Steady Rest Set Up for Motorcycle Fork Leg

[mcman56]

I plan to install bushings at the top of a motorcycle fork leg and found some of the appropriate size. I have read up a bit on here about set up of a steady rest so would like some verification that I have done this correctly. I have used a steady rest before but accuracy wasn't that important.

I made a stepped arbor that fits in a hole centered on the bottom of the leg and bolts on from the inside. I also turned a rod to to be the same diameter of the end to be supported by the steady rest. Pictures are below. My procedure was as follows.
- Steady rest size rod was centered in 4 jaw chuck.
- Steady rest was slid onto rod and bolted down. One by one, a 0.0015 feeler gage was used to ensure a small gap between rod and each leg of the steady rest.
- Steady rest was slid down and arbor with leg was mounted in 4 jaw. This was then centered.
- I went to slide steady rest onto end of fork leg but it was not perfectly aligned. (maybe off by 1/8", see picture) The bottom of the leg that gets pulled to the arbor is a bit beat up so not perfectly flat and I don't see a good way to cut it flat. This bothers me some.
- I loosened the bolt holding the leg to the arbor, slid the arbor in place and locked it down. I tightened the bolt to arbor, applied a little oil and easily spun the spindle by hand. Spinning at 460 rpm seems OK also.
- Is there something else I can to to ensure/ verify alignment?

[Bill Shields]

You are 90% of the way there.

What is driving the leg rotationally?

What keeps the leg from moving along the long axis away from the chuck?

The answer to both may be the same...how is the leg anchored to the aluminum sleeve held in the chuck?

If it is not locked down ..it's a gonna move...

[mcman56]

There is a stepped arbor in the chuck. The stepped part of the arbor is inserted into a deep hole in the bottom of the fork leg. A bolt goes from inside the fork leg into a threaded hole in the middle of the arbor. When the bolt is tightened, it pulls the leg to the arbor and clamps it in place.

[Bill Shields]

[arborist]

I think it is important to true up the the bottom of the fork leg. To do so, reverse your set up and work on the bottom first. Turn up a plug that is a good fit in the top of the fork and set it to run true. Jubilee clip around the top of the fork leg and use it to improvise a drive dog.

Use a (half-)center in the tailstock, locating in the counterbore in the bottom of the fork leg. Skim a narrow steady band (maybe 1/4" wide) on the outside of the leg and face off the bottom of the leg. You do not need to face all the way to the centre, just make a surface that is 90 degrees to the steady band. If the half centre does not work because the counterbore is too large or its end is damaged, turn up a good fitting plug for the counterbore with a female center in its end, and use a standard center. It won't matter if you dig into the plug so you can face the entire bottom true.

Then, when setting up to bore the top of the leg, make a cup-shaped carrier for the bottom, that fits over your narrow steady band. If only part of the bottom is is flat, relieve the carrier so it only bears on true surfaces. Bolt it through as before using an undersize bolt - the geometry of the part determines its truth and any influence from the clamping bolt is removed.

Use the plug you made for the top of the fork at the tailstock end in conjunction with the tailstock to get that end running true. Put on the fixed steady. Remove plug and tailstock. Bore as required.

[mcman56]

I still need to install the bush and test fit but there was an anomaly during machining. I started to get a knocking sound like a nut was loose and rolling around inside the tube. Adding oil to the steady rest/ tube interface usually got rid of the knock. The setup was a bit out of balance so there was a little shake to the machine. My steady rest has simple brass tips without bearings. Can these wear a bit during the run, get loose and cause a knock? There is an arc on the brass tip but it does not perfectly match the OD of the tube so it was not wearing on the full surface. The tubes are some kind of cast aluminium and I found I had to take very small cuts, like 0.010 to get a nice finish.

I was afraid to add the extra step of truing up the bottom surface because it seemed like one more opportunity for me to do something wrong.

[Bill Shields]

Use heavier oil.. maybe way oil or chain saw lube.

If needed get someone to do oil can duty

I have used grease...

It is an art ..like baking a cake.

All ingredients must be correct.

As for something rolling around inside....well -> is there?

You are cutting with the part rotating so that it will keep your draw but tight...?

[Harold_V]

I strongly suspect that the noise you are generating is the result of the piece not being properly supported by the steady. It is knocking against the steady jaws as it rotates. If that's the case, you risk creating a non-symmetrical bore for your bushing.

The steady in use should have intimate contact with the piece being machined. Any clearance will create issues. The clearance should be no greater than that which is required for a film of lubrication.

H

[mcman56]

I pulled it apart and all was tight with nothing loose. No sounds with the setup removed but I will check the gear box oil.

However, the bore come a few thousands off center. I don't have a good way to measure but I can see a step on one side where I sunk the counter bore for the seal area. The tube gets tight when it passes through the bushing and enters the solid part of the bore below. See pics.

I have never tried working with something that long in this lathe. Could I be asking too much from a basic 13 x 40 Enco lathe? If the bed is not straight would the steady rest force the tool post and fork leg in correct alignment? I would like to be able to verify that the bore is on center at the steady rest prior to cutting but I can not think of a way to do that. I don't know what I could reference from.

[Bill Shields]

Nothing wrong with the lathe....for a first time you did a very good job.

[mcman56]

How can I do better and make the part functional?

[Bill Shields]

My guess is that you need to stiffen up on the steady support, since every .001" loose on the steady translates directly to the part.

Ball bearing steady work well.

I have also wrapped the part in a piece of brass shim and lubed the heck out of it.

Shim stays stationary and part rotates inside of it...basically becomes a big journal bearing.

Or you can bore yourself a piece of brass and make a sleeve into which the leg slides to rotate, and figure out a way to anchor it in the steady without squeezing.

Or you can cut the tip of the steady legs to have a matching arc for the OD of where it is guiding the fork leg

Or all of the above.

Like I said...it is an art.

Question: what is the ID of the bore you now have and what bore do you need?

Is the bore straight or tapered ?

This kind of tells us all how many more tries you will get before you are at the aw shoot moment..