worm gear pressed off

Does anyone have any recommendation for the reinstallation of a worm gear to the short shaft on a tr3a? I had the worm gear pressed off one shaft and onto another at machine shop. It was the Nappa shop in Tacoma and they where helpful and did not charge me. At the tr factory they let the end of the rod run long and then pinned it over somehow, creating this bell capped fit on the end that holds the gear tight. However, when I had the worm gear pressed onto the new shaft. I am finding that recreating this penned end is not easy. I have used a ball peen hammer to get it going somewhat, but to get it tight is another issue. In fact, twice now as I have been peening the end over the worm gear has loosened up on the shaft. I am guessing because of the harmonic vibration. I took it back to the shop and they pressed it down again, but when I tried to finish the end, the worm gear starts to loosen. Now I wish I would have dropped it off and just paid them. I am confused on what to do. The last time I took it out we tried to create a flare/bell on the end by putting a ball peen hammer on the end as we pressed it. But, it would not flare. I am thinking these guys would rather see someone else come through the door. Oh my feelings. I must have turned into a sensitive guy.

I probably would have tried to use the press to swage the end back down. Perhaps with a series of punches with different tapers, to avoid having to make a die. Some Loctite would have helped, too.

But I'm not sure what to suggest from where you are now. I assume you've tried standing the shaft on a heavy piece of metal, and using a series of hammer blows around the rim of the shaft rather than trying to hit the center. If the worm is walking up the shaft from the hammer blows, it should go back the other way when you get the lip of the shaft against it.

The other solution is another trip to Tacoma, and this time pay them to fully install the worm, including the peening.

Did they heat the worm before putting it back on? I haven't tried putting one back on, but from what I've read, the worm needs to be put in an oven and heated to something like 350 degrees, then it just slides onto the shaft. When it cools it's tight. But it's still supposed to have the end 'peened', and I don't know how to go about doing that. -I don't suppose this is much help, but I think pressing it back on the shaft without expanding it first is not a good idea.

I did notice as I pulled 3 worms off, some were peened much more than others. All were tight.

Please let me know what you end up doing and how it works out.
Jer

If you have a MIG welder, access to one, or a friend who has one, you could weld a spot to lock it together.

Use a dull(-ish) chisel or similar and hammer to create an asterisk-type pattern on the end of the shaft. The use your largest ball pein to smooth over the peen. Just a suggestion; I've never done one before. But I have used this technique on my lug studs and it worked fine.

Don Elliott said:

If you have a MIG welder, access to one, or a friend who has one, you could weld a spot to lock it together.

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Take my word for it, DO NOT try to spot weld or otherwise, that hardened worm gear to the shaft!
It will only eventually break loose and sooner than later at that!
It should be a very tight pressed fit and if hammer blows are moving it on the shaft I would think it is not a near tight enough fit to ensure it not coming loose while driving the car.
Were it me, I would take it to someone that knows for sure the fitment requirements and proper replacement procedures. A few $ are not worth your safety in my opinion.
Welding a hardened material to a softer one or even two hardened materials together takes specific procedures to be done correctly without risk of failure.
{requires both materials and equipment you do not have at home}

PeterK said:

Use a dull(-ish) chisel or similar and hammer to create an asterisk-type pattern on the end of the shaft. The use your largest ball pein to smooth over the peen. Just a suggestion; I've never done one before. But I have used this technique on my lug studs and it worked fine.

Click to expand...

<span style="color: #990000">PeterK- I am real curious what this technique
is used on lug studs? What circumstances, why? Interesting.

thanks,

dale</span>

Tinster said:

PeterK said:

Use a dull(-ish) chisel or similar and hammer to create an asterisk-type pattern on the end of the shaft. The use your largest ball pein to smooth over the peen. Just a suggestion; I've never done one before. But I have used this technique on my lug studs and it worked fine.

Click to expand...

<span style="color: #990000">PeterK- I am real curious what this technique
is used on lug studs? What circumstances, why? Interesting.

thanks,

dale</span>

Click to expand...

On the TR3-4, the rear lug studs are screwed into the hub from the outside and then peened over in the back. I believe the TR6 has regular type lugs that get pressed in from the back of the hub.

I was unable to get a good picture of the 'peen' on the end of the steering shaft. It is clear that the shaft has a splined end, that is tapered close to what the worm also has on the inside. Please look at the attached pictures. Only the last 1" or so is splined, and the shaft is smaller in diameter than the inside of the worm (where the non-splined worm end will fit). Only the splines hold the worm on the shaft. If you look, the first 1/4" is what is being 'peened' to hold the splines tight inside the worm. The bearing race and/or worm end are not peened, only the shaft. The shaft is not peened in a bunch of places, it is peened uniformly as with a tapered round drift that stretches out the last 1/4" to hold the worm tight to the spline. The shaft is also hard steel, but not as hard as the worm. It must take a lot of force to peen it -or a press of some sort. This is only my observation, and like anything related to safety, if you're not comfortable with these ideas, seek professional help. -and I don't mean that exactly the way it sounds.

I'm going to agree with TexasKnucklehead. In machining classes we called that a sweat fit. As the worm gear cools down and shrinks onto the shaft the shaft heats ups and expands from the transfer of heat from the gear. It will produce such a tight fit it would be hard to press off. Also what else will happen is the hole in the worm gear will also expand and the gear will slid back farther onto the shaft getting the full advantage of the taper fit. Which is probably why when cold pressing it on it wants to walk back off. I would also have a pipe ready the same diameter as the shaft to give the gear a good whack after setting onto the shaft. Let it air cool or stick it into a bucket of sand to slow the cooling process down. The longer it cools the tighter the fit. After the sweat fit it should be tight enough to peen over the edges. What ever you do don't go over the 350 degrees. I seem to remember at 400 degrees the temper or hardness starts to change. You can do this in your oven at home. Just make sure your oven temperature is accurate.

Well, I can't prove it, but I doubt the factory bothered with a sweat fit here. The locking taper and peened end seem plenty adequate to me. After all, it's only the driver pushing/pulling on the steering wheel that tries to move the worm on the splines. The splines themselves take whatever force is needed to turn the car.

I believe the original setup was swaged in a press (using a die to spread the end of the shaft). My suggestion of peening in a bunch of places was intended as an alternate solution, when no press/die is available.

TR3driver said:

After all, it's only the driver pushing/pulling on the steering wheel that tries to move the worm on the splines. The splines themselves take whatever force is needed to turn the car.

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Disclaimer: I haven't had my coffee yet, so may very well be off base here.

When the driver turns the steering wheel and thus the worm, wouldn't the rocker shaft peg pushing back on the spiral groove in the worm (reaction force to worm pushing on peg) cause a force vector that would try to move the worm along the shaft?

I just answered my own question.

Yes, the force would try to move the worm, but it can't go anywhere because of the ball bearings in front and behind.

I'll never pre-coffee post again.

Twosheds said:

I'll never pre-coffee post again.

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No worries; it's a good question (and a good answer).

Well thanks all for your comments and the dialectic you shared. I learned a lot. Where I am at now is I have the end peened some and would have to stretch that out again if the worm was pull off to heat it. In addition, I would probably have to pay them to heat and press it back on and what fun is that. (Cheap)
Don’s idea of welding it a little on the back sounds good especially since Randall cleared up the force and torque problem I had. I could not wrap my mind around where the force would go. I also thought the peg would pull on the unit and try and separate the two. But, now I can see that the worm would be trapped between the bearings and the only force would be the driver and if it is a spilt column the collar connecter would act as a safety stop anyway. I mean if something odd did happen. So, a couple of good tacks should hold everything fine. However, I am talking to guy who has a nice one for sale. My problem is I have purchased two of these shafts with the gear and both times they were not cherry.

Again:
F.W.I.W.
I would advise against relying on any type of weld on those parts.

But then .... I`m just a Welder/Fabricator & Aircraft Engine maintenance Welder with 30+ years total experience and 10 of that in Aircraft Engine reclamation and repair, what do I know!

Were they my parts, I would not do it!

But ...... To each .... His/Her own.

I'm with you, Kerry, even though I just barely know which end of the torch to pick up!

I am not a welder either; heck, yesterday I could not say welllder. However, I bought one of those self-darkening welding helmets and I sure find that helpful, kinda like sliced bread. Anyways, I trust your expertise Awe- Man and will now come up with a different plan. I am curious, however, why earlier you maintained that you could build up the worm gear with weld. It was after reading that that I figured welding would be ok. Perhaps it is the joining of the two different hardened steels? Anyways, one of the guys I play poker with owns a donut shop, and I will take those guys at the machine shop in a box off donuts and see what happens. I am cheap and for me part of fixing one of these cars is the networking. Yes, networking what a nice way to say parsimonious.

I did mention that I PROBABLY could build it up with weld, I also mentioned machining would present a whole different set of problems eg. getting the correct angels and curvature on the worm gear. Building it up by Welding would significantly change the hardness of the gear itself, therefore it would need to be heat treated in order to bring it back to the specific hardness required. As I mentioned in this post 4/10/07 reply to Don Elliot, that welding hardened materials to one another require specific procedures and equipment that WE do not have at home.
Eg. the heat treat oven and the correct weld filler material.
I would only try welding such an item as a last resort and even then it would require further work by both machinist and heat treating. And would very well be cost prohibitive.
Having said all of that, if it was THE ONLY WAY to produce the part needed ..... then and only then I would attempt a weld repair.
I would not try to "Spot Weld" these pieces together because as I mentioned unless you have the correct filler material to produce this "Spot Weld" with, the weld will merely break under the slightest of stress loads.
In order for a spot weld to fuse both pieces together, Although in a localized area, would require heat in the 2,000+ degree range { mild steel becomes liquid at nearly 2,800 degrees} { somewhat less for hardened steel Eg. around 2,500} the cooling rates are somewhat different also. The 300 degree difference is enough to cause a stress riser which in turn equals cracking. Not to mention changing the physical properties of the hardened material in the localized spot welded area. So without the correct filler material for the spot weld and heat treating after to normalize the area ....
I hope you can see what i`m getting at here.
I hope this clarifys what I was refering to with out going into a bunch of terminology.