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As Promised...


As promised folks, an update on the tracks situation. Updates on this thread seem few and far between these days as I'm not getting to the workbench as often as I would like, furthermore it's often one-step-forward and two backwards with these tracks until I work out what I'm doing.


First though; while I was in a lazy mood one day I thought I would tackle something a bit easier and sort out some surface details on this thing - panels and doors and so-forth.


Normally to transfer shapes onto plastic I cut out the relevant shape from the plans and stick it onto the plastic with spray-on adhesive, but today I was feeling especially lazy and could not bothered walking the 10 m to the shed to get the spray. So, instead, I used this alternative method of transferring the shapes.   Cut out the paper pattern, hold it against the plastic sheet and swipe a pencil a hundred times or so from the paper to the sheet. Work all around the outside. This will leave a mark-up as shown below. This is a good way to trace out the shape of paper pattern because the paper does not have a hard enough edge to trace around in the usual way.




The process leaves a sort of 'shadow' mark-out like this.




Which can be accurately cut out as required.




Sticking these details on is now dead easy. Just mark out where they need to go - scrape most of the undercoat off in the relevant spot and stick them on with normal plastic cement. 




Now it's back to the tracks. At the end of the last post I had made a reasonable start on a set, but they laid dead flat.  Now I have to make them curl up and wrap around the drive and idler wheels.  The following sequence is the result of a fair bit of trial and error which involved nicking my finger with a scalpel - hence the blood on the tracks.


Anyway - here's what I came up with in the end. It turns out that it's all fairly obvious...


First - work out where the track must bend and deepen the notches between the track pads at each of those points.  Ensure that the notch - although deepened - does not cut through the entire width of the plastic.  Now gently bend the plastic until it yields (i.e. loses all strength without actually physically breaking off) at the desired point. Now the plastic strip that is the guts of the track is still in one piece but has an adjustable bend in it as shown below.



Repeat the process ensuring that straight lengths of track are left straight and undamaged. Unfortunately some of the little sticky-out bits got a bit bent during some of this but they are all still present so that's a win. 




Now doing things a bit out of sensible sequence (I should have done this first)  I did what @ArnoldAmbrose suggested and laid a strip of thin flexible plastic along the inside of the track to add strength. I also cut several short single links from the inside track layer (the bit with the little short sticky-out bits attached) and put them to one side.




Now the single track lengths can be cemented onto the main track length at just the right position to engage with the drive wheel teeth as shown.




And here's the result -  at least at the front end -  I have not dealt with the rear idler wheels yet.




Not too bad I think! The idea's there,  but I really have messed about doing this and with all of the experimentation and uncertainty involved I've certainty made a messy job of the tracks.


I'm confident I know what I'm doing now though and am playing with the idea of using that knowledge to build a completely new set to a - hopefully - higher standard. 


I've got some annual leave coming up soon - so hope to see some faster progress on this in the next month or two.








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Gidday Steve, it's good to see progress. Will this be a vehicle straight out of the factory (ie pristine) or back from the field (ie muddy, grotty etc)? If the latter then maybe some judicious placing of mud and dirt can hide any of the track hiccups (of which I'm sure will be very few) and save you doing another set. Only you of course can decide if they meet your exacting standards but they look good to me. 👍 Regards, Jeff.

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14 minutes ago, ArnoldAmbrose said:

Gidday Steve, it's good to see progress. Will this be a vehicle straight out of the factory (ie pristine) or back from the field (ie muddy, grotty etc)? 

I’m thinking Lightly weathered, mostly dust, as per service in Afghanistan. Probably not enough mud to hide too many sins.

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Recently I have taken up gaming - Fortnite to be specific - and I must say even though I am very inept it is quite addictive. I can certainly see the appeal.   


My daughters are my coaches and they are teaching me not only how to play but also about gaming culture.  Apparently these days when a gamer achieves something that they are very happy with they exclaim 'POG' very loudly.  Apparently 'gosh I'm happy with that' is not in the current gamer vocabulary. Instead one says 'Pog' - I guess it's quicker and gets you back to shooting people sooner.


So now let's look at my recent work on the tracks. Specifically my attempt to replace the promising but rather messy set that was in the previous post. This time I've tried a slightly different method of fabricating them.  The result - I think -is quite satisfactory. In fact I will simply say "Pog!”


As per @Redshift s timely suggestion some woodwork is involved.  Here is a block of balsa about to become a forming template for my tracks. Once again cut out the shape you need and stick it onto the block with spray on photo adhesive.



Use a rasp and some sandpaper to bring the soft balsa down to the required shape. I would have used a bandsaw, but this was after 8:30 PM and my wife has imposed a curfew on power tools in my shed. ⏱️ Not that it really matters - it's balsa so it only takes a minute or two to get it knocked into order.








Now carefully measure off the length between the tips of the cogs on the drive sprocket. This distance will determine the length of each pad on the tracks because one 'notch' in the sprocket must match one link in the track.




Consequently we need to draw a line every 7.25 mm on this sheet of 2.5mm thick Evergreen plastic.




As per the previous post I then used a combination of scalpels, chisels, files and Olfa cutters to make an evenly spaced series of notches on each track - configured in such a way to create the appearance of pads.  I then carefully worked out the correct position of the track relative to the balsa former and tacked it into place with a series of drawing pins.


One of the great things about balsa is that you can pin things to it very easily. At this point I have not bent the track at all but I have determined exactly which links joins will need to bend and have cut them about 0.5mm deeper than the surrounding straight links.  This is in preparation for the bending step to follow. 






Now for the clever bit.  Boil a kettle... 👍




and hold each length where the track must bend in the steam until it's soft and squishy.




Now bend the plastic until it yields and pin it in place onto the balsa.  Here you can see the result of two separate bending steps - one at the base where the track follows the first road wheel and one where it wraps around the rear idler. 






Once all the bending is done let the entire thing cool down (I stuck mine in the freezer just to speed things up) and then remove the pins.  Sorry about the dreadful photo - will do better next time.




Now remove the balsa former and you are left with this... POG! :thumbsup:




Which now sits here quite nicely.




And from a distance looks pretty good I think! 




'POG' :thumbsup:  (apparently repetition of this phrase is acceptable and is - in fact - encouraged)


The tracks are not finished yet,  there's a lot of tedious detail to add to make them convincing, but I really think that this is the back of this job broken. This is by far the most satisfactory way of making tracks that I've tried and will be my 'go-to' method if I ever need to do something like this again.


I also think that this steaming method of forming polystyrene plastic has potential for wider use. It's simple, quick, safe & effective and can reproduce essentially the exact same thing each time. It's going into my box of tricks for sure.


Best Regards,

Bandsaw Steve





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Gidday Steve, those tracks look rather good, you could be onto a winner here. I might try the steam sometime. In the past I've sometimes used a heat gun, with varying degrees of success or failure. The main problem for me is the very small areas I need to heat, my stuff being a different scale to yours. Steam could be quite a useful trick. Regards, Jeff.

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Can't help feeling that there's a bit missing at the top... and what about the sticky-uppy-triangley-guidey bits? Nevertheless, Pog would appear to be appropriate. Jolly good show old chap.

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Yes quite right @Redshift    there’s still quite a long way to go on these tracks, including the triangular guide bits. IHowever, I think with the basic sructure now sorted, adding all those bits and pieces promises to be a bit more straightforward, 👍

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Teething Problems


'Can't help feeling that there's a bit missing at the top... and what about the sticky-uppy-triangley-guidey bits?'


So said @Redshift  about a week ago - and he was right. The tracks were then - and still are now - far from completed.  This week however they grew some teeth.


Here's how I sorted them out.  Start with a couple of lengths of 'Evergreen Plastic' 'I Beam' plastic as shown.




Use an olfa cutter to remove the topmost bit of the 'I' as shown. Leaving a sort of upside down 'T'.




Now use the tracks to mark out the center of each planned tooth. Note that on the real gun there is one tooth per track link - so the spacing must be one to one with the existing track pads.




Use a plastic template to mark out a bunch of 'exactly the same size and shape' triangles as shown - shade out the waste sections and use a scalpel to cut out each triangle.  Just out of interest; over the last year or so I have moved gradually from using a thin sharp triangular scalpel blade to the rounded one shown here. I'm finding the rounded profiles much more robust and generally easier to control especially where straight cuts must be made - here you just roll the scalpel back and forth a couple of times and the cut is made.




After scoring the base of the waste section between each tooth it's an easy thing to grip to the waste with a pair of tweezers and break it off.




After a bit of cleaning up with a file and some sandpaper here's the result.




And here's the full length for one side.




Not applied to the actual track yet but this is what the teeth will look like when in place.  There's definitively going to have to be a bit of work done on the road wheels to make sure that the teeth slide nicely into the central gap in the center of each wheel.






Teething problems? No not really. Pretty simple in the end. Just a bit tedious to get through - especially twice - which this something this family went through a few years back.


So the tracks are progressing quite nicely. They still look a bit bare though. Now I've got to work out what to do with the outer edge, the bit where each track link is joined with the next and where the cog teeth on the drive wheel grip the track.


Not really sure how I'll do that - but I think I have the start of a couple of ideas. And in any case; the great thing about scratchbuilding is if one way doesn't work out you can always have another crack.


Best Regards,

Bandsaw Steve




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Gidday Steve, I imagine a job such as you've just done would be tedious, but it looks very good. I think it will improve the look of the tracks, though. Aren't you glad you're not doing a squadron (battery, herd, flock or what ever the collective noun is) of these guns?

     I found your comments regarding the rounded scalpel interesting. When I can get one I'll try it. Regards, Jeff.

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