Help me design my CNC lathe

[pippin88]

Hello all.

I'm going to scratch build a CNC lathe.
I've converted a 7x16. It was crap out of the box, with significant quality problems. I've improved some things, but would prefer to put in effort building a better machine rather than polishing a turd.

Objective
Build a CNC lathe - designed for CNC from start

Working area - flexible, but I'd like to be able to turn 300mm long and 200mm diameter.
Auto tool turret at some point, possibly gang tooling first. Probably just start by using my QCTP.
- probably this tool turret: CNC Lathe Turret - Other, STEP / IGES - 3D CAD model - GrabCAD

For hobby use. I don't ever foresee using it for production.

I don't require particularly heavy cuts. I'd be happy with 1-2mm depth of cut for 'heavy work' in aluminium. Would like to be able to handle steel, including the occasional bit of stainless.

What I have
HSR30 linear rails 2x 1metre long, with 6 bearings
- got these cheap, if other rails suit better, I'm happy to buy them. For instance, HSR30 are quite tall (45mm from bottom of rail to top of bearing), which means higher cross slide - the spindle axis has to be higher which brings potential issues.
Current design uses these cut staggered, such that on the Z axis there is a 650mm length with two bearings, and a 520mm length with 1 bearing - this allows 400mm travel.

Steppers + contoller

750W Servo for spindle motor
G320X

Current design:
Based on large section steel RHS. E.g. 200x200x8mm tube.
- possibly with epoxy granite cast in for support and mass.

400mm travel in Z
190mm travel in X

Planning on:
- linear rails
- double nut ballscrews

Spindle:
Looking at cartridge spindles such as: Spindle CNC Lathe Machine,Belt Driven Spindle-in Machine Tool Spindle from Industry & Business on Aliexpress.com | Alibaba Group

Budget
Very flexible. I'd prefer to pay more to do this right the first time. I've done a lot of projects that I've not been satisfied with, often because I've tried to cheap out.
However, I don't really want to spend $10,000

Wants, but not essential
Some live tooling.
Basic drilling (e.g. being able to drill a bolt circle but rotating spindle in increments) - possibly full C Axis

Tools
I've got a CNC converted G0704 clone
General tools

I'm building a metal casting furnace
I plan to purchase a decent size surface plate

Just bought a inverter stick welder, but I've not welded before and don't plan to use welding for this project (except for stand / enclosure)

Thoughts that need addressing
I'm really coming around to the idea of a tailstock, most likely a simple tailstock to allow turning between centres / supporting long work.
For this I envisage a wider base, with the Z axis rails offset to the side (meaning they are more directly under where the turret will be) and a set of rails for the tailstock as well.

What is the optimal offset of the Z axis rails?

Orientation of X axis bearings - upright or upside down? (See attached)
- upright means a long carriage plate, but short cross slide plate.
- upside down means rails contribute to stiffness of cross slide plate.

Other designs
jakemestre has an excellent building happening: http://www.cnczone.com/forums/bencht...ilt-lathe.html

Guldberg [urlhttp://www.cnczone.com/forums/vertical-mill-lathe-project-log/51688-slant-bed-cnc-lathe-scratch.html[/url]

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[rowbare]

You could reduce the spindle height by rotating your rails 90 degrees and mounting them to the side of the base tube.

bob

[Tkamsker]

I also designed a turret Based on Dieters Design but Not pneumatic ,..


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[pippin88]

Bob, that's a good thought and one I had also had, however I rejected it because:
1. Much more machining of tube, and vastly more difficult to achieve alignment
2. Less rigid
3. I'd like the ballscrew centered anyway, so will need some gap above the bed.

Tkamster:
Do you have drawings, pictures and/or video? I'd love to see it as I would like one that didn't require pneumatics.

[Tkamsker]

Hi yes i have on my Old Homepage www.tkamsker.at:8080/web/pub/werkzeugwechsler
I now bought an vmc Mill to do it in Alu and Steel ,.. Its my Winter Project
I have a linuxcnc component for Control (i retrofit a bridgeport 412 now ) ,...


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[pippin88]

Tkamsker - I couldn't see pictures of your actual turret. I found some 3D printed prototypes.

Attached is a revision with a wider base to allow tailstock rails to run along side.

In current form I'd have:

Max turning diameter over cross slide = 175mm
Z travel 400mm
X travel 180mm

Thoughts?

I've also thought about epoxy granite, but hardly anyone seems to have actually completed a machine and it comes with a number of difficulties such as:
- what mix to use
- vibrating and compacting
- mould making

[Tkamsker]

Hi The simply reason is i Do a Bridgeport 412 interact retrofit project First (i documented the atc success ) the linuxcnc component for the atc is the Same aß for the lathe so i hope to finnish retrofit in 4 weeks and Then i can finnish late Turret ..

[pippin88]

Some progress:

I've tracked down a supplier for the RHS tube - 200x200x9mm, 1 metre long.

I've also found two machine shops who will skim cut the top and drill mounting holes for me, for a good price.

I've decided to use the HSR30 rails for the tailstock also. This will make things much easier.
I'll buy new rails for the X axis.

[Fenza CNC]

Hi pippin 88, that spindle you linked was from Alibaba, I'd steer well clear of unrated sellers on Alibaba. It is very easy to be scammed on Alibaba and $1,000 isn't exactly pocket change. I'm sure many of the sellers on there are legit, but they tend to have lots of good feedback. In fact I once got scammed by a 4 year gold-level member with tons of great feedback so maybe I'm biased.

The spindles obviously the heart of the machine so definitely an area to not cheap out. New Hardinge spindles occasionally crop up on eBay from time to time, sometimes at silly low prices from when they went bust. I believe there are some good Taiwanese spindle makers. CELLS TEC is the only one off the top of my head and the quote I had from them wasn't bad at all, I think it was £1,500 for their lower end BT30 milling spindle.
Here's a link to their site CELLS TEC Co., Ltd.

I think your design looks pretty good, only thing I'd think would be maybe thicker RHS than 9mm (can't hurt can it?).

Your use of three carriages per axis is new to me, has this been done before? I can't see why it won't work, so I'm intrigued.

Also if you're planning Epoxy Granite fill or something similar (I think RHS could really benefit from it) maybe think about one larger weight reduction hole in the centre rather than four, it should be more efficient use of the material.

I hope to see your project up and running soon. What kind of tolerances are you expecting to achieve?

Cheers,

Fenza

[pippin88]

Fenza,

I haven't committed to a spindle yet. There is one seller who has communicated well and seems ok, but I am wary in general. At some point someone needs to take a risk to find reputable sellers - I can't find much reference to people buying cartridge spindles.
I may buy a manual lathe spindle +/- headstock.

I can't get less than an 8m length of thicker RHS. So 9mm is it.

I did the design using 3 rather than 4 carriages to allow me to use the current 6 carriages for 2 axes. A single HSR30L carriage is longer than a 7x12 mini lathe bed is wide. I've since decided to use 2 carriages for a tailstock, so I'm buying new rails and carriages for the X axis. I'll have 4 per axis now.

The reason for the 4 holes with epoxy granite was to maintain a central column for compressive strength.

Thanks for your input, I'll post an updated design soon.

[pippin88]

Well, I got all my big RHS steel in. Looks solid.

I've also got to decide what to do with steppers.

I'm redoing my router at present also.
I'm going to use LinuxCNC with a mesanet 7i43 FPGA hardware step generator.

I've got:
3x 387oz-in steppers (Voltage: 50V Max, Current: 3.5A, Inductance: 2.8mH)
A G540.
3x 280oz-in steppers (8 wire http://www.probotix.com/specs/HT23-280-8.pdf) that I can wire bipolar parallel.

So I'm tossing up whether to put 2x 280oz-in in dual drive to move the gantry on the router, and then use 2x 387oz-in on my lathe. Or use the 387oz-in on the router and the 280oz-in on the lathe

I need:
I need 4 drivers for the basic router movement, but I also want a rotary (4th) axis, so I need an extra driver.
- Any suggestions on stepper driver?
- I have a 5amp 570oz-in stepper on my mill currently (under) driven by my G540, so I'm tempted to get a driver that will take full advantage of this stepper.

I'm looking very seriously at a CWD556 - it appears to be the exact same as a Keling 5056D, but is available quite cheaply. Does anyone have any experience with this driver?

(I'll be building an electronics 'cartridge' so that I'll use the same drivers and power supply for mill, lathe, and router. Just remove power and pull cartridge, plug in to next machine and plug in power).

[Tkamsker]

Hi i have now Moved to my New Portal so you could find the pictures of toolchanger at Welcome - tkamsker projecte werkzeugwechsler i also have Moved the drehbank retrofit where you See how I have done it. (I ll do the english translation in Winter too many Projects now )
I am a Little confused about your cartrige plan i understand you have you g540 for your router and want an fpga Board to improve ok why Not use the g540 you have on the lathe ? I woul in any Case like 2 separate power supplys that if i Hit emergency halt on the Mill the lathe can proceed ,..


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[pippin88]

I will be swapping the electronics from one machine to the next.
I will have three machines, but only one G540, 7i43, power supply.

This means I save the cost of 2x G540, power supplies etc.

I will only be using one machine at a time. It would not be possible to use two machines at the same time with this system.

[Tkamsker]

I would then do it totfallt different Look of what In have done F12A Retrofit Iteration1 - tkamsker
There you See 2 examples One is my touchscreen combo where Image an (ugly ) box where you have touchscreen and all in One box so Plug the Steppers from One machine to another and all is Fine just right config and here you go the 2nd box i made there you See triple beast Inside and the yellow box is an pc called ncbox Works also the Idea is to have that Avail for all machines just bring machine mouse Screen Keyboard here you go ,..


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[Fastest1]

I did this at first, running a few machines from 1 controller/BOB/drivers. What a PIA! Yes it works but it is like having an all in 1 machine that you have to change the set up just to complete a simple task. As soon as you start to machine anything, you need all of your tools to be operable. Of course I also understand what budget allows. At 1 time I had 2 machines hooked up to the same box via 3 A/B switches (1 for each axis). Theoretically it worked and in practice however noise was much harder to trace.

[pippin88]

I'm aware of the downsides, but my shed is powered by an extension cord, so I can only safely power one machine at a time anyway. I also only do one offs really, so need to be observing the machine during operation anyway.
If I decide to expand to electronics for each machine in the end it won't be any great loss / extra cost.

[LeeWay]

I did it for awhile as well, but unplugged the motor cables. The two machines had similar sized motors at that time and it worked okay. Didn't last long though.