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Author Topic: CNC CONVERSION - 6" ATLAS LATHE  (Read 54440 times)

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Offline Dan13

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #40 on: September 25, 2009, 01:19:41 AM »
Ha..ha... What a difference to a Sherline ;) 

What's the practical backlash you've got?

Daniel

Offline RICH

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #41 on: September 25, 2009, 06:01:33 AM »
Daniel,
I had the Sherline tweaked quite well, or maybe better said, after lots of testing i knew how to get the most out of it. Being fair to Sherline, it's still a nice little lathe for making small parts.

Practical backlash on the converted Atlas is zero.  The x axis is 0.0003 to .0004" and the Z is slightly under 0.001".
Just using code generated by the wizards, like turning down a  shaft to dimension i was able to get within or better than the X axis backlash. The backlash is a real PITA if your doing threads, not only fine 0-80 but also deeper
threads like 20 or 13. On the small threads, a few thou makes or breaks a usable thread while on the deeper threading 2 thou can create a spindle slowdown, force you to use flank threading, etc. Even though a lot of effort by Art  and testing by users to make the threading cycle work with spindle slow down, there is no comparison if it doesn't happen in the first place.

The intent of this conversion was to build a lathe that could do fine precision work but also be able to do larger work. To that end the goal was achieved.

I still have a number of refinements to make the accessories usable and a fair amount of testing to gain experience
using the new toy.  I guess if I had to do it all over, I should have CNC'd the Atlas a long time ago. If you read the postings, it is obvious i knew what i was after and wanted.

RICH

 

 

Offline Dan13

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #42 on: September 25, 2009, 08:13:48 AM »
Rich,

Obviously looks like you achieved your main goal. Well done!

Like you said, it's a lot easier when you know exactly what you want.

May I ask, how much money did it turn to you?

Daniel

Offline RICH

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #43 on: September 25, 2009, 08:47:58 AM »
"May I ask, how much money did it turn to you?"

Not sure what your asking?

RICH

Offline Dan13

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #44 on: September 25, 2009, 08:58:04 AM »
Reading it again, I am not sure myself what I typed there :D

Wanted to ask how much money have you spent on it so far?

Daniel

Offline RICH

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #45 on: September 25, 2009, 09:44:53 AM »
I had most all the "stuff" to do the conversion. So just a few miscleaneous things needed to be purchased. Say around $140 so far. 
RICH

Offline RICH

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #46 on: September 26, 2009, 10:07:09 PM »
INDEX PULSE – MOUNTING / USING A HALLS SENSOR
Got the index pulse all working. I used a Hall sensor instead of a slotted disc.
Readout is dead on from the 53 – 2400 rpm of the lathe and doesn’t vary. Components amount to a rare earth magnet which is was super glued to a gear inside the spindle housing. The sensor ( SMC D-F7NC )
was mounted onto a steel strip and attached to the casing. The sensor actually has two sensors in it and only one was used. The sensor also has an indicating light to show when it is triggering making for easy alignment and visual confirmation other than using the diagnostics. The sensor components and mounting are shown in figure # 55.

What was really nice was that it could be mounted in close quarters. I didn’t have many options for
mounting a disc and this did the trick. The sensor works from 5 to 24 volt and I already had the wiring inside the controller setup for a 5 volt supply which saved some rewiring. Why did I use this particular
sensor? Well, as a friend pointed out, look in your “junk box” because we have a few of them ( always like to have a spare part !) and there they were. A little guidance from another friend on the pull up resistor and life is good. I didn’t check the generated pulse with an o’scope so I can’t say how good it is, but frankly,
it works, and that’s what is important.

In the last post I showed a ruined ½ - 20 thread. Now I can use the proper chuck and test out some heavier
threading. The ½-20 was again tried ( 863 RPM / 43 IPM and .006” cuts) and was done with ease. I tried a few more threads to build the confidence level up and all was fine.

Picture # 55 & 56 show the results for a ¾-13. It was cut at 115 RPM using flank cutting ( 15 degree ),
.010” first pass / then .003” passes / and I spring pass. The steppers have a lot of torque at that speed and in back gearing the motor has plenty of torque. This is a rather deep sharp vee thread ( 0.0662” )
so the cutting is rather heavy. The RPM / feedrate never changed. The resultant threads pitch and profile
is very good. An increase in RPM and lighter cuts along with a few spring cuts would probably improve finish. But I was interested in timing, rpm and cutting ability.

The next tests will be with longer threading to see if the lead is going to change over the length.
This is a problem that plagues a number of folks when doing threading. Stay tuned!

RICH   

Offline Chaoticone

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #47 on: September 27, 2009, 12:05:56 AM »
Very nice Rich!    :)

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!

Offline Dan13

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #48 on: September 27, 2009, 12:54:15 AM »
Rich,

Looks like a prefect thread, but did you had chatter when you cut it? That's how it looks to me.

Daniel

Offline RICH

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Re: CNC CONVERSION - 6" ATLAS LATHE
« Reply #49 on: September 27, 2009, 09:24:29 AM »
Daniel,
The material is AL 6061. No chatter, but i did have that "crackling sound" at times which indicates that the
chip was breaking and there was work hardening of the material.  The tool is somewhat hung in front of the carriage
so you get some flex of the carriage. ( moment about the carriage Z axis, so whatever play is in the gibs was happening under load) You could see the tool  ( top part and tool mounting slide ) spring down, but again i wanted to see what she would do. I wanted to see if the belt would slip or rpm  or feed rate would change.

There is a fair amount of force when doing this thread. I  have broken a 3/8" diameter  diameter boring bars when doing a 1-8 thread on the 11" manual lathe. I would guess that the tangental force is 100 to 150# ( which is a lot for a little lathe ). Put that load on small part of you toe and you would really feel pain!

The little sherline would never be able to what the converted lathe did. Alll you need is a little backlash
say .002" in the Z, and making a cut it could be 0.005" instead of .003" and you would have disaster as the load
really increases.

Threading is a real true test of the lathe as you need to have accuracy, repeatablity, torque, and overall a good system.
Loads from cutting  are transmitted back into the components of the system. A good example from, a design point of view , would be how many and what size set screws should be put into the collar that acts as a retainer for  preloading of the Z anchor bearing.  Or notice that i deliberately didn't put any screw holes into the top carriage slide where the
tool gets anchored as it is rather thin in section, but, i can bridge across the slide with an adapter piece or plate.

This thread is about more than just here's the conversion. In the beginning there were posts about initial considerations
on components. I didn't take it to any high level of engnineering, but as a designer, the engineering stuff is of interest
to me. I may go into some calc's just for the fun and educational part for some. Then it went into each system and how it was done.

Sorry for rambling on but trying to add some perspective to the conversion.
RICH