# PM-728vt design change request. Potential oil line failure.



## addertooth (Sep 18, 2021)

I have finally got around to figuring out how I am going to mount a DRO to my PM-728vt.  This has meant a lot of crawling around the mill.  I have been pretty pleased with what I have seen, once I started looking at the fabrication of the Mill in detail.

There has been one thing observed which is problematic.   On the left hand side of the mill (under the table), a one-shot plastic oiler line bears against the lead screw which moves the X-Axis of the table.   I ran my finger over the plastic oil tube, and discovered it was already getting a "flat spot" from the rubbing against the rotating lead screw.  The table has been traversed a lot lately, to figure out DRO sensor placement, but still, the Mill only has a couple hours of use on the clock. (Mostly traversing back and forth to figure out DRO bracket placement.)

With a flat-spot already worn after such use, it points to eventual wear-through on this line with extended use, and will result in a lot of oil being dumped when the one-shot system is used.  This could also result in precision surfaces not being properly lubricated (if the person is not alarmed by the increased pool of oil showing up in the tray).  The one-shot system has a reputation for being "leaky", so I could see someone missing the early signs of a line failure.

As former Military, there was a common saying: "Don't come to me with a problem, unless you have the solution in your hip pocket".  So let me propose a simple production fix.   Move the oil manifold one inch to the left.  This will keep the plastic hose from rubbing against the lead screw. 

For the moment, I have an ugly fix for it.  It will be replaced with something better after the DRO install is complete.

See pictures below.


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## Tio Loco (Sep 18, 2021)

Thanks, I'll take a look at mine...


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## koenbro (Sep 18, 2021)

Is your oiler leaking? Mine is and I will take some time figuring out where exactly. 


Sent from my iPhone using Tapatalk Pro


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## rwm (Sep 18, 2021)

Me too.
R


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## addertooth (Sep 18, 2021)

I have looked at the oil leaks briefly. I put a wadded paper towel under the pump, and no oil stains are forming on the top of the wad.   It may just be the lubricated Ways dripping off excessive lubricant after cycling the pump.  Other people have done the same test with a wad of paper towels and reported different results.   I do have oil in my chip tray.


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## rwm (Sep 18, 2021)

My oiler does not leak. But I am not super happy with it. It does not pump correctly unless the reservoir is darn near full. Do you guys have that issue? Is there a better replacement?
Robert


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## addertooth (Sep 18, 2021)

rwm said:


> My oiler does not leak. But I am not super happy with it. It does not pump correctly unless the reservoir is darn near full. Do you guys have that issue? Is there a better replacement?
> Robert


My mill is too low on hours to have used much fluid, so I have not had the chance to experienced its behavior when lower on lubricant. 
I really like the idea of the one-shot oiler, and it was one of the reasons why this mill was selected.   I have had to run older mills, where the beginning of each work day was going around and lubricating the machine before the work begins.  This feature seemed like a time saver.


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## rwm (Sep 18, 2021)

Mine does not seem to interfere:







The line that goes up to the Z axis does not stay primed. It leaks down and fills with air. Anyone else? Is this a valve issue? I thought about adding a check valve on the outflow port.

Robert

Edit: Adder- it appears that your 3 way connector is mounted backwards. Can you flip it?
R


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## addertooth (Sep 18, 2021)

Thanks RWM, it looks like you are right!
I may give this a shot.
I have no clue how this slipped past quality control, PM is normally pretty solid.

By the Way, is this a PM installed DRO, or did you do it yourself.


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## RJSakowski (Sep 18, 2021)

addertooth said:


> I have finally got around to figuring out how I am going to mount a DRO to my PM-728vt.  This has meant a lot of crawling around the mill.  I have been pretty pleased with what I have seen, once I started looking at the fabrication of the Mill in detail.
> 
> There has been one thing observed which is problematic.   On the left hand side of the mill (under the table), a one-shot plastic oiler line bears against the lead screw which moves the X-Axis of the table.   I ran my finger over the plastic oil tube, and discovered it was already getting a "flat spot" from the rubbing against the rotating lead screw.  The table has been traversed a lot lately, to figure out DRO sensor placement, but still, the Mill only has a couple hours of use on the clock. (Mostly traversing back and forth to figure out DRO bracket placement.)
> 
> ...


The solution is shown is Robert's post.  Unscrew the two horizontal lines and loosen the vertical  Remove the mounting screw and rotate the fitting 180º.  Reconnect the lines.
Edit:  I see that Robert covered that in his edit.


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## sunrise305 (Sep 18, 2021)

Are these oilers installed by PM or the factory?


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## rwm (Sep 18, 2021)

Mine is the PM DRO. Very satisfactory.
R


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## rwm (Sep 19, 2021)

Can someone comment on whether their line to the Z stays primed with oil?
Thanks
Robert


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## sunrise305 (Sep 19, 2021)

rwm said:


> Mine does not seem to interfere:
> 
> View attachment 378919
> 
> ...


A one-way valve added to the Z line should solve this problem.


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## addertooth (Sep 19, 2021)

When I use the pump, the Z-Axis is the last to "burp".   They are off a common feed, so the Z line drains down (due to gravity), and continues to flow down the the X and Y axis after pumping.  As several people have mentioned, a one-way ball valve on the Z axis line will fix this.  Those "check valves" cost about ten bucks on eBay.


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## rwm (Sep 19, 2021)

Mine are on separate ports from the pump (unless they are linked internally.) I will look for a check valve. What is the tubing size designation???
Robert


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## addertooth (Sep 19, 2021)

I mis-spoke.  Mine has two lines.  One for lubricating the Z axis, the second line is for everything else.  I see no clear indication the Z axis line has a check valve, and I bet internally the two connections go to the same place.


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## rwm (Sep 20, 2021)

The fitting out of my oiler appears to be M10. The oil lines measure 5/32 OD = 4mm.
I found brass check valves here:









						Fitting Metric M10 M10x1 Male X Compression 4mm OD Tube Check Valve One Way 8iK2  | eBay
					

Check Valve Fitting One Way Direction from M10 Male to Tube (see the arrow on the listed picture). We also provide the Check Valve with the opposite direction.



					www.ebay.com
				




I also ordered a M10 90 deg elbow. I will replace the elbow on the oiler and then add the check valve coming off the elbow. Pretty simple fix if it works. I will keep y'all posted.
Robert


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## rwm (Sep 22, 2021)

I have some news on this. I received my new fittings today and took apart the old line to install them. To my surprise, there is a check valve installed in the factory elbow! Assuming this may be defective, I went ahead and changed the elbow and installed a new inline check valve as shown above. I will monitor this for a week and report back.

Robert


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## rwm (Sep 22, 2021)

Reporting back- my Z axis lines are now filled with air again : (  I must assume that these check valves are not "checking" and that the oil is draining back into the reservoir. I am not sure how to proceed? 
Robert


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## pdentrem (Sep 22, 2021)

Since it is only used when the machine is being used, install a shut off valve in the line, to stop oil flow when idle. Alterately move the oil reservoir higher if possible.
Pierre


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## addertooth (Sep 22, 2021)

A stiffer spring (or spacers under the non-ball bearing end), will increase the "seating force" of the ball bearing.  It may seal better without replacement after that minor change.  If the spring is too stiff, then it won't open the ball/valve-seat opening enough to lubricate the Z-axis.


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## rwm (Sep 23, 2021)

Hmmm. I performed an experiment on this. I took the original check valve and put a vertical length of tubing of about 16" on it. I then filled it with oil and held it vertically overnight. The oil did not leak down at all! The check valve is actually working as intended. This leads me to the conclusion that the oil is leaking antegrade into the ways for the Z axis. That is not something I expected. I am considering replacing the vertical tube with clear tubing so I can see what is actually going on with the oil supply.

Air filled supply tube:






Robert


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## addertooth (Sep 23, 2021)

I flipped the Manifold over to help with the clearance of the oiler line and the lead screw.  It is still making contact, but not as firmly as before.   A message was sent to Precision Matthews with the problem, and a question.  I had asked if the plastic tube is simply pressed into the casting.  They said that was how it was installed on that end.  At this point, it appears that with the manifold being flipped, there is too much plastic hose, which is part of the reason why it is still making contact with the lead screw.  This weekend, the hose will get pulled out and shortened.  I suspect that will deal with the unwanted contact. 

One other minor change was made.  The bolt which holds the manifold to the casting stuck out too far, and looked like it would interfere with a DRO bracket which was going to be installed. When the manifold was flipped, the bolt was screwed deeper into the casting.  The only hiccup was there was a locknut at the casting, and another at the manifold.  Screwing the bolt in further Reduced the gap between these two jam/locking nuts.  My normal 8mm wrench was too fat to tighten one, without turning the other nut as well.  But then, I remember there was a mill in front of me. An 8mm slot was cut in a 1/16th thick piece of metal, and it was used as a "thin wrench" to tighten the nuts.  

It is always important to remember that when you have tools, you can use them to make custom tools.


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## woodchucker (Sep 24, 2021)

addertooth said:


> I ere is too much plastic hose, which is part of the reason why it is still making contact with the lead screw.  This weekend, the hose will get pulled out and shortened.  I suspect that will deal with the unwanted contact.


I don't understand, why can't you just cut it now? Seems like an easy fix.  Just take the hose off the T , cut it, put it back on?
I assume it's got a compression fitting and maybe an insert to keep it's shape?

a 2 minute job.


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## rwm (Sep 24, 2021)

It's a 4mm compression fitting.
R


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## addertooth (Oct 8, 2021)

Unfortunately, I live in Hooterville.  Many parts/supplies are hard to find.  This is especially true of Metric ones.  If you go into a local shop and ask for metric plumbing supplies, you get the look which implies they wonder if your mother knew your father when you were conceived.


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## Christianstark (Oct 8, 2021)

addertooth said:


> Unfortunately, I live in Hooterville.  Many parts/supplies are hard to find.  This is especially true of Metric ones.  If you go into a local shop and ask for metric plumbing supplies, you get the look which implies they wonder if your mother knew your father when you were conceived.


Have you checked with Jeff Bezos?


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## 7milesup (Oct 8, 2021)

I'm thinking that Hooterville might be a rather pleasant place to live.  Easy on the eyes maybe


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