making an IFP tool for a Fox Fork

finished tool with valve stem thingy intserted

closeup showing the ghetto interface of the valvestem and the finished tool

closeup showing the bit and the working end of the finished tool

the feedrate is about 0.125" per minute...so drilling the end hole is by far the most focused and delicate part of this ordeal.

Why?!?!
It was my interpretation that the IFP tool was the fundamental obstacle between the mechanically inclined commoner and a Fox Fork rebuild. At 90 buckers, the IFP tool is hard to justify when sending the fork back to Fox is less than 200 for a rebuild. Intentional? I don't know, but I wasn't willing to settle.

Here's a link to an available IFP tool online.

I find learning the process of how something works far more rewarding than participating in some capitalistic black box system where I can fulfill my own needs and solve my own problems with brute cash power. And so, I set out to do the fox Talas RLC rebuild on my own grad student budget...

Issues in the fork rebuild: Getting started....

Oil:
I saved 8 bucks by getting the fork oil directly from the manufacturer, in this case Torco. The oil Fox uses is Torco RSF Medium Shock Fluid. A quart should last for the rest of your mountain biking life. Total for oil = $22. The buy online feature wasn't working so I had to call in.

For my other less finicky forks, I purchased (locally) synthetic 7W motorcycle fork oil that costs less than $10 per quart. Peter Verdone makes a very good point about oil weights being completely subjective. SAE oils are rated against a set of kinematic viscosity standards and are labeled with a particular grade. Other oils, such as those used in suspension systems, are not subjected to such evaluations by the SAE, and a greater variance in oil viscosities for a specific grade is expected. He lists some suspension oils by viscosity (not grade) for comparison.

Seals:
I went ahead and purchased some enduro fork seals. Not sure how they'll work, but havn't read any real complaints except from the Fox folks...duh.


Making the tool...

Machining the business end:
The only real design concern in machining an IFP tool was the tiny hole in the end. The tool is effectively a glorified basketball needle, and infact I've read of some pressurizing their IFP chamber with a few wraps of electrical tape and a bball needle.

To create this small hole, I purchased 0.0370" (a little bigger than 1/32") drill bits from drill bit city. They sent me a 10 pack for under $15. The bits are tungsten carbide, are especially concentric, and of course gnaw right through my mild steel stock without much problem. I broke the practice bit, but in the process established an appropriate feed rate on the tailstock and then finished the tool without a problem. I was able to sink the bit clear up to the shank.

Before drilling I center punch the stock by pressing a dead center into the part blank with slight pressure. The small bit needs no more than a small divot. I make sure to face the surface beforehand, as well.

Additionally, the size of the tool is limited by the length of the drill bit I use to bore the length out. Fortunately, using a 3/32" bit affords a sufficient column thickness and is just long enough to bore a tool that will fit down into the counterbore of the Talas head.

End Valve:
Initially I purchased stock of such a diameter that would allow me to machine a schrader valve right into the end, purchase some valve cores and thread them down...and waalaa. But that didn't work out. Be advised that schrader valve threads at 32 tpi external and 36 tpi internal are exotic sizes and pitches: taps and dies are not readily available. Coincidentally, the gear I needed on the lathe to run a 32 tpi was missing as well, so I had to conjure another solution.

Regular valve stems are available for well under $1 per stem. So I purchased one, stripped the rubber off the bottom and threaded the brass column in a common metric thread. I bored the large end of the IFP tool and tapped it accordingly. It looks a bit ghetto...whatever.

I'll finish the rebuild next week (as my life projects move forward at a geologic pace) and update the post as to whether this contrivance fulfills it's complete duty. I'll crank out a few more if there are any takers - total machine time is about an hour, with alot of that time boring out the center of the tool. But if I can help anyone from spending 90 bucks on something as silly as an IFP tool, then great, let me know.

Total overhead so far = $66 (including seals and oil)

I have some CAD prints and more photos for later.