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Topic: 1/3 scale PK ripper bmx model!!! (Read 15,756 times)

joe
Sprue Cutter

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Joined: Mar 2011
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Posts: 11

1/3 scale PK ripper bmx model!!!
« Thread Started on Mar 17, 2011, 8:50pm »

hi fellas, heres the build so far of my early 80's SE racing PK RIPPER bmx. its 1/3 scale. ive been doing it for about 3 years on and off in my lunch breaks.

I started with the seat as it was a bit of a sculpt and wasnt sure how well it would go. its made from a vac forming of a former i made from chemiwood. the seat is a kashimax aero, its not finished in these pics, still need the gloss bit putting on.

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next was the tyres so i started by drawing up the nobbles on the computer. there are 3 types on a tioga comp3, 400 on each wheel and i needed some spares so i programmed 900 of em.
first i went about putting all the dot and grooves in with a 0.5mm cutter. when that was all done i turned the whole sheet over and ran along the backs of them with a 13mm bull nose cutter to create a curve on the underside so they would fit on my smooth tyre that i was about to turn on the lathe...
when that was done i cut out all the shapes with a 1mm cutter, then it was just the nauseating job of cleaning them up ie; getting swarf of them.

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here you can see the three different types
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then i had to turn the smooth tyre part, to cut a long story short i had to put a 7mm radius on the main part then there needed to be a little ridge then a 5mm radius until it meets the rim. i had to grind up little steel tools to do this part...

now its just a case of sticking them all on which i'm in the procces of doing. I drew on the computer a circle and 80 lines like slices of cake at every 4.5 degrees, then placed the tyre on the template and drew a line in line with my markings on the paper.
sticking on the central ones is probably the best way as i can line up all the others from there.

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heres pics after i moulded and cast a couple
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heres the bars just after i made them, theyre SE power wings

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frame, at this point i hadnt put the welds on yet. its amde from green model board/chemiwood stuff

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heres the stem, its a tuf neck. still need to do the logo on the machine and i think i'm going to do a brushed aluminium finish on it. the bolts are m3's with the heads slimmed down a bit.

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heres some pics of the forks so far.

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I finished off the welds on the frame using sculpting wax then moulded the whole thing in silicon.

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this is how the dropouts and brake bridge are made, cnc machined then glued on.

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heres some pics of the rest so far...

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heres some pics of the wheels, theyre skyway tuff2's with ally hubs .
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and one for scale.

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heres the brake, its a MX1000, so I started by drawing around the 2 parts then reducing the drawings on a photocopier. The funny ridge that runs all the way around both parts of the caliper was gonna be the main task as most of the technique was simply sticking my drawings to some pre thicknessed material and cutting it out.

So to achieve the ridge around the edge I made both parts undersized by about 0.5mm and glued a .5mm wall to the edge which I could sand down leaving a little wall around the outside.

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The fine detailed parts like the MX logo and the oval for the dia-compe sticker were cnc'd to keep them nice and crisp along with the bits the brake blocks mount to.

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Now I needed to get a nice little radius inside my wall to get the right look. I toyed with the idea of running resin or superglue in there but settled for using milliput.

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I put a little scoopy groove on the back to get that twisted look that they have.

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so with a bit of grey primer and a bit of love they're nearly done. They still need a bit of a tickle and all the nuts and bolts bits doing.

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heres the lever

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Chain...Stainless steel etchings, steel dowel pins and little roller/spacers in between.

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I drew this in CAD then had it 3d printed then molded it and cast it. At first the wall thickness of the grip was too thin and they were falling apart when I tried to demold them. Theres a steel core that goes in the middle of them when they're being molded so i put them in the lathe and skimmed off about 0.2mm to make them slightly thinner therefore making the inside diameter of the grip slightly less, thickening up the wall thickness. It worked perfectly but meant they were a bit small to fit on the bars, so I just wafted a hair dryer over them for about 20 seconds and they slid on perfectly. when they cooled down they shrunk a bit and gripped, spot on. heres some pics...

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heres the frame in primer

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then into white base coat

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then into colour, which is one of the original colours for these and ive been reliably informed is cornflower blue 20 E 51.

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heres the screen ready for printing onto waterslide paper

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and heres the result. gold on brown.

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a bit of care and attention and theyre on. ready for lacquering.

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heres some pics of the tyres getting finished. I mixed a colour for the skin wall and painted the whole thing followed by masking the bit that needed to stay "gum" coloured. the masking was pretty quick and easy as i wanted it a bit "not perfect" to match a real tyre as they're all over the place.

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then painted the whole thing black and demasked.

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so heres the competitionIII transfer, slightly different to before, this was taken from a photo of a tyre then inkjet printed onto transfer paper. the shape in white was screen printed along with the other transfers. then the inkjet bit( which contains no white as printers dont print white) is applied over the white bit and lacquered which makes it as one then can be applied to the tyre

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heres the result

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and here they are with the skyways. the tuffs need a bit of finishing before theyre ready but theyre not far off.

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heres a pic of the cranks (redline flight single pinch)and seat post, theyre chromed brass, the cranks are cnc'd then polished before chroming.

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heres how it looks so far, pedals are on their way and a few more bits need doing but its not far from completion.

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thanks for looking, hope you like it.

Joe

« Last Edit: Mar 17, 2011, 8:50pm by joe »