On Friday 15 May 2015 05:28:35 andy pugh wrote: > On 15 May 2015 at 03:03, Gene Heskett <ghesk...@wdtv.com> wrote: > > I had a session day before yesterday of the back gear countershaft > > squawling pretty bad, so I called Chris at LMS and bought the whole > > headstock for a $132 bill with USPS shipping, and which arrived > > today. > > https://littlemachineshop.com/products/product_view.php?ProductID=2299 >&category=1023914534 ? > > I hadn't realised that the 7x lathes had a back-gear. My 9x (which > seems to be a stretched 7x) had an all-belt arrangement (using the > tiniest of V-belts) > http://www.micro-machine-shop.com/9x20_lathe_belts_1.jpg > You can drive it direct from the motor pulley for high-speeds and from > the low-speed pulley for low speeds by moving the belt around. > The belts don't look big enough for serious work, because they aren't. > I replaced the whole thing with a 1kW motor and dual A-section > V-belts. But if I had had a back gear I think that I would have wanted > to retain it. > > What I don't understand is how it is possible to destroy the pulley. I > can understand stripping the teeth off the belt, but how does the > pulley get damaged?
When the belt starts slipping cogs, the drivers PID cranks up the power, and the pulley, being plastic, the teeth melt from the friction and smear the grooves shut. I believe my jackshaft frame is flexible enough to allow the end of the shaft to rise a few thousandths when there is that much power being transmitted. I have a box with a spare belt and pulley in it someplace in that midden heap out in the shop as I ordered 2 of each the last time I burned them up. But this time I will build some sort of an adjustable jacking screw that I can cause to bear against the bottom of the bed, and stop the flexure. This fix will be independent of replacing the squawling head, but that puppy gets a set of metal gears, and a sealed bottom so I can fill it up far enough that the gears are running knee deep in gear oil. OTOH, I could be tempted to throw more $ at it, and get a South Bend 8k from Grizzly, on sale for a hair under 2g's, but by the time it would be up and running by LCNC, I'd have around 5g's in it. Just the stand is another $930, and the same size chuck I have now is another $250. Carriage drive screw is 38"/965mm long, so the cheap 16mm I have now would grow to a 25mm and to around $300. No clue how much room for the crossfeed screw could be found. So I wind up finding the next weak point in this POS and seeing if I can fix it. This one is sitting on top of a heavy tool box with 6" castors, so its a just a "me" operation to move it around for access to all this BS when I need to. Replacing the belt and pulley, because of all the other stuff I have to clear away for decent access, will be about a 2 day or more job, more if I need to remove the motor and jackshaft in order to make & fit the braceing it needs. Accessing it for later takeup adjustment will I suspect, be equ to the same teardown this will entail. Replacing the head will be all that plus rigging lifting straps to lift it clear of the tool box its on and roll the tool box out of the way. Because of working space vs toys, the "out of the way" will be clear out on the front deck whose planking I am in the process of replacing, waiting on Orkin to come and do away with a batch of carpenter ants. Thats scheduled for Monday next. > I don't think that Poly-V will give you any better results than the > timing belt. But why not swap to a wider timing belt and a profile > that it readily available? > For example, this one: <http://www.bearingboys.co.uk/28-5M-25_Metric_Pilot_Bore_Timing_Pulley- 21256-p> is for a 25mm wide belt and is under 2" dia, The cover restricts the belt & pulley width to 10mm. Its also what my encoder is mounted to at its top edge. Since that will have to be removed to install a fresh belt, milling additional clearance for a 12.7mm wide belt will be investigated but its not that thick IIRC. No flanges on that pulley, so all the guidance is in the placement of the driving pulley on the jackshaft, and its degree of (miss-)alignment to make it run centered on that 10mm wide pulley. However, just sawing the bottom half off will be investigated in the next couple days. I don't think there is anything left that is dependent on that cover below the centerline of the spindle. Hummmm. Time to go make a pot and regroup anyway. It takes at least 2 cups to get my old thinker working right. And that may be just the ticket once I look it over. The problem I see with that is the length of countershaft available to put the pulley on, is not more than 12mm. I'd have to turn its hub down to 10mm thick to be able to get at the tru-arc that holds it. That sort of work I can do on the mill though. All this BS is why I'd consider moving the motor & jackshaft to the left far enough to put about a 2" polygroove pulley on the jackshaft, and a 4" to 5" polygroove on the spindle where the change gears drive gear is sitting & doing nothing now. But then I would have to find another lathe to make the pulleys on while this one is down. The only one I know of locally is a 110 yo Porter, about a 14x72, sitting out in the weather and sans most of the stuff to put a 15 hp motor back on it. Guy want $500 for it, which is about what the well worn chuck weighs. The saddle would be down at least 20 thou by the time the rust was worn off again. I'd have 15+G's in it by the time LCNC was running it. So I quickly, understandably, lost interest. I want to use it, not spend the rest of my allowed time building it. OTOH. what the hell am I doing now? :) Good question, that... Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. 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