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IndustryArena Forum > MetalWorking Machines > Fadal > VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade
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  1. #1
    Join Date
    Jun 2012

    VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    As a follow up to my previous thread about my newly aquired VMC-20 and the bad noise it's spindle was making, I did go ahead and shell out for a refurb spindle, as well as the parts to convert my machine from the crappy 6-belts system to the 2 belts pozi drive system. The stuff arrived today late morning:

    Attachment 280376

    Pretty much Engineering Christmas!

    So, the real work started. I just got this machine so I am still in the process of cleaning it up. I spent most of the morning cleaning the sheet metal, etc. with degreaser. I do that on all my newly aquired machines. I got started really tearing things down at about 1:30 pm. I watched videos, and read instructions from whatever online vendors / fadal parts places that there are. they all give more or less the same instructions. Here's an image of the old spindle removed:

    Attachment 280378

    The only snag that I ran into, apart from how dirty this machine is, including many pieces of 6-belt style belt teeth, and shredded rubber everywhere, was that the spindle retainer, which is a split ring, needs to be unbolded at the split. This is not mentioned in the instructions, or videos from any of the fadal parts vendors. The screw is in the side of the ring, and until you remove it, you cannot split the retainer ring and remove it. The lip of the ring is underneath a thin flange on the spindle - so it doesnt just lift off. You have to loosen that screw in the side of the ring, then you have to pull the ring apart (i used a flat blade screw driver and a lot of finagling). Then you can bring it up and off of the spindle. At that point, all you have to do is put the spindle nose on some wood, then unbolt it at the bottom flange, and put the z-axis up to clear the spindle. Here's another view of the spindle, removed:

    Attachment 280380

    The spindle pulley indeed is removed using heat / two torches and some waiting around. That worked without any trouble what-so-ever. I could have swapped in the refurbed spindle right then, this was by about 5:30 pm (so it took me 4 hours, as a newbie, to remove the spindle). It's really not too bad of a job at all and I think anyone can do it, no problems.

    Where I am into some bad territory is with this pozi drive upgrade. I need to replace the spindle pulley - fine, but I also need to replace the motor side belt pulley. OK... that's not so intuitive. The spindle side pulley is keyed to the motor shaft. This machine has a 5hp motor, which I believe weights somewhere in the neighborhood of 80 to 100 lbs. I do not have any kind of shop crane or hoist that can remove this motor for me. Furthermore, I don't want to pull the motor down from the machine. I don't even want to disconnect the wiring. Also, it's just me working on the machine, I don't have a second hand to help wrestle this damn motor perched on top of $15K worth of 'i dont wanna screw this sh*t up,' or hurt myself. So, if anyone has any suggestions about how to remove the motor from their fadal, I'd be happy to see another way than what I ended up doing. My way worked:

    Attachment 280382

    I ended up moving the z axis up pretty much to it's limit, then sliding a large board under the motor mounting plate. I had the back left motor mount pillar still attached / bolted into the rubber mount. I then unbolted that last remaining pillar and pulled that out and slid a 2x4 underneath the back of the motor mount plate so that the front was supported by a larger board laid flat, and the back supported by a 2x4 on its edge. I added a second large board in front of the motor to allow me to lay the motor down on the two front larger boards, with the wiring still attached and the cat track / cable manager un-strained. This worked, but was pretty perilous. I was able to handle the weight of the motor as the fulcrum was supported by the boards. I had the enclosure doors shut behind me so that if I fell backwards, they'd catch me. Now the motor is in a position where I can work on the pulley. I have ended here for the day, because now I need to think some things through about the position of the pulleys on the motor shaft, and on the spindle:

    Attachment 280386

    Has anyone gone through the 6-belts to pozi drive upgrade? is the spacing different between the two systems? the pulleys are different heights. I will do some CAD of it all to try and convince myself about where this new pozi-drive pulley needs to be on the the motor shaft as far as how far to put it on. On the spindle side, I could put the new pozi pulley on to the same height as the old 6-belts one, but is that the right thing? I have a VMC-4020 too which has the pozi system already, I guess I'll need to tare off the covers at least on that to try and make some measurements.

    Also, I believe I can get the spindle side pulley off with a puller tool, but I am unsure of how to put the new one on. Maybe I can heat that piece too, but that seems like a weird thing to do with a keyed shaft and pulley? Has anyone ever done this pulley job on their spindle motor before? How did you remove the old one? How did you put the new one on? How did you know where to put it on the shaft / depth (especially if you were doing the 6-belts to pozi upgrade)?

    Really this pozi-upgrade is a huge pain in the ass, and there are no instructions from anyone. You'll also find that different vendors include different parts for the kit! wtf! why? shouldn't a kit to accomplish this change-over be the same no matter what?

    By the way, the old spindle bearings feel COMPLETELY bad compared to the new spindle, just turning it by hand you can tell a major difference. The old spindle actually catches in places like it has detents. I am excited to get this thing back together; i bet it will be butter smooth. Hopefully it will pay for itself soon there-after. Not a cheap set of parts to have to buy.

  2. #2
    Join Date
    Jun 2012

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    Alright, so after about 5.5 hours of CAD work, I found that the distance between the top of the motor pulley, and the flat face of the motor (the face that mates with the motor mount plate), ought to be 0.774" (probably 0.775, or 0.78 by design). This number comes from drawing all the parts that go into the pozi drive upgrade / based on real measurements of the actual parts.

    Some related distances:

    motor pulley top to motor face: 0.774"
    motor pulley lower (larger diameter section) top face to motor face: 2.424"
    motor pulley bottom face to motor face: 3.984"

    spindle pulley top most face to casting underneath spindle side belt guard: 3.807"
    spindle pulley underside of larger diameter section to casting underneath spindle side belt guard: 1.663" (the 6 belts distance was 1.762" so its not even close to the same)

    high range belt center height to low range belt center height: 1.65"

    So, these numbers are nice in that they're made from actual high quality measurements of the relevant parts - not crap measurements made when the parts are installed on a machine. These numbers give the ideal case. There is uncertainty about whether or not my machine's casting is made perfectly, whether the pulleys and belt guards sold to me are made well and designed correctly, etc. So in the end, I will have to set the motor side pulley at the nominal / ideal case number shown by my CAD model, I will then install the spindle side pulley to the ideal numbers too, but then I may need to reheat the spindle side pulley, and adjust it slightly.

    I will set the distances using a machined block - as I assume getting the new pulley onto the motor shaft is going to involve heating with torches too. I am about to head down to the chinese tool sellers (HF) and get a hydraulic puller to help remove the existing 6-belts pulley from the motor.

    I'll follow up on how all that goes..

  3. #3
    Join Date
    Jun 2012

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    Here's another image that shows the spindle retainer ring and its screw that is in the side of the ring:

    Click image for larger version. 

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ID:	280468

    I did indeed get the motor side pulley off. I went to HF and bought a hydraulic puller (5 ton). This puller turned out to be too large and I wasn't able to use it. I had also a 3 puller set that is a hand turn one / you turn the screw with a cresent wrench or socket. The cheaper smaller puller did not move the pulley at first, it just started to bend the aluminum pulley. So, I got out the torches again. I left the puller under stress while heating. The pulley began to move until the puller was loose. At this point I stopped heating the pulley and used the puller to move it the rest of the way off of the motor shaft. I believe that If I were to have continued heating, I could have removed the pulley very simply by hand with no puller at all.

    This is an advantage of using aluminum pulleys - the sweat fit method works a treat because it expands so much more than the steel shafts they are paired with.

    I used my machined spacer bar that I made on my other mill at 0.774" when putting the new pulley on. I heated the new pulley for a few minutes with two torches. I then placed the pulley on the motor shaft with great ease - no force required at all. The spacer placed the pulley - exactly where the old one used to be. So during the 6-belts to pozi upgrade, the motor side pulley will go back where the old one used to live. I am unsure about the spindle side pulley yet - my solid model suggests that it will be different.

    Attachment 280466

    I ended the night with the new spindle placed into the casting with the lower flange bolts a bit more than hand tight. I put the retainer ring on the top, but I have not yet tightened it back into place from its side or by the flange bolts on the upper flange.

    Getting the motor back upright wasn't such an impossible task. I just used enough boards for levers and got the two left side bolts in place. Then the air cylinder side went in with some wrangling. I replaced the motor mounts in the mean time too.

  4. #4
    Join Date
    Nov 2003

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    Nice write up. I see a spindle xhange in future on my VMC 15

  5. #5
    Join Date
    Jun 2012

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    Alright, after another days work, here's a video showing the new spindle running:


    The spacing that I calculated using CAD and gave the numbers here previously worked out fine - the belts track well fwd and reverse. I am running a spindle burn in now which is just 25%, 30 min, check temp with IR thermometer, 50% 30 min, 100% 30 min, and if there is no temp rise above 140 deg at the spindle nose then I'm good to go machining.

    Hopefully this machine will pay for itself quickly after all this work - it sure sounds nice now.

    A couple of notes that aren't described in any spindle swap instructions:

    - You have to epoxy the sense magnet into you new spindle pulley if you are doing the pozi upgrade from six belts. You probably have to do it on a spindle swap too since the heat during removal will likely pop the magnet out. You epoxy It back in after the install because you have to heat the pulley during installation too.

    - I had to move the magnet sensor head that is attached to the orientation bridge down a bit due to the pozi drive upgrade, the new pozi drive spindle pulley sits a little lower. I was getting spindle overload errors but that was because the machine wasn't able to see the magnet to count the RPMs. lowering the sensor head fixed it first try.

    - the spindle retainer ring bolts at the top have Teflon tape on them to stop your dowfrost refrigerant from leaking. you have to pull the old tape off and put a new layer of tape on - don't forget to do that. my vmc20 doesn't have a chiller, but the tape was there anyhow.

    best of luck to anyone who goes through this spindle swapping business, and also a pozi drive from 6-belts upgrade. it was pretty hard work which ate up 3 days of my time (working alone), and a lot of $$ in parts. my machine sounds like its back on track now though, and is a welcome addition to my shop as the new fadal - even though its just a little baby fadal compared to my 4020 machine.

  6. #6
    Join Date
    Jun 2014

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    Did a very good job of taking pic and writing up the things you came across. I don't see to much activity on this forum so nice to see someone take time to write up a nice detail procedure on the install. I'm sure it will come in handy for the next guy.

  7. #7
    Join Date
    Jun 2012

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    For a follow up after a few days running, the system is very quiet and I got through a job of 40 parts just fine. These parts had no tapped holes.

    Last night I needed to do a job with tapping. This was a 4-40 roll form tap using a floating tap head because this VMC-20 doesn't have rigid tapping, it uses the mitsubishi inverter drive. I ran the tap cycle with no tool holder in to test it first at 500 RPM in the high range, so S500.2 This test seemed to go well. So I went ahead and put the whole program for this part on, and when the machine got its roughing endmill and went to go to 6000 RPM, the high range belt bound up and screeched some. I was standing there and stopped it right away - so not too much belt damage from this.

    What this means is that my high range belt cannot reverse and stay on track. I did test the high range in reverse, by hand, and at 100 RPM, but it seems anything over about 300 RPM in reverse and the belt wants to jump the track. The low range works fine at all RPMs.

    This concerns me because you would expect both ranges to have trouble, or you would expect fwd and rev to not work. This could be a result of bad spindle pulley spacing, or the wrong motor tension setting. I already messed around with the tensioner steel cable in back of the motor, this actually made the problem worse to tighten that further. leaving it totally slack doesn't get rid of the problem. The low range does work in reverse with the tension on or slack. maybe thats evidence that the low range belt is less likely to slip for some reason.

    So, this leads me to believe that maybe my spindle pulley is sitting a bit low. My spacer according to my solid model needed to be 1.663" I have read other numbers. The spacer sold by fadalcnc.com says 1.67" on it, and I read here on CNC zone an older post saying it should be 1.68". We're talking about 0.01" to 0.02" of error potentially. the belt teeth are spaced at 0.125" so if my spindle pulley is low it could be 8% to 16% too low (on a per tooth basis). yeah, maybe that's enough to cause trouble.

    Especially seeing that the tensioner makes the problem worse - which you would hope that the tensioner would allow you to have some slop in both directions (too loose, too tight, the middle setting works). where my tensioner seems to just barely have the belts working at zero tension, but definitely not working (in reverse only, in the high range only) when there is tension on that steel cable.

    So, it seems it is time to get the torches back out and try again, maybe I'll add 0.015" more gap between the casting and pulley - see if that works. I gotta get this to work because you just cannot use floating tap holders in the low range, the motor is way too slow to reverse and by the time its spinning, the tap holder is stretched way out and eventually hits its limit and breaks the tap. I've got tapping problems with this crappy open loop tapping system, but thats for another thread.

  8. #8
    Join Date
    Jun 2012

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade


    so, I did go ahead and raise the pulley up on the spindle side. I had some 0.02" aluminum sheet metal, so that's the height it changed it by. this means the new spacing should be around 1.685" (according to my measurement of the stack of sheet metal and my previous spacer). This is slightly higher than the largest number I read elsewhere, and listed below. whatever. I figure that if it can almost tolerate 16 thou below, it can do 5 above, especially since the tensioner goes the opposite direction in terms of belt tracking relative to a + height pulley error.

    I heated the pulley, put my new spacer stack under it, lined up the tick marks and went and got some dinner while it cooled down. This rework did not pop the corks out, and did not pop the epoxied in sense magnet. so - all that stuff didn't need to be reworked thankfully.

    On testing this new belt height after getting the belts and belt guards etc, etc all back together, she works a treat. all speeds, both ranges, fwd and reverse. great!

    well... now that the spacing was more like the factory must have intended, it became clear why the idler pulley bell crank for the low range (upper pulley) was included in the 6-beltz to pozi upgrade kit. The low range could no longer switch out when you programmed a change to the high range. the pulley was stuck up against the belt which was squished between the spindle pulley and the idler pulley. I tried adjusting the motor mounts, and all kinds of things and finally had to admit that it wasn't going to work. So, it seems that having the spindle pulley slightly too low allowed the low range idler to work OK, but of course the belts weren't working as described below. interesting. must be just that the tension was different or the idler pulley load was not symmetric up and down the face of the pulley prior to my re-adjustment.

    This meant that I had to disassemble the idler pulleys / belt changer. That sucked. there is a press-fit pin holding it together. It was hard enough to get that out by finding the right drill bit diameter and some careful arbor press work. Putting that assembly back together was an epic task. There are spring washers which you must compress to get the thing re-assembled back onto the shaft that holds the two idler bell cranks on. It took me 2.5 hours to put it back together.

    To change a bell crank you need: an arbor press, plenty of drills / pin sizes, a large Irwin clamp (to compress the stack of bearings), hopefully you can get a second hand to help you use the press / align everything.

    You can bet that they gave the task of assembling that belt changer to 'the new guy' back at the Fadal factory. That'd weed 'em out fast. Also you can bet that there are assemblers that worked at Fadal that properly despise the engineer who designed that thing (not that it doesn't function well enough, but man what an assembly nightmare - bet it looked pretty on paper).

    The new bell crank, which is IDL-0005, the silver colored bell crank / the upper one / low range bell crank, has a different distance between the idler pulley / bearing center and the bell crank mounting center. the difference is about 0.05" offset. but that small gap is enough to not have your low range idler rubbing on the pozi drive spindle pulley, and allows the system to change out of the low range without interference.


    beware, this pozi upgrade wasn't all that easy. you need a lot of patience.

    The machine is working well now, all speeds, both ranges. Goes to show that you really need to do due diligence on thoroughly testing all speeds both directions, even if you think you wont use them.

  9. #9
    Monkeywrench Technician
    Join Date
    Jan 2004

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    Thank you for sharing your experience with us

  10. #10
    Join Date
    Jul 2005

    Re: VMC-20, Spindle Replacement, and 6 Belts to Pozi Drive Upgrade

    Quote Originally Posted by mflux_gamblej View Post
    My spacer according to my solid model needed to be 1.663" I have read other numbers. The spacer sold by fadalcnc.com says 1.67" on it, and I read here on CNC zone an older post saying it should be 1.68". We're talking about 0.01" to 0.02" of error potentially. the belt teeth are spaced at 0.125" so if my spindle pulley is low it could be 8% to 16% too low (on a per tooth basis). yeah, maybe that's enough to cause trouble.
    I realize this thread is 6 years old but I am currently doing this on my fadal 4020. Just for anyone else that happens along looking for the proper dimension, after doing some measuring and calculations it appears that my spacers should be 1.694 to put my pulleys in alignment. Perhaps this is individual to the machine and should be calculated each time.

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