# PM727V Z-Axis Crank Difficulty



## CKel44 (Dec 28, 2020)

Hobby-Machinist / PM727V users:  I've been using my new PM727V several times now and was noticing difficulty in raising the headstock using the crank.  It seemed that way too much effort was required to do this and it is very noisy/notchy.  I've attached a video if interested.

I removed the rear cover and inspected both bevel gears and the Z-axis lead screw.  All were dry or so lightly lubricated that I could not actually tell any was present.  I lubricated the gears and leadscrew which helped slightly.  I also noticed very tight engagement of the bevel gears with absolutely no play.  I don't see that there is any adjustment for the bevel gears if that is the problem.

Has anyone noticed these problems?  Is there a fix?   Please correct/advise me, THANKS! 

Craig


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## benmychree (Dec 28, 2020)

You should be able to remove the crank and housing cover and do something to allow more gear lash, such as facing some material off the back of the gear or it's thrust bearing surface.  Take it apart and take a picture of the gear assembly and post it for further comment.


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## CKel44 (Dec 28, 2020)

THX benmychree, I just checked the diagram of all of column components and the cover is a lot more than just a cover.  It's actually called the 'Z-axis crank base' which the bottom of the lead screw goes through.  It looks like disassembly might have to be top-down.  There are, however, 2 taper pins in the crank base/cover that I have no idea what they do.  Maybe Precision Matthews Technical will chime in here.

As a note, I'm a bit reluctant to completely disassemble the headstock column of my brand new mill...


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## benmychree (Dec 28, 2020)

CKel44 said:


> THX benmychree, I just checked the diagram of all of column components and the cover is a lot more than just a cover.  It's actually called the 'Z-axis crank base' which the bottom of the lead screw goes through.  It looks like disassembly might have to be top-down.  There are, however, 2 taper pins in the crank base/cover that I have no idea what they do.  Maybe Precision Matthews Technical will chime in here.
> 
> As a note, I'm a bit reluctant to completely disassemble the headstock column of my brand new mill...


Yes, you should not have to do this yourself, call the company first.


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## markba633csi (Dec 28, 2020)

You might be able to make a spacer or gasket to move the gears further apart slightly.  Sometimes a slight adjustment to the factory build is required. A piece of thin cardboard or fiberboard might do the trick
-Mark


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## KevinM (Dec 28, 2020)

There are 2 setscrews on the crank handle plate.  Possibly for adjustment.


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## CKel44 (Jan 15, 2021)

markba633csi said:


> You might be able to make a spacer or gasket to move the gears further apart slightly.  Sometimes a slight adjustment to the factory build is required. A piece of thin cardboard or fiberboard might do the trick
> -Mark


THX Mark.  I'll look at it this weekend, but as I mentioned earlier I'm reluctant to tear into a brand new machine.  It should work properly for for at least a few weeks after purchase!


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## CKel44 (Jan 15, 2021)

KevinM said:


> There are 2 setscrews on the crank handle plate.  Possibly for adjustment.


THX KevinM.  Those are taper pins mainly used for initial plate placement, but I'll take another look at that.


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## CKel44 (Jan 15, 2021)

I've contacted Precision Matthews about this and will let you know their reply.

Craig


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## KevinM (Jan 15, 2021)

CKel44 said:


> THX KevinM.  Those are taper pins mainly used for initial plate placement, but I'll take another look at that.


Yeah, I noticed  that yesterday when cranking up the spindle.  My handle was loose when I first got the machine, when I tightened the setscrew  the crank got really stiff.  I loosened it up some and haven't pursued it any further.


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## CKel44 (Jan 16, 2021)

***PROBLEM SOLVED***  

I emailed Precision Matthews, they suggested to first check the Z-axis gib adjustments for excessive tightness, that was not the problem.

Before hearing back from Precision Matthews I removed the Z-axis leadscrew cover plate on top of the column to expose the flange nut on top of the leadscrew.  I don't have the torque spec on that, but I tightened it until slightly snug (it had zero torque on it) and the crank now operates very smoothly.  By tightening that I think I took the severe tightness out of the bevel gears down at the crank by having lifted the leadscrew/bevel gear slightly upwards into its proper position.

Anyhow, problem solved...

Craig


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## GunsOfNavarone (Jan 17, 2021)

You obviously had the tools to correct this issue from the get go, that being said, I'd be severely reluctant to disassemble a new machine w/o talking with manufacturer first.
Nice work glad to see it was a "small" detail that was missed. Now if that were lug nuts on a car, not so small anymore.


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