QCAD - First Artwork

Discussion in 'CAD Corner' started by Lancastrian, 2 November 2019.

  1. Big Train James

    Big Train James Western Thunderer

    Not a Qcad user, so take this with a grain of salt.

    In Autocad, there is a "match properties" command. You would select the entities whose properties you would like to change, and then select the entity whose properties you would like to match. Some other programs do the steps the other way around, but it's the same idea. It would appear that Qcad does not have this same function? At least I could not find any search results in a shallow dive that indicated as such.

    Alternatively, in Autocad one could select entities to change, and then open the properties dialog box. The entity layer will be one of the properties that can be changed, along with a whole host of other things. Selecting the desired layer will move all selected items to that layer. Qcad does appear to have a similar function, if a Google search result from 2018 is still relevant. Any number of entities can be changed, from 1 to all.

    The distinction between the two methods would be that matching properties would be all inclusive, meaning all properties from layer to linetype to color would be matched, while using the properties dialog box allows for individual property manipulation.

    The properties box can be a powerful tool. As an example, in Autocad, I could create a helix of given start diameter, end diameter, number of turns, height, direction, and so on. If I wanted to adjust any of the factors after the helix is created, I could simply change the value in the properties dialog box and the changes would be implemented. There would be no need to recreate the helix with the revised specification. The dialog box is context specific, so it will be populated with fields relevant to whichever type of entity you have selected.

    It might be worth a look.

    Jim
     
  2. ChrisBr

    ChrisBr Active Member

    Even simpler, select the elements you want to transfer, open the Property Editor box and select the relevant layer there. It will work with elements selected from multiple layers, the layer property just shows "Various"
     
  3. J_F_S

    J_F_S Member

    Hi Ian,

    I am not at all sure how much previous experience you have of etched loco design and I apologize if I am teaching you to suck eggs here!

    I assume you started by producing a "General Arrangement" drawing full size for S7 and showing exactly how all the copmponents will be assembled? The creation of the GA is the proper place where all the decision making goes on and, in drawing it all out, all the difficult bits surface and any necessary compromises can be sorted out. In particular, things like metal thicknesses, fold lines, bending allowances tabbing arrangements etc. which all affect the buildability and which must be incorporated into the etched components can all be established.

    In my experience, creating the GA, plus any necessary further assembly drawings takes about 80% of the total design time. Once that phase is complete, all the bits can be extracted and laid out in artwork form in very short order.

    If you have done the GA, it might be a good idea to publish that for critiquing rather than the artwork.

    If you have not done that, I would repectfully suggest that you start again as you are starting in the wrong place!

    To take a few specifc examples from what you have done so far:-

    - how have you decided on the top profile of the mainframes? How will the "bodywork" fit to it, for example, under the front footplating.
    - how much how much joggle have you allowed for in the frame ends - in otherwords, what is the designed minimum radius curve it is intended to traverse and how much side-play / learance does that demand?
    - how have you decided on the frame spacing - again down to the sideplay allowance on the driving wheels and the clearance / thickness of your chosen horn block arrangement. If anyone has told you S7 is "dead scale" they were overlooking the non-scaleability of physics!
    - what arrangement are you proposing for the radial axles - these will be a nightmare to get right and will make the finished loco a nightmare to keep on the rails if they are wrong... If I were you I would build a mock-up for these unless you have already done a few previous examples successfully.

    I have a concern that you are possibly using the full size design as a basis for your work so far. I am afraid that such an approach is doomed to failure since you are not looking to build a full sized loco. And, as has already been pointed out, the original design was no good anyway!

    I hope I do not come across as a smart @rs* who knows it all - because I don't. But I have been developing etched bits and bobs - including several loco chassis - for about 10 years and I do know how to do many, many things wrong and I have learned the hard way that there are too many pitfalls along the line. I would hate for a lot of effort to end in expensive disappointment...

    Best Wishes,
    Howard
     
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  4. J_F_S

    J_F_S Member

    Just by way of illustrating my point above, here is a small part of the "GA" for a Fairburn 2-6-4T I did in P4. It is designed to fit under the Bachmann body (which complicates things a bit!)

    2-6-4 GA.jpg

    You can see how the chassis is laid out for a 990mm radius curve (in practice, the finished job will go down to about 950mm). Also, notice lots of small "scrap" views illustrating how laminations will be built up etc.


    Brk rigging fit small.jpg

    And, to show the kind of issue the GA has to sort out, here is a photo of it being built up - exactly how to fit the brakework (and have it removeable) in the confines behind the cylinders is just one example of modelling challenge to solve in this particular case.

    Hope that helps,
    Howard
     
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  5. Scale7JB

    Scale7JB Western Thunderer

    Completely agree about doing the GA first...!

    image.jpeg

    JB.
     
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  6. Lancastrian

    Lancastrian Western Thunderer

    Oh gawd, do I have to start from scratch ? :oops:
     
  7. Lancastrian

    Lancastrian Western Thunderer

    Well, not quite. Despite the dislike, partly due to the short wheelbase, the class spent up to ten years working some main line services and also from Manchester to Oldham, Rochdale and Bury, and Liverpool to Southport, where they alone could just keep up with the electric trains as the new traction came into use.
    It was only when they were displaced by the superheated 2-4-2T's in 1913 that they were transferred to working as goods engines and the flanges of the centre drivers removed that issues arose with derailments and spreading the track on sharp curves, mainly due to the less than ideal track in goods yards. Additionally their insufficient brake power (for freight working) and 5' 7 5/8" driving wheels made them somewhat unsuitable for these duties.
    Not so much an abject failure, but another small class of locomotives which was eventually replaced by more up to date designs. Of course, some of these were gradually replaced under Josiah Stamp's "scrap and build" policy during Stanier's tenure as CME.

    Howard, any help or advice is always gratefully received.

    Ian
     
  8. Lancastrian

    Lancastrian Western Thunderer

    Plussssssssssss,

    The amount required to extend the frames to length before bending is 0.060122 mm. Should I really be worried about this ?

    Ian
     
  9. J_F_S

    J_F_S Member

    Well, I would not think of it as starting again! Rather, you are just pausing this particular pahse until you have created your GA. Then you can compare what you already have with the GA. If there is no discrepancy then you have lost nothing and the rest of it will proceed with more certainty. If there is a discepancy then you have saved yourself a lot of potential rework!

    If I might make another suggestion - when you are thinking about how to create your component etches, (most CAD packages have lots of alternative methods) have a think about how you will modify / edit them in future. For example, I use an AutoCad lookalike (ProgeCad) and it has the ability to create a "Block" which can be thought of as a sort of self contained drawing and which can include all the layer information (ie for front and back detail, folds etc). Any number of "instances" of the block is then inserted into the final artwork drawing. The benefit of this is that if you need to alter the compnent, you simply edit the Block and every instance of it (including Lefthand / Righthand versions etc) are automatically updated. You can imagine just how much work that saves. Moreover, if you link them correctly, you can include the same Block in different drawings and again update them when a change is needed.

    If as an alternative, you were to create a component in an "outline" layer, then create its front etch fill in another and its back etch fill in a third etc. it then necessary to manipulate each of those as they are effectively, separate entities - unless you set it up cprrectly in the first place. I think that (in this regard only) I am suggesting a diffent approach to Jim's suggestion above - though I fully aggre with his suggestion re the Properties Dialogue which I use for almost everything!

    To illustrate what I mean, here is a very simple artwork I did for a mate - they are just bell cranks for connecting up his points. You can see that I have grabbed one of instances of the bellcrank and moved it aside. You can see that all the layers have moved a a unit - indluding the two halves of the crank, the half etched hinges etc. to show how they all work as a single unit. The complete artwok is for 102 cranks. - ie 102 instances of the same block.

    Block.jpg

    Now here is the thing, after I sent this artwork to my mate, he came back all apologetic and asked my to change the diameter of the pivot hole. He was a bit sheepish as he could see that there are 204 such holes in total. He was surprised when he got the changed artwork back within a couple of minutes.

    The steps I had to take were:-
    - Select the Crank - Block and open it for editing. (note that the pair-of-cranks is a block which includes 2 instances of single crank blocks)
    - Select the hole
    - Change the Diameter property in the Properties Dialog (the hatches change automatically IFF you "Associated" the hatch and its outlines when you created it)
    - Close the Block edit Window.
    The result looks like this:-

    Block2.jpg

    That change took me about 30 seconds!

    You can also imagine that when you are deciding where to put the bits to best fill your fret, being able to just drag them about the screen knowing that you can't accidentally screw them up is a big help!

    There are dozens more little dodges which are essential to an efficient workflow and which are well worth getting to know about right from the outset.

    Just on the 0.06m: firstly, it does not sound a lot - are you SURE you have enough joggle for an overscale curvature? Secondly, beware of "small" discrepancies - they have a habit of accumulating!

    Very glad that you took my bait on the Hoy 2-6-2s! But I have a simple measure - the 2-4-2s were there long before them and were still there long after!

    Hope that helps!

    Best Wishes,
    Howard
     
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  10. BrushType4

    BrushType4 Western Thunderer

    You’re absolutely right Howard. QCad also supports blocks and they work exactly as you’ve described. I use them extensively in my work drawing out buildings.
     
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