from cost?

*rambles*

[Deviant]

Here's a rough idea of what I'm thinking.

This doesn't include the head assembly/tailstock etc.

Just the main body, with the rails and the carriage.

[Stevie]

Mine is running on chrome round ways by Thompson
The tail stock also runs on the same way; the bed is machined (by cnc) out of 7075 T651; the head is the same and carries 2 Taper roller bearings with a 30mm ID
The spindle is 4140 prehard; and carries a 3" 3 jaw
The leadscrews are nothing special; 8mm threaded rod for the X axis; 1/2" 13 UNC for the Z; I checked the travel over 4" and it is dead on; same at 2"; so i was happy with the threaded rod use (note this is high grade rod; B7 grade too) both run bronze nuts; the cross slide is pre loaded with a Sacrificial teflon button; the Z is a 2 nut setup with giudes for the 2nd nut and a spring between the 2; the rear nut is the active nut and fastened to thebottom of the carrage and the total play is just 0.0065" if i put pressure on it towards the chuck; but as this is the cut direction there is no play (I chked it last night)

The tailstock has a #0 morse taper; I have 1 live center (I made it) 3 drill chucks 2 #0 Jacobs and a Rhom 0-1/4

I control the play in the carrage with teflon buttons; and brass wearpads under 5mm setscrews; thetail stock has a similar setup

The steppers are X axis <Compumotor 57-83> with a Zeta4 drive; the Z is a EAD Nema23 with 250 oz/in driven again by a Zeta4
Both run at the 2000 micro step setting; I have taken 0.150"/side cuts in brass with no problem at all

My leadscrew for Z is centered under the rails; to stop jagging (side mount can do that)
The carrage was CNC wire cut for the round rods that it rides on; as for the X axis; it was also wire cut but 45 dgr V ways; the upper traveling part of X is also 4140 prehard steel; the upper has Sacrificial teflon buttons forplay control when it starts to wear (no sign yet)

The main motor just got changed this week; I dropped from a 1/2Hp 120V to a 1/3Hp 120V because i got it brand new off eBay for $20 and it's a very good make; the drive is with step pulleys running a 1/4 diameter Polycord I have 14 speeds and as the main motor is 3450rpm i can hit 10,000rpm

Due to the high useage just 1-2" from the chuck; i have already changed the first set of Thompson shafts to keep it accurate; as this machine can run up to 16 hours in a day; I need to keep on top of maintainance

[Evodyne]

Deviant,

Hi! I've been poking around on ebay quite a bit and you can find complete slide assemblies for less than you could build one. I've bought some with motors,ground ball screws, THK or NSK rails, end of travel limits, and sometimes even linear encoders. Usable sizes too - 48 inches for under $300.

If you want to say "I built it all" then this isn't the way to go. But if the goal is to get your lathe automated cheaply (remember, your time has a cost too), then consider it.

My first router is going to be three such canned units bolted together. The X and Y axis I got as a pair for $100 with thick rails, no slop, 20+ inches of travel each, with motors and end of travel limits, and rated at 0.625 mil/step without microstepping. With two Geckodrives set for x10 microstepping that's 0.0625 mils per step.

Somethig to think about. Good luck!