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Post by Deleted on May 4, 2011 20:22:41 GMT
Pic271 Now things differ between the two halves, first the tops. Using a 1/4 end mill a 1/8 deep recess is machined to give clearance for the 5BA nut at the top of the diaphragm. Attachments:
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Post by Deleted on May 4, 2011 20:25:10 GMT
Pic272 Then the back face is machined leaving the rim 1/8 thick and stopping just as the outer casing of the chamber is reached. Attachments:
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Post by Deleted on May 4, 2011 20:31:20 GMT
Pic273 Next job is to reverse in the jaws and machine the spigot to 1/8, I forgot to take a picture of the top at this stage but this is the bottom having it's spigot faced although it's longer at 5/16. Other jobs for the top before this was a No.30 centre hole drilled , followed buy a 7/32 hole to a depth of 9/32( this will be tapped 1/4x40T later). Attachments:
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Post by Deleted on May 4, 2011 20:33:48 GMT
Pic274 All 8 then had a No.30 hole drilled into the side of each chamber to accept a 1/8 copper tube using the machine vice. Attachments:
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Post by Deleted on May 4, 2011 20:38:00 GMT
Pic275 The bottoms then have a No.22 hole drilled ( tapped later 3/16x40T) on the opposite side to the 1/8 tube which is also spot-faced with a 5/16 end mill. This will be for the cylinder valve body to locate when made.. Attachments:
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Post by Deleted on May 4, 2011 20:40:41 GMT
Pic276 The 4 cylinders so far, jobs left to do here is the 4 No.34 holes around the rim to hold the two halves together and the various tappings to do. Attachments:
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Post by Deleted on May 4, 2011 20:50:12 GMT
Ok now for the question which I think I know but best to check. Here is the cylinder drawing, my question is about the PTFE packing. On looking at Reeves it has listed various sizes of PTFE although only one size is called packing (1/32), the others ( 1/8 and above) are called yarn but are these basically the same stuff? Also I'm guessing that said packing/yarn is wrapped around the piston rod and then compressed into the recess by the gland nut? Have I understood this correctly and is there anything else at this stage that I should be aware of? Pete BTW : I notice the pictures haven't loaded yet, last time this was due to proboards updating so hopefully they'll show eventually. Attachments:
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Post by Shawki Shlemon on May 5, 2011 10:02:50 GMT
I use this stuff for glands , I wrap couple rounds around the shaft then compress it with the gland ( threaded or plain ) , remove the pressure and then just nip . Teflon expands with heat and seal well . after pressing it will take any shape you like and becomes like a new part ( seal ) , it will last forever .
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Post by Deleted on May 5, 2011 10:43:34 GMT
Thanks Shawki, you've answered my question perfectly ..
Many thanks
Pete
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pondok
Part of the e-furniture
My 5" gauge SAR class 15F
Posts: 359
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Post by pondok on May 5, 2011 14:48:08 GMT
My modest contribution: I once wrapped a plaited length of ptfe plumbers tape around the piston rod and pushed it into the gland box, but it was all quite dry and even after nipping up with the gland nut the tape was partly dragged out of the gland nut as it stuck on the piston rod. I pulled it all out and tried again but this time sprayed the tape with WD-40 and that worked perfectly. I think a bit of steam oil will work just as well.
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Post by Deleted on May 7, 2011 17:47:44 GMT
Hi pondok That's for the input, I've just assembled the cylinders and used WD40 as you suggested, works a treat. Ok on to build Pic277 Here the two holes in the bottom half are being threaded, centre one for the piston rod gland nut is 1/4x40T and the other for the cylinder valve is 3/16x40T. Attachments:
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Post by Deleted on May 7, 2011 17:50:30 GMT
Pic278 The cylinder halfs were then moved to the rotary table for the 4 No.34 holes, this is one of the top cylinders Attachments:
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Post by Deleted on May 7, 2011 17:54:03 GMT
Pic279 Next the bottom half was secured in the rotary chuck and the process repeated , the top half was laid on top after the first hole with a 6BA bolt inserted, the other holes where then drilled using the top half as a check that all was ok. Attachments:
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Post by Deleted on May 7, 2011 17:59:04 GMT
Pic280 The securing bolts have to be turned up from 8BA hex bar as they are locating type requiring a plain shank section for good fit into the No.34 holes and then threaded 6BA. I have to say even though there are only 16 of them it's a soul destroying job making bolts, at least I think so.. Attachments:
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Post by Deleted on May 7, 2011 18:13:15 GMT
Pic281 Rather than give pictures for all of the parts being made I'll show what's involved here and describe all together. Piston rod: from 1/8 stainless steel, overall length is 1 9/16 with 7/16 threaded 5BA. The eye is 1/4 BMS drilled No.30 and 1/8 thick to match rod. Gland nut: 5/16 A/F hex bar turned down 1/4 for 1/4 and threaded 5BA Diaphragm disks are both 1/16 thick, top is 5/8 dia and bottom 25/32. They are chamfered to stop the discs cutting into the diaphragm. Diaphragm is 1/16 rubber. This was trapped between both half's, holes drilled and then trapped with the bolts, it was then a simple task to trim the excess with a scalpel. Everything here had to be made which took a little time but I'm happy with the results. Attachments:
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Post by Deleted on May 7, 2011 18:26:33 GMT
Pic282 The finished cylinders, the piston rod eyes are aligned so that they will line up with the brake shaft once fitted( more about that when I make the support bracket) Other thing to mention is the 3/32 PTFE packing used for sealing the piston rod assembly. Testing via sucking the inlet pipes proved that all 4 cylinders work well both opening and closing. According to Don he's designed a dual vacuum system, I'll understand it's workings better when I have a full system to play with, looking forward to that...:-) Next I'll tackle the cylinder valves which although time consuming I'll enjoy building them myself. More soon Pete Attachments:
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Post by Deleted on May 9, 2011 19:36:30 GMT
Just a couple of pictures for tonight guys Pic283 Here is two of the cylinder valves, one left in component form to show what's involved. These were mainly simple turning although it had to be accurate for the striker pin to work properly. The valve body has a turned spigot at one end that is threaded 3/16x40T to fit into the cylinder, there is also a No.47 hole drilled this end for the striker pin to poke through. From the other end first a 1/8 hole is drilled to a depth of 5/8, this is then opened out to 7/32 for 7/16 of which half is tapped 1/4x40T to accept the end cap that also holds one end of the spring central via a small recess. The striker pin is 3mm BMS turned down to 1/16 for around 15mm and then parted at 17.5mm overall. These pieces fit together in the order seen here, I made a slight modification to the striker pin, the pin seemed a little close to the bottom disc in the vac chamber so I threaded the end 8BA just enough for a nut to fit and lock in place at the correct height, the nut was rounded off a little do that it cleared the 3/16x40T thread without fouling. Last job was to drill and silver solder a length of 1/8 copper 5/8 from the spigot end, the valve had been screwed up tight first to make sure the tube was fitted to the correct hex face and will be cut shorter once all components are fitted and piping is run. Attachments:
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Post by Deleted on May 9, 2011 19:48:42 GMT
Pic284 The finished tender cylinders, the two loco cylinders are also nearly finished accept for the 1/8 copper tube outlets on the valves, I won't fit those until the loco is built and I know what clearance of have around the valves to work out which hex face to fit the tubes too. Next job will be the support brackets which I'm going to fix a little differently to Don so that I have easier access to the brake assembly. As has been pointed out before vac brakes don't have a lot of movement, I can't test the full movement yet but seems not much over 1/4". Applying that amount of movement to the brakes now does operate them but may need tweaking a little to lock the wheels fully, looks like I'll have some R&D ahead of me which personally I'll find fun....:-) More soon guys Pete Attachments:
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Post by Deleted on May 13, 2011 21:17:44 GMT
Hi guys Ok today I've finished the final brake parts except for the copper tubing to connect everything together, that's for another day. Pic285 Brake cylinder support brackets, I've deviated from Don again ( making a habit of that) but only in method. Don states to bend up the brackets from 1"x1/16 steel, drill 1/4 hole for bearing which is turned to suit the fulcrum pieces ( next) , braze all together and shape to drawing. I wanted a sharp 90 degree bend with no radius so decided to make the brackets up from two separate pieces. The picture shows the various parts ready for brazing, rather than make all the parts separately I find it easier and quicker to construct as one piece and then to split them up for final shaping. I soft solder the web piece on after these parts are silver soldered and cleaned. Attachments:
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Post by Deleted on May 13, 2011 21:24:41 GMT
Pic286 Here the fulcrums have been machined and fitted to a cylinder, they start of as 1/4 BMS sq bar chucked in the 4 jaw and 1/8 spigot is turned down to 5/32 dia and the the job is parted at 5/16 overall. Finally a hole is drilled into the 3/16 length of 1/4 sq bar and tapped 6BA. Attachments:
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