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Post by terrier060 on May 2, 2018 23:41:31 GMT
Hi Roger I will take another look at it, but I think the drawing that I have may not be detailed enough for such fine analysis. In fact the shape of the base appears to have a different curve in side elevation to front! Chimnat 02 by Ed Cloutman, on Flickr Chimney by Ed Cloutman, on Flickr
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Post by chris vine on May 3, 2018 0:55:14 GMT
Hi Ed,
I have come across the problem of different radii before. Sometimes it is the distance that the fillet/radius reaches to which your eye picks up, rather than the radius (of the radius!) itself. I had this when putting a radius inside a parallelogram years ago. The tighter angles had to have much tighter radii than the obtuse angles in order to make the fillets look the same, IE cut off the same amount of corner.
In your case, if the radii all start at the same height up the chimney, IE a circle some 12" above the smokebox, then the side radii have to reach further down the side of the smokebox than the front and rear radii, which only have to reach to the top of the smokebox. So the side radii have to be bigger. In addition, the side ones don't have to turn through a full 90 degrees as the smokebox sides are running downwards, in a similar direction to the sides of the flare.
I have no idea how a computer can make any sense of this at all!! However watching the video you mentioned makes it a bit clearer.
All clever stuff and, one day, I would love to start 3D modelling too...
Chris.
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Post by Roger on May 3, 2018 5:42:44 GMT
Hi Ed, I wonder if that drawing shows the inside of the chimney on the left and the outside on the right? Looking at the side elevation, the radius isn't constant in that direction, so your model might actually be very close to the intended shape. It looks like the initial shallow radius from the top is very similar in both directions. That's not the case with the short chimney on 1501 which has a well defined small and large radius, which is why you can't do it that way on that design, but have to define the lofts as cross sections in the radial direction or use guide curves.
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Post by terrier060 on May 3, 2018 16:18:43 GMT
Well it appears to have done something Roger! I fell asleep while it was going through the simulation and it looked like this when I woke up. Been doing some heavy gardening. Dome milling path by Ed Cloutman, on Flickr
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Post by Roger on May 3, 2018 17:54:11 GMT
This is a good start! You ought to be able to check the run time of that path, and you'll probably be horrified at how long it is.
This is where the real spade work begins. Removing the stock you don't want quickly is a real challenge. If Fusion allows you to define a 3D model of the stock, that would be a huge help. Mine isn't that smart, it only allows for rectangular stock. This means that you'll get a path like yours where it clears right out to the extremities of the stock, even if it's not there. If you could rough turn a blank and then define that for the CAM stock, it would be a major improvement.
I'm assuming that you're using a Horizontal Roughing operation for this with a large end mill or Ripper to remove the bulk of the stock, and then following it with Horizontal Finishing operations with a Ball nosed cutter. You might find it a lot quicker to remove the middle on the lathe. You can define 'Containment regions' which are just sketches to keep the cutter contained within or excluded from an area.
If you're using a Ball nosed cutter to finish it, you'll find you won't be able to reach the bottom of the flare with that flange in place. You'll probably have to add a bit more to the model in that area so the centre if the ball nose can reach down to the end of the flare if you see what I mean. It's the practical details like these that help decide the best overall strategy from beginning to end.
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Post by terrier060 on May 3, 2018 21:58:34 GMT
Hi Roger. I don't really know what I am doing at the moment - I basically let the software tell me what to do. I used a facing mill to skim the top face, then a 0.5" end mill to rough out first the short parallel part and then the flange. Then I repeated with a smaller cutter, but have not really defined the feed etc. I will do some more study.
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Post by Roger on May 3, 2018 22:36:38 GMT
Fair enough, it's early days. One thing you'll find is that you have to decide on a strategy yourself, the software won't really help you other than displaying the results of your choices. In general, I've found that any geometry that can be machined by simple 2D profiling or pocketing is very much faster and more efficient than using 3D machining. I only use 3D machining operations when I absolutely have to else the machining times become too long. Take a look at the way the tool enters the material. Try to aim for a very shallow approach along the tool path. I use 5 degrees for just about everything and that works pretty well. I wouldn't go any more than that.
I don't know the nomenclature used in Fusion360, but in Alibre 'Roughing' means it's going to remove all of the material defined in the stock model. 'Finishing' means it ignores the stock and only follows the 3D model boundary. I use 'Finishing' strategies for secondary roughing by telling it to leave a lot of stock on the part. Sometimes that's all I use, it depends on the part.
What you'll find is that using big cutters and deep cuts is great for removing material, but you can't then switch to very small cutters. I use a progression of cutters to knock the 'steps' off that are left from the cuts with large diameter tools.
Anyway, playing with it is the best way to learn. Develop an Eagle eye for the entry moves, that's where most of the accidents occur. View it from the side and zoom in to make sure the cutter plunges clear of the work and then slopes in.
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jma1009
Elder Statesman
Posts: 5,901
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Post by jma1009 on May 3, 2018 23:03:41 GMT
Hi Ed,
Your pics of the Stroudley chimney and dome base are excellent. In my case I turned the outside (mean) profile of the chimney and dome bases in the lathe then the rest was a filing job. A decent new bastard half round file makes in my case short work of getting everything else close to size. I enjoy filing.
I have always taken the view that the base of a chimney and dome should not be a circle but an 'oval' on these Victorian locos, if this makes sense. The sides are wider than fore and aft.
I appreciate that on a 7.25" Terrier you have more metal to remove than in 5"g.
Cheers,
Julian
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Post by terrier060 on May 3, 2018 23:42:48 GMT
Thanks Julian - yes you could be right which would explain the slightly different shape of the front and side elevations. You are probably going to shoot me, but I have got the CNC bug - a bit late in life at 72, but I have always enjoyed using CAD both at work and play. All I need is the machine, and before that I need to find space for it! I have made several domes and chimneys the hard way from castings. Now I would like to stand back and let the machine do all the hard work while I get on with something else. We have both seen what can be achieved as I believe like me you have visited Roger. The fine detail he has achieved has to be seen to be believed. If you scale down a rough casting from full size, the result in our scales is as smooth as a babies bottom! That is what Roger achieves. I intend to turn the top in copper, the pipe in steel (probably stainless as I have used that for all the motion work), and the base CNC. The three parts will be located on a sleeve which will be fitted to the smokebox. The flange will cover the fixing screws. Only the weight of the chimney and loose friction-fit will keep the chimney in place. This is the method I have used on my other locos. Below is the simulation of the chimney base. Chimney Flange by Ed Cloutman, on Flickr
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Post by terrier060 on May 4, 2018 0:20:21 GMT
Hi Ed, I have come across the problem of different radii before. Sometimes it is the distance that the fillet/radius reaches to which your eye picks up, rather than the radius (of the radius!) itself. I had this when putting a radius inside a parallelogram years ago. The tighter angles had to have much tighter radii than the obtuse angles in order to make the fillets look the same, IE cut off the same amount of corner. In your case, if the radii all start at the same height up the chimney, IE a circle some 12" above the smokebox, then the side radii have to reach further down the side of the smokebox than the front and rear radii, which only have to reach to the top of the smokebox. So the side radii have to be bigger. In addition, the side ones don't have to turn through a full 90 degrees as the smokebox sides are running downwards, in a similar direction to the sides of the flare. I have no idea how a computer can make any sense of this at all!! However watching the video you mentioned makes it a bit clearer. All clever stuff and, one day, I would love to start 3D modelling too... Chris. Hi Chris - yes it is a new challenge. I love working in 3D, but am very new to it. I have mostly used Blender which is a great free program and worth trying. As with all these things there is masses to help one on YouTube. I have added the steps in Fusion 360 to machine the flange. It is great to watch it taking place as it has an excellent simulation program which suddenly flashed red if there is a tool or tool holder collision. It required quite a long tool to reach the bottom of the flange(about a 3" length. This is where the experience that Roger has comes into its own. I have no idea yet whether the tool would be strong enough.
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Post by terrier060 on May 4, 2018 0:31:43 GMT
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Post by steamer5 on May 4, 2018 0:46:24 GMT
Hi Ed, Some inspiring work going on here! Having had my ancient desktop have a, what’s looking like, terminal hard drive failure......the guy who came & confirmed it wasn’t worth fixing, I’m hopeful he might be able to get my drawing off it, a new computa is on its way! Looking at what you are doing in 3D then maybe it’s time to move on from 2D. What you are doing gives me hope that the change over isn’t too big a leap! Oh the build is coming on nicely too!
Cheers Kerrin
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Post by Roger on May 4, 2018 7:08:03 GMT
Hi Ed, Thanks for filling in some of the blanks. It's easier to see what's going on if you only display the tool path for the current tool,I'm sure you can do that. You'll also find that you need the finish pass to have a very small step over indeed. Something like 0.1mm will almost certainly be needed to get an acceptable finish. If you set that up in the CAM, the job will almost vanish under a carpet of cutter path lines!
What I usually do is do a pre-finishing pass at a much coarser pitch with the finishing cutter to make sure that I'm close to size and that there are no places left where it takes a big cut. That's what happens on concave shapes when you reduce the tool size and it can reach in further. This is not a problem here, but it's the single biggest pain you have to deal with in my opinion. Once you have a pre-finish done, you can really crank up the spindle speed and feedrate, because if you don't it will take forever. Some jobs run at 300mm/min which is ten times faster than the early roughing cuts.
I hope Kerrin and others will be inspired by you showing these steps into the unknown. I'm sure you'll agree that there's nothing that difficult in 3D modelling, experience with 2D takes you most of the way there since almost everything is created from 2D sketches anyway. The only difference is that those sketches can be on any flat surface or plane you create, and the features on those sketches can be stretched as solids or bored as holes through what's already there. Simple really.
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Post by terrier060 on May 4, 2018 10:56:30 GMT
Thanks Roger - I am really enjoying the experience. I have been seriously thinking about the spec of the Tor mach and have decided that the 440 is a lot smaller and cheaper and I probably can squeeze it into my workshop. I know you will advise me to go for the larger machine and I would love to, but I am really only interested in using it for small parts. I have enclosed the spec for you to mull over. Table weight allowance is 150lbs and even with the 4th axis which I may well buy it should cope with the small jobs I intend to use it for. Please have a look at the spec and see what you think. Tormach 440 Spec by Ed Cloutman, on Flickr Ed
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Post by Roger on May 4, 2018 14:01:41 GMT
Hi Ed, At least the smaller machine still has a decent amount of travel. Bigger is always better, within reason, just bear in mind that a more capable CNC machine can completely replace your manual mill so you could have one big machine instead of two light ones. I can feel you clinging to your Manual machine, and that's understandable, but you don't need to worry about that if you get the right CNC machine in its place. Whatever you choose, you'll certainly be able to make reasonbly large items, it will just take a lot longer.
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Post by terrier060 on May 4, 2018 18:19:19 GMT
Hi Ed, Some inspiring work going on here! Having had my ancient desktop have a, what’s looking like, terminal hard drive failure......the guy who came & confirmed it wasn’t worth fixing, I’m hopeful he might be able to get my drawing off it, a new computa is on its way! Looking at what you are doing in 3D then maybe it’s time to move on from 2D. What you are doing gives me hope that the change over isn’t too big a leap! Oh the build is coming on nicely too! Cheers Kerrin Hi Kerrin Fusion 360 has some great tutorials. The bit I like the most is that I have drawn a more-or-less complete set of drawing in 7.25in scale of Fenchurch and was (one day) thinking of seeing if ME magazine would publish them. But now they are doubly useful as I just copy the dxf file into Fusion and the part is there in 2D with all measurements correct. All I need to do is extrude to get the relative thicknesses. But I have struck a problem as you will see below and am asking for Roger's help. Poor Roger - he will get fed up with me. Ed
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Post by terrier060 on May 4, 2018 18:23:07 GMT
Hi Roger - I have struck a problem which you can see on the enclosed model. I can face off OK, but cannot work out how to get Fusion to contour the outside of the part, and then mill away the shaft. Obviously it will have to be turned over to do the underside. Brake hanger CAM by Ed Cloutman, on Flickr
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Post by terrier060 on May 4, 2018 18:31:01 GMT
Hi Ed, At least the smaller machine still has a decent amount of travel. Bigger is always better, within reason, just bear in mind that a more capable CNC machine can completely replace your manual mill so you could have one big machine instead of two light ones. I can feel you clinging to your Manual machine, and that's understandable, but you don't need to worry about that if you get the right CNC machine in its place. Whatever you choose, you'll certainly be able to make reasonbly large items, it will just take a lot longer. Yes I agree the bigger machine is very tempting - just because of the extra weight and stability. And you are quite right, I am nervous about selling my manual machine - just in case I can't get on with CNC. Also I am getting too old to lug about heavy machines. I moved the Myford on my own when it arrived, by taking it all to pieces on the pavement in the street where I lived in Cardiff. Luckily it wasn't raining. I was able to lug all the parts into my front room where it remained in pieces until Jan and I moved into our cottage. Then it went into our outside shed which was boiling hot in summer and freezing cold in winter! Then it came all to pieces again so that I could move it into our extension where it has been the last 30 years! If only I had a bigger workshop.
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Post by Roger on May 4, 2018 18:41:13 GMT
Hi Ed, This is going to be a 2D operation then. The first and most obvious problem is that you have some sharp internal corners which can probably be blended with a fillet. You might also decide to had a fillet on the side, that's something that can still be done with 2D machining by using a Corner Mill, ie an End Mill that has a small radius on the corner.
To machine the profile, you will need to define a sketch that is a continuous line all around the profile including the bosses. That sketch needs to ne drawn on the top surface of the highest boss. Alibre has a 'project to sketch' feature and I'm sure Fusion 360 has the same thing. The idea is that you project what lines and features you want from the model onto that new sketch. You then use a Profiling operation using that sketch. Because it's defined as the top of the part, the cutter knows the Z-axis height for that. You will probably have to tell it how deep the cut needs to be.
It was a surprise to me that you have to essentially redefine things on the 3D model for machining purposes in 2D, but I suppose it's logical. That profile doesn't really exist as a separate entity on the model so you have to spell out what you want.
Clearing the bit in the middle requires a similar technique. Again create a new sketch on the top of the highest boss but this time you're interested in creating a pocket shape that will enable the cutter you choose to cover the whole of the region you want removed. The larger the cutter you use, the bigger the area will be. Again, the depth of cut will probably be put in manually.
It's all a bit knife and fork with 2D machining, but it's so much quicker to do it that way that using 3D machining which inevitably spends a lot of time machining fresh air.
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Post by Roger on May 4, 2018 18:43:25 GMT
Hi Ed, At least the smaller machine still has a decent amount of travel. Bigger is always better, within reason, just bear in mind that a more capable CNC machine can completely replace your manual mill so you could have one big machine instead of two light ones. I can feel you clinging to your Manual machine, and that's understandable, but you don't need to worry about that if you get the right CNC machine in its place. Whatever you choose, you'll certainly be able to make reasonbly large items, it will just take a lot longer. Yes I agree the bigger machine is very tempting - just because of the extra weight and stability. And you are quite right, I am nervous about selling my manual machine - just in case I can't get on with CNC. Also I am getting too old to lug about heavy machines. I moved the Myford on my own when it arrived, by taking it all to pieces on the pavement in the street where I lived in Cardiff. Luckily it wasn't raining. I was able to lug all the parts into my front room where it remained in pieces until Jan and I moved into our cottage. Then it went into our outside shed which was boiling hot in summer and freezing cold in winter! Then it came all to pieces again so that I could move it into our extension where it has been the last 30 years! If only I had a bigger workshop. Well, you're more than welcome to spend a few days here and properly get your feet wet so that you get a feel for what it's all about first hand. Weight is definitely a problem, hence me making the travelling crane. Perhaps that's a project to do first!
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