Lever part 2

Here are a couple more images of the process of machining the lever, which I managed to complete last night.

I attempted to limit the machining processes as much as possible to left hand cutting operations to keep tool changes to a minimum, but the inside radius of the handle needs another tool and is best cut in the other direction.

Here is the scratch pass of the threading operation. I paused after this to check that the thread pitch is indeed 1.5mm.

Then, some 47 passes later, the threading is pretty much done.

A fair amount of sanding and polishing later and here is the finished part on the right with the original and the steel from whence it came on the left. As a side note, the threading at the small end of the lever that keeps the handle in place turns out to be imperial 5/16 - 18. Probably because they could't get the rather exotic blind nuts from a metric supplier. This makes it the one single exception to the otherwise absolute metric rule of the machine.

CNC lathe conversion part 2 - X axis

So I decided to undertake a non-destructive conversion of my King 10x36 Gear head. Not replacing the acme screws with lead-screws means that the mechanical conversion is pretty easy. Backlash and precision are not going to be great, but they may be good enough for the application. Time will tell.



Here is the saddle with the compound and the cross slide removed.
The lead screw is 5/8 x 10tpi acme. This has always been the weak point of this machine. It seems impossible to torque the acme nut to the compound and have the acme nut correctly adjusted to eliminate unreasonable backlash. Fixing that would likely require replacing the bearing, mount and probably also the nut and screw. More trouble that I think it is worth going to at this stage.





A shot of the existing screw and fixed bearing assembly. The double nuts at the end of the journal bearing are a very poor solution as counter-tightening the second nut tends to dramatically alter the load on the bearing.





I'll be using 5mm HTD timing belts and pulleys from SDP/SI (who have a very useful pulley designer on their site) rather than direct drive for this build. The X axis is the tricky one as the pulley plus the belt and the cover have to fit under the cross-slide. I was trying for around 2:1 advantage, but couldn't quite get there on the X. The configuration for the X is 13 double flange : 22 no flange with a 60 tooth belt. The Z is 19 df : 38 nf with a 77 tooth belt. Three of the four hubs all had to be re-bored to the correct shaft size. The 13 tooth was a total pita. 

A 6A25M022NF1508
A 6R25M060150
A 6A25M013DF1506
A 6A25M038NF1510
A 6R25M077150

A 6A25M019DF1508






The disassembled fixed bearing and, at the bottom of the shot, the journal extension with a 0.3745" stub, a section of M10 x 1.5 thread and a 0.5000" shaft to receive the drive pulley.





Here, the existing threads have been cut off the end of the lead screw journal and I'm just about to centre drill, drill out and ream a 0.3750" hole that will receive stub of the new journal extension.





A little loctite and a coffee break later and the new journal is done. 




All finished except for a cover (which turned out to be a little hard than I thought and after a couple of false starts isn't done yet). Note the brass nut replacing the double M10 nuts. This can be tightened to put just the right load on the bearing and then locked in place with a set screw. I dropped a little brass slug into the set screw hole before torquing it down to avoid damaging the screws on the journal.






The stepper (an Oriental Motor PK296DAA I think) and the mounts just fit inside the splash guard. A couple of final thoughts... There is an alternative to this mounting position as the King has an excellent gear box on the saddle to power either the Z or the X axis. Mounting the motor on the drive shaft of the gear box instead of directly to the end of the X lead screw would be very easy. While taking the X axis fixed bearing apart and reassembling it a few times I realized that, in addition to it being the least well-built part of this machine, it also isn't really intended to handle radial loads. While the motor and timing belt aren't particularly large loads, they still shouldn't really be on this bearing. If this proves problematic, I can either attempt to replace the whole bearing assembly with something better off-the-shelf, make a housing for the existing bearing that will handle the load or move the whole shebang to the gear box drive shaft. I decided not to go this route at the start because the gear box will induce considerably more backlash.

CNC lathe conversion part 1 - research

I was not really planning on going here at the beginning of the coffee project, but the prices I'm getting back for some of the parts are making me rethink at least the initial production run. There are some things that I cannot do in the shop: castings, complex cnc parts and plating etc. Cutting tapered parts is also not possible (or at least not practical) and the time I would spend on the learning curve for manual single point metric threading on an inch lathe seems like it might be better spent on tackling the CNC. However, my lathe is manual and possibly not the best starting point for a cnc conversion. I'm also not terribly keen on no longer having any manual control. So, some things to consider. 

(Note - here is a technique for manual metric threading using the half nut to disengage the lead screw.)   https://m.youtube.com/watch?v=HXt4TWa382Q  


Useful lathe CNC conversion posts:

8x12 Harbor Freight conversion
http://plsntcov.8m.com/CNClathe/CNClathe1.html

Excellent conversion of a Jet 13x40 http://www.hobby-machinist.com/threads/converting-a-13x40-manual-lathe-to-cnc-with-servos-and-mach3.33405/

Another excellent conversion using a kit from Billy Tools
longezproject.blogspot.ca/2015/02/cnc-lathe-conversion-part-1.html Possible converts:

Busy Bee 7x12

At 75 lbs there isn't really enough meat on the bones and bore is only 20mm.

Old and tired gearhead on kijiji

More old and tired 36" Logan on lespac

Converting a manual lathe to CNC is quite a bit more invasive than doing a manual mill. All of the elaborate gearing for threading and power feed are dumped along with the compound and the worm screws. All that one really needs is a solid frame, a good apron and the head and tail stock. Finding one with a 3 phase 220V motor would be a bonus, but unlikely. 

...so its back to ballscrews...

For my mill conversion I bought used ground ball screws for the X & Y and a new surplus for the Z from ebay. The precision of all three was C5 if not better. However, the X axis (which is the longest, most expensive and was the hardest to find) has some issues, possible because of a crash courtesy of the previous owner. So I am somewhat ambivalent about going the used route again. However, finding surplus screws of the right dimensions with support blocks is really tough, so the only affordable and convenient options for buying new are Chinese rolled C7 precision grade that come with journals and matching supports. C7 is 0.002" in 12" (in the worst case over the length of the screw) which, given what we are proposing to manufacture here, isn't that bad.

X axis

used THK - 14x4mm 358mm with 235mm travel - with supports and stepper frame - $189

used NSK - 16x5mm 407mm with 282mm travel - with supports and stepper frame - $189

used NSK 20x5 460mm overall with supports - $250

new NSK 25x5 ~440mm overall no supports - $270

surplus THK 14x2mm 416mm overall no supports $200

new Kuroda 12x2?mm ~15.5" overall no supports $90 plus shipping from US



Z Axis - the hard one...

used THK - 20x5mm x 1385mm ROLLED with supports - $239

new C7 Chinese - 20x05 x 1352mm with supports- linearmotionbearings2008 - $105 plus shipping



Update 2016 4 27

A couple of simple conversions using the existing lead screws. The second one is particularly interesting because it doesn't require giving up manual control! 

flashcut cnc
https://www.youtube.com/watch?v=_Polq5piWhQ

optimum
https://www.youtube.com/watch?v=FWg8NzfP108

A conversion of a small grizzly using a kit from BD Tools. Excellent blog about building an airplane too.

http://longezproject.blogspot.ca/2015/02/cnc-lathe-conversion-part-1.html