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Author Topic: Chrisjh Home Built CNC Lathe  (Read 24766 times)

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Chrisjh Home Built CNC Lathe
« on: September 04, 2009, 06:39:25 PM »
Hi All,

I thought that since I got inspiration from this forum I should share what I have acheived so far.

The design started 12 months ago and the actual build started 3 months ago.

Specs as follows:

38mm spindle bore using a Chinese Spindle (bought as a spare part for my manual lathe)

Spindle has a D1-4 and 5MT Chuck Interface so I can use all my Chucks and 5C Collet System from my manual Lathe.

20 x 5 x 640 Z axis ball screw and nut (Hiwin)

16 x 5 x 320 X Axis ball screw and nut (Hiwin)

20mm Linear Rails and Bearings (Hiwin)

Danfoss 0.75KW VFD (240VAC Single Phase I/P, 3 Phase 240VAC O/P, 0-200Hz) with Rototech 3 Phase Motor wired in Delta configuration.

Approx 3:1 Pulley Ratio and Powertwist Belt. (The 150mm pulley is from my old 1968 Datsun 1600 from years ago.  I cut out the centre and replaced it with my own designed and manufactured Taperlock Clamp on to the spindle.)

The current spindle speed is continuously variable from 250 to 1200RPM under Mach3 PWM control.

Smoothstepper and C23 BOB. (I didn't like the PWM to Analogue tacho chip on the C23 BOB, so I built my own much simpler and linear PWM to Analogue Converter and piggybacked it on to the c23).

Spindle Speed Feedback is supplied with an OPB960 IR Opto/Schmitt Trigger through an 8mm Slot Index Pulse generator mounted on the Spindle (CSS works flawlessly).

Meanwell 500W 48VDC PSU adjusted to 42VDC for the Steppers and Stepper Drivers.

Meanwell Dual 5/12VDC PSU to power everything else.

Leadshine M542 Stepper Controllers with 430oz/in Z Stepper and 311oz/in X Stepper.

Leadshine M542 Stepper Drivers.

Most parts are machined or fabricated from Mild Steel including the 1 metre bed (200 x 75 C Section Steel).  Headstock is 16mm thick Steel including a stiffening plate on the underside of the bed.

The bearing blocks are Aluminium treated with Alochrome 1200S machined on my X3 CNC Mill.

Spindle Bearings are 110mm Tapered Roller (Front) and 100mm Double Row Angular (Rear).

Axis bearings are simple Single Row Sealed on the leadscrew support end and angular contact on the motor end.

The stand is 65 x 65 x 5 RHS with adjustable levelling feet.

A slide out chip tray stainer located under the bed and below that is coolant return tray.

The cross slide has plenty of M6 threaded holes for all possible combinations of tooling.  My plan is for gang tooling all designed by yet to be fabricated.

I plan to use a fishtank submersible pump located in a heavy duty plastic bucket (I fed up with the problems I have had with Chinese coolant systems in my cnc mill and cutoff saw).

Here is the first cut done with much trepidation and fear!!!




Brisbane Australia
Re: Chrisjh Home Built CNC Lathe
« Reply #1 on: October 10, 2009, 07:50:02 PM »
Hi Chrisjh

How did the fish tank pump go. I use a electric fuel pump from REPCO and think they cost about $90.


Re: Chrisjh Home Built CNC Lathe
« Reply #2 on: October 10, 2009, 08:53:25 PM »
Haven't got that far yet.

I am still setting up my gang toolpost.  This morning I almost completed a custom LH boring bar that I intend to use as tool 1 in the tooltable.

Coolant will probably be a couple of months away.


Re: Chrisjh Home Built CNC Lathe
« Reply #3 on: February 05, 2010, 04:31:16 PM »
Making Progress!!!

I had a serious vibration problem when doing OD Cuts.  Facing seems to give good results but the surface finish on OD cuts were terrible not to mention the soul destroying noise emanating from the machine when performing OD cuts.

Long story short:
I dismantled the spindle assy from the headstock and checked the bearings.  Ah ah, I noticed that the tapered roller bearing cage was fouling the bearing housing.  This is it, I thought.  I checked my Solidworks models and there should have been clearance?  Problem was that the Solidworks bearing model I downloaded was different from the actual bearing that I had (the cage stuck out approx 1mm more than my CAD model).  This meant that the cage was touching the bearing housing before the outer race bottomed.

I countered bored the spindle housing 3mm deeper and amended the model and drawing.  I reassembled the spindle assy, making sure that the outer race was “bottomed”, and tightened the bearing preload to “tight” with a 150mm pipe extension on the C Spanner and back off a bit.

There was no improvement!!!

I gave up for 3 months and did other things. (Rather despondent mood.  I had convinced myself that I had a terrible design and the bed/frame structure was too weak).

I decided to get scientific about it and measure the flex in the bed/frame structure.  I mounted a dial gauge between the bed and the top of the head stock.  Stuck a 1m long piece of 38mm steel rod in the big 6 jaw chuck sticking out approx 800mm.  I put all my weight (approx 80kg) on to the rod and all I could measure was .003" movement.  Upwards pressure produced similar results.  Not too bad, I thought, so what was wrong?

During this process I noticed a visible minute movement between the front bearing housing and the spindle.  I clamped a piece of 19mm brass rod across the 6 jaw chuck and rotated the spindle until the rod was stopped at the bed/frame.  Then I fitted the C Spanner to the preload nut and extended the handle with a piece of pipe 500mm long.  I was able to tighten the preload nut approx 1 turn (pitch is 1.5mm).  The spindle at this stage could be rotated by hand but I could feed that it was too tight. I backed it off 1/3 turn and the spindle freed up.

I ran the spindle for a few hours and noticed that it sounded better.  I tried and OD cut 0.25mm deep and results were astounding.  The noise and vibration had gone and the surface finish was as expected.
Proof was to make something.  Here it is: http://www.youtube.com/watch?v=9kRHpfDiRsE

Offline budman68

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Re: Chrisjh Home Built CNC Lathe
« Reply #4 on: February 11, 2010, 08:52:43 AM »
Looks like you're doing a great job Chris, I'm hoping to set up some gang tooling on my little Taig lathe in the future.

Thanks for sharing-
Just because I'm a Global Moderator, don't assume that I know anything !

Dave->    ;)
Re: Chrisjh Home Built CNC Lathe
« Reply #5 on: February 27, 2010, 01:16:10 AM »
More Progress!!

I added the coolant plumbing and a parting blade. 

The parting blade is made from an old wood circular saw with tungsten carbide tips.  I got this great idea from Peter on the HSM forum.  Thanks Peter.  There is an excellent thread at http://bbs.homeshopmachinist.net/showthread.php?t=39202 regarding shop made tooling.  I have had great inspirations from that thread.  Peter's idea can be found here : http://bbs.homeshopmachinist.net/showpost.php?p=516034&postcount=328

For Peter's parting blade, I designed and made a special upside down tool holder for the gang tool post.  I am very pleased with the parting results.  Centre line adjustments for the tip are made with a rocking action around the centre of a 16mm Stainless Steel Rod held in the tool post. All I have to do is adjust the two M8 screws at the rear of the assembly to get the tip on centre.

It took me some time (2 days) to work out how to program the gang tool post.  Initially I tried to use Mach3's tool table which worked but the tool table offset calls were causing the tool to go indirectly (not directly as I expected) to the cutting position.  The result was that the cross slide would travel to the X+ limit switch on tools that were not the master. 

Because I did not understand how the tool table movements were programmed internally, I gave up with the tool table approach.  It was not going to work the way I thought it should.  It also added more time to the program with its indirect route. 

I then manually programmed the spot drill and drill to go to their respective absolute positions.  This worked but had the end result of buggering up the Constant Surface Speed (CSS) operation.  Large offsets caused the CSS to command the spindle speed to go too slow (makes sense when I now think about it).

Then I tried G54 to G59 fixture offsets but this had the same problem with CSS.

Then the penny dropped after doing some research with Peter Smid's bible.  I used temporary offset command G52 X??? Z??? to move the non master tools to their respective cutting positions.  This solved the CSS problem and worked so well that I have decided to do all my future programming for the gang tool post this way.

I am currently making drip directing devices for the coolant.  The coolant travels along the frame and drips outside the catch area of my coolant return tray.  Next will be a mudguard (Some call them wings or fenders) for the chuck.  I had to dodge the spray from the chuck a couple of times.

Here is the lathe in action with coolant and parting added:  http://www.youtube.com/watch?v=55SLUjDg5go

Re: Chrisjh Home Built CNC Lathe
« Reply #6 on: October 05, 2011, 05:29:32 AM »

Today I made a thread test gauge, I guess you would call it a go/no go gauge to be used on a part that I make from time to time.

This was my first attempt at internal threading.  I was pleased with the result.



There a few other videos that I have posted on youtube showing other bits being made for those interested.



Offline Hood

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Re: Chrisjh Home Built CNC Lathe
« Reply #7 on: October 09, 2011, 02:06:33 PM »
Looks to be working good for you. Got a fright at first, thought you were away to cut a left hand thread :D
Re: Chrisjh Home Built CNC Lathe
« Reply #8 on: October 10, 2011, 05:59:08 PM »
Hi Hood,

Fear is what I felt when the boring bar with the threading insert plunged for the first time inside the job in the chuck!!!  I cut air just short of the job a few time before I plucked up the courgage to set the Z zero at the face of the stock.  All went well and I feel more confident now.

As you observed, I had to hand code the start of the cut from inside and move out to get a RH thread.

Here is the code I used:

(Cut M27 x 1.5 Internal Thread)

(Select RH External Threading Insert Mounted On LH Boring Bar in Tool Block Hole 4)

(Tip to tip measurement between master tool and threading tool is 94.551mm, therefore X offset for threading tool is 2 x 94.551 = X189.1)

G52 X189.1 Z0 (Temporary Offset Position for Threading Tool Tip)

G00  X-23
G00 Z3 (Clearance for Start of Threading Routine)
G00 X-25.5 (Go to Minor Diameter Position)

G76 X-27 Z3 Q1 P1.5 J0.075 L0 H0.15 I29.5 K-18 C2.5 B0.025 T0

(X=Ø Last Threading Pass, R=Ø 1st Threading Pass, Z=Thread End Position, K=ZStart Position, P=Pitch, J=MinDepth/Pass, H=Depth1stPass, B=DepthLastPass)

(C=X Clearance Rapid Return, Q=Spring Passes, L=ExitAngle/Rev, I=InfeedAngle, T=TaperAngle)

G00 X-23
G00 Z20 (Go to Safe Position)

I use lots of comments in my coding to make it easier for me to recall what I did in the future and to make it easier for me to write the next routine.  Saves me having to use reference material (Mach3 Turn Manual, Rich's excellent threading manual, and Smid's CNC Programming Handbook) all the time.



Offline Hood

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Re: Chrisjh Home Built CNC Lathe
« Reply #9 on: October 11, 2011, 02:16:23 AM »
Oh I know that feeling, was very nervous the first time I did an internal thread on the Computurn.
Comments are good in your code, I should do it more in any hand written stuff I do, the code my CAM produces has comments.