Friday, July 6, 2018

A Safety Cover for the Threading Gears on the LMS3540

In my post about threading problems on Tuesday, I showed the way I was able to get the gears to thread 32 TPI and finer - putting the gears into a position that I can't close the cover over.  I concluded with the statement that
I need some sort of field expedient cover for that.
Yesterday, Mrs. Graybeard provided the answer:

Yes, that's a Mark I, Plain Ole Cardboard Box.  One of the top flats is folded over into the box, and that side gets wedged behind the lever that holds the B/C gears, so the box stays put while everything is turning.  It stops my fingers if they drift over that way.  It'll do for now. 

After that post on Tuesday, I started making some practice pieces preformed to the general shape/length of the real part and threaded 6-32.  Ruined the first two I made (I don't remember why), then got one right.  On the second preform for the piece I need to make, I think I lost count of where I was and moved the cutter too far into the thread and it sheared the stud off.  Then the third and fourth worked the way they should.  3 out of 4 isn't too bad, so time to move onto the real part. 

It threaded just fine.  There are still two operations to do it: cut the slot in the back for the push rod and then drill across the slot for the pin. 

I'm going to do this on the Sherline, but today has been a day of no progress.  The shop computer forgot how to boot and the fan suddenly sounded loud and obnoxious.  It has been behaving like the motherboard battery was on the verge of dying, and it apparently lost its mind.  For weeks or months, it would forget the date & time if I turned off the power strip.  If the power was on, it held up the clock.  So I pulled the covers, replaced the battery and it remembered its setup information.  Including the time.  Then it was time to put the air compressor to use blowing out dust.  Messy, but necessary.  Everything looks like it will be back to normal tomorrow. 


  1. I used to have quite a profitable sideline replacing fans in PC's. The typical low-cost sleeve bearing fans in the power supplies, and also what most builders use, wears out in a few years (or less), along with the fan on the CPU heatsink, and these days, video card fans. I always used ball bearing fans as replacements, and can't ever remembering replacing a fan a second time in the dozens (probably hundreds) of the PC's I fixed over the 25 years I was doing it.

    And the PC always had a whole lot of dust bunnies lurking inside.

    Good to hear you worked it out. When you first started talking about this part, the first thing I wondered was why you didn't just use the lathe, and then I remembered the few times I manually cut threads on a lathe.

    4 hours of set-up for 30 minutes of machining!

    1. 4 hours of set-up for 30 minutes of machining!

      That's way ahead of where I am.

      At the speed my lathe is threading, each of these practice pieces took 3 seconds per pass. I think it was 6 passes, or 18 seconds. I spent about two days getting the gear setup issue ironed out.

      Maybe I can say two days of setup for two minutes of machining.

    2. I didn't have to change gears on that old lather, just move levers, but it still took me that long to read the manual, look up the gear ratios, and then set the levers.

      OH....and learn how to grind a tool properly for threading.

  2. Good combination of "out of the box thinking," or maybe more of "in the box thinking."
    I wonder if there is a MilSpec for "Field Expedient Rotary Hazard Covers."

  3. That may be a decent temporary solution, but it would be far more effective if you were to add a cat to it. Just attach it temporarily. With duct tape. Claw side out, of course...

    But then the damage inflicted might be worse that if you merely got some organic part caught in the gears...


    They work great anywhere you have 12 vDC available. I'm using two in my boat to cool the electronics in the dash. One blowing in, and one sucking out. Does wonders for keeping LCDs readable even though the top of the dash is flat black and in the Florida sun.

    1. Thanks for that reminder link on fans at NewEgg. There was a lot of dust in there, and it has been embarrassingly long since I did that to the PC (which makes me think it's probably time to do this PC again).

      The graphics card has a low profile fan on it and the compressor blew out a lot of crap.

      It's routine maintenance. My wife used to do a lot of the PC work for the contractor on the Cape side, back in the DOS and early Windows days. She says she has seen PCs actually burn because of caked on dust.