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Author Topic: emco pc5 lathe  (Read 4257 times)
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hutchison
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« on: July 02, 2009, 03:18:02 AM »

I picked up this emco pc5 lathe a few years back, its my first refit of a lathe, i've been on manual machines for over a decade, not long enough apparently as im still slaving.  I wanted the lathe to learn a bit about code,  it is greener on the other side isn't it?  Cheesy


   heres a picture of it inside before i finished wiring, and the outside, I also knocked up a quick cabinet so i could control both machines from the same interface, its no good having scores of pc's and screens laying around so i split the duty of the control for with a data switch, it would be nice to have machining centre that does both instead!
 
the lathe now has 2.2nm 4.3Amp motors, origonals were 0.5nm. i knocked up some hand dials for the double ended motors, engraved / divided them out and added handles, why didnt no-one tell me the ballscrews are R/H on the emco, pah!, i went to all that trouble and made the dials to make it a bit more useable .. turned the dials as you would....the slides went the wrong way!!  Cool  you just dont think of these things.

 it now rapids at 1.25m/min, origonals were 550mm/min. I put in some limit switches on all the axis, made the stops adjustable incase i use different tooling.   and a decent angular race on the spindle nose with a preloading mech instead of the standard deep groove bearing. I made a ground collet chuck, and made a set of matched ground tool holders.  i put in a 550w 3ph motor and modified mount plate, the next size up frame to the origonal and nearly double the standard motor torque, also a belt and timing pulley drive further increasing the torque by a 1.1:1 ratio,  it uses a vfd so i got some more torque available on overload!. its got enough beans i think  Wink.    It runs upto 2750rpm standard, i could overspeed it to over 3k but theres not much point really unless i'm drilling tiny holes.

it has all the extra electronic bits that usually go in the cabinet, what more can i say, i just wanted to share it, its just a wee benchtop.

 i'd like to thank arturo from cnc4pc.com for helping me since i started building, and all who support mach, ive probably read your posts at some point or other when up the creek. robin of holland aswell who helped me thru with the elctronic side.  i'm quite happy with my little lathe, it aint a gildemeister! but it's got a place in my workshop, cheers.












« Last Edit: October 03, 2009, 12:05:05 PM by hutchison » Logged
Tweakie.CNC
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« Reply #1 on: July 02, 2009, 11:54:58 AM »

Extremely neat work.

Tweakie.
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hutchison
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« Reply #2 on: October 04, 2009, 10:20:36 AM »

The lathe was running well but i had a few accidents with the bed stops whereby when jogging off the limit switch i pushed the wrong button (home!!) after a software reset and homed again into the deadstop!.. crunch...  it Damaged my 'Z' ballscrew, so i stripped it off to take a look.   Now here is the old emco ballscrew, not really impressed I could bend it with my hands easy, but hey itís only a litte training machine so you can pass on the plastic nut bracket i guess.   There is nothing wrong with an 8mm (5/16) ballscrew but at 508mm long it is definitely a little too flexible.



so i decided to make a steel ballscrew nut bracket, and fit a new ballscrew, the space under the carriage is so tight! i found the design a little testing to fit in a good device to hold the nut in firm without using to difficult a technique and still leaving room for the new screw guard / cover to fit over the top of it.   I came up with a two piece nut which was blocked up on the mill, squared up on the grinder,  then screwcut.



 I wanted to have a firm hold of the ballscrew nut but not too firm that would distort its precision by clamping.    The idea is you simply screw the ballnut into the nut clamp and then bolt on the other half of the bracket so it nips it in place and stops it unscrewing, the clamping dimension is just minus, so it literally may compress it by  1-5 microns.  23,993 - 23,998 as the ballnut is 23,999.  I ground that size on the grinder after leaving some meat on the fitting face.



i decided to go for a 12mm diameter with a 4mm lead, a 16 x 5 I couldnít make it fit in the constricting space.   A 12 x 5 ballscrew would have fitted also but because of the greater lead it would increase the helix angle and reduce the torque transferred, although it would have increased my rapid speed.  So, a 12 x 5 ballscrew gave me a helix angle of  7.62 degrees, a 12 x 4 comes in at 6.09 degrees.  The original thread of 8 x 2.5 gives 5.71 degrees helix.   12 x 4 was a pretty good compromise,  and I calculated if I just put that in, I should increase my rapid speeds to 1.8m/min  from the existing 1.25m/min max.  



 I had to space the ballscrew off on the X plane by 1.5mm away from the bed casting so the square portion of the ball nut bracket cleared the guard (since it was larger diameter!).   to do this I retained the original brackets and modified them.  I basically got some 1/16th gauge plate and made a spacer for the front supporting nut, and for the motor holding bracket at the back I elongated the original fixing holes by 1.7mm.



The existing ballscrew used two tiny ball single row radial bearings to support the rear of the ballscrew on a 6mm diameter (yes 6mm!)..  so out the window that went and in the new ballscrew design I made that diameter 10mm and searched for a suitable bearing.  I found a nice double row radial with some angular contact ability which  could cope with increased forces radially and also increased thrust forces in both axial directions.  Although not quite an angular contact thrust bearing it would be a much better replacement than the original single row radials.  To mount the bearing again the space was tight but I managed to figure in the 26mm bearing o.d into the original rear mount bracket by boring it out to 25.99 (0.01 for the manufacturer recommended preload! To reduce the axial play to within 10-15 microns) so I bored it out and a tiny bit deeper and made a clamping washer like the original, pressed it in, put the washer over the top applied a holding force to it and peened the edges of the mount block over the bearing using a punch, its just to retain the bearing from moving axially thatís all. Once peened I licked it over on the grinder to remove the high spots.


 I made a few hardened thrust spacers for the ballscrew, one for In front of the double row bearing and one for behind it. The one infront sits up against the ballscrew thread form and provides a contact point between it and the ballbearing inner and the spacer behind the bearing provides contact between the bearing inner race again and the timing pulley which actually drives the ballscrew, so nip up the drive pulley and it loads the ballscrew against the bearing,  then it was locked off with a fine pitch grub screw.   I also increased the threaded diameter on the new ballscrew, and had to re-thread the timing pulley with a new fine pitched thread etc. I had to relieve the bacl end of the bed casting a little to clear the hardened thrust spacer diameter, good old grinder came out to play.





Everything fits as planned, and today I fitted up my new guard over the assembly, its so close if I paint the guard the paint will probably scratch off when the machine traverses, so Iím just going to leave it as it is.  







The ballscrew bracket is one of two, the other is going to another retrofitted pc5 in holland.   the ballscrew itself was precision rolled to c3 tolerance to the size I wanted.  I checked it and I now have an error of 0.02mm over 250mm  and an axial play (backlash you might say) of less than ten microns 0.01, this error (running clearence!)  is from the double row radial bearing (the ballscrew itself is preloaded),  if I increased the loading to maybe 15 microns on the major bearing diameter I would have reduced this axial play, but the manufacturer recíd  0.01 so I just did what I was told!.      Itís worked out well for me really Iím happy with those dimensional results,   also Instead of a predicted 1.8m/min and probably because of the brand new screw it runs upto 2.1m/min easy!, I guess it has a good friction co-ef right now.  I cant run it any faster because I am only using 2.2nm motors @ 49Vdc and they stall out over that speed, really..  2m/min is well fast enough for this wee machine! I will only ever make tiny parts on it.



 click here for a movie....

http://www.youtube.com/watch?v=1uW3F-qbZNk

The next job for me is to build a small remote pendant box type thing so I can use it properly, it is labour-some using keys to jog set tools and job.

« Last Edit: October 04, 2009, 11:38:15 AM by hutchison » Logged
Tweakie.CNC
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« Reply #3 on: October 04, 2009, 11:49:05 AM »

Its all impressive but the ballscrew guard is extra impressive. Nice documentation and photos and a credit to your engineering skills.

Tweakie.
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RICH
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« Reply #4 on: October 04, 2009, 12:22:43 PM »

Looks like you will be having some fun making chips. The smaller  lathes don't leave much room for converted items.
 Thanks for the info on the modifciations and do post your testing.
RICH
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hutchison
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« Reply #5 on: October 04, 2009, 12:33:01 PM »

cheers Tweakie,  a tin basher friend folded out the gaurd for me from some 18gauge, It's one of them jobs if you attempt it will make a fool of you every time, best left to the pro's!.

i do look forward to making chips, if i ever get the time!,  it just needs a bit of bringing up to date .
« Last Edit: October 04, 2009, 12:35:50 PM by hutchison » Logged
Dan13
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« Reply #6 on: October 04, 2009, 04:30:08 PM »

Hi,

Really nice modification and very well documented! Might do this on my C5 some day... your info will definitely help.

Thank you for sharing.

Daniel
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Chaoticone
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« Reply #7 on: October 04, 2009, 05:55:06 PM »

Thats a very nice looking machine.  Smiley

Brett
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ostie01
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« Reply #8 on: October 04, 2009, 08:18:11 PM »

I did my first cnc training on a lathe like this 25 years ago.

Nice work by the way.

Jeff
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BarryB
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« Reply #9 on: October 05, 2009, 10:52:05 AM »

Beautiful work, love the neatness of the electronics, makes me want to redo mine;)

Barry
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