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| Myford QC Gearbox Project. |
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| tom osselton:
The snag is, nobody would tell me the value of X!! That's because we can always drink too excess but don't always know Y!! :lol: |
| awemawson:
Slippery slope booze ! Just a little lowers your sense threshold. (Ordered up a generator change over switch and bits today so things can be a bit less scary next time - but when I install it it'll ensure the need never recurs !) |
| Pete W.:
Hi there, all, The latest stage in this project is 'Lead-Screw Modification - Part 1'. I started with a bit of a set back, the spare lead-screw that I thought was the right length for the gear-box turned out to be standard length. So, whichever lead-screw I use, I'd have to shorten it. :( :( :( I'd like to finish the shortened end in the lathe but the bore through my head-stock is 19/32" and the lead-screw diameter is 5/8". Hmmm. :scratch: :scratch: :scratch: And, of course, the lead-screw is too long to work on with one end on the chuck and the outer end in the fixed steady, the lathe carriage would be in mid-air! :D :D :D The 'spare' lead-screw is of the two-piece type, connected by a collar and a couple of roll-pins. If I use that one, maybe I can detach the short head-stock end section and mount that in chuck & fixed steady and finish the cut end in the lathe. :scratch: :scratch: :scratch: Here are the two lead-screws, the original one above and the 'spare' one below: So, lets's start and see how we get on. First, remove the left-hand (head-stock end) lead-screw bearing bracket. This revealed something that forced the which lead-screw decision - the original lead-screw doesn't have the woodruff key slot required by the gearbox output gear (see below). Here are the head-stock ends of both the lead-screws, the original one above and the 'spare' one below: OK, now we know which lead-screw we're going to use. But to get the measure of the amount to be removed, I need to fit the 'spare' screw in place of the original one. So, up to the tail-stock end to remove the lead-screw hand-wheel, cross-pin (a parallel dowel) and thrust collar. That area of the lathe has been undisturbed since about 1971 and those parts have got used to being together. Still, with a little bit of gentle persuasion, I got them all apart and swapped lead-screws. However, I couldn't refit the cross-pin, it just didn't want to go into the cross-hole in the lead-screw end. (The hole for the cross-pin is in the shadow to the right of the lead-screw bearing bracket.) Eventually, I proceeded without fitting it, I'll give it serious attention when I get to the final assembly stage. So, back to the head-stock end. The Beeston Myford instructions say 'feed the gearbox onto the leadscrew and secure it in position with the three screws', that's two 1/4" BSF by 3/4" cap-heads in the two holes I drilled & tapped last time and a lower screw that goes into one of the holes previously occupied by the lead-screw bearing bracket fixings. Well, the top two are a bit fiddly but manageable. The lower one, described in the instructions as 'captive', escaped into the bowels of the gearbox! :bang: :bang: :bang: It's got a slotted mushroom head so you can't hold it on the end of an Allen key and the gear-box innards conceal it from view! :bang: :bang: :bang: So, again, I pressed on without doing that one up. I fitted the woodruff key, then the gear-wheel, spaced off the end of the gear-box casing by with a 15 thou feeler gauge (the shed gremlins had surrendered the feeler gauge set without too much of a fight :lol: :lol: :lol: ). That got me to this stage: The Beeston Myford instructions say that I've got to shorten back that left-hand shaft so that not more than 31 thou is left protruding from the face of the gear hub. So I've measured the total protrusion. Now I've got to take it all apart again and shorten the lead-screw, i.e. actually cut metal, where's the chewing finger-nails smiley? So, once I've done that, I anticipate three issues: 1. If I drive out one of the roll-pins and just work on the short section of lead-screw, will it all go back together without prejudicing my measurement? 2. How do I get the cross-pin back into the tail-stock end of the lead-screw without damaging anything? 3. Shall I go crazy trying to get that lower gear-box fixing screw into position? Here endeth 'Lead-Screw Modification, Part 1'. :nrocks: :nrocks: :nrocks: |
| Pete W.:
Hi there, all, Here is 'Lead-Screw Modification - Part 2': I drove out one of the roll-pins securing the stub extension shaft to the main part of the lead-screw. However, the stub was a very tight (like un-movable!) fit into the collar. I could probably have got it out but it was obvious that it would be as difficult, if not more so, to replace it in the collar so that the roll-pin holes would line up. So I refitted the roll-pin, quick! It had been my intention to make a guide sleeve to fit over the stub shaft to be secured in position with a couple of grub screws and positioned so that its end face defined the end of the shaft after shortening. I proceeded to make that sleeve, now to be used to aid the shortening of the complete lead-screw plus stub shaft by hand. My workshop stock is still in disarray after the roof leak & flood so the only suitable diameter steel I could find was some Peter Stubs silver steel. According to my measurement yesterday, the length of shaft protruding from the drive gear was 2.094 inches. Beeston Myford's instructions specify that, after shortening, the protrusion should be not more than 0.031 inches. I chose to aim for a protrusion of 16 thou so I positioned the sleeve a distance of 2.078 inches from the end of the stub shaft like so: (That picture was taken after I had started to hacksaw off the excess shaft.) The 'back-up' ring is actually the one that previously secured the final driven change-wheel on the end of the original lead-screw. I didn't want it to be the 'front-line' guide for the hacksaw but it seemed prudent to fit it to minimise the possiblilty of the main guide sleeve moving - I didn't tighten the grub-screws too tight for fear of making dents in the stub shaft. In the event, the hacksaw did cut into the face of the guide sleeve so I backed the sleeve off a few thou before cleaning up the cut end of the shaft with a file. I chamfered the shaft end with the file, it's not as neat as it would have been if I'd been able to do it all in the lathe. I'd noticed that the slotted ends of the head-stock push-screws were a few thou proud of the edge of the lathe bed to I removed each in turn and filed enough from its inner end to make the screws under-flush. Then I refitted the lead-screw to the lathe, fed the gear-box onto it and inserted the gear-box fixing screws into their tapped holes in the bed. It's necessary during this operation to ensure that the O-ring is in position aound the lower screw-hole. Viewing the interior of the box with the aid of a torch revealed that my fears about the lower fixing screw had been unfounded, it was still in-position and I was easily able to screw it up. What the torch did reveal, though, was a quantity of steel swarf lying on the bottom of the gear-box. How on earth did that get there?? :scratch: :scratch: :scratch: Removing that will need long tweezers. All of that brought me to this stage: Here's a closer view: The file marks on the end of the shaft are really prominent in that photo, they're not as bad as they look! :bang: :bang: :bang: I measured the protrusion of the shortened shaft from the gear hub at about 6 thou. That's less than I aimed for but it's less than the critical 31 thou so it'll do. It does depend a bit on the set-up of the clearances at the tail-stock end of the lead-screw. The next stage of this project is to fit the cross-pin at the tail-stock end of the lead-screw and then re-assemble the lead-screw hand-wheel and simmonds nut. Then I have to check that the top surface of the gear-box casing (with the lid removed) is parallel to the plane of the lathe bed surface and that the gear-box and lead-screw rotate freely. After that, I have to fit the gear back-plate, then to refit the gear quadrant and tumbler gears and confirm freedom of the whole chain to rotate. Somewhere about there, I have to fill the gear-box to the correct level with SAE 30 motor oil. Then I shall return to the gear cover - I've one more hole to drill and tap and then I have to paint it! |
| lordedmond:
Pete Now you have it sorted do you know that to cut metric threads all you need is a 33t and a 34 t gear to replace the output gear from the banjo if my brain cell is working its a 24 t these are not to nasa standards but are very very close and cheaper that the metric kit ale you retain most of the fine feeds Stuart |
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