this is not for me anymore because mine is totalled from the accident. this is research for the wiki front fork section. i'll buy me another GS500 sometime in september i hope...

anyway this is about designing a custom steering stem when replacing a fork. now i know with some forks you can get away with less work but this is the coolest way.

i'm asking for help with designing the stem.

let's break it down like this:

# the head and the inner thread are to be copied from the fork donor's stem. #the outer thread - i don't think it matters so much how you design it. copy it from either the donor or the original. #the length and diameter of where the upper bearing sits is to be copied from the original stem. #copy the length from the original. i think the diameter is a comprimise between strength, weight and manufacture cost. if it was good on the GS copy it. #i think the slope is there instead of a step for structural strength. copy it. #the original lower bearing sits here... copy it from the original #copy from the donor's stem

By making a length between the head and the outer thread with the bearing's inner diameter you can adjust the chassis necks' position on the forks. this will determine your height at the front.
---------------------------------------------------------------------------------

please comment

the part at the bottom....usually has a groove cut in it....for a snapring
prevents the stem from pulling through

Dont forget to include a slight radius at each diameter change for strength and ensure the bearing land diameters are identical to the original stem, you need to work to within 0.01mm to acomplish a correct fit for the bearings. The threads will have to be machined, doubt you will get a die with those  O/Ds and pitch. I would include a slight shoulder on the press fit diameter to stop it being pressed home too far as well as the circlip facility mentioned by Werase. If the lower clamp has previously had a stem pressed into it, it may well be now slightly oversise and have lost some interference, it needs to be  carefully measured and checked, you dont want to make the shaft too small on the diameter then find it fits into the clamp like a di** in a shirtsleeve. If you wanted to you could cut keyways in the shaft and clamp and fit a parallel key to keep it stiff and tight. What are you going to make it from? I suggest EN19, its a commonly used high tensile alloy steel with good torsional strength and a good corrosion resistance owing to a slight chrome content.

http://www.westyorkssteel.com/Product_Info/Alloy_Steel/alloyst.htm#top%20of%20page

sledge, i didn't undrstand half the post. sorry, i don't speak machineish   .

QuoteDont forget to include a slight radius at each diameter change for strength

do you mean a slope instead of a step?

Quoteensure the bearing land diameters are identical to the original stem

the section which the bearing sits upon?

QuoteThe threads will have to be machined, doubt you will get a die with those  O/Ds and pitch

sorry...

QuoteI would include a slight shoulder on the press fit diameter to stop it being pressed home too far as well as the circlip facility mentioned by Werase

won't the donor stem have these?

Appologies, I will try in simpler terms.

Its vital when maching shafts that step in diameter to include a slight radius at the point of change. A 90deg step will seriously reduce the amount of torsion a shaft can handle and weaken it as a result. On Engineering drawings a step-radius will typically be indicated R=2.5mm. What it means is the step must be rounded and form in section a 90 deg  segment of a circle 5mm in diameter. Your drawing shows a 90 deg shoulder at the bottom of each bearing diameter, this would not be good practise, rather than being a 90deg corner it needs to be a quarter-circle. The inner race of the bearing will have a chamfer which will accomodate the step-radius when it is in position and in your case you will need to identify the  chamfer-radius on the bearing first and make the step-radius to suit. You also need to make the shoulder wide enough to allow the bearing to butt-up to it squarely without it being affected by the step-radius.

The use of the term `slope` is incorrect in this application, a gradual change in diameter along a shaft from one point to another is known as a Taper and over a distance its known as a Tapered section.

Bearing lands or journals are the terms used to identify the sections where the inner-race of the bearings sit. The Gs5 uses 2 industry standard taper- roller bearings on the stem. The top is a ISO-32005 the bottom is a ISO-32006, the inside diameters being 25 and 30 mm respectively. As the bottom bearing needs to be a tight (interference) fit  the diameter at this section should be exactly 30.00 to 30.01mm diameter, this will prevent it moving. The top bearing `floats` to allow for preload, this land needs to be undersize to allow for the required movement of the bearing, 24.96mm diameter will do.

The threads will need to be screwcut on a lathe. Threads are usually made using a tool called a Die, its like a big nut that you screw onto the shaft, it cuts the thread as turns. Owing to the large diameter and fine pitch of the required thread (which has not been specified but I know from experience). I doubt a die is available that will cut the required size. If one is it will cost a fortune and not be freely available. The threads will be a standard size and need to be cut to match the locknuts

I would include a shoulder as an addition to your drawing to prevent the press-fit diameter from being pushed too far into the clamp and to prevent the stem from moving through should it become loose in the clamp. It would be an integral part of the shaft and not transferable from another one. I dont know if the Gs5 stem has one although Werase confirms it does have a circlip groove cut in it

I have tried to keep it simple but find it difficult, before you can design a part you have to know how the part will be correctly made and how to provide all the required information in a drawing and how to identify a suitable material. There is no easy way to explain in depth. If you are going to design a stem with a view to having one made and want to get it right 1st time I suggest you talk face to face with an experienced  machinist who can explain what information is required on the drawing and the operations needed to make one but I do have experience of small-scale Engineering design and will be happy to help you in any way I can.

before i read this i just wanna say - YOU ARE THE MAN!!! sledge  --------->> the man!!!

i've actually understood everything 

okay since this is a little beyond me i will leave it to anyone who'll come along. i think explaining and drawing how to make a custom stem will be nice and helpful in the wiki front fork section. i won't go this deep for it.

thank you sledge.

Thank YOU, you are most welcome. Glad you found my comments helpful  If you want to go further into design I suggest a websearch on `Roarks formulas`and the link explains chamfers and step-radii better than I can.
http://www.tec.nsk.com/Handbook.asp?menu=6,0,0,0&PageID=/TolerancesAndAccuracy/ChamferDimensionLimits2.html