Surface Finish Issues On 12x36 (long Post) + Kb Electronics Vfd Install

Greetings, group.

I still haven't decided what to do about the foot brake situation.

I spent a good portion of yesterday afternoon getting most of the lathe back together. I have encountered another oil leak on the head stock. My repair of the cover gasket is working nicely. The new leak is around one of the shifter shafts (top right as you face the machine). I don't feel up to tearing the machine apart just yet to determine what type & size of seal (if any) lives in there. The manual lists one, but a project for another day.

I obtained one of the digital tachometers from Amazon last week. Fabbing a small bracket to hold the pick-up was a relatively simple task. I used electrical tape to hold the magnet to the left end of the spindle. Another 12 volt wall wart for power, and I have a temporary digital speed readout. It worked the first time. The displayed speeds differ quite a bit (up to about 100RPM) from the placarded speeds on the lathe with the frequency set at 60 hertz. I think that I will base any/all speed considerations off of the tach instead of the placard. Now, I need to construct some type of case or holder for the tach body. That should occupy my Sunday afternoon--unless the DSU (Designated Spousal Unit) has other plans.

I am actually having quite a good time with this project.

Wow, I nearly forgot one of the main purposes for this post. SURFACE FINISH!! I played with some CRS shafting (grade unknown) yesterday. I was able to see a marked improvement in the surface finish since the 3 phase/VFD install. I tried both HSS & Carbide inserts--both showed improvement.
I also tried some 6061--it also showed improvement. I experimented briefly with speed adjustments--more of that as I gain experience with this "new" system.

So, here is the breakdown of costs for this project:

Leeson 3 phase motor (192205.30)---------$213
KB Electronics VFD (inc shipping)----------- 269
KB Electronics IODA Board (required)------ 75
9 conductor shielded cable-------------------- 20
Power cable-------------------------------------- 23
Speed control pot + knob---------------------- 6
Aluminum (VFD mounting bracket)--------- 18
__________________________________
Total-----------------------------------------------$624

Of course, nuts, bolts, eye terminals, etc are not included.

I could have acquired a cheaper VFD; however, I thought I was getting a great deal until I discovered that the IODA board was required for remote operation of the drive. The Leeson motor (and the IODA) was sourced locally here in Delaware (I picked them up at the dealer)--incidentally, their price was the best I could find on the internet. (electricmotorwholesale.com)

Jerry in Delaware
 
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Hi Jerry,

Just a thought, have you tried locking the compound, locking the cross-slide, locking both ?
Has any of these 3 tests changed anything in the finish ?

Sorry if you have tried that, I may have missed it.
 
I normally lock the compound when doing any turning, even threading, so that isn't part of the equation. I do not have a lock on the cross slide, yet, & rarely lock it--might be something new to try.

Overall, the VFD/3 Phase install made a significant improvement in the finish. I have found that RPM changes as small as 20-25 will make a difference. So, if I have the option of a test cut, I can locate the sweet spot to minimize the "roughness".

Matt mentioned something to me when I was chasing this problem around. He said that the term "vibration" that I was using might be more accurately described as "shake". I think that that is a better term. I have observed the light while using the lathe, and since it is on a long flexible neck, the shake is intensified. I have observed (going from memory now) that the most pronounced shake occurs around 675 RPM. That speed is obtainable with the VFD at more than one gear setting--it always seems worse at that speed. I tried with & without the chuck installed with no significant change.

That is about all for now.
Jerry in Delaware
 
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