View Full Version : Forks and Fork offset
04-01-2005, 08:40 AM
When I attended Shelbyville fly-in last September, I fielded allot questions
About the method I used to forum the ends for the engine mount down struts and the caster front end on my dominator.
I’m kind of a perfectionist by nature so it’s hard for me to leave well enough alone, I’m
Constantly trying to improve my skills and methods used in the construction of my
Squadron. One thing I always try to do is forum and bend instead of butt weld joints.
Tools required- you need torch set with a multi-orifice heating tip, you may need framing
Square healthy block steel to press the material against, BFH– big %&*# hammer you will
Also have to construct a forming mandrel, I turned mine on the lathe but you may want to experiment 1 7/8 trailer ball, and finally healthy press, on your first time you may need third Hand as.
Oh I had to remake this part again, cause I added a bit to much offset to the castor to improve the assembly –wrong- my first dominator I followed the plans and placed the
offset at 3 inches and that worked ok, so my thought was if 3 worked 4 would be better
Right –wrong- follow your work instruction . unless you just enjoy making allot parts
My error was pointed out during the event
So what experinces do you guy's have with fork offset
04-01-2005, 10:13 AM
Nice work, Craig! I've had the pleasure (?) of making and reworking a few of those Dominator nose forks. The stock design is fine for a one-place, but it's pretty light-duty for a 2-place trainer flown off grass. Mine cracked and distorted a few times. In the 2-place, nearly the full weight of the front occupant rests on the nosewheel. I think the load on a 1-place is more like 50 lb.
While fixing the forks, I found it very tough to hold alignment of the U-shaped fork. The wheel axle must be precisely parallel to the ground to avoid a tendency to pull in one direction or the other. Did you find a good way to hold the alignment while welding? Ernie probably has a nice, sturdy jig for just this purpose.
At the T-joint at the top of the "U", it's important to leave long "ears" on the vertical shaft tube when you cut the saddle in it. These ears are to wrap down and around the U-tube as far as possible to reinforce the joint. I actually ended up making a full wrapper gusset that goes all the way around the joint and about 1-1/2 inches up the vertical tube on each side. This joint in its original form didn't hold up well on the 2-place.
04-01-2005, 04:23 PM
Where the hell were you guys when I needed this kind of information? :confused:
Here's what I ended up with....no thanks to you all! :mad:
Alot better than the original.
04-01-2005, 05:12 PM
Would I have to modify my steering linkage to use your new forks?
04-01-2005, 05:53 PM
I wrap mine with 1/4 inch of gap, at first I was going to add wrapper but elected to wait and see ! I also use fixture and can build in 2.5 , 3 , 4 inches
of off set since I use TIG welding process, I don't experience allot of warp age of the assembly
04-01-2005, 05:59 PM
This Is what I did on my Air Command didn't care much for the kit option
04-01-2005, 06:08 PM
Craig , Thanks for the pics! Nice work! This is the kind of stuff I like to see. If I wasn't so damn tired, I'd type a bunch of questions for you. Maybe after BD's. Thanks
Tim, you could use the chains & cables ,I guess, but wait till I'm done & the system is tested. I will give a full report with pics. Then we'll talk.
04-01-2005, 06:09 PM
I really like that!!! I am interested in changing mine to somthing like what you have. What are you doing with that jig? Will you be coming to BD's with your machine?
04-02-2005, 04:40 AM
Good morning Craig! What didn't you like about the 4" offset?
What is the caster angle at the 3" offset?
On the AC, What did you make the neck out of ? How do you like that setup?
What angle is the rake?
Did you use springs on the steering linkage? .......etc. , etc.
How do you feel about the side load exerted on those rod ends?
Are they chromoly tubes threaded for 1/4" bolts?
What is the wall thickness of the nosewheel fork leg?
Does heating chromoly tube to cherry red change it's properties?
04-02-2005, 06:30 AM
Very nice work, Craig. I gave up on the round U-hoop and went to a beefed-up square assembly in which the two vertical tubes that carry the wheel axle pass all the way through the cross-piece at the top. I don't have a close-up handy, but I'm sure you get the idea.
You probably won't need a wrapper gusset on a single-place.
04-02-2005, 02:59 PM
A point worth considering when setting up a nose wheel.
04-02-2005, 05:04 PM
Thanks Tim. Makes a lot of sense.
04-02-2005, 07:47 PM
Thanks Tim, but I can't open that file for some reason!?!?
04-02-2005, 08:22 PM
Thanks Tim, but I can't open that file for some reason!?!?
Attached is a screen-capture of Tim's document. The .doc file is a Microsoft Word document.
04-02-2005, 10:39 PM
Thanks Tim I had an article in flying magazine saved but couldn’t find it
I would say the 4 inch offset was dynamically stable and 3 would be closer to
Neutral but failed to really notice it in rough field . I was only acting on the
Observation of others at least I will a have spare.
What is the caster angle at the 3" offset? I will have to measure it but I would
Put all your engineering into the fixture to keep everything straight
On the AC, What did you make the neck out of ? everything 4130 flat .125 made
The plates similar AC except for the extention the neck tube .090 bike hardware
How do you like that setup? I’ll have to do some testing
What angle is the rake? 15 deg same as stock AC. next one I will try 11
Did you use springs on the steering linkage? .......etc. , etc. yes I will shoot
Some more detailed pic’s
How do you feel about the side load exerted on those rod ends? I used same
Thing on my 3DRV this is first run thru may have to make some changes
Are they chromoly tubes threaded for 1/4" bolts? I used rod ends on the pedals
Treaded the bolts into them washers spring back up to the bolt head
What is the wall thickness of the nose wheel fork leg? 1 X .125 with an aluminum rod turned down to fill the inside
Does heating chromoly tube to cherry red change it's properties? Yes It hardens it
So turn your bits slow I try not to go all the way to dull red works fine if it wasn’t enough you will get cracking
I do plan to bring one bird to convention that’s all mom will let me bring she wants to bring the golf cart for oshkosh
04-03-2005, 03:16 AM
Craig ,thank you very much! I hope it all works out for you.
04-03-2005, 09:17 AM
Even in bicycles. Look at the axle of the front wheel in relation to the fork post where it is inserted into the frame tube. The offset causes the axle to create stability.
04-03-2005, 08:54 PM
How did you go about bending that nice hoop?
04-03-2005, 09:12 PM
A friend has a nice bender it takes a 24 inch piece ¾ X .065
It will bend 180 deg on 3 inch radius cold
04-03-2005, 09:39 PM
Definitely sounds like a piece of equipment I would like to own.
04-06-2005, 04:40 AM
I personally have not tried this bender, But if I were buying I would look
At this one. Boy they have a lot of other cool things too !
you would need the 7/8 dies to get the 3" radius :D
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