# Installation of a tachometer in an LMS mini-lathe



## WobblyHand (Sep 28, 2021)

Have a digital tach kit that I'd like to install in my mini-lathe.  I will make an M27x1.5 hex nut to replace the circular jam nut on the spindle.  (I know I can buy the nut for $5, but where's the fun in that?)  The nut will be 12mm wide so I can mount a 12mm magnet.  The 10mmx1 magnet that comes with the kit is a bit wimpy. The magnet will be JB Welded to the nut.  (Once I test it for proper polarity!)  I did wire the unit up and tested that it works.  I used my demagnetizer and spun it and it measured a multiple of the RPM (due to the multiple of magnets!)

What I haven't yet figured out is where on the front plastic cover I can mount the display.  There's not much real estate there.  The control board is mounted to the front of the cover.  I was thinking of the side, but that would require a huge cutout, greatly reducing the integrity of the plastic cover.  In other words, the notch would be nearly the entire width of the side.  Has anyone done a similar install on their mini-lathes?  I'm trying to avoid a wart on top of the lathe.  Horizontal surfaces are prime space, and I'd rather not have a plastic Bud box on top.  Did you have to remove the display from the housing to install it?  It looks pretty easy to pop the board and display out of the case.

In a couple of minutes I will post some pictures, so there's some context.


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## WobblyHand (Sep 28, 2021)

After removing the housing from the tach, there's a way to shoehorn it in, I think.  Whether it will operate there or not, we shall see.  I'd like to pick up the mains from the inside of the box.  I don't have enough plugs at my location, and I am already swapping plugs for power right now.





Hopefully I can get some new decals.  Looks like the display will be in the middle of the indicator table.

The display was soldered in place incorrectly.  The assemblers pushed in the center then soldered it.  There is a noticeable sway to the display.
Maybe I will resolder it.  The display height is 8mm from the board.  The plastic cover panel of the lathe is 3mm thick.  If I use a 5mm spacer the display will be flush to the surface.  I conveniently happen to have some 5mm MF hex spacers.


The pocket knife under the board I bought in China in 2007.  You can see the corkscrew is pulled out.  That was from first use, trying to uncork a wine bottle.  I was so astonished that I brought it home and have kept it.  It's a reminder to me that quality isn't hypothetical, it actually matters.


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## addertooth (Sep 29, 2021)

Consider making a spider for your mini-lathe once you are set up for cutting that thread as well. It will do far more for you than a simple jam nut.


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## wachuko (Sep 29, 2021)

That looks like the perfect place for it.

Take a good photo of the label in case you have to print one yourself… But LMS should have those labels available…

To power the display, I used an old 12volt power supply from a network hub…

Oh, and I got a multiple outlet just for the lathe…. Between the magnifying lamp, RPM display, lathe…I just could not do without it…only one plug next to the lathe as well…


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## tghsmith (Sep 29, 2021)

there is room to shoehorn a display in front.. this is the macpod tach kit, simple no fuss, plugs into the LMS wiring.. https://macpod.net/misc/sx2_tachometer/sx2_tachometer_kit_v2.php


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## Suzuki4evr (Sep 29, 2021)

tghsmith said:


> there is room to shoehorn a display in front.. this is the macpod tach kit, simple no fuss, plugs into the LMS wiring.. https://macpod.net/misc/sx2_tachometer/sx2_tachometer_kit_v2.php


Looks like you worked that guy to the bone.


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## WobblyHand (Sep 29, 2021)

tghsmith said:


> there is room to shoehorn a display in front.. this is the macpod tach kit, simple no fuss, plugs into the LMS wiring.. https://macpod.net/misc/sx2_tachometer/sx2_tachometer_kit_v2.php


3x the cost, and currently not available.  Besides, I like my digits are green! ;^)

Seriously, did look into this at one time.  Couldn't tell if it would really work for what I had.  Not obvious (to me) how to mount the display unit board behind the main power board.  Actually, disassembly looks like an interesting puzzle.


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## WobblyHand (Sep 29, 2021)

wachuko said:


> That looks like the perfect place for it.
> 
> Take a good photo of the label in case you have to print one yourself… But LMS should have those labels available…
> 
> ...


Turns out the label isn't listed in the parts diagram.  Have to email LMS to see if they have it under some other place.  Good call on taking a picture. 

I have a bunch of old 12V supplies.  Think I have 4 to choose from.

Think I am going to extend the electrical box.  See if I can gang 4 more outlets.  Tired of plug swapping.  A multi-outlet is good too.   I'll see if I can get a 4 foot electrical strip and mount it to the back of the lathe stand.  I'd like the outlets to be covered, or at least the ones not in use.  I do get chips flying.  Eventually I will run another circuit to the area, it's long overdue.  Haven't hooked up my mill power feed, because I'm out of outlets!  No shortage of projects...


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## WobblyHand (Sep 29, 2021)

addertooth said:


> Consider making a spider for your mini-lathe once you are set up for cutting that thread as well. It will do far more for you than a simple jam nut.
> 
> View attachment 380186


I really should make that.  I could mill a flat on it to mount the magnet.  Yeah, I'm going to do that.


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## WobblyHand (Sep 29, 2021)

LMS has the label.  So I can get another one.  Costs a whopping $3 or so.


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## wachuko (Sep 29, 2021)

WobblyHand said:


> LMS has the label.  So I can get another one.  Costs a whopping $3 or so.


Make sure you look at everything they have so you can spend more than the 3.00 for the label


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## WobblyHand (Sep 29, 2021)

wachuko said:


> Make sure you look at everything they have so you can spend more than the 3.00 for the label


It does irk me to spend a very high percentage of the total order on shipping.  Spending $8 for shipping on a $3 label, just _ISN'T_ right.  At the very least I need to fill the flat rate box, right?  Don't worry, I'll find something.  I'm on their email list.


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## WobblyHand (Sep 30, 2021)

tghsmith said:


> there is room to shoehorn a display in front.. this is the macpod tach kit, simple no fuss, plugs into the LMS wiring.. https://macpod.net/misc/sx2_tachometer/sx2_tachometer_kit_v2.php


I take my comment back.  There's room in the front.  Your picture proves it.  It seems one has to remove the boards for either install.  Once that is done there's room in the front face.  I like the front mount better.

Since you have done it, can you provide some hints on the disassembly order?  Mine seems to be a jungle of tangled wires.  Any guidance would be appreciated.


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## tghsmith (Sep 30, 2021)

I just removed the switches and board, had to make some stand-off spacers , used a little hot glue to hold the main switch nuts in place during re-assembly.. I did take a few pictures to make sure everything went back correctly..


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## chip maker (Sep 30, 2021)

WobblyHand said:


> It does irk me to spend a very high percentage of the total order on shipping.  Spending $8 for shipping on a $3 label, just _ISN'T_ right.  At the very least I need to fill the flat rate box, right?  Don't worry, I'll find something.  I'm on their email list.


 I sure Agree their shipping is super high for what they are shipping. I've held off ordering parts from them because of the high shipping. I don't think there is an option with them to use a fixed box size and than who knows if they would even use it.


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## WobblyHand (Sep 30, 2021)

chip maker said:


> I sure Agree their shipping is super high for what they are shipping. I've held off ordering parts from them because of the high shipping. I don't think there is an option with them to use a fixed box size and than who knows if they would even use it.


I don't think they are _really bad_.  They do give some options on shipping, including flat rate boxes.  I think shipping has gone up quite a bit in general.  Buying one little item from them doesn't make sense if you aren't local.  But, it's rarely a problem, I usually find enough interesting things to make it worthwhile.


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## chip maker (Oct 1, 2021)

Doesn't seem to work for me if I add more things price seems to just increase with the extra added items. I'm not sure if it is shipping or handling charges will have to check that out.


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## WobblyHand (Oct 1, 2021)

chip maker said:


> Doesn't seem to work for me if I add more things price seems to just increase with the extra added items. I'm not sure if it is shipping or handling charges will have to check that out.


One thing to be aware of is it has to fit in the flat rate box.  The boxes are rarely the right shape.  LMS does pack pretty well, so it takes up some space.  Can tell you, they are NOT the worst of the bunch.


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## WobblyHand (Oct 1, 2021)

Ok, back to machining.  Step one:  Make the spider.  Found a piece of 1.75" 4140 and chopped off a piece for the spider.  That was my first mistake.  Wasn't thinking yesterday. Should have left the piece whole.  So later on, I will have to make a mandrel so I can turn the outside diameter, or find a good way to turn 1/2 the OD at a time and blend the crossover.  Chucked it up in the four jaw.  Faced the ends.

Drilled a 5/8" hole, then a 3/4" hole with some MT2 drills.  Was slow going, but mostly uneventful.  Then bored it through to 19mm.  Having larger size drills was great.  Minimized the amount of tedious boring.  Had yet another lapse, see a pattern here?, and decided to continue boring to 21.5mm.  Not a disaster, but on retrospect, should have left it narrower bore.



Next I will bore a 0.600 deep section to 24.32mm ID.  That's what I calculated to be the correct ID for the measured spindle thread.  I have had good luck (so far) using ID = measured OD - (0.866 x pitch_distance x 2).  The threaded part is 0.500" deep.  The extra depth is to give clearance for the threading tool.  I will internally thread the nut to M27-1.5 using a home made LH threading tool, with the lathe in reverse.  Boring to a blind shoulder is always fun.  I installed the fine feed gear set from LMS a week ago and it both gives a nicer finish and makes boring a lot less exciting.  So I can easily stop the depth to within 0.005" and finish the last bit by hand.


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## WobblyHand (Oct 1, 2021)

Well, must not have been my day.  After learning about modified flank inside threading (in another thread), I proceeded to get everything set up. 

Except for one key thing, I swapped the B & C gears.  Basically installed the stack of gears upside down.  This does not give one the desired results.  Yeah, so I cut a 0.888 mm thread, instead of the required 1.5 mm.  Because of my setup, it was difficult to get a thread pitch gauge in, so I didn't notice it right away.  I had to have the dial indicator in the tailstock side, because the stem was hitting the headstock.  This meant both the boring bar holder (used to hold my threading tool) and the dial indicator were preventing access to the bore.  So I painted myself into a machining corner.


On the plus side, I did learn how to do modified flank inside threading.  The tool cut well.

So I have to flip the part around, indicate it to the nice through bore hole I made and re-bore it to the correct size and depth for the threaded section.  Then finally thread it again.  That isn't happening today.  Afraid I used up my blunder quota for the day.  Tomorrow is a new day.


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## WobblyHand (Oct 2, 2021)

And today is a new day!  Upon reflection, and the fact that I only had cut 0.25mm deep threads, and full depth threads are 1.3mm, I decided to flip the gears on the B/C shaft.  And cut some threads.  Apparently have a bit of deflection due to the home made bar and HSS cutting bit.  

What that last sentence really means is the nut didn't fit!  Can't say I am surprised.  (Just because I had a perfect fit twice in a row, doesn't mean it always works!)  It's pretty close, but not quite deep enough.  I suspect the tip of my tool bit is a little flatter, or missing a tiny piece at the tip.  There's a flat spot where there shouldn't be.  For some reason my grinds leave the HSS weakened.  That's a topic for a different post.  The ID seems to be about correct, maybe the major diameter isn't correct due to the blunter tip.  I can line up the pieces, but it just shows no inclination to start threading.  Yes, I measured the spindle pitch, and it matches the 1.5mm pitch I cut.

I can see why people make a male test piece - so you don't have to take the nut out of the chuck.  Going to do that now.  Have a piece of 1.25" OD 1144 that would work.  After a few iterations, I got it.  Used thread wires to measure the spindle thread and cut until the test piece matched.  Wish I could internally thread as well as these external ones came out.


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