pre and post galvanizing advice

catman275 · Aug 3, 2019

Hi folks
I hope to be getting a bulkhead, radiator panel shotted and galved in the next few weeks.
What have people done regarding the threaded holes in the parts? and did it work?
I mentioned to the guy who is going to blast it for me about putting screws in the holes first and he didn't advise it because he said they could seize up on the threads after galving. Any thoughts on that?
I have bolted a piece of angle across the bottom .

Post galving .... How much t-wash would I expect to need for the job? I don't want to get a load and not use it.
Has anyone brushed on epoxy primer? How did it end up?

cheers Peter

Thor 1950 · Aug 3, 2019

get the right size taps and retap the thread. then on reassembly put some coppercoat anti sieze on the threads. just a smidge does the job

Dippypud · Aug 3, 2019

Thor 1950 said:
get the right size taps and retap the thread. then on reassembly put some coppercoat anti sieze on the threads. just a smidge does the job

Chasing threads will not only remove the excess zinc, but often removes much, if not all of the zinc coating and eliminates the corrosion protection on the threaded portion of the fastener....

Chasing, if not performed with extreme precision, can also remove additional steel from the threaded portion of the fastener resulting in threads that are undersized and out of tolerance...

Your best bet is to to drive hardwood plugs into the holes from both sides ...

Thor 1950 · Aug 3, 2019

Dippypud said:
Chasing threads will not only remove the excess zinc, but often removes much, if not all of the zinc coating and eliminates the corrosion protection on the threaded portion of the fastener....

Chasing, if not performed with extreme precision, can also remove additional steel from the threaded portion of the fastener resulting in threads that are undersized and out of tolerance...

Your best bet is to to drive hardwood plugs into the holes from both sides ...

Dippy the galvanize is 840f plus a little could char the wood and still get galvanization on the threads. also I doubt galavanizer will allow it.
So you have used your recommended process then with success?

I said retap . Not a thread chaser

Dippypud · Aug 3, 2019

Thor 1950 said:
Dippy the galvanize is 840f plus a little could char the wood and still get galvanization on the threads. also I doubt galavanizer will allow it.
So you have used your recommended process then with success?

Yes, the wood will actually take the heat for a short period of time and even if it chars, the carbon seems to keep the zinc from sticking... I know soot makes a good release agent so maybe that's why it works. it really doesn't burn that bad...

They still had to be unscrewed with a pair of pliers and the threads were nice and clean...

Dippypud · Aug 3, 2019

Thor 1950 said:
Dippy the galvanize is 840f plus a little could char the wood and still get galvanization on the threads. also I doubt galavanizer will allow it.
So you have used your recommended process then with success?

I said retap . Not a thread chaser

So, in reply to the edited portion of your post, would you suggest a roll-over tap ?

Thor 1950 · Aug 3, 2019

Dippypud said:
So, in reply to the edited portion of your post, would you suggest a roll-over tap ?

whats a roll over tap

Thor 1950 · Aug 3, 2019

Dippypud said:
So, in reply to the edited portion of your post, would you suggest a roll-over tap ?

These are what I was referring to

Dippypud · Aug 3, 2019

Thor 1950 said:
I said retap . Not a thread chaser

To 'chase' a thread, means to clean it ...

To 're-tap' a thread, which one of your three pictured taps would you use ?

Dippypud · Aug 3, 2019

Thor 1950 said:
whats a roll over tap

I think you call them 'roll form' taps, a roll over tap doesn't cut, it just pushes the material ...

Citizen Kane · Aug 3, 2019

Just run a tap through the holes afterwards, biggest pain is clearing out the holes for the vent panel hinge pins. Don't worry about removing all the galvanising from the treaded holes, zinc has a "throwing power" and can protect adjacent areas of bare steel.

You will need typically a couple of litres of T wash, epoxy primer can then be applied directly by brush, roller or spray, if you go down the brush route I would get a "slow" hardener to give more chance of keeping a wet edge. You can safely spray epoxy primer without an air fed mask, its not isocyanate based but you will still need a suitable face mask to protect yourself.

Don't see the point of using copper grease on bolts, its for anti seize applications, just use something like cavity wax on the threads and bolts, this will protect you from the main enemy which is corrosion. Its also perfectly acceptable to use stainless fasteners on galvanised parts.

Dippypud · Aug 3, 2019

Thor 1950 said:
These are what I was referring to

View attachment 185894

This is a spark plug thread chaser ;

Thor 1950 · Aug 3, 2019

Dippypud said:
To 'chase' a thread, means to clean it ...

To 're-tap' a thread, which one of your three pictured taps would you use ?

depends on the hole you are putting it in

Dippypud · Aug 3, 2019

Thor 1950 said:
depends on the hole you are putting it in

No, it should depend on what the hole is for ?

Engine threaded blind holes need a different type of tap to seat belt securing bolt holes ...

Kiwi Landie · Aug 4, 2019

I galv'd all the steel panels/parts on my landie and just used a bog standard tap to run through the threads afterwards. I made no effort to keep the zinc out.
The only one that gave a little drama was one of the steering relay locator ring bolts. But it was an easy fix. I drilled it marginally undersize and then the tap went in no problem.
I had to drill out one of the shock absorber mount tubes to get the bolt in. It was just a bit tight without running the drill through. All the others were fine.

Cheers
Andrew

catman275 · Aug 4, 2019

Thanks for the feedback guys, always interesting to hear different views/ideas.
I just remembered the shotblast guy said that some people put wax in the threads for protection.
I thought that would melt straight away, unless he was pulling my old todger.
I do have some taps in my tap and reamer tray. Unfortunately not the ones I need except for the 2BA for the radiator panel.
Anyone know what size thread the windscreen hinge bolts are?Cant seem to find that.
I'll post that again as a seperate enquiry.
cheers again Peter

Wildefalcon · Aug 6, 2019

I used silicone on the threads when doing my chassis. It worked quite well, didn't need to clean the threads for the relay.

Kiwi Landie · Aug 6, 2019

Windscreen hinge bolts are 1/4" UNF 28 TPI.

(Same as the relay retainer ring!)

Cheers
Andrew

windy81 · Aug 6, 2019

Dippypud said:
Chasing threads will not only remove the excess zinc, but often removes much, if not all of the zinc coating and eliminates the corrosion protection on the threaded portion of the fastener....

Zinc isn't a paint, it still works, even if you g clamped a bit of it to wherever you didn't want to rust.

Webley1991 · Aug 6, 2019

Kiwi Landie said:
Windscreen hinge bolts are 1/4" UNF 28 TPI.

The later ones were M8x1.25 . It depends on the year.

pre and post galvanizing advice

Well-Known Member

Well-Known Member

Never Knowingly Understood

Well-Known Member

Never Knowingly Understood

Never Knowingly Understood

Well-Known Member

Well-Known Member

Never Knowingly Understood

Never Knowingly Understood

Well-Known Member

Never Knowingly Understood

Well-Known Member

Never Knowingly Understood

Active Member

Well-Known Member

Well-Known Member

Active Member

Well-Known Member

Well-Known Member

Similar threads