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Australian Rocketry • CNC'ing a small lathe - pimping the unpimpable... - Page 4
Page 4 of 6

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Wed Jun 15, 2011 7:11 am
by cha05cat
If you need a hand with the GCode then I would be happy to drop around some time to assist.

The last time I used it was like 3 Years ago, however between us it shouldn't be too hard.

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Wed Jun 15, 2011 7:58 pm
by cryoscum
How easy was that!?! 2 iterations on the Z-axis, then chopped the code to do 100mm long move for better accuracy, another finetune (it moved 104mm when it should have done 100mm) and all fixed up. Then X-axis, which was only out by a small bit and all done. The correct number of steps ended up being 2680 for Z and 2010 for x.

Watching it mock-cut a half-sphere now...

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Wed Jun 15, 2011 8:28 pm
by Space Mark
Awesome work cryoscum. Looking to see what comes out of it!

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Thu Jun 16, 2011 8:31 am
by PK
OK, time to tune the thing.

You will need a dial gauge and magnetic base for this. Get one if you don't have one, they're pretty useful on a lathe. If you can get your hands on a dial test indicator (DTI) at the same time then do so, you won't regret it.

Anyhow the basic process is.
Motor tuning-> set axis speed to max, set axis acceleration low (say 200mm/s/s)

Set the dial gauge up on the axis a bit like this:

Here I was using the gauge to check the repeatability of proximity sensors as home switches.


Run this code.

G92 X0
G1 X20 F100
G1 X0
M01
M47

Run it a few times and tweak the gauge so that it reads zero when the axis returns to the starting position.

Now start winding up that F setting. Keep going up until the motor stalls or the axis doesn't come back to the same point (lost steps)
If you get to a point where it's not stalling or missing steps but you can't go any faster then go into ports and pins and increase the kernel speed, reboot, then go back to motor tuning and crank it up higher. (nb, if you have to do that bit on the second axis, you'll need to go back and repeat the tuning on the first).
Once you know the absolute top speed you can get. motor tuning-> set the max velocity to 75% of that value.

Now repeat the process with acceleration.


PK

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Thu Jun 16, 2011 9:40 pm
by cryoscum
Hi All

Tuning all done. Ended up sticking with 45kHz kernel speed, inspite of the fact that I had good success up to 75kHz. This way I got about 1.3m per minute on the X-axis and about 900mm per minute on Z. Seems all good.


Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Thu Jun 16, 2011 10:35 pm
by air.command
Very impressive work cryoscum! What do you think you'll be putting it to work on first?

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Thu Jun 16, 2011 10:46 pm
by ROCKet STAR

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Fri Jun 17, 2011 5:39 am
by cryoscum
Thanks gents. I thought I'd do a 5:1 Von Karman 29mm nose cone positive first, making a mould following the usual process described elsewhere on the forum.

For just for a bit of fun I'd like to see how fast I can get a G76T...

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Fri Jun 17, 2011 3:32 pm
by Space Mark
Is your lathe the same as this one?
http://www.ebay.com.au/itm/SIEG-C2-12-X ... 3f0acb8a3b

They look very similar?

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Fri Jun 17, 2011 7:13 pm
by cryoscum
Hi Space Mark

Close, its a Sieg C3 rebranded as a CarbaTec C3.

Cheers
Nic

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Sat Jun 25, 2011 9:23 am
by cryoscum
Not sure this is the right spot for it on the forum, but it is closely linked to this thread, so here goes anyway:

Given the completion (mostly) of the CNC lathe, I thought it's time to do something worthwhile with it, not just cutting shapes to test it. I thought I'd do a 29mm NC, something small to start off with.

First some research:
http://en.wikipedia.org/wiki/Nose_cone_design
Seems that an LD-Haack NC (aka Von Karmen) is the most efficient for transonic, and beyond, flights - not the conical shape that seems to be a common misconception.
1.JPG
1.JPG (33.7 KiB) Viewed 2885 times

Also note the following:
2.jpg
2.jpg (94.26 KiB) Viewed 2885 times


So my task seems clear, namely a 29mm dia Von Karmen with a 1:5 fineness ratio.
Spreadsheet time to generate the points.
3.JPG
3.JPG (84.65 KiB) Viewed 2885 times


For 1.5mm increments of X, here are the numbers:
(NB: Note that the calcs are in the standard Carthesian coordinate system, but for the lathe X is actually along the Z-axis and and Y along the lathe's X-axis)

x (metres) Theta y (metres)
0 0 0
0.00150 0.18033 0.00065
0.00300 0.25538 0.00109
0.00450 0.31320 0.00148
0.00600 0.36216 0.00183
0.00750 0.40547 0.00216
0.00900 0.44479 0.00248
0.01050 0.48110 0.00278
0.01200 0.51505 0.00307
0.01350 0.54707 0.00335
0.01500 0.57749 0.00362
0.01650 0.60655 0.00388
0.01800 0.63444 0.00414
0.01950 0.66131 0.00439
0.02100 0.68728 0.00463
0.02250 0.71246 0.00487
0.02400 0.73692 0.00511
0.02550 0.76074 0.00534
0.02700 0.78398 0.00556
0.02850 0.80669 0.00578
0.03000 0.82892 0.00600
0.03150 0.85070 0.00622
0.03300 0.87207 0.00643
0.03450 0.89307 0.00664
0.03600 0.91371 0.00685
0.03750 0.93403 0.00705
0.03900 0.95406 0.00725
0.04050 0.97380 0.00745
0.04200 0.99328 0.00764
0.04350 1.01251 0.00783
0.04500 1.03152 0.00802
0.04650 1.05032 0.00821
0.04800 1.06891 0.00840
0.04950 1.08731 0.00858
0.05100 1.10554 0.00876
0.05250 1.12361 0.00894
0.05400 1.14152 0.00912
0.05550 1.15928 0.00929
0.05700 1.17691 0.00947
0.05850 1.19440 0.00964
0.06000 1.21178 0.00981
0.06150 1.22905 0.00997
0.06300 1.24621 0.01014
0.06450 1.26327 0.01030
0.06600 1.28024 0.01047
0.06750 1.29712 0.01063
0.06900 1.31393 0.01079
0.07050 1.33066 0.01095
0.07200 1.34732 0.01110
0.07350 1.36392 0.01126
0.07500 1.38046 0.01141
0.07650 1.39695 0.01156
0.07800 1.41339 0.01171
0.07950 1.42979 0.01186
0.08100 1.44615 0.01200
0.08250 1.46248 0.01215
0.08400 1.47877 0.01229
0.08550 1.49505 0.01244
0.08700 1.51130 0.01258
0.08850 1.52754 0.01272
0.09000 1.54377 0.01285
0.09150 1.55999 0.01299
0.09300 1.57620 0.01313
0.09450 1.59242 0.01326
0.09600 1.60864 0.01339
0.09750 1.62488 0.01352
0.09900 1.64112 0.01365
0.10050 1.65739 0.01378
0.10200 1.67368 0.01391
0.10350 1.69000 0.01403
0.10500 1.70635 0.01416
0.10650 1.72273 0.01428
0.10800 1.73916 0.01440
0.10950 1.75563 0.01452
0.11100 1.77215 0.01464
0.11250 1.78873 0.01476
0.11400 1.80537 0.01488
0.11550 1.82208 0.01499
0.11700 1.83886 0.01510
0.11850 1.85572 0.01522
0.12000 1.87266 0.01533
0.12150 1.88969 0.01544
0.12300 1.90681 0.01554
0.12450 1.92404 0.01565
0.12600 1.94138 0.01576
0.12750 1.95884 0.01586
0.12900 1.97642 0.01596
0.13050 1.99414 0.01606
0.13200 2.01200 0.01616
0.13350 2.03001 0.01626
0.13500 2.04818 0.01636
0.13650 2.06653 0.01645
0.13800 2.08506 0.01655
0.13950 2.10378 0.01664
0.14100 2.12272 0.01673
0.14250 2.14188 0.01682
0.14400 2.16127 0.01691
0.14550 2.18093 0.01699
0.14700 2.20085 0.01708
0.14850 2.22107 0.01716
0.15000 2.24161 0.01724
0.15150 2.26248 0.01732
0.15300 2.28373 0.01740
0.15450 2.30537 0.01747

Will post more later...

Cheers
Nic

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Sun Jun 26, 2011 9:56 pm
by cryoscum
I've simplified the shape and did the Gcode programming to get to this:
1.JPG
1.JPG (47.07 KiB) Viewed 2855 times

Will cut the shoulder manually, because it would require a tool change.
Still need to do a dry run and then play around with the feed rates, but I think its all there now...

Cheers
Nic

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Mon Jun 27, 2011 6:37 pm
by cryoscum
The above code was 'hand written' as I'm still looking for something cheap and simple to do the roughing cut coding, but its probably good to do it the long way at least once.

Test drove the code on some 30mm HDPE stock. First did a 24mm version of the code (left in the photo), but the HDPE gets 'unpredictable' when it gets too thin - tip got buggered. The 29mm version (right) worked OK. Total cutting time about 8 minutes and it generates mountains of swarf that needs to be cleared as it'll jam the whole lot if you let it.

1.JPG
1.JPG (49.77 KiB) Viewed 2832 times


Looks like it may be on to the mill next?

Cheers
Nic

PS Don't try to flame polish HDPE, it doesn't work!

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Mon Jun 27, 2011 7:12 pm
by RobAust
Hey Nic,

I think your just about safe to safe; "the unpimpable has been pimped".......

Great post from the start to the outcome, keep posting your results.

Regards,

RobW

Re: CNC'ing a small lathe - pimping the unpimpable...

Posted: Mon Jun 27, 2011 7:30 pm
by air.command
Very nice work there Nic! :D Do you think you'll need to add a cover for the belt to stop the swarf getting into the belt or pulleys?