Been working on a Denford ORAC retrofit for much longer than I’m willing to admit but it’s getting close enough that I figured I’d stick m’toe in the water and join the fun.

I bought it from a fellow in Detroit and had it shipped by truck to me here in west Tennessee, USA.  I work for the local Jaguar-Land Rover dealer so am experienced with British engineering.

It was purchased with nothing other than the bare lathe and the stripped clean base unit.  I also have a Denford Micromill converted to Mach control and had bought a spare SmartStep/3 controller for it so that’s the controller I chose to use for the ORAC.  Meager budget & all y’know.

The ORAC base unit had no structure underneath the lathe other than the sheet metal top and I felt it would flex so I added some crosswise angle iron braces with vertical brackets to tie the top more rigidly to the bottom which has lengthwise stiff channels.  It all seems very rigid now.

I added a couple Home Depot drawer slides and a piece of aluminum plate to use as a pull-out equipment tray as I knew I’d be putzing around with electronics a lot and needed good access to it all.  The big aluminum plate serves as a dandy heat sink as well.  The original front panel was missing so I cobbled up one from a piece of heavy gauge metal shelving hinged with a piece of B727 access panel hinge that was given to me.

The missing original motor was ½ hp AC  w/VFD but I got a brand new ¾ hp Baldor DC motor off eBay cheap..  It was way too big to go in the original location and had to be mounted on the “back porch” and a hole cut in the back panel for the belt.  The KBIC-120 SCR speed control & motor made such a loud buzzing noise I had to mount the motor on rubber isolators I got from a parted-out treadmill.  It’s whisper quiet now.

I made some aluminum adaptors to fit a pair of NEMA 23 steppers that a kind forum member here gave me and made the X-axis cable sheath from the braided stainless steel covering off an old washing machine hose I’ve saved for years.  Must have some Scottish blood in me, eh Hood?

The last pic is the adjustable ER32 collet chuck I rigged up.  I added 4 brass tipped screws to allow precise adjustments of the chuck before the flange nuts are fully tightened.  The chuck flange I.D. is a little bigger than the EMCO spindle snout to allow enough movement to exactly dial in collets if their runout is excessive or when working with existing parts that have features that aren’t concentric.  I’m real happy with the way it works.

Next up is a twin QCTP plate to be added to the carriage and then learning tool offsets & the like.  Not looking forward to that.

Looks good. The electronics on runners is a nice touch.

Must have some Scottish blood in me, eh Hood?
...
I added 4 brass tipped screws

You've got a lot to learn. You could acheive the same thing with 3 screws and saved some brass and a screw

Looks good. The electronics on runners is a nice touch.

Quote from: DICKEYBIRD on August 21, 2012, 01:16:10 PM

Must have some Scottish blood in me, eh Hood?
...
I added 4 brass tipped screws

You've got a lot to learn. You could acheive the same thing with 3 screws and saved some brass and a screw

Now THAT'S funny!:)

Looks good! Offsets and programming should be easier than what you've done so far

Dan

Looks good! Offsets and programming should be easier than what you've done so far

Dan

Thanks Dan, I hope you're right.  I get by OK with stuff I can hold in my hand and beat the heck out of until it fits but software gives me the willies.  Hammers don't mean a thing to software.

Made a bit more forward progress on the little ORAC.  Made up a 5/8 x 4 x 11" add-on tool holder plate so a 2nd QCTP can be mounted on t'back side.  Drilled/tapped 3 holes to allow some flexibility in where to mount the QCTP stud.  The 3 little button head screws give access to oil the ballscrew and the slides, added a couple sheet metal covers to keep the swarf out of the moving bits.  The little 6mm tee-bolts are are hard to find for the C8 carriage slots but I found that ZF wide head auto transmission pan screws (had a sackful of lightly used ones on hand) are a perfect fit with a bit milled off each side.  That should quiet my Scottish ancestors.

Made up a replacement end plate to fit the missing one on the original ORAC belt cover.  Also made a tommy bar and extended spanner wrench to tighten the cr@p out of the ER32 collet nut.  Spanner extension is just a length of electrical conduit smashed flat on one end & hammered down onto the wrench with a rivet made from a soft nail to secure it.

Hi Guys
Didn't know there were so many Orac owners here on the mach site i have 2 of the Denford Orac lathes one has been in operation under mach for about 4 yrs now the other is setting waiting for what i don't know one day i will get around to it, basically i took all the original electronics out and installed a 4PNC break out board and gecko drives works like a champ i like the collect closer really nice work.

Dennis

Thanks Dennis, glad to hear from a fellow ORAC owner!  A good little machine methinks.   Haven't done much real work with mine yet but it's getting there.

What kind of tool holder setup do you have?  QCTP or gang or??  Got any pics or a link to a thread?

A little update on the ORAC project.  I wanted X-axis homing to be as accurate and repeatable as possible so I installed a N.O. microswitch on the X slide which closes near the end of travel and sends the signal on to the B.O.B when the disc mounted on the stepper shaft closes the opto.  The opto sensor/boards came from the Netherlands off ebay for $7.95 each, free shipping!  I made a pair of plastic mount blocks and the sensors are held in place by a couple drops of superglue.

After a few iterations of microswitch adjustments, the X homing is dead accurate and repeatable.  I can see no variance whatsoever in a DTI attached to the side over many, many homing moves. 









The maintenance guy at work gave me a neat little aluminum weatherproof box so I mounted it to the X slide for a place to put the wiring connections and mount the Z opto sensor board.  I made an adjustable Z axis stop rod holder which allows easy changes of the Z home position.  I didn’t want it permanently mounted at the far end of Z travel to prevent a long wait for the carriage to run all the way to the end then back to the work position each time it homes.  It can easily be reset if a job comes along with long stock.

Oh yeah, another feature is the black nylon screw holding the stop rod in place.  Being the realist that I am, I figure if it over-travels for some reason, the screw will allow the rod to slip and hopefully won’t punch a hole the box before I hit the esc key.

ORAC update:

I decided to add spindle reversing.  Initially got it working OK controlled from Mach with a big DPDT relay switched by one of the small relays on the B.O.B.  After advice from others, I got really worried about screwing up the G-code and frying my KB speed control by reversing directions with the spindle still spinning down so I ditched that plan.

A knowledgeable friend recommended another type of KB controller that (safely) does the reversing with onboard circuitry so off to ebay I went.  I got lucky &  found a N.I.B. KBCC-125R for $65.00 + shipping and pounced on it.  It has a more modern controller, an APRM-3 reversing module and a big dynamic braking resistor all mounted on a huge heat sink.  A very serious piece of kit!

It was way too big to fit in the enclosure so I picked up a 4x8x12” electrical box from H.D. to put it in and mounted it on the back side.  I followed KB’s recommendations & routed the control wiring in a separate conduit kept well away from mains power & the motor leads.  I also added a small 12vdc fan on the bottom with vent holes at the top to allow airflow across the heatsink fins & the resistor.  I will add some screening on the vent holes as soon as I get my hands on some.

It works GREAT.  It smoothly & quickly comes to a stop from full speed, switches direction and spins right back up to speed, no muss, no fuss.  After adjustments, the speed tracks the commands from Mach within 5 to 30 rpm from 150 to 1600 rpm in both directions.  The 30 rpm variance is in reverse.  I guess the motor timing isn’t perfectly symmetrical but hey, it’s closer than I’ll ever need!