Rusted

Thanks. There is an RCD in the CU. Not sure of its abilities on the far end of a 30m long extension cable though. Incorporating an earth into an all 2-pin socket, reversible plug system in an outhouse would seem to be voluntary. British bought items used to "tingle" badly if a 2-pin plug was fitted, the earth wire discarded, and then plugged in "the wrong way." Metal sewing machines for example. I used to mark the plugs with red and green tape to ensure they went in correctly until we quickly stopped using them altogether. The Danish 10A standard CU fuse used to blow the whole house[!] system regularly on UK electric kettles. Max 2KW locally on a standard 2-pin plug! Everything electrical, over here, is sold with moulded on, 2-pin, reversible plugs. Only washing machines use the Shuko plug. Even if you only have a standard 2 pin socket! Just to add to the confusion they use 3-phase in domestic situations. Kitchen cookers use a unique, multi-pin plug. Which is fitted by the dealer, at considerable extra charge, on purchase. DHWs are strictly an electrician's job too. As is all "outside" work. Because it is so expensive to hire an electrician nobody fits a night and day proximity sensor in their outside lighting. It must cost Denmark heavily in the global CO2 stakes to have a 24x365, "Close Encounters landing strip" in every garden! It seemed very odd when we first came over here to see a spaghetti of flex and multi-sockets running across the poshest of rooms for table lamps, TVs and audio equipment. The number of wall sockets always seemed to be decades behind even 1950s UK standards everywhere we went. Hiring an electrician is to be robbed. £100 per hour minimum, even years ago, plus travelling time, meal breaks, maternity leave, school uniforms, etc, etc. Literally everything is plus 25% VAT. Electrical wiring items, which can be bought for very small change at all DIY outlets, suddenly cost £50 each for a simple 2-pin socket and wall receptacle. We paid more, for a few additional sockets in the kitchen, than a whole house rewire in Wales! I even chased a one meter drop of plaster myself to save literally £hundreds on the final bill! Normal practice is plastic conduit down the wall! Or naked cable and clips!

Thank you both for your input. All good stuff. Note that I now live in Denmark. Where earthing and three pin plugs are rare except in new installations. I was having some new 2 pin sockets fitted by electricians and asked for an earth rod. They seemed quite shocked but allowed me to drive an earth rod outside the house to kill the hum on my British Hifi. I was then able to use 3-pin earthed plugs and sockets but only on a multi-socket strip for the Hifi. Everything else remained 2 pin. When I built the observatory I had no plans for anything but a twin core extension lead and a flying lead multisocket. But, the AWR drives were giving me a tingle so I ordered a 2m rod online and earthed the mounting. At the same time I connected the earth leads on the AWR system for the first time. All the metal plates of the mounting are all in intimate contact with each other. I have plans to house the two [2 pin] 6 x multi-sockets in the observatory in a proper weatherproof box. The mains wiring is protected by a device in the consumer unit and an old fashioned 10A cartridge fuse again in the CU. All sockets and lights in the property are on the same 10A circuit!

Thanks Gina. I haven't noticed any tingles since the earth rod went in. From fuzzy memory, I think there was 60V AC on the mounting. This only occurred when the 12V drive PS was switched on. I've bought a new multi-meter since then so I should check again. With and without the earth connected.

Thanks. It is only the mounting I am earthing. Home made and mostly raw aluminium plate. It isn't earthed by the timber pier. The obs. floor is timber boarding. The Obs. is mostly plywood and timber. I was getting a strange "tickle" through my fingertips. Mostly on the bare metal telescopes and accessories when I touched them. Possibly leakage from the 12V drives PS? 2-core, no earth in and out. I could also get a very dim glow from a neon "test" screwdriver. So I bought a 2m earthing rod and sank it into the wet clay at the foot of the obs. 6mm^2 cable running straight down the timber pier from the mounting to the rod. Which has its own massive cable clamp with rain cap. The free end needed proper termination. I thought there might be some rule about clamping. Hence the thread.

Hi, Thanks for the suggestions for sealing over the joint. I would never have thought of that.

Hi, How should I properly terminate the observatory end of a 6mm^2 stranded earth cable from the local 2m earth rod? Temporarily, I have just wrapped the cable around a handy screw head on the bare aluminium mounting with a large washer to contain the loose strands. It looks horribly amateur and may even corrode over time. So I thought I'd use a suitably large, car type, crimping eye to be trapped under the same screw head. Any better ideas? Thanks.

Thank you both for your posts. Michele, The milling machine example of hobbing shows a typical problem of clearance along the tangent of the wormwheel. The chuck is almost rubbing on the largest wormwheel. Some sort of rigid and accurate extension is necessary. It must help to clear the chuck as the wormwheel diameters grow larger while still providing the drive to the tap. If a lathe is being used then the tailstock is usually much narrower and an MT center can provide extra clearance. A typical 3-jaw chuck would be even larger and force the need for an even longer extension. Markus, I couldn't afford a metal cut-off saw as well as the mitre saw. So I just set the speed to the lowest available. I didn't want a refund or a discount. I just wanted a much better wormwheel. It didn't happen. So I no longer protect the vendor from the hideous truth about his trading standards. I'm too far away to have started a "Sale of Goods" case against him.

Thanks. The plates were mostly cut out with a powered jigsaw, lubricated with lamp oil [UK: paraffin] and then filed straight by hand. Only later did I obtain a sliding, 12" DeW, miter saw which could manage aluminium with far greater speed and accuracy. Cut-offs up to 6" [or so] were relatively painless, even in 20mm thick alu. But I never had the nerve to saw the long sides on my table saw. Besides, DeWalt specifically warns against such use. The problem with sawing aluminium with a circular saw is the swarf. It flies everywhere and can't be easily collected. Non-magnetic and a shop vac with "turbo" sawdust separation might be damaged. So I had to use a dustpan and brush over several months until it was mostly all gone.

Thanks Peter and welcome back! I'd love to see a photo of your wheel hobbing arrangements if such exists. There are a great many potential questions: But: Did you use straight fluted taps or spiral? Threaded "machine" taps or the "manual" type? Unfortunately I never found a dividing head with my name on it. Far too expensive back then! So I used large, home made, dividing disks on the outer end of the lathe mandrel for [gear] wheel cutting.

Thanks Simon. I wasn't aware that lens coatings were vulnerable to dew damage. I made a half-hearted job of wrapping the objective ends of the OTAs in camping mattress foam. Not ideal as the closed cell stuff is too stiff to go over objective cells. Something softer would help the wrapping process. Online research suggests that insulating the dome roof would help to reduce radiation to the night sky. I'm using agricultural fleece as a stand-off lining but it's probably more cosmetic than thermal. Lining the dome with foam is doable but the plywood seams leak in places. I am torn between re-covering the dome in full gores of heavy PVC tarpaulin. Or re-cladding in full length aluminium gores. Access is poor because of the working height. Making large wormwheels demands expensive materials. Thick rounds of free machining aluminium. One mistake, and you have to use the blank for a smaller wheel. You can't arbitrarily change the tooth count. The teeth ought to be gashed at the correct angle before hobbing to ensure the correct tooth count. Which means some way of dividing the blank while the gashing is going on. Either using a fly cutter or a slitting saw of the correct diameter and angle to match the worm thread. The wheel needs to be mounted on a hub which is never removed from its concentric [between centers] holder until completed. Ideally the worm should be a common [if rather large] thread for which [machine] threading preferably spiral taps are available and affordable. A purpose built, wheel cutting "engine" or specialist jig is probably necessary because of the poor access to the wheel circumference on most lathes. The length of the tangent must allow for the hobbing tap to be supported rigidly from both ends. The investment in amateur-built equipment could still be quite considerable at start-up and probably slow to pay for itself. At a professional tooling and equipment level it would be a foolish investment due to lack of demand and the high price putting off customers! I vaguely remember Peter Drew mentioning that he has some experience in wormwheel manufacture.

Here are some better images of the PST interior if you can get the covering plate off despite the pink thread locker. The prism slides in a track with two pins for alignment. While the fibrous pad is supposed to keep the prism in contact with the greasy track but obviously fails to do so quite regularly. So that the prism is no longer parallel to the top of the black box. Which is the ideal set-up. I used a small mirror to capture my rusty ITF with the camera. The angle is too oblique otherwise while it is still in place in the black box. In theory you can unscrew the eyepiece holder with its mounted ITF and IBF filters. Overcoming the thread locker will be your challenge. I fixed the [empty] black box down on the bench with two sturdy, padded F-clamps. While I used a 2' pipe on the arm of a brand new Python rubber strap wrench and nearly broke the strap! Hope this helps.

Thank you Simon. I am well aware of wormwheel and worm and wheel gashing, hobbing and machining. I have even made a few smaller wormwheels an worms myself over the decades. I have a 9" Ø S&B toolroom lathe. I once made a huge dividing wheel in polycarbonate and a fly-cutting shaft with belt drive, high speed motor. All in anticipation of doing lots of gear cutting. Then I became sidetracked on other projects and trusted Beacon Hill to supply the goods. Heating several hundreds pounds of aluminium, iron and stainless steel in a mounting is asking for the impossible in a deliberately draughty dome. Everything is literally dripping with dew in the mornings and often for most of the day. I could indeed cover the mounting with an insulating cover overnight but that can't possibly extend to the telescopes as well. Though I have recently purchased some heating straps and controller. And, a secondhand hair drier from a charity shop. A panic reaction to hours of precious solar imaging time being lost to objective dew after recent cold nights. Even then it takes ages to rid the large lenses of dew. I am very wary of leaving anything running overnight due to the risk of fire.

Episode 14: Worm drives: I am strictly a "make it up as you go along" designer these days. My earliest trials with the worm drive layouts was using wood blocks for support. Wood is easy to work with and avoids wasting irreplaceable aluminium scrap. What turns up at a scrap yard is fleetingly available and once gone is well and truly gone. If you find something useful you buy it at the price they ask. The RA wormwheel sat at the top of the Polar Axis shaft for a year or more before I finally moved it down to the bottom. To do this, I had to make room on the south side of the huge timber and plywood pier. That meant shifting the whole [massive] mounting southwards on the pier. Every change I made required the hefty, builder's, folding stepladders be carried up and erected on the observatory floor. Once bridged above the mounting, into a stable A-frame and lashed firmly together at the top I could use my chain hoist. This is not without its dangers, despite the stabilizer bars resting on the floor. So I always guyed the stepladders to the dome perimeter for safety. I have lifted the massive mounting up through the stairwell to the observatory several times now. For the lift off the ground floor I use a massive, square steel tube bridged across the base ring and pier. This is an early photo of the lift while the observatory was still under construction. Scrap metal box section turned up just when I needed it to house the stepper motors and support the worm bearings. It was spot on for size but needed a lot of cosmetic cleaning up. The clearances for the motor were minimal which required CSK fixing screws for the worm bearings. I had to invent a way to countersink the the holes on the inside of the boxes! Assorted earlier images:

Appreciation for "Work of art" depends on whether that was irony or sarcasm.

Thank you both. The bearings in the link would be a straight swap for the present ones by size. Though I'd need to check for the availability of seals and all stainless steel construction. The last thing I want is rusty bearings from exposure to damp in a constantly cycling temperature regime. Everything suffers from heavy condensation out in my well ventilated observatory. First I ought to check the forces required at the rims of the wormwheels to get a better idea of the tangential loads on the worm bearings. The AWR micro-step drives provide an acceleration and deceleration ramp with each movement. It is certainly very smooth. With zero visible backlash to slews despite the long and heavy refractors. The 180/12 is over 7' long. Meanwhile, the worm's bearing support structure needs serious reinforcement to gain any advantage from better bearings. A hinged and sprung, perpendicular, motor/worm mounting arrangement is under serious consideration to minimize [known] concentricity issues. If the mounting was ever truly finished it wouldn't be so much fun any more. I'd need to start building something else. If it was a commercial product I'd probably be moaning about its minor foibles. But then, it doesn't owe me a near fortune for its load capacity. And, it's only a Mk1. Built from the cheapest [mostly scrap] materials to hand at the time.

The worm bearings were mentioned earlier: S6000Z stainless steel, deep groove, twin metal shields. 10x 26 x 8mm. No manufacturer's name visible. Deep groove bearings provide some resistance to side loads but they are hardly taper roller. EDIT: After endless searching it seems that 10mm bore taper roller bearings are as rare as... well, rare things. They exist, but nobody [so far] lists then in the UK. 15mm is the minimum standard bore. With the few, small bore exceptions being on Chinese manufacturer's websites. The logical thing to do, if needs must, is to add thrust ball bearings to the existing bearings.

The moment you shove your altazimuth around manually you may apply an overturning force well beyond the CofG's theoretical comfort zone. If the static : dynamic friction ratio goes sideways you may well have a distinct "timber!" scenario. Particularly when pointing into the velocity "black hole" up around the zenith. The azimuth cannot rotate so all the manual effort goes directly into tilting instead. All this, just as you have achieved the highest C of G of the whole instrument.

If the pipe is disposable you could fill it with something rigid like concrete. But is the pipe anchored immovably at the bottom? This is where flexure is most likely.

Really excellent images! I'd be "over the moon" if I'd managed that level of detail.

All true, if the quality of machining supported the theory. I was even advised against lubrication by BH! Note that I was expecting the "stainless steel worms" advertised on the Beacon Hill website to this day. "The finest wormwheel sets available to astronomers in this country!" Then, when I assembled the drives for the first time I could hear a nasty "graunching" on every worm rotation. Slews became a constant reminder of the poor workmanship of both worms and wheels. The worms were actually eccentric! So I resorted to metal polish paste. A fine abrasive for cleaning chrome on old cars. It didn't want to be a liquid or it might have found its way into the bearings. I spun the RA worm using an electric drill and applied the paste. It helped to polish the worm and the roughness of the machining improved. Sufficient to end the horrible noises during slews. Though there was no sign of any change on the wormwheel teeth. Which were very rough and black with grime on receipt. I had cleaned them thoroughly with a toothbrush and washing up liquid. Copy and Paste from the Beacon Hill website this very morning: 7.02.2020 "Worm and Wheel Sets The matching stainless steel worms are held in sealed roller bearings in substantial brackets and are fully adjustable to eliminate any developing end float. They are the most accurate worm and wheel sets available to astronomers in this country." £400 GBP + £60 delivery charges. Higher than the advertised prices [even today] and not to the ordered specification of 50mm bore. In fact the worms are clearly of brass and the bearings are plain ball journal bearings. With no obvious adjustment for end float and held in place by a thin film of shellac! [sic] The solitary grub screw locked the races solid in the flimsy off-cut of aluminum channel profile, if over-tightened in the slightest.

I agree with Don that the present clamping system is far too short. It ought to grip, via a full depth collet, over the entire length of the spigot. The present system relies on a close fit at the tip of the tube being clamped. A far from ideal situation given the range of dimensions to be found in different receptacles. My use and recommendation of three thumbscrews is a personal choice which I find is safe under heavy loads. I like my 2" Baader Grip-lock too on plain 2" fittings for its grip and release again under heavy loads. In an ideal world there would be slip-on bands to fill the undercuts when the user so desires. A bronze sleeve could be sprung into the undercuts and simply left there. There is no reason why some manufacturers couldn't ask for $199 each for these [Chinese manufactured] "patented" bands. Fortunately Darwin has dictated that I am never required to struggle with expensive undercuts.

Thanks. Re: Bearings: I'll get back to you on that. Easier in daylight when I'm not needed at dinner. BTW: I have tried lapping the worms/wheels with assorted materials but is incredibly slow going even when the worms are motor driven.

That's a fascinating idea Simon! Affordable too these days. Not sure how I'd cope with the extra width. Though, as you say, the plain shank 10mm model would avoid the need for an angle grinder on an MT. Cantilever the outer supports on a solid bar, or angle profile, without needing to replace the existing worm bearing housings. Nor even disturb the belt drives. A nice and easy, bolt on-solution. Quite literally, lateral thinking. Thanks for sharing your inspiration! EDIT: Your link has awakened my interest in the bearings used in the BH worm housings. I shall have to see if I can find a serial number to confirm angular contact type.

Thanks. The 50mm bore, flange bearings are very large, self-centering in spherical housings and have a load capacity well beyond the needs of a humble telescope mounting. I considered end loading the PA bearings [from below] but it never seemed necessary. I merely push the hefty bottom clamping collar upwards as hard as I can while tightening the three, large collar screws. I have considered using a strong coil spring to achieve the same end loading but finding a suitable example to slide over a 50mm shaft is difficult. I have a simple test of any equatorial mounting: Point it at the pole and then rattle the OTA up and down while holding the focuser body or locked barrel. Any flexure, or bearing play, is instantly sensed through the fingers. Particularly with such long and heavy refractors like mine providing plenty of leverage. I still plan to spring load the worms on sturdy hinges. Presently I am using a pin to provide spring loaded rotation into the worm wheel. I believe a suitably tight, brass door hinge would be far superior. The worm bearing, profile housings are weak and need considerable reinforcement over and above my present arrangements. I need to add considerable cross sections to properly support the bearings against end loading. Taper roller, thrust bearings, or even axial thrust, ball bearings, on the worm shafts would be better. Sadly, the worm shaft extensions are miserably mean. I am trying to avoid couplers just to hang the belt drive pulleys onto something more solid. The shoulders on the worm shafts cannot be brought inwards, to make room for better bearings, because of clearance problems on the large, wormwheel rims.

Hi Simon, Absolutely incredible work! You are astonishingly inventive and creative! I went for minimalism and simplicity. The Tollok bushes were a wonderful discovery for so heavy a mounting. Encasing them in serious cross sections maximized their stiffness on top of incredible shaft grip. They are normally used for seriously heavy chain sprockets and multi-V belt drives on heavy machinery. My stepper motors are micro-step driven by AWR[Tech] with Intelligent Handset 2, simple handset and ASCOM[AWR] driver. Not without endless problems but the latest ASCOM[AWR] driver is a vast improvement. I was absolutely hopeless before that! Beacon Hill is/was still going when I bought my wheels and worms 3-4 years ago. The owner is aging and strictly pre-computer. The website hasn't changed in years and can probably be ignored. A telephone call will discover what can still be managed. Or [rather] promised. Eventually... There was talk of finding a new wormwheel maker at the time I was involved. Both wormwheels are 287T. 11" RA and 8.75" Dec. I asked for the 14" but they couldn't supply by then. 287 is far better than finer toothed IMO for DIY mountings. They are more "forgiving." The BH worm housings are terribly flimsy and poorly designed. Needing lots of mods even to make them work as intended. Very poor bearing retention and no real stiffness to the skinny, channel profile. The worms moved sideways out of their housings almost on the first slew! Unbelievable! The worm shafts are almost worthlessly short for timing belt drive sprockets. I shall make some massive worm housings with far better and bigger bearings... one day. A new episode is due. Probably about worm housings, their mounting and driving.