jem
Elder Statesman
Posts: 1,072
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Post by jem on Oct 19, 2019 16:43:59 GMT
Can you get left hand spiral milling cutters, that would solve your problem Roger on cutting hexagons as above? I am sure that I picked up one once!
best wishes for a most interesting thread
Jem
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Andrew C
Part of the e-furniture
Posts: 447
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Post by Andrew C on Oct 19, 2019 17:41:01 GMT
Hi Roger
Do you intend to thin out the whole of the safety valve bonnet? or just the top where it can bee seen? and leave the bottom once you are at the base of the valves. just make the hole big enough for the boiler bush. You still would need to cut the two side slots for the top feeds, and there would be a bit more meat to solder the clack covers to.
Just a thought.
Regards,
Andrew
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Post by Roger on Oct 19, 2019 18:32:43 GMT
Can you get left hand spiral milling cutters, that would solve your problem Roger on cutting hexagons as above? I am sure that I picked up one once! best wishes for a most interesting thread Jem Hi Jem, You can, but they're not mainstream stock so are expensive if you can find them at all. It's a good solution, especially if you've got a lot of them to do. Since they're outside cuts, you only need one size really. I ought to look out for one on eBay at the right price for this sort of job.
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Post by Roger on Oct 19, 2019 18:38:21 GMT
Hi Roger Do you intend to thin out the whole of the safety valve bonnet? or just the top where it can bee seen? and leave the bottom once you are at the base of the valves. just make the hole big enough for the boiler bush. You still would need to cut the two side slots for the top feeds, and there would be a bit more meat to solder the clack covers to. Just a thought. Regards, Andrew Hi Andrew, Yes, it's all going to be pretty thin because the safety valve and top feed unit it covers is large. There might be some places it could be a little thicker, but I'll probably just make it the same thickness throughout. I'll probably cut out the shoulders while it's still on the mandrel, using a small cutter to keep the forces low and enabling a thin bridging piece to be left around the base of the skirt to hold it together during machining. I haven't given a lot of thought to attaching the shoulders, hopefully I can jig them and Silver Solder those on. It doesn't have to be a perfect joint, the joint on the real thing is a bit scrappy. 20191019_211808 by Timothy Froud, on Flickr 20191019_211718 by Timothy Froud, on Flickr
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Post by Roger on Oct 19, 2019 20:49:57 GMT
So this it the lump of Brass I'm going to make the Safety Valve Bonnet from. It's 75mm diameter which is about 8mm too big and about 15mm too long. Here it's getting the attachment hole for the M10 Cap screw and the two 4mm dowels 20191019_125431 by Timothy Froud, on Flickr The mandrel has the same 4mm dowels and an M10 thread about 30mm deep. I've added some permanent Loctite to the face and some screwlock to the thread, I don't want this coming loose. The cleaned up area on the mandrel is the reference for tool setting and clocking up. 20191019_132250 by Timothy Froud, on Flickr I'm roughing out a decent amount of stock so I don't have to machine that on the mill. I'm just plunging in with the 3mm wide parting blade which is razor sharp and makes short work of it. 20191019_143318 by Timothy Froud, on Flickr The diameter I'm touching with the wobbler was first clocked, spinning the chuck on its axis. It's vital that this is true to the centre of rotation as it's Zero in the Z-axis for the 3D model in the CAM output. Here I'm using the wobbler on the front and back at the same height so I know I can get the true middle of the bar and hence the centre of rotation in the Y-axis. 20191019_150253 by Timothy Froud, on Flickr The end of the stock needs to be about 0.2mm outside of the Zero in the X-axis so I know it will clean up. I'm using the wobbler to find the end and then moving in the wobbler radius plus 0.2mm before setting the X-axis DRO to zero. 20191019_150619 by Timothy Froud, on Flickr Then I'm noving to the chuck face and making a note of the reading when it finds the edge. That's the only way to find my way back to the X-axis position if the power is lost or the machine is shut down. The rotary table is set to zero so I can flip it over to 180 degrees for the other side. 20191019_150939 by Timothy Froud, on Flickr I'm using Horizontal Finishing instead of removing all the stock (that's already been turned off). That would have saved a lot more time if the CAM program would behave itself and create an entry path, but it won't. So I'm left with a slow plunge straight into the edge of the job which takes a lot more time. The quill was moved down by hand to touch the tool on the turned portion of the Steel mandrel. I've made a note of the radius of that, and that's the value that's put in the Z-axis DRO so the machine has a reference to the centre of the bar which is zero. This is not the way most CNC machines work. You normally have to set the tool heights off the machine. There are pros and cons for each, but I like the flexibility this arrangement gives. I've also checked that I can reach the zero point in the Z-axis without running out of travel on the knee. 20191019_160140 by Timothy Froud, on Flickr 20191019_162147 by Timothy Froud, on Flickr 20191019_172313 by Timothy Froud, on Flickr 20191019_175906 by Timothy Froud, on Flickr 20191019_182446 by Timothy Froud, on Flickr 20191019_211155 by Timothy Froud, on Flickr You can see the difference in the two sides from this angle. Remember this is sitting on a tapered barrel. In this view, the boiler axis would be left to right. I've gone 1mm below the centre line to make sure it doesn't leave a wafer when both sides are machined. You can set max and min absolute heights when you set up the machining operation in the CAM module. 20191019_211205 by Timothy Froud, on Flickr Flipping it over, I've made a few changes to the path to get it to stay with the head down for more of the cut. This will save a lot of time. Here's a wobbly video of the cut progressing, you can see it stays down at the end of the cut and goes down at an angle to the next one. This is the sort of situation where it can all go horribly wrong, taking too big a cut. You have to be very cautious about feeds and speeds and slow it up on the first couple of these to see how it behaves. 20191019_211628 by Timothy Froud, on Flickr 20191019_213133 by Timothy Froud, on Flickr
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Post by Roger on Oct 20, 2019 14:16:52 GMT
The top end of the Safety Valve Bonnet will need finishing off where it's attached to the mandrel, and that poses the problem of how to hold it. Since there's a tapered internal portion, I suppose you could use that, but it would probably require a split sleeve since the top is bigger than the outside of the tapered portion. Since I've now got a 3D printer, another solution is to hold the skirt in a printed fixture such as this. I've used three fixings so that I can hold the base in the 3-jaw chuck. There's room under the lugs to put a 5mm nut and washer. Fixture by Timothy Froud, on Flickr Obviously this requires the shape to be pretty true to the 3D model, but doubtless there will be a little flexiblilty in the fixture. In any case, the whole face doesn't have to be a perfectly clamped setup, so long as it gets a good grip on it. Exploded fixture assembly by Timothy Froud, on Flickr
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Post by Roger on Oct 20, 2019 19:41:59 GMT
So this is how it looks after the initial roughing out with a 12mm flat bottomed cutter. The finish is of course absolutely dire, but of no consequence. I've left 0.5mm stock for the next two cuts. 20191020_104131 by Timothy Froud, on Flickr 20191020_104137 by Timothy Froud, on Flickr I've hung the 8mm ball nosed cutter out this far because the centre of the ball needs to be able to reach down to 1mm below the centre line of the part, so that's a full 5mm further down than the tip. It's easy to get caught out by this sort of thing and crash the chuck into the part. The tool height is being set to the known radius I noted earlier for this part of the mandrel. That makes the tip of the ball exactly zero as far as the model is concerned which is the centre of rotation of the rotary table. 20191020_104808 by Timothy Froud, on Flickr 20191020_110320 by Timothy Froud, on Flickr The step over is a bit coarse on this side... 20191020_122224 by Timothy Froud, on Flickr ... so I halved it on the other side. This takes the 0.5mm remaining stock down to 0.2mm 20191020_133154 by Timothy Froud, on Flickr I'm using my utility program to flip the sign in the Y-axis and saving the program as "Y-mirrored ... " so I can see I'm using the right file. The utility program does add a comment inside the G-Code to say Y-mirror as a double check. It's easy to get muddled up and scrap the job so you have to be really careful to only use the Mirrored versions when the rotary table is set to 180 degrees! 20191020_142658 by Timothy Froud, on Flickr Finally, here's the fine finishing cut with a 0.15mm overlap which takes it down to 0.1mm from size. I'm going to leave it like that for hand finishing and to allow for any runout on the tool which might otherwise take it under size. It's so thin that I don't want to lose thickness unnecessarily. It's hopefully going to end up 0.8mm thick. Againm the ball nosed cutter is going 1mm below the join line. 20191020_151718 by Timothy Froud, on Flickr 20191020_164311 by Timothy Froud, on Flickr 20191020_173009 by Timothy Froud, on Flickr Both sides done, and you can see that it could have used to have been even finer on the overlap. I'd normally use 0.1mm but I knew I only had today to get this done and I didn't want to stop mid cut because it leaves a witness. I'm using a fairly large ball nose diameter so the finish is pretty good anyway. The finish on the top is plenty good enough but the sides will need some hand finishing. The good thing is that the finished surface is at the full depth of the scollups, so once they've been smoothed over, it will be exactly to size. The setup must have been good, and the backlash compensation not bad either because there's no step that I can feel on the side at all. How round it is is another matter, but I don't suppose it will be far out. 20191020_201402 by Timothy Froud, on Flickr 20191020_201429 by Timothy Froud, on Flickr Anyway, so far, so good, I've been preparing the programs for machining the inside, so I'll tackle that on Tuesday. I'm tied up all day tomorrow on another job, so it's going to have to wait. I'm much heartened though, I thought this might be a nightmare, but so far it's proving to be fairly straightforward. I suppose that's down to good planning and a solid setup as well as not being too greedy in the depth of cuts. I can see now that there's a 'skim' option on the clearance settings to the retract height, so that's something I will experiment with before I tackle another job like this, because it could save a huge amount of time.
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,976
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Post by JonL on Oct 20, 2019 22:57:26 GMT
Lovely work; well done Roger.
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Post by Roger on Oct 21, 2019 20:40:52 GMT
No time on 1501 today, I've had to work all day for a change. However, I printed this overnight so that was here to greet me when I got home this evening. That took 8 hours 43minutes according to the display. That's because I printed it with four perimeters, 20% infill and 0.15mm layer height to make it strong and accurate. You can see the support material that was selected for on the slicer to cope with the fact that the lugs on the LH part are overhanging. You can get away with bridges where it can string across a gap, but not where there's nothing on the other side to join up to as a support. In these cases you have to tell it to use supports, this time only from the bed up to the lugs. It's pretty fragile you you can break the supports away when it's finished. Flat supported surfaces to leave a pretty horrible finish on the supported face, but in this case it doesn't matter. 20191021_201823 by Timothy Froud, on Flickr
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Post by Roger on Oct 22, 2019 20:54:04 GMT
A full days machining today to make up for yesterdays lack of progress. Setting this up accurately is absolutely vital to getting the thickness of the part nice and even. To that end, I'm clocking around the outside of the conical section as close to the skirt as possible. I'm assuming that the rotary table isn't perfectly upright. I could have used the inside diameter which was turned on the lathe, but it's better to use something that was created by the last operation. It's surprisingly round, considering the way it was made. I reckon it's no more than ten microns out. 20191022_114936 by Timothy Froud, on Flickr If you recall, I measured the distance from the end of the stock to the face of the chuck when it was in the horizontal position, so I'm using that to set the tool to that -ve distance like this. I've zeroed the DRO on the quill as a sanity check... 20191022_120922 by Timothy Froud, on Flickr ... moving the Z axis up to zero, the top is -0.18mm which would be -0.2mm if it was perfectly measured. Anyway, it's enough to satisfy me that it's safe to continue with the quill locked up at zero on the DRO. 20191022_121018 by Timothy Froud, on Flickr I'm machining the whole of the inside profile with individual radial operations, reducing the stock left each time. There isn't a clearance option with this kind of function. I've guessed the first offset to be 12mm which just clipped the edge at this point. I'm running it very slowly indeed and checking to see if it's going to take too deep a cut. As it happens, it's not enough, so I changed it to 11.5mm to remove a bit more... 20191022_121624 by Timothy Froud, on Flickr 20191022_121718 by Timothy Froud, on Flickr ... and this was the result. 20191022_124131 by Timothy Froud, on Flickr So I proceeded to take 1mm cuts each time... 20191022_141903 by Timothy Froud, on Flickr ... gradually removing the bulk of the material. You have to be cautious with the feeds because although it's happy to cut on the way down, when it moves across and starts the upward cut, the side of the cutter is plunged into a near vertical inside diameter and it can be a bit brutal. 20191022_145624 by Timothy Froud, on Flickr At this stage there's 1.5mm still to go, so it's time to switch from the 10mm flat bottomed cutter to a Ball nosed one. 20191022_153401 by Timothy Froud, on Flickr I've reduced the step over to start to get a smoother finish, as we head towards the final size. Leaving it too rough will end up with a poor finish if you switch straight to a very small step over. 20191022_155446 by Timothy Froud, on Flickr 20191022_170920 by Timothy Froud, on Flickr 20191022_171200 by Timothy Froud, on Flickr This is with a finer step over and only removing 0.35mm as it's starting to get thin 20191022_172110 by Timothy Froud, on Flickr 20191022_183903 by Timothy Froud, on Flickr Finally were' down to 0.2mm step over at the outside which obviously is a lot finer at the middle. This cut takes us to zero stock so it ought to be to size. Measuring the thickness of the edge, it's 0.85mm whereas it's supposed to be 0.8mm. I'd left an additional 0.1mm on the outside because runout of the cutter would make it go undersize. As it happens, it's not too bad. 20191022_212325 by Timothy Froud, on Flickr 20191022_212334 by Timothy Froud, on Flickr And finally, the 3D printed fixture fits like a glove, so I'm calling this step done. 20191022_212602 by Timothy Froud, on Flickr
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timo
E-xcellent poster
Completing 3 1/2 Rainhill .Building 5" Railmotor and waiting to start 3 1/2" King
Posts: 234
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Post by timo on Oct 22, 2019 21:36:34 GMT
Roger,
Amazing!
Tim
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Post by Roger on Oct 22, 2019 21:40:07 GMT
Glad you like it Tim, it actually wasn't as hard as I thought it would be. Still, it's not finished yet, and I can still cock it up!
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timo
E-xcellent poster
Completing 3 1/2 Rainhill .Building 5" Railmotor and waiting to start 3 1/2" King
Posts: 234
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Post by timo on Oct 22, 2019 21:45:31 GMT
Roger,
It looks terrifyingly difficult to me! It is so thin at the end of the machining sequence. I am glad that Rail Motor is only loosely based on a prototype so there is lots of leeway. Don't want to think about the 3 1/2" King....
Tim
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Post by Roger on Oct 22, 2019 22:06:20 GMT
Roger, It looks terrifyingly difficult to me! It is so thin at the end of the machining sequence. I am glad that Rail Motor is only loosely based on a prototype so there is lots of leeway. Don't want to think about the 3 1/2" King.... Tim In the end you just have to set it up as accurately as you can and trust that the depths and geometry are correct. It doesn't really matter that it's thin, that just means you can't take liberties with how aggressively you cut it. Of course it shows if it's not an even thickness though. I reckon I could have cut it to 0.4mm thick which would have been closer to scale, but it would have been too flimsy, I'll probably thin the edges out a little to make it look thinner. It's not as difficult as it looks, especially when you've done a few things like this.
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Post by delaplume on Oct 23, 2019 10:36:48 GMT
Quote}------- "Still, it's not finished yet, and I can still cock it up!"........Don't you dare !!..LoL !!.....
Roger,.........My Gob is well and truly smacked------my ghast likewise flabbered !!
Those things are a pain at the best of times even when using a decent casting for instance but here we have a Master Class demon-stration ( Apologies to Fred Dibnah ) before our very eyes through the "magic" of modern technology....
I think a lot of non-GWR folk don't appreciate the different variations that were fitted due mainly to what boiler the covers were on top of......For instance think of the difference in size between a King boiler and that of a small prairie ( 45xx )....The King's Flower Pot is quite short and dumpy whereas the 45's is tall and the base is severely angled due to it being positioned on a short cone ....
The 15xx's Std.No.10 Boiler is not too bad in either respect giving a reasonable height and an almost flat bottom...
Have you given any thought as to how the shoulders will be made ??
Keep the faith !!
Alan
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pault
Elder Statesman
Posts: 1,500
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Post by pault on Oct 23, 2019 11:56:43 GMT
Hi Roger A very nice bit of work, far better than tin bashing. One thing you might want to consider is what happens to the steam coming out of the safety valves. On one GWR loco I was involved with, the steam used to mainly come out around the cut outs in the bonnet where the boiler feeds go in. this was cured with a tube which went over the safety valves and directed the steam upwards.
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Post by Roger on Oct 23, 2019 18:04:04 GMT
Quote}------- "Still, it's not finished yet, and I can still cock it up!"........Don't you dare !!..LoL !!..... Roger,.........My Gob is well and truly smacked------my ghast likewise flabbered !! Those things are a pain at the best of times even when using a decent casting for instance but here we have a Master Class demon-stration ( Apologies to Fred Dibnah ) before our very eyes through the "magic" of modern technology.... I think a lot of non-GWR folk don't appreciate the different variations that were fitted due mainly to what boiler the covers were on top of......For instance think of the difference in size between a King boiler and that of a small prairie ( 45xx )....The King's Flower Pot is quite short and dumpy whereas the 45's is tall and the base is severely angled due to it being positioned on a short cone .... The 15xx's Std.No.10 Boiler is not too bad in either respect giving a reasonable height and an almost flat bottom... Have you given any thought as to how the shoulders will be made ?? Keep the faith !! Alan Thanks Alan, The shoulders will also be machined from solid, in that case 25mm round brass bar. Watch this space...
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Post by Roger on Oct 23, 2019 18:07:13 GMT
Hi Roger A very nice bit of work, far better than tin bashing. One thing you might want to consider is what happens to the steam coming out of the safety valves. On one GWR loco I was involved with, the steam used to mainly come out around the cut outs in the bonnet where the boiler feeds go in. this was cured with a tube which went over the safety valves and directed the steam upwards. Thanks Paul, That's certainly something I could fit. I'll probably wait and see what happened before making a decision though. You're probably right.
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Post by Roger on Oct 23, 2019 21:33:19 GMT
If you recall, I'd made a note of the X DRO position of the chuck face when this was originally set up in this orientation, and this is why it was necessary. The end of the part has been machined away, so that end can't be used as a reference any more. 20191023_094015 by Timothy Froud, on Flickr A quick sanity check to see if zero looks right. 20191023_094107 by Timothy Froud, on Flickr Again, the tool is set on the known radius of the mandrel 20191023_101007 by Timothy Froud, on Flickr I've machined this in two operations on each side to shorten the cutting time. I've created a tool path for the top 8mm which only cleans up the flange, there's no point in the tool following the whole cutout profile. 20191023_180128 by Timothy Froud, on Flickr There's plenty of material left on the skirt to make it strong for the next operation. 20191023_180137 by Timothy Froud, on Flickr While it was still on the mandrel, it was easier to hold it in the 'Vice on a stick' so I could remove the machining marks. If I did this again, I'd have done another cut with much finer step over. 20191023_181025 by Timothy Froud, on Flickr Anyway, an hour with a needle file and various emery papers got it to this semi-finished state. 20191023_194307 by Timothy Froud, on Flickr 20191023_195534 by Timothy Froud, on Flickr Time to part it off carefully. The Brass piece in the drill chuck is to stop it falling off and getting a dent. 20191023_200924 by Timothy Froud, on Flickr I stopped the cut as it was nearing the finish and pulled the chuck over by hand before breaking it off the last bit. 20191023_201549 by Timothy Froud, on Flickr 20191023_201619 by Timothy Froud, on Flickr The fixture fits a treat and really gets hold of it... 20191023_202809 by Timothy Froud, on Flickr ... although you can't hold it that tightly in the chuck. It's enough to gingerly tidy up the inside and get rid of most of the unwanted material. 20191023_205015 by Timothy Froud, on Flickr Back onto the mill for the top rim details. The fixture has been tapped down onto the parallels, it needs to be dead flat on the top. the centre needs to be really accurate too. This is done with the quill locked to the same position on the locking handle. There's a scribed line I've added so I know it's always done up to the same tightness so it's repeatable if there's any movement as it locks. It doesnt' matter what orientation this is set up in because the top is circular. 20191023_211216 by Timothy Froud, on Flickr I don't really want to rely on the fixture to set the tool height. Fortunately the underside of the shoulder cutout to the top is a figure I can find from the 2D drawing output. I've found some Silver Steel that just happend to nicely wedge between the top of the fixture and the underside of the cutout. 20191023_213023 by Timothy Froud, on Flickr That allowed the tool to be dropped onto the rod to set it to the top of the radius. I entered the negative value of this in the X DRO and set the quill DRO too. 20191023_213517 by Timothy Froud, on Flickr This is with the Z-axis moved up to zero and the quill moved down so the tool just touched the top of the job. There's 0.3mm still to come off and that looks right, so I moved the tool out of the way and locked the quill up at zero. 20191023_213636 by Timothy Froud, on Flickr I guessed the initial offset as 2.5mm which was a touch high, so this is the cut with it at 1.5mm still to go. The cuts are all in the downwards direction, I'm stopping it from doing a continuous cut because I don't want it to pull out of the chuck. The forces are pretty small, but a sideways engagement on the near vertical part could nudge it over. 20191023_215241 by Timothy Froud, on Flickr I then copied and pasted another series of operations and altered the cut to leave 0.2mm less on each one. The overlap on the outside is 2mm and each pass round takes about half an hour. I'm taking this gently because I don't want to risk anything moving at this late stage. I'm stopping at 0.4mm stock still to go so I can measure the rim and then create the final finishing operations based on what that measurement it. I've made the material just inside the rim slightly thinner and made sure there's a pronounced drop to give the impression of the rolled edge.
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Post by Oily Rag on Oct 23, 2019 21:39:52 GMT
Crikey
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