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Last updated: 7 October 2004
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Last updated: 7 October 2004 |
Subject: ETX 105 and focuser #1244 misconception Sent: Thursday, April 10, 2003 09:16:42 From: jason@durrant394.fslife.co.uk (Jason Durrant) Many people have reported that the focuser #1244 fits the 105 but does not work. It's the other way around. It does not fit at all. Whilst it may look as though it fits, the reaction arm (The moulded part that slips over the side of the tube). Pushes the focuser gears apart by deforming the shape of the focuser case. That is why it feels such a tight fit. There is a way of making the focuser fit. Using a file you can file down the plastic on the inside of the reaction arm. Whilst it looks ugly, once fitted no-one can tell because it is on the inside. Regards Jason Durrant
Subject: RE: #1244 Focusser on ETX 105 Sent: Friday, April 30, 2004 05:33:25 From: "Stephen Bird" (stephen.bird@bt.com) To: niall@njs101.com Niall, I saw your article on the ETX pages and wondered if you could offer some advice before I lose patience with the #1244 focusser fitting to my ETX105. Having been bought the focusser as a present, so not wanting to ask for the receipt and go through the pain of returning it, thus upsetting the kind intentions of the purchaser, I find it an extremely bad fit. It would seem that the best advice BC&F can give is: Focus the scope manually on a distant object so that you have a reasonable mid focus position set up. Then the brass gear should be fitted to the focus shaft with the boss towards the main body of the scope and the grub screw located in the groove in the focus shaft. This then supposedly gives the correct position for the focus shaft gear. Next remove the short fixing screw at the rear of the scope, that will be replaced by the longer screw that will hold the focusser body in place. Then the body of the focusser unit should be fitted in place on the scope, meshing the gears carefully. But because the #1244 was originally designed for the ETX90, but with the ETX105 and afterthought, the fit of the focusser body to the scope is tight. It is therefore necessary to first push the focusser body firmly home and ensure that it is square to the scope body before tightening the long fixing screw. If it is not fitted firmly and squarely then problems can occur. This worries me somewhat as it is a very tight fit and I wondered if you had any other tips you could offer to ensure a correct fit and trouble free operation before I embark on the above strategy, such as gear lubrication and alignment. Many thanks and regards Stephen BirdAnd:
From: "Niall Saunders" (niall@njs101.com) Hi Stephen, I am perhaps not the best person to ask. I never actually fitted Nick's focuser to my ETX-105, all I did was repair and lubricate it. I have had the focuser on and off my ETX-125 several times (whilst completing the repair for Nick, and preparing the pictures for Mike's site). I know (or at least believe) that Nick has re-fitted his by now, and (presumably) has not had any problems doing so. That is why I am copying your original message to him, along with this reply from me (and am also copying it to Mike, as there may yet be a 'definitive' answer forthcoming from other ETX users). I do not see any advantage in the first sentence of advice from BC&F. There is no 'endstop' inside the focuser mechanism, and so it should not matter where the focuser of the scope is sitting at the start of things. You just need to be 'mid-way' in order to be able to release the original focus knob, and to attach the new drive gear. I agree with their second step - for the ETX-105, the grub screw on the driven gear must 'bite' into the groove machined on the ETX-105 focus shaft (see my pictures), and this means that the 'boss' of the driven gear must face the OTA. The 'short fixing screw' is the one that is 'above' the focus shaft (next to the upper viewport). Before fitting the focuser, I would be making sure that the gear train inside the focuser has at least SOME lubrication. There was no evidence of any in Nick's unit (although he may have cleaned the mechanism prior to sending it to me for repair) and I would definitely not be happy running the unit without some grease in there. And, by grease I mean use something like Vaseline Petroleum Jelly, or an equivalentsilicone grease. Don't go mad, just make sure that there is enough to lightly coat the various meshed gear surfaces. And make sure that the 'long' brass drive gear (along which the driven gear 'slides' as the focus shaft screws in and out of the OTA housing) has enough grease along its whole length. What you need to ensure, as the body of the focuser is screwed home, is that the long brass gear (which you obviously will not be able to see at this point) remains parallel to the shaft of the focuser - this is essential in order to keep the driving and driven gears in a constant mesh. If, as the long fixing screw is tightened, the body settles in a position that suggest the gears will end up out of parallel alignment, then you may need to consider some form of 'packing shim' between the focuser body and the OTA. It may be easiest to look at the orientation of the two parts as you slowly tighten the fixing screw, and see where 'first contact' is made. If the unit is then going to be driven out of alignment by further tightening, you could just use double-sided (foam) sticky pads (readily available from any stationary supplier) to 'build up' a shim to take out any gaps that you notice. The adhesive pads (with their foam inner) will also give a more positive support to the focuser, as well as allowing for some lateral movement. And you would not then have to screw the fixing screw so tight as to cause the distorted alignment in the first place. It may not be correct to get the body of the focuser 'true and square' to the body of the OTA - rather, it is essential to get the two gears to be parallel, and this you have to estimate, as you cannot see what is actually happening. The only way to tell is by 'listening', not to the higher pitched whine of the main motor/gearbox, but the much lower pitched 'rumble' of the meshed output gears. This should be steady, and if it is, it should also result in a 'steady whine' for the remainder of the geartrain, indicating that there is an even and balanced load being presented by the output gears. Hope this is of some help. Perhaps Nick, or others, can also contribute from their experiences. Cheers, Niall SaundersAnd:
Thanks for the prompt response. I think BC&F meant mid way to allow for removal of the focus knob and fitting of the gear, I was just putting the phone call in to writing so my vague interpetation to a certain extent causing problems there. The problem with getting the brass focus shaft gear to mesh with the final drive long brass gear in the focusser housing is simply that the focusser body is not a sufficient size match to fit to the telescope body. If the fixing screw is fully tightened, the body of the focusser distorts, and this causes misalignment of the two brass gears. The result is they mesh either too tightly or two loosely during a full cycle and eventually slip. There was absolutely no lubrication whatsoever on any of the gears, bone dry! This is easily rectified, but of course as usual Meades standards of quality control for accessoriesis shown to be lacking. If I attach the focusser body,without the gear on the focus shaft, this shows the extent of the profile mismatch. You begin to feel resistance as the focusser body and scope body meet, before the focus shaft has entered the focusser housing. With a 5mm gap between the focusser housing and the back of the scope, considerable distortion and twisting of the focusser housing has occurred and this would result, if the focus shaft gear was fitted, in the misalignment and gear slip I described above. To be honest, I missed out the part of the BC&F conversation where they said the #1244 was designed for the ETX90 and not really suitable for the ETX105. I questioned this as the Meade website clearly labels it as for BOTH the 90 and the 105, but BC&Fsaid they had fitted it to a coupleof 105's none-the-less. So it looks like that to get it to fit, I need to grind the focusser body down a little until the profile matches better. Such is life! Regards Stephen BirdAnd more:
I wish I had actually tried out Nick's focuser on my ETX-105 before I sent it back to him!! I have attached two pictures, trying to understand what your problem is. Am I right is guessing that the interference comes when the yellow-highlighted area on the focuser body starts to meet the OTA (at the same time as the locating post on the focuser enters the screw hole on the OTA)? Moreover, does the problem really start to appear as the 'red' area starts to interfere? Further, is there far less effect due to the 'green' area?And:If that is the case then, yes, it may have to be a case of getting out the Dremel and reshaping the red/yellow areas on the casing of the focuser. But, before you do that, I would be sending a letter to BC(&F (or the Meade UK folks) stating that this is what you are going to have to do, because their advertising is misleading. And that you expect your warranty on the focuser to be UN-AFFECTED by your actions. Put he ball in their court, lack of purchase receipts notwithstanding. I recollect that this IS a known issue regarding these focusers. They should either replace your unit with the CORRECT one (at no cost to yourself), or they should allow you to carry out a modification (at no risk to yourself). Speak to them again. Just explain, politely, that 150-worth of focuser should do the job that Meade advertises, and claims, it can. If BC&F themselves state that they have successfully fitted the focuser to "a couple of 105's", them ask them to look out a focuser that they HAVE successfully fitted to one of their 105's, and to send it to you as replacement/exchange for your problematic one. They should not need your proof of purchase for this, in fact if you agreed to cover postage charges (sending your unit to them with a return, postage-paid, jiffy bag enclosed) it shouldn't cost them ANYTHING, and they end up with a happy Meade customer. Good luck, Niall 
Hi, yes, you have it in one. First contact is the yellow highlighted area which does indeed contact the OTA as the locating post begins to enter the screw fixing hole. On your pictures the yellow area on the focusser body contacts the OTA higher up than the red mark shown on your OTA picture. If you look at the focusser body, the recess (indented area)between the yellow and green highlighted areas looks to be designed to contact the OTA at the point where the rounded area meets the straight flat part of the OTA moulding. It would seem that the diameter of the focusser body moulding in the yellow and green areas is too small to clear the slightly larger diameter ETX105 OTA body compared to the ETX90 OTA body. It looks like I will need to grind away the yellow area, but maybe not the green area as the OTA changes from the round to flat profile at this point and clearance looks sufficient. As to warranty, not much hope there. The focusser was a present from an overseas friend, and regardless, BC&F would rather refund money than warrant an altered item. I also have a sneaking suspicion that the locating post is a tight fit as well, but until I attend to the focusser body it will be hard to confirm this. I will proceed with caution and let you know how I got on. Regards Stephen BirdAnd:
If you can take some decent digital pictures, it may help simplify things for others who are, doubtless, going to be in the same boat. (Why, oh why, do Meade have such a propensity for shooting themselves in the foot all the time!!). Cheers, NiallAnd an update:
Niall, I have ground it down and it fits and works perfectly now. In the end, I had to take it down level with the recess / groove that you can see in your pictures. It needed to be ground both above and belowthe groove and more at the leading edge in order to get a good fit. Once done the locating post fastened all the way in and seated nicely and there was sufficient play to get some adjustment before tightening the locating post screw up. The gears now mesh perfectly and you get a nice even note at each speed as the motor runs. Listening to the note as the motor runs is the only way to check that you have the gears meshed straight and true. If they are not adjusted correctly the note changes pitch up and down as it rotates due to the variation in the tightness of the meshing gears each revolution. I'll post some digital shots of the mod over the weekend and write down the process I used. BC&F called me just now and said good luck! Many thanks for the help. Regards Stephen BirdAnd:
Congratulations Stephen, Just a case of 'mind over matter' - you don't mind, and it doesn't matter! Cheers, Niall
Subject: Modifying the #1244 Electric Focusser for the ETX105 Sent: Sunday, May 2, 2004 11:49:04 From: "Stephen Bird" (stephen.bird@btconnect.com) As promised, the process I used to modify the #1244 electric focusser to fit an ETX105. Please feel free to amend as necessary and post on the ETX site. Modifying the #1244 Electric Focusser to fit the ETX105 Meade sell the #1244 Electric Focusser as capable of fitting both the ETX90 and the ETX105. In actual fact a number of people have found that the #1244 fits the ETX90 which it was originally designed for, but it does not easily fit to the ETX105. If you are lucky enough to have an ETX105 AND have managed to fit the #1244 to it without modification well done. I was not so lucky, but with help from the ETX site and Niall Saunders I was able to do a simple modification and get the #1244 to fit perfectly and adjusted to give trouble free operation. The problem is quite simple, the OTA of an ETX105 is of a larger diameter than the ETX90, which is kind of obvious I guess. The #1244 is designed to fit to the OTA of the ETX90 and if you look at the picture below you will see that it has a locating post and a rounded inner edge with a groove in the centre. These align perfectly with the ETX90, not so the ETX105.And:The locating post and inner rounded edgearemeant to fit to the profile of the ETX105 OTA, which you can see below. You can also see the rounded inner edge of the #1244 highlighted with yellow and green. These are the areas that need to be modified to fit the larger diameter of the ETX105 if you want to avoid the risk of distorting the #1244, and worse still the gears slipping and becoming damaged, since in my case and I suspect others, if you do force the unmodified #1244 in to place the gears will not mate squarely. That groove on the inner rounded edge (BETWEEN THE YELLOW AND GREEN HIGHLIGHTED AREAS BELOW) is supposed to sit on the OTA where the tube goes from the rounded to the flat section. It does on the ETX90, but on the ETX105, the larger OTA diameter means it sits just below and consequently does not allow correct mating of the #1244 with the OTA, pushing the #1244 housing out of shape. AT THIS POINT YOU INVALIDATE THE MEADE WARRANTY ON THE #1244, SO YOU NEED TO DECIDE IF YOU WANT AN ELECTRIC FOCUSSER OR A REFUND! I OPTED FOR THE ELECTRIC FOCUSSER!! As an aside, I noticed that the brass final drive gears were not lubricated. I undid the two screws you can see in the abovepicture and found that the #1244 had not seen any lubricant at all! So I applied the smallest amount of lubricant to the two plastic gears and the two brass gears to ensure smooth running. If you do this take carewhen youdisassemble and reassemble the #1244, one of the two internal plastic gears its shaft and the internal brass gear can easily part company with the housing. 
To get the #1244 to fit now requires a leap of faith. You need to grind the yellow and green areas away until the profile fits the ETX105 OTA. I found that you need to take the surface down to the level of the bottom of the groove. A dremel, file or sandpaper will do the job, but tape over the large gear hole aboveand the two smaller motor ventilation holes on the other side of the #1244 first to pevent dust entering the unit. Then grind away until it looks like this. 
Finally fit the modified #1244 to the ETX105, you should find thatthe fixing screwnow seats and fastens firmly without distorting the case, or requiring any brute force. In addition you can rotate the #1244 a few degrees either way from the vertical to get some adjustment to mate the gear teeth correctly. You play this by ear (literally) as it is adjusted correctly when the note from the motor and gears during operation is constant throughout a complete cycle. If the note varies in pitch, then the gears are not mated properly and may slip or bind. Here is how mine looked when finished. Just got to fit a longer cord and route it with the dew heater power lead and LPI lead so it doesn't get caught as the scope moves! 
Hope this helps. Acknowledgements to Niall Saunders for some of the pictures and Mike's ETX site for the confidence to take the leap of faith!! Regards Stephen Bird 
From: "Nick Howes" (nick@yamaha.co.uk) Just to chip in (just got back from a long business trip) that Niall's focuser mod works so well, Meade should make it as standard this way !!