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

[Uguessedit]

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]

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]

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]

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]

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]

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]

Well I stayed up near all night and rebuilt my mill

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

 

[Uguessedit]

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]

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]

It sounds great now and the finish is outstanding.