Re re post maybe? : I am re thinking my seat.
 

If this is a recent post I am sorry I cant find the thread.... If a mod sees this and the thread is not missing please delete one of them. But if its not I will write a condensed version and add to it later. I have aquired a second rider. I dont plan on having anyone over her weight on the back as I am not so keen on second riders after someone almost dragged me into a pole. I have a buck for a monocoque seat but I dont think I will use it for saftey reasons.

I want to ask the engineers and people good at math what Titanium or aluminum tubing I should use. I am thinking grade 2 titanium for the seat frame or aluminum tube. The problem is I dont know what shape of aluminum I would use and what thickness. The second rider is 45kilo wet and I am 78 kilo after a mad burger binge and a dunk in the pool. Grand total I would like to be able to bounce off this frame is 160 kilo just to be safe. I have seen so many titanium seats that I have a good idea what kind of frame to make I just dont know the thickness.

Sorry, not my wheelhouse. You might try Brett (skokie).

Seat frame? Are you meaning sub frame? Seats don't have frames, they typically are flat plate or contoured material.
For a seat base, you could use the stock one as a buck, or form one by hand with 1/4" Kydex reinforcing as needed with aluminum. The seat supports rider the weight by contact points on the sub frame, the seat base itself does not need to be stand along structurally able to hold rider weight.
If your looking to replace the steel sub frame with something else unless you have a a budget in the 10's of thousands for R&D, engineering and non destructive computer modeling, You best be way overbuilding it if guessing, or somewhat overbuilding is modeling it after a sub frame made from a different bike but close to the same design. Thats not a bike part you can afford to have catastrophically fail while on the road.

Short of specialty suppliers, Grade 2 Ti in tube is all your going to find... its is the most commonly used, and thus what is stocked.
Tube diameter and wall thickness is the question and the answer is... who the feck knowns, to get a "real" answer would take a mock up and destructive testing then R&D and build/ try it again.. Or build it in CAD, then do non destructive failure testing on a computer.. Easily done, just time and more cash than 99 5oth year anniversary VTR1000Fs are worth.

So first WHAT are you building a seat base or a subframe?

I meant the subframe. I originally was going to do a monocoque tail but now I have a semi regular second rider and cant risk the tail snapping. I found a full TI bikr build I think I can copy the subframe on.

What's wrong with the original subframe?

See word "original "
LOL

I would make a trellis design using 4130 chromoly steel tube in something like a mix of 3/4" and 3/8" tube... Mostly because its stronger then mild steel used on the OEM design, it can be smaller in diameter, thinner wall due to its extra strength and I can fabricate and weld it... I can not Tig Ti or aluminum at this time.....so I don't fabricate with it.

Unless you need to fit something that wont fit on the OEM one or just want a new look, Id bet what you build will weaight about what the OEM one does .

That's like asking what's wrong with a stock SuperHawk.

OCMD, baby.

Capn. May have been joking. No spelling Corrections from me. I teach english... Still cant spell.

Eric.... Please enlighten me as to why you cant weld TI? I really need to know before I do this.
Chromoly is good but I want either aluminum as it matches the .... Uh... Frame?? I(ts early... ) or Titanium to match my pipes and because of its corrosion resistqnce. Its gonna get sprayed by the rear tire every ride.

Not it cant be welded.. I CANT WELD IT.
You can technically MIG weld Ti and Aluminum , and I have, but it does not do the materials justice ,nor produce the same aesthetically pleasing results of a well used TIG welder.,,,and I do not currently have a TIG welder

Steel painted or better yet powder coated is highly corrosion resistant...Looked at that stock steel sub frame lately?

Personally I would not put a passenger on a home made sub frame.... less so on one that was made from alternative materials with a non stock design with weight savings and any kind of minimalist design to it... Having it fail on me causing a crash is one thing, having it fail on a passenger is not an option.

Eric I mean why cant you? I need to know because I am a home gamer. I wouldnt even think about MIG o this project but grade 2 seats arent uncommon. I imagine you are worried about pennetration heat ect. The same things I woild worry about. I am going to pay a pro to do mine because I dont have the machine in japan still... I actually trust home gamer work as long as the math is good. The easy thing for me to do is build two... Its just costly. I am not pissing on you I am asking because I know you know yoir stuff very very well. If I could do any calculations besides basic loads I wouldnt have asked. I cant dream to get it rigjt until I hold some stock in my paw and check it out.

The second part of this is the fact that my subframe is getting a little nasty. Whatever paint or coating has been blown away by sand sprays and shes grown a nice red beard. Theres a guy who built a nice subframe that I am going to mail.

Passenger saftey is no1 I agree. I disagree a little bit on the fact that I think a guy lile Eric or even my self couldnt make something as good or to factory spec. If I could autoclave and sonically test my carbonfiber I would continue wit an all cf part. If a weld breaks on a titanium 4 point mount 2 piece sub it wont fall off but a crack in carbon usually. Rips like a mofo. Ill make a drawing hopefully this week and I will throw it through cad month. The monster pc is lacking a monitor and my laptop isnt so healthy. Its 4am sorry for being rambly and incoherant as usual... Ill try to not fldrag this out like the gas tank ended up and finish before xmas so I can show you what I was asking about. I have a hard time with words. But for real man if theres anything crazy about titanium I have forgotten please let me know as I am inches from getting some stock.

Its a concern based on failures Ive seen in my own fabrication and that of others.
If I were to do this and wanted Aluminum I would follow the OEM design minus clean up of unused OEM tabs, holes ect... Id choose material of the same or larger diameter and Id use square tube that had radius corners and .125 " wall at least if not thicker. I would plate or brace all corners (one or the other depending on the load direction... .. so the top of the sub frame would get plated on corners the down legs braced.
I would build a jig to create itm not just for the building, but so I could check for deformation, later after some use..if needed straighten / replace damaged sections and then reinforce.

If I used Ti it would be welded seam round tube of the same general OD as stock ... all attachments or contact points that needed flat would be added to the round tube, not section or cut out the tube and Id use .050 wall or so. And Id add some additional bracing supporting the passenger load area of the subframe so the rear most part does not deform and sag down under additional momentary load that will happen when you hit a G out of pot hole that uses all the suspension and bottoms out the shock.

What you described is pretty well my plan. I also umderstand your concern for it bustng up and its a fear of mine as well bit I have seen factory subs break too. Usually right at the welds. I may not post for a while on this as I will do what I was beig lazy on and draw it up in cad. The material I am thinking of is grade 2 TI .34" thick with a .65" od. Its odd to use non fractions with imperial measurments but thats what the supplier is using. Ill probably gusset against the welds o the inside. It will mimic the steel frame but be round stock and a bit shorter because I am going to only use two pieces and have them bent. Into loops. I am going to try to flattwn the ends for mounting so I will actually have only two welds beaides the gussets and that will be to mate the loops up.

RedStormJ, if you've got a dimensioned sketch I would be more than happy to do CAD and FEA for you - while not perfectly accurate it will indicate weak points and max displacement. Let me know!

Ya man I,ll tale you up on that. Let me fix my monitor issue and I will totally build up a sketch. Itll take a month probably. I am not so good at modeling. I a. Actually going to try fixing my issue tonight so Ill hit you up around NOV?