Denford Lathe Retrofit

[John Stevenson]

Jim,
Not having a pop at you it's just that Mach works different ways for different people.
It's a complex mix and computer and machine.

Couple of years back i spent a whole week doing nothing but threading and reporting back to Art, try a new driver, rinse and repeat.

It's not a question of a nut having 1.5 to 2D length but more about the thread deteriorating over it's length and believe me a piece of al thread is accurate enough.

This is a classic example.



just two passes but you can see that after the first short length it's starting to go out of pitch but different error on each pass with the result that the last bit of thread is useless.

It's all down to the single pulse, Mach can't use a multi line encoder [ yet ] so we are stuck with it and it is the pulse.

EMC can use a multi line encoder and it threads perfectly and accurately.

I use my cnc for some threading production jobs but they are only 10mm [ 3/8" ] long and they come out OK.

[outback]

John;

I just ran a test where I cut 10 TPI over 5". I figure .100 per thread would be an easy measurement. I made the cut in 2 passes just deep enough to scribe a line. The second pass followed the first pass so perfectly it removed
no material.

With an eye glass and steel rule I can see the last thread was off about .010"
I really expected much worse. Either I got lucky or it works darn good.

However, I did calibrate the Z axis from the "settings window". It came out
to 4067.7 steps per. Before I calibrated the lathe it was off by half a thread
in 5". People with error may need to calibrate there machine.

Milton:
I figured speed control was going to eat up more time than it was worth. I'm not using homing or limit switches for the same
reason. I'm taking this project to a point where I think I can make money with it and no further. The computer does start and stop the spindle though. Maybe someday I'll set it up with auto coolant.


I would post a picture but I'm getting ready to leave for vacation.
Jim

[loply]

I'm very interested by this discussion as I'm slowly working my way towards converting a Denford Viceroy to CNC.

I had planned to use Mach3 but after this thread think I'll go with LinuxCNC instead. One of the main things I'll do with it is relatively long threads...

[DICKEYBIRD]

I had planned to use Mach3 but after this thread think I'll go with LinuxCNC instead. One of the main things I'll do with it is relatively long threads...

While you're getting it up & working smoothly with EMC, make sure & take lots of notes so you can train me how to make it work.

[DICKEYBIRD]

Wow, just noticed your location. Are you in Yorkshire anywhere near sunny Brighouse where the Denfords were built?

[outback]

Here is a pic of the threads and a steel rule to show how well mach3 did after 2 passes. I thought Mach3 did a great job, better than I expected.



large pic 5" of threads

Jim

[John Stevenson]

Very good results Jim.
In the big picture you can see the start of it widening the threads on the last inch.

As I say it's very machine and computer dependant, the people having the most trouble are the ones with the mini lathes where the spindle HP is lacking and any deviation in speed affects the thread.

If I was getting these threads I'd be very happy as it's rare for a CNC lathe to have to do long threads, most are just short fixings on turned parts.

Edit to say one of the best mods you can make to a conversion is to overpower the lathe if possible to keep a constant spindle HP.

[outback]

Man, that looks great Jim! Now you can whip out an ER-32 (or 40) collet chuck whenever you want. The taper and 1.5mm threads should be easy-peasy. A self improving lathe; I love it!
.

That brings up a great question. How is this lathe set up with collets?
A 5C collet would be to large. Has it ever been done?

Jim

[DICKEYBIRD]

I've seen 5C chucks installed on Emco C8's but the spindle has only a 20mm hole so what's the use? Plus they're so BIG to go on such a little feller.

I put a flanged style ER32 chuck on my C8 clone years ago & love it. I bought another one to go on the Denford. They have to be modified to fit but it's no biggie. I also bought a Maritool ball bearing equipped collet nut to go with it.

Here's one like I bought recently although it's a few dollars higher than mine. http://www.ebay.com/itm/ER32-COLLET-...item5d3426cd39 Can't seem to find a link to the other supplier right now. His was $29.99 + $10.50 shipping. His didn't come with a wrench but I had extras already. Hard to make one for that price and the quality is good.

I'm going to bore the backside oversize on the new one to give it plenty of wobble room and drill & tap 4 holes around the perimeter & install 4 brass tipped setscrews to make it a poor man's set-tru rig.

The paying work I'm getting lately involves repairing/modifying existing small parts that aren't necessarily straight & true so I have to be able to dial-in a feature precisely before cutting. The ER collets leave no marks like a 4-jaw can and they grip like the dickens but I can still dial in individual parts as needed. Slick, eh?

[EVguru]

Very good results Jim.
In the big picture you can see the start of it widening the threads on the last inch.

As I say it's very machine and computer dependant, the people having the most trouble are the ones with the mini lathes where the spindle HP is lacking and any deviation in speed affects the thread.

I still think it may be worth adding a speed feedback to a VFD. Most (even the cheap Chinese ones) have a built in PID function that accepts a 0 or 4-20mA input that could be used with a suitable encoder (certainly better than one pulse per rev).