My Z axis quit working on my Bridgeport Boss 5. The motor has holding torque and when I hit the jog button it steps back and forth about one step, it turns freely with the machine off. Any suggestions?

Yes, a few. First, put it in setup, jog, and step. If it does not advance one thou each time you press the - key, it is very possible that you have a blown transistor. They usually short, so the rotor of the motor cannot get away from that field.
This is extremely common but can be minimized. How long have you had the machine? How familiar are you with where the components are? Do you have any spare 2N6547 transistors? Can you use a meter to find a shorted transistor using the diode check (voltage drop across a semi-conductor junction) feature on the meter?

George

They can be found on Ebay.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=41941&item=3853160222&tc=photo

Thanks guys, I'm home for lunch so I called the local electronics supplier. They are expecting their shipment today and are holding 4 of them for me. Should I try to get those diodes as well? The ebay ad just says 1000V fast recovery, do I need any more info than that to buy them? I've had this machine about 5 monthes. I bought it as a hobby and to make a few bucks selling little things. I've been teaching myself G-code as well as how to setup the machine and have made some nice parts with it so far. I have little doubt I blew whatever is blown since I wrote bad code several times and had a G00 rather than G01 for a Z movement which crashed the tool into the stock. Overall the machine is in good shape for something that was in a production environment. I'll check back later when I have the parts.

I want extend a huge thank you to George (machinetek) who spent over an hour on the phone with me talking about oru favorite brand of cars while he helped me troubleshoot the machine. Turns out one of the transistors is shorted and I'll have a new one tommorrow so if all goes well I'll be up and running again. Seems George and I have a mutual friend who put us in touch. I wish I knew more about CNC and hopefully as I learn I can start to answer questions rather than just ask them. It's communities like this that really make life grand. I'll let you guys know when I have it running.

-Christian

It's fixed! What a relief, I went ahead a replaced all four transistors with 2N6547's per George's suggestion. Now I'm back on schedule and can cut parts tommorrow. Yeah! :D

Well,

Ever since you fellas helped the last time this machine has been running great but today the spindle jammed about 1/4" below the home position. The stepper can't move it up or down and the spindle motor won't turn it. I can't turn it by hand either. Spindle brake engages and disengages just fine. Any ideas?

Oh Boy! Does the Hi/Low shift lever move on the right side of the head? If so does anything else move, like the quill?
With the brake off, you are telling me that you cannot turn the spindle.
The quill will not move if you try and turn the Z motor pulley with the drives off.

I have seen under a very heavy intermittant cut, the spindle splines get a twist and get jammed in the splined gear hub. Then the side lever moves up and down with the quill. But it can still turn.
I have seen the chrome peel off the quill and the quill jam inside the housing. Very bad situation but the spindle will still turn.
Take a break, walk away, and come back with a clear analytical mind and tell us what you find.

George

Well I pulled the belt cover off the Z-axis thinking the belt had popped off but it's still on there. The shift lever does move because I tried to put it in low and turn the spindle on, still wouldn't turn. I opened the front cover and nothing appears bent or damaged. I took the wiper off the bottom to see if a chip got jammed, nothing. It's weird. I felt like giving it a rap with a deadblow but I'm scared of that idea. There's a collet holder in the spindle so I tried to turn the nut on it with a wrench but no go there either although I didn't use much force for fear of doing more damage.

George, got your email earlier, I've sent some jokes my father sent me. Thanks for the help. I'm going to do a bit more inspecting.

-Christian

Is there any possibility that the pulley on the Z-axis motor is binding up against the motor or the housing? If it had been binding previously, that could have caused your earlier transistor failure. In 25 years of running my BOSS 5, I've never had the Z-axis bind up that way. If the spindle itself isn't turning, you may have a seized bearing in the quill, but that wouldn't account for the quill not going up and down. You may have a problem in the top end, perhaps a total disintegration of the speed-changer mechanism. That could put a torque on the quill that could cause it to bind up past the point where you could move it with hand tools. Sounds like you have a serious mess. I'm sorry

These two issues should be seperate.
You did not mention if you could turn the z motor pulley.
You did not say if the spindle brake was released.
Could be electrical issue with a dead control meaning a missing phase.
Pictures were great! thanks.

George

OK,

I was able to turn the quill motor and one I get it about 1/2-3/4" down it will move up and down fine. The brake is released and I've removed the air from the machine. Well I should say I think the brake is released, the lever that actuated it moves up and down and it's in the off position with no air to the machine.

Seems to me like the spindle drive shaft is bent, twisted or both but I can't be sure yet. The spindle motor does run but only if I pull the hi/lo lever in the middle where the gears are disengaged and hold it there so I don't grind the gears. If I do that the motor spins but I still can't turn the spindle.

Is it even remotely possible to by replacement parts for this machine? Will I have to sell my first born? LOL.

I've got all the manuals at home so I'm going to take a look there for an exploded diagram so I can see how it's put together. This is kinda depressing, I've been having a lot of fun with it lately now that I've gotten good with canned cycles, loops and macros. Still lots to learn but it's neat watching the machine run.

Oh and Fred, no binding of the pulleys, that's the first thing I checked, well after checking the belt anyway. I'm going to take a closer look to see what I have to do to get a look at the brake so I can be sure it's disengaged.

BTW the largest endmill I've ever used was a 1/2" I don't load the machine all that much but I do frequently run near the top of the RPMS cutting aluminum with a small endmill.

Is it possible the topend lube is messed up and the gear case ran dry? I notice way oil on the floor when I run the machine a lot and the ways are in great shape. The quill always appears to be well lubed as well.

OK the brake does in fact work. If I hold the gear selector between gears and turn the spindle motor on it spins then turning it off the brake grabs and stops the motor. With the brake in the off position the motor spins down when turned off. I cannot budge the spindle in any position but it does go up and down much better now. It didn't look dry but I squirted some way lube on the spindle ballscrew and the outside of the spindle anyway and it seems to have helped that problem. I'm beginning to wonder about the top end oiling though. Is the gear case fed by the auto oiler or does it have it's own lube?

Well I got it working. I have a huge endmill holder I'll never use so against my better judgement I installed it and put a big pipe wrench on it. That still wouldn't turn the spindle so I put a pipe on the pipe wrench and that got it to turn a little. Just for the heck of it I tried starting in backgear and it turned fine. Tried high and that worked was well. I did put quite a bit of way oil inside the quill housing so that might have helped. Wierd, no funny noises and the quill ran cool for half an hour.

I'm gonna pull those lube lines up in the head and see if oil comes through, if not I'll figure out a solution like maybe a top reservoir that gravity feeds everything. Or maybe I'll replace the lines who knows. I figure it's safe to say I need at least one spindle bearing. No big deal there I was going to replace them when I teardown for new controls anyhow.

Spindle jammed again. I notice the lower bearing collar has turned from where it was so I figure the bearing is bad. Anyone have a part number for a Boss 5 lower spindle bearing?

The fact that if you moved the lever to neutral and the spindle ran means that everything in the belt housing is good. It means that your problem is in the lower unit. It may have overheated and expanded binding the quill for a while untill it cooled.
You are observant to notice that the nose piece turned. This may mean that you caught a chip between the spindle and nose piece and it may have welded the two. I saw this a lot on the first generation 3 axis EZTRAKs. Never on a BOSS CNC, but there is a first time for everything.
Lower the quill about an inch, remove the set screw from the back of the quill, unscrew the nose and tap out the spindle from above. It will come out as a cartridge (assembly). Examine carefully to see what the problem may be. It it indeed needs bearings, my suggestion is to send the assembly to C & M Precision Spindles in Tualatin, Oregon. For a few dollars more that the cost of a set of bearings, they will rebuild the spindle and regrind the taper so you will have as close to zero run out as possible.

George

George,

The nose piece I'm refering to is the one just below the chrome portion of the quill, it has two holes for a spanner, I assume this is the bearing retainer? Below that is a collar about 1" high and black in color, this turns with the spindle. Inside that collar are the dog teeth for the 30 taper tooling. I'm looking at the maintence manual but I'm not clear on how it comes apart. The 1" collar has two set screws on it's OD. I assume this needs to be removed to get the rest out.

Thank you for the suggestion of C&M spindles, I will look into that. Any idea "ballpark" what I might expect to spend for new bearings and service?

According to the manual the bearings are lifetime lubricated with the auto lube to the head lubing the quill. Here is what I think is happening:

One or more bearings has enough runout to cause the spindle to jam at a slight angle, when this happens the quill becomes stuck on the splined upper portion and requires some effort to get moving again. One I free the quill I can start to turn the spindle with a pipe wrench (ugh I hate that). I get the spindle a little free and it will start and run in back gear, after a few moments I can switch to hi gear and everything works fine. Tonight I ran the machine about an hour at 2000rpms before it locked the spindle and sheared off a 1/4 endmill in the part.

While we are on the subject, I'm making a series of slightly different parts on a jig. Program size according to windows is 9K, how much memory does a Boss 5 actually have?

If I read what you're saying correctly a chip got lodged between the spindle and the bearing retaining collar causing it to weld and jam spinning the collar about 60 degrees in the process until the spindle just locks up. Is that a correct interpretation to what you are saying?

With my wife out of work this machine has become more than a hobby, I make parts to sell to car enthusiasts and I've got orders in the pipeline. Do you suppose I could take the spindle out, check and clean everything and put it back together for a few weeks until I get caught up? My typical work week for the machine is a few hours a night and about 8-10 on the weekend. Programs typically run 20-40 minutes with about 10 minutes between cycles. I could make these parts on my manual mill but they'd take hours compared to minutes with all the angles and circular pockets involved.

I think I might have found the problem but I won't know until I run the spindle for awhile. On the spindle nose is a black collar that screws on and is held by set screws. This collar somehow threaded it's way up til it touched the quill nose and rubbed against the bottom of the quill galling both parts. I loosened it and moved it down a bit and the spindle is running fine at max rpm right now. I'll post later after I let it run for an hour or so. Much thanks for the help so far.

-Christian

Ah HA! You must have a power draw bar! That is called a "skirt" by the maker. It is to protect you from the keys grabing you as easily. Yes, if the set screws are not tight, this will move when the spindle is turned on due to its mass (in spite of the fact that it is aluminum). It can and has spun up to the quill nose and locked up the spindle. You do not need this piece but I do not suggest you remove it for your safety.
I believe that there was a later design with a step in it so it will go up only so far and not bind the spindle.
Good observation!
I am glad you are keeping your head above water.

George

Thanks George,

I'm still a newbie at threading on the lathe but my plan is to make one with a step like the later design you talk about. Any good reason why it has to be threaded? I mean I could grind a few flats in the threads for the set screws to engage better and then just have a slip on ring.

Spindle ran perfectly for just over and hour. I'm running a few parts on it now so I can check it under load. I really hope I've got it solved.

One question that's been nagging me. I remember you mentioned when we spoke on the phone about slowing down the rapids to take some load of off the servos. I run a lot of aluminum jobs, is there any way to speed up the feedrate? On a few parts I set the machine to 32ipm then turn the feed adjustment to 125% for a nicer finish and faster production. Also is the top speed 4200 or 3000 rpms? The speed plate "redlines" at 3000 but the manual talks about calibrating at 4200, I've never run the spindle that fast, assuming my spindle is fine is it OK to run that speed?

Alternative 1: cut s snap ring groove in spindle to limit up travel of the skirt.
Alternative 2: "spot drill" holes in the spindle body for the set screws.

Just like Bridgeport changed the rating of this motor to 3 HP intermittant, 2 continuous, you can run the spindle up to 4200 but there is more stress on all the components and monitor spindle temperature. I would consider that speed intermittant use.

I will scan the RCK set up and post it here. This uses stepping motors with an open position loop. Push it too hard or too fast and it will stall and there will be error message as you would get with a servo set up and a position loop (encoders).
Trial and error will be necessary.

George

Ugh, the Z-axis is broke again. The first thing I thought of was a blown transistor so I checked them for continuity and sure enough one of them was shorted out. I replaced it with the only spare I have and checked the axis, it moved just fine. Then I buttoned everything up and the Z won't move. I opened the quill panel and everything looked fine. I can turn the motor shaft with the machine off and the quill goes up and down with little effort. I then check all the fuses in the side panel and they are fine. I took the belt of the Z stepper and it just doesn't turn, acts like a bad transistor! It whines when I hit the jog button and that's it, seems to wobble within one step.

I can't find my notes from the last time it broke down, I do remember checking the transistors for voltage but can't remember how. Oh I also swapped the X driver board for the Z driver board and still no luck. Could something have been damaged when the spindle jammed? Any ideas what to check next and how?

The machine ran fine all day yesterday, this evening I came in to finish up some parts and it flat out doesn't work. As usual any help is greatly appreciated.

OK, I went and got my box of extra parts for this mill. I swapped out the ACC board, tried 4 driver boards, another bank of transitors and still no luck. I even flipped the ACC board over. I'm gonna try another ERS, RCK and XDI board next. At this point with the belt off if I keep jogging the Z-1" the shaft will turn about one tooth every now and then. I also have an SMS board that I'll try as well. Right now I'm stumped unless it's a bad stepper, I sure hope not. I picked up the maintence manual as well. I've got the machine in a corner at work that they were kind enough to let me use since they have 3 phase power and more room to work than I have at home. I was hoping I'd be at home by now watching TV, not gonna happen tonight.

It is time to take a step back. You have 3 identical axis. Compare them. The measurements on the X and y should be identical and you should find something that does not match with the Z.
First I would measure the DC voltage with respect to ground at the DC drive fuses. I will ask again if these are screw in or plug in. You may have a bad bridge rectifier.

George

Thanks George,

The machine does have push in fuses. Somewhere along the way here I lost a transistor on the Y axis as well so I can't compare that one right now. Earlier I was getting 3.9-4.5 volts on both the X and Y (they were very close, I think 4.3 and 4.4), the Z was giving me millivolts and floating all over. Now I measure 3.95 volts at the X, 1.65 at the Y, and still millivolts at the Z. Prior to losing the Y axis I adjusted the amperage on X and Y down from 8.6 to 8.2 on the ACC board.

The transistors that went bad are shorted to ground internally. Judging by what you've told me as well as reading the manual I concur that it points toward the rectifier. Problem is since the fuses have been updated there are no longer terminals 31,32,33. I assume these are X,Y,Z. The manual mentions checking the rectifier between 31 and 39, 32 and 39, 33 and 39 as well as a terminal on the tranformer output. Can you explain that procedure a bit, I'm not certain I understand it correctly. Do you know the part number for the bridges, perhaps tommorrow I can find out if they are available localy. I did replace the SMS board, didn't make a difference. I didn't bother with the other boards. Tommorrow I'll put new transistors in for the Y-axis but I'm concerned as to why they blew out.

George,

Here is where I am at. I check all the transistors and found 3 that where definately bad. I've replaced those and all three axis are working. Most of the good transistors were a little over or a little under 0.5v some as low as .480 but they are working. I also checked the regulators following your method and I got in the 0.451-0.464 range on all tests, nothing tested at the 0.5v you suggest. I started up the machine and ran a check of the X,Y,Z voltage. My earlier numbers where to what I thought was a ground but was not. I got 12.25 for X, 14.20 for Y, and 10.00 for Z. Next I will shutdown and test the amperage at each fuse. To be on the safe side I'm going to shut down and pull the fuses one at a time firing up with the DMM across the fuseholder. I'll adjust to 8 amps on the ACC board. What should I do about the range of voltages at the axis?

You do not have the meter on OHMs but on diode test. It is measuring the voltage drop across the semi-conductor junction. All those readings are good as they are close to half a volt. A germanium junction has a different voltage drop. I believe it is closer to .2 volts.

The voltage at standstill is a function of the type of transistors you have put in and the current setting. I do not believe you are using Motorolla 2N6547 but generic replacements. Am I right or wrong?

George

George,

I've got a mix and match of 3 different kinds in there right now. It's the best I could do with the used spares I got with a bunch of boards off ebay. My plan is to buy a good set and set them up on the blocks ready to go into the machine. Given that I work full time and only have limited time for making parts on the CNC it's worth it to me to spend a little to insure less down time, plus this way I can just swap out transistor blocks when I have a problem.

I notice my machine has diodes across the transistors terminals but my spares do not, was this an upgrade and should I include them in my spare blocks?