PM-932M-PDF Power Downfeed Remove-Clean-Replace

[Lynrob]

After reading Ratz' post about all of the junk he found in his PDF gearbox, I decided to bite the bullet and take mine off to see how it looked. Unlike Ratz, I am not an experienced machinist so I was somewhat reluctant to take apart something that was working but Ray encouraged me to give it a try, so I did. Removing the gearbox could hardly be simpler. I first moved the table all the way to the left to limit the exposure if I were to drop something. I also put a thick dense rubber pad on the remaining part of the table as added protection. Next I removed the SHCS (Socket Head Cap Screw) and washer that is in the center of the quill lever assembly directly between the two quill levers. With a little back and forth, the whole thing came right off. The first photo below shows what I found underneath. There was a little grit but, overall, not too bad.

Next, I loosened the 6mm SHCS located at each corner of the gearbox. Once they were fairly lose but still engaged, I inserted a sharp flat bladed screwdriver (I know... that's not what a screwdriver is supposed to be used for) in the seam between the gearbox and the head and gave it several light taps until the parts separated. Then I tapped on all sides with a dead blow mallet as I gently pulled the gearbox away from the head. Once I was pretty sure the gearbox was free enough to remove I pulled out all four SHCS and removed the gearbox. Photos 2 through 4 show what I found. The ring in photo #2 had the worst contamination, but it wasn't grinding grit like I was expecting, instead it was more like Bondo dust or paint flakes. Anyway it cleaned up quickly. Photo #3 shows what that ring was (left-hand) threaded onto. Overall, not too bad, just minor contamination. I removed the two slot headed screws shown in #3 and pulled off the flange that the screws retain. Inside, there are two spring loaded pawls that engage the larger ring gear shown in the picture. It was pretty clean inside so I didn't remove the pawls. I just rinsed everything good with WD-40. Before I replaced the flange, though, I found that the ring gear did not revolve freely. I couldn't see a way to easily remove and I didn't want to bite off more than I could chew so I just kept turning it back and forth and spraying it with WD-40 until it was free. I didn't really find what was causing it to be stiff but it seemed to be getting better the more I fiddled with it so I just kept it up until it felt reasonably free. I then re-rinsed the pawls and coated them with a light coat of grease.

Next I cleaned up the gears. Again, they weren't too badly contaminated so I just rinsed liberally with WD-40 and scrubbed off the grease with an old toothbrush. I had noticed before I took the gear box off that whenever I turned quill feed wheel on the front of the mill, I could hear a crackling sound which I took to be grit in the gears. With the gearbox off, I was able to determine that the crackling sound was caused but air getting trapped in the grease on the gears and making a popping sound when the bubbles burst. I am not sure what kind of grease is used at the factory, but it seemed pretty stiff to me considering the low speed, low load usage these gears will see. Since I now know that it is easy to change if I ever need to I opted to use a lighter NLGI grade 0 grease. If you are interested, it is John Deere Special-Purpose Corn Head Gun Grease AN102562 which, as the name implies is designed for use in corn harvesters. Anyway, it's great stuff. It has extreme pressure and rust preventatives, it is good at all temperatures and it stays where you put it even though it is fairly soft. It is specifically designed for use on slow-speed gears.

Once I got the old grease out and the new grease in, I found the entire gear train much easier to spin (Photo 5). By the way, if any of you were wondering where the oil that you put in the little oil cap on top of the gearbox goes, you can see it in the lower left of photo #5. Looks to me like it just drips oil on the brass gear. I did the same type of clean up to the quill lever assembly and then put everything back together. It is fairly easy to reassemble. The two tabs on the left-hand threaded ring in photo #2 must be lined up with the slots in the gear casing and the worm gear that drives everything must be properly engaged. Don't force anything! When it's all lined up it will just slid into place. In Photo #3 there are two holes to the right of the ring gear I talked about earlier. One hole is threaded and the other is not. The non-threaded hole receives a dowel pin in the gearbox and there is another one just like it on the left-hand side. These pins really help to line thing up but mine were loose so I had to make sure to push them into position.

The first time I re-mounted the gearbox, everything seemed great until I engaged the power feed. The power feed didn't work and there was a rhythmic clicking sound coming from inside. I thought I had screwed up big time and expected to find powdered gears when I opened things back up. Luckily there was no damage. As far as I can determine, the drive pinion from the head has a clutch mechanism on it that maybe protects the gear train if its load capacity is exceeding some limit. The worm gear on the drive pinion has a castellated top that mates to similar castellated part coming down from the top. There is a spring below the worm gear that pushes it up and keeps the castellated parts mated. The angles of the mating castellated parts are such that they exert some downward pressure on the worm gear as the torsional load increases. I think that if load gets heavy enough, the castellated parts will cam out and slip rather than forcing the gear train to take an excessive load. I believe the clicking I was hearing was the two castellated parts sliding by each other. I don't know what caused the issue. I looked everything over and remounted the gearbox to the head just as I had before but this time, luckily, it worked.

That's pretty much it. I think that my particular machine would have worked for years as it was but it is quieter and it has a much better feel to it now and I have peace of mind knowing that my gearbox isn't doubling as a grinder. Thanks to Ratz for giving me the idea and to Ray for encouraging me to go for it. I am glad I did. I now know much more about my mill and am more confident and less fearful of screwing it up.

I apologize for the organization of this post. I wanted to display the photos with text in between but couldn't figure out how to do it. This is my first post with pictures so obviously, I have a lot to learn. As I said I am a neophyte when it come to machining and my primary purpose of being in this forum it to learn and give back a little when I think my limited experience might be useful to someone else. I hope you will all feel free to shoot this full of holes and tell me what I might have done differently or better. I will continue to makes the same mistakes unless someone points out my errors. Thanks to all of you who have posted! I have learned a lot!!

 

[Ratz]

Lynrob, congratulation on taking a plunge and removing feedbox. Thank you for your time to post such a detailed procedure and your findings. You did a nice job.
<O</O
It is good to see the pictures of other machine components. Your machine is definitely cleaner, however looking at the 2[SUP]nd[/SUP] photo of the nut with two tabs on it, it is hard to believe that it is a component of precision machinery.
<O</O
I like to expand on your reassembly and experience of slipping clutch. It appears to me that the feedbox cast iron housing is machined undersize as in my case.
If you recall my picture (and I am attaching it again), the feedbox had a piece of junk aluminum ruler (acting as a shim) glued to the front surface of the feedbox housing. I experienced the same thing when I assembled it without the shim. What happened is that the bronze gear in your last picture is too tight against the worm gear, which is the drive for the power down feed.
<O</O
If you recall from my post I fabricated a 0.030” shim (by my measurement of my machine. This number will likely vary with different machines so do not take this number as a fix for all cases) which took care of things. I suspect your machine is just on the border line and maybe you did not tightened four bolt as tight the second time. It will probably wear in and you will be fine. Since I am too anal about machinery, I would likely take it of, purchase something like 0.005” brass shim stock and make a gasket/shim for the mating surface. I had to make one which was 0.030” for mine. Having said that, I would contact Matt at Quality Machine Tools and ask him if this is OK, as I am describing my experience and my view of this particular machinery, which may void your warranty.
<O</O
I suspect the factory had some issues with this and some machines like mine was so tight that their fix was to toss in a piece of aluminum to gain clearance.
With the piece of aluminum (as in my case) the whole feedbox is out of alignment. If one takes a look at your last picture again, the thicker worm gear with green grease is out of alignment with the driven gear. That is why I made a new shim which made the feedbox housing sit squarely on the gear head.
<O</O
Cheers to all
<O</O
Radek

 

[Ratz]

To further expand on this issue, I am attaching a picture of my first drawing of the return spring modification with the final product described in my other post.
<O</O
http://www.hobby-machinist.com/showthread.php?t=22195
<O</O
The picture is for those who may be too intimidated to attempt feedbox removal.
<O</O
In this post Lynrob wonderfully describes the cleaning procedure. If you feel uneasy to proceed, then look at Lynrob’s last picture and look at the bronze gear.
<O</O
Then look at my black and white picture and you will see that particular gear mating with the drive worm gear. On top of the worm gear you can see the clutch which he refers to as slipping during his first reassembly.
<O</O
It is very easy, to take the front aluminum cover off and expose this gear and clutch. Since this gear is part of the feedbox you can take a sample of the grease and rub it between your fingers to see if any grit is present. Take a flashlight and look inside and keep taking samples of grease from as far as you can reach. Give it a good visual inspection. If you are satisfied, you done. However remember that you are inspecting only part of the power feed system and will likely miss the aluminum spacer which only makes the feedbox misaligned on the gear head body.
<O</O
To remove front cover remember to make note which lever fits where. They are both the same but the holes for roll pins are not drilled on the center of the shaft. There is good possibility the reassembling it if the holes do not mach one could spoil one or both levers when taping the roll pins back in. Remove the six small screws and slightly bent the plate that it clears the gear selector shafts and the manual feed handle base.
<O</O
Radek

 

[Lynrob]

Thanks Radek! I now understand why you needed the 0.030 shim. It did not occur to me to take off the front cover when things weren't working. I now wish I had so I could have confirmed the issue. I think that since things appear to be working well in my case I'll leave well enough alone for now. I exercised the PDF some more yesterday and it seem to work well. I didn't put much of a load on if though. I'll load if more and see if the clutch starts to slip. If the clutch slips I'll have to dive back in.

Thanks for for taking the time to share your experience.

Lyn

 

[chuckorlando]

Nice write up.

 

[Ray C]

Hi all... I've got a little family gathering going on but sometime today, I'll post a description and photos of why the unit sometimes does not go back together the same way it came apart -and it leads to the worm gear safety mechanism to kick in which causes the spring overload to do it's job and prevent damage. There are two reasons. Hint. Shims are not needed but, correct axial alignment of the concave spur gear are necessary and, the PDF spindle handle knobs can be impeded for two common causes.

Also, I'll provide some insight why you think your bearings are leaking -while in-fact, they are not...

When my family gathering is settled-out, I'll post some tips that will shed a LOT of light on what's going on (and how you can damage things if you're not careful).

Ray

 

[zmotorsports]

Nice post. Thanks for taking the time to share.

Overall, how is your 932 working for you?

Mike.

 

[Ray C]

OK, all family members are adequately watered and fed...

This thread is devoted to background information about oiling the spindle and greasing PM45/932 PDF gearbox. The pictures of gear mechanisms only apply to models with the PDF (Power spindle DownFeed) option.

As part of routine use, the top drive-end of the spindle splines should be oiled. I just use way oil and dribble several pumps of oil down the splines as shown here:



Even though oil is slippery, it can't escape the forces of gravity so, the oil you pour-in at the top eventually ends up here:



... The oil that shows-up down at that rubber ring does not originate from the internal gearbox and does not indicate a problem with your bearing seals.

A few notes: I'm demonstrating on a PM45 that's about 5-6 years old. The collar at the base of the spindle support tube is now cast iron and looks like this as demonstrated on my new PM45-CNC. The 932's are the same design as this:




Note that in my first picture, I installed a lightweight aluminum ring where the current cast iron collar is located. That aluminum ring is a non-intrusive (aka non-Warranty voiding) fixture for hanging TDI's and a 6" caliper to serve as a DRO. (The older machines did not have a built-in DRO scale).

The upshot: If you see oil around that rubber ring, you are to be congratulated for taking the effort of oiling the internal spindle shaft. Just wipe it off if it drips on your workpiece.

IF you have genuinely leaking bearing seals, the oil will not show-up on the rubber seal but rather, it will leak out of the very bottom where the R8 orifice is located or, it will fill the spindle support tube and leak out of the hole as shown below. I'm shining a flashlight which exposes the actual spindle shaft.



For the sake of completeness, IF you have a truly leaking spindle bearing seal, it could leak-out of the very bottom (by the R8 orifice) of the lower spindle bearing housing as shown:



Finally, if you should need to remove your oil seals for whatever reason, prying them out with a screwdriver will destroy them. Order new ones before you start the process.

Care and feeding of the PDF Gearbox:

I'm not going to describe how to remove the PDF gearbox as, Lynrob had done a fine job. It's not rocket science but rather, 4 bolts and 1 screw. If it takes you more than 3 minutes to remove it, you're doing something wrong.

The PDF gearbox is "open-air" accessible through the bottom-side of the mill head. Just see the open-air in the upper-right side of the big gear on the shaft. When the machines are assembled, the last thing they do is take grinders to remove external burrs on major parts of the casting then, they apply the epoxy/bondo and paint. In that process, "stuff" gets in the PDF gears. You don't like it -and neither do I. It exists nonetheless.



In the following photo with the front cover of the machine removed, please note the spring tensioned worm gear and scalloped interface at the top. It is a safety mechanism actuated in several ways. Also note the concave spur gear meshed with the worm gear. That spur gear is housed inside the external PDF gearbox.



Here's the external PDF gearbox removed (see below)... Key point here! That spur gear can be moved slightly left or right on it's shaft. When you reassemble the gearbox onto the side of the unit, the spur gear must align with the worm gear. If you (attempt to) assemble the unit with the spur gear pushed to it's left or right furthest extent, it could be "Game Over" for both gears.



Once again, note the photo below of the tabs I'm pointing to. That collar unscrews and if you unscrew it, make sure you keep track of how many turns there were. Those tabs must be returned to the corresponding section of the side casting AND at the proper depth -or you will have problems.



In any event, once you have this apart, clean and re-grease as you see fit. Those gears are very low speed. High performance grease is not necessary.

After you have reassembled things, the spindle leverage arms must be set properly and when using PDF (or not using it) the arms must be either fully engaged or released. Any intermediate position will drive both aspects of the PDF internal gears and the safety worm gear will need to kick-in and do it's job (which it does faithfully).

See Below: The center screw must always be tight. It had a tendency to come loose so I tossed a star washer on there. The thumb screw (as shown) must either be set to allow PDF or disallow it. (BTW: The other little lever is used to set the large collar to lock-in a desired PDF drilling depth). If that screw comes loose and the whole spindle arm mechanism shifts off the shaft, it will result in the PDF being partially engaged and the safety mechanism worm gear will have to do it's job.



Once again, the spindle arms must be fully retracted or fully engaged as shown in the two following pictures. The little thumb tab is used to lock-out the spindle PDF from being engaged.




And finally, here are a couple photos of the overall side gearbox. This is what mine looks like after 5-6 years of use. Until this issue recently came up, I was never curious enough to look in there. The photos are taken as it was opened the first time. I subsequently wiped it out with a rag, and slathered some new grease in there. I was half tempted not to bother...



And for reasons I cannot understand, a photo which I didn't intend to use is being displayed. That little lever is what locks the depth collar for setting a drilling depth.

...Hope this was informative...


Ray

EDIT: I added the work in bold "NOT", in reference to oil originating from the gearbox and leaking onto the rubber seal at the spindle base.

 

[Lynrob]

Thanks Ray! You filled several gaps in my understanding of how things work. One thing you talked about has me concerned. You said to keep track of the how far the tabbed collar is screwed on and to set it back to that position if you take it off. Unfortunately I didn't know that when I disassembled my gear box. When I put it back together, I just bottomed it out then backed it off enough for the tabs to align with the slots in the gearbox. What is the correct procedure? Things seem to be working great, is there any reason for me to take the gearbox off again to set that collar? What are the symptoms if it isn't adjusted properly?

Please pardon all the questions and thanks for your willingness to share what you know.

 

[Ray C]

Thanks Ray! You filled several gaps in my understanding of how things work. One thing you talked about has me concerned. You said to keep track of the how far the tabbed collar is screwed on and to set it back to that position if you take it off. Unfortunately I didn't know that when I disassembled my gear box. When I put it back together, I just bottomed it out then backed it off enough for the tabs to align with the slots in the gearbox. What is the correct procedure? Things seem to be working great, is there any reason for me to take the gearbox off again to set that collar? What are the symptoms if it isn't adjusted properly?

Please pardon all the questions and thanks for your willingness to share what you know.

When you press or pull on the spindle lever handles to engage/dis-engage PDF, it may prevent PDF from being fully engaged or disengaged. Anytime you get into one of those "half-way" situations, energy from the shaft turns the worm gear and it just spins and slips. As best I can tell, that's it's only purpose -and is pretty clever if you ask me. I'm studying the photos and gear arrangement as a learning exercise. There is a LOT going on with those gears.

Anyhow, if it's working, don't break into a sweat. If that collar is too far out, the housing either won't go back on or, you'll never be able to fully engage/dis-engage the PDF.

I also meant to mention that the housing has a couple alignment pins. One of mine slipped out and it's conceivable to not notice it missing. -Don't forget the alignment pins...

And finally, I had to change one word of my earlier post as I omitted the word "NOT". The oil that shows-up on the top-side of the rubber seal of the collar support is NOT coming from bad bearing oil seals. It's just the run-down from when you lube the drive-end of the spindle.

And finally, I'm not an expert on that gearbox and everything I know about it was from 1.5 hours of analyzing it. I currently need that mill to finish the other job I'm working on and I took a risk opening-up a can of worms.

-and thank you, Lynrob for not being upset that I posted so much in your thread.


Ray