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[UPDATE#2]Some 4130 homemade porn [short ride report]

troy

Turbo Monkey
Dec 3, 2008
1,006
739
So...I always wanted to make my own DH frame and I finally made it! It's my 1st frame and it's TIG welded 4130n steel.
-"High pivot",
- horst link,
- idler,
- 10,5"x3,5" shock,
- 8" of travell
- 1,5", low HT
- 7075 T651 links
- 24mm pivots
- PM 74 brake mount
- 150x12 Maxle type rear end
I want to run only 5/6 smallest gears and a small chainring. Had gr8 deal on RF Atlas FR 100mm bb cranks and wasn't sure about 83mm cranks Qfactor (i have no tube bender so I was affraid of crank arm/chainstay interference...). Anyway i can always make it 83mm if needed.

Geo:
47.25 (1200mm) WB
17.125 (435mm) CS
64* HA
13.5" (343mm) BB
1" (25mm) reward axle path

Front end weights ~5.5 lb IIRC, have to put the whole frame on scale this weekend but i'm thinking ~11lb for the frame only. Sry for crapy pics, MOAR, better ones after the weekend probably...
What do You guys think? :D

NEW PHOTOS
 

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Sandwich

Pig my fish!
Staff member
May 23, 2002
21,030
5,918
borcester rhymes
I dig it, but I'd probably ditch the complication of the horst in favor of some brake squat and less derailleur banging. I'd also recommend making the chainstays as short as possible, as you'll add quite a bit of length through travel. If you have 1" of growth, you may have almost 18" stays at sag
 

jackalope

Mental acuity - 1%
Jan 9, 2004
7,596
5,894
in a single wide, cooking meth...
I (very) hesitantly clicked on this thread given that there's a poster named "4130biker", but I am relieved this is just a cool garage build thread. Good stuff man, and like others have said, post up moar pix as you get further along :thumb:
 

troy

Turbo Monkey
Dec 3, 2008
1,006
739
you may have almost 18" stays at sag
Yup! It is 18.1" at sag, but I wanted it like that. Got Corsair Maelstrom that has 16.95" CS static and ~17.9" at sag and wanted something little more sluggish. Corsair has much shorter WB tho, so we will see :) This frame is just a test mule, to verify suspenion behaviour and geometry.

Bottom brackets for the pivots seems like a nice move.
Thanks! Came up with this idea, because I don't have acces to any milling machine or some other fancy tools to machine bearing slots (sry I don't know how is it called in english...) after welding. It is heavier, but bearings are big, well sealed, easy to service and even if something will fail I can get those BBs in every bike shop. Actualy, everything was made by hand using paper templates, bow saw and a single half-round file :) (except of using waterjet to cut those aluminium links and rear dropouts, some CS/ST bits and using a simple lathe to make a HT).

I (very) hesitantly clicked on this thread given that there's a poster named "4130biker"
LOL :D
 

4130biker

PM me about Tantrum Cycles!
May 24, 2007
3,882
447
I (very) hesitantly clicked on this thread given that there's a poster named "4130biker", but I am relieved this is just a cool garage build thread. Good stuff man, and like others have said, post up moar pix as you get further along :thumb:
:rofl:

Imagine the relief I felt!

Troy- love the bike! Excited to see it built up. What did you use for your chainstay to "spindle" clamps at the main pivot?
Also, where did you source the rectangular chromo if you don't mind me askin?
 

HardtailHack

used an iron once
Jan 20, 2009
6,626
5,442
Cool, so sorta like a home made Ghost DH but cr-mo, I like it!

Also, from memory Santa Cruz may have also used BB's as pivots in the Bullit? It's a top idea, nice big cheap bearings that are easy to replace.


EDIT, Post mount brake boss, smart man! It shits me to see companies to make perfectly machined DO's only to run a shitful IS mount, I'm too fat for them, with a 7+ inch rotor the calipers move around a bit under brakes.
 
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blindboxx2334

Turbo Monkey
Mar 19, 2013
1,340
101
Wets Coast
can someone please explain why he went with tig instead of mig? i thought all steel was usually done with a mig.

Yes, i am an idiot when it comes to burning things together.
 

TrumbullHucker

trumbullruxer
Aug 29, 2005
2,284
719
shimzbury, ct
@blindboxx2334
TIG and MIG can do both materials ( aluminum, steel ) with proper setup

from my experience and my .02, TIG is cleaner, stronger, and the ability to control your heat with the foot pedal, and your filler rod input, is huge
you can weld a dh steel frame just fine with MIG, but theres just alot more pros to TIG.
 

blindboxx2334

Turbo Monkey
Mar 19, 2013
1,340
101
Wets Coast
huh, cool. i thought steel was almost always mig and stainless was always tig.

again, i dont know anything about burning stuff together. although id like to learn.
 

shirk007

Monkey
Apr 14, 2009
499
354
MIG is going to blow holes in thin gauge bike tubing.

If you're building a huck tank with heavy gauge tubing you could maybe get away with MIG but good luck on proper thin gauge stuff.
 

4130biker

PM me about Tantrum Cycles!
May 24, 2007
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447
Is the same true for 7000 series aluminum?
I'm no metallurgist, but I believe the above answer about 7005 is correct.

PS wasn't saying 4130 can't be heat treated, just that it doesn't need to be for a frame.
 

4130biker

PM me about Tantrum Cycles!
May 24, 2007
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MIG is going to blow holes in thin gauge bike tubing.

If you're building a huck tank with heavy gauge tubing you could maybe get away with MIG but good luck on proper thin gauge stuff.
absolutely- and to add to that, even if you manage to get it to work, you run the risk of over heating the chromoly, and its going to look pretty rough compared to TIG.

Not that it can't be done- I'm pretty sure dcamps gearbox bikes were MIG welded, but not sure of his tubing selection.
 

HardtailHack

used an iron once
Jan 20, 2009
6,626
5,442
That is quite crafty. Don't you want press in bearings though? they work sooooo much better for bottom brackets [SARCASM]
Yup, my six month old frame is getting binned in a week or two because of PF BB and poor manufacturing.
 

troy

Turbo Monkey
Dec 3, 2008
1,006
739
:rofl:

Imagine the relief I felt!

Troy- love the bike! Excited to see it built up. What did you use for your chainstay to "spindle" clamps at the main pivot?
Also, where did you source the rectangular chromo if you don't mind me askin?
You mean what material i used for spindles or those CS clamps? Tubes came from the aircraftspruce.com

heat treat? do you have to heat treat 4130 before GTAW?
You can do it, but You have to use different welding rod and have really good welder familiar with this material. As i'm not doing any stress relieving I decided to use thicker, more ductile tubing (0.049"/1.25mm mostly ) in normalized state rather than risking a crack after welding.

howd you make your jig? did you do any "stress test" kinda shiz in solidworks or whatever program you used?
Made a simple jig using plywood sheet and V-blocks. Did FEA fatigue analysis of the front end.

can someone please explain why he went with tig instead of mig? i thought all steel was usually done with a mig.

Yes, i am an idiot when it comes to burning things together.
MIG doesn't work well on small dia. tubing. It's easy to burn a hole in those thin walled tubes. Puddle has to move realy fast and it difficult to move MIG welding gun around tight radius. It has too much heat input as well so You end up with much bigger heat affected zone, weaker frame, more prone to cracking. TIG welding rods are ususaly "cleaner" as well. Basicly You want to use TIG or O/A. MIG is not recommended.
 
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dcamp29

Monkey
Feb 14, 2004
589
63
Colorado
absolutely- and to add to that, even if you manage to get it to work, you run the risk of over heating the chromoly, and its going to look pretty rough compared to TIG.

Not that it can't be done- I'm pretty sure dcamps gearbox bikes were MIG welded, but not sure of his tubing selection.

yeah- first ones were MIG- worked fine on thin 4130 (.035" or .049" walls)- just had to stop and go to prevent torching giant holes in the tubes. Penetration was fine- I would do test pieces and cut them apart to verify. I switched to TIG later and that obviously works better :)


OP: Nice work!
 

4130biker

PM me about Tantrum Cycles!
May 24, 2007
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yeah- first ones were MIG- worked fine on thin 4130 (.035" or .049" walls)- just had to stop and go to prevent torching giant holes in the tubes. Penetration was fine- I would do test pieces and cut them apart to verify. I switched to TIG later and that obviously works better :)


OP: Nice work!
Still inspired by what you did on those bikes- one of my favorite bike-related articles ever.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,915
1,200
What do You guys think?
This is absolutely brilliant! Nice work, keen to see the finished product.
I think most of your number and design choices are better than a lot of manufacturers.
 

troy

Turbo Monkey
Dec 3, 2008
1,006
739
Thx Udi!
Front end weights 6lb and the whole frame 12,5 lb + shock (Roco WC + 300 lbs spring with steel hardwear) = 14.9 lb total... so kinda heavy, but steel axles and HT inserts are not very lightweight (~1lb), and CS+SS are much different (and much heavier) than what is shown on 3d model from the 1st post.

Troy- was referring to the CS clamps.
Checked it again, it was s355 steel.

OP: Nice work!
Oh man, You and Your DC special #4 were the reason why I decided to design a frame by myself. I'he started working on that thing back in 2008 IIRC ond it was designed as a carbon, internally geared bike. Got some old screenshots:



Unfortunately guy, who was doing CNC work for me back then, screwed me over and I abandoned that idea. Year or two later I started working on steel version of that thing (without "g-box") in my free time and here it is.
 

dcamp29

Monkey
Feb 14, 2004
589
63
Colorado
Rad! Would have been awesome to get it done in carbon, but for home-builds it's hard to beat 4130.

Make sure to post up some more pics as the build continues!