Purchased an 08 Tripower from John last year. I had read about most of the issues before purchasing so I went in with eye almost completely open
I purchased everything that was on sale in the flyer. Machine,DRO, and Stepper kit. I am a complete machining novice so I am useing this machine as a learning tool. I see now that I Will eventually get a more serious dedicated mill. For now this is fine.
After much fiddling and moderate learning curve I figured out to program the parts I wanted. The machines issues revealed themselves to me as I went. Most are fixable so I have been tuning and fixing it for the last 6 months. My lastest adventure was Adding ball screws to all three axis. The reason I did this was that the backlash would change during machining due to varying friction on brass acme nuts. The (single) ball Nuts still have backlash, but it seems to remain constant so Mach 3 can compensate for that that fairly well.
After bring things up to a bare minimum to consistently do what I wanted to do I went ahead and purchased basic Rhino Cam from Mec soft (visual mill) for my Rhino program. Rhino Cam comes with a Mach 3 post and so far it works perfectly. Before I was hand typing code and using wizards. Again a good learning experience.
Backlash was coming from many places. I have narrowed it down during upgrades and reassembly. Before, the thrust washers all had play. The drive cogs for the CNC were had slight play on the acme screws. Acme nuts were horribly sloppy. Belts were very loose with no way to tighten them up. Bearings had (bumpy) spots. Gear teeth were binding in Z feed. Power feed in Z was chewing itself up into steel grit. Motor drive belts were turning to dust and made a burning smell because none of the pulley were aligned. Head jiggles more on the Y than X. lathe gear box leaks. Missing screws in the motor wiring boxes so the plates were semi open. The BOLT on DRO kit was joke the machine's holes were so far off that the install was basically from scratch with all new holes. The Z did eventually go in with out modification. Some bushing on this machine were a joke, as little as 2 percent contact in my estimation. The manual Z crank being the worst. The Y feed Drive motor end being next worse and the Main bushing for the Z feed being pretty damn sloppy.
So far I have remounted the existing motors so they line up with the next pully.
I broke down the Z feed head and deburred all the gear teeth. I made a new bushing for the Hand crank and shimmed the crank gear. I also ground the interior surface of the casting so the hand crank thrust bearing would sit true. It was lumpy rough casting on the inside.
I installed new thrust bearings ( old ones had inconsistent sized needles) and shims,for the Z feed and also ground the interior of the casting same as the Crank hole. I bored the acme threads from the Z feed core and welded a flange to the nut (after lathing a nice seat for it) Then I screwed in a single ball nut which still fits in the housing with no modification to the housing. I copied the four bolt adjustment design in the new flange so I could tune the alignment of the Z nut. While a pain in the but it worked out well. I reassembled leaving the power feed gears out.
Purchased 6 feet of 3/4 ball screw from Mcmaster and Machined the ends myself for X,y, and Z (1 foot 5/8ths) ball screws and installed.
Next came the Z feed arm plate which sits at an angle were it should be square. This puts deflection in the ball screw so I leveled the seat where the ball screw interfaces. Cleaned up the casting so I does not look so damn sloppy, but for the most part left it alone.
Mounted gecko in the Tripower case. It came already mounted in a separate box which was not as advertised. CNC kits are supposed to be bolt in to the housing provided on the machine, but I am now told that is only for servo kits not stepper kits... whatever...
Changed all the stepper mounts so they can be adjusted for belt tightness. Just slotted the holes and cut relief where required. Some of the belts were quite loose with the factory holes.
I have done my best to stop the leaking lathe gear box, but I fear it is coming from one of those casting defects rather than a plug or gasket. Its not ideal, but It requires an ounce every few hours. When I finish my bushings I will open up the access plate and look for defects. Some automotive sealant should fix it if I can find it.
One of the next things on the list will be the 5th tower Mod.
I appreciate the forum and I have gained much insight from here.
Hi, Small Block,
I used 5/8ths ball screw on the Z
Being a novice at lathe work I had some dum luck... I used cheap carbide and the fastest rpm the machine would turn. first thing that happened was a chip came off the carbide. Then it cut fantastic. I was able to take the hardened layer off with a few heavy passes. The chip curl was coming off at orange heat. Deflection was minimal and managed a fairly consistent pass with almost zero taper. I practiced on the extra material first. I was just winging it, but it work well. The chip gave me just the kind of geometry I needed, but like I said dumb luck. Once I had the shaft sizes set I was under the hard layer and was able to run hand dies to thread the ends.
On the nuts I turned the end thread down until it was the same diameter as the acme nut then slid it into the block and clamped it same as the acme nuts. That just leaves a trace of thread left over. Never even had to take the block out. That worked really well for me since inside threads would be a bit daunting for me at this point.
I did not realize the X was a left hand thread. I installed a right hand thread and later played with the setting in mach until the orientation of my projects match the Mach display. Had not realized implications to the power feeds, but now that its done I am not too worried about it. The work I want to do is mainly CNC guided.
I appreciate the kudos on the screws, but I just went with what seemed like the least risk. Shoptask wanted me to send them my z box. And my acme screws to cut up. They said they can't get the screw ends right now so they would have to use mine. Well if they messed that up I would be out of luck and $750. I can cut and weld those myself. Then I considered making unions then I jumped in and went for it. I still have my acme intact save for the Z which cut the end off of already. XY could be reinstalled no problem.
I started with the Z feed. $10 a foot for 5/8ths from Mcmaster. not a lot of risk. Once I had that going well I ordered a full bar of 3/4. They must have been out of the black coated stuff that I ordered, because they sent me the hardened stainless steel version which is much more than the $24 a foot that I paid.
The 5/8 nut is very tight with nearly zero backlash. The 3/4 versions are very sloppy. Next time I will double up.
I should have taken photos of everything as I went. That is my usual practice. I was under a time crunch so just concentrated on the work.
Its not perfect, but I know a lot more for next time.
Did you have another lathe to use, or did you disassemble, measure everything, reassemble, cut the screws and then do the conversions?
I've been wanting to put ball screws in my Bridgemill, but don't want to have to pull it apart multiple times.
If you actually look at the machine the Y axis should be a left hand thread also. But with CNC it really doesn't matter. This is just for the application. As it might not work for a machine with twin lead screws. If someone wants measurements for the tripower message me and I will measure the screws .I have had problems with machining the ends since you need to cut the key ways if you want to use the manual feed also.
You made me look twice...The two Helix gears reverse the rotation of the Y screw. I am holding the factory Y in my hand. It is right hand thread (at least on mine).
I still could have done the key way on the tripower, but do to bad planning I had no screws in the machine and no key way yet. I have a little Taig I used to complete the keyway.
Your right . I depends weather the drive gear is on top or bottom. Is the stock lead screw acme thread or UN thread. I know its 3/4 - 10 but the type of thread I don't know. The mill gear box shaft is 5/8 - 16 UN thread.
I can tell left from right, Thats as far as I have come on threads...