Ask an Engineer

[Ocean1]

there is a thread I posted about a guy who made inlet manifolds (reed rubbers) at home for a RD somewhere.
...

What on earth is he using?

I've done similar with potable silicone. In fact there's several litres still under a bench here somewhere that must be close to the end of it's shelf life...

[husaberg]

What on earth is he using?

I've done similar with potable silicone. In fact there's several litres still under a bench here somewhere that must be close to the end of it's shelf life...

Rubber... There is or was a thread where he datails it throughly more likely a RD yamaha forum one i guess, If you google his user name it might pop up.
I was surprised how quick i found the video. They look very professional right down to the parts numbers......

http://www.precisiontradingsystems.c...s_its_made.htm

[Seraph]

Would 40nb Apl5l bgrade seamless sch80 suffice for fork legs strength wise?

[Grumph]

Would 40nb Apl5l bgrade seamless sch80 suffice for fork legs strength wise?

what wall thickness is it going to finish up - and what end use ? street or motocross ?

from memory that's pretty close to what Ceriani used for stanchions back in the day.

Edit - on thinking a bit more, what surface finish are you planning on ? ideally the sequence is, grind, hard chrome, finish grind...but you want something which doesn't suffer badly from hydrogen embrittlement - and that I don't personally know about this material. Suppliers should have that info, along with any suggested heat treatments to remove the hydrogen.

[Ocean1]

Would 40nb Apl5l bgrade seamless sch80 suffice for fork legs strength wise?

What's important for forks is that the stanchions are stiff, and all carbon steels have pretty much the same elasticity. Ultimate elastic limits are almost irrelevant, well before you bend them anywhere near that the tube has distorted more than the clearance between the stanchions and the sliders and they've seized, dramatically increasing load.

So the trick is to specify tube diameter and wall thickness that will take the load of your intended design and use without distorting that much. You can work that out, but to be honest my attempts rarely describe what happens in the real world. It's just easier to look at what works in similar equipment and start from there, let Mr Honda pay for the hundreds of iterations required to get it right.

Having said that once you've figured out the dimensions req'd the extra cost of 4130 chromoly isn't much beside the cost of making them.

If you want to try anyway these are the numbers you probably need to use:

what wall thickness is it going to finish up - and what end use ?

Several times over the years I've bought fork stanchions to use for completely unrelated projects simply because it's a known quantity and quality. In fact in one instance the prototype led rapidly to an order for about 20 units, asap. I had all sorts of trouble trying to explain an order for 20 Honda XR400 fork stanchions.

[Seraph]

I should have mentioned this will be for rear legs on a springer around about 1300 long, 4130 would have been ideal but my triples for this set are a rather funny diameter. I wanted plenty of material to turn down and still leave some beef..
I know the numbers but in a real world situation I honestly dont know what id be looking at in terms of pressure and stress put on them.. I can design machine and weld but when it comes to the math im a little lost

[Ocean1]

I should have mentioned this will be for rear legs on a springer around about 1300 long, 4130 would have been ideal but my triples for this set are a rather funny diameter. I wanted plenty of material to turn down and still leave some beef..
I know the numbers but in a real world situation I honestly dont know what id be looking at in terms of pressure and stress put on them.. I can design machine and weld but when it comes to the math im a little lost

Join the club.

I like leading link setups for that application though, standard forks at that length on that much rake have too much stiction.

I'd have thought there would be plenty of technical data available on US chopper sites though, no?

[Seraph]

Join the club.

I like leading link setups for that application though, standard forks at that length on that much rake have too much stiction.

I'd have thought there would be plenty of technical data available on US chopper sites though, no?

There's some, but nothing in the diameter range im looking at (50mm..) most of the build material seems to be DOM or good ol erw..

[Grumph]

There's some, but nothing in the diameter range im looking at (50mm..) most of the build material seems to be DOM or good ol erw..

which says something too....

You could check it the good old rough way...take a 2G bump load at the axle and multiply it by say 4 for the load adjacent to the bottom triple clamp. Tube specs should give you the yeild point. If the calculation is less than the yeild stress, she'll be sweet.

Load on front wheel (laden, worst case scenario) at a guess 200Kg (rough guess...) X 2G = 400. Times 4 equals 1600Kg at the bottom triple...Divided by the two tubes is 800Kg each. This is bump case - not running into a wall....

A good quality 50mm OD tube shouldn't bend at that...And given it's a springer, at least some of the loads will be taken higher up the tube rather than reacted at the axle - which will reduce the loads too.

[Brian d marge]

If its for the rear tubes on a springer , ya dont need anything fancy. It isnt a sliding surface so you dont need a Hard finish.

From Memory a mild steel DOM would be fine ,I will check though , Remember Stiffness is a product of size not material, The reason why USD forks are large dia but very thin wall thickness

Finally if you are building springers , the americans have been there done that , there are a few plans already on the net ,

Stephen

[Ocean1]

which says something too....

You could check it the good old rough way...take a 2G bump load at the axle and multiply it by say 4 for the load adjacent to the bottom triple clamp. Tube specs should give you the yeild point. If the calculation is less than the yeild stress, she'll be sweet.

Load on front wheel (laden, worst case scenario) at a guess 200Kg (rough guess...) X 2G = 400. Times 4 equals 1600Kg at the bottom triple...Divided by the two tubes is 800Kg each. This is bump case - not running into a wall....

A good quality 50mm OD tube shouldn't bend at that...And given it's a springer, at least some of the loads will be taken higher up the tube rather than reacted at the axle - which will reduce the loads too.

Aye, in fact around half the normal suspension axle load will be on the front compression rods, so that'd be well conservative.

In which case 50mm sounds big, (given a couple of mm wall thickness), and I don't remember having seen a springer front end main tube that big.

Edit: was looking for examples and came across this: http://www.tonyfoale.com/Articles/Steer/STEER.htm

[Seraph]

Well by the sounds of it I should be fine.. 50mm is more of a aesthetic choice than function.. well ill get everything turned down monday and see how it does

thanks!

[bogan]

There's at least one place in ChCh who can vulcanise same. Try the yellow pages local to you for rubber bits makers - rollers etc.

So, the shit I got locally isn't very fuel safe and has turned to shit. Who are the guys in ChCh, a good recommendation is well worth the shipping there and back... Figure I can just machine a pocket into the bit of ali they now sit against and get it vulcansied in there for a permanent solution.

[Grumph]

So, the shit I got locally isn't very fuel safe and has turned to shit. Who are the guys in ChCh, a good recommendation is well worth the shipping there and back... Figure I can just machine a pocket into the bit of ali they now sit against and get it vulcansied in there for a permanent solution.

Conveyor Belt specialists in ChCh were one of the places I meant. The other was a little place round the corner from Mace eng who seem to have disappeared post quakes. Local to you i'm sure there's a conveyor belt place who can do vulcanising. Again, check your local yellow pages for rubber products places.
I've only just realised my favourite small outfit referred to above has gone. Bugger it - they did all sorts of little bits of rubber mounts. very useful.

[husaberg]

Conveyor Belt specialists in ChCh were one of the places I meant. The other was a little place round the corner from Mace eng who seem to have disappeared post quakes. Local to you i'm sure there's a conveyor belt place who can do vulcanising. Again, check your local yellow pages for rubber products places.
I've only just realised my favourite small outfit referred to above has gone. Bugger it - they did all sorts of little bits of rubber mounts. very useful.

I had a tiki tour around central city last week there is so much stuff gone, it was bloody hard to navigate at all, with few landmarks.
Where I used to live (The old Para building), where I used to work Whiting's, Where I used to drink, where I used to get my lunch... all gone