Lathe conversion from stock to CNC

Soundreflections wrote:

I have a 4 jaw chuck, for which I have started turning an adaptor plate, but stopped when I realised I need highest precision possible for the recesses, as the plate needs to fit my lathe's faceplate snugly, and the chuck needs to snug in as well

You just need something that can screw onto the spindle nose. It need not be terribly precise at first. (though will be an interesting excercise in internal threading).
You then mount it on the spindle, and machine OD and register in-situ to take the chuck. Then it _has_ to be true.

If you want to then clean up the back face, re-mount the three-jaw, mount a bar in that then mount the4-jaw on the bar.

I am keen to know how you think I can mount the compound vertically

As JT says, a bit of sturdy angle would work (possibly with a welded gusset).
Bolt it to the cross-slide (I am not sure how, this is the hardest part) and face it off with a lathe tool held in the 4-jaw chuck (crosswise, like a big fly-cutter).
Then bore a hole to suit the compound-slide pivot pin. Probably with a drill mounted in the chuck, followed by a lathe boring-bar mounted eccentrically in a 4-jaw chuck (an adjustable boring bar would be better, of course). Maybe this one:-)
global.ebay.com/Wohlhaupter-UPA2-5702/261069311985/item (actually I was going to post a joke link to a $2000 tool, but that one is a significant bargain at the current price)

Drill more holes at the correct centres for the hold-down bolts, then mount it properly.

Then face it off with the scary fly-cutter again, and drill a second hole. The size of this one doesn't matter, but needs to be smaller than the compound slide register.

Then put the lathe back together, and turn a spigot to fit in the second hole snugly, and to suit the recess in the compound slide base.

Soundreflections wrote:

OK, Only one pic survived - I must still figure quite how pictures work in this forum.

You can only insert one pic using the button, but you can link to several usingtags. There is a button above the edit window that you can use to not really help with the tags.

I always just edit the post and move the tag where I want it...

John

The vise appears a bit on the large size compared to the rest of the components. You could just have a plate mounted to the compound with some tapped holes in it and clamp your work down. For fly cutting like Andy said you just need to adjust the vertical axis (the compound) to center your material then using the crossfeed you can fly cut the material to size. More ways to skin a cat as we say around here than the cat cares to know about. You can also get machinist angles... I assume that you use mm so your not in the US?

John

Soundreflections wrote:
[quoteWhat PC card would you recommend, to be able to handle 2/3 axis, I want to put dual encoders on the spindle, but the encoders I have available may have too many holes, it will be high frequency if it works[/quote]

Why dual encoders?

If you want to go much above 20kHz count rate on the encoder then you can't use the p-port any more, so that would be ) only 300 rpm for a 1024 (4096 count, allowing for quadrature) encoder.

My lathe uses the Mesa 7i43 card, which connects to the parallel port and can measure 10MHz encoder counts, and produce similarly fast stepper pulses. I am not sure that I would use the same thing again, as other boards have been developed in the meantime, but at $80 and easy cabling it is still quite an attractive option. You would probably also want to budget for at least one $45 7i42TA with that.

Other options would be the Pico PPMC (Also connects to the p-port, but moves the counting and step generation to hardware): www.pico-systems.com/univstep.html
It is a bit more plug-and-play than the Mesa 7i43 system, and the price ($250) is similar by the time you have added connector cards to the Mesa.

Mesa also offers the 5i25/7i76 combination for stepper machines. That's a low-profile PCI card and a remote breakout . for $200 including the cable. (there is also a 6i25 PCIe card which is equivalent)
Quite a popular combination but only handles 1 encoder in the normal configuration. Swapping the 7i76 for a 7i77 makes for a very easy conversion to a servo system. You can connect all sorts of other IO to both the 7i76 and the 5i25 in addition, up to several hundred IO pins

I wouldn't bother with anything other than Pico or Mesa, just because both offer support here on the forum and mailing list.

How do I determine what size / rating servos I would need? Or does one just get the biggest one can afford and hope?

Good question. I have a big NEMA 23 stepper on my lathe Z rated at 3Nm, and that works fine most of the time, but can't really handle toolpost drilling. The X axis is a much smaller 2Nm NEMA23 stepper, and that is very much OK. The problem with bigger steppers is that they become more sluggish, losing torque more rapidly with speed than smaller ones. At some speed point there is a crossover where the little stepper makes more torque than the big one. My steppers are all connected via belts, which adds to the complexity because then you can play around on the speed/torque curve.

My next lathe will probably be servo, but that is mainly because I have servos found cheap on eBay.