TS Fork Springs

[Marcus]

Hi Everyone,

I am missing the fork springs for my 1925 TS, when I went to the UK a few months ago I ordered a set from the spares, however they were for the earlier forks with the formed loop on both ends of the springs. The type I need are plain springs and have the end fittings that screw into the springs.
Can anyone tell me if these are available or if not I will need to get some wound, however, I don't have any details. Could someone please tell me how many coils, the free length and diameter of the coils and also the diameter of the spring wire. I would also be very grateful for a sketch with dimensions for the fittings that screw into the ends of the springs and then attach the springs to the forks so that I can make some.

Many Thanks
Marcus

[Marcus]

I found a photo of the forks and by scaling off a known dimension, I believe theses are what it should be, but I still don't know the gauge of the wire, if someone could please measure it.

Free Length = 6 inches
Outside diameter = 1 1/2 inches
Number of coils = 18
Wire gauge = unknown

If I've got these wrong I will be pleased to be corrected.

And a sketch with dimensions of the ends that screw into the ends of spring please.

Thanks

Marcus

[Hutch]

Hi Marcus,

I have a few  used rough TS / CW springs with the ends removed so I have been able to measure these dimensions for you;

"Free Length = 6 inches"

Note some of these springs have been slightly stretched at the ends where the screw in fitting goes. No idea what the spring length was originally as all these springs have been used.

Spring 1   5.84"
Spring 2   5.77"
Spring 3   5.78"
Spring 4   5.73"
Spring 5   5.81"
Spring 6   5.78"


"Outside diameter = 1 1/2 inches"

Spring 1   1.37"
Spring 2   1.39" some surface rust
Spring 3   1.39" some surface rust
Spring 4   1.37"
Spring 5   1.37"
Spring 6   1.37"

So diameter is probably 1 3/8"

"Number of coils = 18"

Yes all 6 have 18 full turns

"Wire gauge = unknown"

Spring 1   0.212"
Spring 2   0.218"
Spring 3   0.218"
Spring 4   0.208"
Spring 5   0.208"
Spring 6   0.212"

So possibly SWG (British) 5 or approx.7/32" diameter wire ?



A pair of these used springs are possibly surplus to my requirements but would probably take a bit of work to clean up and polish adequately for nickel plating if that was the finish you were going to use. They would be ok for painting tho'. PM me if you are interested.

I have some new springs which came with a job lot - origin unknown, length 5.74", diameter 1.38", wire diameter 0.209" 19 turns rather than 18 - so they will be slightly softer than used original springs shown above.

"And a sketch with dimensions of the ends that screw into the ends of spring please."


The ends appear to be cast  (i would assume them to be more uniform in appearance if they were forged?)- I would guess the original material is steel rather than iron but not 100% sure as I have had one shatter when I unscrewed it out of the spring (this procedure can be interesting as the spring grips the fitting quite tightly and it is hard to get a good hold on the spring! If I had to do it again I might make a jig to make the job easier). I don't have enough spares of these for a full set of the ends but PM me as I have a spare rough one you could use as a pattern or I can sketch it for you.

It would be interesting to see what dimensions other forum members have for their vintage 2 3/4hp fork springs?

Cheers

Hutch

[Marcus]

Hi Hutch,

Thank you for the trouble you have gone to measuring these, it gives some great data and I think we can be pretty sure now on what the original sizes would have been. Its almost always that the original dimension would have been to the nearest large fraction. So I am happy that the length would have been 5 3/4" long and the variation will be due to stretch over the years.  The photo I went from has some light load on the springs so I'm happy with 5 3/4.

The diameter as you say would almost certainly have been 1 3/8" as I imagine there would be some slight variation as spring manufacture is not as accurate as machining a part.

Some variation in the measured spring wire diameter but as you say 100 years of rust will have taken its toll. So yes 5g at 0.212" is the closest size and that's what I will use.

Rob in Melbourne contacted me to say that he has a spare spring which he is happy to lend me to copy and it has the ends and also the shoulder bolt so I can get a pair made locally and do a CAD drawing of the ends and have them laser cut in steel.

Thanks again for your work on this, once I have the drawing done of the ends I will post it here in case it helps someone in future who needs to get some made.

Cheers

Marcus

[Hutch]

No worries Marcus,

When you get the spring end from Rob it will be a much better guide than a rough sketch by me - in particular the "thread" part for the spring. I think it would be quite tricky to completely cut them out with a laser cutter in one go and they may require a second operation after cutting? First thought is to use a Lathe and tool post grinder, but the "thread" pitch is a strange one (maybe a bit over 3tpi to 3.5 tpi ??) and I think less than the lowest my old Hercus will do (4tpi? will have to check that).

I think there are two possible threads for the shoulder nuts? - I will check.  Which ones you need may depend on your actual spindle / fork setup? I think from memory Chris's nut and bolt guide has the two options?

Have fun!

Cheers

Hutch

[Marcus]

Thanks for posting those Hutch, I hadn't seen them before and was guessing at what they looked like.

I will get them Laser cut and the radius that is on the eye I can do carefully on the linisher and where is winds into the spring I can do with a small round file.

I'll post some photos when they are finished.

Regarding the thread for the shoulder bolts, according to the list of threads they are;

Forks spring anchors on later forks. Qty 2 fork end.                                    3/8” x 20 tpi. BSF.
Fork spring anchors outer end and special pivot nuts. Qty 4                        3/8” x 28 tpi.

The parts are in my workshop on the other side of Auckland so I will need to double check to make sure


Cheers

Marcus

[Marcus]

Thanks to Hutch and Rob in Melbourne who lent me an original spring and end fitting, I have had a couple of new springs wound and drawn up and had laser cut, the end fittings. I have also made the other parts shown in the last photo. If anyone needs any of these let me know and I will see if I can help.

Marcus