Old Bill Posted October 28, 2009 Share Posted October 28, 2009 Thanks for the suggestion, Johnny. Yes, lost wax would be very good. There are other options too such as making it in polystyrene and pouring the metal onto the top to burn it out or by just making the elbow and simply brazing the flange onto the side afterwards. What is intriguing me at the moment is that somebody made 5000 of these, ninety years ago, using wooden patterns and I can't see how it was done! These old time pattern makers were very clever chaps and I would love to have had the opportunity to work with them. No doubt it will become clear in the end but for the moment it is still a puzzle! Cheers! Steve Quote Link to comment Share on other sites More sharing options...
Runflat Posted October 29, 2009 Share Posted October 29, 2009 Steve, does the original pump that you copied from not have any casting marks that would give you a clue? Quote Link to comment Share on other sites More sharing options...
Johnny Posted October 29, 2009 Share Posted October 29, 2009 Steve, does the original pump that you copied from not have any casting marks that would give you a clue? I can't see any obvious casting marks or joins, so it looks to have been made as a single piece. Looking at it again, the main problem looks to be the flange for the threaded connector, as this is at an unusual angle compared to the rest of it. Could it be sandcast almost vertically but at a slight angle? The tube pointing downwards, but angled so that the flat face of the flange for the thread is square in the mould. This might allow the top half of the sand box to be lifted off (the join would have to be around the centreline of the flange). This would be an unusual way of doing it, but is the only way I can see that this could be sand cast. Not easy to explain, but I hope this makes sense! Quote Link to comment Share on other sites More sharing options...
Gordon_M Posted October 29, 2009 Share Posted October 29, 2009 Nice to know I'm useful for something. I am indeed a trained foundry and patternmaking technician, but it's been 30 years since I admitted that. First - gunmetal is the right choice for that. Second - as drawn and photographed it wont be made in a simple two-part mould with one core. If I had to guess I'd suggest that it was made upside down from the photo, with the main bore being made by the single core (the side flange bore would be drilled from side I expect. The clue to this is the three 'ears' which will only really draw conventionally in that orientation. So how did they do the fiddly bit of the outside profile that won't draw - basically under the main tube? Well the joint line would have been down the main tube, kind of S-bend across to the middle of the side flange. The outside profile under the main tube would be formed by a second 'core' It could be done by techniques such as 'drawbacks' or 'oddsides' but simplicity would suggest that the whole outer rim was formed by a circular sort of external 'core' (ah - how it all comes back :-D) Since we are in the real world, and you will only want one or two of them, I'd suggest the lost wax process, but without the wax. Carve the thing out of high density polyurethance foam, not the packaging rubbish, but the denser type they use for floatation rings and life preservers, then just pour it in gunmetal. Speak to the foundry first and get their advice too. I wouldn't even bother with a core, I'd do it solid and then machine out the main bore from both ends and the side bore from its own face. Quote Link to comment Share on other sites More sharing options...
Old Bill Posted October 29, 2009 Share Posted October 29, 2009 Thanks for all of that. There is lots of food for thought there. We are off to the foundry on Monday so I shall ask their opinion too. Cheers! Steve Quote Link to comment Share on other sites More sharing options...
Great War truck Posted October 31, 2009 Author Share Posted October 31, 2009 Steve has sent me an update and some more photos of his pattern making. The first three patterns are now complete. This one you have seen before but it is now painted and hopefully will produce the inlet side cover. This is the simplest of the lot. The next one is for the actual rotor and has both a plug and a core box. The core box should produce a piece of sand which can be fitted into the cavity left by the plug allowing the bronze to form both the top and bottom of the rotor and the vanes as well. The result should look like this This is the main mounting bracket It is the most challenging one to date and requires three core boxes this time The intention is that the main plug is moulded leaving the flanges in the cope and drag (top and bottom mould boxes) and a tapered square hole in between. Two rectangular cores are made and dropped in and the third cylinderical core is laid in the centre. He has tried to make the pattern foolproof by planing off the corners of the pattern and adding wedges into the corners of the core boxes. This should prevent the cores from being put in the wrong way around. It is the moment of truth on Monday as we are off to the foundry to see what they say. Wish us luck! Quote Link to comment Share on other sites More sharing options...
Enigma Posted November 1, 2009 Share Posted November 1, 2009 OK, good luck!!! Quote Link to comment Share on other sites More sharing options...
Great War truck Posted November 1, 2009 Author Share Posted November 1, 2009 The new half shaft turned up on Friday. It is a lovely job and very quick. Less than two weeks from order to delivery and the company have been very nice to deal with too. It cost £373, so good job we already had one. Quote Link to comment Share on other sites More sharing options...
Alex van de Wetering Posted November 2, 2009 Share Posted November 2, 2009 Tim, the work you guys are doing is very inspiring to say the least. Every few days I have a look at your thread and it's great to see which techniques and materials you use to bring the old Dennis back to life. I am really interested how the casting progresses; I don'y kno if porrible, but it would be great to see some pictures of the actual casting process and the steps leading to it. I think most of us only dream of having missing parts casted, so it's great to see someone actually doing it! Keep up the excellent work! Alex Quote Link to comment Share on other sites More sharing options...
Great War truck Posted November 2, 2009 Author Share Posted November 2, 2009 Thanks for that Alex. I dont think we will be able to get photos of this casting process as it is all done in a bit of a hazardous environment and i cant imagine they would appreciate us being there to take photos. But Steve can no doubt explain the process if he has a moment. The good news is that Steve and Tony visited the foundry today and they were very happy with his patterns and will do a cast shortly. Steve in the meantime will start on the next patterns. Over the weekend they started reassembling the diff. The bearings went on beautifully (thanks Chris) as did the new coupling, after a little easing with a file. Once the worm shaft was back together, they tipped the differential housing on end and simply dropped the whole assembly into it. A bit of waggling and a final thump with the mallet and it was home. It is now all bolted up, turns freely and awaits the completion of the wheel assembly. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted November 3, 2009 Author Share Posted November 3, 2009 Tony and Steve had a go at reassembling the differential wheel. That all went OK after a bit of thought on how to approach it. The fun bit was in working out how to fill it with oil as it has no fill plug! In the end, they just poured it into the case before fitting the other half and relied on the thickness of the oil to limit the leakage rate. Our nice new bearings are are all on and protected and we plan to fit it all back into the casting tomorrow to put them out of harms way. Plan now is to get the whole lot back in the axle over Christmas. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted November 4, 2009 Author Share Posted November 4, 2009 The rebuilding of the differential has now been completed. It all turns very smoothly with no backlash which is very pleasing. The next step is to put it into the lorry. So we have to move the buildup of junk in and around the lorry. Pull it all the way out. Then using the chain block on the RSJ above the garage door we should be able to drop it in. It will be a big exercise so it will need all of us to be there. No date is fixed for it yet. Quote Link to comment Share on other sites More sharing options...
Great War truck Posted November 4, 2009 Author Share Posted November 4, 2009 If you are feeling keen, here is a video clip of the worm turning. The highlight of entertainment - so i told my wife. She did not comment, so obviously overwhelmed with it all. Quote Link to comment Share on other sites More sharing options...
Minesweeper Posted November 4, 2009 Share Posted November 4, 2009 With this part of the exercise just completed, I notice that the number of "hits" on this particular topic has amazingly exceeded the 30,000 mark. I must say that Tim,Steve and I have been totally surprised and overwhelmed at the amount of interest that it has created as relating the whole story here, really started quite by accident. This is the fourth old truck that we have worked on and it has always been our policy to take as many photographs of the bits as we have proceeded with the work - mainly to remind us on how to put them back together again after we have taken them apart! The photographs of the other three trucks were taken with film cameras - which could have been an expensive exercise if we had taken as many photographs of them as we have of the Dennis - but with the advent of the good, cheap digital camera, that new technology has loaned itself to comprehensively recording the Dennis restoration - as we have taken approaching 2,500 photographs. And that number of photographs and the wonderful availibilty of the HMVF to set out the story has enabled us to tell the tale. We are grateful to everybody for their interest and to Jack and the whole of HMVF Team for making the facilty available. Tony Quote Link to comment Share on other sites More sharing options...
Johnny Posted November 4, 2009 Share Posted November 4, 2009 If you are feeling keen, here is a video clip of the worm turning. Fantastic stuff, the quality of your work is breathtaking. This thread is an inspiration to us all! Are you still concerned about the corrosion on the worm drive, or does it clear that area? Quote Link to comment Share on other sites More sharing options...
Asciidv Posted November 4, 2009 Share Posted November 4, 2009 With the pace of this restoration it is easy to skip past parts of it where really we should stop and marvel. I am still stuck at the pump elbow! I have been trying to pull the pattern out of the sand for the past few days without any success. Even using solid modelling does not make it much easier to visualise. In fact just drawing the part is difficult - far easier to use a block of wood, some filler and some basic hand tools.... Barry. Quote Link to comment Share on other sites More sharing options...
Minesweeper Posted November 4, 2009 Share Posted November 4, 2009 Johnny - the bearing surfaces on both the worm and the worm wheel are fine and the new bearings have fitted beautifully and are not a problem. There was some heavy rust at the ends of the actual worm but we have cleaned that off as best possible - and those areas are mainly away from where the worm wheel runs on it. So we will just live with those. The actual worm wheel is of course, made from bronze and this is where the heaviest wear is. A lot of metal has been worn away and obviously it will be the weakest part now. We are resolved to give it a try and just see what happens. It is still mating very smoothly and without back-lash with the worm. A new Bronze Wheel will cost a lot of money and we would rather not get involved with that if we can get away with it. Hopefully, the lorry will never have a lot of heavy use and gentle handling will lengthen the odds for survival! Tony Quote Link to comment Share on other sites More sharing options...
Minesweeper Posted November 4, 2009 Share Posted November 4, 2009 'evening Barry! What an interesting exercise you have completed in drawing out that "Elbow" on your computer - totally beyond me! Steve is at present in Ireland (work) and will not be home until tomorrow but I know for sure that he will wish to comment on your computer model. We have been looking at all sorts of problems with this particular pattern but the Foundryman did not seem at all troubled by it when we talked to him about it and simply said that he can adjust the sand mould after it has been made. I am not quite sure how - but he was confident! Perhaps Steve can elaborate. Tony Quote Link to comment Share on other sites More sharing options...
Stormin Posted November 5, 2009 Share Posted November 5, 2009 If the elbow was as modelled then the mould should be able to be split horizontally about a line through the centre of the main flange, with the main flange and outlet tube being vertical. The problem is the real part is not quite as modelled. The small flange face is not parallel to the main tube centreline. Also being picky the ears for the bolt holes on the main flange are not evenly spaced on the original. The only ways I can see are as has already been suggested a second "external core" piece is let in to the main mould for the side flange, or omit ears of side flange from pattern and a bit of artisitic sand carving once the mould has been made. The first method may result in a small amount of extra casting flash to be fettled afterwards as the molten bronze finds the additional joints in the mould. Quote Link to comment Share on other sites More sharing options...
Gordon_M Posted November 5, 2009 Share Posted November 5, 2009 It'll be hell to make as it is, but let's have a think about this. It would be relatively straightforward to fill in the section between the main pipe and the big flange, turning the thing into a larger 'lump' I'll admit. This would be relatively straightforward to make as a two-part mould with a single core. Once cast, the small flange holes could be drilled / tapped as required, and the filled-in section could be machined out, at least far enough to get the bolt hole and so on back where it belong. In other words - cheat. Cast it in a lump and machine out as much of the tricky bit as you have to. This is exactly what we would have done back in the day. Gordon Quote Link to comment Share on other sites More sharing options...
Asciidv Posted November 5, 2009 Share Posted November 5, 2009 Norman, you couldn't really tell from that screen shot but the flange is angled to the main bore - see below. The model wasn't meant to be a perfect representation but just something to visualise how things might go, but we don't mind you being 'picky'! Gordon, yes cheating is easy. I imagine you mean something like this without any 'ears' on the flange. But to have the ears, having an external core part for the flange seems the only positive and repeatable way of producing the part. We will just have to wait for Steve to give a full description of how it is done.... Barry. Quote Link to comment Share on other sites More sharing options...
Gordon_M Posted November 6, 2009 Share Posted November 6, 2009 You could do it pretty much like that last image but still draw the ears with a little extra taper - soon cleaned off afterwards. The ears would almost draw as they are. Basically, add as little extra material as you need to so that you can cast it without megabucks pattern work, then just machine off. Quote Link to comment Share on other sites More sharing options...
Old Bill Posted November 6, 2009 Share Posted November 6, 2009 This one is proving to be quite a puzzle but I think I have a plan now. We went to the foundry on Monday where the moulder was extremely helpful. He said that the patterns I had made would be fine and he could do them. They are doing a gunmetal pour within the next month so we should get the first three castings before Christmas. Following on from Johnny’s suggestion, I have found this picture and you can see evidence of the split along the top centre-line which is just where I would split it if it did not have the side flange. I asked the moulder about this elbow and he thinks he can do it if he manually cuts the sand along this line after the first ramming before turning the mould box over to do the other half. I just have to be careful to make sure the draft angles are correct for this line. Now Gordon pointed out that the ‘ears’ on the flange can’t draw sideways. However, the one on the left is just about on the centre line and will almost draw with just a little more metal. The one in the bottom right is the same but you can see that some more metal has been added and it is slightly miss-shapen. There is nothing that I couldn’t sort with a file in a moment or, as they have done here, just left. I think I will have a go at making it like this and see how I get on. Thank you for all of your thoughts and comments. There is nothing like a challenge! Steve Quote Link to comment Share on other sites More sharing options...
Gordon_M Posted November 7, 2009 Share Posted November 7, 2009 I think that's pretty much it. That's a soft material, so removing excess would be no big deal. I think I'd leave some extra raw material round the little flange, and maybe go for minimum bore on the core and clear it out afterwards, as I'd expect the core to move to one side on a setup like that. We need pics of the finished item...:-D Quote Link to comment Share on other sites More sharing options...
Old Bill Posted November 7, 2009 Share Posted November 7, 2009 Yes, I will certainly post pics of the finished items. I will start on this pattern tomorrow and see how it goes. Steve Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.