nolipoli Posted June 9, 2015 Posted June 9, 2015 The design has changed a bit due to a few minor reasons. This is the design I've decided to go with. It's based on the DW link with at the rear. Shock length is 200mm eye to eye and short chainstays to make it very active. Seat tube is 31.8mm at 78 degrees, a long reach top tube and a 1.5inch headtube at 64.5 degree. Rear travel is 150mm and the fork must be 160mm. The frame will be contructed out of bi-directional carbon and aluminium inserts for pivots and BB. No place for any front derraileur. I'll pop it into CAD soon to see to resultsThat looks pretty, but one question...While playing with mine, I eventually settled on a 75 degree seat tube as I was worried about putting too much weight on my hands (normal mtb angle is around 73-74 degrees). How did you get to this number?
Burner Posted June 9, 2015 Author Posted June 9, 2015 That looks pretty, but one question...While playing with mine, I eventually settled on a 75 degree seat tube as I was worried about putting too much weight on my hands (normal mtb angle is around 73-74 degrees). How did you get to this number?This is just personal preference. In fact, this angle does not mean anything on its own. It has to be relative to the BB and probably the front triangle design. What you actually want to know is balance when on the climbs. I measured my seat position and based on the frame's design/layout, I've come to this angle. I enjoy technical climbs through the trail and roots, and being in a more upright position for this (as if you're standing) works well for me on very steep sections. When I descend, I'm off the saddle and almost on the back wheel anyways. Don't be fooled by random lengths and angles on frame specs, it gives an idea of what the bike's fit should be but its not accurately shown relative to the rest of the frame because its the manufacturer's intellectual property.
nolipoli Posted June 9, 2015 Posted June 9, 2015 Yeah, normally what is shown as the seat angle is actually the effective one, as calculated by drawing a horizontal line from the top of the head tube, and measuring angle from the centre of BB to the intersection of the seat tube and the horizontal line. The actual seat tube, as you say, varies quite substantially.
Burner Posted June 9, 2015 Author Posted June 9, 2015 Yeah, normally what is shown as the seat angle is actually the effective one, as calculated by drawing a horizontal line from the top of the head tube, and measuring angle from the centre of BB to the intersection of the seat tube and the horizontal line. The actual seat tube, as you say, varies quite substantially.Spot on. Also depending on the design, i.e. if the bike has a low stand over height then the top tube is longer.
nolipoli Posted June 12, 2015 Posted June 12, 2015 Burner, this may be a pretty random question, but are you placing your bearings in the main triangle, or in the linkages? I have been looking at both options, and each has pros and cons - mostly trade-offs of manufacturing ease, although if in the linkages they will be placed wider and will be more stable.
Burner Posted June 12, 2015 Author Posted June 12, 2015 That's a good question. To be honest I was thinking of putting the bearing in the frame, but as you say with the bearings in the linkage it should be much stiffer. It should be easier to produce too. Nice one!
nolipoli Posted June 13, 2015 Posted June 13, 2015 Front triangle is coming together quite nicely. All mitres have been done by hand with a hacksaw and file - very satisfying!
Jimmy 2.0 Posted June 13, 2015 Posted June 13, 2015 Front triangle is coming together quite nicely. All mitres have been done by hand with a hacksaw and file - very satisfying! image.jpgFront triangle is coming together quite nicely. All mitres have been done by hand with a hacksaw and file - very satisfying! image.jpg are you using a jiganaught jig?
amasendeinja Posted June 14, 2015 Posted June 14, 2015 ...Burner, cool project you got going here. Would love to see the end result when you get it built. Just an observation on your seat tube angle: if your scaled up drawing has the seat height correct then I believe that you would be way too forward on the bike. If you draw a vertical line down from the centre of the seat clamp to intersect the chainstays it looks like the line would intersect way forward of the halfway mark on your chainstays, putting you very "forward heavy". I am no frame builder or designer but if you look at trail bikes you will typically find this line intersects at almost exactly halfway along the chainstays. For enduro and DH even past the halfway mark (measuring from the BB back). Cross country bikes generally more forward of the halfway mark, but this is no XC bike you're building. Anyway, maybe it's just the way the drawing looks on my phone. Out of interest what are the mechanical trail and front centre numbers on this machine and how tall are you? Following this thread
SimpleDom Posted June 14, 2015 Posted June 14, 2015 Very soon, I will hate this thread. Because, there will be unique unobtainable beauty, and jealousy makes you nasty.
nolipoli Posted June 14, 2015 Posted June 14, 2015 are you using a jiganaught jig?Jamie, It is a Jigganaught jig. My wife had it sent out from the States for me. The thing is though, that I reckon for half the money you could have something CNC'd here in SA. I have also discovered that the curved edges that the jig comes with are pretty stupid, because you can't use them as datums for angles. It is a great idea, but could do with a little refinement.
Burner Posted June 15, 2015 Author Posted June 15, 2015 Burner, cool project you got going here. Would love to see the end result when you get it built. Just an observation on your seat tube angle: if your scaled up drawing has the seat height correct then I believe that you would be way too forward on the bike. If you draw a vertical line down from the centre of the seat clamp to intersect the chainstays it looks like the line would intersect way forward of the halfway mark on your chainstays, putting you very "forward heavy". I am no frame builder or designer but if you look at trail bikes you will typically find this line intersects at almost exactly halfway along the chainstays. For enduro and DH even past the halfway mark (measuring from the BB back). Cross country bikes generally more forward of the halfway mark, but this is no XC bike you're building. Anyway, maybe it's just the way the drawing looks on my phone. Out of interest what are the mechanical trail and front centre numbers on this machine and how tall are you? Following this threadI get what you're saying, however, this bike is based on my seating position and measurements (just an experimental exercise). I've noticed a few custom builds and boutique manufacturers playing with these angles, check the attached image. It might not work for everyone but it might also have its place in the market....nevertherless, I enjoy the challenge Front triangle is coming together quite nicely. All mitres have been done by hand with a hacksaw and file - very satisfying! image.jpgLooking great nolipoli!!! I truly enjoy you being part of this thread. I know how much work goes into pipe mitres....I feel for you brother What material is the frame made of?
Gerlach Posted June 15, 2015 Posted June 15, 2015 So this is my first topic...I've been toying with the idea to build my own frame and maybe some other custom bits. I've got experience in metal works, composites, plastics and product design....even built a variety of race cars from the ground up Inspiration:Trek, PYGA, Morewood and Momsen to mention a few Reasons:I like the challenge; I looooooove mtbiking; I have some tweaks I feel will make the manufacturers' above bikes suit my ride style a little bit more, like a custom fit (for my type of riding)........and I have some tooling that might help. Let me just say that I love Trek bikes, their little details just make all the difference. Makes you feel like you're on a real special machine, almost boutique like. The abp system and the floating rear end really makes an accurate race bred feel when bombing down trails. PYGA and Morewood have taken some inspiration from these and Momsen has taken some brave leaps too. I love the fact that mtbiking has come to this stage where we have such a huge range of race bred machines to choose from, almost like looking at Lotus, Porsche, Ferrari, Koeniggsegg etc. I will be posting my ideas, designs and progress in here. Feel free to comment, criticize and add suggestions.Burner, ons ken mekaar al tydjie. Moet laat nooit iemand vir jou se jy klan dit nie doen nie. Die ouens wat al uit die 90's en vroe 2000' down hill ry wat my ken, sal weet wat ek en my pa gedoen het, en ek sit nog met die raam . Ons het n down hill raam van niks af gebou, op die Orange 222 se specs. Sal kyk waar ek fotos het. Net na dit het Morewood die mark in getree ook.
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