Half shaft resto

[Alan S.]

Re: Half shaft resto

Hi Jordon,
Boy, you've really put a lot of thought and effort into your half shafts with quite a remarkable result.
I put semi gloss clear on my half shafts and drive shaft as you're planing to do. I started out with a VERY thorough but very LIGHT coat and have been surprised how well the paint has held off the start of rust. I would think that how the car is used and housed will have an impact on how much protection the surfaces will need.
Just a thought for your consideration.
Regards,
Alan

[Tom R.]

Re: Half shaft resto

Also remember the chassis parts are difficult to judge. Low light conditions, or worse yet shadows on a sunny day, and poor access make for a lot of latitude under the car.

As a chassis judge, the undercarriage gets a "shot" or to look with a high quality flashlight, looking for finish. I liken the shot to what we describe when we recollect factory workers bending over with a spray gun to "shoot" the cover or wheelwell, targeted, quick and move on.

In the event the half shaft (or draft shaft) looks too nice, cast blast, black paint, than it gets subjected to further study. So I suspect a set like those shown above would pique our curiosity to understand what techniques were applied...of course in the event we need to tap those techniques for our personal use.

[Greg G.]

Re: Half shaft resto

The second photo I posted is of the drive shaft, which is not shot blasted. I suspect for the shot blasted half-shafts the heat affected zone would be diminished, and perhaps even removed, by the shot blasting process. The first photo seems to show that.

Terry I noticed that the 2nd photo is a drive shaft and does show how the HAZ should look.


A quote (from the 65) judging manual says "Driveshafts and half shafts are natural finish extruded steel tubes welded to natural forged steel yokes. Original tubes should not show evidence of patterned surface or a turned in the lathe appearance. The weld bead shows a moderate amount of discoloration due to heat".

And " Big block cars use a shot peened half-shaft and yoke assembly with a dab of lime green on the shaft."

I know that the Judging manuals do not cover all that needs to be known but if I understand this right;

1. The small block shafts would show a shinier surface with distinct HAZ from being welded both on the cap ends and longitudinally.

2. The big block shafts would show little or no HAZ and would not have any shine to them.


So, is the 1st photo an original big block that hasn't been touched in anyway since it came from the factory, i.e. ever been bead blasted? This would support statement number 2, above.

I attached the pics of some shafts that I done but I have included two pics of a set that I shot peened that show some of the HAZ coming through (can be seen if you zoom in) and a set of half shafts that would be ok for a SB and a drive shaft.

So judges how would these score?

Greg

[Terry M.]

Re: Half shaft resto

Terry I noticed that the 2nd photo is a drive shaft and does show how the HAZ should look.

So, is the 1st photo an original big block that hasn't been touched in anyway since it came from the factory, i.e. ever been bead blasted? This would support statement number 2, above.

Greg

Greg,
The photos are of a 1972 with 4 miles showing on the odometer. It is a 5-Star BowTie Award winner. The car is a 454/M40 -- BB Automatic. I actually took the photos to show the differential tag and the driveshaft stencil -- but as often happens, there is enough other detail to fuel this discussion.

I believe this history supports your second statement.

[Greg G.]

Re: Half shaft resto

Thanks, that clears things up in my mind. The photos I attached look very close to what yours show. What do you think?

Greg

[Terry M.]

Re: Half shaft resto

Greg,
The half shafts look good, but the level of pitting on the cast ends might be less. Someplace I have the words from the print, and I'll post them if I can find them, but basically the instructions were to protect the holes where the trunnion goes. I suspect whatever they used extended over the casting to some extent. It is certainly not worth the effort to change these, but if you ever get the chance to do another set, consider shielding the cast ends a bit.

In the third picture I like the top shaft HAZ. I think the lower shaft HAZ, especially the left weld, has the HAZ short of the weld bead. The weld bead would be the source of the heat, so it should be heated as well as the shaft.

I hope others will offer their opinion. I can't be the only one with the stones to put his opinion on the line.

[Greg G.]

Re: Half shaft resto

Terry good points,

I appreciated the time for you replies. The '65 Judging Manual says ...."steel tubes welded to natural forged steel yokes."...... and "Big block cars use shot peened half shaft and yoke assembly".

So do you think the yoke would be shot peened and either machined afterwards or just the machined areas protected before shot peening?

Some of the yoke surface on my example may have been affected by surface rust before I restored them.

Greg

[Terry M.]

Re: Half shaft resto

I believe the shot peening operation was after machining. My belief is that the machined ends were welded to the tubes in an automated operation.

Then a number of the shafts were sent to be shot blasted. The instructions say to protect the machined areas -- I don't know how. If it was to push a tube through the holes in the ends, or hang the shafts from something through the trunnion holes -- I don't know.

I think typically the shot peening operation is also automated -- that is the shafts went through the shot booth on a mechanized transfer line. I would think there was some way to rotate the shaft while in the shot cabinet so that all of the circumference would be treated.

The shot peening operation strengthens the surface of the tube. When a torque, or twisting moment is applied to a shaft, most of the force is near the outer surface of the shaft -- that is why a tube is used, rather than a solid shaft. Strengthening the surface makes the tube more resistant to twisting.

http://www.aerospace-technology.com/contractors/manufacturing/wheelabrator/

[Harmon C.]

Re: Half shaft resto

Most half shafts will get a deduction for one of the following finish reasons. To much rust,not enough rust as delivered should have flash rust,clear coat of any kind,bead blasted finish, no weld seam heated area,cast blast,ect.ect. Their is a good chance most half shafts lose one point for one of the above reasons.
Best way I see it is spend more time on parts you can get 100% correct and take the one point deduction on the half shafts.
If a perfect 100% NCRS judging score is your goal their is a good chance you won't enjoy judging.

[Jordan S.]

Re: Half shaft resto

The genius in your restoration method is the application of the blackening solution...the HAZ is a tough look to replicate, but yours looks pretty close to how I think it would have appeared.

My thought was always that the longitudinal seam should have about the same degree of blackening as the yoke welds because the steel had to have been subjected to similar heat levels in both cases, but that was without any real knowledge of the processes. The longitudinal weld was done at a different time in the manufacturing sequence, and is virtually invisible (has no visible weld bead) compared to the yoke welds.

The bead blasting is pretty straight forward for most of us. My opinion is the cross hatch sanding with four grades of paper is masochistic overkill. The surface appearance can also be restored close to freshly fabricated tube by simply burnishing the bead blasted surface with steel wool.

Depending on how much rust you started with, the cross hatch sanding may, in my opinion, needlessly remove or alter original texture detail such as the shot peened appearance for big block cars mentioned by Patrick (Bead blasting would also slightly alter the surface texture, but it's the best alternative I know for removing the rust).

I've not seen an original big block half shaft, but I believe the shot peened look for big block cars mentioned by Patrick would be closer to the appearance immediately after bead blasting without any further treatment, but in your case, I wouldn't mess with the results you've obtained. In my opinion, fresh shot peening would be a dull dark matte gray, where freshly bead blasted steel is a lighter matte silver-gray.

Thanks Chuck. I Really like the current look of my half shaft and will do the other to match.

I'm also very appreciative to all those that have posted here. The pics and info really help define what we are trying to re-create.

Jordan

[Harmon C.]

Re: Half shaft resto

As a chassis judge, the undercarriage gets a "shot" or to look with a high quality flashlight, looking for finish. I liken the shot to what we describe when we recollect factory workers bending over with a spray gun to "shoot" the cover or wheelwell, targeted, quick and move on.

In the event the half shaft (or draft shaft) looks too nice, cast blast, black paint, than it gets subjected to further study. So I suspect a set like those shown above would pique our curiosity to understand what techniques were applied...of course in the event we need to tap those techniques for our personal use.

The chassis judge I see working the field today brings his own mat or cardboard lays down under the car on his back looks like he enjoys his work and picks the chassis apart with a fine tooth comb. I see no breaks because of low light or hard to see. He then just gives a fair judging of what he sees with a high power light. The days of long wet grass at a regional are in the past.

[Patrick H.]

Re: Half shaft resto

The chassis judge I see working the field today brings his own mat or cardboard lays down under the car on his back looks like he enjoys his work and picks the chassis apart with a fine tooth comb. I see no breaks because of low light or hard to see. He then just gives a fair judging of what he sees with a high power light. The days of long wet grass at a regional are in the past.

Being a chassis judge and also having run a Regional, you're correct on both accounts.
I wear old clothes and prepare to get dirty. In fact, even with our indoor Regional we supplied Tyvek suits for the chassis judges so that they could stay clean (and keep our nice Regional shirts clean). I usually have 2 different flashlights with me to analyze parts and finishes. LED lights and incandescent lights both show different things.

I don't foresee many Regional events in the northern half of the country being outdoors again due to weather concerns. Carlisle 2007 showed the folly of using big tents.

Patrick

[Chuck S.]

Re: Half shaft resto

...In the third picture I like the top shaft HAZ. I think the lower shaft HAZ, especially the left weld, has the HAZ short of the weld bead. The weld bead would be the source of the heat, so it should be heated as well as the shaft...

I concur with your observations, Terry...I also noticed that the HAZ seemed to start where the weld ended, instead of the actual weld being the source of the heat.

This replication of the HAZ looks genuine, as if it were done with real heat. I have heard of this being done in shaft restoration. I don't have any specific metallurgical knowledge to back it up, but personally, I would be reluctant to apply enough heat to these welds to "blue" them. Perhaps no adverse effects are realized, only further stress relief, but I would prefer "cold" methods to replicate this appearance.

...The shot peening operation strengthens the surface of the tube. When a torque, or twisting moment is applied to a shaft, most of the force is near the outer surface of the shaft -- that is why a tube is used, rather than a solid shaft. Strengthening the surface makes the tube more resistant to twisting...

Your reasons for shot peening are correct, but the primary reason a tube is used instead of a solid shaft is that it permits a much lighter shaft with the same strength.

Basic machine design says that the moment of inertia, one of the primary section characteristics affecting strength, is increased dramatically by moving the mass of the section as far from the center of section mass as possible...to wit, the strongest, lightest cross section is a tube which has all of its mass as far from the center as possible. That's why aerospace vehicles are virtually always circular in cross section. A circular section allows the tube wall thickness and weight to be further reduced. Ultimately, long thin circular section components properly designed for torsion will fail in a different manner, such as column buckling.

[Terry M.]

Re: Half shaft resto

Chuck,
I believe we are singing the same song -- just in different keys. In spite of working with engineers for my entire career, I don't speak or write good engineereze

There is no, or little, strength advantage to a solid bar in a twisting moment. So certainly the weight penalty of a solid bar would be a negative in the suto business. Later Corvette half shafts showed up in aluminum, but at a larger diameter than the steel.

The shot peening strengthens the outer surface of the tube, and this is a major advantage in increasing the strength of the tube.

I once saw a picture of a shaft (prop shaft to use the proper term) in which the longitudinal HAZ was twisted over 180*. No break, but it looked like the next run would have turned it into a pretzel. Some real power and very sticky tires combined to make the weakest link the prop shaft.