Any Tips on Cutting Fishmouth for SF?

[trikeman]

I have been collecting parts for my SF for some time. I got the wheels months ago, and the steel has been waiting to be cut. I put it on the back burner, since I had not been able to scrounge a suitable rear suspension bike with 26" wheels, although I did have a 24". This weekend, I hit the jackpot at the local thrift and came way with this guy that looks like it was ridden less than 50 miles since coming from the store.

http://www.atlantamusclecars.com/Oct12/IMG_1504.JPG

I have read the plans in the book many times, and have always been a bit scared off by the idea of having to eyeball the compound angle fit on the fish mouth front crossbar. I liked the idea that joe came up with for a jig to at least hold the wheel at a 90 degree angle while you try to fit it, but wondered if anyone else has come up with any other neat tricks to make this part easier?

http://www.lucidscience.com/forum/topic.asp?TOPIC_ID=1824

I have often thought that if you made a jig to just put the front tabs at a 15 degree angle, and then made a template to cut the 1.5" tube to give you 75 degree caster and 15 degrees to make the wheel axle horizontal, you would not be far enough off to matter with the average wheel. I could be wrong about that.

[John Lewis]

Go here and get Giles Puckets Tube Mitre program. I use it a lot.Works for me.

http://moz.geek.nz/mozbike/giles.html

JohnLewis

edit. Just reread your post. May not be quite what you want. Still a useful program.

[trikeman]

Thanks, but nope. Not at all what I need. I have used Giles program and it works quite well, but it wont show you how to miter a square tube to fit a round tube at a compound angle.

Since several members have now completed quite nice SFs, perhaps I am fearing it too much. It just seems like holding something up to something else at multiple angles then grinding is a bit tricky. After all, what is the saying - "do the thing you fear and the death of fear is certain." Too much engineer in me wanting everything laid out in precise measurements.

[TheKid]

I wanted a wider track, so once I determined how wide I wanted to make it, I cut a length of tubing 37" long and marked the center. I cut the two ends at 15 degrees for the camber angle, and cut the fishmouths. I then cut the center to make the crossmember 45 degrees. The crossmember was welded to the frame, then I assembled the rear. I tack welded the head tubes in place, then used Joe's jig to hold the wheels at 90 degrees. From there it was easy to tap the head tubes into place so they had exactly the same caster angle, and the kinpins pointed to the tire-to-ground patch.

[SirJoey]

Too much engineer in me wanting everything laid out in precise measurements.

Man, I can sooooooo relate to that!

http://img185.imageshack.us/img185/9206/signaturehalloweenvr0.jpg

[jimFPU]

I can relate to the engineer thing...but I'm turning into a garage hacker more everyday, as I just want to ride one of these things that I built!!

[TheKid]

After hours of drawing different designs, I came up with compound miters for the crossmember to get both camber for center point steering, and the desired caster for self centering front wheels. It worked great, but looked ugly. Then Brad came along and started showing the progress for the Streefox in the old forum. The crossmember was so simple, it never entered my mind, because I kept thinking there was complicated math based on everything I read about tadpole designs. Using Brad's boomerang shaped crossmember as a basis, I worked with cardboard models to get a better picture. What I found was, if you set the headtubes at 15 degrees with a straight crossmember, you get pretty close to center point steering with 20" wheels. But if the crossmember is then cut in half and set at 45 degrees in the shape of a boomerang, you not only get center point steering, but enough caster to give you self centering steering. If you leave a little leeway in your fishmouths, you can increase or decrease the caster as you see fit. If you build the Fox with a level boom, then you may want to increase the caster angle. But if you build it with the boom slightly lower in the rear, the caster angle may be satisfactory as is. I can tell you this. In the two years I spent building my tadpole, I tried a number of different caster angles based on other builder's recommendations. Anywhere from 8-15 degrees gave fair to excellent results. However, as I got further away from 10 degrees either way, the handling became less than optimum.
BTW, Joe's jig was a big help in holding the wheels steady while the headtubes were tacked in place. It allowed for fine tuning in getting center point steering and exact caster angles for both wheels, without having to tighten the steering tubes without bearings to stop it from turning in the head tube while making the adjustments.

[John Lewis]

This spreadsheet by Peter Eland may be of interest. I used it when building my tadpole.

http://www.eland.org.uk/steering.html

John Lewis

[trikeman]

Thanks Kid. There is a lot I am going on have to study in what you have written. When I first read what you wrote, I thought maybe the 75 degree caster angle shown in Figure 5-53 was not accounted for, but I think you are saying that ALL the angles are adequately taken care of by your method. Just to make sure I get it straight, let me restate it.

1. Cut the cross member to whatever length you need for your track, and mark it in the middle.
2. Notch both ends of the cross member to achieve the 15 degree angles needed for center point steering with an average 20" wheel.
3. Cut the cross member in half at 22.5 degrees and weld them to the frame at the resulting 45 degrees bend.
4. Use Joe's wheel holding jig to position the wheels and king pins into the cross member and tack weld them.
5. Tap everything into final position and finish welds.
6. The 75 degree caster angle will take care of itself (more or less).

If I am understanding it, its so simple that even I can understand it, and much easier to fabricate (no complicated double compound fishmouths). I thought about doing the cardboard myself. This may spur me on to try that before using steel.

I can already see how it works by taking a rolled up piece of paper and holding it in front of me on the table leaning 15 degrees inward at the top. Then, imagine it is attached at the base by a 20" string and rotate it counter clockwise about 22 degrees I can see the caster angle increasing.

Brilliant noodling on your part. I still can't help wondering if there is a catch somewhere. After all, everyone else is cutting complicated compound angles on the cross tube and ending up in almost the same place as your simple method. Perhaps its just a matter of degree which doesn't matter much, as you allude to in your range of caster angles that work.

[TheKid]

6. The 75 degree caster angle will take care of itself (more or less).

Pretty much. It looks like you got what I was saying. A cardboard scale model frame helps a lot. On the actual frame, I cut the 15 degree angles before fishmouthing, in case I wanted to get more or less caster. For more caster, cut the fishmouth on top toward the rear, and toward the front on the bottom.
In addition, When I made the kingpins using Brad's method, I made sure I cut the steering tube perfectly square. Then I cut a 3 1/2" long piece of 1/2"x1 1/2" flat bar in the center at a 15 degree angle to get the axle mounting tabs. I drilled the holes for the axle holes where Brad indicated, then ground off the excess when I welded the tabs to the steering tubes. I also made sure the tubes were identical after welding the tabs on.
Here are some pics to show what we're talking about. The ruler is the boom, the bolts are 1/2 of the crossmembers, the clothespins are the kingpins. The first 2 pics show both at a 90 degree angle to the boom. It's hard to see in the pics, but the clothespins are 90 degrees straight up and down. The angles showing the kingpin inclination are approximate. The left side of the ruler is the front of the trike.

http://i192.photobucket.com/albums/z66/edpol_photos/steering%20angles/000_0537Small.jpg

http://i192.photobucket.com/albums/z66/edpol_photos/steering%20angles/000_0538Small.jpg

The next 2 pics show one crossmember at a 90 degree angle to the boom, and one at approximately 22.5 degrees to the boom. Notice that the clothespin on the 22.5 degree angle is tilted toward the rear, and the kingpin inclination stays just about the same.

http://i192.photobucket.com/albums/z66/edpol_photos/steering%20angles/000_0539Small.jpg

http://i192.photobucket.com/albums/z66/edpol_photos/steering%20angles/000_0540Small.jpg

[moejosteve]

Did you build your's the way you described? Does it work?

[rickairmed]

I had a brain fart the other day while thinking this through on my baby baby Fox build once you have one fishmouth right before welding the head tube wrap the crossmember with some paper and trace the fishmouth . Then mark the 4 edges of the crossmember on the paper before removing it ( use a sharpie for this ) then remove it and trim out the fishmouth with scissors . Then simply wrap it around the other side of the crossmember ( inside out ) and trace it this should give you an exact copy of your first fishmouth on the other side rather than having to work to make the 2 match.


Rick

[Richie Rich]

....once you have one fishmouth right before welding the head tube wrap the crossmember with some paper and trace the fishmouth.... Then simply wrap it around the other side of the crossmember ( inside out ) and trace it....
RickThat's almost the same technique I used when I built my StreetFox front end. However, I made the cardboard template BEFORE doing any metal cutting or welding. Instead of scissors, I used a paper hole punch to 'nibble' away the cardboard. It's much easier to make corrections to cardboard than to metal. :)

.....Richie Rich....
.
http://farm4.static.flickr.com/3203/3132697476_0e88d8a7d2.jpg

[moejosteve]

I'm top posting for lack of clutter on Mr. Trikeman's post. So I had a friend CAD this up to get the actual caster using Kid's approach. He's a smart feller like Mr. Kid... He pointed out the obvious that if you weld the 15 deg camber (by the way it is actually -15 deg), then cut the crossmember, one would have to swing it the full 90 degrees to get the 15 caster (or 75deg from the ground plane). That being said, at 22.5 deg swing (1/2 of the 45), you will get 6 deg caster.

Great solution if you are cool with 6 degrees of caster. Brad (or whomever)will have to advise on how it would handle... Thanks for playing along.:sleep1: time for night-night...

Thanks Kid. There is a lot I am going on have to study in what you have written. When I first read what you wrote, I thought maybe the 75 degree caster angle shown in Figure 5-53 was not accounted for, but I think you are saying that ALL the angles are adequately taken care of by your method. Just to make sure I get it straight, let me restate it.

1. Cut the cross member to whatever length you need for your track, and mark it in the middle.
2. Notch both ends of the cross member to achieve the 15 degree angles needed for center point steering with an average 20" wheel.
3. Cut the cross member in half at 22.5 degrees and weld them to the frame at the resulting 45 degrees bend.
4. Use Joe's wheel holding jig to position the wheels and king pins into the cross member and tack weld them.
5. Tap everything into final position and finish welds.
6. The 75 degree caster angle will take care of itself (more or less).

If I am understanding it, its so simple that even I can understand it, and much easier to fabricate (no complicated double compound fishmouths). I thought about doing the cardboard myself. This may spur me on to try that before using steel.

I can already see how it works by taking a rolled up piece of paper and holding it in front of me on the table leaning 15 degrees inward at the top. Then, imagine it is attached at the base by a 20" string and rotate it counter clockwise about 22 degrees I can see the caster angle increasing.

Brilliant noodling on your part. I still can't help wondering if there is a catch somewhere. After all, everyone else is cutting complicated compound angles on the cross tube and ending up in almost the same place as your simple method. Perhaps its just a matter of degree which doesn't matter much, as you allude to in your range of caster angles that work.

[Locutus]

So would that make the camber 15-6=9 degrees?

[moejosteve]

So would that make the camber 15-6=9 degrees?

The camber basically wouldn't change much, if at all. Looks like it may move to 14 deg. As I see it, the axial angle of the kingpin doesn't change in reference to the ground much by swinging the x-member forward 22.5 deg. The location of the axis changes, the position of the fork tube inside the headtube changes (if the tabs/axles are installed), but the camber angle holds. :rolleyes4: This stuff is way more than my brain can hold at one time,

OH LOOK! A bunny!

as my attention span is about as long as my, er, a, attention span. It might be time for my 2 hours of sleep... Check ya' later.

[trikeman]

You can set the intial angle at something different than 15 degrees, since both angles will change when you cut and re-weld the cross piece. II seem to remember something like 18 degrees might work for the initial angle, but its been awhile since I thought about it. As SJ said there is a certain amount of slop that is tolerable on this.

[rickairmed]

My method was pretty much the same as Kids and looking at my angle guage on the Tadpole right now I am sitting right at 79* . I would say thats close enough to 75* since this thing wont be taking astronauhts anywhere outside of the stratosphere anytime soon :D.

Rick

[Richie Rich]

Don't forget about that rear suspension. We're making measurements without a load on the trike. Depending upon your weight, you may pick up a degree or three once you're sitting on it.

Same goes for seat angle.

...Richie...
.

[SirJoey]

...joe came up with for a jig to at least hold the wheel at a 90 degree angle while you try to fit it...TM, do you have a link to this, or maybe pics or something?


http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif

[trikeman]

TM, do you have a link to this, or maybe pics or something?


http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif

Afraid I don't. It was in the old forum, which now seems to have gone belly up for good, although Kat hasn't removed the links.

[SirJoey]

Afraid I don't. It was in the old forum...Hmmm... bummer. Well, thanx anyway. Quite a few of these have
been built though, so maybe somebody else has come up with something.

With everybody seemingly going "tad-crazy" lately,
several new SFs have recently rolled off the line,
& everybody's freakin' out over the Warrior, :gossip:
I seem to be missing the tad-party, but now that I have
the SF plans, I'm seriously contemplating JOINING that party! :thinking:


http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif

[trikeman]

I'm ashamed to admit I built the wheels for mine almost 2 years ago, and haven't touched em since.

[SirJoey]

I built the wheels for mine almost 2 years ago...BUILT the wheels? :confused:

What'd you do, build some of those monsters with 20mm axles & disc brake adaptors or something?
I was just gonna use the BMX wheels from my "Lil Hornet", if I do this, since it's dismantled anyway.


http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif

[trikeman]

BUILT the wheels? :confused:

What'd you do, build some of those monsters with 20mm axles & disc brake adaptors or something?
I was just gonna use the BMX wheels from my "Lil Hornet", if I do this, since it's dismantled anyway.


No. Long before Brad had the StreetFox available, I had dreams of building one of 25Hz's trikes. One day I saw some wheel chair hubs (1/2" axles) on eBay for almost nothing. I bid on them and got them. Laced up a set of old rims off a donor BMX and they currently live in my garage waiting for their day:

http://farm4.static.flickr.com/3475/3875733581_6b82e83d07.jpg

http://farm4.static.flickr.com/3497/3875733659_9996e9c7fe.jpg

[SirJoey]

Laced up a set of old rims off a donor BMX and they currently live in my garage waiting for their day:Oh, ok. I gotcha. Nice work, too!
Maybe you should consider building a trike to go along with 'em... :laugh3:


http://img384.imageshack.us/img384/7131/sirjoeysigmedij1.gif