# PM 1236 lathe,  speed and feed question



## RockwellHardness (Nov 5, 2013)

Hello fellow travelers, 

I have the 1236 up and running,  and  with the help of the PDF instructions  Ray  C.  created  I have been able to run in all modes.   

I can see the instructions for threading will be helpful if I ever do threading.     

My question is about the feed rate selection plate:  On the far left of the plate,  shown are gear selections,  I can not noodle these out,   they do not match the  3 gears in anyway I can figure out.   ( this is my first lathe )  

On the the  pitch  threading plate,  the gear diagrams make sense. 

thanks,

RH


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## Ray C (Nov 5, 2013)

OK, this is easy to answer...  Have a look at the IPR (Inches Per Revolution) chart below.  The top table is for millimeters per rev and the bottom table is for inches per rev.  The inches is the lower of the two charts.  This table shows two things.  On the left, you'll see a horizontal and vertical squiggly line (kinda looks like this -\/\/-).  The horizontal symbol means the carriage movement and the vertical symbol means the crossfeed movement.  

If we use an example of 0.005 IPR (find that value on the lower chart under the D5 column) it means that for every revolution of the chuck, the carriage will move 0.005" because, looking to the far left, you will see the horizontal symbol.  If you look right below the 0.005, you will see 0.001 and on the far left, it shows the vertical symbol, which means with that gear setting, the crossfeed will move 0.001 per revolution.

How to set the gears:  Look all the way to the left  of the 0.005 and you'll see two staggered gears.  This means that the gears on the side of the gearbox need to be set in that position.  Look at the numbers on the top and bottom of those staggered gears.  The top gear needs to be the 24 tooth gear and the bottom gear needs to be the 48 tooth gear.

Finally, the dials on the front panel need to be set to "D" and "5" and the feed rod needs to be set to the SII position.

Simple as that.  Here's something to know:  If you leave it at D5 but switch from SII to SI, you will get exactly 1/2 the other results because, the "S" dial is a speed-doubler.  SII moves twice as fast as SI so, leaving everything else the same but moving from SII to SI you will get 0.00025 IPR on the carriage and 0.0005 IPR on the crossfeed.

You will notice that some of the numbers are repeated...  This is because that table is not printed to 4 digits past the decimal. Looking directly under D5 and B5, you will see two values of 0.002.  -Most likely, the leftmost one is 0.002 and the right-side one is possibly 0.0018.  They rounded the numbers to 3 places to fit on the chart.  BTW:   I usually leave my machine on the 0.005 setting because 0.005 IPR is a nice medium cut and 0.00025 is a nice fine cut.  






Does that help?

Ray


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## Ray C (Nov 5, 2013)

Word of caution:

There is a M and S setting on one of the dials.  M position activates the LeadScrew.  S position activates the FeedRod.

Never, Ever, Ever... engage the M-setting (leadscrew) and activate the halfnut lever if you intend to have a speed setting designed for a surface cut using the feedrod.  Why?  The carriage might take off like a rocket ship and crash.

As you know, there are forward and reverse gears on the front panel.  Also, the apron has a lever to either move the carriage or (mutually exclusively) engage the crossfeed.  It's up to you to set things to move in the proper direction and use the proper apron setting to either move the carriage or crossfeed.

When you're first starting, always make sure you have plenty of travel to not crash and don't let the crossfeed move toward you and reach the end of it's travel.  The system has bushings with roll pins in various places that will snap if you crash something but, don't take the chance.  Also, in the manual I wrote, I show what directions things move in given various lever settings.


Ray


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## Tony Wells (Nov 5, 2013)

Normally, there is a safety detent position, a neutral, so to speak in the feed selection lever system to prevent such an occurrence. If the apron is set up to feed, the half-nuts will not engage.

At least on most every lathe I have seen. I am not familiar with the specifics of that particular machine. And it is a safety feature to prevent just what Ray is describing. Engaging the half-nuts at 1000 rpm can be a hair raising experience if you aren't ready for it.


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## Ray C (Nov 5, 2013)

Indeed, you cannot simultaneously engage the crossfeed and the carriage travel at the same time nor, can you engage the halfnut lever when the carriage is engaged via the feedrod.  There are mechanical lock-outs to prevent that.

You can however setup the gears that will spin the leadscrew very fast and if you engage the halfnut lever, that carriage will move really darn fast...  EG:  Lets say you setup the gears so the feedrod would move the carriage at say 0.048 IPR then, you set the drive selector from FeedRod to LeadScrew.  If you engage that halfnut lever, the carriage is going to make tracks -fast.


Ray



Tony Wells said:


> Normally, there is a safety detent position, a neutral, so to speak in the feed selection lever system to prevent such an occurrence. If the apron is set up to feed, the half-nuts will not engage.
> 
> At least on most every lathe I have seen. I am not familiar with the specifics of that particular machine. And it is a safety feature to prevent just what Ray is describing. Engaging the half-nuts at 1000 rpm can be a hair raising experience if you aren't ready for it.


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## Ray C (Nov 5, 2013)

Perhaps this too will help but first, another word of caution.  When changing gears, always engage the safety switch.  You really don't want your fingers getting caught in those rotating gears!!!

In this (albeit blurry) picture, notice that I'm pointing at three gears all in-line with each other.  This configuration is always for a threading setup using the LeadScrew.




In this photo, notice the little spacer I'm pointing at.  Remove the screw, the little spacer and the gear then, put the pacer on first and the gear next.  That will move the drive line to the "staggered" position thus utilizing the 100 tooth gear.  When in that mode, the gears are setup for a specific feed using the FeedRod.




Finally, you need to loosen the nut on the pivot arm and the nut on the large gear to adjust everything to mesh properly.  There should be a little wiggle room between the gears.  Don't mesh them really tight against each other.  If you do, it will make a really loud whining noise.  



Ray


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## RockwellHardness (Nov 6, 2013)

Thanks Ray and Tony,   I will study what  you have written  tomorrow.

RH


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## RockwellHardness (Nov 6, 2013)

Hi Ray,

I have studied  your pictures and writings,  thanks much.  

Ok,  I think what was throwing me is that  the machine came with the bottom gear on the 127 tooth gear,  not the 120 tooth gear.  It was set up for threading, I see that now.  In fact now it now seems so simple,  how come I was confused ?! :lmao:

So I will take off the lower gear as per your explanation and  align it  with the 120 tooth gear for turning operations,  it will be awhile  ( or maybe never ) before I do any threading.

So now I will continue with degreasing and lubing, fine tuning the gibs etc,  then on to the 932 and repeat the process.  

I found out while doing the cleaning on the LMS mini mill I had for a couple of months before I decided to go in whole hog,   :nuts:     that  rubbing the sliding / mating surfaces with a 3m  green nylon pad (very fine abrasive )  that it smooths things out nicely,  and combined with DuPont teflon spray with Molybdenum makes things slide so nice.  It goes on very low viscosity and then eventually thickens up,  and stays stuck to the metal very well.  This may not be a good way to go if the machine was in use daily, but for infrequent use,  it may be the better way to go, as it will not drip off or gunk up.  

Has this idea been discussed before, or other methods for lubing ?

Thanks,

RH


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