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Post by Roger on Oct 30, 2014 12:55:02 GMT
A milling machine will transform what you can do, that's well worth buying. Tiny cuts are all very well on a light machine if you can get a CNC to turn the handles while you have a cup of tea, but otherwise it seriously limits its use.
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Post by GWR 101 on Oct 30, 2014 13:31:14 GMT
Hi DC, not sure about how much extra work to make from solid as I have not seen the drawings for Juliet 1. Juliet 2 has valve chests on top of the cylinders, I machined all mine before I had a milling machine using the lathe where possible and a night school miller when needed. I feel its a great advantage to have your own miller as you can leave the work piece set up at the end of a shift (I now have a very good second hand one and find it a great asset). There is probably more work in making from solid but how much is dependent on the design but if there is a significant cost saving then it is a way to go. Regards Paul
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dc309
Seasoned Member
Posts: 146
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Post by dc309 on Oct 30, 2014 20:23:23 GMT
I'll probably invest in buying a set of castings this time round then I think. My wheels should arrive tomorrow hopefully, I've already got my axle and axlebox material ready to go. It will be another week before I get anything done as I'm otherwise engaged this weekend
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Post by GWR 101 on Oct 31, 2014 0:04:13 GMT
Hi, hope all goes well with the wheels its been ages since I machined mine and I don't think there were any surprises. I machined the horns, axles and axlebox's to the drawing and they seem ok. Regards Paul
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dc309
Seasoned Member
Posts: 146
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Post by dc309 on Nov 4, 2014 21:49:28 GMT
Hi, Whilst I haven't been able to do any machining recently, I've had a go at learning CAD (which seems to be popular on here at the moment!). I'm finding it quite difficult to get my head around it, but I've got a few bits done. I know that it isn't as good as Rob's 15xx drawings or Roger's 15xx drawings, but here is my attempt at a simple coupling rod
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Post by Rob on Nov 4, 2014 21:58:05 GMT
I disagree entirely DC, I think that's every bit as good as what I've done, in fact, nothing I've done is such a complex shape CAD certainly is a popular topic at the moment. When you start deviating from the drawings it really does help no end.
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dc309
Seasoned Member
Posts: 146
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Post by dc309 on Nov 4, 2014 22:02:21 GMT
Thank you for your kind words Rob. I'm sure with a bit more practice I might be able to draw the rest of the loco (he says)! I've not attempted an assembly yet, but there is only one way to learn how to do it I guess
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Post by Rob on Nov 4, 2014 22:11:07 GMT
That was my view - get stuck in Out of curiosity, what CAD software are you using?
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Post by Roger on Nov 4, 2014 22:15:13 GMT
I agree with Rob, it's a good model. The main thing is that you've made the shape you wanted and now you know one way of doing it. Things like the scollups can be done in several ways. I tend to make the whole part in the way I'd make it. In other words I'd model the part at the full width and then cut out the scollup from the side. If you end up using CAM, I'd advise that you make sure that the cuts you make like that don't extend beyond the boundary of the physical part. That's because the software looks at all the sketches and thinks that the bounding box for the whole model is defined by those. If you extend sketches beyond the part you mean to end up with, you can end up with issues when you set the machine zero to the corner of the job because the corner may not be where you think it is. I think it's a good habit to get into even if you don't use CAM now.
I'd also add the holes in the rod ends as a separate sketch, again for CAM reasons. If you never intend to use CAM then it's not so important but I've found that a model that's made up of many named sketches is easier to modify at a later date than one that has loads of holes on the profile with the whole thing extruded. It's purely a matter of personal preference and you will find out what works for you, there are very few 'right' ways to go about these things.
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dc309
Seasoned Member
Posts: 146
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Post by dc309 on Nov 4, 2014 22:22:34 GMT
I've been given a copy of Autodesk Inventor 2011 to learn on. I'm finding it quite hard at the moment (it took me about 2 1/2 hours to draw that simple part out) but I will get there Thanks Roger! I made the scollups by just adding fillets in the sketch so when it was extruded, they were added in. I'm quite pleased with the way that it has turned out, so I may crack on and move onto the next part of the valve gear. I think I can cope with the simple parts, but when it comes to drawing the cylinders with the ports etc I may struggle!
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Post by Roger on Nov 5, 2014 8:43:55 GMT
I've been given a copy of Autodesk Inventor 2011 to learn on. I'm finding it quite hard at the moment (it took me about 2 1/2 hours to draw that simple part out) but I will get there Thanks Roger! I made the scollups by just adding fillets in the sketch so when it was extruded, they were added in. I'm quite pleased with the way that it has turned out, so I may crack on and move onto the next part of the valve gear. I think I can cope with the simple parts, but when it comes to drawing the cylinders with the ports etc I may struggle! You'll find that you re-use the same techniques all the time, there aren't a huge number of the fundamental ones you use all the time. Each new issue you come across and solve will get used again so it's a productive process. The hardest part with cylinders is the drillways because you will probably need to define a new plane at the right orientation to sketch on. Alibre is a but clumsy in my opinion when it comes to this, Autodesk might be better. You'll get much quicker with practice, it takes me very little time to knock up a model these days, you'll soon be the same. Good fun isn't it!
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dc309
Seasoned Member
Posts: 146
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Post by dc309 on Nov 5, 2014 18:39:58 GMT
I'm going to have a go at a few more bits tonight after tea, so I'll let you know how I get on. Not quite at the cylinder stage just yet!
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
Posts: 2,269
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Post by smallbrother on Nov 5, 2014 21:23:28 GMT
I'm stuck trying to marry up the frames at right angles with the buffer beams, and getting the brackets in place!
The 50+ year old drawings are the least of my worries......
Pete
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dc309
Seasoned Member
Posts: 146
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Post by dc309 on Nov 5, 2014 23:10:50 GMT
I have started to do a frame assembly, but I've had so much trouble trying to get things to line up with each other. The frames need more holes putting in, but here is the assembly as it stands so far;
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Post by Roger on Nov 6, 2014 8:42:47 GMT
Excellent work. I know what you mean about getting things to line up. I presume you used constraints? Don't be tempted to move things into the correct positions manually, you'll end up with an assembly that can fall apart or one that looks like things mate when they don't. It always looks a bit strange when you pull items onto a sheet to assemble them because they are often in entirely the wrong orientation. I always lock the main part in position first. Then I use constraints on faces to get the part to drag itself round to the correct orientation. That takes a bit of getting used to. On Alibre with the Quick Constraint feature you can reverse the connection if it mates it the wrong way round. Using the fixing holes on mating parts is favourite where possible. You model is a bit tricky because there are no obvious things to mate in the vertical direction. In cases like that, you can use say the top of the frame as one half of the constraint, and the top of the buffer as the other. Then use an offset in that mating constraint to put them the desired distance from the top. Anyway, that's great progress.
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Post by Rob on Nov 6, 2014 10:42:39 GMT
I agree with Roger. It took me some time experimenting with the various different constraint options before I got to grips with it. It also helped that I finally found the 'free-rotate' camera option (In Cubify, that's the left and right mouse buttons together) which helps the process no end.
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Post by Roger on Nov 6, 2014 11:27:42 GMT
I agree with Roger. It took me some time experimenting with the various different constraint options before I got to grips with it. It also helped that I finally found the 'free-rotate' camera option (In Cubify, that's the left and right mouse buttons together) which helps the process no end. I'll have to try that, I've not heard of that one!
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Post by Deleted on Nov 6, 2014 11:47:29 GMT
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Post by Rob on Nov 6, 2014 11:58:41 GMT
I'll have to try that, I've not heard of that one! It makes things so much easier! I had been fighting with the pre-defined views, but the ability to alter the angle slightly, or rotate around a particular location is fantastic. I thought at the time it was odd that they didn't seem to have a free camera mode on any of the usual buttons you associate with 3D programs, and it wasn't until I was messing about with the laptop that I found it. Holding down both buttons on my laptop imitates the scroll wheel button of a standard mouse, and it was as I was doing this to 'drag' the view, that I clicked the right button slightly before the left, which enabled the rotate camera mode. As the mouse has a scroll wheel button by default, there's no conflict in functionality so this option works all the time regardless of click order.
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Post by Deleted on Nov 6, 2014 14:51:29 GMT
Just a quick note for anyone building the Stephenson link version of Juliet. A friend asked me to look at the valve gear design and modify it if necessary as he wants to build one but had heard bad things about the original valve gear design. I've completely redesigned the valve gear and produced a pdf showing the changes and new dimensions for parts. The modification is basically altering the suspension point of the expansion link from the end to the middle and recalculating the length of the eccentric rods, position of the weighshaft, eccentric throw, etc. I've also done a drawing showing how to set the position of the eccentrics accurately using Don's jig method. The new design is much better the original LBSC one and gives very good valve events in forward and reverse at all cut offs whereas LBSC's is poor.
I haven't 3D modelled the new design to make sure everything fits properly (although I'm pretty sure it will) but could do so if anyone wants to try it.
John
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