# PM833t Blew my gearbox tonight anyone convert these to belt drive?



## Uguessedit (May 16, 2019)

Not sure what happened but I believe the gearbox just imploded inside. High screech and sudden locking of the motor. Guessing gearbox since I can reverse the motor and get it to unlock and start again. As soon as I try and milk something it screeches and stops sending and OL code to my vfd screen. Hoping someone here has done a belt drive conversion. I have the materials and several belts here to start and a good idea what to do since it was previously a planned project anyways but it’s different than an rf45 so I don’t know entirely what I’m getting into or if more parts and materials will be necessary. The plan is a 5-3/4 pulley to a 1-3/4 to gear down and probably a 1:1 or perhaps even 4”-3” on the high side to overdrive it some. I have a pit of angular contact bearings here for the spindle. Guessing this will take me several weeks if I need to order anything more. I’m waiting on slotted retaining nuts which are coming from China so that’s sure to hold it up. I just added a Y a is and Z axis powerfeed too. Go figure it was running so smooth.


----------



## Bob Korves (May 16, 2019)

Take it apart and find the problem(s).  It might just be one gear, or something equally simple.  Parts are available for those mills.  Trying to convert it to a different style drive will likely be much more work that repairing it, and may turn into heartache when the new design fails.  You will not know the answer until you take it apart, and it will not likely fix itself.  You have everything to gain and nothing to lose by taking it apart and assessing the damage.


----------



## darkzero (May 16, 2019)

I agree with Bob. This is a Taiwan machine so I highly doubt there's a major problem causing the issue but of course anything can happen. This model also has a 5 yr warranty, I'm not sure when you purchased it but IIRC this model hasn't been available for 5 yrs yet. I believe they came out (from QMT) in 2016-2017. You'll have no problems with warranty if something failed from normal use. Might want to give Matt a quick phone call to see if he's encountered this problem before. If yes it may save you some time of troubleshooting from scratch.


----------



## davidpbest (May 16, 2019)

I agree with Bob and Will.   Take it apart (you're going to have to at some point anyway) and diagnose the problem.   Could be as simple as a tapered pin coming loose.   As someone who owned the real Rong Fu 45 for 18 years, then "upgraded" to a knee mill, I can honestly say I'd take a functioning gear head mill any day over a belt driven head.   Call Matt and discuss.   It's under warranty and Matt is responsive.   If there's an issue with the robustness of the gear train, I'm quite certain Matt would want to know.


----------



## 7milesup (May 16, 2019)

As an owner of an 833T, I would like to know what went wrong.  As David pointed out, I would think that Matt would be interested.   Tear it apart and see what is going on.


----------



## jbolt (May 16, 2019)

Even if you were planning on the belt drive conversion I would get whatever you can replaced under warranty so you have the parts if you ever decide to go back.

In response to the belt drive conversion. On most of the RF clone conversions the spline sleeve with gear that drives the spindle spline is modified by turning the sleeve to remove the gear. The sleeve is inverted so it sticks up for the belt drive pulley to mount to. During disassembly you would have to determine if this method would work on that model.


----------



## darkzero (May 16, 2019)

Uguessedit said:


> Well I stayed up near all night and rebuilt my mill



So does this mean it's working fine now? What was it?


----------



## Uguessedit (May 16, 2019)

Well I stayed up through the night and tore it down and rebuilt her. She is up and running with new angular contact Nachi 7207BMU and 7206BMU .0002 runout not terrible. I have blown gears before in this mill so it’s not unheard of but this time it was spindle bearing failure. I am still moving forward on a belt drive I really don’t have much confidence the gears are all getting sharp tips on them so it’s only a matter of time before another one goes they are wearing down. Besides that will be a nice fit with my servos and ball screws that have been sitting on the shelf. Been too busy to complete the task.


----------



## Uguessedit (May 16, 2019)

To use AC bearings I had to machine the spindle race down approx .046-.048 otherwise I couldn’t get any preload on the bearings and were loose fitting. Tossed it in the lathe and spun it down a smidgen and bam that solved my issue. You either have to shim the outer race of the top bearing up or machine the spindle so inner race can go down. I chose spindle since no shims on hand and it made more sense since I won’t ever use factory bearings again.


----------



## Uguessedit (May 16, 2019)

It sounds great now and the finish is outstanding.


----------



## Uguessedit (May 16, 2019)

In case that video upload didn’t work.


----------



## Uguessedit (May 16, 2019)

7milesup said:


> As an owner of an 833T, I would like to know what went wrong.  As David pointed out, I would think that Matt would be interested.   Tear it apart and see what is going on.


Matt or his staff has been aware of issues I’ve had since I bought this. I was an unfortunate customer who probably received the only lemon. They have repacked parts a few times and only a small margin of the issues I’ve had. I have gotten through most and many I’ve made my own parts for it to get it back up and running fast since I cannot wait weeks or even months for replacement parts since I use the mill on a daily basis. It had issues from the first day I set it up and still has some like the spindle randomly dropping into the parts I’m machining destroying end mills and the part I’m machining. Looks lead nuts, broken gears in the housing. Motor burnt out the first year so I upgraded rather than warranty it was faster. The list goes on and it’s been a love and hate relationship with this mill. I would’ve purchased two more but the service I received was a bit put off by one of his staffers so I went and purchased my from grizzly a G0771which amazingly has been an almighty beast of mills with near zero issues. Only thing is it’s smaller and cannot products some of the parts I need the extended travel of the 833 which I modified to 24” x 13.5”. Whether he cares or not I don’t know but I’ve lived with it the casting is amazing. And when I have it dialed in it works well.


----------



## Uguessedit (May 16, 2019)

Well I agree with your comment at the same time it’s always a big deal for me when I machine is down since starting a hobbyist it lead into making a living out of my garage pursuing my hobby. I’ve had gear box issue in the past and likely in the future as they are wearing down so a belt drive is in order. I have the materials I need ordered when they get here I will pursue it and fill the head with granite epoxy in hopes to remove some chatter. It’s a love hate with this mill. If they ever start stocking parts readily available I’d consider buying more of their products despite my issues.



davidpbest said:


> I agree with Bob and Will.   Take it apart (you're going to have to at some point anyway) and diagnose the problem.   Could be as simple as a tapered pin coming loose.   As someone who owned the real Rong Fu 45 for 18 years, then "upgraded" to a knee mill, I can honestly say I'd take a functioning gear head mill any day over a belt driven head.   Call Matt and discuss.   It's under warranty and Matt is responsive.   If there's an issue with the robustness of the gear train, I'm quite certain Matt would want to know.


----------



## Uguessedit (May 16, 2019)

7milesup said:


> As an owner of an 833T, I would like to know what went wrong.  As David pointed out, I would think that Matt would be interested.   Tear it apart and see what is going on.


 Here is one of the issues I’ve had since purchasing. 




I fixed it quit a bit it used to veer off 1/8 inch easily. I cannot do any precision machining with the factory machine unlike my grizzly G0761 which has been amazing. I know they call the PM833t a precision machine but if it is always marking 3/8 paths 7/16 that’s not good enough for me. It works for basic non precision parts I. An manipulate and live with. It’s had many issues including the Down feed housing falling off while I was machining. I cannot tell you how many loose, stripped out bolts came with this mill it has been a lot of work on my end overhauling it. I let it sit for nearly 6 months because the issues were so bad at one time and other obligations  prevented me from finding the time to repair it when the factory rep I talked to wasn’t returning my calls or dealing with it after a couple weeks it arrived I asked for a new mill without all the problems and was ignored. I’m sure they pay attention to forums but for myself who had little interest in making it a publicized event lived with the loss the pst couple years. It took approximately a year before they finally began to help and with all the issues they wanted to deal over email versus the telephone then so it was slow and tedious I eventually gave up and waiting for 8 weeks to get any parts was ridiculous. I had a 10” lathe from Grizzly awhile back that was a lemon with vfd issues they finally took the lathe back and gave me credit for a new machine. I had already purchased a Bolton lathe so that’s where I purchased the G0761 which has been near flawless since arrival. Only issue Grizzly had was the powerfeed recently went haywire 5 days before end of warranty running full speed randomly. Probably the same as the PM833t powerfeed that failed me right away. Grizzly had me ship back and a new one is headed here in a couple days. Can’t complain their service is exceptional. So those are some of the issues you asked about. I’m not going to go on and on about them like I said it’s a love hate relationship and I deal with it.


----------



## Uguessedit (May 16, 2019)

Here are more examples of a part I just ran. It’s dimensional off from the drawings because the table walks. It could be improperly scraped or defect gibs I don’t know exactly the lead nuts have been changed under warranty and I did just tighten and loctite them again last night through my overhaul because the lead nut was once again loose. That may just be a design flaw I’m not entirely certain of either. This is just elaborating on one of the issues I described above. I would suspect nobody else has these issues or I’d be hearing about them online. I think if you’re delivered a sound machine then that’s what you probably got. Mine was probably assembled on a Friday when everyone wanted to go home.


----------



## Uguessedit (May 17, 2019)

Here are photos of the lower bearing that went out you can see it’s quite burnt and the quill full of aluminum flakes from milling. I had consciously been blowing air through the holes in attempt to keep it clean but I think it’s just a bad design to have access holes in the housing. Those holes are to access the lower bearing so you can knock the lower bearing race out. Thing is that other quills I have here they cast grooves into the lower end casting overlapping the race so that you can reach down from the top and tap the race out with a 3/8 rod and it works even better than this particular design. I’m going to cut some Delrin plugs and see if I can insert them flush and still maintain the quill going up and down. The lower bearing pretty much fell apart and all I had to do was tap the races out. Upper popped out during disassembly. A couple months back when I was servicing the mill and changing fluid my manual stated to fill 3qts in the gear box and it really only needs 2. I thought at the time it may have washed out the lower bearing. I suspect that was the demise. It’s a good thing I keep a shelf of spare parts given 4 mills here all use the same bearings and share some interchangeable parts. These new bearings are doing good. The temp does get up to 175F inside the spindle so as long as I don’t see anything too much hotter I won’t worry of it. So far I’m happy and makes you wonder what a set of Abec 7’s would do performance wise if notable differences. Is it possible to get better than .0002 runout is the real question accommodating for spindle errors. I have stick of 2-1/2 4140 I have been considering machining a bt30 spindle for it. Took measurements while it was out so I may decide to tackle that while I’m at it. Probably wouldn’t need to spline the spindle given I’d get rid of the fine feed.


----------



## RIMSPOKE (May 25, 2019)

DO THE NEW BEARINGS MAKE IT ANY QUIETER ? 
I HAVE BEEN THINKING ABOUT THIS UPGRADE . 

I NEVER RUN MY PM-833T AT THE HIGHEST SPEED BECAUSE OF THE NOISE 
AND QUICK HEAT BUILDUP IN THE SPINDLE . 

MY 833 IS A YEAR OLDER THAN YOURS BUT NOWHERE NEAR AS HIGH MILEAGE . 
THE NOISE HAS BOTHERED ME FROM DAY 1 .


----------



## COMachinist (Apr 3, 2021)

Uguessedit said:


> Here are photos of the lower bearing that went out you can see it’s quite burnt and the quill full of aluminum flakes from milling. I had consciously been blowing air through the holes in attempt to keep it clean but I think it’s just a bad design to have access holes in the housing. Those holes are to access the lower bearing so you can knock the lower bearing race out. Thing is that other quills I have here they cast grooves into the lower end casting overlapping the race so that you can reach down from the top and tap the race out with a 3/8 rod and it works even better than this particular design. I’m going to cut some Delrin plugs and see if I can insert them flush and still maintain the quill going up and down. The lower bearing pretty much fell apart and all I had to do was tap the races out. Upper popped out during disassembly. A couple months back when I was servicing the mill and changing fluid my manual stated to fill 3qts in the gear box and it really only needs 2. I thought at the time it may have washed out the lower bearing. I suspect that was the demise. It’s a good thing I keep a shelf of spare parts given 4 mills here all use the same bearings and share some interchangeable parts. These new bearings are doing good. The temp does get up to 175F inside the spindle so as long as I don’t see anything too much hotter I won’t worry of it. So far I’m happy and makes you wonder what a set of Abec 7’s would do performance wise if notable differences. Is it possible to get better than .0002 runout is the real question accommodating for spindle errors. I have stick of 2-1/2 4140 I have been considering machining a bt30 spindle for it. Took measurements while it was out so I may decide to tackle that while I’m at it. Probably wouldn’t need to spline the spindle given I’d get rid of the fine feed.


Wow sorry to here you are having so much trouble. This being a Taiwan  mill supersizes me. They usually are really good machines for Hobby shop use. Since you say you use it every day and your going to CNC it wouldn’t a Tormach be a better choice for light production work. I know CNCNY has used one in his production jobs for years. If you need something heavier go with a used Haas, their small mills are on ebay used all the time.  You are not going to like those AC bearings they don’t last at all. I have done my G0704 CNC conversion AC bearings twice in the last 4 years. Mine only get maybe 5 hr a month of use, if that. If you have need every day for a CNC job you have enough work to use a industrial level machine. Tormach 770 or a small Haass machine. By the way check out Clough42 on youtube. He put an ATC30 spindle on his Grizzly0704 conversion and it will do as much as a Tormach mill will. I would also consider ball slides on the Z,X,Y axis and have Mark build your electronics cab. 
Just my 2 cents worth.
CH


----------



## 7milesup (Apr 3, 2021)

The last reply was almost 2 years ago.  I think, but not 100% sure, that this is the guy running the mill at 5000rpm or something like that.

But you are right, a HAAS would probably be a better fit for him if he is doing production work.

EDIT:  Post #11 shows his VFD control at what looks like 75hz, or maybe it is 7500rpm.  Hard to tell but it is not stock, that is for sure.


----------



## nighthawkFmobil (Apr 5, 2021)

This is Glen Edwards! Glen please update us here at hobby-machinist as well as youtube. I'm curious how things are going. I'm sure theres people interested in your 2 pulley kit. How's the 3hp motor holing up?


----------



## kb58 (Apr 5, 2021)

He's got more patience than me. Running a business, I'd have replaced it long ago and moved on, instead of expecting a hobby machine to hold up under constant use.


----------



## COMachinist (Apr 6, 2021)

Boy that was stupid of me but showed up as an unread post for some strange reason. I read this forum every day, but only the new posts. Not sure what happened but this one would have been way down the list?
CH


----------



## 7milesup (Apr 6, 2021)

Don't feel bad COMachinist.  The email notification with this website has some errors.   There will be times that I don't get any emails only to find out there has been 20 replies since I was on.


----------



## nighthawkFmobil (Apr 6, 2021)

I'm glad you bumped it CO. I was wondering if glen was ever on hobby-machinist


----------



## qualitymachinetools (Apr 8, 2021)

There is a whole lot more to this than was written a couple years back. Someone named "Glenn Edward" isn't even a customer of ours. The person who made these videos doesn't use his real name for some reason, but its the internet, oh well. 

             The 3600 RPM Replacement motor at 75HZ is 4500RPM on the motor, when the original is 1800RPM. And thats just what is in the one video, I am sure it was pushed much faster than that.  He did a lot of nice upgrades and pushed the heck out of the machine, but its not like it had a problem at anywhere near factory speeds.     There is so much more to this one.       Waiting on parts, well someone emailed and said they needed parts, email address was different than the original order (Which I know now, but had no idea who it was at the time) and came through with a different name than he ordered the machine under.        Tried to get in touch a few times, over 2 months later he finally replied back.       That was the delay, it wasn't months to get parts once we had the actual order.             Oh well its the internet, old news and no problem with the customer, but since this came up and people will see it, I just had to clear it up.  Nowhere near what it seems.


----------



## nighthawkFmobil (Apr 8, 2021)

That's understandable, I actually just did that to the company I bought a 3d printer through. They owed me an extruder because the one they sent me wasnt printing properly out of the box but it was still manageable so I kind of ignored my responsiblity of sending them my purchase info and address.  Two months later I sent them the info and got my extruder and ptfe tubes within a few days from china via DHL i believe. 

Not proud of the situation but it definitely happens hahah.


----------

